JP7741297B2 - Communication method and apparatus - Google Patents

Description

This application relates to the field of communications technology, and in particular to communications methods and devices.

Currently proposed user equipment (UE) relay technologies include a relay scheme in which a remote UE appears to the radio access network (RAN). In this relay scheme, the remote UE can perform a path switch, or in other words, a link switch. For example, the remote UE may switch from a direct link to a base station to an indirect link for indirect communication with the base station. The indirect link here is a relay link. Specifically, the remote UE is connected to the base station via a relay UE.

The path switch process of the remote UE includes the process of switching from a direct link to an indirect link, the process of switching from an indirect link to a direct link, and the process of switching between indirect links. When switching to an indirect link (including switching from a direct link to an indirect link or switching between indirect links), the mainstream solutions currently being discussed are as follows: the base station configures the remote UE to perform measurements, the remote UE sends the measurement results to the base station, and the base station decides whether the remote UE should perform a path switch. If the base station determines that the remote UE should perform a path switch, the base station separately sends configuration information to the remote UE and relay UE to configure the path switch.

In the path switch method, if the relay UE rejects the related configuration, for example, if the relay UE rejects providing relay service for the remote UE, the relay UE must perform processing based on the configuration failure case . The relay UE will enter a radio resource control (RRC) reestablishment procedure and can only continue operation after the RRC reestablishment is successful. This will obviously cause a degradation of the service quality of the relay UE.

Embodiments of this application provide a communication method and apparatus for improving the service quality of relay UEs.

According to a first aspect, a first communication method is provided. The method may be executed by a first terminal device or a chip system, which can realize the functions of the first terminal device. The first terminal device is, for example, a terminal device that provides relay service for another terminal device in a relay scenario. The method includes the steps of: receiving a first message from a network device, where the first message is for inquiring whether the first terminal device is capable of providing relay service, or the first message includes configuration information, and the configuration information is for configuring the first terminal device to provide relay service for a second terminal device; and sending a second message to the network device, where if the first message is for inquiring whether the first terminal device is capable of providing relay service, the second message indicates whether the first terminal device is capable of providing relay service, or if the first message includes configuration information, the second message indicates whether configuration of the first terminal device has been completed, or the second message indicates whether the first terminal device is capable of providing relay service.

In this embodiment of the present application, regardless of whether the first terminal device can provide relay service for the second terminal device, the first terminal device can send a second message to the network device for notification, thereby allowing the network device to know whether the first terminal device can provide relay service for the second terminal device. Therefore, if the first terminal device refuses to provide relay service for the second terminal device, the network device can also know this case, so that the first terminal device does not need to enter an RRC re-establishment procedure and can continue to operate normally within the coverage of the network device, in order to improve the service quality of the first terminal device and reduce resources consumed in the RRC re-establishment procedure. In this application, the RRC re-establishment procedure has the same meaning as the RRC re-establishment process in the following description.

Referring to the first aspect, in a first optional implementation of the first aspect, the second message indicates that the first terminal device determines that the configuration has failed or indicates that the first terminal device refuses to provide relay service for the second terminal device, and the method further includes a step of skipping initiating an RRC re-establishment process.

With reference to the first aspect or the first optional implementation of the first aspect, in a second optional implementation of the first aspect, when the first message is for inquiring whether the first terminal device can provide a relay service, the first message includes one or more of the following: an identifier of the second terminal device, integrity protection algorithm information or integrity protection rate information, encryption algorithm information or encryption rate information, PQI or 5QI, QoS, network slice information, or computing capability information.

The first message may include one or more of the aforementioned information. In addition to the aforementioned information, the first message may include other information. Based on one or more of the aforementioned information, the first terminal device may identify capabilities that need to be met by the relay service, thereby allowing the first terminal device to more accurately determine whether the relay service can be provided.

With reference to the first aspect, the first optional implementation of the first aspect, or the second optional implementation of the first aspect, in a third optional implementation of the first aspect, the second message indicates that configuration of the first terminal device has failed or indicates that the first terminal device refuses to provide the relay service, and the second message further includes a cause value, which indicates a cause for the refusal by the first terminal device to provide the relay service.

The second message may include a cause value, which may indicate the cause of the refusal by the first terminal device to provide relay service, allowing the network device to determine the cause of the first terminal device's inability to provide relay service. In this way, the network device can take corresponding measures. For example, the network device may again search for a terminal device that can provide relay service for the second terminal device.

With reference to the third optional implementation of the first aspect, in a fourth optional implementation of the first aspect, the reason for refusing to provide relay service by the first terminal device is one of the following:
The first terminal device does not support the configuration of the Uu interface included in the first message;
The first terminal device does not support the PC5 interface configuration included in the first message;
the admission control performed by the first terminal device to the second terminal device is unsuccessful;
The first terminal device does not support the integrity protection algorithm included in the first message;
The first terminal device does not support the 5QI or PQI included in the first message;
The first terminal device is unable to identify the QoS flow ID indicated by the first message;
The first terminal device does not support the network slicing indicated by the first message;
The battery power of the first terminal device is insufficient;
The PDCP of the first terminal device is overloaded, or the first terminal device does not support the computing capability indicated by the first message.

The above provides some reasons why a first terminal device may refuse to provide relay service. In addition to the reasons mentioned above, the first terminal device may refuse to provide relay service for other reasons. The reasons why a first terminal device may refuse to provide relay service are not limited.

With reference to the first aspect or any one of the first optional implementation of the first aspect to the fourth optional implementation of the first aspect, in a fifth optional implementation of the first aspect, the first message is for inquiring whether the first terminal device is capable of providing a relay service, the second message indicates that the first terminal device is capable of providing a relay service, and the method further includes receiving configuration information from the network device and performing configuration based on the configuration information to provide the relay service.

If the first message is to inquire whether the first terminal device can provide relay service, it is highly likely that the first message will not include configuration information. In this case, if the second message indicates that the first terminal device can provide relay service, the network device may resend the configuration information to the first terminal device, so that the first terminal device can perform configuration based on the configuration information to provide relay service.

With reference to the first aspect or any one of the first optional implementation of the first aspect to the fifth optional implementation of the first aspect, in a sixth optional implementation of the first aspect, the first message is an RRC reconfiguration message or a message specifically for inquiring whether the terminal device is capable of providing relay services.

The first message may be implemented by using an existing message, for example, by using an RRC reconfiguration message. In this way, no other messages need to be newly added, and compatibility with existing technologies is promoted. Alternatively, the first message may be implemented by using another message. For example, the first message is newly added in this embodiment of the application, and the first message may be for inquiring whether the terminal device is capable of providing relay services. In this way, no existing messages need to be modified.

With reference to the first aspect or any one of the first optional implementation of the first aspect to the sixth optional implementation of the first aspect, in the seventh optional implementation of the first aspect, the second message is an RRC reconfiguration complete message or a message specifically indicating whether the terminal device provides relay services.

For example, regardless of whether the second message indicates success (e.g., indicates that the first terminal device is capable of providing relay service or indicates that configuration has been completed) or failure (e.g., indicates that the first terminal device refuses to provide relay service or indicates that configuration has failed), the same message may be used as the second message. For example, an RRC reconfiguration complete message may be used, or a newly added message may be used. The same type of message or the same message may indicate success or failure, eliminating the need to introduce excessive message types to reduce the number of message types that the network device needs to identify. Alternatively, the second message may indicate success and failure by using different messages. In this case, for example, the second message may indicate success by using an RRC reconfiguration complete message, and the second message may indicate failure by using a newly added message. Different messages indicate success and failure, respectively, allowing the network device to determine success or failure based on the type of the second message, thereby increasing the efficiency of determining success or failure by the network device.

With reference to the first aspect or any one of the first optional implementation of the first aspect to the seventh optional implementation of the first aspect, in the eighth optional implementation of the first aspect, when the second message indicates that the configuration has failed, the second message is a failure information message or an SUI message.

If the second message can indicate success and failure by using different messages, for example, if the second message indicates failure, the second message may be a failure information message or an SUI message, or if the second message indicates success, the second message may be an RRC reconfiguration message or another message. Existing messages separately indicate success or failure, which can improve the efficiency of determining success or failure by network devices, does not require new messages to be added, and promotes compatibility with existing technologies.

According to a second aspect, a second communication method is provided. The method may be performed by a network device or a chip system, which can realize the functions of the network device. For example, the network device is an access network device, such as a base station. The method includes the steps of: sending a first message to a first terminal device, where the first message is for inquiring whether the first terminal device can provide a relay service, or the first message includes configuration information, and the configuration information is for configuring the first terminal device to provide a relay service for a second terminal device; and receiving a second message from the first terminal device, where if the first message is for inquiring whether the first terminal device can provide a relay service, the second message indicates whether the first terminal device can provide a relay service, or if the first message includes configuration information, the second message indicates whether configuration of the first terminal device has been completed, or the second message indicates whether the first terminal device can provide a relay service.

With reference to the second aspect, in a first optional implementation of the second aspect, the method further includes a step of the first terminal device determining not to perform RRC re-establishment.

With reference to the second aspect or the first optional implementation of the second aspect, in the second optional implementation of the second aspect, when the first message is for inquiring whether the first terminal device can provide a relay service, the first message includes one or more of the following: an identifier of the second terminal device, PC5 or Uu interface parameters, integrity protection algorithm information or integrity protection rate information, encryption algorithm information or encryption rate information, PQI or 5QI, QoS, network slice information, or computational capability information.

With reference to the second aspect, the first optional implementation of the second aspect, or the second optional implementation of the second aspect, in a third optional implementation of the second aspect, the second message indicates that configuration of the first terminal device has failed or indicates that the first terminal device refuses to provide the relay service, and the second message further includes a cause value, which indicates a cause for the refusal by the first terminal device to provide the relay service.

With reference to the third optional implementation of the second aspect, in a fourth optional implementation of the second aspect, the reason for refusing to provide relay service by the first terminal device is as follows:
The first terminal device does not support the configuration of the Uu interface included in the first message;
The first terminal device does not support the PC5 interface configuration included in the first message;
the admission control performed by the first terminal device to the second terminal device is unsuccessful;
The first terminal device does not support the integrity protection algorithm included in the first message;
The first terminal device does not support the 5QI or PQI included in the first message;
The first terminal device is unable to identify the QoS flow ID indicated by the first message;
The first terminal device does not support the network slicing indicated by the first message;
The battery power of the first terminal device is insufficient;
The PDCP of the first terminal device is overloaded, or the first terminal device does not support the computing capability indicated by the first message.

With reference to the second aspect or any one of the first optional implementation of the second aspect to the fourth optional implementation of the second aspect, in a fifth optional implementation of the second aspect, the first message is for inquiring whether the first terminal device is capable of providing a relay service, the second message indicates that the first terminal device is capable of providing a relay service, and the method further includes a step of transmitting configuration information to the first terminal device.

With reference to the second aspect or any one of the first optional implementation of the second aspect to the fifth optional implementation of the second aspect, in the sixth optional implementation of the second aspect, the first message is an RRC reconfiguration message.

With reference to the second aspect or any one of the first optional implementation of the second aspect to the sixth optional implementation of the second aspect, in the seventh optional implementation of the second aspect, the second message is an RRC reconfiguration complete message or a message specifically indicating whether the terminal device provides relay services.

With reference to the second aspect, or any one of the first optional implementation of the second aspect to the seventh optional implementation of the second aspect, in the eighth optional implementation of the second aspect, when the second message indicates that the configuration has failed, the second message is a failure information message or an SUI message.

With reference to the second aspect or any one of the first optional implementation of the second aspect to the eighth optional implementation of the second aspect, in a ninth optional implementation of the second aspect, the second message indicates that the first terminal device refuses to provide the relay service, and the method further includes a step of sending a third message to the second terminal device, the third message indicating that the first terminal device refuses to provide the relay service or indicating that the first terminal device reselects a terminal device that can provide the relay service.

If the first terminal device refuses to provide relay service, the network device may notify the second terminal device, so that the second terminal device may take corresponding measures. For example, the second terminal device may resume measurements to search for terminal devices that can provide relay service.

With reference to the ninth optional implementation of the second aspect, in a tenth optional implementation of the second aspect, the third message further includes information about one or more terminal devices, and the one or more terminal devices are not capable of providing relay services.

One or more terminal devices may not be able to provide relay services. Therefore, when performing measurements, the second terminal device may not need to measure one or more terminal devices in order to meet the energy saving requirements of the second terminal device.

With reference to the second aspect or any one of the first optional implementation of the second aspect to the tenth optional implementation of the second aspect, in an eleventh optional implementation of the second aspect, the method further includes the steps of receiving a fourth message from the second terminal device, where the fourth message indicates an energy saving requirement, and transmitting first information to the second terminal device, where the first information includes information about M terminal devices, where the M terminal devices do not need to be measured or refuse to provide relay service, and M is a positive integer.

If the second terminal device has an energy saving requirement, the second terminal device may notify the network device. After learning that the second terminal device has an energy saving requirement, the network device may send first information to the second terminal device. The M terminal devices indicated by the first information may not need to be measured or may refuse to provide relay service. Therefore, after receiving the first information, when performing measurements, the second terminal device may not need to measure the M terminal devices in order to reduce power consumption caused by measurements and meet the energy saving requirement.

With reference to the eleventh optional implementation of the second aspect, in a twelfth optional implementation of the second aspect, the fourth message further includes second information, the second information includes information about N terminal devices, the N terminal devices refuse to provide relay service, and N is a positive integer.

For example, if the second terminal device determines, based on historical information, that N terminal devices refuse to provide relay service for the second terminal device, the second terminal device may add information about the N terminal devices to a blacklist and transmit the blacklist to the network device. Therefore, when configuring the second terminal device to perform measurements, the network device may consider not configuring the second terminal device to measure the N terminal devices in order to reduce invalid measurement processes for the second terminal device.

For technical effects provided by the second aspect or optional implementations of the second aspect, please refer to the description of the technical effects of the first aspect or corresponding implementations.

According to a third aspect, a third communication method is provided. The method may be performed by a second terminal device or a chip system, and the chip system can realize the functions of the second terminal device. The second terminal device is, for example, a terminal device that needs to perform relaying by using another terminal device in a relay scenario. The method includes: transmitting measurement results to a network device, where the measurement results include a measurement report for at least one terminal device; and performing a first action when a first condition is met; and skipping performing the first action otherwise, where the first action includes one or more of the following: transmitting a discovery message, measuring another terminal device, or transmitting new measurement results to the network device.

The first operation may be considered an operation related to the measurement process. In other words, in this embodiment of the application, if the first condition is not met, the second terminal device may not perform the first operation. Since the second terminal device transmits the measurement results to the network device, and the network device can determine whether the second terminal device can perform path switching based on the measurement results, the network device's decision is not significantly affected even if the second terminal device no longer performs measurements and no longer transmits new measurement results to the network device. In addition, in this manner, the measurement process of the second terminal device may be reduced, the resources consumed in the measurement process may be reduced, and the battery power of the second terminal device may be saved.

With reference to the third aspect, in a first optional implementation of the third aspect, after transmitting the measurement result to the network device, the method further includes a step of starting a timer, wherein the first condition is that the timer has expired.

In this manner, satisfaction of the first condition means that the timer has expired, and non-satisfaction of the first condition means that the timer has not expired. Using a timer to determine whether to perform the first action is a simple manner, which helps promote the technical solution in this embodiment of this application to more terminal devices for use.

Referring to the third aspect, in a second optional implementation of the third aspect, the first condition is that a third message is received from the network device, and the third message indicates that the first terminal device refuses to provide the relay service or indicates that a terminal device capable of providing the relay service should be reselected.

In this method, satisfaction of the first condition means that a third message is received from the network device, and failure to satisfy the first condition means that a third message is not received from the network device. Using the message from the network device to determine whether to perform the first action can make the decision result more accurate and more compatible with the current situation.

With reference to the second optional implementation of the third aspect, in a third optional implementation of the third aspect, the third message further includes information about one or more terminal devices, and the one or more terminal devices are not capable of providing relay services.

With reference to the third aspect or any one of the first optional implementation of the third aspect to the third optional implementation of the third aspect, in a fourth optional implementation of the third aspect, the method further includes the steps of: sending a fourth message to the network device, where the fourth message indicates an energy saving requirement; and receiving first information from the network device, where the first information includes information about M terminal devices, where the M terminal devices do not need to be measured or refuse to provide relay service, and M is a positive integer.

With reference to the fourth optional implementation of the third aspect, in a fifth optional implementation of the third aspect, the fourth message further includes second information, the second information includes information about N terminal devices, the N terminal devices refuse to provide relay service, and N is a positive integer.

With reference to the third aspect or any one of the first optional implementation of the third aspect to the fifth optional implementation of the third aspect, in a sixth optional implementation of the third aspect, the method further includes receiving measurement configuration information from the network device and performing measurements based on the measurement configuration information to obtain measurement results, and the step of transmitting the measurement results to the network device includes transmitting the measurement results to the network device when a reporting condition for the measurement report is satisfied.

The network device sends measurement configuration information to the second terminal device to configure the second terminal device to perform measurements. The second terminal device may obtain measurement results after performing the measurements. The measurement results include, for example, measurement reports obtained by measuring one or more terminal devices. If reporting conditions for the measurement report are met, the second terminal device may transmit the measurement results to the network device, so that the network device can obtain the measurement results of the second terminal device and select a terminal device that can provide relay service for the second terminal device.

With reference to the third aspect or any one of the first optional implementation of the third aspect to the sixth optional implementation of the third aspect, in the seventh optional implementation of the third aspect, when the first operation includes sending a discovery message, the method further includes the steps of sending the discovery message and stopping sending the discovery message when the first condition is not satisfied.

If the first operation includes transmitting a discovery message, and if the second terminal device did not originally transmit the discovery message, the second terminal device may continue not transmitting the discovery message when the first condition is not met, or if the second terminal device originally transmitted the discovery message, the second terminal device may stop transmitting the discovery message to reduce power consumption when it is determined that the first condition is not met.

With reference to the third aspect or any one of the first optional implementation of the third aspect to the sixth optional implementation of the third aspect, in an eighth optional implementation of the third aspect, when the first operation includes transmitting new measurement results to the network device, the method further includes the steps of receiving a discovery message from the second terminal device, measuring the discovery message of the second terminal device to obtain the new measurement results, and skipping transmitting the new measurement results to the network device when the first condition is not satisfied and the reporting condition for the measurement report is satisfied.

If the second terminal device receives a discovery message from the first terminal device, the second terminal device may measure the discovery message to obtain new measurement results. If the first operation includes transmitting a new measurement report to the network device (in other words, the first operation includes transmitting a measurement report to the network device), when the first condition is not met, even if the reporting condition for the measurement report is met, the second terminal device does not transmit the new measurement report to the network device to reduce power consumption.

For technical effects provided by some optional implementations of the third aspect, please refer to the description of the technical effects of the corresponding implementations of the second aspect.

According to a fourth aspect, a fourth communication method is provided. The method may be executed by a second terminal device or may be executed by a chip system, which can realize the functions of the second terminal device. The second terminal device is, for example, a terminal device that needs to perform relaying by using another terminal device in a relay scenario. The method includes the steps of receiving configuration information from a first network device, where the configuration information is for configuring the second terminal device to switch to communicate with a third network device via the first terminal device or for configuring the second terminal device to be handed over to the second network device; performing a path switch based on the configuration information; and determining that the path switch is successful when a first condition is met; and otherwise determining that the path switch has failed.

In this embodiment of the application, the second terminal device may determine whether the path switch is successful or unsuccessful based on the first condition. That is, this embodiment of the application provides a method for the second terminal device to determine whether the path switch is successful. If the path switch is unsuccessful, the second terminal device may perform a corresponding operation, for example, continue to perform communication within the coverage of the source network device, or enter a new cell through cell reselection in order to resume service of the second terminal device as soon as possible and improve service continuity.

With reference to the fourth aspect, in a first optional implementation of the fourth aspect, after receiving the configuration information from the first network device, the method further includes a step of starting a timer, wherein the first condition is that the timer has not expired.

In this method, satisfaction of the first condition means that the timer has not expired, and non-fulfillment of the first condition means that the timer has expired. The second terminal device can determine whether the path switching is successful or unsuccessful based on the timer. The determination method is simple and easy to implement. The technical solution in this embodiment of this application can also be applied to terminal devices with low capabilities.

With reference to the fourth aspect, in a second optional implementation of the fourth aspect, the configuration information is for configuring the second terminal device to switch to communicate with the third network device through the first terminal device, and the first condition is:
Receive feedback from the first terminal device when the number of times of sending the connection establishment request message to the first terminal device is less than or equal to M, where M is the maximum number of retransmissions;
The method includes: security verification for the first terminal device is successful; or a connection establishment request message is sent to the first terminal device; and a connection establishment response message is received from the first terminal device, the connection establishment response message indicating that the connection establishment is accepted.

If the second terminal device determines whether the path switching is successful based on a timer, the timing duration of the timer is usually not set too short. Otherwise, the determination result of the second terminal device may be inaccurate. However, if the second terminal device does not use a timer but determines whether the path switching is successful by using one of the above-mentioned conditions, a shorter time is required to make the determination, and the efficiency is higher, so that the second terminal device can take corresponding measures as soon as possible and determine whether the path switching is successful as soon as possible so as to reduce the service interruption time.

With reference to the fourth aspect, the first optional implementation of the fourth aspect, or the second optional implementation of the fourth aspect, in a third optional implementation of the fourth aspect, it is determined that the path switching has failed, and the method further includes a step of transmitting failure information to the first network device via the first path, where the failure information indicates that the path switching has failed and the first path is the communication path between the second terminal device and the first network device before the path switching, and a step of continuing to communicate with the first network device via the first path.

The first path is the communication path between the second terminal device and the first network device before the path switch. For example, the first path is the second terminal device-first network device, or the second terminal device-first terminal device-first network device. If the second terminal device has not disconnected from the first network device via the first path before successfully performing the path switch, the second terminal device may perform the method. After the first network device receives the failure information, the second terminal device may continue to communicate with the first network device via the first path. That is, because the original communication path has not been disconnected, the second terminal device may continue to communicate via the original communication path and does not need to reselect a communication path. In other words, the second terminal device does not initiate an RRC connection re-establishment process to improve the service continuity of the second terminal device.

With reference to the fourth aspect, the first optional implementation of the fourth aspect, or the second optional implementation of the fourth aspect, in a fourth optional implementation of the fourth aspect, it is determined that the path switching has failed, and the method further includes a step of sending an RRC connection re-establishment request message to the first network device via a first path, where the RRC connection re-establishment request message requests the first network device to re-establish the RRC connection, and the first path is the communication path between the second terminal device and the first network device before the path switching.

If the second terminal device has not disconnected from the first network device via the first path before successfully performing the path switch, the second terminal device may also perform the method to re-establish an RRC connection within the coverage of the first network device, thereby communicating with the first network device via the new connection.

With reference to the third optional implementation of the fourth aspect or the fourth optional implementation of the fourth aspect, in a fifth optional implementation of the fourth aspect, the first route is a route for connecting to the first network device via a third terminal device, or the first route is a route for connecting directly to the first network device.

With reference to the fourth aspect, the first optional implementation of the fourth aspect, or the second optional implementation of the fourth aspect, in a sixth optional implementation of the fourth aspect, it is determined that the path switch has failed, and the method further includes a step of performing cell reselection to reselect the first cell, and a step of initiating an RRC connection reestablishment process in the first cell, or a step of initiating an RRC connection establishment process in the first cell.

For example, if the second terminal device disconnects the first path between the second terminal device and the first network device, the second terminal device may perform the method. Alternatively, the second terminal device may also perform the method even if the second terminal device does not disconnect the first path between the second terminal device and the first network device.

According to a fifth aspect, a fifth communication method is provided. The method may be executed by a first network device or may be executed by a chip system, where the chip system can realize the functions of the first network device. The method includes receiving failure information or an RRC connection re-establishment request message from a second terminal device via a first path, where the failure information indicates that a path switch has failed, and the RRC connection re-establishment request message requests the first network device to re-establish the RRC connection, and the first path is a communication path between the second terminal device and the first network device before the path switch.

With reference to the fifth aspect, in a first optional implementation of the fifth aspect, failure information is received, and the method further includes a step of determining, by the second terminal device, not to initiate RRC connection re-establishment.

For the technical effects provided by the fifth aspect or the first optional implementation of the fifth aspect, please refer to the description of the technical effects of the fourth aspect or the corresponding implementation.

According to a sixth aspect, a sixth communication method is provided. The method may be executed by a second terminal device or may be executed by a chip system, and the chip system can realize the functions of the second terminal device. The second terminal device is, for example, a terminal device that needs to perform relaying by using another terminal device in a relay scenario. The method includes the steps of receiving configuration information from a first network device, where the configuration information is for configuring the second terminal device to switch to communicate with a third network device via the first terminal device or for configuring the second terminal device to be handed over to the second network device; performing a path switch based on the configuration information; and determining that the path switch has failed when a second condition is met.

In this embodiment of the application, the second terminal device may determine whether the path switching has failed based on a second condition. That is, this embodiment of the application provides a method for the second terminal device to determine whether the path switching has failed. If the path switching has failed, the second terminal device may perform a corresponding operation, for example, continue to initiate re-establishment within the coverage of the source network device, enter a new cell through cell reselection to perform re-establishment, initiate re-establishment by using the first terminal device, or select a new relay terminal device through reselection or selection of a relay terminal device and initiate re-establishment by using the relay terminal device, in order to resume service for the second terminal device as soon as possible and improve service continuity.

With reference to the sixth aspect, in a first optional implementation of the sixth aspect, after receiving the configuration information from the first network device, the method further includes a step of starting a timer, wherein the second condition is that the timer has expired.

In this method, the satisfaction of the second condition means that the timer has expired. The second terminal device can determine whether the path switching is successful or unsuccessful based on the timer. The determination method is simple and easy to implement. The technical solution in this embodiment of this application can also be applied to terminal devices with low capabilities.

With reference to the first implementation of the sixth aspect, in a second optional implementation of the sixth aspect, the following condition is satisfied:
The establishment of a PC5 connection between the second terminal device and the first terminal device is completed;
The second terminal device successfully randomly accesses the third network device;
The second terminal device sends an RRC reconfiguration complete message to a lower layer of the second terminal device and receives an acknowledgement feedback from the lower layer;
the second terminal device receives second instruction information from the third network device, the second instruction information indicating to the second terminal device to stop the timer;
the second terminal device receives third instruction information from the first terminal device, the third instruction information instructing the second terminal device to stop a timer, or the third instruction information indicating that the first terminal device has successfully randomly accessed the third network device;
The second terminal device receives fourth indication information from the first terminal device, and the fourth indication information indicates that a Uu radio link failure (RLF) has occurred in the first terminal device, or that the first terminal device has failed to randomly access the third network device; or establishment of a PC5 connection between the second terminal device and the first terminal device has failed, or a PC5 RLF has been determined; and when one or more of these are satisfied, the timer is stopped.

If the second terminal device determines whether a route switch has failed based on whether a timer has expired, the timer's timing duration is typically not set too short, and the timer needs to be stopped in a timely manner to avoid determining that the route switch has failed because the timer has not been stopped.

In a third optional implementation of the sixth aspect, with reference to the sixth aspect, the first optional implementation of the sixth aspect, or the second optional implementation of the sixth aspect,
The second condition is that the timer has expired,
The second condition is that the second terminal device receives fourth indication information from the first terminal device, and the fourth indication information indicates that a Uu RLF has occurred in the first terminal device or that the first terminal device has failed to randomly access the third network device, or the second condition is that establishment of a PC5 connection between the second terminal device and the first terminal device has failed or a PC5 RLF has been determined.

If the second terminal device determines whether the path switching has failed based solely on whether the timer has expired, the timer's timing duration is typically not set too short. When a failure occurs, the second terminal device still needs to wait. In this implementation, when a failure occurs, the failure can be determined quickly, and the restart process can begin as soon as possible to improve the continuity of service for the second terminal device.

With reference to the sixth aspect, the first optional implementation of the sixth aspect, the second optional implementation of the sixth aspect, or the third optional implementation of the sixth aspect, in a fourth optional implementation of the sixth aspect, the method further includes the second terminal device sending an RRC connection re-establishment request message to the first network device through a first path, the RRC connection re-establishment request message requesting the first network device to re-establish the RRC connection, and the first path being a communication path between the second terminal device and the first network device before the path switch.

If the second terminal device has not disconnected from the first network device via the first path before successfully performing the path switch, the second terminal device may also perform the method to re-establish the RRC connection within the coverage of the first network device, thereby communicating with the first network device via the new connection.

With reference to the fourth optional implementation of the sixth aspect, in the fifth optional implementation of the sixth aspect, the first route is a route for connecting to the first network device via a third terminal device, or the first route is a route for connecting directly to the first network device.

With reference to the sixth aspect, the first optional implementation of the sixth aspect, the second optional implementation of the sixth aspect, or the third optional implementation of the sixth aspect, in a sixth optional implementation of the sixth aspect, the method further includes performing cell reselection to reselect the first cell, and initiating an RRC connection reestablishment process in the first cell or initiating an RRC connection establishment process in the first cell.

For example, if the second terminal device disconnects the first path between the second terminal device and the first network device, the second terminal device may perform the method. Alternatively, the second terminal device may also perform the method even if the second terminal device does not disconnect the first path between the second terminal device and the first network device.

According to a seventh aspect, a communication device is provided. The communication device may include modules configured to perform the method according to the first aspect or any one of the optional implementations of the first aspect, and may include, for example, a processing unit and a transceiver unit. Optionally, a storage unit may be further included.

For example, the processing unit is configured to receive a first message from the network device via the transceiver unit, the first message including configuration information, or the first message is for inquiring whether the communication device is capable of providing a relay service, and the configuration information is for configuring the communication device to provide a relay service for a second terminal device.

The processing unit is further configured to send a second message to the network device via the transceiver unit, the second message indicating that configuration of the communication device has been completed or has failed, the first message including the configuration information, or the second message indicating that the communication device is capable of providing relay service or is refusing to provide relay service.

According to an eighth aspect, a communication device is provided. The communication device may include modules configured to perform the method according to the second aspect or any one of the optional implementations of the second aspect, and may include, for example, a transceiver unit and a processing unit. Optionally, a storage unit may be further included.

For example, the processing unit is configured to send a first message to the first terminal device via the transceiver unit, the first message including configuration information, or the first message is for inquiring whether the first terminal device is capable of providing a relay service, and the configuration information is for configuring the first terminal device to provide a relay service for the communication device.

The processing unit is further configured to receive a second message from the first terminal device via the transceiver unit, the second message indicating that configuration of the first terminal device has been completed or has failed, the first message including configuration information, or the second message indicating that the first terminal device is capable of providing relay service or refuses to provide relay service.

According to a ninth aspect, a communications device is provided. The communications device may include modules configured to perform the method according to the third aspect or any one of the optional implementations of the third aspect, and may include, for example, a transceiver unit and a processing unit. Optionally, a storage unit may be further included.

For example, the processing unit is configured to transmit the measurement results to the network device via the transceiver unit, the measurement results including a measurement report for at least one terminal device.

The processing unit is further configured to perform a first operation when a first condition is met, and to skip performing the first operation otherwise, where the first operation includes one or more of the following: sending a discovery message, measuring another terminal device, or sending new measurement results to the network device.

According to a tenth aspect, a communication device is provided. The communication device may include modules configured to perform the method according to the fourth aspect or any one of optional implementations of the fourth aspect, and may include, for example, a transceiver unit and a processing unit. Optionally, a storage unit may be further included.

For example, the processing unit may be configured to receive configuration information from a first network device via the transceiver unit, the configuration information being for configuring the communication device to switch to communicate with a third network device via the first terminal device, or for configuring the communication device to be handed over to a second network device.

The processing unit is further configured to perform path switching based on the configuration information.

The processing unit is further configured to determine that the path switching is successful when the first condition is met, and to determine that the path switching is unsuccessful otherwise.

According to an eleventh aspect, a communication device is provided. The communication device may include modules configured to perform the method according to the fifth aspect or any one of optional implementations of the fifth aspect, and may include, for example, a transceiver unit and a processing unit. Optionally, a storage unit may be further included.

For example, the processing unit is configured to receive failure information or an RRC connection re-establishment request message from the second terminal device via the transceiver unit, where the failure information indicates that a path switch has failed, the RRC connection re-establishment request message requests the first network device to re-establish the RRC connection, and the first path is a communication path between the second terminal device and the first network device before the path switch.

According to a twelfth aspect, a communication device is provided. The communication device may include modules configured to perform the method according to the sixth aspect or any one of optional implementations of the sixth aspect, and may include, for example, a transceiver unit and a processing unit. Optionally, a storage unit may be further included.

For example, the processing unit is configured to receive configuration information from a first network device via the transceiver unit, the configuration information being for configuring the second terminal device to switch to communicating with a third network device via the first terminal device, or for configuring the second terminal device to be handed over to the second network device.

The processing unit is further configured to perform path switching based on the configuration information.

The processing unit is further configured to determine that the path switching is successful when the first condition is met, and to determine that the path switching is unsuccessful otherwise.

According to a thirteenth aspect, a chip system is provided. The chip system includes one or more processors and a communication interface. The processor is coupled to the communication interface and configured to implement a method according to the first aspect or any one of the optional implementations of the first aspect. Optionally, the chip system may further include a memory. For example, the processor may read and execute a software program stored in the memory to implement a method according to the first aspect or any one of the optional implementations of the first aspect.

According to a fourteenth aspect, a chip system is provided. The chip system includes one or more processors and a communication interface. The processor is coupled to the communication interface and configured to implement a method according to the second aspect or any one of the optional implementations of the second aspect. Optionally, the chip system may further include a memory. For example, the processor may read and execute a software program stored in the memory to implement a method according to the second aspect or any one of the optional implementations of the second aspect.

According to a fifteenth aspect, a chip system is provided. The chip system includes one or more processors and a communication interface. The processor is coupled to the communication interface and configured to implement a method according to the third aspect or any one of the optional implementations of the third aspect. Optionally, the chip system may further include a memory. For example, the processor may read and execute a software program stored in the memory to implement a method according to the third aspect or any one of the optional implementations of the third aspect.

According to a sixteenth aspect, a chip system is provided. The chip system includes one or more processors and a communication interface. The processor is coupled to the communication interface and configured to implement a method according to the fourth aspect or any one of the optional implementations of the fourth aspect. Optionally, the chip system may further include a memory. For example, the processor may read and execute a software program stored in the memory to implement a method according to the fourth aspect or any one of the optional implementations of the fourth aspect.

According to a seventeenth aspect, a chip system is provided. The chip system includes one or more processors and a communication interface. The processor is coupled to the communication interface and configured to implement a method according to the fifth aspect or any one of the optional implementations of the fifth aspect. Optionally, the chip system may further include a memory. For example, the processor may read and execute a software program stored in the memory to implement a method according to the fifth aspect or any one of the optional implementations of the fifth aspect.

According to an eighteenth aspect, a chip system is provided. The chip system includes one or more processors and a communication interface. The processor is coupled to the communication interface and configured to implement a method according to the sixth aspect or any one of the optional implementations of the sixth aspect. Optionally, the chip system may further include a memory. For example, the processor may read and execute a software program stored in the memory to implement a method according to the sixth aspect or any one of the optional implementations of the sixth aspect.

According to a 19th aspect, a first communication system is provided. The first communication system includes the communication device according to the 7th aspect or the chip system according to the 13th aspect, and includes the communication device according to the 8th aspect or the chip system according to the 14th aspect.

According to a twentieth aspect, a second communication system is provided. The second communication system includes the communication device according to the eighth aspect or the chip system according to the fourteenth aspect, and includes the communication device according to the ninth aspect or the chip system according to the fifteenth aspect.

According to a 21st aspect, a third communication system is provided. The third communication system includes the communication device according to the 10th aspect or the chip system according to the 16th aspect, and includes the communication device according to the 11th aspect or the chip system according to the 17th aspect.

According to a 22nd aspect, a fourth communication system is provided. The fourth communication system includes the communication device according to the 12th aspect or the chip system according to the 18th aspect, and includes the communication device according to the 11th aspect or the chip system according to the 17th aspect.

According to a twenty-third aspect, a computer-readable storage medium is provided. The computer-readable storage medium is configured to store a computer program. When the computer program is executed on a computer, the computer is enabled to perform a method according to any one of the preceding aspects.

According to a 24th aspect, there is provided a computer program product comprising instructions. The computer program product is configured to store a computer program. When the computer program is executed on a computer, the computer is enabled to perform a method according to any one of the preceding aspects.

In an embodiment of this application, if a first terminal device refuses to provide relay service for a second terminal device, the network device can also know this case, so that the first terminal device does not need to enter an RRC re-establishment procedure and can continue to operate normally within the coverage of the network device to improve the service quality of the first terminal device and reduce resources consumed in the RRC re-establishment procedure.

FIG. 10 is a diagram of a scenario in which a remote terminal device performs a path switch. FIG. 10 is a diagram of a scenario in which a remote terminal device performs a path switch. FIG. 10 is a diagram of a scenario in which a remote terminal device performs a path switch. FIG. 10 is a diagram of a scenario in which a remote terminal device performs a path switch. 10 is a flowchart of switching from a direct link to an indirect link by a remote terminal device. 2 is a flowchart of a first communication method according to an embodiment of the present application. 4 is a flowchart of a second communication method according to an embodiment of the present application. 4 is a flowchart of a third communication method according to an embodiment of the present application. 10 is a flowchart of a fourth communication method according to an embodiment of the present application. 10 is a flowchart of a fifth communication method according to an embodiment of the present application. 10 is a flowchart of a sixth communication method according to an embodiment of the present application. 10 is a flowchart of a seventh communication method according to an embodiment of the present application. 10 is a flowchart of an eighth communication method according to an embodiment of the present application. 1 is a schematic block diagram of a terminal device according to an embodiment of the present application; 1 is a schematic block diagram of a communication device according to an embodiment of the present application;

To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the following further describes the embodiments of this application in detail with reference to the accompanying drawings.

To facilitate understanding by those skilled in the art, some terms in the embodiments of this application are explained and described below.

In an embodiment of this application, the terminal device is a device having wireless transceiver functionality and may be a fixed device, a mobile device, a handheld device (e.g., a mobile phone), a wearable device, an in-vehicle device, or a wireless device (e.g., a communication module, modem, or chip system) built into any of the above devices. Terminal devices are configured to connect people, things, machines, and the like, and can be widely used in various scenarios, including, but not limited to, the following scenarios: cellular communication, device-to-device (D2D) communication, vehicle-to-everything (V2X), machine-to-machine/machine type communication (M2M/MTC), internet of things (IoT), virtual reality (VR), augmented reality (AR), industrial control, self-driving, telemedicine, smart grid, smart furniture, smart office, smart wearable, smart transportation, smart city, unmanned aerial vehicles, and robots. Terminal devices can sometimes be referred to as user equipment (UE), terminal, access station, UE station, remote station, wireless communication device, user equipment, or the like. For ease of explanation, in the embodiment of this application, an example in which the terminal device is a UE is used for explanation. A remote UE is a UE that requires another UE to provide relay service to access the network. A relay UE is a UE that provides relay service for another UE.

In embodiments of this application, network devices include, for example, access network devices and/or core network devices. An access network device is a device having wireless transceiver functionality and configured to communicate with terminal devices. Access network devices include, but are not limited to, base stations (BTS, NodeB, eNodeB/eNB, or gNodeB/gNB), transmission reception points (TRPs) in the aforementioned communication systems, later evolved base stations in the 3rd generation partnership project (3GPP), access nodes in wireless fidelity (Wi-Fi) systems, wireless relay nodes, wireless backhaul nodes, and the like. A base station may be a macro base station, a micro base station, a picocell base station, a small cell, a relay station, or the like. Multiple base stations may support the aforementioned network using the same access technology or different access technologies. A base station may include one or more co-site or non-co-site transmission and reception points. Alternatively, the network device may be a radio controller, a central unit (CU), and/or a distributed unit (DU) in a cloud radio access network (CRAN) scenario. Alternatively, the network device may be a server, a wearable device, an in-vehicle device, or the like. For example, a network device in a vehicle-to-everything (V2X) technology may be a road side unit (RSU). The following describes an access network device by using an example in which the access network device is a base station. The base station may communicate with a terminal device or may communicate with the terminal device via a relay station. The terminal device may communicate with multiple base stations in different access technologies. The core network device is configured to realize functions such as mobility management, data processing, session management, and policy and charging. The names of devices that realize core network functions in systems using different access technologies may be different. This is not limited in the embodiments of this application. A 5G system is used as an example. The core network device may include an access and mobility management function (AMF), a session management function (SMF), a user plane function (UPF), or the like.

In the embodiments of this application, the communication device configured to realize the functions of a network device may be a network device itself, or may be a device capable of supporting a network device in realizing the functions, such as a chip system. The device may be installed within a network device. In the technical solutions provided in the embodiments of this application, an example in which the device configured to realize the functions of a network device is a network device is used to explain the technical solutions provided in the embodiments of this application.

In the embodiments of this application, unless otherwise specified, quantities of nouns are "singular or plural," i.e., express "one or more." "At least one" means one or more, and "multiple" means two or more. The term "and/or" describes an association relationship between associated objects and expresses that three relationships may exist. For example, A and/or B may express the following three cases: only A is present, both A and B are present, and only B is present. A and B may be singular or plural. The character "/" generally indicates an "or" relationship between associated objects. For example, A/B refers to A or B. "At least one of" or similar expressions refers to any combination of these items and includes any combination of singular items or multiple items. For example, at least one of a, b, or c expresses a, b, c, a and b, a and c, b and c, or a, b, and c. a, b, and c may be singular or plural.

Sequential numbers such as "first" and "second" in the embodiments of this application are intended to distinguish between multiple objects and are not intended to limit the size, content, order, time sequence, priority, or importance of the multiple objects. For example, the first message and the second message may be the same message or different messages. In addition, such names do not indicate that the two messages differ in transmission order, amount of information, content, priority, importance, or the like.

Currently proposed UE relay technologies include a relay method in which the remote UE appears to the RAN. In this relay method, the remote UE can perform path switching.

The path switch process of the remote UE includes a process of switching from a direct link to an indirect link, a process of switching from an indirect link to a direct link, and a process of switching between indirect links. Please refer to Figures 1A to 1D. Figure 1A illustrates a scenario in which the remote UE switches from an indirect link to a direct link, or a scenario in which the remote UE switches from a direct link to an indirect link. For example, the remote UE is a smartwatch. An embedded subscriber identity module (eSIM) card may be installed in the smartwatch, and the smartwatch can communicate directly with an access network device by using the eSIM card. A user carries the smartwatch to run without carrying a mobile phone. In this case, the smartwatch can communicate directly with an access network device through the Uu interface while outdoors. When the user returns home after running, the smartwatch detects the presence of the mobile phone through the sidelink (SL). In this case, to use the mobile phone as a relay UE, the smartwatch may automatically switch from a direct link between the smartwatch and the access network device to an indirect link for relaying performed by using the mobile phone, or the smartwatch may switch from a direct link between the smartwatch and the access network device to an indirect link for relaying performed by using the mobile phone based on a user operation, thereby communicating with the network via the mobile phone, thereby reducing the power consumption of the smartwatch.

Figure 1B illustrates a scenario in which a remote UE switches between indirect links. For example, the remote UE is a smartwatch. A user owns a smartwatch and a mobile phone. Initially, the mobile phone is the relay UE for the smartwatch and provides relay services for the smartwatch. After the user enters a vehicle, the smartwatch may switch from the indirect link for relaying performed by using the mobile phone to the indirect link for relaying performed by using the vehicle to use the vehicle as the new relay UE, thereby communicating with the network via the vehicle, thereby reducing the power consumption of the smartwatch and the mobile phone.

Figure 1C illustrates a scenario in which a remote UE switches from an indirect link to a direct link, or a scenario in which a remote UE switches from a direct link to an indirect link. For example, the remote UE is a smartwatch. The user performs an outdoor activity. Because an eSIM card is installed in the smartwatch, the smartwatch can communicate directly with access network device 2 by using the eSIM card. Then, the user enters a vehicle, and the vehicle travels to another city. In the vehicle's traveling process, the smartwatch automatically (or based on the user's operation) switches from the direct link for direct communication with access network device A to the indirect link for relaying performed by using the vehicle, in order to reduce the power consumption of the smartwatch. Because the vehicle is in a traveling state, access network device B connected to the vehicle and access network device A may be different access network devices.

Figure 1D illustrates a scenario in which a remote UE switches between indirect links. For example, the remote UE is a smartwatch. The user drives vehicle A to a location. When the user enters vehicle A, the smartwatch may establish a connection to vehicle A to use vehicle A as the smartwatch's relay UE, thereby communicating with the network via vehicle A. The user then changes vehicles and enters vehicle B. During the vehicle B journey, the communication quality between the smartwatch and vehicle B gradually deteriorates. In this case, the smartwatch may automatically (or based on a user operation) switch from the indirect link for relaying performed by vehicle B to the indirect link for relaying performed by vehicle B to improve the communication quality of the smartwatch. In addition, since vehicle B is in a traveling state and vehicle B may also be in a traveling state, the access network device serving vehicle B and the access network device serving vehicle B may be different access network devices.

The scenarios shown in Figures 1A and 1B are intra-gNB switching scenarios, while the scenarios shown in Figures 1C and 1D are inter-gNB switching scenarios.

When switching to an indirect link (including switching from a direct link to an indirect link or switching between indirect links), the mainstream solutions currently being discussed are as follows: the base station configures the remote UE to perform measurements, the remote UE performs measurements based on discovery messages from other UEs, the remote UE sends the measurement results to the base station, and the base station decides whether the remote UE should perform a path switch. If the base station determines that the remote UE should perform a path switch, the base station sends configuration information separately to the remote UE and relay UE to configure the path switch. For example, for the process of a remote UE switching from a direct link to an indirect link, please refer to the procedure shown in Figure 2.

S201: The remote UE performs data transmission with the base station.

S202: The base station sends an RRC message to the remote UE, and the remote UE receives the RRC message from the base station. The RRC message includes, for example, measurement configuration information, which is used by the remote UE to measure or select other UEs.

S203: The remote UE measures or selects other UEs. For example, the remote UE may trigger the other UEs to send discovery messages, so that the remote UE measures discovery messages from the other UEs to complete measurement or selection of the other UEs.

S204: The remote UE transmits the measurement result to the base station, and the base station receives the measurement result from the remote UE; or the remote UE transmits the selection result to the base station, and the base station receives the selection result from the remote UE. In Figure 2, transmitting the measurement result is used as an example.

The measurement result may be, for example, a measurement report, or may include the ID of the relay UE. The selection result may be, for example, the result of the remote UE selecting a relay UE, or may include ID information of the relay UE. Optionally, measurement information of the remote UE may also be included.

S205: The base station determines whether the remote UE should perform a path switch based on the measurement result or the selection result. If the base station determines that the remote UE should perform a path switch, S206 and S207 are executed; otherwise, S206 and S207 are not executed.

S206: The base station sends an RRC reconfiguration message to the relay UE, and the relay UE receives the RRC reconfiguration message from the base station. To distinguish it from other RRC reconfiguration messages, the RRC reconfiguration message in S206 is called RRC reconfiguration message 1.

The RRC reconfiguration message 1 may include information configured by the base station for the relay UE, such as configuration information for the Uu interface and sidelink (SL) configuration information. The sidelink is a link between the remote UE and the relay UE. The relay UE provides relay services for the remote UE through the sidelink. After receiving the RRC reconfiguration message 1, the relay UE may perform configuration based on the information included in the RRC reconfiguration message 1, such as configuring the Uu link and sidelink.

S207: The base station sends an RRC reconfiguration message to the remote UE, and the remote UE receives the RRC reconfiguration message from the base station. To distinguish it from other RRC reconfiguration messages, the RRC reconfiguration message in S207 is called RRC reconfiguration message 2.

The RRC reconfiguration message 2 may include information configured by the base station for the remote UE, such as configuration information for the Uu interface and configuration information for the sidelink. After receiving the RRC reconfiguration message 2, the remote UE may perform configuration based on the information included in the RRC reconfiguration message 2, such as configuring the Uu link and the sidelink.

According to the normal procedure, after the configuration of the remote UE and the relay UE is completed, the relay UE can provide relay service for the remote UE, allowing the remote UE to communicate with the base station through the relay UE. However, it is highly likely that the configuration of the relay UE fails or that the relay UE refuses to provide relay service for the remote UE. In this case, the relay UE cannot notify the base station. Therefore, the relay UE must perform processing based on the configuration failure case . The relay UE enters the RRC re-establishment procedure and can only continue to operate after the RRC re-establishment is successful. This obviously causes a degradation of the service quality of the relay UE.

In consideration of this, a technical solution is provided in an embodiment of this application. In this embodiment, regardless of whether the first terminal device is able to provide relay service, the first terminal device can send a second message to the network device for notification, thereby allowing the network device to know whether the first terminal device is able to provide relay service. Therefore, if the first terminal device refuses to provide relay service, the network device can also know this case, so that the first terminal device does not need to interrupt its current communication and can continue to operate normally within the coverage of the network device, in order to improve the service quality of the first terminal device and reduce resources consumed in the RRC re-establishment procedure.

The technical solutions provided in the embodiments of this application may be applied to a 4th generation (4G) system, such as a long term evolution (LTE) system, a 5G system, such as a new radio (NR) system, or a next-generation mobile communication system or another similar communication system. This is not limited to this. In addition, the technical solutions provided in the embodiments of this application may be applied to a device-to-device (D2D) scenario, such as an NR-D2D scenario, or a V2X scenario, such as an NR-V2X scenario, for example, an Internet of Vehicles, such as V2X or vehicle-to-vehicle (V2V), or may be applied in fields such as intelligent driving, driver assistance, or intelligent connected vehicles.

For application scenarios of the embodiments of this application, please refer to Figures 1A, 1B, 1C, or 1D. The access network device in Figures 1A to 1D is, for example, a base station. The access network device corresponds to different devices in different systems. For example, the access network device may correspond to an eNB in a 4G system, or to a 5G access network device, e.g., a gNB, in a 5G system. Of course, the technical solutions provided in the embodiments of this application may alternatively be applied to future mobile communication systems. Therefore, the access network device in Figures 1A to 1D may alternatively correspond to a network device in a future mobile communication system. Figures 1A to 1D use an example in which the access network device is a base station. In fact, referring to the foregoing description, the access network device may alternatively be a device such as an RSU.

The following describes the methods provided in the embodiments of this application with reference to the accompanying drawings. In the accompanying drawings corresponding to the embodiments of this application, all steps indicated by dashed lines are optional steps.

An embodiment of this application provides a first communication method. Figure 3 is a flowchart of the method. The method relates to a process of switching to an indirect link. The process described below uses an example in which the method is applied to the network architecture shown in any one of Figures 1A to 1D.

If the technical solution provided in this embodiment of the application is applied to the network architecture shown in any one of Figures 1A to 1D, the second terminal device in the following description may be the remote terminal device shown in any one of Figures 1A to 1D. If the technical solution provided in this embodiment of the application is applied to the network architecture shown in Figure 1A, the first terminal device in the following description may be the relay terminal device in Figure 1A, and the network device in the following description may be the access network device in Figure 1A. If the technical solution provided in this embodiment of the application is applied to the network architecture shown in Figure 1B, the first terminal device in the following description may be the relay terminal device 1 or relay terminal device 2 in Figure 1B, and the network device in the following description may be the access network device in Figure 1B. If the technical solution provided in this embodiment of the application is applied to the network architecture shown in Figure 1C, the first terminal device in the following description may be the relay terminal device in Figure 1C, and the network device in the following description may be the access network device 1 in Figure 1C. If the technical solution provided in this embodiment of the application is applied to the network architecture shown in FIG. 1D, the first terminal device in the following description may be the relay terminal device 1 in FIG. 1D, and the network device in the following description may be the access network device 1 in FIG. 1D, or the first terminal in the following description may be the relay terminal device 2 in FIG. 1D, and the network device in the following description may be the access network device 2 in FIG. 1D. In addition, the following description uses an example in which the second terminal device is a remote UE and the first terminal device is a relay UE.

S301: The remote UE performs data transmission with the network device.

S302: The network device sends an RRC message to the remote UE. Accordingly, the remote UE receives the RRC message from the network device. The RRC message includes, for example, measurement configuration information, which is used by the remote UE to measure other UEs.

Alternatively, the network device may transmit broadcast information to the remote UE. Thus, the remote UE receives the broadcast information from the network device. The broadcast information may be included, for example, in a system message or in another broadcast message. The broadcast information may include relevant information used by the remote UE to select a relay UE, for example, measurement configuration information for configuring measurements to be performed by the remote UE to select a relay UE.

S303: The remote UE measures or selects other UEs. For example, the remote UE may send a discovery message to trigger other UEs to send a discovery message, and the remote UE may then measure the discovery message from the other UE to complete the measurement or selection of the other UE. Figure 3 uses an example in which the remote UE measures other UEs.

The remote UE may measure other UEs by measuring discovery messages from the other UEs, or may measure other information from the other UEs, for example, measuring data signals from the other UEs. This is not limited here. The remote UE may select other UEs based on the measurement results.

S304: The remote UE transmits the first result to the network device. Accordingly, the network device receives the first result from the remote UE. The first result may be, for example, a measurement result or a selection result. In FIG. 3, an example in which the first result is a measurement result is used.

The measurement result is, for example, a measurement report obtained by the remote UE by measuring at least one UE. The selection result is the result of the remote UE selecting a relay UE, and includes, for example, the ID of the selected relay UE. Optionally, measurement information of the remote UE and the like may further be included.

If the application scenario of this embodiment of this application is switching between indirect links, all communications between the remote UE and the network device in steps S301 to S304 are performed through forwarding via the relay UE connected to the remote UE before the link switching, and the relay UE in the following description is the relay UE connected to the remote UE after the link switching.

S305: The network device determines whether the remote UE should perform a path switch based on the measurement result or the selection result. If the network device determines that the remote UE should perform a path switch, S306 and S307 are executed; otherwise, S306 and S307 are not executed.

S306: The network device transmits a first message to the relay UE. Accordingly, the relay UE receives the first message from the network device. In this embodiment of the present application, the first message is, for example, an RRC reconfiguration message.

The RRC reconfiguration message may include configuration information, which may be for configuring the relay UE to provide relay service for the remote UE. For example, the configuration information may include configuration information for the Uu interface and configuration information for the sidelink. The sidelink is a link between the remote UE and the relay UE. The relay UE provides relay service for the remote UE through the sidelink. After the relay UE receives the RRC reconfiguration message, if the relay UE determines that relay service can be provided for the remote UE, the relay UE may perform configuration based on the configuration information included in the RRC reconfiguration message, for example, configure the Uu link and the sidelink. If the relay UE refuses to provide relay service for the remote UE, the relay UE does not need to perform configuration based on the configuration information included in the RRC reconfiguration message.

In the RRC reconfiguration message, the relevant configuration for performing relaying by the relay UE and the Uu configuration for the service of the relay UE may be indicated separately, for example, by different information elements. For example, the Uu configuration for the service of the relay UE may be carried in the original information element, and the relevant configuration for performing relaying by the relay UE may be carried in a newly added information element, or an additional indication may be newly added for the relevant configuration for performing relaying by the relay UE to indicate that the configuration is for supporting the relay service.

S307: The relay UE sends the second message to the network device. Therefore, the network device receives the second message from the relay UE.

The second message may indicate that the configuration of the relay UE has been completed, or may indicate that the configuration of the relay UE has failed. Alternatively, the second message may indicate that the relay UE is capable of providing relay service, or may indicate that the relay UE refuses to provide relay service. If the second message indicates that the configuration of the relay UE has been completed, the second message may also be considered to implicitly indicate that the relay UE is capable of providing relay service. If the second message indicates that the configuration of the relay UE has failed, the second message may also be considered to implicitly indicate that the relay UE refuses to provide relay service.

In this embodiment of the application, the first message and the second message may be the same type of message. For example, both are RRC reconfiguration type messages. The first message is an RRC reconfiguration message and the second message is an RRC reconfiguration complete message. Alternatively, the first message and the second message may be different types of messages. For example, the first message is an RRC reconfiguration message and the second message is a sidelink UE information (SUI) message.

In addition, the second message may indicate success (including indicating that the configuration of the relay UE has been completed or that the relay UE can provide relay service for the remote UE) or failure (including indicating that the configuration of the relay UE has failed or that the relay UE refuses to provide relay service for the remote UE). In this case, the second message may indicate success and failure by using the same type of message or the same message. For example, the second message is an RRC reconfiguration complete message, and the RRC reconfiguration complete message may indicate success or failure. If the RRC reconfiguration complete message indicates failure, a first information element may be newly added to the RRC reconfiguration complete message, and the first information element indicates failure. In this case, after receiving the second message, the network device needs to analyze the message body of the second message to determine success or failure. The same type of message or the same message can indicate both success and failure, eliminating the need to use excessive types of messages, thereby simplifying the process of identifying different types of messages by the network device.

Alternatively, the second message may indicate success or failure by using a different type of message. For example, when the second message indicates success, the second message may be an RRC reconfiguration complete message. When the second message indicates failure, the second message may be an SUI message or a failure information message, or may be a newly added message in this embodiment of the application. For example, the second message may be a message specifically indicating whether the terminal device provides relay service. In this case, the network device does not need to parse the message body of the second message, but can determine success or failure based on the type information carried in the message header of the second message. This helps reduce the operational load on the network device.

For example, if the relay UE performs configuration based on the configuration information included in the RRC reconfiguration message and determines that the configuration is successful and that the relay service can be provided, the second message may indicate that the configuration of the relay UE is complete or that the relay UE is capable of providing the relay service. In another example, if the relay UE performs configuration based on the configuration information included in the RRC reconfiguration message and the configuration fails, the second message may indicate that the configuration of the relay UE has failed or may indicate that the relay UE refuses to provide the relay service. In another example, if the relay UE determines that some of the parameters in the configuration information included in the RRC reconfiguration message are not supported, the second message may indicate that the relay UE refuses to provide the relay service. In yet another example, if the relay UE does not perform configuration based on the configuration information included in the RRC reconfiguration message and determines that it refuses to provide the relay service, the second message may indicate that the relay UE refuses to provide the relay service.

In an optional implementation, if the second message indicates that the configuration of the relay UE has failed or that the relay UE refuses to provide relay service, the second message may further include a cause value. The cause value may indicate the cause of the refusal to provide relay service by the relay UE, thereby allowing the network device to clarify the cause when the relay UE is unable to provide relay service and the network device to take corresponding measures. Alternatively, the cause value may implicitly indicate that the configuration has failed. That is, if the second message includes an indication of a cause value, it indicates that the configuration has failed or that the relay service is refused to be provided. If the second message does not include an indication of a cause value, it indicates that the configuration has succeeded or that relay service can be provided. The causes of refusal to provide relay service by a relay UE include the following: the relay UE does not support the configuration of the Uu interface (i.e., does not support the configuration of the Uu interface included in the configuration information); the relay UE does not support the configuration of the PC5 interface (i.e., does not support the configuration of the PC5 interface included in the configuration information); admission control performed by the relay UE for the remote UE fails; the configuration performed by the relay UE based on the configuration information fails; the relay UE does not support the integrity protection algorithm configured by using the configuration information (does not support the integrity protection algorithm information included in the configuration message); the relay UE does not support the 5G QoS identifier (5QI) or PC5 5G QoS identifier (PC5 5QI, PQI) configured by using the configuration information; the relay UE cannot identify the quality of service (QoS) flow ID indicated by the configuration information; the relay UE does not support the network slice indicated by the configuration information; the relay UE has insufficient battery power; The reasons for refusing to provide relay service by the relay UE may include one or more of the following: the packet data convergence protocol (PDCP) of the UE is overloaded; or the relay UE does not support the computing capabilities indicated by the configuration information. For example, the reason for refusing to provide relay service by the relay UE is that the relay UE does not support the configuration of the Uu interface; the reason for refusing to provide relay service by the relay UE is that the relay UE does not support the configuration of the PC5 interface; the reason for refusing to provide relay service by the relay UE is that the relay UE cannot identify the QoS flow ID indicated by the configuration information; or the reason for refusing to provide relay service by the relay UE is that the relay UE does not support the network slicing indicated by the configuration information; and the relay UE has insufficient battery power.

If the second message indicates success and failure by using the same type of message or the same message, optionally, if the second message indicates failure, a first information element and a second information element may be newly added to the second message, where the first information element may indicate failure and the second information element is for carrying a cause value. For example, the second message is an RRC reconfiguration complete message, and the RRC reconfiguration complete message may indicate success or may indicate failure. If the RRC reconfiguration complete message indicates failure, a first information element and a second information element may be newly added to the RRC reconfiguration complete message, where the first information element indicates failure and the second information element is for carrying a cause value.

Alternatively, if the second message indicates success and failure by using a different type of message, optionally, if the second message indicates failure, a third information element may be added to the second message, where the third information element is for carrying a cause value. For example, when the second message indicates success, the second message may be an RRC reconfiguration complete message. When the second message indicates failure, the second message may be an SUI message, where a third information element is newly added to the SUI message, and the third information element may carry a cause value. Because the second message indicates success and failure by using a different type of message, it can be known that the second message implicitly indicates failure. In this case, a small amount of information element is newly added to the second message. This helps reduce transmission overhead.

S308: The relay UE does not initiate the RRC re-establishment process.

If the second message indicates that the configuration of the relay UE has failed or that the relay UE refuses to provide relay service, S308 may be executed. In this case, since the network device knows that the relay UE does not provide relay service, the relay UE does not need to initiate an RRC re-establishment process and continues to perform normal communication with the network device. This improves the service quality of the relay UE and reduces the resources consumed in the RRC re-establishment procedure. It may be understood that the relay UE not initiating an RRC re-establishment process may mean that the relay UE continues to communicate with the network device through the existing RRC connection.

The fact that the relay UE does not initiate the RRC re-establishment process can be expressed as follows: The relay UE continues to apply the configuration of the connection between the relay UE and the network device before the first message is received. In other words, the status of the connection between the relay UE and the network device does not change. In other words, if the configuration of the connection between the relay UE and the network device (in other words, the status of the connection) does not change, it may implicitly indicate that the relay UE does not initiate RRC re-establishment.

However, if the second message indicates that the configuration of the relay UE has been completed or that the relay UE can provide relay service, S207 shown in FIG. 2 may be executed. In addition, after the configuration of the remote UE has also been completed, the relay UE can provide relay service.

Alternatively, S207 shown in FIG. 2 may have occurred even if the second message indicated that the configuration of the relay UE had failed or that the relay UE refused to provide relay service. For example, S207 may have been executed before the network device received the second message. In this case, the remote UE must determine that the path switch has failed. How the remote UE determines that the path switch has failed is described in the following embodiment.

In this embodiment of the application, regardless of whether the relay UE can provide relay service, the relay UE can send a second message to the network device for notification, so that the network device can know whether the relay UE can provide relay service. Therefore, if the relay UE refuses to provide relay service, the network device can also know this case, so that the relay UE does not need to enter the RRC re-establishment procedure and can continue to operate normally within the coverage of the network device, in order to improve the service quality of the relay UE and reduce the resources consumed in the RRC re-establishment procedure.

An embodiment of this application provides a second communication method. Figure 4 is a flowchart of the method. The method relates to a process of switching to an indirect link. In the process described below, an example is used in which the method is applied to the network architecture shown in any one of Figures 1A to 1D. For the devices in Figures 1A to 1D that are the relay UE, remote UE, and network device in this embodiment of this application, please refer to the description of the first communication method.

S401: The remote UE performs data transmission with the network device.

S402: The network device sends an RRC message to the remote UE. Accordingly, the remote UE receives the RRC message from the network device. The RRC message includes, for example, measurement configuration information, which is used by the remote UE to measure other UEs.

Alternatively, the network device may transmit broadcast information to the remote UE. Thus, the remote UE receives the broadcast information from the network device. The broadcast information may be included, for example, in a system message or in another broadcast message. The broadcast information may include relevant information used by the remote UE to select a relay UE, for example, measurement configuration information for configuring measurements to be performed by the remote UE to select a relay UE.

S403: The remote UE measures or selects other UEs. For example, the remote UE may send a discovery message to trigger other UEs to send discovery messages, so that the remote UE can measure discovery messages from other UEs to complete measurement or selection of the other UEs. In Figure 4, an example in which the remote UE measures other UEs is used.

The remote UE may measure other UEs by measuring discovery messages from the other UEs, or may measure other information from the other UEs, such as data signals from the other UEs. This is not limited here. The remote UE may select other UEs based on the measurement results.

S404: The remote UE transmits the first result to the network device. Accordingly, the network device receives the first result from the remote UE. The first result may be, for example, a measurement result or a selection result. In FIG. 4, an example in which the first result is a measurement result is used.

The measurement result is, for example, a measurement report obtained by measuring at least one UE. The selection result is the result of selecting a relay UE by the remote UE, and includes, for example, the ID of the selected relay UE. Optionally, measurement information of the remote UE and the like may further be included.

If the application scenario of this embodiment of this application is switching between indirect links, all communications between the remote UE and the network device in steps S401 to S404 are performed through forwarding via the relay UE connected to the remote UE before the link switching, and the relay UE in the following description is the relay UE connected to the remote UE after the link switching.

S405: The network device determines whether the remote UE should perform a path switch based on the measurement result or the selection result. If the network device determines that the remote UE should perform a path switch, proceed to S406; otherwise, the subsequent steps are not executed.

S406: The network device sends a first message to the relay UE. Accordingly, the relay UE receives the first message from the network device. The first message may be for inquiring whether the relay UE can provide relay service. In this embodiment of the present application, the first message may be, for example, an RRC reconfiguration message, or the first message may be a message that is newly added in this embodiment of the present application and is specifically for inquiring whether the terminal device can provide relay service.

In this embodiment of the application, the network device does not first send configuration information to the relay UE, but first inquires whether the relay UE can provide relay service by using a first message. If the relay UE can provide relay service, the network device may send configuration information to the relay UE, thereby making the transmission of the configuration information more effective. Alternatively, the network device sends one or more sets of configuration information to the relay UE to inquire whether the relay UE can provide relay service based on the corresponding configuration.

In an optional implementation, the first message may include one or more of the following: a remote UE identifier, integrity protection algorithm information or rate information, encryption algorithm information or rate information, PQI or 5QI, QoS, network slice information, configuration information, or computing capability information. For example, the first message includes a remote UE identifier, the first message includes a PQI, the first message includes configuration information, or the first message includes a remote UE identifier and network slice information. The first message may be for implicitly inquiring whether the relay UE is capable of providing relay service by using one or more of the foregoing included in the first message. Alternatively, the first message may further include inquiry information in addition to one or more of the foregoing, where the inquiry information is for inquiring whether the relay UE is capable of providing relay service. For a description of the configuration information, please refer to the embodiment depicted in FIG. 3.

Integrity protection algorithm information or integrity protection rate information, encryption algorithm information or encryption rate information, configuration information, PQI or 5QI, QoS, network slice information, computing capability information, and the like are all capabilities required by the remote UE, or in other words, capabilities required by the relay UE to perform relaying. The first message includes information about the relevant capabilities required by the relay UE to perform relaying, thereby allowing the relay UE to better determine whether it can provide relay service for the remote UE. For example, if the relay UE does not have the capabilities indicated by the first message, the relay UE can decide to refuse to provide relay service for the remote UE, thereby making the relay UE's decision more accurate. In an embodiment of this application, the UE identifier is, for example, the UE ID, and the UE ID is, for example, the UE's layer 2 ID or the ID of an application (APP) installed for the UE that requires relay service.

S407: The relay UE sends a second message to the network device. Accordingly, the network device receives the second message from the relay UE. The second message may indicate that the relay UE is able to provide the relay service, or may indicate that the relay UE refuses to provide the relay service.

In an optional implementation, when the first message includes one or more sets of configuration information, if the second message indicates that the relay UE is capable of providing a relay service, the second message may further include first indication information indicating the configuration information for which the relay UE is capable of providing a relay service. That is, the first indication information indicates that the UE is capable of providing a relay service for one or more sets of configuration information.

In an optional implementation, if the second message indicates that the relay UE refuses to provide the relay service, the second message may further include a cause value. The cause value may indicate the reason for the refusal to provide the relay service by the relay UE, so that the network device can determine the reason why the relay UE cannot provide the relay service, and the network device can take corresponding measures. Causes for refusing to provide relay service by the relay UE may include one or more of the following: the relay UE does not support the configuration of the Uu interface (i.e., does not support the configuration of the Uu interface included in the first message); the relay UE does not support the configuration of the PC5 interface (i.e., does not support the configuration of the PC5 interface included in the first message); admission control performed by the relay UE for the remote UE fails; the relay UE does not support the integrity protection algorithm configured by using the first message; the relay UE does not support the 5QI or PQI configured by using the first message; the relay UE cannot identify the QoS flow ID indicated by the first message; the relay UE does not support the network slicing indicated by the first message; the relay UE has insufficient battery power; the relay UE's PDCP is overloaded; or the relay UE does not support the computing capability indicated by the first message. For example, the reason for refusing to provide the relay service by the relay UE is that the relay UE does not support the configuration of the Uu interface, the reason for refusing to provide the relay service by the relay UE is that the relay UE does not support the configuration of the PC5 interface, the reason for refusing to provide the relay service by the relay UE is that the relay UE cannot identify the QoS flow ID indicated by the first message, or the reason for refusing to provide the relay service by the relay UE is that the relay UE does not support the network slicing indicated by the first message and the relay UE has insufficient battery power.

For further details of S407, such as the implementation of the second message, please refer to S307 in the embodiment shown in Figure 3.

If the second message indicates that the relay UE can provide relay service and does not include configuration information, the process may proceed to S408 and S409. Alternatively, if the second message indicates that the relay UE can provide relay service and does include configuration information, the process may proceed to S409, and S408 need not be executed. If the second message indicates that the relay UE refuses to provide relay service, S410 may be executed. In addition, if the second message indicates that the relay UE refuses to provide relay service, the network device knows that the relay UE does not provide relay service, so the relay UE does not need to initiate an RRC re-establishment process and continues to communicate normally with the network device. Therefore, the service quality of the relay UE is improved, and resources consumed in the RRC re-establishment procedure are reduced.

The fact that the relay UE does not initiate the RRC re-establishment process can be expressed as follows: The relay UE continues to apply the configuration of the connection between the relay UE and the network device before the first message is received. In other words, the status of the connection between the relay UE and the network device does not change. In other words, if the configuration of the connection between the relay UE and the network device (in other words, the status of the connection) does not change, it may implicitly indicate that the relay UE does not initiate RRC re-establishment.

S408: The network device sends an RRC reconfiguration message to the relay UE. Thus, the relay UE receives the RRC reconfiguration message from the network device. To distinguish it from other RRC reconfiguration messages, the RRC reconfiguration message in S408 is referred to as RRC reconfiguration message 1.

The RRC reconfiguration message 1 may include configuration information. For example, the configuration information is referred to as configuration information 1. The configuration information 1 includes, for example, configuration information for the Uu interface and configuration information for the sidelink. The sidelink is a link between the remote UE and the relay UE. The relay UE provides relay service for the remote UE through the sidelink. If the relay UE can provide relay service for the remote UE, the network device may send configuration information 1 to the relay UE. After receiving the RRC reconfiguration message 1, the relay UE may perform configuration based on the configuration information 1, for example, configure the Uu link and the sidelink.

In this embodiment of the application, the network device sends configuration information 1 after the relay UE determines that relay service can be provided, but the configuration of the relay UE may still fail. For example, the relay UE enters an area with a weak signal, or the relay UE still does not support some of the parameters included in configuration information 1, and some of the parameters are not included in the first message. In this case, if the configuration of the relay UE has failed, the relay UE may send a second message to the network device. In this case, the second message may indicate that the configuration has failed.

S409: The network device sends an RRC reconfiguration message to the remote UE, and the remote UE receives the RRC reconfiguration message from the network device. To distinguish it from other RRC reconfiguration messages, the RRC reconfiguration message in S409 is referred to as RRC reconfiguration message 2.

The RRC reconfiguration message 2 may include information configured by the network device for the remote UE. For example, the information included in the RRC reconfiguration message 2 is referred to as configuration information 2, and the configuration information 2 may include configuration information for the Uu interface and configuration information for the sidelink. If the relay UE can provide relay services for the remote UE, the network device may send the configuration information 2 to the remote UE. After receiving the RRC reconfiguration message 2, the remote UE may perform configuration based on the configuration information 2, for example, configure the Uu link and the sidelink.

After the configuration of the remote UE and relay UE is completed, the relay UE can provide relay services for the remote UE, allowing the remote UE to communicate with network devices through the relay UE.

S410: The relay UE does not initiate the RRC re-establishment process.

If the second message indicates that the configuration of the relay UE has failed or that the relay UE refuses to provide relay service, S410 may be executed. In this case, since the network device knows that the relay UE does not provide relay service, the relay UE does not need to initiate the RRC re-establishment process and continues to perform normal communication with the network device to improve the service quality of the relay UE and reduce resources consumed in the RRC re-establishment procedure.

For further details on S410, please refer to S308 in the embodiment shown in Figure 3.

In this embodiment of the application, the network device may inquire whether the relay UE can provide relay service by using a first message. For example, the first message is a message specifically for inquiring whether the terminal device can provide relay service, and the second message is not an RRC reconfiguration complete message. In this case, in this embodiment of the application, it is equivalent to not using a message in the RRC re-establishment process and not changing the existing RRC re-establishment procedure. In this way, the technical solution in this embodiment of the application can be better compatible with existing technologies.

Next, one problem is considered. From the above procedure, it can be known that the remote UE needs to measure other UEs to realize path switching. If the reporting conditions for the measurement report are met, the remote UE may transmit the measurement results to the network device. Regardless of whether the remote UE transmits the measurement results to the network device, the measurement process may be performed continuously, which consumes high battery power of the remote UE. In addition, the remote UE usually performs measurements based on a discovery message. In this case, the other UE (e.g., a relay UE) needs to send a discovery message, so that the remote UE performs measurements based on the discovery message. However, it is possible that one UE does not continuously send discovery messages. Therefore, the remote UE needs to first send a discovery message to the other UE, which requests, for example, a corresponding service (e.g., a relay service). After receiving the discovery message, the other UE sends a discovery message to the remote UE if the service can be provided. In this case, the remote UE may perform measurements based on the received discovery message. It may be noted that in order to stimulate the relay UE to send a discovery message to the remote UE, the remote UE may need to send the discovery message multiple times and receive the discovery message multiple times, which also requires consuming a large amount of resources.

To solve this problem, an embodiment of this application provides a third communication method. According to this method, measurement resources can be saved and battery power of the remote UE can be saved. Figure 5 is a flowchart of the method. The method may relate to a process of switching from a direct link to an indirect link, a process of switching between direct links, a process of switching from an indirect link to a direct link, or a process of switching between indirect links. In the process described below, an example is used in which the method is applied to the network architecture shown in any one of Figures 1A to 1D.

If the technical solution provided in this embodiment of the application is applied to the network architecture shown in any one of Figures 1A to 1D, the second terminal device in the following description may be the remote terminal device shown in any one of Figures 1A to 1D. If the technical solution provided in this embodiment of the application is applied to the network architecture shown in Figure 1A, the first terminal device in the following description may be the relay terminal device in Figure 1A, and the network device in the following description may be the access network device in Figure 1A. If the technical solution provided in this embodiment of the application is applied to the network architecture shown in Figure 1B, the first terminal device in the following description may be the relay terminal device 1 or the relay terminal device 2 in Figure 1B, and the network device in the following description may be the access network device in Figure 1B. If the technical solution provided in this embodiment of the application is applied to the network architecture shown in Figure 1C, the first terminal device in the following description may be the relay terminal device in Figure 1C, and the network device in the following description may be the access network device 1 or the access network device 2 in Figure 1C. If the technical solution provided in this embodiment of the application is applied to the network architecture shown in FIG. 1D, the first terminal device in the following description may be the relay terminal device 1 in FIG. 1D, and the network device in the following description may be the access network device 1 in FIG. 1D, or the first terminal in the following description may be the relay terminal device 2 in FIG. 1D, and the network device in the following description may be the access network device 2 in FIG. 1D.

In addition, the following description uses an example in which the second terminal device is a remote UE and the first terminal device is a relay UE. Relay terminal device 1 and relay terminal device 2 in FIG. 5 simply indicate that there may be multiple UEs that can serve as relay UEs, and the remote UE may measure multiple UEs when performing measurements.

S501: The remote UE performs data transmission with the network device.

S502: The network device sends an RRC message to the remote UE. Accordingly, the remote UE receives the RRC message from the network device. The RRC message includes, for example, measurement configuration information, which is used by the remote UE to measure other UEs.

Alternatively, the network device may transmit broadcast information to the remote UE. Thus, the remote UE receives the broadcast information from the network device. The broadcast information may be included, for example, in a system message or in another broadcast message. The broadcast information may include relevant information used by the remote UE to select a relay UE, for example, measurement configuration information for configuring measurements to be performed by the remote UE to select a relay UE.

S503: The remote UE measures or selects other UEs. For example, the remote UE may send a discovery message to trigger other UEs to send discovery messages, so that the remote UE can measure discovery messages from other UEs to complete measurement or selection of the other UEs. Figure 5 uses an example in which the remote UE measures other UEs.

The remote UE may measure other UEs by measuring discovery messages from the other UEs, or may measure other information from the other UEs, for example, measuring data signals from the other UEs. This is not limited here. The remote UE may select other UEs based on the measurement results.

S504: The remote UE transmits the first result to the network device. Accordingly, the network device receives the first result from the remote UE. The first result may be, for example, a measurement result or a selection result. In FIG. 5, an example in which the first result is a measurement result is used.

The measurement result may include, for example, a report of measuring at least one UE by the remote UE. The selection result may be a result of selecting a relay UE by the remote UE, and may include, for example, the ID of the selected relay UE. Optionally, measurement information of the remote UE and the like may also be included.

In this embodiment of the application, after the remote UE transmits the measurement result, if the first condition is not met, the remote UE does not perform the first action, and the first action may be considered to be an action related to the measurement process.

The first operation may include one or more of the following: sending a discovery message, measuring other UEs, or transmitting a new first result to the network device (in other words, transmitting the first result to the network device). For example, the first operation includes sending a discovery message, the first operation includes measuring other UEs, the first operation includes transmitting the new first result to the network device, or the first operation includes sending a discovery message and measuring other UEs.

For example, if the first operation includes sending a discovery message, but does not include measuring other UEs, and does not include sending a new first result to the network device, the remote UE may not send the discovery message if the first condition is not met (e.g., if the remote UE has previously sent a discovery message, the remote UE stops sending the discovery message if the first condition is not met). However, if the remote UE receives a discovery message from another UE, the remote UE may still perform measurements based on the received discovery message and measurement configuration information at S502 to obtain new measurement results. When a reporting condition for the measurement report is met, the remote UE may further send a new first result to the network device. Alternatively, if the first operation includes measuring other UEs, but does not include sending a discovery message, and does not include sending a new first result to the network device, the remote UE may not measure the other UEs if the first condition is not met. Because the other UEs do not need to be measured, the remote UE may not need to send a discovery message, or the remote UE may send a discovery message but not perform measurements even if the remote UE receives a discovery message from the other UE. In addition, because the other UEs do not need to be measured and therefore do not need to send a new first result to the network device, the remote UE does not obtain a measurement report. Alternatively, if the first operation includes sending a new measurement result to the network device, but does not include sending a discovery message, and does not include measuring other UEs, the remote UE may or may not send a discovery message if the first condition is not met. Additionally, if the remote UE receives a discovery message from another UE, the remote UE may still perform measurements based on the received discovery message, but a measurement report may not be formed after the remote UE performs the measurements. That is, measurements may be performed, but no measurement report may be obtained. Alternatively, if the remote UE performs measurements, the remote UE may instead obtain a measurement report. However, even if the reporting conditions for the measurement report are met, the remote UE does not send the measurement report to the network device.

In this embodiment of the application, the first condition is related to a timer. See explanation below.

S505: The remote UE starts a timer.

For example, when S504 is completed, i.e., when the transmission of the measurement results to the network device is completed, the remote UE may start a timer. Satisfaction of the first condition may mean, for example, that the timer has expired, and non-satisfaction of the first condition may mean, for example, that the timer has not expired.

S506: If the timer has not expired, the remote UE does not perform the first action.

In other words, in this embodiment of the application, if the timer has not expired, the remote UE does not need to perform the first operation. Because the remote UE transmits the measurement results to the network device, and the network device can determine whether the remote UE can perform a path switch based on the measurement results, the network device's decision is not significantly affected even if the remote UE does not perform measurements and does not transmit new measurement results to the network device. In addition, this method can reduce the measurement process of the remote UE, reduce resources consumed in the measurement process, and save battery power of the remote UE.

S507: When the timer expires, the remote UE may perform a first action.

If the timer has expired and the remote UE does not receive configuration information (for configuring the remote UE to perform a path switch) from the network device, the remote UE may continue to perform the first operation to again transmit new measurement results to the network device. Of course, here it is simply described that if the timer has expired and the remote UE does not receive configuration information (for configuring the remote UE to perform a path switch) from the network device, the remote UE may perform the first operation. However, whether to perform the first operation depends on the implementation of the remote UE. Here, the possibility is simply described and does not constitute a limitation on the behavior of the remote UE. For example, if the timer has expired, the remote UE may measure other UEs. When the reporting conditions for the measurement report are met, the remote UE transmits new measurement results to the network device. If the network device determines, based on the new measurement results, that the remote UE can perform a path switch, the network device may send configuration information separately to the remote UE and the relay UE (in the case of switching to an indirect link).

In this embodiment of the application, after transmitting the measurement result to the network device, the remote UE may start a timer. When the timer has not expired, the remote UE may not need to perform measurement-related operations, in order to reduce the measurement process of the remote UE and save resources required in the measurement process. In addition, because the remote UE reduces related operations, the battery power of the remote UE may also be saved.

An embodiment of this application provides a fourth communication method. Figure 6 is a flowchart of the method. The method may relate to a process of switching from a direct link to an indirect link, a process of switching between direct links, a process of switching from an indirect link to a direct link, or a process of switching between indirect links. In the process described below, an example is used in which the method is applied to the network architecture shown in any one of Figures 1A to 1D. For details of the relay UE, remote UE, and network device in this embodiment of this application, such as the devices in Figures 1A to 1D, please refer to the description of the third communication method.

In addition, the following description uses an example in which the second terminal device is a remote UE and the first terminal device is a relay UE. Relay terminal device 1 and relay terminal device 2 in FIG. 6 simply indicate that there may be multiple UEs that can serve as relay UEs, and a remote UE may measure multiple UEs when performing measurements. In the following description, the relay UE that serves as the first terminal device is, for example, relay terminal device 1.

S601: The remote UE performs data transmission with the network device.

S602: The network device sends an RRC message to the remote UE. Accordingly, the remote UE receives the RRC message from the network device. The RRC message includes, for example, measurement configuration information, which is used by the remote UE to measure other UEs.

Alternatively, the network device may transmit broadcast information to the remote UE. Thus, the remote UE receives the broadcast information from the network device. The broadcast information may be included, for example, in a system message or in another broadcast message. The broadcast information may include relevant information used by the remote UE to select a relay UE, for example, measurement configuration information for configuring measurements to be performed by the remote UE to select a relay UE.

S603: The remote UE measures or selects other UEs. For example, the remote UE may send a discovery message to trigger other UEs to send a discovery message, and the remote UE may then measure the discovery message from the other UE to complete the measurement or selection of the other UE. Figure 6 uses an example in which the remote UE measures other UEs.

The remote UE may measure other UEs by measuring discovery messages from the other UEs, or may measure other information from the other UEs, for example, measuring data signals from the other UEs. This is not limited here. The remote UE may select other UEs based on the measurement results.

S604: The remote UE transmits the first result to the network device. Accordingly, the network device receives the first result from the remote UE. The first result may be, for example, a measurement result or a selection result. In FIG. 6, an example in which the first result is a measurement result is used.

The measurement result may include, for example, a report of measuring at least one UE by the remote UE. The selection result may be a result of selecting a relay UE by the remote UE, and may include, for example, the ID of the selected relay UE. Optionally, measurement information of the remote UE and the like may also be included.

In this embodiment of the present application, after the remote UE transmits the first result, if the first condition is not met, the remote UE does not perform the first action, and the first action may be considered to be an action related to the measurement process. For a description of the first action, please refer to the embodiment shown in Figure 3.

In this embodiment of the application, the first condition relates to messages from network devices. See the description below.

S605: The network device determines whether the remote UE should perform a path switch based on the measurement result or the selection result. If the network device determines that the remote UE should perform a path switch, S606 and S607 are executed, or S608 and S609 are executed. If the network device determines that the remote UE should not perform a path switch, the subsequent steps may not be executed, or S610 may be executed.

S606: The network device sends a first message to the relay UE. Accordingly, the relay UE receives the first message from the network device.

For further details on S606, please refer to S306 in the embodiment shown in Figure 3.

S607: The relay UE sends the second message to the network device. Therefore, the network device receives the second message from the relay UE.

The second message may indicate that the configuration of the relay UE has been completed, or may indicate that the configuration of the relay UE has failed. Alternatively, the second message may indicate that the relay UE is capable of providing relay service, or may indicate that the relay UE refuses to provide relay service. For example, in this embodiment of the application, the second message indicates that the configuration of the relay UE has failed, or indicates that the relay UE refuses to provide relay service.

For further details on S607, please refer to S307 in the embodiment shown in Figure 3.

S608: The network device sends a first message to the relay UE. Accordingly, the relay UE receives the first message from the network device. The first message may be for inquiring whether the relay UE can provide relay service.

For further details on S608, please refer to S406 in the embodiment shown in Figure 4.

S609: The relay UE sends the second message to the network device. Therefore, the network device receives the second message from the relay UE.

The second message may indicate that the configuration of the relay UE has been completed, or may indicate that the configuration of the relay UE has failed. Alternatively, the second message may indicate that the relay UE is capable of providing relay service, or may indicate that the relay UE refuses to provide relay service. For example, in this embodiment of the application, the second message indicates that the configuration of the relay UE has failed, or indicates that the relay UE refuses to provide relay service.

For further details on S609, please refer to S407 in the embodiment shown in Figure 4.

Processes S606 and S607 are parallel to processes S608 and S609, and only one of the processes needs to be executed.

S610: The network device sends a third message to the remote UE. Accordingly, the remote UE receives the third message from the network device. The third message may indicate that the relay UE refuses to provide the relay service, or may indicate that the relay UE reselects a UE that can provide the relay service. The third message may be, for example, an RRC message, or another message.

S611: The remote UE performs a first operation.

In this embodiment of the application, if the remote UE receives the third message from the network device, the first condition is deemed to be met and the first operation may be performed. If the remote UE does not receive the third message from the network device, the first condition is deemed not to be met. When the first condition is not met, the remote UE does not need to perform the first operation in order to reduce the measurement process of the remote UE and save resources required in the measurement process. In addition, because the remote UE reduces measurement-related operations, the battery power of the remote UE may also be saved. However, when the first condition is met, the remote UE knows that a UE capable of providing relay service needs to be reselected. In this case, the remote UE may trigger a measurement process to select another relay UE.

In an optional implementation, after S604 is executed or before S604 is executed, the remote UE may further send a fourth message to the network device. The fourth message may indicate an energy saving requirement, which may be understood as the fourth message indicating that the remote UE has an energy saving requirement. In this case, after receiving the fourth message, the network device may determine that the remote UE has an energy saving requirement. In this case, optionally, the network device may further send first information to the remote UE. Thus, the remote UE receives the first information from the network device. The first information may be included in the third message or may be transmitted by using another message. The first information may include information about M UEs. The information about the UEs may be, for example, UE identifiers, where M is a positive integer. The M UEs are UEs that do not need to be measured or UEs that refuse to provide relay service. If the remote UE receives the first information, the remote UE does not need to measure the M UEs. This reduces the measurement process of the remote UE and reduces the power consumption of the remote UE to meet the energy saving requirements of the remote UE.

Optionally, the fourth message may further include information about N UEs. The information about the UEs may be, for example, UE identifiers, where N is a positive integer. The N UEs may be, for example, UEs that refuse to provide relay service. For example, if the remote UE determines, based on historical information, that N UEs have refused to provide relay service for the remote UE, the remote UE may add the information about the N UEs to a blacklist and send the blacklist to the network device. In this way, when configuring the remote UE to perform measurements, the network device may consider not configuring the remote UE to measure N UEs to reduce invalid measurement processes for the remote UE. If the fourth message includes information about N UEs and the network device sends the first information, M UEs may be determined by the network device based on N UEs and several other factors. For example, M UEs is N UEs. In this case, M=N. Alternatively, M UEs and N UEs have no intersection. Alternatively, the M UEs and the N UEs have some commonality but are not exactly the same.

In this embodiment of the present application, if the remote UE does not receive a third message from the network device after the remote UE transmits the measurement result to the network device, the remote UE may not need to perform measurement-related operations, thereby reducing the measurement process of the remote UE and saving resources required in the measurement process. In addition, because the remote UE reduces related operations, the battery power of the remote UE may also be saved.

Next, another problem is considered. Currently, the remote UE can either succeed or fail in a path switch. However, when the remote UE fails in a path switch, the remote UE cannot make a decision. Specifically, the remote UE cannot determine when a path switch has failed. A possible consequence is that the remote UE cannot continue to operate.

Therefore, an embodiment of this application provides a fifth communication method. According to this method, the remote UE can determine when a path switch has failed, so that the operation of the remote UE can continue. Figure 7 is a flowchart of the method. The method may relate to a process of switching from an indirect link to a direct link. The process described below uses an example in which the method is applied to the network architecture shown in Figure 1A or Figure 1C.

If the technical solution provided in this embodiment of this application is applied to the network architecture shown in FIG. 1A, it indicates that the source network device before the remote UE performs a path switch and the target network device after the remote UE performs a path switch are the same network device. In this case, the first terminal device in the following description may be the relay terminal device in FIG. 1A, the second terminal device in the following description may be the remote terminal device in FIG. 1A, the network device in the following description may be the access network device in FIG. 1A, and the network device is both the source network device and the target network device. If the technical solution provided in this embodiment of this application is applied to the network architecture shown in FIG. 1C, it indicates that the source network device before the remote UE performs a path switch and the target network device after the remote UE performs a path switch are different network devices. In this case, the first terminal device in the following description may be the relay terminal device in FIG. 1C, the second terminal device in the following description may be the remote terminal device in FIG. 1C, and the network device in the following description (which is also called the first network device, and the first network device is the source network device) may be access network device 1 in FIG. 1C. In addition, the following further relates to the target network device, which may be called the second network device, and may be access network device 2 in FIG. 1C.

In addition, the following description uses an example in which the second terminal device is a remote UE and the first terminal device is a relay UE. In addition, this embodiment of the application uses an example in which the source network device and the target network device are different network devices.

S701: The remote UE performs data transmission with the source network device.

S702: The source network device sends an RRC message to the remote UE. Accordingly, the remote UE receives the RRC message from the source network device. The RRC message includes, for example, measurement configuration information, which is used by the remote UE to measure a reference signal from the source network device.

S703: The remote UE measures the reference signal from the network device.

For example, the remote UE may receive a synchronization signal block (SSB) or a channel state information reference signal (CSI-RS) from the source network device, and the remote UE may measure the strength of the received signal to complete measurements for the source network device. In addition, the remote UE may further measure the target network device. For example, the remote UE receives an SSB or CSI-RS from the target network device. The remote UE may measure the strength of the received signal to complete measurements for the target network device.

S704: The remote UE transmits the measurement results to the source network device. Accordingly, the source network device receives the measurement results from the remote UE. The measurement results include, for example, a measurement report obtained by measuring at least one frequency or cell.

Communication between the remote UE and the source network device in steps S701 to S704 is performed through forwarding via the relay UE.

S705: The source network device makes a handover decision. Based on the measurement results, the source network device determines whether the remote UE can perform a path switch. In this embodiment of the application, based on the measurement results, the source network device determines whether the remote UE can be handed over from the relay UE to the target network device. If the source network device determines that the remote UE can be handed over from the relay UE to the target network device, S706 is executed.

S706: The source network device sends a handover request message to the target network device. Accordingly, the target network device receives a handover request message from the source network device. The handover request message may indicate that the remote UE should be handed over to the target network device.

S707: The target network device sends a handover request acknowledgement message to the source network device. Accordingly, the source network device receives a handover request acknowledgement message from the target network device. The handover request acknowledgement message may indicate that the remote UE is allowed to be handed over to the target network device, or may indicate that the remote UE is not allowed to be handed over to the target network device.

If the handover request acknowledgement message indicates that the remote UE is allowed to be handed over to the target network device, proceed to S708; otherwise, no subsequent steps are performed.

If the target network device and the source network device are the same network device, after S705, S706 and S707 do not need to be performed and the process proceeds to S708.

S708: The source network device sends an RRC reconfiguration message to the remote UE. Thus, the remote UE receives the RRC reconfiguration message from the source network device.

The RRC reconfiguration message may include configuration information. The configuration information may be for configuring the remote UE to be handed over to the target network device. For example, the configuration information may include configuration information for the Uu interface. The configuration information for the Uu interface may include an identifier of the target network device, a user ID (e.g., C-RNTI) used by the relay UE during access, and a timer configured to determine whether the access is successful, such as the duration of T304. Optionally, a random access resource configuration and a contention-free preamble configuration for the relay UE to access the network device may also be included.

S709: The remote UE performs a path switch based on the configuration information. For example, the remote UE performs configuration based on the configuration information, and the remote UE initiates random access to the target network device. If the remote UE succeeds in the random access, the remote UE is successfully handed over to the target network device.

When the first condition is met and the remote UE successfully accesses the target network device, the remote UE may determine that the path switch is successful. If the first condition is not met and the remote UE fails to access the target network device, the remote UE may determine that the path switch is unsuccessful.

In this embodiment of the application, the first condition may relate to a timer. See discussion below.

S710: The remote UE starts a timer.

For example, the remote UE may start a timer after S708 is executed, or in other words, after the remote UE receives configuration information from the source network device. The timer may be T304 or another newly introduced timer. This is not limited here.

S711: The remote UE initiates random access to the target network device.

If the remote UE successfully accesses the target network device before the timer expires, the remote UE determines that the path switch is successful. If the remote UE has not successfully accessed the target network device when the timer expires, the remote UE determines that the path switch has failed. In this embodiment of the application, whether the path switch is successful is determined by using a timer. This method is simple and easy to implement. The timing duration of the timer can be determined by the remote UE. For example, the remote UE can determine the time for accessing the network device based on historical information and set that time as the timing duration of the timer. Alternatively, the timing duration of the timer can be configured by the network device in S708 and notified to the remote UE. Alternatively, the timing duration of the timer can be specified in the protocol. If the random access is successful, the timer can be stopped to avoid timer expiration.

If the remote UE successfully accesses the target network device before the timer expires, the remote UE may perform normal communication within the coverage of the target network device, and subsequent steps do not need to be performed. If the remote UE has not successfully accessed the target network device when the timer expires, the following steps may be performed.

S712: The remote UE sends failure information to the source network device via the first path. Thus, the source network device receives the failure information from the remote UE via the first path. The failure information may indicate that the path switch has failed. The failure information may be, for example, an RRC message. For example, the failure information may be a failure information message, a master cell group failure information (MCG failure information) message, an RRC reconfiguration complete message, or a UE information response message, or may be another newly added RRC message. This is not limited here.

The first path is the communication path between the remote UE and the source network device before the remote UE performs a path switch. Since this embodiment of the present application uses an example in which the scenario of switching from an indirect link to a direct link is used, the first path is the communication path in which the remote UE is connected to the source network device via the relay UE. In other words, the first path is remote UE - relay UE - source network device.

If the remote UE has not disconnected from the source network device via the first path before successfully performing the path switch, the remote UE may perform S712. After the source network device receives the failure information, the remote UE may continue to communicate with the source network device via the first path. That is, because the remote UE has not disconnected the original communication path, the remote UE may continue to communicate via the original communication path and does not need to reselect a communication path. In other words, the remote UE does not initiate an RRC connection re-establishment process to improve the service continuity of the remote UE.

S713: The remote UE sends an RRC connection re-establishment request message to the source network device via the first path. Thus, the source network device receives the RRC connection re-establishment request message from the remote UE.

S712 and S713 are parallel steps, and only one of S712 and S713 needs to be executed. If the remote UE has not disconnected from the source network device via the first path before successfully executing the path switch, the remote UE may alternatively execute S713 to re-establish an RRC connection within the coverage of the source network device, thereby communicating with the source network device through the new connection.

S714: The remote UE performs cell reselection.

The remote UE may enter an RRC idle state and perform cell reselection in the RRC idle state. For example, the cell reselected by the remote UE is referred to as the first cell.

S715: The remote UE initiates an RRC connection reestablishment process in the first cell, or initiates an RRC connection establishment process in the first cell.

If the first cell stores the remote UE's context, the remote UE may initiate an RRC connection re-establishment process in the first cell. If the first cell does not store the remote UE's context, the remote UE may initiate an RRC connection establishment process in the first cell. For example, the remote UE may initiate an RRC connection re-establishment process in the first cell. If the first cell stores the remote UE's context, the remote UE's RRC connection re-establishment process has a high probability of success. If the first cell does not store the remote UE's context and the remote UE's context cannot be obtained through the network device interface, the remote UE's RRC connection re-establishment process may fail. If the remote UE's RRC connection re-establishment process fails, the remote UE restarts the RRC connection establishment process in the first cell. Alternatively, since the first cell does not store the remote UE's context, the remote UE may directly initiate the RRC connection establishment process in the first cell to reduce the probability of RRC re-establishment failure.

The three solutions S712, S713, and S714, and S715, are parallel, and only one of the three solutions needs to be implemented.

In this embodiment of the application, the remote UE may determine whether the path switch is successful or unsuccessful based on a timer. The determination method is simple and easy to implement. The technical solution in this embodiment of the application can also be applied to UEs with low capabilities. In addition, if the path switch fails, the remote UE may perform corresponding operations, such as continuing to communicate within the coverage of the source network device, or entering a new cell through cell reselection, in order to resume the service of the remote UE as soon as possible and improve service continuity.

An embodiment of this application provides a sixth communication method. According to this method, the remote UE can also determine when a path switch has failed, allowing the operation of the remote UE to continue. Figure 8 is a flowchart of the method. The method may relate to a process of switching between indirect links, or a process of switching from a direct link to an indirect link. The process described below uses an example in which the method is applied to the network architecture shown in any one of Figures 1A to 1D.

If the technical solution provided in this embodiment of this application is applied to the network architecture shown in FIG. 1A, it indicates that the source network device before the remote UE performs a path switch and the target network device after the remote UE performs a path switch are the same network device. In this case, the first terminal device in the following description may be the relay terminal device in FIG. 1A, the second terminal device in the following description may be the remote terminal device in FIG. 1A, the network device in the following description may be the access network device in FIG. 1A, and the network device is both the source network device and the target network device. If the technical solution provided in this embodiment of this application is applied to the network architecture shown in FIG. 1B, it indicates that the source network device before the remote UE performs a path switch and the target network device after the remote UE performs a path switch are the same network device. In this case, the first terminal device in the following description may be the relay terminal device 1 or the relay terminal device 2 in FIG. 1B, the second terminal device in the following description may be the remote terminal device in FIG. 1B, the network device in the following description may be the access network device in FIG. 1B, and the network device is both the source network device and the target network device. If the technical solution provided in this embodiment of this application is applied to the network architecture shown in FIG. 1C, it indicates that the source network device before the remote UE performs a path switch and the target network device after the remote UE performs a path switch are different network devices. In this case, the first terminal device in the following description may be the relay terminal device in FIG. 1C, the second terminal device in the following description may be the remote terminal device in FIG. 1C, and the network device in the following description (which is also referred to as the first network device, and the first network device is the source network device) may be the access network device in FIG. 1C. In addition, the following also relates to a target network device, which may be referred to as the second network device and may be the access network device 2 in FIG. 1C. Alternatively, the source network device may be access network device 2 in FIG. 1C, and the target network device may be access network device 1 in FIG. 1C. If the technical solution provided in this embodiment of the present application is applied to the network architecture shown in FIG. 1D, it indicates that the source network device before the remote UE performs the path switch and the target network device after the remote UE performs the path switch are different network devices. In this case, the first terminal device in the following description may be relay terminal device 1 in FIG. 1D, the second terminal device in the following description may be the remote terminal device in FIG. 1D, and the network device in the following description (which is also referred to as the first network device, and the first network device is the source network device) may be access network device 1 in FIG. 1D. In addition, the following further relates to the target network device, which may be referred to as the second network device and may be access network device 2 in FIG. 1D. Alternatively, the first terminal device may be relay terminal device 2 in FIG. 1D, the source network device may be access network device 2 in FIG. 1D, and the target network device may be access network device 1 in FIG. 1D.

In addition, the following description uses an example in which the second terminal device is a remote UE and the first terminal device is a relay UE. In addition, this embodiment of the application uses an example in which the source network device and the target network device are different network devices.

S801: The remote UE performs data transmission with the source network device.

S802: The source network device sends an RRC message to the remote UE. Accordingly, the remote UE receives the RRC message from the source network device. The RRC message includes, for example, measurement configuration information, which is used by the remote UE to measure other UEs.

Alternatively, the network device may transmit broadcast information to the remote UE. Thus, the remote UE receives the broadcast information from the network device. The broadcast information may be included, for example, in a system message or in another broadcast message. The broadcast information may include relevant information used by the remote UE to select a relay UE, for example, measurement configuration information for configuring measurements to be performed by the remote UE to select a relay UE.

S803: The remote UE measures or selects other UEs. For example, the remote UE may send a discovery message to trigger other UEs to send discovery messages, so that the remote UE can measure discovery messages from other UEs to complete measurement or selection of the other UEs. In Figure 8, an example in which the remote UE measures other UEs is used.

The remote UE may measure other UEs by measuring discovery messages from the other UEs, or may measure other information from the other UEs, for example, measuring data signals from the other UEs. This is not limited here. The remote UE may select other UEs based on the measurement results.

S804: The remote UE transmits the first result to the network device. Accordingly, the network device receives the first result from the remote UE. The first result may be, for example, a measurement result or a selection result. In FIG. 8, an example in which the first result is a measurement result is used.

The measurement result may include, for example, a report of measuring at least one UE by the remote UE. The selection result may be a result of selecting a relay UE by the remote UE, and may include, for example, the ID of the selected relay UE. Optionally, measurement information of the remote UE and the like may also be included.

If the application scenario of this embodiment of this application is switching between indirect links, all communications between the remote UE and the network device in steps S801 to S804 are performed through forwarding via the relay UE connected to the remote UE before the link switching, and the relay UE in the following description is the relay UE connected to the remote UE after the link switching.

S805: The source network device makes a handover decision. Based on the measurement result, the source network device determines whether the remote UE can perform a path switch. In this embodiment of the application, based on the measurement result, the source network device determines whether the remote UE can be handed over from the relay UE to the target network device. If the source network device determines that the remote UE can be handed over from the relay UE to the target network device, S806 is executed.

S806: The source network device sends a handover request message to the target network device. Accordingly, the target network device receives a handover request message from the source network device. The handover request message may indicate that the remote UE should be handed over to the target network device. The target network device serves the relay UE. Because the remote UE will switch to performing communication via the relay UE, the source network device will request a handover from the target network device serving the relay UE.

S807: The target network device sends an RRC reconfiguration message to the relay UE. Thus, the relay UE receives the RRC reconfiguration message from the target network device. For example, the RRC reconfiguration message is called RRC reconfiguration message 1.

The RRC reconfiguration message may, for example, include configuration information, and may implement the function of the first message in the embodiment shown in FIG. 3. Alternatively, the RRC reconfiguration message may, for example, be for inquiring whether the relay UE is capable of providing relay services, and may implement the function of the first message in the embodiment shown in FIG. 4.

S808: The relay UE transmits a second message to the target network device. Accordingly, the target network device receives the second message from the relay UE. If the RRC reconfiguration message in S807 implements the function of the first message in the embodiment shown in FIG. 3, the second message in S808 may implement the function of the second message in the embodiment shown in FIG. 3. Alternatively, if the RRC reconfiguration message in S807 implements the function of the first message in the embodiment shown in FIG. 4, the second message in S808 may implement the function of the second message in the embodiment shown in FIG. 4. S808 may be an optional step. The transmission is not performed, the relay UE determines that the reconfiguration has failed, and the relay UE is triggered to enter an RRC connection re-establishment procedure.

In this embodiment of the application, for example, the second message indicates that the configuration has failed or that the relay UE refuses to provide relay service. For further details, see S306 or S307 in the embodiment shown in FIG. 3, or S406 or S407 in the embodiment shown in FIG. 4.

S809: The target network device sends a handover request acknowledgement message to the source network device. Thus, the source network device receives the handover request acknowledgement message from the target network device.

The handover request acknowledge message may indicate that the remote UE is authorized to be handed over to the target network device, or may indicate that the remote UE is not authorized to be handed over to the target network device. In this embodiment of the application, the second message indicates that the configuration has failed or that the relay UE refuses to provide relay service, so the handover request acknowledge message may indicate that the remote UE is not authorized to be handed over to the target network device.

S807 comes after S806, and S810 comes after S809. However, the order of S807 and S809 is not limited. For example, the target network device may perform S809 after configuring the relay UE, or may perform S809 first and then query the relay UE or configure the relay UE. If the target network device and the source network device are the same network device, S806 and S809 do not need to be performed.

S810: The source network device sends an RRC reconfiguration message to the remote UE. Thus, the remote UE receives the RRC reconfiguration message from the source network device. For example, the RRC reconfiguration message is called RRC reconfiguration message 2.

The RRC reconfiguration message may include configuration information for configuring the remote UE to switch to an indirect path and communicate with the target network device via the relay UE. For example, the configuration information may include configuration information for the Uu interface, which may include information about the Uu configuration of the relay UE, and the configuration information may further include a user ID for access of the relay UE (e.g., the ID is a cell radio network temporary identifier (C-RNTI)), or may further include a random access resource configuration and a contention-free preamble configuration for the relay UE to access the network device. In another example, the configuration information may include configuration information for the remote UE, which may include a user ID (e.g., C-RNTI) of the remote UE, or may include configuration information for the PC5 of the remote UE. For example, the PC5 configuration information of the remote UE includes one or more of the following: configuration information of the PC5 radio link control (RLC), a logical channel ID (LCID) corresponding to the PC5 RLC entity, or a correlation between the LCID corresponding to the PC5 RLC entity and a data radio bearer (DRB) ID. In another example, the configuration information may include information related to a timer, which may be used by the remote UE to determine whether a path switch has failed. The timer may be, for example, timer T304 or another newly introduced timer. This is not limited here. The source network device may choose to configure different timers depending on whether the remote UE should perform a path switch or a general switch. For example, if the remote UE should perform a path switch, a new timer may be configured for the remote UE. If the remote UE should perform a general switch, timer T304 may be configured for the remote UE. Alternatively, the source network device may configure timer T304 for the remote UE by using a general RRC reconfiguration message without using an RRC reconfiguration with sync message. The source network device may add a new information element, for example, a fourth information element, to the RRC reconfiguration message to indicate that the remote UE needs to switch to an indirect path (i.e., a path for communicating with the network via a relay), and the fourth information element may include the configured timer. The ID of the remote UE may also be included in the fourth information element. This is not limited here. The related information of the timer included in the configuration information may include the timer duration, the timer duration and offset duration, or the offset duration. The offset duration may be determined based on the status of the relay UE. For example, the offset duration may be set differently in three cases where the relay UE is in an RRC idle state, an RRC inactive state, and an RRC connected state. For example, when the relay UE is in an RRC connected state, the offset duration may be set to be short or even 0. If a remote UE performs a path switch to access the network through a relay UE in the RRC connected state, the relay UE in the RRC connected state does not need to perform a random access process for the Uu interface. If a remote UE performs a path switch to access the network through a relay UE in the RRC idle state or the RRC inactive state, the relay UE in the RRC idle state or the RRC inactive state does not need to perform a random access process for the Uu interface. Therefore, when a remote UE performs a different path switch, the duration for establishing a connection between the remote UE and a network device may also be different. For example, the remote UE may determine the duration of a timer configured to determine whether a path switch has failed as follows: The duration of the timer received by the remote UE is X. If the relay UE is in the RRC idle state, the offset duration is Y, where Y is greater than 0. If the relay UE is in the RRC connected state, the offset duration is 0. When a remote UE switches to access a network via a relay UE, if the relay UE is in the RRC idle state, the duration of the timer used by the remote UE to determine whether a path switch has failed is set to X+Y. If the relay UE is in the RRC connected state, the duration of the timer used by the remote UE to determine whether a path switch has failed is set to X+0. In other words, the offset duration may be determined based on the status of the relay UE to effectively reduce the duration the remote UE needs to wait when switching to a relay UE in the RRC connected state fails, thereby allowing the remote UE to enter the status recovery process as soon as possible.

S811: The remote UE performs a path switch based on the configuration information. For example, the remote UE performs configuration based on the configuration information, and the remote UE requests a connection to the relay UE. If the connection between the remote UE and the relay UE is successfully established, the remote UE successfully switches to communicating with the network via the relay UE. When the first condition is met and the connection between the remote UE and the relay UE is successfully established, the remote UE may determine that the path switch is successful. If the first condition is not met and the connection between the remote UE and the relay UE fails to be established, the remote UE determines that the path switch has failed.

In this embodiment of the application, the first condition may relate to a timer. See discussion below.

S812: The remote UE starts a timer.

For example, after S810 is executed, or in other words, after the remote UE receives configuration information from the source network device (the configuration information is, for example, included in an RRC reconfiguration message that does not carry a synchronization reconfiguration information element, an RRC reconfiguration message that carries a fourth information element, or an RRC reconfiguration message that carries a synchronization reconfiguration information element), the remote UE may start a timer. The timer may be timer T304 or another newly introduced timer. This is not limited here. The timing duration and/or offset duration of the timer may be configured by using the RRC reconfiguration message in S810, by using a broadcast message, or by the relay UE. The remote UE may determine the timing duration of the timer based on the configured timing duration and/or offset duration of the timer. For example, the remote UE directly determines the timing duration of the timer based on the RRC reconfiguration message. In another example, the remote UE determines the timing duration of the timer based on a broadcast message. In another example, the remote UE determines the timing duration of the timer based on the timing duration configured using the broadcast message and the offset duration configured using the RRC reconfiguration message. For example, the timing duration of the timer is the sum of the timing duration configured using the broadcast message and the offset duration configured using the RRC reconfiguration message. In yet another example, the remote UE determines the timing duration of the timer based on the timing duration configured using the RRC reconfiguration message or the broadcast message and the offset duration configured using the PC5 RRC message received from the relay UE. For example, the timing duration of the timer is the sum of the timing duration configured using the RRC reconfiguration message or the broadcast message and the offset duration configured using the PC5 RRC message. Because the offset duration is set based on the status of the relay UE, this can better help the remote UE determine the required waiting time to determine whether a path switch has failed.

S813: The remote UE requests the establishment of a connection to the relay UE. For example, the remote UE sends a connection establishment request to the relay UE. After the relay UE receives the connection establishment request, the relay UE replies to the remote UE with a connection establishment response message. If the connection establishment response message indicates that the connection establishment is permitted, the connection between the remote UE and the relay UE is successfully established. After the relay UE receives the connection establishment request, the relay UE replies to the remote UE with a connection establishment response message. If the connection establishment response message indicates that the connection establishment is not permitted, or if the relay UE replies without a connection establishment response message, the connection establishment between the remote UE and the relay UE fails.

The timer related to the first condition, i.e., the timer started in S812, may be stopped when certain conditions are met. For example, the timer may be stopped when any one of the first, second, third, or fourth stop conditions is met. The following is a brief description of these stop conditions.

For example, the first stop condition is as follows: A PC5 RRC connection between the remote UE and the relay UE is successfully established. In this case, the timer may be stopped. For example, if the remote UE receives a connection establishment response message returned by the relay UE, and the connection establishment response message indicates that connection establishment is permitted, the remote UE may stop the timer.

If the connection between the remote UE and the relay UE is successfully established before the timer expires, the remote UE determines that the path switch is successful. If the connection between the remote UE and the relay UE is not established when the timer expires, the remote UE determines that the path switch has failed. In this embodiment of the application, whether the path switch is successful is determined by using a timer. This method is simple and easy to implement. The timing duration of the timer can be determined by the remote UE. Alternatively, see the descriptions of S810 and S812. For example, the remote UE can determine the time required to establish a connection to another UE based on historical information and determine that time as the timing duration of the timer. Alternatively, the timing duration of the timer can be configured by the network device and notified to the remote UE. Alternatively, the timing duration of the timer can be specified in the protocol.

If the connection between the remote UE and the relay UE is successfully established before the timer expires, the remote UE may perform normal communication via the relay UE and the subsequent steps do not need to be performed. However, if the connection between the remote UE and the relay UE has not been established when the timer expires, the process may proceed to the subsequent steps.

For example, the second stop condition is as follows: The RRC layer of the remote UE sends an RRC reconfiguration complete message to a lower layer of the remote UE, and the RRC layer receives acknowledgement feedback from the lower layer. The lower layer here is, for example, a packet data convergence protocol (PDCP) layer, a radio link control (RLC) layer, or a media access control (MAC) layer. If the timer of the remote UE expires, the remote UE determines that the path switch has failed. In this embodiment of the application, whether the path switch is successful is determined by using a timer. This method is simple and easy to implement. The timer setting method is similar to that in the first stop condition. The details will not be described again here. If the timer of the remote UE expires, the remote UE can proceed to the subsequent step.

For example, the third stop condition is as follows: The remote UE receives an acknowledgement indication from the relay UE, and the acknowledgement indication is sent, for example, by the source network device via the relay UE. If the timer of the remote UE expires, the remote UE determines that the path switch has failed. In this embodiment of the application, whether the path switch is successful is determined by using a timer. This method is simple and easy to implement. The timer setting method is similar to the setting method in the first stop condition. The details will not be described again here. If the timer of the remote UE expires, the remote UE can proceed to the subsequent step.

For example, the fourth stop condition is as follows: the remote UE receives indication information from the relay UE, the indication information is carried, for example, by using a PC5 RRC message, and the indication information indicates to the remote UE to stop the timer or indicates that the relay UE has successfully accessed the network device.

The relay UE may determine when to send the indication information to the remote UE based on the status of the relay UE. For example, if the relay UE is in an RRC connected state, the relay UE may send the indication information to the remote UE when or after a connection to the remote UE is successfully established. If the relay UE is in an RRC idle state or an RRC inactive state, the relay UE may send indication information to the remote UE when random access is completed, or may send indication information to the remote UE when it determines that the RRC connection has been successfully established or resumed (e.g., after successfully receiving an RRC setup message, an RRC establishment, or an RRC resume message), or may send indication information to the remote UE when it determines that the RRC connection has been successfully established or resumed (e.g., after the relay UE stops timer T300 or timer T319). If the timer of the remote UE expires, the remote UE determines that the path switch has failed. In this embodiment of the present application, whether the path switch is successful is determined by using a timer. This scheme is simple and easy to implement. The timer setting method is similar to that in the first stop condition. Details will not be described again here. If the timer of the remote UE expires, it can proceed to the next step.

S814: The remote UE transmits failure information to the source network device via the first path. Thus, the source network device receives the failure information from the remote UE via the first path. The failure information may indicate that the path switch has failed.

The first path is the communication path between the remote UE and the source network device before the remote UE performs a path switch. If this embodiment of the application is applied to a scenario in which the remote UE switches between indirect links, the first path is the communication path in which the remote UE is connected to the source network device via the relay UE. That is, the first path is remote UE - relay UE - source network device. In this case, the relay UE is the relay UE connected to the remote UE before the remote UE performed the path switch. However, if this embodiment of the application is applied to a scenario in which the remote UE switches from a direct link to an indirect link, the first path is the communication path in which the remote UE is directly connected to the source network device. That is, the first path is remote UE - source network device.

For further details on S814, please refer to S712 in the embodiment shown in Figure 7.

S815: The remote UE sends an RRC connection re-establishment request message to the source network device via the first path. Thus, the source network device receives the RRC connection re-establishment request message from the remote UE. Alternatively, after performing relay re-selection, the remote UE may select another relay UE and initiate RRC connection re-establishment by using the other relay UE.

S814 and S815 are parallel steps, and only one of S814 and S815 needs to be executed. If the remote UE has not disconnected from the source network device via the first path before successfully executing the path switch, the remote UE may alternatively execute S815 to re-establish an RRC connection within the coverage of the source network device, thereby communicating with the source network device through the new connection.

S816: The remote UE performs cell reselection.

The remote UE may enter an RRC idle state and perform cell reselection in the RRC idle state. For example, the cell reselected by the remote UE is referred to as the first cell.

S817: The remote UE initiates an RRC connection reestablishment process in the first cell, or initiates an RRC connection establishment process in the first cell.

The three solutions S814, S815, and S816 are parallel to S817, and only one of the three solutions needs to be implemented.

For further details on S817, please refer to S715 in the embodiment shown in Figure 7.

In this embodiment of the application, the remote UE may determine whether the path switch is successful or unsuccessful based on a timer. The determination method is simple and easy to implement. The technical solution in this embodiment of the application can also be applied to UEs with low capabilities. In addition, if the path switch fails, the remote UE may perform corresponding operations, such as continuing to communicate within the coverage of the source network device, or entering a new cell through cell reselection, in order to resume the service of the remote UE as soon as possible and improve service continuity.

An embodiment of this application provides a seventh communication method. According to this method, the remote UE can also determine when a path switch has failed, allowing the remote UE to continue operating. Figure 9 is a flowchart of the method. The method may relate to a process of switching between indirect links or a process of switching from a direct link to an indirect link. In the process described below, an example is used in which the method is applied to the network architecture shown in any one of Figures 1A to 1D. For the devices in Figures 1A to 1D that are the relay UE, remote UE, and network device in this embodiment of this application, please refer to the description of the sixth communication method. Relay terminal device 1 and relay terminal device 2 in Figure 9 simply indicate that there may be multiple UEs that can serve as relay UEs, and the remote UE may measure multiple UEs when performing measurements.

In this embodiment of the application, an example is used in which the source network device and the target network device are the same network device. In addition, the following description uses an example in which the second terminal device is a remote UE and the first terminal device is a relay UE.

S901: The remote UE performs data transmission with the network device.

S902: The network device sends an RRC message to the remote UE. Accordingly, the remote UE receives the RRC message from the network device. The RRC message includes, for example, measurement configuration information, which is used by the remote UE to measure other UEs.

Alternatively, the network device may transmit broadcast information to the remote UE. Thus, the remote UE receives the broadcast information from the network device. The broadcast information may be included, for example, in a system message or in another broadcast message. The broadcast information may include relevant information used by the remote UE to select a relay UE, for example, measurement configuration information for configuring measurements to be performed by the remote UE to select a relay UE.

S903: The remote UE measures or selects other UEs. For example, the remote UE may send a discovery message to trigger other UEs to send discovery messages, so that the remote UE can measure discovery messages from other UEs to complete measurement or selection of the other UEs. In Figure 9, an example in which the remote UE measures other UEs is used.

The remote UE may measure other UEs by measuring discovery messages from the other UEs, or may measure other information from the other UEs, for example, measuring data signals from the other UEs. This is not limited here. The remote UE may select other UEs based on the measurement results.

S904: The remote UE transmits the first result to the network device. Accordingly, the network device receives the first result from the remote UE. The first result may be, for example, a measurement result or a selection result. In FIG. 9, an example in which the first result is a measurement result is used.

The measurement result is, for example, a measurement report obtained by the remote UE by measuring at least one UE. The selection result is the result of the remote UE selecting a relay UE, and includes, for example, the ID of the selected relay UE. Optionally, measurement information of the remote UE and the like may further be included.

If the application scenario of this embodiment of this application is switching between indirect links, all communications between the remote UE and the network device in steps S901 to S904 are performed through forwarding via the relay UE connected to the remote UE before the link switching, i.e., relay terminal device 2 in Figure 9, and the relay UE in the following description is the relay UE connected to the remote UE after the link switching, i.e., relay terminal device 1 in Figure 9.

S905: The network device determines whether the remote UE should perform a path switch based on the measurement result or the selection result. If the network device determines that the remote UE should perform a path switch, the subsequent steps are executed; otherwise, the subsequent steps are not executed.

S906: The network device sends a first message to the relay UE. Accordingly, the relay UE receives the first message from the network device.

For further details on S906, please refer to S306 in the embodiment shown in Figure 3.

S907: The relay UE sends the second message to the network device. Therefore, the network device receives the second message from the relay UE.

The second message may indicate that the configuration of the relay UE has been completed, or may indicate that the configuration of the relay UE has failed. Alternatively, the second message may indicate that the relay UE is capable of providing relay service, or may indicate that the relay UE refuses to provide relay service. For example, in this embodiment of the application, the second message indicates that the configuration of the relay UE has failed, or indicates that the relay UE refuses to provide relay service.

For further details on S907, please refer to S307 in the embodiment shown in Figure 3.

S908: The network device sends a first message to the relay UE. Accordingly, the relay UE receives the first message from the network device. The first message may be for inquiring whether the relay UE can provide relay service.

For further details on S908, please refer to S406 in the embodiment shown in Figure 4.

S909: The relay UE sends the second message to the network device. Therefore, the network device receives the second message from the relay UE.

The second message may indicate that the configuration of the relay UE has been completed, or may indicate that the configuration of the relay UE has failed. Alternatively, the second message may indicate that the relay UE is capable of providing relay service, or may indicate that the relay UE refuses to provide relay service. For example, in this embodiment of the application, the second message indicates that the configuration of the relay UE has failed, or indicates that the relay UE refuses to provide relay service.

For further details on S909, please refer to S407 in the embodiment shown in Figure 4.

Processes S906 and S907 are parallel to processes S908 and S909, and only one of the processes needs to be executed.

Alternatively, steps S906 to S909 may not be performed. Instead, the network device normally sends an RRC reconfiguration message to the relay UE in an existing manner, where the RRC reconfiguration message includes configuration information. After receiving the RRC reconfiguration message, the relay UE may perform the configuration. If the configuration is successful, the relay UE may send an RRC reconfiguration complete message to the network device. If the configuration fails or the relay UE refuses to provide relay service, the relay UE may enter an RRC reestablishment process.

S910: The network device sends an RRC reconfiguration message to the remote UE. Accordingly, the remote UE receives the RRC reconfiguration message from the network device.

The RRC reconfiguration message may include configuration information. The configuration information may be for configuring the remote UE to switch to communicating with the target network device via the relay UE. For example, the configuration information may include configuration information for the Uu interface.

S911: The remote UE performs a path switch based on the configuration information. For example, the remote UE performs configuration based on the configuration information, and the remote UE requests a connection to the relay UE. If the connection between the remote UE and the relay UE is successfully established, the remote UE successfully switches to communication with the network via the relay UE.

When the first condition is met, the remote UE may determine that the path switch is successful. If the first condition is not met, the remote UE may determine that the path switch is unsuccessful.

In this embodiment of the application, failure to satisfy the first condition may be failure to establish a direct communication connection. For example, this may include condition 1, condition 2, or condition 3.

Condition 1: Feedback is received from the relay UE when the number of times a connection establishment request message is sent to the relay UE is less than or equal to M, where M is the maximum number of retransmissions. A prerequisite for using condition 1 is that if the relay UE does not accept the establishment of a connection to the remote UE, the relay UE does not reply to the remote UE with a connection establishment response message.

The remote UE may send a connection establishment request message to the relay UE by using a retransmission mechanism. That is, if the connection establishment request message is unsuccessful the first time it is sent, the connection establishment request message may be retransmitted again. However, the number of retransmissions is limited, where M is the maximum number of retransmissions. If the remote UE still does not receive feedback from the relay UE after sending the connection establishment request message to the relay UE M times, this indicates that the connection establishment has failed. Therefore, if feedback is received from the relay UE when the number of times the connection establishment request message is sent to the relay UE is M or less, this indicates that the connection establishment has been successful. If feedback is still not received from the relay UE when the number of times the connection establishment request message is sent to the relay UE is M or more, this indicates that the connection establishment has failed. If the connection establishment has failed, the remote UE cannot communicate through the relay UE, and the path switch has failed. Therefore, condition 1 may be used to determine whether the path switch is successful.

Condition 2: Security verification for the relay UE is successful.

After the remote UE sends a connection establishment request message to the relay UE, if the relay UE agrees to establish a connection, the relay UE sends security-related parameters to the remote UE, and the remote UE needs to perform configuration based on the security-related parameters. However, the configuration of the remote UE may fail. For example, if some parameters (e.g., integrity protection algorithm) sent by the relay UE cannot be supported by the remote UE, the configuration of the remote UE may fail. If the remote UE fails to perform configuration based on the security parameters, security verification for the relay UE is considered to have failed. If the remote UE successfully performs configuration based on the security parameters, security verification for the relay UE is considered to have succeeded. If security verification for the relay UE is successful, the remote UE may perform communication via the relay UE, and the path switch is successful. If security verification for the relay UE fails, the remote UE cannot perform communication via the relay UE, and the path switch is failed. Therefore, condition 2 can be used to determine whether the path switch is successful.

Condition 3: A connection establishment request message is sent to a relay UE, a connection establishment response message is received from the relay UE, and the connection establishment response message may indicate that the connection establishment is accepted (or permitted). A prerequisite for using condition 3 is that the relay UE replies to the remote UE with a connection establishment response message, regardless of whether the relay UE accepts the establishment of a connection to the remote UE.

The remote UE sends a connection establishment request message to the relay UE. The relay UE replies with a connection establishment response message. If the connection establishment response message indicates that the connection establishment is accepted, the remote UE may perform communication via the relay UE, and the path switch is successful. However, if the connection establishment response message indicates that the connection establishment is not accepted, the remote UE cannot perform communication via the relay UE, and the path switch is unsuccessful. Therefore, condition 3 can also be used to determine whether the path switch is successful.

Which of the three conditions above is used by the remote UE to determine whether the path switch is successful may be determined by the remote UE, configured by the network device, or specified in the protocol. By using the conditions above, the remote UE can flexibly and quickly determine whether the path switch is successful. If the path switch fails, this solution can reduce or avoid communication interruptions and enable the remote UE to quickly enter the link resumption step to improve service continuity, compared to a solution in which whether the path switch is successful is determined by using a timer.

Alternatively, in this embodiment of the present application, the remote UE may not use the aforementioned conditions, but may determine whether the path switch is successful by using a timer. For a manner in which the determination is performed by using a timer, please refer to the description of the embodiment shown in Figure 8.

In addition, optionally, in the embodiment shown in FIG. 8, the remote UE may alternatively not use a timer to determine whether the path switch is successful, but may instead use one of the three conditions described above to determine whether the path switch is successful. For the determination method, please refer to the description in this embodiment of this application.

If the remote UE determines that the path switch has failed, the remote UE may perform normal communication via the relay UE and the subsequent steps do not need to be performed. If the remote UE determines that the path switch has failed, the remote UE may proceed to the following steps.

S912: The remote UE transmits failure information to the network device via the first path. Thus, the network device receives the failure information from the remote UE via the first path. The failure information may indicate that the path switch has failed.

The first path is the communication path between the remote UE and the network device before the remote UE performs a path switch. If this embodiment of the application is applied to a scenario in which the remote UE switches between indirect links, the first path is the communication path in which the remote UE is connected to the network device via a relay UE. That is, the first path is remote UE - relay UE - network device. In this case, the relay UE is the relay UE connected to the remote UE before the remote UE performed a path switch. However, if this embodiment of the application is applied to a scenario in which the remote UE switches from a direct link to an indirect link, the first path is the communication path in which the remote UE is directly connected to the network device. That is, the first path is remote UE - network device.

For further details on S912, please refer to S712 in the embodiment shown in Figure 7.

S913: The remote UE sends an RRC connection re-establishment request message to the source network device via the first path. Thus, the source network device receives the RRC connection re-establishment request message from the remote UE.

S912 and S913 are parallel steps, and only one of S912 and S913 needs to be executed. If the remote UE has not disconnected from the source network device via the first path before successfully executing the path switch, the remote UE may alternatively execute S912 to re-establish an RRC connection within the coverage of the source network device, thereby communicating with the source network device through the new connection.

S914: The remote UE performs cell reselection.

The remote UE may enter an RRC idle state and perform cell reselection in the RRC idle state. For example, the cell reselected by the remote UE is referred to as the first cell.

S915: The remote UE initiates an RRC connection reestablishment process in the first cell, or initiates an RRC connection establishment process in the first cell.

The three solutions S912, S913, and S914 and S915 are parallel, and only one of the three solutions needs to be implemented.

For further details on S915, please refer to S715 in the embodiment shown in Figure 7.

In this embodiment of the present application, the remote UE may determine whether the path switch is successful or unsuccessful based on different conditions. Compared with the method of determining whether the path switch is successful by using a timer, performing the determination by using the aforementioned conditions can reduce the time required for the determination process and improve the efficiency of the determination, so that the remote UE can more quickly know whether the path switch is successful so as to take corresponding measures more quickly and reduce the service interruption time. In addition, if the path switch fails, the remote UE may perform corresponding operations, such as continuing to perform communication within the coverage of the source network device, or entering a new cell through cell reselection, so as to resume the service of the remote UE as soon as possible and improve service continuity.

Next, an embodiment of this application provides an eighth communication method. According to this method, the remote UE can also determine when a path switch has failed, so that the operation of the remote UE can continue. Figure 10 is a flowchart of the method. The method may relate to a process of switching between indirect links, or a process of switching from a direct link to an indirect link. The process described below uses an example in which the method is applied to the network architecture shown in any one of Figures 1A to 1D.

If the technical solution provided in this embodiment of this application is applied to the network architecture shown in FIG. 1A, it indicates that the source network device before the remote UE performs a path switch and the target network device after the remote UE performs a path switch are the same network device. In this case, the first terminal device in the following description may be the relay terminal device in FIG. 1A, the second terminal device in the following description may be the remote terminal device in FIG. 1A, the network device in the following description may be the access network device in FIG. 1A, and the network device is both the source network device and the target network device. If the technical solution provided in this embodiment of this application is applied to the network architecture shown in FIG. 1B, it indicates that the source network device before the remote UE performs a path switch and the target network device after the remote UE performs a path switch are the same network device. In this case, the first terminal device in the following description may be the relay terminal device 1 or the relay terminal device 2 in FIG. 1B, the second terminal device in the following description may be the remote terminal device in FIG. 1B, the network device in the following description may be the access network device in FIG. 1B, and the network device is both the source network device and the target network device. If the technical solution provided in this embodiment of this application is applied to the network architecture shown in FIG. 1C, it indicates that the source network device before the remote UE performs a path switch and the target network device after the remote UE performs a path switch are different network devices. In this case, the first terminal device in the following description may be the relay terminal device in FIG. 1C, the second terminal device in the following description may be the remote terminal device in FIG. 1C, and the network device in the following description (which is also referred to as the first network device, and the first network device is the source network device) may be the access network device in FIG. 1C. In addition, the following also relates to a target network device, which may be referred to as the second network device and may be the access network device 2 in FIG. 1C. Alternatively, the source network device may be access network device 2 in FIG. 1C, and the target network device may be access network device 1 in FIG. 1C. If the technical solution provided in this embodiment of the present application is applied to the network architecture shown in FIG. 1D, it indicates that the source network device before the remote UE performs the path switch and the target network device after the remote UE performs the path switch are different network devices. In this case, the first terminal device in the following description may be relay terminal device 1 in FIG. 1D, the second terminal device in the following description may be the remote terminal device in FIG. 1D, and the network device in the following description (which is also referred to as the first network device, and the first network device is the source network device) may be access network device 1 in FIG. 1D. In addition, the following further relates to the target network device, which may be referred to as the second network device and may be access network device 2 in FIG. 1D. Alternatively, the first terminal device may be relay terminal device 2 in FIG. 1D, the source network device may be access network device 2 in FIG. 1D, and the target network device may be access network device 1 in FIG. 1D.

In the following description, an example is used in which the second terminal device is a remote UE and the first terminal device is a relay UE. In addition, this embodiment of the application uses an example in which the source network device and the target network device are different network devices.

S1001: The remote UE performs data transmission with the source network device.

S1002: The source network device sends an RRC message to the remote UE. Accordingly, the remote UE receives the RRC message from the source network device. The RRC message includes, for example, measurement configuration information, which is used by the remote UE to measure other UEs.

Alternatively, the network device may transmit broadcast information to the remote UE. Thus, the remote UE receives the broadcast information from the network device. The broadcast information may be included, for example, in a system message or in another broadcast message. The broadcast information may include relevant information used by the remote UE to select a relay UE, for example, measurement configuration information for configuring measurements to be performed by the remote UE to select a relay UE.

S1003: The remote UE measures or selects other UEs. For example, the remote UE may send a discovery message to trigger other UEs to send discovery messages, whereby the remote UE may measure discovery messages from other UEs to complete measurement or selection of the other UEs. In Figure 10, an example in which the remote UE measures other UEs is used.

The remote UE may measure other UEs by measuring discovery messages from the other UEs, or may measure other information from the other UEs, for example, measuring data signals from the other UEs. This is not limited here. The remote UE may select other UEs based on the measurement results.

S1004: The remote UE transmits the first result to the network device. Accordingly, the network device receives the first result from the remote UE. The first result may be, for example, a measurement result or a selection result. In FIG. 10, an example in which the first result is a measurement result is used.

The measurement result may include, for example, a report of measuring at least one UE by the remote UE. The selection result may be a result of selecting a relay UE by the remote UE, and may include, for example, the ID of the selected relay UE. Optionally, measurement information of the remote UE and the like may also be included.

If the application scenario of this embodiment of this application is switching from a direct link to an indirect link, the measurement result may further include a result of measuring the serving cell, i.e., a result of measuring the network device. If the application scenario of this embodiment of this application is switching between indirect links, all communications between the remote UE and the network device in S1001 to S1004 are performed through forwarding via the relay UE connected to the remote UE before the link switch, and the relay UE in the following description is the relay UE connected to the remote UE after the link switch. The first result may further include a result of measuring the relay UE connected to the remote UE before the link switch.

S1005: The source network device makes a handover decision. Based on the measurement result, the source network device determines whether the remote UE can perform a path switch. In this embodiment of the application, based on the measurement result, the source network device determines whether the remote UE can be handed over from the relay UE to the target network device. If the source network device determines that the remote UE can be handed over from the relay UE to the target network device, S1006 is executed.

S1006: The source network device sends a handover request message to the target network device. Accordingly, the target network device receives the handover request message from the source network device. The handover request message may indicate that the remote UE should be handed over to the target network device. The target network device serves the relay UE. Because the remote UE will switch to performing communication via the relay UE, the source network device will request handover from the target network device serving the relay UE.

S1007: The target network device sends an RRC reconfiguration message to the relay UE. Thus, the relay UE receives an RRC reconfiguration message from the target network device. For example, the RRC reconfiguration message is called RRC reconfiguration message 1.

The RRC reconfiguration message may, for example, include configuration information, and the RRC reconfiguration message may, for example, implement the function of the first message in the embodiment shown in FIG. 3. Alternatively, the RRC reconfiguration message may, for example, be for inquiring whether the relay UE is capable of providing relay services, and the RRC reconfiguration message may, for example, implement the function of the first message in the embodiment shown in FIG. 4. Alternatively, if the relay UE is unable to configure the relevant configuration after the configuration is performed by using the RRC reconfiguration message, the relay UE triggers a reconfiguration failure, and then the relay UE enters an RRC connection re-establishment procedure.

S1008: The relay UE sends a second message to the target network device. Thus, the target network device receives the second message from the relay UE. If the RRC reconfiguration message at S1007 implements the function of the first message in the embodiment shown in FIG. 3, the second message at S1008 may implement the function of the second message in the embodiment shown in FIG. 3. Alternatively, if the RRC reconfiguration message at S1007 implements the function of the first message in the embodiment shown in FIG. 4, the second message at S1008 may implement the function of the second message in the embodiment shown in FIG. 4.

In this embodiment of the application, for example, the second message indicates that the configuration has failed or that the relay UE refuses to provide relay service. For further details, see S306 or S307 in the embodiment shown in FIG. 3, or S406 or S407 in the embodiment shown in FIG. 4. If the configuration performed by using the configuration message in S1007 has failed, S1008 may be an optional step. The sending is not performed, the relay UE determines that the reconfiguration has failed, and the relay UE is triggered to enter an RRC connection re-establishment procedure.

S1009: The target network device sends a handover request acknowledge message to the source network device. Accordingly, the source network device receives a handover request acknowledge message from the target network device.

The handover request acknowledge message may indicate that the remote UE is authorized to be handed over to the target network device, or may indicate that the remote UE is not authorized to be handed over to the target network device. In this embodiment of the application, the second message indicates that the configuration has failed or that the relay UE refuses to provide relay service, so the handover request acknowledge message may indicate that the remote UE is not authorized to be handed over to the target network device.

S1007 comes after S1006, and S1010 comes after S1009. However, the order of S1007 and S1009 is not limited. For example, the target network device may perform S1009 after configuring the relay UE, or may perform S1009 first and then query the relay UE or configure the relay UE. If the target network device and the source network device are the same network device, S1006 and S1009 do not need to be performed.

S1010: The source network device sends an RRC reconfiguration message to the remote UE. Accordingly, the remote UE receives an RRC reconfiguration message from the source network device. For example, the RRC reconfiguration message is called RRC reconfiguration message 2.

The RRC reconfiguration message may include configuration information, which may be for configuring the remote UE to switch to an indirect path and communicate with the target network device via the relay UE. For further details of S1010, such as the implementation of the configuration information, see S810 in the embodiment shown in FIG. 8.

S1011: The remote UE performs a path switch based on the configuration information. For example, the remote UE performs configuration based on the configuration information, and the remote UE requests a connection to the relay UE. If the second condition is met, it may be determined that the remote UE has failed the path switch.

In this embodiment of the application, the second condition may relate to a timer and a received indication. For example, if a configured timer expires, if establishment of a connection between the remote UE and the relay UE fails before the timer expires, or if an RLF indication sent by the relay UE is received before the timer expires, the remote UE determines that the path switch has failed. For more details, see the description below.

S1012: The remote UE starts a timer.

For example, the remote UE may start a timer after S1010 is executed, or in other words, after the remote UE receives configuration information (which may be included in a general RRC reconfiguration message) from the source network device. The timer may be, for example, timer T304, or another newly introduced timer. This is not limited here. For details such as the configuration method of parameters such as the timing duration of the timer, please refer to S812 in the embodiment shown in FIG. 8. In addition, the timer may be stopped in specific scenarios. For specific stopping conditions, please refer to the following description of S1013.

S1013: The remote UE requests the establishment of a connection to the relay UE. For example, the remote UE sends a connection establishment request to the relay UE. After the relay UE receives the connection establishment request, the relay UE replies to the remote UE with a connection establishment response message. If the connection establishment response message indicates that the connection establishment is permitted, the connection between the remote UE and the relay UE is successfully established. After the relay UE receives the connection establishment request, the relay UE replies to the remote UE with a connection establishment response message. If the connection establishment response message indicates that the connection establishment is not permitted, or if the relay UE replies without a connection establishment response message, the connection establishment between the remote UE and the relay UE fails.

When one or more of the following scenarios occur, it may be directly determined that the establishment of the connection between the remote UE and the relay UE has failed. When it is determined that the connection establishment has failed, it may be determined that the path switch has failed. Optionally, the configured timer may be stopped. In other words, when one or more of the following scenarios occur, it may be determined that the connection establishment has failed without waiting for the timer, thereby reducing the waiting time of the remote UE. Optionally, if it is determined that the connection establishment has failed, the remote UE may be further triggered to perform RRC re-establishment.

Scenario 1: When the number of times a connection establishment request message is sent to a relay UE reaches M, no feedback is still received from the relay UE, and M is the maximum number of retransmissions.

The remote UE may send a connection establishment request message to the relay UE by using a retransmission mechanism. That is, if the connection establishment request message is sent unsuccessfully once, the connection establishment request message may be retransmitted again. However, the number of retransmissions is limited, where M is the maximum number of retransmissions. If the remote UE still does not receive feedback from the relay UE after sending the connection establishment request message to the relay UE M times, it indicates that the connection establishment has failed. If the number of times the connection establishment request message is sent to the relay UE is M or more and feedback from the relay UE is still not received, it indicates that the connection establishment has failed. If the connection establishment has failed, the remote UE cannot perform communication via the relay UE, and the path switch has failed.

Scenario 2: Security verification performed by the remote UE against the relay UE fails.

After the remote UE sends a connection establishment request message to the relay UE, if the relay UE agrees to establish a connection, the relay UE sends security-related parameters to the remote UE, and the remote UE needs to perform configuration based on the security-related parameters. However, the configuration of the remote UE may fail. For example, if some parameters (e.g., integrity protection algorithm) sent by the relay UE cannot be supported by the remote UE, the configuration of the remote UE may fail. If the remote UE fails to perform configuration based on the security parameters, security verification with the relay UE is considered to have failed. If the remote UE successfully performs configuration based on the security parameters, security verification with the relay UE is considered to have succeeded. If security verification with the relay UE fails, the remote UE cannot perform communication via the relay UE. This indicates that connection establishment has failed and path switch has failed.

Scenario 3: A connection establishment request message is sent to a relay UE, a connection establishment response message is received from the relay UE, and the connection establishment response message may indicate that the connection establishment is rejected.

The remote UE sends a connection establishment request message to the relay UE. If the relay UE replies with a connection establishment response message, and the connection establishment response message indicates that the connection establishment is accepted, the remote UE can communicate via the relay UE. However, if the connection establishment response message indicates that the connection establishment is not accepted, the remote UE cannot communicate via the relay UE. This indicates that the connection establishment has failed and the path switch has failed.

In addition, the timer related to the second condition, i.e., the timer started in S1012, may be stopped when certain conditions are met. For example, the timer may be stopped when any one of the first, second, third, fourth, or fifth stop conditions is met. For the first to fourth stop conditions, please refer to the description of S813 in the embodiment shown in FIG. 8. The fifth stop condition will be briefly explained below.

For example, the fifth stop condition is as follows: The remote UE determines that establishment of a connection to the relay UE has failed, or determines a PC5 RLF between the remote UE and the relay UE, the remote UE receives a Uu RLF indication from the relay UE, or the remote UE receives an access failure indication from the relay UE. If the fifth stop condition is met, the remote UE may stop the timer and determine that the path switch has failed. If the timer of the remote UE has expired, the remote UE determines that the path switch has failed. In this embodiment of the application, whether the path switch is successful is determined by using a timer. This method is simple and easy to implement. The timer setting method is similar to the setting method in the first stop condition. The details will not be described again here. The fifth stop condition includes multiple conditions. The condition is introduced to quickly determine whether the path switch has failed before the timer expires, reducing the waiting time of the remote UE and accelerating the speed at which the remote UE resumes service.

After it is determined that the path switch has failed, you can proceed to subsequent steps.

S1013a: If the configuration information in S1010 includes the configuration information of the relay UE, the remote UE transmits the configuration information to the relay UE. Thus, the relay UE receives the configuration information from the remote UE. The configuration information transmitted by the remote UE to the relay UE may be the configuration information in S1010, or may be the configuration information of the relay UE included in the configuration information in S1010.

S1013b: If the connection between the relay UE and the remote UE is successfully established, the remote UE sends an RRC reconfiguration complete message to the network device via the relay UE. Accordingly, the network device receives the RRC reconfiguration complete message from the relay UE.

The configuration sent by the remote UE to the relay UE is the default PC5 RLC configuration. The PC5 RLC configuration may include a default LCID, a default parameter configuration, and the like. The relay UE can successfully receive an RRC reconfiguration complete message from the remote UE even in RRC idle or RRC inactive state in order to use the default parameter configuration, thereby triggering entry into the RRC connected state. If PC5 connection establishment fails in S1013, S1013b may not be successfully executed.

S1013c: If the relay UE is in an RRC idle state or an RRC inactive state, access to the target network device is triggered after the first PC5 message is received from the remote UE.

S1014: The remote UE transmits failure information to the source network device via the first path. Thus, the source network device receives the failure information from the remote UE via the first path. The failure information may indicate that the path switch has failed.

The first path is the communication path between the remote UE and the source network device before the remote UE performs a path switch. If this embodiment of the application is applied to a scenario in which the remote UE switches between indirect links, the first path is the communication path in which the remote UE is connected to the source network device via the relay UE. That is, the first path is remote UE - relay UE - source network device. In this case, the relay UE is the relay UE connected to the remote UE before the remote UE performed the path switch. However, if this embodiment of the application is applied to a scenario in which the remote UE switches from a direct link to an indirect link, the first path is the communication path in which the remote UE is directly connected to the source network device. That is, the first path is remote UE - source network device.

For further details on S1014, please refer to S712 in the embodiment shown in Figure 7.

S1015: The remote UE sends an RRC connection re-establishment request message to the source network device via the first path. Thus, the source network device receives the RRC connection re-establishment request message from the remote UE. Alternatively, after performing relay re-selection, the remote UE selects another relay UE and initiates connection re-establishment.

S1014 and S1015 are parallel steps, and only one of S1014 and S1015 needs to be executed. If the remote UE has not disconnected from the source network device via the first path before successfully executing the path switch, the remote UE may alternatively execute S1015 to re-establish an RRC connection within the coverage of the source network device, thereby communicating with the source network device through the new connection.

S1016: The remote UE performs cell reselection.

The remote UE may enter an RRC idle state and perform cell reselection in the RRC idle state. For example, the cell reselected by the remote UE is referred to as the first cell.

S1017: The remote UE initiates an RRC connection re-establishment process in the first cell, or initiates an RRC connection establishment process in the first cell.

The three solutions S1014, S1015, and S1016 are parallel to S1017, and only one of the three solutions needs to be implemented.

For further details on S1017, please refer to S715 in the embodiment shown in Figure 7.

In this embodiment of the application, the remote UE may determine whether the path switch is successful or unsuccessful based on a timer. The determination method is simple and easy to implement. The technical solution in this embodiment of the application can also be applied to UEs with low capabilities. In addition, if the path switch fails, the remote UE may perform corresponding operations, such as continuing to communicate within the coverage of the source network device, or entering a new cell through cell reselection, in order to resume the service of the remote UE as soon as possible and improve service continuity.

The following describes an apparatus configured to perform the aforementioned method in an embodiment of this application, with reference to the accompanying drawings. Therefore, all of the above content can be used in subsequent embodiments. Repeated content will not be described again.

An embodiment of this application provides a communication device. The communication device may be a terminal device or a circuit. The communication device may be configured to perform the operations performed by the terminal device in the aforementioned method embodiments.

When the communication device is a terminal device, FIG. 11 is a simplified schematic diagram of the structure of the terminal device. For ease of understanding and illustration, FIG. 11 uses an example in which the terminal device is a mobile phone. As shown in FIG. 11, the terminal device includes a processor, memory, radio frequency circuitry, an antenna, and input/output devices. The processor is primarily configured to process communication protocols and communication data, control the terminal device, execute software programs, process data for the software programs, and so on. The memory is primarily configured to store software programs and data. The radio frequency circuitry is primarily configured to convert between baseband signals and radio frequency signals and process radio frequency signals. The antenna is primarily configured to transmit and receive radio frequency signals in the form of electromagnetic waves. The input/output device, such as a touchscreen, display, or keyboard, is primarily configured to receive data input by a user and output data to the user. It should be noted that some types of terminal devices may not have input/output devices.

When data needs to be transmitted, the processor performs baseband processing on the data to be transmitted and outputs the baseband signal to the radio frequency circuit. After performing radio frequency processing on the baseband signal, the radio frequency circuit transmits the radio frequency signal in the form of electromagnetic waves through an antenna. When data is to be transmitted to a terminal device, the radio frequency circuit receives the radio frequency signal through the antenna, converts the radio frequency signal to a baseband signal, and outputs the baseband signal to the processor. The processor converts the baseband signal to data and processes the data. For ease of explanation, FIG. 11 shows only one memory and one processor. In an actual terminal device product, there may be one or more processors and one or more memories. The memory may also be referred to as a storage medium, storage device, or the like. The memory may be located independently of the processor or integrated with the processor. This is not limited to this embodiment of the application.

In this embodiment of the present application, the antenna and radio frequency circuit having receiving and transmitting functions may be considered as a transceiver unit of the terminal device (the transceiver unit may be one functional unit, and the functional unit may realize the transmitting function and the receiving function, or the transceiver unit may include two functional units, i.e., a receiving unit capable of realizing the receiving function and a transmitting unit capable of realizing the transmitting function), and the processor having processing functions may be considered as a processing unit of the terminal device. As shown in FIG. 11, the terminal device includes a transceiver unit 1110 and a processing unit 1120. The transceiver unit may also be referred to as a transceiver, a transceiver device, or the like. The processing unit may also be referred to as a processor, a processing board, a processing module, a processing device, or the like. Optionally, the components within the transceiver unit 1110 configured to realize the receiving function may be considered as a receiving unit, and the components within the transceiver unit 1110 configured to realize the transmitting function may be considered as a transmitting unit. That is, the transceiver unit 1110 includes a receiving unit and a transmitting unit. A transceiver unit may sometimes be referred to as a transceiver, transceiver circuitry, or the like. A receiving unit may sometimes be referred to as a receiver, receiver circuitry, or the like. A transmitting unit may sometimes be referred to as a transmitter, transmitter circuitry, or the like.

It should be understood that the transceiver unit 1110 is configured to perform transmission and reception operations on the first terminal device side or the second terminal device side in any one of the embodiments shown in Figures 3 to 10, and the processing unit 1120 is configured to perform operations other than transmission and reception operations on the first terminal device side or the second terminal device side in any one of the embodiments shown in Figures 3 to 10.

When the communication device is a chip-type device or circuit, the device may include a transceiver unit and a processing unit. The transceiver unit may be an input/output circuit and/or a communication interface. The processing unit may be an integrated processor, a microprocessor, or an integrated circuit.

Figure 12 is a schematic block diagram of another communication device 1200 according to an embodiment of the present application. For example, the communication device 1200 is, for example, a terminal device or a network device. For example, the communication device 1200 can implement the functions of a first terminal device in the embodiment shown in Figure 3 or the embodiment shown in Figure 4, or the functions of a network device in the embodiment shown in Figure 3 or the embodiment shown in Figure 4. Alternatively, the communication device 1200 can implement the functions of a second terminal device in the embodiment shown in Figure 5 or the embodiment shown in Figure 6, or the functions of a network device in the embodiment shown in Figure 5 or the embodiment shown in Figure 6. Alternatively, communication device 1200 may implement the functionality of the second terminal device in any one of the embodiments shown in FIG. 7 to FIG. 9, or may implement the functionality of the first network device in any one of the embodiments shown in FIG. 7 to FIG. 9 (in the embodiment shown in FIG. 9, the source network device and the target network device are the same network device and may both be referred to as the first network device). Alternatively, communication device 1200 may implement the functionality of the second terminal device in the embodiment shown in FIG. 10, or may implement the functionality of the first network device in the embodiment shown in FIG. 10.

The communication device 1200 includes a transceiver unit 1220 and a processing unit 1210. Optionally, the communication device 1200 may further include a storage unit, which may be in communication with the processing unit 1210 and is not shown in FIG. 12 . Alternatively, the communication device 1200 may not include a storage unit, and the storage unit may be located outside the communication device 1200. For example, the communication device 1200 may be a terminal device, a chip used in a terminal device, or another combined component or part having the functionality of a first terminal device or a second terminal device. Alternatively, the communication device 1200 may be a network device, a chip used in a network device, or another combined component or part having the functionality of a network device. When the communication device 1200 is a terminal device or a network device, the processing unit 1210 may include a processor, such as a baseband processor. The baseband processor may include one or more central processing units (CPUs). The transceiver unit 1220 may be a transceiver. The transceiver may include an antenna, a radio frequency circuit, and the like. The transceiver may include a transmitter and a receiver, or the transceiver may realize the functions of the transmitter and the receiver. Alternatively, the transmitter and the receiver may be two functional modules separately deployed, but the two functional modules are collectively referred to as a transceiver in this embodiment of the application. When the communication device 1200 is a part having the functions of a terminal device or a network device, the transceiver unit 1220 may be a radio frequency unit, and the processing unit 1210 may be a processor, for example, a baseband processor. When the communication device 1200 is a chip system, the transceiver unit 1220 may be an input/output interface of the chip (e.g., a baseband chip), and the processing unit 1210 may be a processor of the chip system and may include one or more central processing units. It should be understood that the processing unit 1210 in this embodiment of the present application may be realized by a processor or processor-related circuit components, and the transceiver unit 1220 may be realized by a transceiver or transceiver-related circuit components.

In an implementation, when the communication device 1200 is configured to realize the functionality of the first terminal device in the embodiment shown in FIG. 3, the processing unit 1210 may be configured to perform all operations other than the transmitting and receiving operations performed by the first terminal device in the embodiment shown in FIG. 3, e.g., S308, and/or may be configured to support other processes of the technology herein. The transceiver unit 1220 may be configured to perform all receiving and transmitting operations performed by the first terminal device in the embodiment shown in FIG. 3, e.g., S303, S306, and S307, and/or may be configured to support other processes of the technology herein.

In an implementation, when the communication device 1200 is configured to realize the functionality of the network device in the embodiment depicted in FIG. 3, the processing unit 1210 may be configured to perform all operations other than the transmit and receive operations performed by the network device in the embodiment depicted in FIG. 3, e.g., S305, and/or may be configured to support other processes of the technology herein. The transceiver unit 1220 may be configured to perform all receive and transmit operations performed by the network device in the embodiment depicted in FIG. 3, e.g., S301, S302, S304, S306, and S307, and/or may be configured to support other processes of the technology herein.

In an implementation, when the communication device 1200 is configured to realize the functionality of the first terminal device in the embodiment shown in FIG. 4, the processing unit 1210 may be configured to perform all operations other than the transmitting and receiving operations performed by the first terminal device in the embodiment shown in FIG. 4, e.g., S410, and/or may be configured to support other processes of the technology herein. The transceiver unit 1220 may be configured to perform all receiving and transmitting operations performed by the first terminal device in the embodiment shown in FIG. 4, e.g., S403, S406, S407, and S408, and/or may be configured to support other processes of the technology herein.

In an implementation, when the communication device 1200 is configured to realize the functionality of the network device in the embodiment depicted in FIG. 4, the processing unit 1210 may be configured to perform all operations other than the transmit and receive operations performed by the network device in the embodiment depicted in FIG. 4, e.g., S405, and/or may be configured to support other processes of the technology herein. The transceiver unit 1220 may be configured to perform all receive and transmit operations performed by the network device in the embodiment depicted in FIG. 4, e.g., S401, S402, S404, S406, S407, S408, and S409, and/or may be configured to support other processes of the technology herein.

In an implementation, when the communication device 1200 is configured to realize the functionality of the second terminal device in the embodiment shown in FIG. 5, the processing unit 1210 may be configured to perform all operations other than the transmission and reception operations performed by the second terminal device in the embodiment shown in FIG. 5, e.g., S505, S506, and S507, and/or may be configured to support other processes of the technology herein. The transceiver unit 1220 may be configured to perform all reception and transmission operations performed by the second terminal device in the embodiment shown in FIG. 5, e.g., S501, S502, S503, and S504, and/or may be configured to support other processes of the technology herein.

In an implementation, when the communication device 1200 is configured to realize the functionality of the network device in the embodiment depicted in FIG. 5, the processing unit 1210 may be configured to perform all operations other than the transmit and receive operations performed by the network device in the embodiment depicted in FIG. 5 and/or may be configured to support other processes of the technology herein. The transceiver unit 1220 may be configured to perform all receive and transmit operations, e.g., S501, S502, and S504, performed by the network device in the embodiment depicted in FIG. 5 and/or may be configured to support other processes of the technology herein.

In an implementation, when the communication device 1200 is configured to realize the functionality of the second terminal device in the embodiment shown in FIG. 6, the processing unit 1210 may be configured to perform all operations other than the transmitting and receiving operations performed by the second terminal device in the embodiment shown in FIG. 6, e.g., S611, and/or may be configured to support other processes of the technology herein. The transceiver unit 1220 may be configured to perform all receiving and transmitting operations performed by the second terminal device in the embodiment shown in FIG. 6, e.g., S601, S602, S603, S604, and S610, and/or may be configured to support other processes of the technology herein.

In an implementation, when the communication device 1200 is configured to realize the functionality of the network device in the embodiment depicted in FIG. 6, the processing unit 1210 may be configured to perform all operations other than the transmit and receive operations performed by the network device in the embodiment depicted in FIG. 6, e.g., S605, and/or may be configured to support other processes of the technology herein. The transceiver unit 1220 may be configured to perform all receive and transmit operations performed by the network device in the embodiment depicted in FIG. 6, e.g., S601, S602, S604, and S606 to S610, and/or may be configured to support other processes of the technology herein.

In an implementation, when the communication device 1200 is configured to realize the functionality of the second terminal device in the embodiment shown in FIG. 7, the processing unit 1210 may be configured to perform all operations other than the transmitting and receiving operations performed by the second terminal device in the embodiment shown in FIG. 7, e.g., S709, S710, and S714, and/or may be configured to support other processes of the technology herein. The transceiver unit 1220 may be configured to perform all receiving and transmitting operations performed by the second terminal device in the embodiment shown in FIG. 7, e.g., S701, S702, S703, S704, S708, S711, S712, S713, and S715, and/or may be configured to support other processes of the technology herein.

In an implementation, when the communication device 1200 is configured to realize the functionality of the first network device in the embodiment depicted in FIG. 7, the processing unit 1210 may be configured to perform all operations other than the transmitting and receiving operations performed by the first network device in the embodiment depicted in FIG. 7, e.g., S705, and/or may be configured to support other processes of the technology herein. The transceiver unit 1220 may be configured to perform all receiving and transmitting operations performed by the first network device in the embodiment depicted in FIG. 7, e.g., S701, S702, S704, S706, S707, S708, S712, S713, and S715, and/or may be configured to support other processes of the technology herein.

In an implementation, when the communication device 1200 is configured to realize the functionality of the second terminal device in the embodiment shown in FIG. 8, the processing unit 1210 may be configured to perform all operations other than the transmitting and receiving operations performed by the second terminal device in the embodiment shown in FIG. 8, e.g., S811, S812, and S816, and/or may be configured to support other processes of the technology herein. The transceiver unit 1220 may be configured to perform all receiving and transmitting operations performed by the second terminal device in the embodiment shown in FIG. 8, e.g., S801, S802, S803, S804, S810, S813, S814, S815, and S817, and/or may be configured to support other processes of the technology herein.

In an implementation, when the communication device 1200 is configured to realize the functionality of the first network device in the embodiment shown in FIG. 8, the processing unit 1210 may be configured to perform all operations other than the transmitting and receiving operations performed by the first network device in the embodiment shown in FIG. 8, e.g., S805, and/or may be configured to support other processes of the technology herein. The transceiver unit 1220 may be configured to perform all receiving and transmitting operations performed by the first network device in the embodiment shown in FIG. 8, e.g., S801, S802, S804, S806, S809, S810, S814, S815, and S817, and/or may be configured to support other processes of the technology herein.

In an implementation, when the communication device 1200 is configured to realize the functionality of the second terminal device in the embodiment shown in FIG. 9, the processing unit 1210 may be configured to perform all operations other than the transmitting and receiving operations performed by the second terminal device in the embodiment shown in FIG. 9, e.g., S911 and S914, and/or may be configured to support other processes of the technology herein. The transceiver unit 1220 may be configured to perform all receiving and transmitting operations performed by the second terminal device in the embodiment shown in FIG. 9, e.g., S901, S902, S903, S904, S910, S912, S913, and S915, and/or may be configured to support other processes of the technology herein.

In an implementation, when the communication device 1200 is configured to realize the functionality of the first network device in the embodiment shown in FIG. 9, the processing unit 1210 may be configured to perform all operations other than the transmitting and receiving operations performed by the first network device in the embodiment shown in FIG. 9, e.g., S905, and/or may be configured to support other processes of the technology herein. The transceiver unit 1220 may be configured to perform all receiving and transmitting operations performed by the first network device in the embodiment shown in FIG. 9, e.g., S901, S902, S904, S906 to S910, S912, S913, and S915, and/or may be configured to support other processes of the technology herein.

In an implementation, when the communication device 1200 is configured to realize the functionality of the second terminal device in the embodiment shown in FIG. 10, the processing unit 1210 may be configured to perform all operations other than the transmission and reception operations performed by the second terminal device in the embodiment shown in FIG. 10, e.g., S1011, S1012, and S1016, and/or may be configured to support other processes of the technology herein. The transceiver unit 1220 may be configured to perform all reception and transmission operations performed by the second terminal device in the embodiment shown in FIG. 10, e.g., S1001, S1002, S1003, S1004, S1010, S1013, S1013a, S1013b, S1013c, S1014, S1015, and S1017, and/or may be configured to support other processes of the technology herein.

In an implementation, when the communication device 1200 is configured to realize the functionality of the first network device in the embodiment shown in FIG. 10, the processing unit 1210 may be configured to perform all operations other than the transmitting and receiving operations performed by the first network device in the embodiment shown in FIG. 10, e.g., S1005, and/or may be configured to support other processes of the technology herein. The transceiver unit 1220 may be configured to perform all receiving and transmitting operations performed by the first network device in the embodiment shown in FIG. 10, e.g., S1001, S1002, S1003, S1004, S1010, S1013, S1013a, S1013b, S1013c, S1014, S1015, and S1017, and/or may be configured to support other processes of the technology herein.

Additionally, the transceiver unit 1220 may be a single functional module, and the functional module may complete both transmission and reception operations. For example, the transceiver unit 1220 may be configured to perform all transmission and reception operations performed by a terminal device or a network device in any one of the embodiments shown in FIG. 3 to FIG. 10. For example, when performing reception operations, the transceiver unit 1220 may be considered a reception unit, and when performing transmission operations, the transceiver unit 1220 may be considered a transmission unit. Alternatively, the transceiver unit 1220 may be two functional modules. The transceiver unit 1220 may be considered a general term for the two functional modules. The two functional modules include a reception unit and a transmission unit. The transmission unit is configured to complete transmission operations. For example, the transmission unit may be configured to perform all transmission operations performed by a terminal device or a network device in any one of the embodiments shown in FIG. 3 to FIG. 10. The reception unit is configured to complete reception operations. For example, the receiving unit may be configured to perform all receiving operations performed by the terminal device or network device in any one of the embodiments shown in FIG. 3 to the embodiment shown in FIG. 10.

For specific functions that can be implemented by the processing unit 1210 and the transceiver unit 1220, please refer to the description of the operations performed by the terminal device in any one of the embodiments shown in FIG. 3 to FIG. 10, or refer to the description of the operations performed by the network device in any one of the embodiments shown in FIG. 3 to FIG. 10. Details will not be described again.

It should be understood that the processor referred to in the embodiments of this application may be a CPU, or may be another general-purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), or another programmable logic device, a discrete gate or transistor logic device, a discrete hardware component, or the like. The general-purpose processor may be a microprocessor, or the processor may be any conventional processor or the like.

It should be noted that when the processor is a general-purpose processor, a DSP, an ASIC, an FPGA or another programmable logic device, a discrete gate or transistor logic device, or a discrete hardware component, the memory (storage module) may be integrated into the processor.

It should be noted that memory in this specification is intended to include, but is not limited to, these memories and any other suitable types of memory.

It should be understood that the sequence numbers of the above processes do not imply an execution order in the embodiments of this application. The execution order of the processes should be determined based on the functions and internal logic of the processes, and should not constitute any limitations on the implementation process of the embodiments of this application.

In combination with the examples described in the embodiments disclosed in this specification, those skilled in the art will recognize that the units and algorithm steps can be realized by electronic hardware or a combination of computer software and electronic hardware. Whether a function is performed by hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art may use different methods to realize the function for each specific application, but the implementation should not be considered beyond the scope of this application.

In some embodiments provided in this application, it should be understood that the disclosed systems, devices, and methods may be realized in other manners. For example, the device embodiments described above are merely examples. For example, the division into units is merely a logical division of function, and other divisions may occur during actual implementation. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not implemented. In addition, mutual couplings or direct couplings or communication connections shown or discussed may be realized through some interfaces. Indirect couplings or communication connections between devices or units may be realized in electronic, mechanical, or other forms.

Units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, i.e., they may be located in one location or distributed across multiple network units. Some or all of the units may be selected based on the actual requirements for achieving the objectives of the solution in the embodiment.

In addition, the functional units in the embodiments of this application may be integrated into a single processing unit, each of the units may exist physically alone, or two or more units may be integrated into a single unit.

When a function is realized in the form of a software functional unit and sold or used as an independent product, the function may be stored in a computer-readable storage medium. Based on such understanding, the technical solution in this application, the portion contributing to the prior art, or some of the technical solutions may be realized in the form of a software product. A computer software product is stored in a storage medium and includes some instructions for instructing a computer device (which may be a personal computer, a server, a network device, or the like) to perform all or some of the steps of the method in the embodiments of this application. The aforementioned computer-readable storage medium may be any available medium that can be accessed by a computer. By way of example, and not limitation, computer-readable media may include random access memory (RAM), read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), compact disc read-only memory (CD-ROM), universal serial bus flash disk, removable hard disk, another compact disc storage, magnetic disk storage medium, another magnetic storage device, or any other medium capable of containing or storing expected program code in the form of instructions or data structures that can be accessed by a computer. Additionally, by way of example and not limitation, many types of RAM may be used, such as static random access memory (SRAM), dynamic random access memory (DRAM), synchronous dynamic random access memory (SDRAM), double data rate synchronous dynamic random access memory (DDR SDRAM), enhanced synchronous dynamic random access memory (ESDRAM), synchlink dynamic random access memory (SLDRAM), or direct rambus random access memory (DR RAM).

The above description is merely a specific implementation of this application, and the scope of protection of the embodiments of this application is not limited thereto. Any modifications or substitutions that are easily understood by those skilled in the art within the technical scope disclosed in the embodiments of this application fall within the scope of protection of the embodiments of this application. Therefore, the scope of protection of the embodiments of this application is subject to the scope of protection of the claims.

1110 Transceiver Unit
1120 Processing Unit
1200 Communication Equipment
1210 Processing Unit
1220 Transceiver Unit

Claims (10)

A communication method applied to a second terminal device, comprising:
receiving configuration information from a first network device, the configuration information for configuring the second terminal device to switch to communicate with a third network device via the first terminal device, the configuration information including information about a first timer, the information about the first timer being for path switching;
starting the first timer,
establishing a connection to a second terminal device, said connection being used by said second terminal device to communicate with a third network device via said first terminal device;
sending an RRC reconfiguration complete message to the first terminal device , wherein the RRC reconfiguration complete message is communicated by using a default PC5 RLC configuration, and the RRC reconfiguration complete message is for triggering the first terminal device, which is in an RRC idle state or an RRC inactive state, to enter an RRC connected state . the RRC reconfiguration complete message is an RRC reconfiguration complete message sent by the second terminal device to the third network device;
The method of claim 1 further comprising: 2. The method of claim 1, wherein the configuration information includes the information about the first timer, and the method further comprises: configuring, by the second terminal device, the first timer based on the information about the first timer. The method is performed under the following conditions:
The second terminal device sends the RRC reconfiguration complete message to a lower layer of the second terminal device and receives an acknowledgement feedback from the lower layer, wherein the lower layer is an RLC layer;
The method of claim 1 , further comprising stopping the first timer when one or more of the following conditions are satisfied: The method comprises:
The method of claim 1 , further comprising the step of performing a re-establishment of a connection between the second terminal device and the first network device when the first timer expires. The step of performing a re-establishment of a connection between the second terminal device and the first network device comprises:
performing a re-establishment of the connection between the second terminal device and the first network device by using a relay device; or
6. The method of claim 5 , comprising performing a re-establishment of a connection between the second terminal device and the first network device by using a cell. A communication method applied to a first network device, comprising:
A method comprising: a step of sending configuration information to a second terminal device, the configuration information being for configuring the second terminal device to switch to communicate with a third network device via a first terminal device, the configuration information including information about a first timer, the information about the first timer being for path switching. 8. The method of claim 7, wherein the information about the first timer is for configuring the first timer, and when the first timer expires, the second terminal device determines that the path switch has failed . A communication device comprising a transceiver unit and a processing unit, said transceiver unit being coupled to said processing unit, said communication device being capable of performing the method of any one of claims 1 to 8 . 9. A computer-readable storage medium configured to store a computer program, the computer program, when executed in a computer, enabling the computer to perform the method of any one of claims 1 to 8 .