JP7821082B2 - Communication system, base station device, and terminal device - Google Patents

Description

This disclosure relates to a communication system, a base station device, and a terminal device.

Currently, the 3GPP (3rd Generation Partnership Project) is considering RedCap (Reduced Capability) (see, for example, Non-Patent Document 1). RedCap is a standard that limits some NR (New Radio) functions (e.g., bandwidth and MIMO) for use with IoT (Internet of Things) devices. 3GPP is also discussing the Early Indication function in relation to RedCap.

The Early Indication function notifies the base station that a UE (User Equipment) is a RedCap UE via a RACH (Random Access Channel) message. For example, in the event of a disaster, the base station determines whether the UE is a RedCap UE based on the Early Indication notification and restricts the connection of UEs determined to be RedCap UEs. This reduces the possibility of critical communications being disrupted by simultaneous connections from a large number of UEs during a disaster, for example.

3GPP TSG RAN WG1 Meeting #106-e, 16-27 August 2021, R1-2108271, RAN1 agreements for Rel-17 NR RedCap

From the perspective of communication connectivity, it is being considered to make RedCap UE a dual UE. Dual UEs have the ability to connect to NR cells in addition to RedCap cells. It is also expected that a single base station will deploy both RedCap cells and NR cells. When it is necessary to switch the cell to which a RedCap UE is connected between these RedCap cells and NR cells, it is desirable to be able to switch the cell to which a RedCap UE is connected using processing that reduces the number of sequences and processing load.

One aspect of the present disclosure aims to provide a communications system, base station device, and terminal device that, when a base station configures a normal first cell and a second cell corresponding to a terminal with reduced functionality, can reduce the number of sequences and processing load when switching the connection destination cell of a terminal device between the first cell and the second cell.

A communication system according to one aspect of the present disclosure includes a base station device that configures a normal first cell and a second cell corresponding to a terminal with reduced functionality, and a terminal device that can selectively connect to the first cell and the second cell. In a process for connecting to one of the first and second cells, the terminal device transmits first information to the one cell indicating that the terminal device is a terminal with reduced functionality compared to a normal terminal. When the base station device receives the first information from the terminal device and a predetermined switching condition is satisfied, it allocates radio resources for wireless communication between the terminal device and the other of the first and second cells, and connects the terminal device to the other cell.

A base station device according to one aspect of the present disclosure includes a wireless communication unit that performs wireless communication with a terminal device, and a control unit that controls the wireless communication unit to configure a normal first cell and a second cell corresponding to a terminal with reduced functionality. During processing for the terminal device to connect to one of the first cell and the second cell, the wireless communication unit receives first information indicating that the terminal device is a terminal with reduced functionality compared to a normal terminal. When the wireless communication unit receives the first information and a predetermined switching condition is satisfied, the control unit allocates wireless resources for wireless communication between the terminal device and the other of the first cell and the second cell, and connects the terminal device to the other cell.

A terminal device according to one aspect of the present disclosure is a terminal device comprising: a normal first cell configured by a base station device; a second cell corresponding to a terminal with reduced functionality; a wireless communication unit capable of selectively performing wireless communication; and a control unit that controls the wireless communication unit. When the terminal device hands over from a third cell configured by another base station device to the first cell, the wireless communication unit transmits to the first cell a message including first information indicating that the terminal device is a terminal with reduced functionality compared to a normal terminal. After transmitting the message, when the control unit is notified by the first cell of the timing at which to start communication with the second cell, it connects to the second cell at the timing based on the wireless resources allocated by the base station device.

A terminal device according to one aspect of the present disclosure is a terminal device comprising: a normal first cell configured by a base station device; a second cell corresponding to a terminal with reduced functionality; a wireless communication unit capable of selectively performing wireless communication; and a control unit that controls the wireless communication unit. When the terminal device performs a procedure for connecting to the second cell, the wireless communication unit transmits to the second cell a message including first information indicating that the terminal device is a terminal with reduced functionality compared to a normal terminal. After transmitting the message, if the control unit is notified by the second cell of the timing at which communication with the first cell should be initiated, the control unit connects to the first cell at the timing based on the wireless resources allocated by the base station device.

1 is an overall configuration diagram of a communication system according to a first embodiment. FIG. 2 is a block diagram showing the electrical configuration of the terminal device. FIG. 2 is a block diagram showing the electrical configuration of a base station device. 4 is a processing flowchart of a terminal device according to the first embodiment. 4 is a processing flowchart of a base station device according to the first embodiment. FIG. 2 is a sequence diagram relating to cell connection in the communication system according to the first embodiment. FIG. 10 is a sequence diagram relating to cell connection in a communication system according to a comparative example. FIG. 10 is an overall configuration diagram of a communication system according to a second embodiment. 10 is a processing flowchart of a terminal device according to the second embodiment. 10 is a processing flowchart of a base station device according to the second embodiment. FIG. 10 is a sequence diagram relating to cell connection in a communication system according to a second embodiment. FIG. 10 is a sequence diagram relating to cell connection in a communication system according to a comparative example.

Embodiments of the present disclosure will be described below with reference to the drawings. Note that in the drawings, identical or equivalent elements are designated by the same reference numerals, and duplicate descriptions will be omitted.

First Embodiment
The configuration of a communication system 100 according to the first embodiment will be described. Fig. 1 is a diagram showing the overall configuration of the communication system 100 according to the first embodiment. Fig. 2 is a block diagram showing the electrical configuration of a terminal device 110. Fig. 3 is a block diagram showing the electrical configuration of a base station device 120.

As shown in FIG. 1, the communication system 100 includes a terminal device 110 and a base station device 120. The base station device 120 configures a normal first cell and a second cell corresponding to a terminal with reduced functionality. The terminal device 110 can selectively connect to the first cell and the second cell. In the following description, an NR (New Radio) cell is exemplified as the first cell, and a RedCap (Reduced Capability) cell is exemplified as the second cell.

The terminal device 110 is UE (User Equipment) that supports the 5G standard and the LTE (Long Term Evolution)/4G standard. The terminal device 110 has fewer functions than a normal terminal and is, for example, a small sensor configured as an IoT (Internet of Things) device. The terminal device 110 may be an IoT device other than a small sensor, or a wireless communication device that is not an IoT device (for example, a smartphone, tablet, laptop PC, etc.).

Multiple base station devices 120 can communicate with terminal devices 110 located within the cells within which each base station device 120 can communicate. These base station devices 120 are connected to a core network device (not shown). The core network device constitutes a backbone network (hereinafter collectively referred to as the network) that controls, for example, the Internet, fixed telephone networks, and mobile networks.

In the example of FIG. 1, two base station devices 120, base station A and base station B, are provided in the communication system 100. Base station A is a 5G wireless base station that configures an NR cell 131 and communicates via NR with UEs located in the NR cell 131. Base station A is, for example, a gNB (next generation NodeB) that configures a RAN (Radio Access Network).

Furthermore, base station A configures RedCap cell 132, which supports the RedCap function. RedCap cell 132 is deployed so as to overlap with at least a portion of NR cell 131. In this example, almost the entire RedCap cell 132 overlaps with almost the entire NR cell 131. Therefore, terminal device 110 present in the range of NR cell 131 is also present in RedCap cell 132. Base station A can communicate with RedCap UE present in RedCap cell 132.

Base station B is an LTE/4G radio base station that constitutes LTE cell 133 and communicates via LTE with UEs located within the LTE cell 133. Base station B is, for example, an eNB (Evolved NodeB) that constitutes a RAN. In this example, a portion of LTE cell 133 is deployed so as to overlap with NR cell 131 and RedCap cell 132. In other words, NR cell 131, RedCap cell 132, and LTE cell 133 are located in a positional relationship in which they are adjacent cells.

In the communication system 100, a terminal device 110 can select the optimal base station device 120 for its current location while moving, and communicate with a core network device via this selected base station device 120. For example, if a large number of terminal devices 110 simultaneously connect to a single base station device 120 during a disaster, there is a possibility that highly urgent communications may be disrupted. To reduce the possibility of such highly urgent communications being disrupted, base station A supports the RedCap function.

RedCap is a standard that restricts some NR functions (e.g., bandwidth, MIMO, etc.) for use with IoT devices, etc. RedCap UE is a UE that supports RedCap functions and has an Early Indication function that notifies the base station that it is a RedCap UE via a RACH (Random Access Channel) message. The terminal device 110 in this example is a RedCap UE. Furthermore, the terminal device 110 is a dual UE that can selectively connect to the NR cell 131 and the RedCap cell 132 when it is located in both the NR cell 131 and the RedCap cell 132.

As shown in FIG. 2, the terminal device 110 includes a control unit 201, a memory unit 202, a wireless communication unit 203, an output unit 204, and an operation unit 205. The control unit 201 is, for example, a processor such as a CPU. The control unit 201 may be an MCU (Micro Control Unit) or MPU (Micro Processor Unit), or may be an FPGA (Field Programmable Gate Array), ASIC (Application Specific Integrated Circuit), or other circuit with a calculation function.

The memory unit 202 is a device capable of storing programs and data, such as ROM, RAM, cache memory, or flash memory. The memory unit 202 stores control programs for controlling the terminal device 110 and various application programs that users can use on the terminal device 110.

The wireless communication unit 203 is a communication module for performing wireless communication via an antenna, and performs wireless communication with the base station device 120. The output unit 204 is a device that outputs information in a manner that can be perceived by the user, such as a display, lamp, speaker, vibrator, etc. The operation unit 205 is a button, switch, key, touch panel, etc. that the user uses to operate the terminal device 110.

In this example, the wireless communication unit 203 is capable of selectively performing wireless communication with the first cell and the second cell. In processing to connect to one of the first and second cells, the control unit 201 transmits first information to the one of the cells, indicating that the terminal device 110 is a terminal with reduced functionality compared to a normal terminal. In the following description, RedCap information indicating that the terminal device 110 is a RedCap UE is used as an example of the first information.

As shown in FIG. 3, each of the multiple base station devices 120 includes a control unit 301, a memory unit 302, a wireless communication unit 303, etc. The control unit 301 is, for example, a processor such as a CPU, but may also be an MCU or MPU, or an FPGA, ASIC, or other circuit with a calculation function. The memory unit 302 is a device capable of storing programs and data, such as a ROM, RAM, cache memory, flash memory, etc.

The memory unit 302 stores a control program for controlling the base station device 120 and various data necessary to provide the RAN. The wireless communication unit 303 is a communication module for performing wireless communication via an antenna, and performs wireless communication with the terminal device 110 as well as with the network.

In this example, the control unit 301 controls the wireless communication unit 303 to configure a first cell and a second cell. The wireless communication unit 303 receives first information during processing for the terminal device 110 to connect to one of the first and second cells. When the wireless communication unit 303 receives the first information and a predetermined switching condition is satisfied, the control unit 301 allocates wireless resources for wireless communication between the terminal device 110 and the other of the first and second cells, and connects the terminal device 110 to the other cell.

The following describes the various processes executed in the communication system 100 of the first embodiment, particularly the process performed when the terminal device 110 hands over from an LTE cell to an NR cell. Figure 4 is a processing flowchart for the terminal device 110 according to the first embodiment. Figure 5 is a processing flowchart for the base station device 120 according to the first embodiment. Figure 6 is a sequence diagram related to cell connection in the communication system 100 according to the first embodiment.

In this embodiment, the following control is performed in the terminal device 110, which is a dual UE. When the terminal device 110 hands over from a third cell configured by another base station device 120 to the first cell, the radio communication unit 203 transmits a message including first information to the first cell. After transmitting this message, if the first cell notifies the control unit 201 of the timing to start communication with the second cell, the control unit 201 connects to the second cell at the notified timing based on the radio resources allocated by the base station device 120.

An example of the processing flow of the terminal device 110 that realizes the above control will be described with reference to Figure 4. In S401, the terminal device 110 is located in an LTE cell. In S403, the control unit 201 determines whether an RRC (Radio Resource Control) Reconfig message has been received from the LTE cell. If an RRC Reconfig message has been received, in S405 the control unit 201 determines whether the Reconfig message is a handover instruction to an NR cell. If the RRC Reconfig message is a handover instruction to an NR cell, in S407 the control unit 201 executes a handover procedure to the NR cell. Note that if an RRC Reconfig message has not been received, or if the RRC Reconfig message is not a handover instruction to an NR cell, the control unit 201 returns the processing to S403.

In the example of Figure 1, terminal device 110 is located in LTE cell 133 and periodically receives a neighboring cell measurement instruction from LTE cell 133. In response to the neighboring cell measurement instruction, terminal device 110 measures the communication quality (e.g., radio wave strength) of the cell neighboring LTE cell 133 and transmits a Measurement Report indicating the measurement results to LTE cell 133. In this case, NR cell 131 and RedCap cell 132 configured by base station device 120 (i.e., base station A) are detected as neighboring cells. The Measurement Report includes the communication quality of LTE cell 133 and the communication qualities of the neighboring cells, NR cell 131 and RedCap cell 132.

When another base station device 120 (i.e., base station B) constituting the LTE cell 133 determines, for example, based on a Measurement Report, that the communication quality of the NR cell 131 is higher than the communication quality of the LTE cell 133, it transmits an RRC Reconfig message, which is a handover instruction to the NR cell 131, to the terminal device 110. In the terminal device 110, the handover procedure to the NR cell 131 is executed in S407 described above.

Under the LTE standard, handover from an LTE cell to a RedCap cell is not performed. Therefore, even if the communication quality of RedCap cell 132 is higher than the communication quality of NR cell 131 and LTE cell 133, LTE cell 133 does not send a handover instruction to RedCap cell 132 to terminal device 110. In this way, when dual UE terminal device 110 moves from LTE cell 133 into the range of NR cell 131 and RedCap cell 132, it is handed over to NR cell 131, but not to RedCap cell 132.

Returning to Figure 4, when the handover procedure to the NR cell is completed, in S409 the control unit 201 includes RedCap information indicating that the terminal device 110 is a RedCap UE in an RRC Reconfig complete message indicating the completion of the handover to the NR cell, and transmits this message to the NR cell. In S411, the control unit 201 determines whether a notification of communication switching timing has been received from the NR cell.

When notification of communication switching timing is received, in S413 the control unit 201 starts data communication with the RedCap cell using the radio resources allocated by the base station device 120 at this communication switching timing. In other words, the terminal device 110 starts data communication with the RedCap cell at the timing notified by this NR cell, without starting data communication with the NR cell that is the handover destination.

On the other hand, if no notification of communication switching timing is received after S409 is executed, in S415 the control unit 201 starts data communication with the NR cell that is the handover destination. After executing S413 or S415, the control unit 201 ends the flowchart in Figure 4 and performs communication control in the same manner as conventionally.

In this embodiment, the following control is performed in a base station device 120 (e.g., base station A) that configures an NR cell and a RedCap cell. When the terminal device 110 performs a handover from a third cell configured by another base station device 120 to one of the cells, a first cell, the wireless communication unit 303 receives a message including first information from the terminal device 110. When the wireless communication unit 303 receives the message including the first information and the second cell is not under restriction, the control unit 301 connects the terminal device 110 to the other cell, the second cell.

An example of the processing flow of the base station device 120 that realizes the above control will be described with reference to Figure 5. In S501, the control unit 301 determines whether an RRC Reconfig complete message has been received from the terminal device 110. If an RRC Reconfig complete message has been received from the terminal device 110, in S503 the control unit 301 determines whether this message indicates completion of handover to an NR cell. If the RRC Reconfig complete message indicates completion of handover to an NR cell, in S505 the control unit 301 determines whether this message includes RedCap information. Note that if an RRC Reconfig complete message has not been received or if the RRC Reconfig complete message does not indicate completion of handover to an NR cell, the control unit 301 returns the processing to S501.

If the RRC Reconfig complete message includes RedCap information, in S507 the control unit 301 determines whether the RedCap cell configured by the base station device 120 is under restriction. If the RedCap cell is not under restriction, in S509 the control unit 301 performs intra-base station cooperation processing between the NR cell and the RedCap cell. The intra-base station cooperation processing is a process of adjusting the timing for switching the connection destination cell of the terminal device 110 between the NR cell configured by the base station device 120 and the RedCap cell.

In the example of Figure 1, when the control unit 301 of base station A does not restrict the connection of RedCap UEs in RedCap cell 132, it performs intra-base station cooperation processing between NR cell 131 and RedCap cell 132. This intra-base station cooperation processing allocates (schedules) radio resources to control wireless communication between the terminal device 110 and RedCap cell 132, and determines the timing to switch the connection destination cell of the terminal device 110 from NR cell 131 to RedCap cell 132. Because both NR cell 131 and RedCap cell 132 are configured by the same base station device 120 (base station A), the timing of communication switchover between these cells can be determined by internal processing of the base station device 120.

After allocating the radio resources as described above, the control unit 301 notifies the terminal device 110 from the first cell of the timing at which communication with the second cell should be started. In the example of FIG. 5, in S511, the control unit 301 notifies the terminal device 110 of the above-mentioned communication switching timing from the NR cell. In S513, the control unit 301 starts data communication between the terminal device 110 and the RedCap cell at the communication switching timing notified to the terminal device 110, using the radio resources allocated as described above.

On the other hand, if the RRC Reconfig complete message does not include RedCap information in S505, the terminal device 110 that has been handed over to the NR cell is not a RedCap UE. Therefore, if the terminal device 110 is a 5G terminal that can connect to an NR cell, in S515 the control unit 301 starts data communication between the NR cell at the handover destination and the terminal device 110. Also, if the RedCap cell is restricted in S507, the terminal device 110's connection to the RedCap cell is restricted, so in S515 the control unit 301 starts data communication between the NR cell at the handover destination and the terminal device 110. After executing S513 or S515, the control unit 301 ends the flowchart in FIG. 5 and performs communication control in the same manner as conventionally.

With reference to Figure 6, a specific aspect of cell connection in the communication system 100 according to the first embodiment will be described. For example, the terminal device 110 moves from the LTE cell 133 into the range of the NR cell 131 and the RedCap cell 132 (see Figure 1). In this case, when a neighboring cell measurement instruction is transmitted from the LTE cell 133 to the terminal device 110 in T601, a Measurement Report in which the NR cell 131 is measured as a neighboring cell is transmitted from the terminal device 110 to the LTE cell 133 in T602.

At T603, an RRC Reconfig message, which is a handover instruction to the NR cell 131, is transmitted from the LTE cell 133 to the terminal device 110, and the terminal device 110 is handed over to the NR cell 131. At T604, an RRC Reconfig complete message, indicating completion of the handover to the NR cell 131, is transmitted from the terminal device 110 to the NR cell 131 (S401 to S409). This RRC Reconfig complete message includes RedCap information.

Base station A, which received the above RRC Reconfig complete message, does not restrict the RedCap cell 132. Therefore, in T605, intra-base station cooperation processing between the NR cell 131 and the RedCap cell 132 is executed. As a result, radio resources are scheduled for wireless communication between the RedCap cell 132 and the terminal device 110, and in T606, the NR cell 131 notifies the terminal device 110 of the communication switching timing (S501 to S511, S411). In T607, data communication between the RedCap cell 132 and the terminal device 110 is started at this communication switching timing (S413, S513).

Here, specific aspects of cell connection in a communication system according to a comparative example will be described. Figure 7 is a sequence diagram of cell connection in a communication system according to a comparative example. In the comparative example of Figure 7, similar to the above embodiment (see Figure 6), the terminal device 1110 moves from the LTE cell 1133 into the range of the NR cell 1131 and the RedCap cell 1132. However, in the comparative example, control is performed differently from that in the above embodiment, as follows:

At T604, an RRC Reconfig complete message indicating completion of handover to the NR cell 1131 is transmitted from the terminal device 1110 to the NR cell 1131, but this RRC Reconfig complete message does not include RedCap information. After handover to the NR cell 1131, a neighboring cell measurement instruction is transmitted from the NR cell 1131 to the terminal device 1110. At T701, the terminal device 1110 receives the neighboring cell measurement instruction and recognizes the RedCap cell 1132 as a neighboring cell based on the measurement results.

The terminal device 1110, which is a dual UE, preferentially connects to a RedCap cell over an NR cell. Therefore, the terminal device 1110 performs disconnection processing with the NR cell 1131, which is the handover destination, in T702, and performs connection processing with the RedCap cell 1132 in T703. When the RedCap cell 1132 notifies the terminal device 1110 that the connection is OK in T704, a connection is established between the terminal device 1110 and the RedCap cell 1132. Thereafter, as in the above embodiment, data communication between the RedCap cell 1132 and the terminal device 1110 begins in T607.

In the above comparative example, when terminal device 1110 hands over from LTE cell 1133 to NR cell 1131, it performs disconnection processing for NR cell 1131 and then performs connection processing for RedCap cell 1132 (T701 to T704). As a result, the number of control sequences for switching the connection destination cell of terminal device 1110 between NR cell 1131 and RedCap cell 1132 increases, resulting in a large processing load on the entire system. In contrast, according to the above embodiment, it is possible to switch the connection destination cell of terminal device 1110 between NR cell 131 and RedCap cell 132 with a smaller number of sequences and processing load than in this comparative example.

Second Embodiment
A second embodiment of the present disclosure will be described, focusing on differences from the first embodiment. Fig. 8 is an overall configuration diagram of a communication system 100 according to the second embodiment. As shown in Fig. 8, the communication system 100 according to the second embodiment includes a terminal device 110 and a base station device 120, similar to the first embodiment. In this example, the terminal device 110 is present in the NR cell 131 and the RedCap cell 132 configured by the base station device 120. However, since the terminal device 110 is in a power-off state, it is not connected to either the NR cell 131 or the RedCap cell 132.

The following describes the various processes executed in the communication system 100 of the second embodiment, particularly the processes executed when the terminal device 110 performs a RACH procedure to a RedCap cell. Figure 9 is a processing flowchart of the terminal device 110 according to the second embodiment. Figure 10 is a processing flowchart of the base station device 120 according to the second embodiment. Figure 11 is a sequence diagram related to cell connection in the communication system 100 according to the second embodiment.

In this embodiment, the following control is performed in the terminal device 110, which is a dual UE. When the terminal device 110 performs a procedure for connecting to the second cell, the radio communication unit 203 causes the terminal device 110 to transmit a message including first information to the second cell. After transmitting the message including the first information, if the second cell notifies the control unit 201 of the timing at which communication with the first cell should be initiated, the control unit 201 connects to the first cell at the notified timing based on the radio resources allocated by the base station device 120.

An example of the processing flow of the terminal device 110 that realizes the above control will be described with reference to Figure 9. In S901, the control unit 201 determines whether broadcast information of the RedCap cell has been acquired. The broadcast information of the RedCap cell is transmitted from the base station device 120 to the terminal in the RedCap cell, and notifies the terminal of information related to RedCap. The broadcast information of the RedCap cell includes notification settings for Early Indication for RedCap UE. The terminal device 110 that has received the broadcast information of the RedCap cell is controlled to perform notification based on the Early Indication function in the RACH procedure of S903, which will be described later. Note that if broadcast information of the RedCap cell has not been acquired, the control unit 201 returns the processing to S901.

In the example of Figure 8, when the terminal device 110 is powered on, the terminal device 110 receives broadcast information about the RedCap cell 132 transmitted from the base station device 120. As a result, the terminal device 110, which is a RedCap UE, recognizes the RedCap cell 132, which is a neighboring cell, and initiates a RACH procedure to the RedCap cell 132, as described below. In addition, the terminal device 110 turns on the Early Indication notification setting.

At S903, the control unit 201 starts the RACH procedure to the RedCap cell and executes the Early Indication function in this RACH procedure. Specifically, the control unit 201 transmits a RACH preamble including RedCap information as RACH Message 1 to the base station device 120. As mentioned above, the RedCap information indicates that the terminal device 110 is a RedCap UE. In this way, the terminal device 110 notifies the base station device 120 that it is a RedCap UE using the Early Indication function.

Furthermore, in S903, the control unit 201 includes UE information in the above-mentioned RACH preamble and transmits it to the RedCap cell. The UE information indicates that the terminal is compatible with the communication standard of the NR cell (i.e., an NR-compatible UE), and more specifically, indicates that the terminal behaves as a UE that is compatible with normal NR (not RedCap). In other words, in this example, the RACH preamble transmitted in S903 includes RedCap information and UE information. Alternatively, at least one of the RedCap information and the UE information may be transmitted to the RedCap cell together with the RACH preamble as data separate from the RACH preamble.

In S905, the control unit 201 determines whether a connection permission to the NR cell has been received from the NR cell. In this example, the connection permission to the NR cell has the function of notifying the timing of communication switching to the NR cell. If a connection permission to the NR cell is received, in S907 the control unit 201 uses the radio resources allocated by the base station device 120 to connect to the NR cell at the communication switching timing notified in this connection permission, and starts data communication with the NR cell. In other words, the terminal device 110 starts data communication with the NR cell at the timing notified from this RedCap cell, without first starting data communication with the RedCap cell with which the RACH procedure was performed.

On the other hand, if permission to connect to the NR cell is not received, in S909 the control unit 201 connects to the RedCap cell that first performed the RACH procedure and starts data communication with the RedCap cell. After executing S907 or S909, the control unit 201 ends the flowchart in Figure 9 and performs communication control in the same manner as conventionally.

In this embodiment, the following control is performed in a base station device 120 that constitutes an NR cell and a RedCap cell. When the terminal device 110 performs a procedure to connect to one of the cells, the second cell, the wireless communication unit 303 receives a message including first information from the terminal device 110. When the wireless communication unit 303 receives a message including the first information, and this message includes second information indicating that the terminal device 110 is a terminal that supports the communication standard of the first cell, and the second cell is under restriction, the control unit 301 connects the terminal device 110 to the other cell, the first cell. In the following description, the aforementioned UE information is used as an example of the second information.

An example of the processing flow of the base station device 120 that realizes the above control will be described with reference to Figure 10. In S1001, the control unit 301 determines whether there is a RACH procedure from the terminal device 110 to the RedCap cell. For example, if a RACH preamble including RedCap information is received from the terminal device 110, the control unit 301 determines that there is a RACH procedure to the RedCap cell. If there is no RACH procedure to the RedCap cell, the control unit 301 returns the processing to S1001.

If there is a RACH procedure to the RedCap cell, in S1003 the control unit 301 determines whether the RedCap cell constituted by the base station device 120 is under restriction. If the RedCap cell is under restriction, in S1005 the control unit 301 determines whether the terminal device 110 is an NR-compatible UE. For example, if the RACH preamble contains the above-mentioned UE information, the control unit 301 determines that the terminal device 110 is an NR-compatible UE.

In this case, in S1007, the control unit 301 performs intra-base station cooperation processing between the NR cell and the RedCap cell. In the example of FIG. 8, if the RedCap cell 132 on which the terminal device 110 has initiated the RACH procedure is restricted, the control unit 301 performs intra-base station cooperation processing between the NR cell 131 and the RedCap cell 132. In this intra-base station cooperation processing, radio resources are allocated (scheduled) to control radio communication between the terminal device 110 and the NR cell 131, and the timing for switching the connection destination cell of the terminal device 110 from the RedCap cell 132 to the NR cell 131 is determined. Therefore, as in the first embodiment, the timing for switching communication between the NR cell 131 and the RedCap cell 132 can be determined by internal processing of the base station device 120.

After allocating the radio resources as described above, the control unit 301 notifies the terminal device 110 from the first cell of the timing at which communication with the first cell should be started. In the example of FIG. 10, in S1009, the control unit 301 notifies the terminal device 110 of an NR cell permission notification including the above-mentioned communication switching timing from the RedCap cell. In S1011, the control unit 301 starts data communication between the terminal device 110 and the NR cell at the communication switching timing notified to the terminal device 110, using the radio resources allocated as described above.

If the second cell is not under restriction, the control unit 301 connects the terminal device 110 to the second cell. In the example of FIG. 10, if the RedCap cell is not under restriction in S1003, the terminal device 110 can connect to the RedCap cell, so in S1013 the control unit 301 connects the RedCap cell and the terminal device 110 and starts data communication.

Note that if UE information is not included in the RACH preamble in S1005, it is determined that the terminal device 110 is not an NR-compatible UE. In this case, the terminal device 110 cannot connect to both the RedCap cell and the NR cell, so in S1015 the control unit 301 rejects the connection of the terminal device 110. After executing S1011, S1013, or S1015, the control unit 301 ends the flowchart in FIG. 10 and performs communication control in the same manner as conventionally.

With reference to Figure 11, a specific aspect of cell connection in the communication system 100 according to the second embodiment will be described. For example, the terminal device 110 is switched from power off to power on while being within the coverage area of the NR cell 131 and the RedCap cell 132 (see Figure 8). In this case, at T1101, the broadcast information of the RedCap cell 132 is received by the terminal device 110, and at T1102, the RACH procedure is initiated between the terminal device 110 and the RedCap cell 132 (S901 to S903). The RACH preamble transmitted in this RACH procedure includes RedCap information and UE information.

In the base station device 120 that received the above RACH preamble, the RedCap cell 132 is restricted. Therefore, in T1103, intra-base station cooperation processing between the NR cell 131 and the RedCap cell 132 is executed. As a result, radio resources are scheduled for wireless communication between the NR cell 131 and the terminal device 110, and in T1104, permission to connect to the NR cell 131 is notified to the terminal device 110 (S1001-1009, S905). In T1105, wireless communication between the NR cell 131 and the terminal device 110 is initiated at the communication switching timing notified in this connection permission (S907, S1011).

Here, specific aspects of cell connection in a communication system according to a comparative example will be described. Figure 12 is a sequence diagram of cell connection in a communication system according to a comparative example. In the comparative example of Figure 12, similar to the above embodiment (see Figure 11), the terminal device 2110 is powered on within the range of the NR cell 2131 and the RedCap cell 2132. However, in the comparative example, control is performed differently from the above embodiment as follows.

At T1102, the RACH procedure is initiated between the terminal device 2110 and the RedCap cell 2132, but the terminal device 2110 does not transmit RedCap information or UE information during this RACH procedure. In this case, since the RedCap cell 2132 is under restriction, at T1201, a connection NG to the RedCap cell 2132 is transmitted to the terminal device 110.

Meanwhile, the terminal device 2110 located in the NR cell 2131 also receives broadcast information from the NR cell 2131. In T1203, the terminal device 2110 receives the broadcast information from the NR cell 2131 and starts a RACH procedure to the NR cell 2131. In T1204, when the NR cell 2131 notifies the terminal device 2110 that the connection is OK, connection processing between the terminal device 2110 and the NR cell 2131 is performed. Thereafter, as in the above embodiment, data communication between the NR cell 2131 and the terminal device 2110 starts in T1105.

In the above comparative example, when the terminal device 2110 is powered on within the range of the NR cell 2131 and the RedCap cell 2132, the connection to the NR cell 2131 is rejected, and the RACH procedure to the RedCap cell 2132 is then repeated (T1201 to T1204). As a result, the number of control sequences to switch the connection destination cell of the terminal device 2110 between the NR cell 2131 and the RedCap cell 2132 increases, resulting in a large processing load on the entire system. In contrast, according to the above embodiment, the connection destination cell of the terminal device 110 can be switched between the NR cell 131 and the RedCap cell 132 with a smaller number of sequences and a smaller processing load than in this comparative example.

<Notes>
The present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment.

For example, the configuration and control of the communication system 100, terminal device 110, base station device 120, etc. are not limited to the above embodiment. The first cell is not limited to an NR cell, but may be any cell that supports a normal terminal. Furthermore, the second cell is not limited to a RedCap cell, but may be any cell that supports a terminal with reduced functionality. The terminal with reduced functionality is not limited to a RedCap UE, but may be, for example, a terminal with reduced bandwidth or number of antennas compared to a normal terminal, or a terminal in which some functions have been simplified or omitted.

100: Communication system, 110: Terminal device, 120: Base station device, 201: Control unit, 203: Wireless communication unit, 301: Control unit, 303: Wireless communication unit

Claims (9)

a base station device that configures a normal first cell and a second cell corresponding to a terminal with reduced functionality;
a terminal device selectively connectable to the first cell and the second cell;
In a process for connecting to one of the first cell and the second cell, the terminal device transmits first information indicating that the terminal device is a terminal with reduced functions compared to a normal terminal to the one cell;
the base station device receives the first information from the terminal device, and when a predetermined switching condition is satisfied, allocates radio resources for radio communication between the terminal device and the other cell of the first cell and the second cell, and connects the terminal device to the other cell.
Communication system. a wireless communication unit that performs wireless communication with a terminal device;
A base station device including: a control unit that controls the radio communication unit to configure a normal first cell and a second cell corresponding to a terminal with reduced functionality,
The wireless communication unit receives first information indicating that the terminal device is a terminal with reduced functions compared to a normal terminal, in a process for the terminal device to connect to one of the first cell and the second cell,
When the wireless communication unit receives the first information and a predetermined switching condition is satisfied, the control unit allocates wireless resources for wireless communication between the terminal device and the other cell of the first cell and the second cell, and connects the terminal device to the other cell.
Base station equipment. the wireless communication unit receives a message including the first information from the terminal device when the terminal device is handed over from a third cell configured by another base station device to the first cell, which is one of the cells;
When the wireless communication unit receives the message and the second cell is not under restriction, the control unit connects the terminal device to the second cell, which is the other cell.
The base station device according to claim 2 . After allocating the radio resources, the control unit notifies the terminal device from the first cell of a timing to start communication with the second cell.
The base station device according to claim 3 . The wireless communication unit receives a message including the first information from the terminal device when the terminal device performs a procedure for connecting to the second cell, which is the one of the cells;
When the wireless communication unit receives the message, and second information indicating that the terminal device is a terminal compatible with the communication standard of the first cell is included in the message and the second cell is under restriction, the control unit connects the terminal device to the first cell, which is the other cell.
The base station device according to claim 2 . The control unit connects the terminal device to the second cell when the second cell is not under restriction.
The base station device according to claim 5 . After allocating the radio resources, the control unit notifies the terminal device from the first cell of a timing to start communication with the first cell.
The base station device according to claim 5 . a wireless communication unit capable of selectively performing wireless communication with a normal first cell configured by a base station device and a second cell corresponding to a terminal with reduced functions;
a control unit that controls the wireless communication unit,
the wireless communication unit, when the terminal device is handed over from a third cell configured by another base station device to the first cell, transmits a message including first information indicating that the terminal device is a terminal with reduced functions compared to a normal terminal to the first cell;
and when the control unit is notified by the first cell of a timing to start communication with the second cell after transmitting the message, the control unit connects to the second cell at the timing based on radio resources allocated by the base station device.
Terminal device. a wireless communication unit capable of selectively performing wireless communication with a normal first cell configured by a base station device and a second cell corresponding to a terminal with reduced functions;
a control unit that controls the wireless communication unit,
When the terminal device performs a procedure for connecting to the second cell, the wireless communication unit transmits, to the second cell, a message including first information indicating that the terminal device is a terminal with reduced functions compared to a normal terminal;
and when the control unit is notified by the second cell of a timing to start communication with the first cell after transmitting the message, the control unit connects to the first cell at the timing based on radio resources allocated by the base station device.
Terminal device.