JP7768982B2 - Radio base station, terminal, and radio communication method - Google Patents

Description

The present disclosure relates to a radio base station, a terminal, and a radio communication method that support conditional handover.

The 3rd Generation Partnership Project (3GPP) is developing specifications for the 5th generation mobile communication system (5G, also known as New Radio (NR) or Next Generation (NG)), and is also developing specifications for the next generation, known as Beyond 5G, 5G Evolution, or 6G.

For example, 3GPP Release 16 specifies conditional handover (CHO), which allows a user equipment (UE)-initiated handover to be performed when certain execution conditions are met.

In CHO, candidate cells for handover and the conditions for executing handover (also called transition) to those candidate cells are set in advance for the terminal.

This allows the terminal to hand over to the target radio base station (also called the target cell) without waiting for a handover instruction from the network.

In addition, 3GPP is also studying CHO (CHO with SCG configuration) for candidate cells (secondary cells (SCells)) that make up a secondary cell group (SCG) (Non-Patent Document 1).

"LS on Conditional Handover with SCG configuration scenarios", R2-2104348, 3GPP TSG-RAN WG2 Meeting #113bis Electronic, 3GPP, April 2021

However, the current CHO cannot handle cases where handover to a candidate cell that constitutes the SCG fails, making it difficult for the UE and radio base station (gNB) to operate properly.

The following disclosure has been made in consideration of this situation and aims to provide a radio base station, terminal, and radio communication method that can achieve appropriate operation when handover using CHO with SCG configuration fails.

One aspect of the present disclosure comprises a receiver (RRC/Xn processing unit 120) that receives a handover abort message from a source radio base station, and a transmitter (RRC/Xn processing unit 120) that transmits a release request message for the target radio base station to a target radio base station within a cell group, wherein the transmitter is a radio base station (gNB100) that transmits the release request message including a reason for the release request.

One aspect of the present disclosure is a radio base station (gNB100) that includes a transmitter (RRC/Xn processing unit 120) that transmits a release-required message of the local radio base station to a target radio base station within a cell group, and a control unit (control unit 140) that controls a timer for conditional handover, and the transmitter transmits the release-required message in response to the expiration of the timer or the status of the radio resources at the local radio base station.

One aspect of the present disclosure is a terminal (UE200) that includes a control unit (control unit 240) that controls the execution of conditional handover, and a transmission unit (RRC processing unit 220) that transmits a response to a setting request only to the control unit 240 if the conditional handover fails and another candidate cell is selected.

One aspect of the present disclosure is a terminal (UE200) that includes a control unit (control unit 240) that controls the execution of a conditional handover, and a transmission unit (RRC processing unit 220) that, if the conditional handover fails, transmits a report including information indicating the failure to one or both of the primary cell and secondary cell among the candidate cells.

One aspect of the present disclosure is a wireless communication method including the steps of receiving a handover abort message from a source radio base station and transmitting a release request message for the target radio base station to a target radio base station in a cell group, wherein the transmitting step transmits the release request message including a reason for aborting the handover.

FIG. 1 is a diagram showing the overall configuration of a wireless communication system 10. Figure 2 is a functional block diagram of gNB100. FIG. 3 is a functional block diagram of the UE 200. FIG. 4 is a diagram showing a sequence example (part 1) of CHO with SCG configuration according to the first operation example. FIG. 5 is a diagram showing a sequence example (part 2) of the CHO with SCG configuration according to the operation example 1. FIG. 6 is a diagram showing a sequence example (part 1) of CHO with SCG configuration according to the second operation example. FIG. 7 is a diagram showing a sequence example (part 2) of CHO with SCG configuration according to the second operation example. FIG. 8 is a diagram illustrating an example of a sequence of a CHO with SCG configuration according to the third operation example. Figure 9 is a diagram showing an example of the hardware configuration of gNB100 and UE200.

The following describes the embodiments based on the drawings. Note that identical or similar symbols are used to designate identical functions and configurations, and descriptions of these will be omitted where appropriate.

(1) Overall Schematic Configuration of Wireless Communication System Fig. 1 is a diagram showing the overall schematic configuration of a wireless communication system 10 according to this embodiment. The wireless communication system 10 is a wireless communication system conforming to 5G New Radio (NR) and includes a Next Generation-Radio Access Network 20 (hereinafter, NG-RAN 20) and a terminal 200 (User Equipment 200, hereinafter, UE 200).

The wireless communication system 10 may be a wireless communication system conforming to a method called Beyond 5G, 5G Evolution, or 6G, or may be a wireless communication system conforming to Long Term Evolution (LTE).

The NG-RAN 20 includes a radio base station 100 (hereinafter, gNB 100). Note that the specific configuration of the wireless communication system 10, including the number of gNBs and UEs, is not limited to the example shown in Figure 1. Furthermore, in the case of a wireless communication system conforming to LTE, an eNB may be used instead of a gNB.

NG-RAN 20 actually includes multiple NG-RAN nodes, specifically gNBs (or ng-eNBs), and is connected to a 5G-compliant core network (5GC, not shown). Note that NG-RAN 20 and 5GC may also be simply referred to as the "network."

gNB100 is a radio base station that complies with NR and performs NR-compliant radio communications with UE200. gNB100 and UE200 are capable of supporting Massive MIMO, which generates more directional beams by controlling radio signals transmitted from multiple antenna elements, Carrier Aggregation (CA), which aggregates and uses multiple component carriers (CCs), and Dual Connectivity (DC), which enables simultaneous communication between the UE and multiple NG-RAN nodes.

In this embodiment, Multi-Radio Dual Connectivity (MR-DC) may be implemented in which one of the gNB100s constitutes a master node (MN) and the other gNB100 constitutes a secondary node (SN).

In other words, UE200 supports dual connectivity, connecting to multiple gNB100s (which can also be read as cells, same below).

Any gNB100 may be included in a master cell group (MCG), and other gNB100 may be included in a secondary cell group (SCG). The gNB100 may also be referred to as a wireless communication node, node, or network device.

The type of DC may be Multi-RAT Dual Connectivity (MR-DC), which uses multiple radio access technologies, or NR-NR Dual Connectivity (NR-DC), which uses only NR. MR-DC may also be E-UTRA-NR Dual Connectivity (EN-DC), in which the eNB constitutes the master node (MN) and the gNB constitutes the secondary node (SN), or NR-E-UTRA Dual Connectivity (NE-DC), which is the reverse.

In a DC, a master cell group (MCG) and a secondary cell group (SCG) may be configured. The MCG may include a primary cell (PCell), and the SCG may include a secondary cell (SCell).

SCells may also include primary/secondary cells (PSCells). A PSCell is a type of SCell, but may be interpreted as a special SCell with functions equivalent to those of a PCell. Similar to a PCell, a PSCell may perform functions such as transmitting the PUCCH (Physical Uplink Control Channel), performing a contention-based random access procedure (CBRA), and monitoring radio link quality (downlink radio quality).

UE200 can transition between cells formed by gNB100. "Transition" typically refers to handover between cells, but may also include behavior of UE200 that changes the cell to which it is connected, such as cell reselection.

In particular, in this embodiment, the wireless communication system 10 may support conditional handover (CHO). CHO may be interpreted as a handover procedure that is executed only if an execution condition is met.

CHO may be defined as a handover executed by UE200 when one or more handover execution conditions are met. UE200 may start evaluating the execution conditions when it receives a CHO configuration and stop evaluating the execution conditions when a handover (legacy handover or conditional handover) is executed.

The CHO configuration includes the CHO candidate cell settings generated by the candidate cell (candidate gNB) and the execution conditions generated by the source cell (gNB) from which the handover originates.

The execution conditions may consist of one or two trigger conditions (CHO event A3/A5 as specified in 3GPP TS38.331). A single reference signal (RS) type may be triggered, and up to two different trigger quantities (e.g., Reference Signal Received Power (RSRP) and Reference Signal Received Quality (RSRQ), RSRP and Signal-to-Interference plus Noise power Ratio (SINR), etc.) may be simultaneously set for the evaluation of the CHO execution conditions for a single candidate cell.

Note that if UE200 receives an HO instruction (also called an HO command) (without CHO configuration) before the CHO execution conditions are met, it may execute the HO procedure (see 3GPP TS38.300 Chapter 9.2.3.2) regardless of the previously received CHO configuration.

(2) Functional Block Configuration of Wireless Communication System Next, a functional block configuration of the wireless communication system 10 will be described. Specifically, the functional block configurations of the gNB 100 and the UE 200 will be described.

Figure 2 is a functional block diagram of gNB100. Figure 3 is a functional block diagram of UE200. Note that Figures 2 and 3 only show the main functional blocks relevant to the description of the embodiments, and that gNB100 and UE200 have other functional blocks (e.g., power supply units, etc.). Also, Figures 2 and 3 show the functional block configurations of gNB100 and UE200; for the hardware configuration, please refer to Figure 9.

(2.1) gNB100
As shown in FIG. 2, the gNB 100 includes a radio communication unit 110, an RRC/Xn processing unit 120, a handover processing unit 130, and a control unit 140.

The wireless communication unit 110 transmits downlink signals (DL signals) in accordance with NR. The wireless communication unit 110 also receives uplink signals (UL signals) in accordance with NR.

As mentioned above, a cell group may include an MCG and an SCG. gNB100 may belong to either an MCG or an SCG. In other words, gNB100 can constitute either an MN or an SN.

Furthermore, in relation to the handover of UE200, gNB100 may constitute the source radio base station of the handover source, or the target radio base station of the handover destination (transition destination). When constituting a source radio base station, it may be expressed as S-MN or S-SN, depending on whether it is an MN or SN, respectively.

On the other hand, when configuring a target radio base station, it may be expressed as T-MN or T-SN depending on whether it is an MN or SN. Also, in CHO, if there are multiple candidate cells for handover, they may be expressed as T-MN1, T-MN2, T-SN1, T-SN2, etc.

The RRC/Xn processing unit 120 performs various processes related to the radio resource control layer (RRC) and the Xn interface. Specifically, the RRC/Xn processing unit 120 can send an RRC Reconfiguration to the UE 200. The RRC/Xn processing unit 120 can also receive an RRC Reconfiguration Complete from the UE 200, which is a response to the RRC Reconfiguration.

The RRC/Xn processing unit 120 may also send and receive various messages via the Xn interface with other gNBs 100. These messages may include messages related to handover of the UE 200 (which may include CHO) and messages related to cell group configuration.

Note that for radio base stations that support LTE (Evolved Universal Terrestrial Radio Access Network (E-UTRAN)), the X2 interface may be used instead of the Xn interface. Alternatively, the Xn and X2 interfaces may be used together.

Specifically, the RRC/Xn processing unit 120 may receive a handover cancel message from the source radio base station. In this embodiment, the RRC/Xn processing unit 120 may constitute a receiving unit. More specifically, the RRC/Xn processing unit 120 may receive a handover cancel message (HO cancel) when the gNB 100 constitutes a T-MN.

HO cancel may be sent by the S-MN and used to cancel the CHO of UE200.

The RRC/Xn processing unit 120 may also transmit a target radio base station release request message to the target radio base station within the cell group. In this embodiment, the RRC/Xn processing unit 120 may constitute a transmitting unit that transmits the release request message.

Specifically, when the gNB 100 configures a T-MN, the RRC/Xn processing unit 120 may send an S-node Release request to the target cell (gNB) included in the SCG. More specifically, the RRC/Xn processing unit 120 may send an S-node Release request including the reason for the release request to the T-SN. The reason for the release request may be that the CHO has been canceled or that the CHO to another candidate cell has been completed.

The RRC/Xn processing unit 120 may also transmit a release-required message for the local station to a target radio base station within the cell group. In this embodiment, the RRC/Xn processing unit 120 may constitute a transmission unit that transmits the release-required message.

Specifically, when the gNB100 configures a T-SN, the RRC/Xn processing unit 120 may send an S-node Release required to the T-MN in the MCG, indicating that the T-SN needs to be released.

The RRC/Xn processing unit 120 may send an S-node Release required to the T-MN depending on the expiration of the timer or the state of the radio resources in the local station. The timer may be started at the timing of the addition or change of an SN (which may also be expressed as an S-node), and for example, T_Dcoverall, TXn_Dcoverall, etc. may be used. In particular, in this embodiment, it may be interpreted as a timer that is started at the timing of the addition of an SN that can be applied to CHO, and measures a predetermined period of time. For convenience, below, it may be expressed as T_Dcoverall_CHO, TXn_Dcoverall_CHO, etc.

The handover processing unit 130 performs processing related to handover of the UE 200. Specifically, the handover processing unit 130 can perform processing related to normal handover of the UE 200 (which may also be called legacy handover) and conditional handover (CHO).

In particular, for a CHO, the destination cell may constitute an MCG and an SCG. Such a CHO may also be called a CHO with SCG configuration.

The control unit 140 controls each functional block that constitutes the gNB 100. In particular, in this embodiment, the control unit 140 can perform control over RRC inter-node messages related to CHO and timers for CHO.

Specifically, the control unit 140 may perform control regarding HO-related messages sent and received between the source radio base station and the target radio base station, and messages regarding SN (SgNB) addition, modification, and release.

The control unit 140 may also control the timer for CHO. Specifically, the control unit 140 may control T_Dcoverall_CHO and TXn_Dcoverall_CHO, which are started at the timing of adding an SN, etc.

(2.2) UE200
As shown in FIG. 3 , the UE 200 includes a radio communication unit 210 , an RRC processing unit 220 , a handover execution unit 230 , and a control unit 240 .

The wireless communication unit 210 transmits uplink signals (UL signals) in accordance with NR. The wireless communication unit 210 also receives uplink signals (DL signals) in accordance with NR.

The wireless communication unit 210 supports dual connectivity (DC) and can simultaneously connect to multiple gNB100 to send and receive wireless signals (which may also be interpreted as component carriers, etc.). In other words, the wireless communication unit 210 can simultaneously communicate with gNB100s belonging to an MCG or SCG.

The RRC processing unit 220 performs various processes in the radio resource control layer (RRC). Specifically, the RRC processing unit 220 can send and receive messages in the radio resource control layer. In this embodiment, the RRC processing unit 220 may constitute a receiving unit that receives messages in the radio resource control layer.

The RRC processing unit 220 can receive RRC Reconfiguration from the network, specifically, from the NG-RAN 20. The RRC processing unit 220 can also send RRC Reconfiguration Complete, which is a response to the RRC Reconfiguration, to the network.

Furthermore, the RRC processing unit 220 may transmit a configuration request only to the primary cell (PCell) when CHO with a specific target radio base station fails and another candidate cell is selected in the reconnection procedure. In this embodiment, the RRC processing unit 220 may configure a transmission unit that transmits the configuration request.

Specifically, if CHO fails and another candidate cell (which may include the PCell and PSCell) is selected, the RRC processing unit 220 may transmit a response to the RRC configuration request only to the PCell. Specifically, the RRC processing unit 220 may apply RRC reconfiguration and transmit RRC Reconfiguration Complete, which is a response to the RRC reconfiguration, to the T-MN that forms the PCell. Note that RRC Reconfiguration Complete may be interpreted as a message indicating that the RRC reconfiguration has been applied.

Alternatively, the RRC processing unit 220 may send the configuration request to the PCell and SCell (which may include the PSCell).

Furthermore, if CHO fails, the RRC processing unit 220 may transmit a report including information indicating failure to one or both of the primary cell (PCell) and the secondary cell (SCell (which may include PSCell)) among multiple candidate cells. In this embodiment, the RRC processing unit 220 may be configured as a transmitting unit that transmits a report including CHO failure information.

Specifically, if the CHO with SCG configuration fails, the RRC processing unit 220 may send a Radio Link Failure (RLF) report to the network containing information indicating the failure.

The RLF report may include information on the case where the first CHO fails, and information on the case where the second or subsequent CHO fails. Furthermore, as described above, the RLF report may include information indicating with which cell the CHO failed. A CHO failure may be determined by whether the random access (RA) procedure is successful, or more simply, whether the transmission of the Random Access Channel (RACH) is successful. RACH failure may be simply referred to as a connection failure, or may be expressed as a failedTargetPCell or failedTargetPSCell.

Note that the second or subsequent CHO failure may be determined based on a specific timer. For example, the RRC processing unit 220 may determine a new CHO failure while timer T311 is running, which starts when the RRC connection re-establishment procedure begins and stops when an appropriate NR cell or a cell using another radio access technology (RAT) is selected.

In addition, CHO information regarding SCell may be included, for example, in SCG Failure Information rather than in the RLF report.

The handover execution unit 230 executes handover of the UE 200. Specifically, the handover execution unit 230 can execute processing related to normal handover (legacy handover) and conditional handover (CHO).

In the case of CHO, the handover execution unit 230 may transition to a candidate cell when an execution condition is met. As described above, the execution condition may be determined based on the quality of the reference signal (RS), specifically, the RSRP, RSRQ, or SINR value.

Furthermore, the destination of a CHO may not necessarily involve an SCG, or may involve an SCG (CHO with SCG configuration). In other words, the destination cell of a CHO may be a single cell, or may consist of multiple cells (which may be interpreted as a cell group) according to a DC.

The control unit 240 controls each functional block constituting the UE 200. In particular, in this embodiment, the control unit 240 may control the execution of a conditional handover (CHO), specifically, the execution of a CHO with SCG configuration.

For a CHO with SCG configuration, the control unit 240 can perform control regarding the selection of other candidate cells if the CHO fails.

For example, if the first CHO fails and another candidate cell is selected, the control unit 240 may control the RRC configuration request (e.g., RRC Reconfiguration) to be sent only to the PCell of the other candidate cells.

Alternatively, if the initial CHO fails and another candidate cell is selected, the control unit 240 may control the transmission of the configuration request (to both the PCell and SCell (which may include the PSCell) of the other candidate cell.

Furthermore, for a CHO with SCG configuration, the control unit 240 may control the transmission of a report (RLF report) containing information about the cell group if the CHO fails.

For example, if the CHO with SCG configuration fails, the control unit 240 may control the generation of an RLF report including information indicating that the CHO with SCG configuration has failed for either or both of the PCell and SCell among multiple candidate cells.

The RLF report may further include at least one of identification information, quality information, time information, activation status, etc. regarding the failed cell. The activation status may include an indication that the SCG is deactivated.

(3) Operation of the Wireless Communication System Next, a description will be given of the operation of the wireless communication system 10. Specifically, the description will be given of the operation related to conditional handover (CHO), particularly when a candidate cell for handover constitutes a cell group, specifically, when the candidate cell constitutes an SCG (CHO with SCG configuration).

(3.1) Operation example 1
In the CHO with SCG configuration, in determining whether an execution condition is satisfied (which may also be referred to as CHO condition evaluation), the Source PCell can transmit a handover cancel message, specifically, HO cancel, to a Target PCell that does not satisfy the execution condition.

In addition, the Target PCell (which may be expressed as T-MN) can send an S-node Release request to the Target SCell (which may be expressed as T-SN) in response to HO cancel. In this operation example, the S-node Release request may include the reason for the handover cancellation.

Figure 4 shows an example sequence (part 1) of CHO with SCG configuration related to operation example 1. As shown in Figure 4, S-MN, S-SN, T-MN1, T-MN2, and T-SN can perform operations related to adding an SCG (SgNB) in response to a handover request (HO request).

This sequence is specified in 3GPP TS38.300 Chapter 9.2.3.2 (CHO related) and 3GPP TS38.423 Chapter 8.3.1. Note that while only one T-SN is shown in Figure 4, there may be two or more T-SNs (same below).

Specifically, when a Target PCell (T-MN2) that is a candidate for CHO receives an HO cancel from a Source PCell (which may also be expressed as an S-MN) and then sends an S-node Release request to the T-SN that sent the SgNB addition request, it may include a cause value of CHO/HO cancel in the S-node Release request.

Alternatively, the T-SN that receives the SgNB addition request may use a timer to adjust the timing of sending an S-node Release required to the Target PCell (T-MN2), indicating that the T-SN needs to be released.

Figure 5 shows a sequence example (part 2) of CHO with SCG configuration related to operation example 1. As shown in Figure 5, T-SN may provide new CHO timers, T_Dcoverall_CHO and TXn_Dcoverall_CHO (tentative names), in addition to the existing T_DCoverall and TXn_DCoverall.

When TXn_Dcoverall_CHO (or T_Dcoverall_CHO, hereinafter the same) expires, the T-SN may trigger the S-NG-RAN node initiated S-NG-RAN node Release procedure and send S-node Release required.

The T-SN may also include a cause value (timer T_Dcoverall_CHO/TXn_Dcoverall_CHO expiry) in the S-node Release required, indicating that TXn_Dcoverall_CHO has expired. TXn_Dcoverall_CHO may be used in the case of NR (Xn interface), and T_Dcoverall_CHO in the case of LTE (X2 interface).

Alternatively, if radio resources related to the T-SN become insufficient before TXn_Dcoverall_CHO expires, the T-SN may trigger the S-NG-RAN node initiated S-NG-RAN node Release procedure and send an S-node Release required. The radio resources related to the T-SN may be radio resources within the SN (radio base station) in question, or may be radio resources used by and indirectly affected by other nodes connected to the SN in question.

The T-SN may also include a cause value (no radio resource available for CHO) in the S-node Release required to indicate a lack of radio resources.

Note that the S-NG-RAN node initiated S-NG-RAN node Release procedure may also be triggered by a lack of radio resources related to T-SN, as described above, and may therefore be executed before the expiration of TXn_Dcoverall_CHO.

(3.2) Operation example 2
In the CHO with SCG configuration, after synchronization with a candidate cell of the CHO fails, timer T311 is started, and the UE 200 is assumed to perform cell reselection. Note that synchronization with the candidate cell may be interpreted as connection or configuration with the candidate cell. Typically, as described above, this may be interpreted as RACH transmission being unsuccessful.

In this operation example, if UE200 selects another CHO candidate cell, UE200 may select the selected cell and send an RRC configuration request (e.g., RRC Reconfiguration). The RRC configuration request may be an RRC Reconfiguration Complete or another RRC message.

Also, as described above, T311 may start at the beginning of the RRC connection re-establishment procedure and stop upon selection of a suitable NR cell or a cell using another radio access technology (RAT).

Figure 6 shows an example sequence (part 1) of CHO with SCG configuration relating to operation example 2. As shown in Figure 6, when synchronization with a candidate cell fails (RACH transmission fails) and UE200 selects another CHO candidate cell, it may apply (or transmit) RRC Reconfiguration to both the Target PCell and the Target SCell (PSCell) (option 1).

Alternatively, if UE200 fails to synchronize with a candidate cell (RACH transmission fails) and selects another CHO candidate cell, it may apply (or transmit) RRC Reconfiguration to only one of the candidate cells (Option 2).

Furthermore, after receiving the configuration request (e.g., RRC Reconfiguration Complete), the Target PCell (T-MN2) may send an SN Reconfiguration Complete to the T-SN. Furthermore, the T-MN2 may send an SN Reconfiguration Complete to another T-SN (e.g., T-SN2).

Figure 7 shows a sequence example (part 2) of CHO with SCG configuration related to operation example 2. As shown in Figure 7, UE 200 may apply RRC Reconfiguration only to the Target PCell. This is because the PSCell may already be released compared to the PCell.

(3.3) Operation example 3
When the CHO with SCG configuration fails, the UE 200 may transmit the following RLF report: Fig. 8 illustrates an example of a sequence of the CHO with SCG configuration according to the third operation example.

For example, if UE200 fails to synchronize with both the target PCell and the target SCell (PSCell) during the first CHO (CHO First failure, Failure 1 in Figure 8), it may include the failed target PCell ID, target SCell ID, PCell/PSCell (serving cell) quality, neighboring cell quality of the PCell/PSCell, and candidate target PCell ID/quality in the RLF report.

On the other hand, if UE200 successfully synchronizes with the target PCell but fails to synchronize with the target SCell (PSCell) during the initial CHO, it may include the target PCell ID with which synchronization was successful, the target SCell ID with which synchronization failed, the PCell/PSCell (serving cell) quality, the neighboring cell quality of the PCell/PSCell, and the candidate target PCell ID/quality in the RLF report or SCG Failure Information.

Furthermore, when UE200 performs cell reselection during the startup (operation) of T311 after CHO First failure and applies a configuration request (RRC Reconfiguration) to the selected candidate PSCell (i.e., the second CHO), it may operate in accordance with any of the following:

If synchronization with both the target PCell and the target SCell (PSCell) fails during the second CHO (CHO Second failure, Failure 2 in FIG. 8), UE 200 may include the failed target PCell ID, target SCell ID, PCell/PSCell (serving cell) quality, neighboring cell quality of the PCell/PSCell, and candidate target PCell ID/quality in the RLF report, similar to the CHO First failure. Note that in this case, information related to the first failure may also be included.

On the other hand, if UE200 succeeds in synchronizing with the target PCell but fails in synchronizing with the target SCell (PSCell) in the second CHO, it may include the target PCell ID with which synchronization was successful, the target SCell ID with which synchronization failed, the PCell/PSCell (serving cell) quality, the neighboring cell quality of the PCell/PSCell, and the candidate target PCell ID/quality in the RLF report or SCG Failure Information, as in the case of CHO First failure. Note that in this case, information related to the first failure may also be included.

In addition, when the SCG related to the CHO is in an inactive state (deactivated state), an indication indicating that the SCG is in a deactivated state may be included.

(4) Actions and Effects According to the above-described embodiment, the following actions and effects can be obtained. Specifically, the gNB 100 (T-MN) can transmit an S-node Release request including the reason for the release request to the T-SN.

In addition, gNB100 (T-SN) can send S-node Release required to T-MN depending on the expiration of a timer (e.g., TXn_Dcoverall_CHO) or the state of radio resources at its own station.

If CHO fails and UE200 selects other candidate cells (which may include PCell and PSCell), it can send an RRC configuration request to PCell only or to PCell and PSCell.

This allows gNB100 and UE200 to perform appropriate operations when handover using CHO with SCG configuration fails.

More specifically, in the CHO with SCG configuration, the procedures for releasing SNs that were not the target of CHO and the method for applying RRC Reconfiguration to candidate target cells after a CHO First failure have been clarified, making it possible to more reliably realize the CHO with SCG configuration.

In addition, since it is possible to report RLF reports (SCG Failure Information) regarding CHO First failure and CHO Second failure, it can contribute to optimizing settings (parameters) for CHO with SCG configuration.

(5) Other Embodiments Although the embodiments have been described above, it will be obvious to those skilled in the art that the present invention is not limited to the description of the embodiments, and that various modifications and improvements are possible.

For example, in the above-described embodiment, conditional handover (CHO) has been described as an example, but similar operations may also be applied to other similar operations, such as a conditional SCG change. In this case, cell may be read as cell group, etc.

In addition, the terms primary cell and secondary cell may be replaced with other synonymous terms, such as state cell, sub-cell, first cell, second cell, master, sub, etc.

In addition, in the above description, the words configure, activate, update, indicate, enable, specify, and select may be read as interchangeable. Similarly, the words link, associate, correspond, and map may be read as interchangeable, and the words allocate, assign, monitor, and map may also be read as interchangeable.

Furthermore, specific, dedicated, UE-specific, and UE-individual may be read as interchangeable. Similarly, common, shared, group-common, UE-common, and UE-shared may be read as interchangeable.

Furthermore, the block diagrams (Figures 2 and 3) used to explain the above-mentioned embodiments show functional blocks. These functional blocks (components) are realized by any combination of hardware and/or software. Furthermore, there are no particular limitations on the method of realizing each functional block. That is, each functional block may be realized using a single device that is physically or logically coupled, or may be realized using two or more physically or logically separated devices that are connected directly or indirectly (e.g., using wires, wirelessly, etc.) and these multiple devices. A functional block may also be realized by combining software with the single device or multiple devices.

Functions include, but are not limited to, judgment, determination, assessment, calculation, computation, processing, derivation, investigation, search, confirmation, reception, transmission, output, access, resolution, selection, election, establishment, comparison, assumption, expectation, regard, broadcasting, notifying, communicating, forwarding, configuring, reconfiguring, allocating, mapping, and assignment. For example, a functional block (component) that performs transmission functions is called a transmitting unit or transmitter. As mentioned above, there are no particular limitations on how these functions are implemented.

Furthermore, the above-mentioned gNB100 and UE200 (the device) may function as a computer that performs processing of the wireless communication method of the present disclosure. Figure 9 is a diagram showing an example of the hardware configuration of the device. As shown in Figure 9, the device may be configured as a computer device including a processor 1001, memory 1002, storage 1003, communication device 1004, input device 1005, output device 1006, bus 1007, etc.

In the following explanation, the term "apparatus" can be interpreted as a circuit, device, unit, etc. The hardware configuration of the apparatus may be configured to include one or more of the devices shown in the figure, or may be configured to exclude some of the devices.

Each functional block of the device (see Figure 2.3) is realized by any hardware element of the computer device or a combination of such hardware elements.

In addition, each function of the device is realized by loading specified software (programs) onto hardware such as processor 1001 and memory 1002, causing processor 1001 to perform calculations, control communication via communication device 1004, and control at least one of reading and writing data in memory 1002 and storage 1003.

The processor 1001, for example, runs an operating system to control the entire computer. The processor 1001 may be configured as a central processing unit (CPU) including interfaces with peripheral devices, a control unit, an arithmetic unit, registers, etc.

The processor 1001 also reads programs (program code), software modules, data, etc. from at least one of the storage 1003 and the communication device 1004 into the memory 1002, and executes various processes in accordance with these. The program used is a program that causes a computer to execute at least some of the operations described in the above-mentioned embodiments. Furthermore, the various processes described above may be executed by a single processor 1001, or may be executed simultaneously or sequentially by two or more processors 1001. The processor 1001 may be implemented by one or more chips. The program may also be transmitted from a network via a telecommunications line.

Memory 1002 is a computer-readable recording medium and may be composed of, for example, at least one of Read Only Memory (ROM), Erasable Programmable ROM (EPROM), Electrically Erasable Programmable ROM (EEPROM), Random Access Memory (RAM), etc. Memory 1002 may also be referred to as a register, cache, main memory, etc. Memory 1002 can store a program (program code), software module, etc. that can execute a method according to one embodiment of the present disclosure.

Storage 1003 is a computer-readable recording medium and may be composed of, for example, at least one of an optical disk such as a Compact Disc ROM (CD-ROM), a hard disk drive, a flexible disk, a magneto-optical disk (e.g., a compact disk, a digital versatile disk, a Blu-ray® disk), a smart card, a flash memory (e.g., a card, a stick, a key drive), a floppy disk, a magnetic strip, etc. Storage 1003 may also be referred to as an auxiliary storage device. The above-mentioned recording medium may be, for example, a database, a server, or other suitable medium including at least one of memory 1002 and storage 1003.

The communication device 1004 is hardware (transmitting/receiving device) for communicating between computers via at least one of a wired network and a wireless network, and is also referred to as, for example, a network device, network controller, network card, or communication module.

The communication device 1004 may be configured to include high-frequency switches, duplexers, filters, frequency synthesizers, etc. to realize, for example, at least one of Frequency Division Duplex (FDD) and Time Division Duplex (TDD).

The input device 1005 is an input device (e.g., a keyboard, mouse, microphone, switch, button, sensor, etc.) that accepts input from the outside. The output device 1006 is an output device (e.g., a display, speaker, LED lamp, etc.) that outputs to the outside. Note that the input device 1005 and the output device 1006 may be integrated into one device (e.g., a touch panel).

Furthermore, each device such as the processor 1001 and memory 1002 is connected by a bus 1007 for communicating information. The bus 1007 may be configured using a single bus, or may be configured using different buses between each device.

Furthermore, the device may be configured to include hardware such as a microprocessor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a programmable logic device (PLD), or a field programmable gate array (FPGA), and some or all of the functional blocks may be realized by such hardware. For example, the processor 1001 may be implemented using at least one of these pieces of hardware.

Furthermore, the notification of information is not limited to the aspects/embodiments described in the present disclosure, and may be performed using other methods. For example, the notification of information may be performed by physical layer signaling (e.g., Downlink Control Information (DCI), Uplink Control Information (UCI)), higher layer signaling (e.g., RRC signaling, Medium Access Control (MAC) signaling, broadcast information (Master Information Block (MIB), System Information Block (SIB))), other signals, or a combination thereof. Furthermore, RRC signaling may be referred to as an RRC message, and may be, for example, an RRC Connection Setup message, an RRC Connection Reconfiguration message, etc.

Each aspect/embodiment described in this disclosure may be applied to at least one of systems using Long Term Evolution (LTE), LTE-Advanced (LTE-A), SUPER 3G, IMT-Advanced, 4th generation mobile communication system (4G), 5th generation mobile communication system (5G), Future Radio Access (FRA), New Radio (NR), W-CDMA (registered trademark), GSM (registered trademark), CDMA2000, Ultra Mobile Broadband (UMB), IEEE 802.11 (Wi-Fi (registered trademark)), IEEE 802.16 (WiMAX (registered trademark)), IEEE 802.20, Ultra-WideBand (UWB), Bluetooth (registered trademark), or other suitable systems, and next-generation systems enhanced based on these. Furthermore, multiple systems may be combined (e.g., a combination of at least one of LTE and LTE-A with 5G).

The order of the procedures, sequences, flowcharts, etc. of each aspect/embodiment described in this disclosure may be changed unless inconsistent. For example, the methods described in this disclosure present elements of various steps using an example order and are not limited to the particular order presented.

Specific operations described in this disclosure as being performed by a base station may in some cases be performed by its upper node. In a network consisting of one or more network nodes having a base station, it is clear that various operations performed for communication with a terminal may be performed by at least one of the base station and another network node other than the base station (such as, but not limited to, an MME or S-GW). While the above example illustrates a case where there is one other network node other than the base station, a combination of multiple other network nodes (e.g., an MME and an S-GW) may also be used.

Information, signals (information, etc.) may be output from a higher layer (or lower layer) to a lower layer (or higher layer). They may also be input and output via multiple network nodes.

Input and output information may be stored in a specific location (e.g., memory) or managed using a management table. Input and output information may be overwritten, updated, or appended. Output information may be deleted. Input information may be sent to another device.

The determination may be made based on a value represented by a single bit (0 or 1), a Boolean value (true or false), or a numerical comparison (e.g., comparison with a predetermined value).

Each aspect/embodiment described in this disclosure may be used alone, in combination, or switched between depending on the implementation. Furthermore, notification of specified information (e.g., notification that "X is true") is not limited to being done explicitly, but may also be done implicitly (e.g., not notifying the specified information).

Software shall be construed broadly to mean instructions, instruction sets, code, code segments, program code, programs, subprograms, software modules, applications, software applications, software packages, routines, subroutines, objects, executable files, threads of execution, procedures, functions, etc., whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise.

Software, instructions, information, etc. may also be transmitted or received via a transmission medium. For example, if software is transmitted from a website, server, or other remote source using wired technologies (such as coaxial cable, fiber optic cable, twisted pair, Digital Subscriber Line (DSL)), and/or wireless technologies (such as infrared, microwave), these wired and/or wireless technologies are included within the definition of transmission media.

The information, signals, etc. described in this disclosure may be represented using any of a variety of different technologies. For example, data, instructions, commands, information, signals, bits, symbols, chips, etc. that may be referred to throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or magnetic particles, optical fields or photons, or any combination thereof.

Note that terms explained in this disclosure and terms necessary for understanding this disclosure may be replaced with terms having the same or similar meanings. For example, at least one of a channel and a symbol may be a signal (signaling). Furthermore, a signal may be a message. Furthermore, a component carrier (CC) may be called a carrier frequency, a cell, a frequency carrier, etc.

As used in this disclosure, the terms "system" and "network" are used interchangeably.

Furthermore, the information, parameters, etc. described in this disclosure may be expressed using absolute values, relative values from a predetermined value, or other corresponding information. For example, radio resources may be indicated by an index.

The names used for the parameters described above are not intended to be limiting in any way. Furthermore, the mathematical formulas, etc. using these parameters may differ from those explicitly disclosed in this disclosure. The various channels (e.g., PUCCH, PDCCH, etc.) and information elements may be identified by any suitable names, and therefore the various names assigned to these various channels and information elements are not intended to be limiting in any way.

In this disclosure, terms such as "base station (BS)," "radio base station," "fixed station," "NodeB," "eNodeB (eNB)," "gNodeB (gNB)," "access point," "transmission point," "reception point," "transmission/reception point," "cell," "sector," "cell group," "carrier," and "component carrier" may be used interchangeably. Base stations may also be referred to by terms such as macrocell, small cell, femtocell, and picocell.

A base station can accommodate one or more (e.g., three) cells (also called sectors). When a base station accommodates multiple cells, the base station's overall coverage area can be divided into multiple smaller areas, and each smaller area can be provided with communication services by a base station subsystem (e.g., a small indoor base station (Remote Radio Head: RRH)).

The terms "cell" or "sector" refer to part or all of the coverage area of a base station and/or a base station subsystem that provides communication services within that coverage area.

In this disclosure, terms such as "Mobile Station (MS)," "user terminal," "User Equipment (UE)," and "terminal" may be used interchangeably.

A mobile station may also be referred to by those skilled in the art as a subscriber station, mobile unit, subscriber unit, wireless unit, remote unit, mobile device, wireless device, wireless communication device, remote device, mobile subscriber station, access terminal, mobile terminal, wireless terminal, remote terminal, handset, user agent, mobile client, client, or some other suitable terminology.

At least one of the base station and the mobile station may be referred to as a transmitting device, a receiving device, a communication device, etc. At least one of the base station and the mobile station may be a device mounted on a mobile body, or the mobile body itself. The mobile body may be a vehicle (e.g., a car, an airplane, etc.), an unmanned mobile body (e.g., a drone, an autonomous vehicle, etc.), or a robot (manned or unmanned). At least one of the base station and the mobile station may also be a device that does not necessarily move during communication operations. For example, at least one of the base station and the mobile station may be an Internet of Things (IoT) device such as a sensor.

Furthermore, the base station in the present disclosure may be read as a mobile station (user terminal, the same applies hereinafter). For example, each aspect/embodiment of the present disclosure may be applied to a configuration in which communication between a base station and a mobile station is replaced with communication between multiple mobile stations (which may be called, for example, Device-to-Device (D2D), Vehicle-to-Everything (V2X), etc.). In this case, the mobile station may be configured to have the functions possessed by a base station. Furthermore, terms such as "uplink" and "downlink" may be read as terms corresponding to communication between terminals (for example, "side"). For example, terms such as uplink channel and downlink channel may be read as side channel.

Similarly, a mobile station in the present disclosure may be interpreted as a base station, in which case the base station may have the functions of a mobile station.
A radio frame may be composed of one or more frames in the time domain. Each of the one or more frames in the time domain may be called a subframe. A subframe may further be composed of one or more slots in the time domain. A subframe may have a fixed time length (e.g., 1 ms) that is independent of numerology.

Numerology may be a communication parameter that applies to at least one of the transmission and reception of a signal or channel. Numerology may indicate, for example, at least one of the following: subcarrier spacing (SCS), bandwidth, symbol length, cyclic prefix length, transmission time interval (TTI), number of symbols per TTI, radio frame structure, specific filtering operations performed by the transceiver in the frequency domain, and specific windowing operations performed by the transceiver in the time domain.

A slot may consist of one or more symbols in the time domain (such as Orthogonal Frequency Division Multiplexing (OFDM) symbols or Single Carrier Frequency Division Multiple Access (SC-FDMA) symbols). A slot may also be a time unit based on numerology.

A slot may include multiple minislots. Each minislot may consist of one or more symbols in the time domain. A minislot may also be called a subslot. A minislot may consist of fewer symbols than a slot. A PDSCH (or PUSCH) transmitted in a time unit larger than a minislot may be called PDSCH (or PUSCH) mapping type A. A PDSCH (or PUSCH) transmitted using a minislot may be called PDSCH (or PUSCH) mapping type B.

Radio frame, subframe, slot, minislot, and symbol all represent time units for transmitting signals. Other names may also be used for radio frame, subframe, slot, minislot, and symbol.

For example, one subframe may be referred to as a transmission time interval (TTI), multiple consecutive subframes may be referred to as a TTI, or one slot or one minislot may be referred to as a TTI. In other words, at least one of the subframe and the TTI may be a subframe (1 ms) in existing LTE, a period shorter than 1 ms (e.g., 1-13 symbols), or a period longer than 1 ms. Note that the unit representing the TTI may be referred to as a slot, minislot, etc. instead of a subframe.

Here, TTI refers to, for example, the smallest time unit for scheduling in wireless communication. For example, in an LTE system, a base station schedules each user terminal by allocating radio resources (such as frequency bandwidth and transmission power that can be used by each user terminal) in TTI units. However, the definition of TTI is not limited to this.

The TTI may be a transmission time unit for a channel-coded data packet (transport block), code block, code word, etc., or may be a processing unit for scheduling, link adaptation, etc. When a TTI is given, the time interval (e.g., the number of symbols) to which the transport block, code block, code word, etc. is actually mapped may be shorter than the TTI.

Note that when one slot or one minislot is referred to as a TTI, one or more TTIs (i.e., one or more slots or one or more minislots) may be the smallest time unit for scheduling. Furthermore, the number of slots (minislots) that make up the smallest time unit for scheduling may be controlled.

A TTI with a time length of 1 ms may be referred to as a regular TTI (TTI in LTE Rel. 8-12), normal TTI, long TTI, regular subframe, normal subframe, long subframe, slot, etc. A TTI shorter than a regular TTI may be referred to as a shortened TTI, short TTI, partial TTI (partial or fractional TTI), shortened subframe, short subframe, minislot, subslot, slot, etc.

Note that a long TTI (e.g., a normal TTI, a subframe, etc.) may be interpreted as a TTI having a time length of more than 1 ms, and a short TTI (e.g., a shortened TTI, etc.) may be interpreted as a TTI having a TTI length shorter than the TTI length of a long TTI and equal to or greater than 1 ms.

A resource block (RB) is a resource allocation unit in the time domain and frequency domain, and may include one or more consecutive subcarriers in the frequency domain. The number of subcarriers included in an RB may be the same regardless of numerology, for example, 12. The number of subcarriers included in an RB may also be determined based on numerology.

Furthermore, the time domain of an RB may include one or more symbols and may be one slot, one minislot, one subframe, or one TTI in length. One TTI, one subframe, etc. may each consist of one or more resource blocks.

In addition, one or more RBs may also be referred to as a physical resource block (PRB), a sub-carrier group (SCG), a resource element group (REG), a PRB pair, an RB pair, etc.

A resource block may also be composed of one or more resource elements (REs). For example, one RE may be a radio resource area of one subcarrier and one symbol.

A Bandwidth Part (BWP) (which may also be referred to as a partial bandwidth) may represent a subset of contiguous common resource blocks (RBs) for a given numerology on a given carrier, where the common RBs may be identified by their index relative to a common reference point for that carrier. PRBs may be defined in a given BWP and numbered within that BWP.

BWPs may include a BWP for UL (UL BWP) and a BWP for DL (DL BWP). One or more BWPs may be configured for a UE within one carrier.

At least one of the configured BWPs may be active, and the UE may not expect to transmit or receive a given signal/channel outside of the active BWP. Note that the terms "cell," "carrier," etc. in this disclosure may be read as "BWP."

The above-described structures of radio frames, subframes, slots, minislots, and symbols are merely examples. For example, the number of subframes included in a radio frame, the number of slots per subframe or radio frame, the number of minislots included in a slot, the number of symbols and RBs included in a slot or minislot, the number of subcarriers included in an RB, as well as the number of symbols within a TTI, symbol length, and cyclic prefix (CP) length can be varied in various ways.

The terms "connected," "coupled," or any variation thereof, refer to any direct or indirect connection or coupling between two or more elements, and may include the presence of one or more intermediate elements between two elements that are "connected" or "coupled" to each other. The coupling or connection between elements may be physical, logical, or a combination thereof. For example, "connected" may be read as "access." As used in this disclosure, two elements may be considered to be "connected" or "coupled" to each other using one or more wires, cables, and/or printed electrical connections, as well as electromagnetic energy having wavelengths in the radio frequency range, microwave range, and optical (both visible and invisible) range, as some non-limiting and non-exhaustive examples.

The reference signal may also be abbreviated as Reference Signal (RS) or may be called a pilot depending on the applicable standard.

As used in this disclosure, the phrase "based on" does not mean "based only on," unless expressly stated otherwise. In other words, the phrase "based on" means both "based only on" and "based at least on."

The "means" in the configuration of each of the above devices may be replaced with "part," "circuit," "device," etc.

As used in this disclosure, any reference to an element using a designation such as "first," "second," etc. does not generally limit the quantity or order of those elements. These designations may be used in this disclosure as a convenient method of distinguishing between two or more elements. Thus, a reference to a first and a second element does not imply that only two elements may be employed therein or that the first element must precede the second element in some way.

When the terms "include," "including," and variations thereof are used in this disclosure, these terms are intended to be inclusive, similar to the term "comprising." Furthermore, when the term "or" is used in this disclosure, it is not intended to be an exclusive or.

In this disclosure, where articles are added by translation, such as a, an, and the in English, this disclosure may include the noun following these articles being plural.

As used in this disclosure, the terms "determining" and "determining" may encompass a wide variety of actions. "Determining" and "determining" may include, for example, judging, calculating, computing, processing, deriving, investigating, looking up, searching, inquiring (e.g., searching a table, database, or other data structure), and ascertaining something that is considered a "determination." Also, "determining" and "determining" may include receiving (e.g., receiving information), transmitting (e.g., sending information), input, output, accessing (e.g., accessing data in memory), and other actions that are considered a "determination." Furthermore, "judgment" and "decision" can include regarding resolving, selecting, choosing, establishing, comparing, etc. as having been "judged" or "decided." In other words, "judgment" and "decision" can include regarding some action as having been "judged" or "decided." Furthermore, "judgment (decision)" can be interpreted as "assuming," "expecting," "considering," etc.

In this disclosure, the term "A and B are different" may mean "A and B are different from each other." The term may also mean "A and B are each different from C." Terms such as "separate" and "combined" may also be interpreted in the same way as "different."

Although the present disclosure has been described in detail above, it will be clear to those skilled in the art that the present disclosure is not limited to the embodiments described herein. The present disclosure can be implemented in modified and altered forms without departing from the spirit and scope of the present disclosure as defined by the claims. Therefore, the description of the present disclosure is intended to be illustrative and does not have any limiting meaning on the present disclosure.

10. Wireless communication systems
20NG RAN
100 gNB
110 Radio Communication Department
120 RRC/Xn processing unit
130 Handover processing unit
140 Control Unit
200 UE
210 Radio Communication Department
220 RRC processing unit
230 CHO Executive Department
240 Control Unit
1001 processor
1002 memory
1003 Storage
1004 Communication equipment
1005 Input Device
1006 Output Device
1007 Bus

Claims (2)

a control unit that performs control to add a target radio base station as a secondary radio base station in response to a handover request from a source radio base station specifying itself as a target radio base station;
a receiving unit for receiving a handover abort message from the source radio base station;
a transmitter for transmitting a release request message to the target radio base station;
The radio base station, when receiving the handover abort message, includes a reason for the release request in the release request message. adding the target radio base station as a secondary radio base station in response to a handover request from the source radio base station specifying the target radio base station as the target;
receiving a handover abort message from the source radio base station;
transmitting a release request message to the target radio base station;
The wireless communication method, wherein, in the transmitting step, if the handover abort message is received, the release request message includes a reason for the release request .