Radio base station, terminal, and radio communication method

Abstract

To provide a terminal, a communication method, and a communication system capable of achieving an appropriate operation when conditional handover fails.SOLUTION: In a radio communication system, a terminal 200 includes a control unit for controlling execution of conditional handover, and a radio communication unit for transmitting a report including information indicating an identifier of a primary cell and an identifier of a primary secondary cell in which the handover has failed to a network when the conditional handover has failed.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to a radio base station, a terminal, and a radio communication method that support conditional handover. [Background technology]

[0002] The 3rd Generation Partnership Project (3GPP) has developed 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.

[0003] For example, 3GPP Release 16 specifies a conditional handover (CHO), which allows a user equipment (UE)-initiated handover to be performed when a specific execution condition is met.

[0004] In CHO, candidate cells for handover and conditions for executing handover (which may also be called transition) to the candidate cells are set in advance for the terminal.

[0005] This enables the terminal to perform handover to the target radio base station (which may also be referred to as a target cell) without waiting for a handover instruction from the network.

[0006] Furthermore, 3GPP is also studying CHO (CHO with SCG configuration) to candidate cells (secondary cells (SCells)) that constitute a secondary cell group (SCG) (Non-Patent Document 1). [Prior art documents] [Non-patent literature]

[0007] [Non-Patent Document 1] "LS on Conditional Handover with SCG configuration scenarios", R2-2104348, 3GPP TSG-RAN WG2 Meeting #113bis Electronic, 3GPP, April 2021 Summary of the Invention

[0008] However, the current CHO cannot handle cases where handover to a candidate cell that constitutes an SCG fails, and there is a problem that the UE and radio base station (gNB) have difficulty operating properly.

[0009] Therefore, the following disclosure has been made in consideration of the above circumstances, and aims to provide a radio base station, a terminal, and a radio communication method that can achieve appropriate operation when handover using CHO with SCG configuration fails.

[0010] One aspect of the present disclosure includes 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 a target radio base station to a target radio base station in 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.

[0011] 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 radio base station to a target radio base station in a cell group, and a controller (control unit 140) that controls a timer for conditional handover, and the transmitter transmits the release-required message in response to expiration of the timer or the state of radio resources in the radio base station.

[0012] 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 transmits a response to a setting request only to the control unit 240 if the conditional handover fails and another candidate cell is selected.

[0013] 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 a primary cell and a secondary cell among candidate cells.

[0014] 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. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a diagram showing the overall schematic configuration of a wireless communication system 10. As shown in FIG. [Figure 2] Figure 2 is a functional block diagram of gNB100. [Figure 3] FIG. 3 is a functional block diagram of the UE 200. [Figure 4] FIG. 4 is a diagram showing a sequence example (part 1) of CHO with SCG configuration according to the first operation example. [Figure 5] FIG. 5 is a diagram showing a sequence example (part 2) of CHO with SCG configuration according to the first operation example. [Figure 6] FIG. 6 is a diagram showing a sequence example (part 1) of CHO with SCG configuration according to the second operation example. [Figure 7] FIG. 7 is a diagram showing a sequence example (part 2) of CHO with SCG configuration according to the second operation example. [Figure 8] FIG. 8 is a diagram illustrating an example of a sequence of CHO with SCG configuration according to the third operation example. [Figure 9] FIG. 9 is a diagram showing an example of the hardware configuration of gNB100 and UE200. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, embodiments will be described with reference to the drawings. Note that the same or similar reference numerals are used to designate the same functions or configurations, and descriptions thereof will be omitted as appropriate.

[0017] (1) Overall configuration of wireless communication system 1 is a schematic diagram of the overall 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).

[0018] The wireless communication system 10 may be a wireless communication system conforming to a scheme called Beyond 5G, 5G Evolution, or 6G, or may be a wireless communication system conforming to Long Term Evolution (LTE).

[0019] The NG-RAN 20 includes a radio base station 100 (hereinafter, gNB 100). Note that the specific configuration of the radio communication system 10, including the number of gNBs and UEs, is not limited to the example shown in Fig. 1. In addition, in the case of a radio communication system conforming to LTE, an eNB may be used instead of a gNB.

[0020] The 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). The NG-RAN 20 and the 5GC may also be simply referred to as a "network."

[0021] The gNB 100 is a radio base station that complies with NR and performs NR-compliant radio communication with the UE 200. The gNB 100 and the UE 200 are capable of supporting Massive MIMO, which generates highly 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 simultaneously communicates between the UE and multiple NG-RAN nodes.

[0022] In this embodiment, Multi-Radio Dual Connectivity (MR-DC) may be implemented in which one of the gNBs 100 constitutes a master node (MN) and the other gNBs 100 constitute secondary nodes (SNs).

[0023] In other words, UE200 supports dual connectivity, connecting to multiple gNB100s (which may also be read as cells, same below).

[0024] Any of the gNBs 100 may be included in a master cell group (MCG), and the other gNBs 100 may be included in a secondary cell group (SCG). The gNBs 100 may be referred to as wireless communication nodes, nodes, or network devices.

[0025] The type of DC may be Multi-RAT Dual Connectivity (MR-DC) that uses multiple radio access technologies, or NR-NR Dual Connectivity (NR-DC) that 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) in which the opposite is true.

[0026] In the 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).

[0027] Furthermore, SCells may include primary / secondary cells (PSCells). A PSCell is a type of SCell, but may be interpreted as a special SCell with the same functions as a PCell. A PSCell may perform functions such as transmitting a PUCCH (Physical Uplink Control Channel), performing a contention-based random access procedure (CBRA), and monitoring radio link quality (downlink radio quality monitoring), just like a PCell.

[0028] The UE 200 can transition between cells formed by the gNB 100. The "transition" typically means handover between cells, but may also include behavior of the UE 200 such that the connected cell is changed, such as cell reselection.

[0029] 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.

[0030] CHO may be defined as a handover executed by UE 200 when one or more handover execution conditions are met. UE 200 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.

[0031] 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.

[0032] The execution condition may consist of one or two trigger conditions (CHO event A3 / A5 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 evaluation of the CHO execution condition for a single candidate cell.

[0033] In addition, if UE200 receives an HO instruction (which may also be called an HO command) (without CHO configuration) before the CHO execution condition is met, it may execute the HO procedure (see 3GPP TS38.300 Chapter 9.2.3.2) regardless of the previously received CHO configuration.

[0034] (2) Functional block configuration of wireless communication system Next, a description will be given of the functional block configuration of the wireless communication system 10. Specifically, the functional block configurations of the gNB 100 and the UE 200 will be described.

[0035] Fig. 2 is a functional block diagram of the gNB100. Fig. 3 is a functional block diagram of the UE200. Note that Figs. 2 and 3 only show main functional blocks relevant to the description of the embodiments, and that the gNB100 and UE200 have other functional blocks (e.g., a power supply unit, etc.). Figs. 2 and 3 show functional block configurations of the gNB100 and UE200, and for the hardware configuration, please refer to Fig. 9.

[0036] (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.

[0037] The wireless communication unit 110 transmits downlink signals (DL signals) conforming to NR, and also receives uplink signals (UL signals) conforming to NR.

[0038] As described above, a cell group may include an MCG and an SCG. The gNB 100 may belong to either an MCG or an SCG. That is, the gNB 100 may constitute either an MN or an SN.

[0039] In addition, in relation to the handover of the UE 200, the gNB 100 may constitute a source radio base station of the handover source, or may constitute a 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 an SN, respectively.

[0040] 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 MN or SN. Also, when there are multiple candidate cells for handover in CHO, they may be expressed as T-MN1, T-MN2, T-SN1, T-SN2, etc.

[0041] The RRC / Xn processing unit 120 executes various processes related to the radio resource control layer (RRC) and the Xn interface. Specifically, the RRC / Xn processing unit 120 can transmit 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.

[0042] Furthermore, the RRC / Xn processing unit 120 may transmit and receive various messages via the Xn interface with other gNBs 100. The messages may include a message related to handover (which may include CHO) of the UE 200 and a message related to setting of a cell group.

[0043] In the case of a radio base station that supports LTE (Evolved Universal Terrestrial Radio Access Network (E-UTRAN)), an X2 interface may be used instead of an Xn interface, or both the Xn and X2 interfaces may be used.

[0044] 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 configure a receiving unit. More specifically, when the gNB 100 configures a T-MN, the RRC / Xn processing unit 120 may receive a handover cancel message (HO cancel).

[0045] The HO cancel may be sent by the S-MN and used to cancel the CHO of the UE 200.

[0046] Furthermore, the RRC / Xn processing unit 120 may transmit a target radio base station release request message to the target radio base station in the cell group. In this embodiment, the RRC / Xn processing unit 120 may constitute a transmission unit that transmits the release request message.

[0047] Specifically, when the gNB 100 configures a T-MN, the RRC / Xn processing unit 120 may transmit an S-node Release request to a target cell (gNB) included in the SCG. More specifically, the RRC / Xn processing unit 120 may transmit 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 CHO has been canceled or that CHO to another candidate cell has been completed.

[0048] Furthermore, the RRC / Xn processing unit 120 may transmit a release-needed message for the target radio base station in the cell group. In this embodiment, the RRC / Xn processing unit 120 may constitute a transmission unit that transmits the release-needed message.

[0049] Specifically, when the gNB 100 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.

[0050] The RRC / Xn processing unit 120 may transmit 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 adding or changing 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, the timer may be interpreted as being started at the timing of adding an SN that can be applied to CHO, etc., and measuring a predetermined time. Hereinafter, for convenience, the timer may be expressed as T_Dcoverall_CHO, TXn_Dcoverall_CHO, etc.

[0051] The handover processing unit 130 executes processing related to handover of the UE 200. Specifically, the handover processing unit 130 can execute processing related to normal handover of the UE 200 (which may also be referred to as legacy handover) and conditional handover (CHO).

[0052] In particular, with regard to CHO, the transition destination cell may configure the MCG and the SCG, and such a CHO may be referred to as a CHO with SCG configuration.

[0053] The control unit 140 controls each functional block that configures the gNB 100. In particular, in this embodiment, the control unit 140 can execute control related to RRC inter-node messages related to CHO and timers for CHO.

[0054] Specifically, the control unit 140 may perform control regarding HO-related messages transmitted and received between the source radio base station and the target radio base station, and messages regarding SN (SgNB) addition, modification, and release.

[0055] Furthermore, the control unit 140 may control a 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, for example.

[0056] (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.

[0057] The wireless communication unit 210 transmits an uplink signal (UL signal) conforming to NR. The wireless communication unit 210 also receives an uplink signal (DL signal) conforming to NR.

[0058] The wireless communication unit 210 supports dual connectivity (DC) and can simultaneously connect to and transmit and receive wireless signals (which may also be interpreted as component carriers, etc.) with multiple gNBs 100. In other words, the wireless communication unit 210 can simultaneously communicate with gNBs 100 belonging to an MCG or an SCG.

[0059] The RRC processing unit 220 executes various processes in the radio resource control layer (RRC). Specifically, the RRC processing unit 220 can transmit and receive messages of the radio resource control layer. In this embodiment, the RRC processing unit 220 may constitute a receiving unit that receives messages of the radio resource control layer.

[0060] 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 transmit RRC Reconfiguration Complete, which is a response to the RRC Reconfiguration, to the network.

[0061] Furthermore, when CHO with a specific target radio base station fails and another candidate cell is selected in the reconnection procedure, the RRC processing unit 220 may transmit the configuration request only to the primary cell (PCell). In this embodiment, the RRC processing unit 220 may configure a transmission unit that transmits the configuration request.

[0062] Specifically, when CHO fails and another candidate cell (which may include a PCell and a 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 the RRC Reconfiguration Complete may be interpreted as a message indicating that application of the RRC reconfiguration has been completed.

[0063] Alternatively, the RRC processing unit 220 may transmit the configuration request to the PCell and SCell (which may include the PSCell).

[0064] Furthermore, if CHO fails, the RRC processing unit 220 may transmit a report including information indicating failure to one or both of a primary cell (PCell) and a secondary cell (SCell (which may include a PSCell)) among multiple candidate cells. In this embodiment, the RRC processing unit 220 may be configured as a transmission unit that transmits a report including CHO failure information.

[0065] Specifically, when the CHO with SCG configuration fails, the RRC processing unit 220 may transmit a Radio Link Failure (RLF) report including information indicating the failure to the network.

[0066] The RLF report may include information when the first CHO fails and information when the second or subsequent CHO fails. Furthermore, as described above, the RLF report may include information indicating with which cell the CHO has failed. The CHO failure may be determined based on whether the random access (RA) procedure is successful or not, in short, whether the transmission of the Random Access Channel (RACH) is successful or not. The RACH failure may be simply called a connection failure or the like, or may be expressed as a failedTargetPCell or a failedTargetPSCell or the like.

[0067] 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 a timer T311 is running, which starts when the RRC connection re-establishment procedure starts and stops when an appropriate NR cell or a cell using another radio access technology (RAT) is selected.

[0068] Furthermore, the information of the CHO regarding the SCell may be included in, for example, the SCG Failure Information, instead of the RLF report.

[0069] The handover execution unit 230 executes handover of the UE 200. Specifically, the handover execution unit 230 can execute processes related to normal handover (legacy handover) and conditional handover (CHO).

[0070] In the case of CHO, the handover execution unit 230 may transition to the candidate cell when an execution condition is satisfied. As described above, the execution condition may be determined based on the quality of the reference signal (RS), specifically, the value of RSRP, RSRQ, or SINR.

[0071] In addition, the destination of the CHO may not necessarily be accompanied by an SCG, or may be accompanied by an SCG (CHO with SCG configuration). In other words, the destination cell of the CHO may be a single cell, or may be composed of multiple cells (which may be read as a cell group) according to the DC.

[0072] 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.

[0073] Regarding the CHO with SCG configuration, if the CHO fails, the control unit 240 can execute control regarding the selection of another candidate cell.

[0074] For example, when the first CHO fails and another candidate cell is selected, the control unit 240 may perform control such that an RRC configuration request (for example, RRC Reconfiguration) is transmitted only to the PCell among the other candidate cells.

[0075] Alternatively, when the first CHO fails and another candidate cell is selected, the control unit 240 may perform control to transmit the configuration request (to both the PCell and SCell (which may include the PSCell) of the other candidate cell.

[0076] Furthermore, for a CHO with SCG configuration, the control unit 240 may perform control so that, if the CHO fails, a report (RLF report) including information about the cell group is transmitted.

[0077] For example, when the CHO with SCG configuration fails, the control unit 240 may perform control so as to generate an RLF report including information indicating that the CHO with SCG configuration has failed for either or both of the PCell and the SCell among multiple candidate cells.

[0078] The RLF report may further include at least one of identification information about the failed cell, quality information, time information, activation status, etc. The activation status may include an indication that the SCG is deactivated.

[0079] (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).

[0080] (3.1) Example 1 In the CHO with SCG configuration, in determining whether an execution condition is satisfied (which may also be called 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.

[0081] Furthermore, the Target PCell (which may be expressed as T-MN) can transmit 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 canceling handover.

[0082] Fig. 4 shows a sequence example (part 1) of CHO with SCG configuration according to operation example 1. As shown in Fig. 4, the S-MN, S-SN, T-MN1, T-MN2, and T-SN can perform operations related to the addition of an SCG (SgNB) in response to a handover request (HO request).

[0083] This sequence is specified in 3GPP TS38.300 Chapter 9.2.3.2 (related to CHO) and 3GPP TS38.423 Chapter 8.3.1, etc. Although only one T-SN is shown in Figure 4, there may be two or more T-SNs (same below).

[0084] 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 transmits an S-node Release request to the T-SN that transmitted the SgNB addition request, the Target PCell (T-MN2) may include a cause value called CHO / HO cancel in the S-node Release request.

[0085] 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.

[0086] Fig. 5 shows a sequence example (part 2) of CHO with SCG configuration according to operation example 1. As shown in Fig. 5, T-SN may provide new timers for CHO, T_Dcoverall_CHO and TXn_Dcoverall_CHO (tentative names may be used), in addition to the existing T_DCoverall and TXn_DCoverall.

[0087] 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 an S-node Release required.

[0088] Furthermore, the T-SN may include a cause value (timer T_Dcoverall_CHO / TXn_Dcoverall_CHO expiry) indicating that TXn_Dcoverall_CHO has expired in the S-node Release required. Note that TXn_Dcoverall_CHO may be used in the case of NR (Xn interface), and T_Dcoverall_CHO may be used in the case of LTE (X2 interface).

[0089] Alternatively, if radio resources related to the T-SN become insufficient before TXn_Dcoverall_CHO expires, the T-SN may trigger an S-NG-RAN node initiated S-NG-RAN node Release procedure and transmit an S-node Release required. The radio resources related to the T-SN may be radio resources within the SN (radio base station) or may be radio resources used by and indirectly affected by other nodes connected to the SN.

[0090] Furthermore, the T-SN may include a cause value (no radio resource available for CHO) indicating a lack of radio resources in the S-node Release required.

[0091] As mentioned above, 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, and therefore may be executed before the expiration of TXn_Dcoverall_CHO.

[0092] (3.2) Example 2 In the CHO with SCG configuration, it is assumed that after synchronization with a candidate cell of the CHO fails, timer T311 is started and the UE 200 performs 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.

[0093] In this operation example, when the UE 200 selects another CHO candidate cell, the UE 200 may select the selected cell and transmit an RRC configuration request (for example, RRC Reconfiguration). The RRC configuration request may be an RRC Reconfiguration Complete or another RRC message.

[0094] Also, as described above, T311 may start at the start of the RRC connection re-establishment procedure and stop when an appropriate NR cell or a cell using another radio access technology (RAT) is selected.

[0095] Fig. 6 shows a sequence example (part 1) of CHO with SCG configuration according to operation example 2. As shown in Fig. 6, when synchronization with a candidate cell fails (RACH transmission fails) and another CHO candidate cell is selected, UE 200 may apply (or transmit) RRC Reconfiguration to both the Target PCell and the Target SCell (PSCell) (option 1).

[0096] Alternatively, if UE200 fails to synchronize with a candidate cell (RACH transmission fails) and selects another CHO candidate cell, UE200 may apply (or transmit) RRC Reconfiguration to only one of the candidate cells (option 2).

[0097] Furthermore, after receiving the configuration request (for example, RRC Reconfiguration Complete), the Target PCell (T-MN2) may transmit SN Reconfiguration Complete to the T-SN. Furthermore, the T-MN2 may transmit SN Reconfiguration Complete to another T-SN (for example, T-SN2).

[0098] Fig. 7 illustrates a sequence example (part 2) of CHO with SCG configuration according to operation example 2. As illustrated in Fig. 7, UE 200 may apply RRC Reconfiguration only to Target PCell. This is because PSCell may have already been released compared to PCell.

[0099] (3.3) 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.

[0100] For example, if UE200 fails to synchronize with both the target PCell and the target SCell (PSCell) in the first CHO (CHO First failure, Failure 1 in FIG. 8), UE200 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.

[0101] On the other hand, if UE200 succeeds in synchronizing with the target PCell but fails in synchronizing with the target SCell (PSCell) in the initial CHO, UE200 may include the target PCell ID with which synchronization was successful, the target SCell ID with which synchronization was unsuccessful, 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.

[0102] Furthermore, after the CHO First failure, when UE200 performs cell reselection during the startup (operation) of T311 and applies a configuration request (RRC Reconfiguration) to the selected candidate PSCell (i.e., the second CHO), UE200 may operate in accordance with one of the following manners.

[0103] Even if synchronization with both the target PCell and the target SCell (PSCell) fails in the second CHO (CHO second failure, Failure 2 in FIG. 8 ), the 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 be further included.

[0104] On the other hand, if synchronization with the target PCell is successful but synchronization with the target SCell (PSCell) is unsuccessful in the second CHO, the UE 200 may include the target PCell ID with which synchronization is successful, the target SCell ID with which synchronization is unsuccessful, 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, similar to the CHO first failure. Note that in this case, information related to the first failure may also be included.

[0105] Furthermore, when the SCG related to the CHO is in an inactive state (deactivated state), a display indicating that the SCG is in a deactivated state may be included.

[0106] (4) Actions and Effects According to the above-described embodiment, the following advantageous 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.

[0107] In addition, the gNB100 (T-SN) can send an S-node Release required to the T-MN depending on the expiration of a timer (e.g., TXn_Dcoverall_CHO) or the state of radio resources in the local station.

[0108] If CHO fails and UE 200 selects another candidate cell (which may include a PCell and a PSCell), UE 200 can transmit an RRC configuration request to only the PCell or to the PCell and the PSCell.

[0109] As a result, gNB100 and UE200 can perform appropriate operations when handover using CHO with SCG configuration fails.

[0110] More specifically, in the CHO with SCG configuration, the procedure 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 are clarified, making it possible to more reliably realize the CHO with SCG configuration.

[0111] 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 the settings (parameters) for CHO with SCG configuration.

[0112] (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.

[0113] For example, in the above-described embodiment, the conditional handover (CHO) has been described as an example, but the same operation may be applied to other similar operations, for example, a conditional SCG change, etc. In this case, the cell may be read as a cell group, etc.

[0114] In addition, the terms primary cell and secondary cell may be replaced with other synonymous terms, such as state cell, secondary cell, first cell, second cell, master, sub, etc.

[0115] Also, in the above description, "configure," "activate," "update," "indicate," "enable," "specify," and "select" may be interchangeable. Similarly, "link," "associate," "correspond," and "map" may be interchangeable, and "allocate," "assign," "monitor," and "map" may also be interchangeable.

[0116] Furthermore, specific, dedicated, UE-specific, and UE-dedicated may be interchangeable. Similarly, common, shared, group-common, UE-common, and UE-shared may be interchangeable.

[0117] Furthermore, the block diagrams (FIGS. 2 and 3) used in the description of the above-described embodiments show functional blocks. These functional blocks (components) are realized by any combination of at least one of hardware and software. Furthermore, the method of realizing each functional block is not particularly limited. 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 (for example, by wire, wirelessly, etc.) and these multiple devices. The functional block may also be realized by combining the single device or multiple devices with software.

[0118] Functions include, but are not limited to, judgment, determination, judgment, calculation, computation, processing, derivation, investigation, search, confirmation, reception, transmission, output, access, resolution, selection, election, establishment, comparison, assumption, expectation, consideration, broadcasting, notifying, communicating, forwarding, configuring, reconfiguring, allocating, mapping, and assignment. For example, a functional block (component) that performs transmission is called a transmitting unit or transmitter. As mentioned above, there are no particular limitations on how each is implemented.

[0119] Furthermore, the above-described 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, a memory 1002, a storage 1003, a communication device 1004, an input device 1005, an output device 1006, a bus 1007, etc.

[0120] In the following description, the term "apparatus" can be interpreted as a circuit, a device, a unit, etc. The hardware configuration of the apparatus may be configured to include one or more of the apparatuses shown in the drawings, or may be configured to exclude some of the apparatuses.

[0121] Each functional block of the device (see Figure 2.3) is realized by any hardware element of the computer device or a combination of the hardware elements.

[0122] 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.

[0123] The processor 1001 controls the entire computer by running, for example, an operating system, and may be configured as a central processing unit (CPU) including an interface with peripheral devices, a control unit, an arithmetic unit, a register, and the like.

[0124] The processor 1001 also reads programs (program codes), 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 programs used are those that cause 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 one 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 programs may be transmitted from a network via a telecommunications line.

[0125] The memory 1002 is a computer-readable recording medium and may be configured by, for example, at least one of a read-only memory (ROM), an erasable programmable ROM (EPROM), an electrically erasable programmable ROM (EEPROM), a random access memory (RAM), etc. The memory 1002 may also be called a register, a cache, a main memory (primary storage device), etc. The memory 1002 can store a program (program code), a software module, etc., that can execute a method according to an embodiment of the present disclosure.

[0126] Storage 1003 is a computer-readable recording medium, and may be, 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 disc), 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 appropriate medium including at least one of memory 1002 and storage 1003.

[0127] The communication device 1004 is hardware (transmission / reception device) for communicating between computers via at least one of a wired network and a wireless network, and is also called, for example, a network device, a network controller, a network card, or a communication module.

[0128] The communication device 1004 may be configured to include a high-frequency switch, a duplexer, a filter, a frequency synthesizer, etc. to realize, for example, at least one of Frequency Division Duplex (FDD) and Time Division Duplex (TDD).

[0129] The input device 1005 is an input device (for example, a keyboard, a mouse, a microphone, a switch, a button, a sensor, etc.) that receives input from the outside. The output device 1006 is an output device (for example, a display, a speaker, an LED lamp, etc.) that outputs to the outside. The input device 1005 and the output device 1006 may be integrated into one device (for example, a touch panel).

[0130] Furthermore, each device such as the processor 1001 and the memory 1002 is connected to 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.

[0131] 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 the hardware. For example, the processor 1001 may be implemented using at least one of these pieces of hardware.

[0132] 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, the 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, or the like.

[0133] Each aspect / embodiment described in the present disclosure may be applied to at least one of a system using Long Term Evolution (LTE), LTE-Advanced (LTE-A), SUPER 3G, IMT-Advanced, a 4th generation mobile communication system (4G), a 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 system, and a next-generation system extended based on these. Furthermore, a combination of multiple systems (e.g., a combination of at least one of LTE and LTE-A and 5G) may also be applied.

[0134] The order of the procedures, sequences, flowcharts, etc. of each aspect / embodiment described in this disclosure may be changed unless it is consistent. 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.

[0135] In the present disclosure, a specific operation described as being performed by a base station may also be performed by its upper node in some cases. 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 (for example, an MME or an S-GW, etc., but are not limited to these). Although 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 (for example, an MME and an S-GW) may also be used.

[0136] Information, signals (information, etc.) may be output from a higher layer (or a lower layer) to a lower layer (or a higher layer), or may be input / output via multiple network nodes.

[0137] The input and output information may be stored in a specific location (for example, memory) or may be managed using a management table. The input and output information may be overwritten, updated, or added to. The output information may be deleted. The input information may be sent to another device.

[0138] The determination may be made based on a value represented by one bit (0 or 1), a Boolean value (true or false), or a numerical comparison (e.g., comparison with a predetermined value).

[0139] Each aspect / embodiment described in this disclosure may be used alone, in combination, or switched depending on the implementation. Furthermore, notification of predetermined information (e.g., notification that "X is true") is not limited to being done explicitly, but may be done implicitly (e.g., by not notifying the predetermined information).

[0140] 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.

[0141] Software, instructions, information, etc. may also be transmitted or received over 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), then these wired and / or wireless technologies are included within the definition of transmission media.

[0142] 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.

[0143] 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.

[0144] As used in this disclosure, the terms "system" and "network" are used interchangeably.

[0145] Furthermore, the information, parameters, etc. described in the present disclosure may be expressed using absolute values, may be expressed using relative values ​​from a predetermined value, or may be expressed using other corresponding information. For example, a radio resource may be indicated by an index.

[0146] The names used for the above-described parameters are not intended to be limiting in any way. Furthermore, the mathematical expressions 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.

[0147] 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.

[0148] A base station can accommodate one or more (e.g., three) cells (also called sectors). When a base station accommodates multiple cells, the overall coverage area of ​​the base station 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)).

[0149] The terms "cell" or "sector" refer to part or all of the coverage area of ​​a base station and / or base station subsystem that provides communication services within that coverage area.

[0150] In this disclosure, the terms "Mobile Station (MS)," "user terminal," "User Equipment (UE)," "terminal," etc. may be used interchangeably.

[0151] 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.

[0152] At least one of the base station and the mobile station may be called 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 object, or the mobile object itself. The mobile object may be a vehicle (e.g., a car, an airplane, etc.), an unmanned mobile object (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 include devices that do 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.

[0153] Furthermore, a base station in the present disclosure may be read as a mobile station (user terminal, the same applies hereinafter). For example, the aspects / embodiments 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) or Vehicle-to-Everything (V2X)). In this case, the mobile station may be configured to have the functions of 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.

[0154] 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.

[0155] Numerology may be a communication parameter applied to at least one of transmission and reception of a signal or channel, such as 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 a transceiver in the frequency domain, and specific windowing operations performed by a transceiver in the time domain.

[0156] A slot may consist of one or more symbols in the time domain (such as an Orthogonal Frequency Division Multiplexing (OFDM) symbol, a Single Carrier Frequency Division Multiple Access (SC-FDMA) symbol, etc.) A slot may be a numerology-based time unit.

[0157] 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.

[0158] The radio frame, subframe, slot, minislot, and symbol all represent time units for transmitting signals, and may be referred to by other names corresponding to the radio frame, subframe, slot, minislot, and symbol.

[0159] For example, one subframe may be called a transmission time interval (TTI), multiple consecutive subframes may be called a TTI, or one slot or one minislot may be called a TTI. That is, 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 called a slot, minislot, etc., instead of a subframe.

[0160] Here, TTI refers to, for example, the smallest time unit for scheduling in wireless communication. For example, in an LTE system, a base station performs scheduling to allocate radio resources (such as frequency bandwidth and transmission power that can be used by each user terminal) to each user terminal in TTI units. However, the definition of TTI is not limited to this.

[0161] The TTI may be a transmission time unit for a channel-encoded data packet (transport block), a code block, a 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 a transport block, a code block, a code word, etc. is actually mapped may be shorter than the TTI.

[0162] When one slot or one minislot is called a TTI, one or more TTIs (i.e., one or more slots or one or more minislots) may be the minimum time unit for scheduling. Also, the number of slots (minislots) constituting the minimum time unit for scheduling may be controlled.

[0163] A TTI having a time length of 1 ms may be called 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 called a shortened TTI, short TTI, partial or fractional TTI, shortened subframe, short subframe, minislot, subslot, slot, etc.

[0164] In addition, 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.

[0165] 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.

[0166] 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. Each TTI, subframe, etc. may be composed of one or more resource blocks.

[0167] Note that one or more RBs may also be called a physical resource block (PRB), a sub-carrier group (SCG), a resource element group (REG), a PRB pair, an RB pair, or the like.

[0168] Furthermore, a resource block may be composed of one or more resource elements (REs). For example, one RE may be a radio resource region of one subcarrier and one symbol.

[0169] A Bandwidth Part (BWP) (which may also be referred to as a fractional 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 of the carrier. PRBs may be defined in a given BWP and numbered within that BWP.

[0170] The BWP 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.

[0171] 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 the active BWP. Note that the terms "cell," "carrier," etc. in this disclosure may be read as "BWP."

[0172] The above-described structures of the radio frame, subframe, slot, minislot, and symbol 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, the number of symbols in a TTI, the symbol length, the cyclic prefix (CP) length, and other configurations can be changed in various ways.

[0173] 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.

[0174] The reference signal may also be abbreviated as Reference Signal (RS), and may also be called a pilot depending on the applicable standard.

[0175] 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."

[0176] The "means" in the configuration of each of the above devices may be replaced with "part," "circuit," "device," etc.

[0177] 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.

[0178] When used in this disclosure, the terms "include," "including," and variations thereof are intended to be inclusive, similar to the term "comprising." Furthermore, when used in this disclosure, the term "or" is not intended to be an exclusive or.

[0179] In this disclosure, where articles are added by translation, such as a, an, and the in English, the disclosure may include that the nouns following these articles are in the plural form.

[0180] 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 in a table, database, or other data structure), ascertaining, and the like. "Determining" and "determining" may also include receiving (e.g., receiving information), transmitting (e.g., sending information), input, output, accessing (e.g., accessing data in memory), and the like. 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.

[0181] In the present 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 "coupled" may also be interpreted in the same way as "different."

[0182] Although the present disclosure has been described in detail above, it is 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. [Explanation of symbols]

[0183] 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

1. a control unit for controlling execution of a conditional handover; a transmitter configured to transmit a report to a network when the conditional handover fails, the report including information indicating an identifier of a primary cell where the handover failed and an identifier of a primary secondary cell; A terminal comprising:

2. The terminal of claim 1 , wherein the report is an RLF report.

3. controlling execution of a conditional handover; If the conditional handover fails, sending a report to the network, the report including information indicating an identifier of the primary cell where the handover failed and an identifier of the primary secondary cell. A communication method for a terminal including:

4. A communication system including a terminal and a base station, The terminal a control unit for controlling execution of a conditional handover; a transmitter configured to transmit, to the base station, a report including information indicating an identifier of a primary cell where the handover has failed and an identifier of a primary secondary cell where the handover has failed, if the conditional handover has failed. Communication system.

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