Wireless Base Station

Abstract

The gNB (100A) includes: a receiving unit (120) which receives setting information of cells under each target gNB from multiple target gNBs (100B, 100C); a control unit (140) which includes a list of setting information of multiple cells in a specific message; and a sending unit (110) which sends a specific message to the terminal (200).

Description

Technical Field

[0001] The present invention relates to a wireless base station. Background Art

[0002] In the 3rd Generation Partnership Project (3GPP), Long Term Evolution (LTE) was standardized, and LTE-Advanced (hereinafter referred to as LTE including LTE-Advanced) was standardized for the purpose of further speeding up LTE. In addition, in 3GPP, the specifications of the successor systems of LTE, such as 5G or New Radio (NR), are further studied.

[0003] In the conventional handover (HO) process, the network determines a target radio base station (also called a target cell) based on quality information such as a measurement report sent from a terminal, and after preparing for the handover, a handover command (handover command) is sent to the terminal.

[0004] However, when the terminal passes an appropriate switching point during the preparation process for switching on the network side, there is a problem that the wireless link may be momentarily interrupted because the terminal does not receive a switching command from the source wireless base station (also called the source cell) and transfers to the target wireless base station.

[0005] Therefore, in order to solve this problem, a process called Conditional HO (conditional handover) has been studied (Non-Patent Document 1).

[0006] In Conditional HO, the source radio base station notifies the terminal in advance of setting information of the target candidate cell including the target candidate cell and the conditions for transition to the target candidate cell.

[0007] Specifically, in response to a request from the source radio base station, the target radio base station transmits to the source radio base station the target candidate cell setting information including the identification information of the subordinate cell and the relocation condition for the subordinate cell.

[0008] The source radio base station notifies the terminal of the received setting information of the target candidate cell.

[0009] When the migration condition to the target candidate cell is met, the terminal does not wait for the handover command, but performs a random access process with the target wireless base station managing the target candidate cell and migrates to the target wireless base station. Thus, instantaneous interruption of the wireless link can be avoided.

[0010] Prior art literature

[0011] Non-patent literature

[0012] Non-patent document 1: “New WID: NR mobility enhancements”, RP-190489, 3GPP TSG RAN Meeting #83, 3GPP, March 2019 Summary of the invention

[0013] However, in Conditional HO, when the source radio base station receives setting information of target candidate cells from a plurality of target radio base stations, there is the following problem.

[0014] Specifically, when the source radio base station notifies the terminal of the setting information of each target candidate cell using a dedicated message, a large number of radio resources are allocated to the transmission of the message, and the network throughput may decrease.

[0015] Therefore, the present invention has been made in view of such a situation, and an object thereof is to provide a radio base station capable of avoiding a decrease in network throughput even when a terminal migrates to a target radio base station based on setting information of a target candidate cell.

[0016] A wireless base station (100A) of one embodiment of the present invention comprises: a receiving unit (120), which receives setting information of cells under each target wireless base station (100B, 100C) from each target wireless base station; a control unit (140), which includes a list of setting information of multiple cells in a specific message; and a sending unit (110), which sends the specific message to a terminal (200). BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a diagram schematically showing the overall structure of the wireless communication system 10 .

[0018] Figure 2 This is the functional block structure diagram of gNB100A, 100B, and 100C.

[0019] Figure 3 It is a functional block diagram of the terminal 200.

[0020] Figure 4 is a diagram showing the timing of the Conditional HO procedure.

[0021] Figure 5 It is a diagram showing a recovery sequence from a radio link failure (RLF) in a conventional handover (HO) procedure.

[0022] Figure 6This is a diagram showing a recovery sequence from a radio link failure (RLF) in the Conditional HO procedure (action example 1).

[0023] Figure 7 This is a diagram showing a recovery sequence from a radio link failure (RLF) in the Conditional HO procedure (action example 2).

[0024] Figure 8 This is a diagram showing a recovery sequence from a radio link failure (RLF) in the Conditional HO procedure (action example 3).

[0025] Fig. 9 This is a diagram for explaining the information element (IE) in VarRLF-Report.

[0026] Fig.10 This is a diagram for explaining the information element (IE) within RRC Reconfiguration Complete.

[0027] Fig.11A It is a diagram used to illustrate the information elements (IE) within RRC Setup Complete.

[0028] Fig. 11B It is a diagram used to illustrate the information elements (IE) within RRC Setup Complete.

[0029] Fig.12 It is a diagram for explaining the information element (IE) within RRC Reestablishment Complete.

[0030] Fig.13 It is a diagram for explaining the information element (IE) within RRC Resume Complete.

[0031] Fig.14 It is a diagram used to illustrate the information element (IE) in the UE Information Request (UE Information Request).

[0032] Fig.15A This is a diagram for explaining the information elements (IE) in the UE Information Response.

[0033] Fig. 15B This is a diagram for explaining the information elements (IE) in the UE Information Response.

[0034] Fig. 15C This is a diagram for explaining the information elements (IE) in the UE Information Response.

[0035] Fig.16 It is a diagram showing the RRC Reconfiguration Complete transmission timing in the Conditional HO process.

[0036] Fig.17 This is a diagram showing the HO suspension sequence (operation example 1) in the Conditional HO procedure.

[0037] Fig.18 This is a diagram showing the HO suspension sequence (operation example 2) in the Conditional HO procedure.

[0038] Fig.19 This is a diagram showing a HO change sequence (action example 1) in the Conditional HO procedure.

[0039] Fig. 20 This is a diagram showing the HO change sequence (action example 2) in the Conditional HO procedure.

[0040] Fig.21 This is a diagram showing the HO change sequence (action example 3) in the Conditional HO procedure.

[0041] Fig. 22 It is a diagram showing the action flow of gNB100A that encapsulates the setting information of the target candidate cell.

[0042] Fig.23 This is a diagram for explaining the structure of RRC Reconfiguration in the Conditional HO procedure (structure example 1).

[0043] Fig.24 This is a diagram for explaining the structure of RRC Reconfiguration in the Conditional HO procedure (structure example 2).

[0044] Fig.25 This is a diagram showing a transaction ID assignment sequence (operation example 1) in the Conditional HO process.

[0045] Fig.26 This is a diagram showing a transaction ID assignment sequence (action example 2) in the Conditional HO process.

[0046] Fig. 27 It is a diagram showing a recovery sequence from a handover failure (HOF) in the Conditional HO procedure.

[0047] Fig.28 The diagram shows an operation flow of the terminal 200 for recovering a radio bearer after a radio link failure (RLF) in the Conditional HO procedure.

[0048] Fig.29 The diagram is used to explain the conditions for recovering a radio bearer after a radio link failure (RLF) in the Conditional HO procedure.

[0049] Fig.30 This is a diagram showing an example of the hardware structure of gNB100A, 100B, 100C and terminal 200. DETAILED DESCRIPTION

[0050] Hereinafter, the embodiments will be described based on the drawings. In addition, the same or similar reference numerals are given to the same functions and structures, and the description thereof will be appropriately omitted.

[0051] (1) Overall schematic structure of wireless communication system

[0052] Figure 1 1 is a diagram schematically showing the overall structure of a wireless communication system 10 according to the present embodiment. The wireless communication system 10 is a wireless communication system based on the New Radio (NR) standard and includes a Next Generation-Radio Access Network (NG-RAN, not shown) and a terminal 200 .

[0053] NG-RAN includes radio base stations 100A, 100B, and 100C (hereinafter referred to as gNB100A, 100B, and 100C). In addition, the specific structure of the wireless communication system 10 including the number of gNBs and UEs is not limited to Figure 1 Example shown.

[0054] NG-RAN actually includes multiple NG-RAN nodes, specifically, gNB (or ng-eNB), which is connected to the core network (5GC, not shown) based on NR. In addition, NG-RAN and 5GC can also be simply expressed as "network".

[0055] gNB100A, 100B, and 100C are wireless base stations based on NR, respectively, and perform wireless communications based on NR with terminal 200. Each of gNB100A, 100B, and 100C and terminal 200 can support Massive MIMO (Massive MIMO) that generates beams with higher directivity by controlling wireless signals sent from multiple antenna elements, carrier aggregation (CA) that bundles and uses multiple component carriers (CCs), and dual connectivity (DC) that simultaneously communicates between multiple NG-RAN nodes and terminals. In addition, CC can also be called a carrier.

[0056] gNB100A, 100B, and 100C each form one or more cells and manage the cells. Terminal 200 can migrate between cells formed by gNB100A, 100B, and 100C. In addition, "migrating between cells formed by gNB100A, 100B, and 100C" can be expressed as "migrating between gNB100A, 100B, and 100C" or "migrating between wireless base stations 100A, 100B, and 100C". In addition, "cells under gNB100A, 100B, and 100C" refers to "cells formed by gNB100A, 100B, and 100C".

[0057] The so-called "migration" typically refers to switching between cells or switching between gNBs, but it may also include cell reselection, or the behavior of the terminal 200 such as changing the destination cell or destination gNB.

[0058] The "target cell" typically refers to the cell of the migration destination to which the terminal 200 is to migrate, but may also include a cell to which the terminal 200 can migrate (a potential target cell). In addition, the "target gNB" typically refers to the gNB of the migration destination to which the terminal 200 is to migrate, but may also include a gNB to which the terminal 200 can migrate (a potential target gNB). In this embodiment, gNB100B and 100C are target gNBs. In addition, a cell to which the terminal can migrate may also be referred to as a candidate cell. In addition, a gNB to which the terminal can migrate may also be referred to as a candidate gNB.

[0059] On the other hand, the "source cell" refers to the cell of the migration party. The "source gNB" refers to the gNB of the migration party. In this embodiment, gNB100A is the source gNB.

[0060] In the wireless communication system 10, the terminal 200 performs a conditional handover (hereinafter referred to as Conditional HO) procedure. In addition, the Conditional HO procedure may be simply referred to as a CHO procedure.

[0061] As described below, in the Conditional HO process, the source gNB 100A notifies the terminal 200 in advance of the candidate cell of the migration destination to which the terminal 200 is to migrate (hereinafter referred to as the target candidate cell). When the migration condition to the target candidate cell is met, the terminal 200 performs a random access (RA) process with the target gNB 100B (or target gNB 100C) that manages the target candidate cell without receiving a switching command from the source gNB, and migrates to the target gNB 100B (or target gNB 100C).

[0062] In addition, the wireless communication system 10 may include an Evolved Universal Terrestrial Radio Access Network (E-UTRAN) instead of NG-RAN. In this case, the E-UTRAN includes a plurality of E-UTRAN nodes, specifically, eNBs (or en-gNBs), connected to a core network (EPC) based on LTE.

[0063] (2) Functional block structure of wireless communication system

[0064] Next, the functional block structure of the wireless communication system 10 is described. Specifically, the functional block structure of gNB100A, 100B, 100C and terminal 200 is described. In the following, only the parts related to the features in this embodiment are described. Therefore, gNB100A, 100B, 100C and terminal 200 naturally also have other functional blocks that are not directly related to the features in this embodiment.

[0065] Figure 2 This is a functional block diagram of gNB100A, 100B, and 100C. In addition, since gNB100A, 100B, and 100C have the same structure, the description of gNB100B and 100C is omitted. Figure 2 As shown, gNB100A has a sending unit 110, a receiving unit 120, a retaining unit 130 and a control unit 140.

[0066] The transmitting unit 110 transmits a downlink signal (DL signal) based on NR. The receiving unit 120 receives an uplink (UL signal) based on NR. Specifically, the transmitting unit 110 and the receiving unit 120 perform wireless communication with the terminal 200 via a control channel or a data channel.

[0067] The transmitting unit 110 transmits a signal based on NR to other gNBs, and the receiving unit 120 receives a signal based on NR from other gNBs.

[0068] The transmission unit 110 transmits an RRC message such as RRC Reconfiguration, which will be described later, to the terminal 200 .

[0069] When gNB100A is the source gNB, the transmitting unit 110 transmits the CHO request (CHOrequest) described later to the target gNB. When gNB100A is the target gNB, the transmitting unit 110 transmits the CHO request ACK, HO cancellation, and HO modification (HO modification) described later to the source gNB. CHO requestACK includes the setting information of the target candidate cells under the target gNB.

[0070] The receiving unit 120 receives RRC messages such as RRC Reconfiguration Complete (RRC ReconfigurationComplete), RRC Reconfiguration Complete 1 (RRC Reconfiguration Complete1), RRC Reconfiguration Complete 2 (RRC Reconfiguration Complete2), RRC Setup Complete (RRC Setup Complete), and RRC Reestablishment Complete (RRC Reestablishment Complete) from the terminal 200, which will be described later.

[0071] When gNB100A is the source gNB, the receiving unit 120 receives the CHO request ACK, HO cancellation and HO modification described below from the target gNB. When gNB100A is the target gNB, the receiving unit 120 receives the CHO request described below from the source gNB.

[0072] When gNB100A is the source gNB, the maintenance unit 130 maintains the setting information of the target candidate cells under the target gNB.

[0073] The control unit 140 controls the functional blocks that constitute gNB100A.

[0074] When gNB100A is the target gNB, the control unit 140 decides to delete the setting information of the target candidate cell based on the status of the target candidate cell under gNB100A.

[0075] When gNB100A is the target gNB, the control unit 140 causes the sending unit 110 to send HO cancellation indicating the deletion of the setting information of the target candidate cell under gNB100A to the source gNB.

[0076] In the case where gNB100A is the target gNB, when the terminal 200 does not migrate within the specified time according to the setting information of the target candidate cell under gNB100A, the control unit 140 enables the sending unit 110 to send HO cancellation to the source gNB.

[0077] When gNB100A is the target gNB, the control unit 140 determines the change of the setting information of the target candidate cell according to the status of the target candidate cell under gNB100A.

[0078] When gNB100A is the target gNB, the control unit 140 causes the sending unit 110 to send the HO modification indicating the change of the setting information of the target candidate cell under gNB100A to the source gNB.

[0079] When gNB100A is the source gNB, the control unit 140 includes a list of setting information of target candidate cells under multiple target gNBs in the RRC Reconfiguration.

[0080] Figure 3 2 is a functional block diagram of the terminal 200. Figure 3 As shown, the terminal 200 includes a transmitting unit 210 , a receiving unit 220 , a holding unit 230 , and a control unit 240 .

[0081] The transmitting unit 210 transmits an uplink (UL signal) based on NR. The receiving unit 220 receives a downlink signal (DL signal) based on NR. Specifically, the transmitting unit 210 and the receiving unit 220 perform wireless communication with gNB100A~100C via a control channel or a data channel.

[0082] The transmitting unit 210 transmits RRC messages such as RRC Reconfiguration Complete, RRC ReconfigurationComplete1, RRC Reconfiguration Complete2, RRC Setup Complete, and RRCReestablishment Complete, which will be described later.

[0083] The receiving unit 220 receives an RRC message such as RRC Reconfiguration described later.

[0084] The holding unit 230 holds the setting information of the target candidate cell under the target gNB. The setting information of the target candidate cell is included in the RRC Reconfiguration.

[0085] The control unit 240 controls each functional block constituting the terminal 200 .

[0086] The control unit 240 does not perform the re-establishment process (RRC Reestablishment process) accompanied by RLF, but performs the RA process between the terminal 200 and the target gNB and migrates to the target gNB.

[0087] The control unit 240 does not perform the RRC Reestablishment process when RLF occurs, but migrates to the target gNB based on the setting information of the target candidate cell under the target gNB.

[0088] The control unit 240 performs the RA process between the terminal 200 and the target gNB based on the setting information of the target candidate cell under the target gNB, without receiving a switching command, and migrates to the target gNB.

[0089] The control unit 240 migrates to the target gNB without performing the RRC Reestablishment process accompanied by the HOF.

[0090] The control unit 240 includes RLF detection information including RLF information notifying the occurrence of RLF, information of the cell where RLF is detected, location information of the terminal 200 where RLF is detected, etc. in the above-mentioned RRC messages such as RRC Reconfiguration Complete, RRC Reconfiguration Complete2, RRC Setup Complete, and RRC Reestablishment Complete.

[0091] When the receiving unit 220 receives RRC Reconfiguration including the setting information of the target candidate cell, the control unit 240 causes the transmitting unit 210 to transmit RRC Reconfiguration Complete 1 before starting the RA procedure. In addition, after transmitting RRC Reconfiguration Complete 1, the receiving unit 220 receives RRC Reconfiguration including the setting information of the changed target candidate cell.

[0092] When the receiving unit 220 receives the setting information of the target candidate cell under the target gNB using the RRC Reconfiguration to which the transaction ID is assigned by the source gNB, the control unit 240 includes the transaction ID in RRCReconfiguration Complete1. The control unit 240 causes the transmitting unit 210 to transmit the RRCReconfiguration Complete1 to the source gNB.

[0093] When the receiving unit 220 receives the setting information of the target candidate cell under the target gNB to which the transaction ID is assigned by the target gNB, the control unit 240 includes the transaction ID in RRC Reconfiguration Complete 2. After the success of the RA process, the control unit 240 causes the sending unit 210 to send the RRC ReconfigurationComplet2 to the target gNB.

[0094] The control unit 240 maintains all or part of the setting information of the target candidate cell under the target gNB shared between the terminal 200 and the target gNB during HOF, and includes it in RRC Reconfiguration Complete2. The maintained setting information includes security information, identification information of the terminal 200, etc. The control unit 240 causes the sending unit 210 to send the RRC Reconfiguration Complete2 to the target gNB after the success of the RA process.

[0095] When performing the migration process to the target gNB, the control unit 240 restores the radio bearer that was stopped between the terminal 200 and the target gNB.

[0096] When the RA process is performed during migration to the target gNB, the control unit 240 restores the radio bearer that was stopped between the terminal 200 and the target gNB.

[0097] When the receiving unit 220 receives a message indicating the resumption of the radio bearer during the migration to the target gNB, the control unit 240 resumes the radio bearer that was stopped between the terminal 200 and the target gNB.

[0098] (3) Operation of wireless communication system

[0099] Next, the operation of the wireless communication system 10 will be described. Specifically, after describing the Conditional HO process, the following operations will be described in sequence.

[0100] Recovery from Radio Link Failure (RLF) during Conditional HO

[0101] RRC Reconfiguration Complete sending timing in Conditional HO process

[0102] Handover (HO) abort during Conditional HO,

[0103] Handover (HO) changes during Conditional HO,

[0104] Structure of RRC Reconfiguration in Conditional HO

[0105] Transaction identifier (ID) assignment during Conditional HO

[0106] Recovery from Handover Failure (HOF) during Conditional HO

[0107] Recovery of radio bearers after radio link failure (RLF) during Conditional HO

[0108] (3.1) Conditional HO process

[0109] Figure 4 2 is a diagram showing the timing of the Conditional HO process. Figure 4 As shown, when the source gNB100A discovers the target gNB100B and 100C based on the measurement report received from the terminal 200, it sends a ConditionalHO request (CHO request: CHO request) (S11) to the target gNB100B and 100C.

[0110] When the target gNB100B receives a CHO request from the source gNB100A, it sends a CHO request response (CHO request ACK: CHO request ACK) (S13) containing the setting information of the cell under the target gNB100B (also called the target candidate cell) to the source gNB100A. The setting information of the target candidate cell includes the information of the target candidate cell and the migration conditions to the target candidate cell.

[0111] Similarly, when the target gNB100C receives a CHO request from the source gNB100A, it sends a CHO request response (CHO requestACK) (S13) including the setting information of the cell under the target gNB100C (referred to as the target candidate cell) to the source gNB100A. The setting information of the target candidate cell includes the information of the target candidate cell and the migration conditions to the target candidate cell.

[0112] When the source gNB100A receives the CHO request ACK from the target gNB100B and 100C, it sends a radio resource control (RRC) reconfiguration message (RRC Reconfiguration) (S15) including the Conditional HO configuration (CHO configuration) to the terminal 200. The CHO configuration includes the setting information of the target candidate cells sent from the target gNB100B and 100C respectively.

[0113] When the terminal 200 receives the CHO configuration from the source gNB 100A, it monitors the Conditional HO condition (CHO condition) (S17). Specifically, the terminal 200 determines whether the migration condition to the target candidate cell included in the setting information of each target candidate cell is met.

[0114] When the terminal 200 determines that the migration condition to the target candidate cell is met through the movement of the terminal 200, etc., it is decided to start the handover (HO) to the target candidate cell without receiving the handover command from the source gNB100A (S19). In this embodiment, the terminal 200 decides to start the HO to the target candidate cell under the target gNB100B. The target candidate cell of the migration destination that meets the migration condition is also called a CHO cell.

[0115] In addition, the source gNB100A can receive information about the target candidate cells only from the target gNB100B and 100C in S13. In this case, the source gNB100A sends a CHO configuration including information about the target candidate cells and conditions for the terminal 200 to trigger a handover (HO) to the terminal 200 in S15.

[0116] In this case, the terminal 200 determines in S17 whether the conditions for triggering HO are met. When the terminal 200 determines that the conditions for triggering HO are met through the movement of the terminal 200, etc., in S19, the target candidate cell of the migration destination is determined, and the handover to the target candidate cell is started. For example, the terminal 200 determines the target candidate cell of the migration destination based on the priority of each target candidate cell assigned by the source gNB 100A, the state of the cell included in the information of each target candidate cell, etc.

[0117] When the terminal 200 decides to start HO to the target candidate cell under the target gNB100B, a random access (RA) process is performed between the target gNB100B and the terminal 200, and synchronization is established between the target gNB100B and the terminal 200 (S21). As a result, the terminal 200 is connected to the target gNB100B.

[0118] When the terminal 200 is connected to the target gNB100B, an RRC reconfiguration completion message (RRCReconfiguration Complete) (S23) is sent to the target gNB100B.

[0119] (3.2) Recovery from RLF during Conditional HO

[0120] Next, recovery from RLF in the Conditional HO procedure will be described. First, recovery from RLF in the conventional HO procedure will be described.

[0121] Figure 5 FIG. 1 is a diagram showing a recovery sequence from RLF in a conventional HO process. Figure 5 As shown, when the source gNB100A discovers the target gNB100B based on the measurement report received from the terminal 200, it sends a HO request (HOrequest) (S51) to the target gNB100B.

[0122] When the target gNB100B receives the HO request from the source gNB100A, it sends a HO request response (HO request ACK) (S53) containing information of the cell under the target gNB100B (referred to as the target cell) to the source gNB100A.

[0123] When the source gNB100A receives the HO request ACK from the target gNB100B, it sends an RRC reconfiguration message (RRC Reconfiguration) (S55) including a handover command (HO command) to the terminal 200. The HO command includes information of the target cell sent from the target gNB100B.

[0124] When the terminal 200 receives the HO command from the source gNB100A, a random access (RA) process is performed between the target gNB100B and the terminal 200, and an attempt is made to establish synchronization between the target gNB100B and the terminal 200 (S57).

[0125] When RLF occurs during the execution of the RA process in S57 and the RA process fails, the terminal 200 performs cell reselection (S59). When the terminal 200 decides to reconnect with the cell under the target gNB100B, the RRC reestablishment process is performed between the target gNB100B and the terminal 200.

[0126] Specifically, the terminal 200 sends an RRC reestablishment request message (RRCReestablishment request) (S61) to the target gNB100B. When the target gNB100B receives the RRC reestablishment request (RRCReestablishment request) from the terminal 200, it sends an RRC reestablishment message (RRC Reestablishment) (S63) to the terminal 200. RRC Reestablishment contains setting information for reestablishing an RRC connection (RRC connection) between the target gNB100B and the terminal 200.

[0127] When the terminal 200 receives the RRC Reestablishment from the target gNB100B, the RRC connection is reestablished between the target gNB100B and the terminal 200, and an RRC reestablishment completion message (RRC ReestablishmentComplete) (S65) is sent.

[0128] In S65, the terminal 200 includes the RLF information in the RRC Reestablishment Complete and makes an RLF notification. In order to notify the network side that an RLF has occurred between the terminal 200 and the target gNB 100B, the RLF information is included in the RRC Reestablishment Complete.

[0129] When the target gNB100B receives RRC Reestablishment Complete from the terminal 200, it sends RRC Reconfiguration (S67) to the terminal 200. When the terminal 200 receives RRC Reconfiguration from the target gNB100B, it performs reconfiguration of the RRC connection and sends RRC Reconfiguration Complete (S69) to the target gNB100B.

[0130] (3.2.1) Action Example 1

[0131] Next, the action example 1 of recovery from RLF in the Conditional HO process is described. In this action example, when RLF occurs and the RA process fails in the Conditional HO process, the terminal 200 reselects the target candidate cell (CHO cell) of the migration destination, and after executing the RA process, uses the RRC reconfiguration complete message (RRCReconfiguration Complete) to notify the network side of the occurrence of RLF.

[0132] Figure 6 This is a diagram showing the recovery sequence from RLF in the Conditional HO procedure (action example 1). Figure 6 S101~S109 are Figure 4 Since the processing of S11 to S19 is the same as that of S11 to S19, the description thereof will be omitted.

[0133] When the terminal 200 decides to start HO to the target candidate cell under the target gNB100B without receiving a switching command from the source gNB100A, a random access (RA) process is performed between the target gNB100B and the terminal 200, and an attempt is made to establish synchronization between the target gNB100B and the terminal 200 (S111).

[0134] When RLF occurs during the execution of the RA process in S111 and the RA process fails, the terminal 200 reselects a target candidate cell (CHO cell) of the migration destination that meets the migration conditions (S113). In this embodiment, the terminal 200 reselects a target candidate cell under the target gNB100B.

[0135] When the terminal 200 reselects a target candidate cell under the target gNB100B, a random access (RA) process is performed between the target gNB100B and the terminal 200, and synchronization is established between the target gNB100B and the terminal 200 (S115). As a result, the terminal 200 is connected to the target gNB100B.

[0136] When the terminal 200 is connected to the target gNB100B, an RRC reconfiguration completion message (RRCReconfiguration Complete) (S117) is sent to the target gNB100B.

[0137] In S117, the terminal 200 includes the RLF information in the RRC Reconfiguration Complete to perform RLF notification. In order to notify the network side that an RLF has occurred between the terminal 200 and the target gNB 100B, the RLF information is included in the RRC Reconfiguration Complete. For example, the RLF information is represented by 1 bit. In this case, for example, when an RLF has occurred, it is set to "1" as the RLF information, and when an RLF has not occurred, it is set to "0" as the RLF information.

[0138] Thus, the RLF information is included in the message indicating that the Conditional HO process is completed (ie, indicating that terminal 200 has applied the setting information of the target candidate cell).

[0139] In S117, the terminal 200 may include the RLF information and the RLF detection information in the RRC ReconfigurationComplete. The RLF detection information includes, for example, cell information such as the identifier of the cell where the RLF is detected (in this embodiment, the cell under the target gNB100B), location information of the terminal 200 where the RLF is detected (global navigation satellite system (GNSS) information, etc.), radio access technology (RAT) information where the RLF is detected, frequency information used when the RLF is detected, bandwidth part (BWP) information used when the RLF is detected, and at least one of the locations where the RLF is detected (global positioning system (GPS) information, etc.).

[0140] In addition, similar to S13, the source gNB100A can receive information about target candidate cells only from the target gNB100B and 100C in S103. In this case, the terminal 200 reselects the target candidate cell (CHO cell) of the migration destination in S113 based on the priority of each target candidate cell assigned by the source gNB100A, the state of the cell contained in the information of each target candidate cell, etc.

[0141] As described above, in the case of recovering from RLF using reselection of the CHO cell, the terminal 200 is able to migrate to the target gNB and recover from the RLF as early as possible without performing the RRC Reestablishment procedure.

[0142] (3.2.2) Action Example 2

[0143] Next, the action example 2 of recovery from RLF in the Conditional HO process is described. In this action example, in action example 1, when the terminal 200 receives the RRC Reconfiguration from the source gNB100A in S105, it immediately sends the RRC reconfiguration complete message 1 (RRC Reconfiguration Complete1).

[0144] Figure 7 This is a diagram showing the recovery sequence from RLF in the Conditional HO procedure (action example 2). Figure 7 S101~S115 are related to Figure 6 Since the processing of S101 to S115 is the same as that of S101 to S115, the description thereof will be omitted.

[0145] like Figure 7 As shown, when the terminal 200 receives RRC Reconfiguration from the source gNB100A, it immediately sends RRCReconfiguration Complete1 (S105a).

[0146] When the terminal 200 is connected to the target gNB100B through the RA process of S115, it sends an RRC reconfiguration completion message 2 (RRC Reconfiguration Complete2) or an RRC setup completion message (RRC SetupComplete) to the target gNB100B (S117a).

[0147] In addition, RRC Reconfiguration Complete1 and RRC Reconfiguration Complete2 have the same structure as RRC Reconfiguration Complete.

[0148] In S117a, the terminal 200 includes the RLF information in RRC Reconfiguration Complete2 or RRC Setup Complete to make an RLF notification. In addition, in S117a, the terminal 200 may include the RLF information and the RLF detection information in RRC Reconfiguration Complete2 or RRC Setup Complete.

[0149] (3.2.3) Action Example 3

[0150] Next, the action example 3 of recovery from RLF in the Conditional HO process is described. In this action example, in action example 1, when RLF occurs in the Conditional HO process and the RA process fails, the terminal 200 reselects a migration destination cell other than the target candidate cell (a migration destination cell other than the CHO cell) to perform the RRCReestablishment process.

[0151] Figure 8 This is a diagram showing the recovery sequence from RLF in the Conditional HO procedure (action example 3). Figure 8 S101~S111 are related to Figure 6 Since the processing of S101 to S111 is the same as that of S101 to S111, the description thereof will be omitted.

[0152] In addition, in this action example, the source gNB100A discovers only the target gNB100B based on the measurement report received from the terminal 200. Therefore, the source gNB100A sends a CHO request (S101) to the target gNB100B, and receives a CHO request ACK (S103) containing the setting information of the target candidate cell from the target gNB100B.

[0153] When RLF occurs during the execution of the RA process in S111 and the RA process fails, the terminal 200 reselects a target candidate cell (CHO cell) of the migration destination that meets the migration conditions. However, in the case where there is no target candidate cell of the migration destination that meets the migration conditions, the terminal 200 reselects a cell of the migration destination other than the target candidate cell (a migration destination cell other than the CHO cell) (S131). In this embodiment, the terminal 200 reselects a cell under the target gNB100C.

[0154] When the terminal 200 decides to reconnect with the cell under the target gNB100C, the RRC Reestablishment process is performed between the target gNB100C and the terminal 200.

[0155] Specifically, the terminal 200 sends an RRC Reestablishment request (S133) to the target gNB100C. When the target gNB100C receives the RRC Reestablishment request from the terminal 200, it sends an RRC Reestablishment (S135) to the terminal 200. The RRC Reestablishment includes setting information used to reestablish the RRC connection between the target gNB100C and the terminal 200.

[0156] When the terminal 200 receives the RRC Reestablishment from the target gNB100C, the RRC connection is reestablished between the target gNB100C and the terminal 200, and RRC Reestablishment Complete (S137) is sent.

[0157] In S137, the terminal 200 includes the RLF information in the RRC Reestablishment Complete to make an RLF notification. In addition, in S137, the terminal 200 may include the RLF information and the RLF detection information in the RRC Reestablishment Complete.

[0158] (3.2.4) Information Element (IE)

[0159] Next, the IE of each message used in the above-mentioned RLF notification is described.

[0160] Fig. 9 This is a diagram for explaining IE in VarRLF-Report. Fig. 9 As shown, terminal 200 includes the RLF information in rlf-Report-r16 in VarRLF-Report. In addition, terminal 200 may include the RLF information and RLF detection information in rlf-Report-r16 in VarRLF-Report.

[0161] Fig.10 This is a diagram for explaining the IE in RRC Reconfiguration Complete. Fig.10 As shown in FIG. 1 , when the RLF information is included in the VarRLF-Report, the terminal 200 Figure 6 In S117 of the RRC Reconfiguration Complete, the RLF information is included in rlf-InfoAvailable-r16 in the RRC Reconfiguration Complete. In addition, the terminal 200 may include the RLF information and the RLF detection information in rlf-InfoAvailable-r16 in the RRC Reconfiguration Complete.

[0162] In addition, as described above, RRC Reconfiguration Complete2 has the same structure as RRC Reconfiguration Complete. Therefore, when the RLF information is included in VarRLF-Report, the terminal 200 Figure 7In S117a of RRC Reconfiguration Complete2, the RLF information is included in rlf-InfoAvailable-r16. In addition, the terminal 200 may include the RLF information and the RLF detection information in rlf-InfoAvailable-r16 in RRC Reconfiguration Complete2.

[0163] Fig.11A and Fig. 11B This is a diagram for explaining the IE in RRC Setup Complete. Fig.11A As shown in FIG. 1 , when the RLF information is included in the VarRLF-Report, the terminal 200 Figure 7 In S117a of the RRC Setup Complete, the RLF information is included in rlf-InfoAvailable-r16 in the RRC Setup Complete. In addition, the terminal 200 may include the RLF information and the RLF detection information in rlf-InfoAvailable-r16 in the RRC Setup Complete.

[0164] Fig.12 FIG. 1 is a diagram for explaining IE in RRC Reestablishment Complete. Fig.12 As shown in FIG. 1 , when the RLF information is included in the VarRLF-Report, the terminal 200 Figure 8 In S137, the RLF information is included in rlf-InfoAvailable-r16 in RRC Reestablishment Complete. In addition, the terminal 200 may include the RLF information and the RLF detection information in rlf-InfoAvailable-r16 in RRC Reestablishment Complete.

[0165] Fig.13 This is a diagram for explaining the IE in RRC Resume Complete. As described in "(3.9) Restoration of radio bearers after RLF in Conditional HO process" below, RRC ResumeComplete is used by terminal 200 to notify the network that "restoration of radio bearers has been completed based on the reception of an RRC message indicating restoration of radio bearers".

[0166] like Fig.13As shown, when the RLF information is included in VarRLF-Report, the terminal 200 may include the RLF information in rlf-InfoAvailable-r16 in RRC Resume Complete for notifying that the recovery of the radio bearer is completed after the recovery from RLF. In addition, the terminal 200 may include the RLF information and RLF detection information in rlf-InfoAvailable-r16 in RRC Resume Complete.

[0167] Fig.14 FIG. 1 is a diagram for explaining an information element (IE) in a UE Information Request. The terminal 200 can notify the network of the occurrence of RLF according to a request from the network. Fig.14 As shown, the network requests the terminal 200 to send an RLF notification using rlf-ReportReq-r16 in the UEInformation Request.

[0168] Figures 15A to 15C This is a diagram for explaining the IE in the UE Information Response. When the network requests RLF notification using the UE Information Request, Fig.15A As shown, the terminal 200 includes the RLF information in rlf-Cause-r16 in the UE Information Response. In addition, the terminal 200 may include the RLF information and the RLF detection information in rlf-Cause-r16 in the UE Information Response.

[0169] (3.2.5) Others

[0170] In action examples 1 and 2, the message including the RLF information is a message indicating completion of the Conditional HO process (i.e., indicating that the setting information of the target candidate cell has been applied) (e.g., RRC Reconfiguration Complete, RRC Reconfiguration Complete2, RRC Setup Complete), but is not limited thereto.

[0171] For example, the message including the RLF information may be an initial RRC message sent to the target gNB of the migration destination. In addition, the message including the RLF information may be a message having a specific identifier. As the identifier, a transaction identifier, a packet data convergence protocol (PDCP) sequence number (SN), a PDCP count value, a radio link control (RLC) sequence number (SN), or a hybrid automatic repeat request process (HARQ process) identifier may be listed.

[0172] In addition, the terminal 200 may notify the network side of the RLF information at a timing other than the Conditional HO process.

[0173] In action examples 1 to 3, terminal 200 includes RLF information and RLF detection information in the same message, but is not limited to this, and these information may also be included in different messages. In addition, in the case of an instruction from the network, terminal 200 may include RLF information in the message. Similarly, in the case of an instruction from the network, terminal 200 may include RLF detection information in the message.

[0174] When multiple RLFs occur, the terminal 200 may include multiple RLF detection information in the same message and send it to the target gNB of the migration destination. In addition, the terminal 200 may include only a predetermined number of RLF detection information (for example, one RLF detection information) in the same message and send it to the target gNB of the migration destination.

[0175] In the case where multiple RLFs occur, the terminal 200 may prioritize multiple RLF detection information. For example, in the case where RLF is detected through the same frequency as the frequency used in the cell under the target gNB of the migration destination, the terminal 200 prioritizes the RLF detection information including the information of the frequency. In addition, the terminal 200 may send multiple RLF detection information to the target gNB of the migration destination according to the priority specified by the network.

[0176] In addition, when multiple RLF detection information are included in the same message, if the maximum size allowed by the message is exceeded, the terminal 200 may delete a part of the RLF detection information from the message. In this case, the terminal 200 may notify the target gNB of the migration destination that a part of the RLF detection information has been deleted.

[0177] In addition, when RLF is detected again after generating a message including a plurality of RLF detection information, terminal 200 may regenerate the message.

[0178] (3.3) RRC Reconfiguration Complete Sending Timing in Conditional HO

[0179] Next, the timing of sending RRC Reconfiguration Complete in the Conditional HO process is described. Figure 4 In the Conditional HO process shown, the terminal 200 sends RRC Reconfiguration Complete when the RA process is successful. In contrast, in this operation, when the terminal 200 receives RRC Reconfiguration, it immediately sends RRC Reconfiguration Complete. That is, the terminal 200 sends RRC Reconfiguration Complete before starting the RA process.

[0180] Fig.16 It is a diagram showing the RRC Reconfiguration Complete transmission timing in the Conditional HO process. Fig.16 S151~S155 are related to Figure 4 Since the processing of S11 to S15 is the same as that of S11 to S15, the description thereof will be omitted.

[0181] When the terminal 200 receives the RRCReconfiguration including the CHO configuration from the source gNB100A, it immediately obtains the setting information of the target candidate cell and sends RRCReconfiguration Complete1 (S155a) to the source gNB100A.

[0182] When the terminal 200 sends RRC Reconfiguration Complete1 to the source gNB100A, the CHO condition is monitored (S157). Specifically, the terminal 200 determines whether the migration condition to the target candidate cell included in the setting information of each target candidate cell is satisfied.

[0183] When the RRC processes are executed in parallel, the processes on the radio base station side become complicated, so when the terminal 200 changes the setting information of the target candidate cell, it is necessary to use RRC Reconfiguration to notify the change after receiving RRCReconfiguration Complete notifying that the reconfiguration of the RRC connection has been completed.

[0184] Therefore, when the source gNB100A changes the setting information of the target candidate cell, in S155a, after receiving RRC Reconfiguration Complete1 from the terminal 200, it uses RRC Reconfiguration to notify the terminal 200 of the change in the setting information of the target candidate cell (S159).

[0185] In S159, the source gNB100A includes the setting information of the changed target candidate cell in RRCReconfiguration. In addition, the source gNB100A may include the difference between the setting information of the changed target candidate cell and the setting information of the target candidate cell sent in S155 in the new RRC Reconfiguration.

[0186] The RRC Reconfiguration sent in S155 is also called a first setting message. The RRC Reconfiguration Complete1 sent in S155a is also called a completion message for the first setting message. The RRC Reconfiguration sent in S159 is also called a second setting message.

[0187] When the terminal 200 receives the RRC Reconfiguration from the source gNB100A, it immediately obtains the setting information of the changed target candidate cell and sends RRC Reconfiguration Complete1 (S159a) to the source gNB100A. The terminal 200 updates the setting information of the target candidate cell obtained in S155 according to the setting information of the changed target candidate cell.

[0188] When the terminal 200 determines that the migration condition to the target candidate cell is met through the movement of the terminal 200, etc., it is decided to start the handover (HO) to the target candidate cell without receiving the handover command from the source gNB100A (S161). In this embodiment, the terminal 200 decides to start the HO to the target candidate cell under the target gNB100B.

[0189] When the terminal 200 decides to start HO to the target candidate cell under the target gNB100B, a random access (RA) process is performed between the target gNB100B and the terminal 200, and synchronization is established between the target gNB100B and the terminal 200 (S163). As a result, the terminal 200 is connected to the target gNB100B.

[0190] When the terminal 200 is connected to the target gNB100B, it sends RRC ReconfigurationComplete2 or RRC Setup Complete (S165) to the target gNB100B.

[0191] In addition, in S159, the source gNB100A sends RRC Reconfiguration to the terminal 200 in order to change the setting information of the target candidate cell, but the present invention is not limited to this. For example, in order to change the configuration (UE configuration) of the terminal 200, the source gNB100A may send RRC Reconfiguration to the terminal 200 in addition to the setting information of the target candidate cell.

[0192] In this case, the source gNB100A includes the changed UE configuration in the RRCReconfiguration. In addition, the source gNB100A may include the difference between the changed UE configuration and the previously sent UE configuration in the RRC Reconfiguration.

[0193] (3.4) HO termination during Conditional HO

[0194] Next, the HO termination in the Conditional HO process is explained. In this action, after the target gNB sends the setting information of the target candidate cell to the source gNB, it instructs the source gNB to delete the setting information of the target candidate cell. In this embodiment, the target gNB100B instructs the source gNB100A to delete the setting information of the target candidate cell.

[0195] (3.4.1) Action Example 1

[0196] First, operation example 1 of HO termination in the Conditional HO process is described. Fig.17 This is a diagram showing the HO suspension sequence (operation example 1) in the Conditional HO procedure. Fig.17 S201 to S207 shown are Fig.16 Since S151 to S157 shown are the same processes, their description is omitted.

[0197] In addition, the CHO request ACK sent in S203 is also called the first message. The HO cancellation sent in S209 is also called the second message.

[0198] When the target gNB100B identifies that the subordinate target candidate cell is in a state that is not suitable for the migration of the terminal 200, it sends a HO cancellation message (HO cancellation) (S209) to the source gNB100A.

[0199] Specifically, when the target gNB100B decides that the load in the subordinate target candidate cell increases and the target candidate cell is in a state that is not suitable for the migration of the terminal 200, HO cancellation can be sent in S209.

[0200] In this case, when multiple terminals migrate to the target candidate cell under the target gNB100B, and the number of connected terminals exceeds the maximum number of connected terminals allowed by the target candidate cell, the target gNB100B may determine that the target candidate cell is in a state that is not suitable for the migration of the terminal 200.

[0201] For example, in call acceptance control (CAC), in the target candidate cell under the target gNB100B, when the number of connected terminals exceeds the maximum number of UE contexts, the target gNB100B determines that the target candidate cell is in a state that is not suitable for terminal 200 migration.

[0202] In addition, when the terminal 200 does not migrate to the target candidate cell within the specified time according to the setting information of the target candidate cell under the target gNB100B (for example, when the terminal 200 is in an inactive state even after the specified time), the target gNB100B may send HO cancellation in S209.

[0203] In addition, when the target gNB100B receives a UE context release from a gNB or ng-eNB other than the source gNB, the target gNB100B can send HO cancellation in S209.

[0204] In addition, in S209, the target gNB100B may send HO cancellation directly to the source gNB100A. In this case, Xn signaling is used, for example, in sending the HO cancellation. Instead of this, the target gNB100B may send HO cancellation to the source gNB100A via the core network. In this case, NG signaling is used, for example, in sending the HO cancellation.

[0205] When the source gNB100A receives HO cancellation from the target gNB100B, in S205a, after receiving RRC Reconfiguration Complete1 from the terminal 200, RRC Reconfiguration is used to notify the terminal 200 of the change in the setting information of the target candidate cell (S211).

[0206] Specifically, the source gNB100A includes information indicating deletion of the setting information of the target candidate cell under the target gNB100B in the RRC Reconfiguration. In addition, the source gNB100A may include the CHO configuration that deletes the setting information of the target candidate cell under the target gNB100B in the RRC Reconfiguration.

[0207] When the terminal 200 receives RRC Reconfiguration from the source gNB100A, it immediately sends RRC Reconfiguration Complete1 (S211a) to the source gNB100A. Based on the reception of RRC Reconfiguration, the terminal 200 deletes the setting information of the target candidate cell under the target gNB100B.

[0208] When the terminal 200 determines that the migration condition to the target candidate cell is met through the movement of the terminal 200, etc., it is decided to start the handover (HO) to the target candidate cell without receiving the handover command from the source gNB100A (S213). In this embodiment, the terminal 200 decides to start the HO to the target candidate cell under the target gNB100C.

[0209] When the terminal 200 decides to start HO to the target candidate cell under the target gNB100C, a random access (RA) process is performed between the target gNB100C and the terminal 200, and synchronization is established between the target gNB100C and the terminal 200 (S215). As a result, the terminal 200 is connected to the target gNB100C.

[0210] When the terminal 200 is connected to the target gNB100C, it sends RRC ReconfigurationComplete2 or RRC Setup Complete (S217) to the target gNB100C.

[0211] (3.4.2) Action Example 2

[0212] Next, operation example 2 of HO termination in the Conditional HO procedure will be described. Fig.18 This is a diagram showing the HO suspension sequence (operation example 2) in the Conditional HO procedure. Fig.18 The S231 to S239 shown are Fig.17 Since S201 to S209 shown are the same processes, their description is omitted.

[0213] In addition, in this action example, the source gNB100A discovers only the target gNB100B based on the measurement report received from the terminal 200. Therefore, the source gNB100A sends a CHO request (S231) to the target gNB100B, and receives a CHO request ACK (S233) containing the setting information of the target candidate cell from the target gNB100B.

[0214] When the source gNB100A finds the target gNB100C located around the source gNB100A after receiving the HO cancellation from the target gNB100B, it sends a CHO request (S241) to the target gNB100C.

[0215] When the target gNB100C receives the CHO request from the source gNB100A, it sends a CHO request ACK (S243) containing the setting information of the target candidate cell under the target gNB100C to the source gNB100A.

[0216] When the source gNB100A receives HO cancellation from the target gNB100B and receives CHO request ACK from the target gNB100C, after receiving RRC Reconfiguration Complete1 from the terminal 200 in S235a, RRC Reconfiguration is used to notify the terminal 200 of the change in the setting information of the target candidate cell (S245).

[0217] Specifically, the source gNB100A deletes the setting information of the target candidate cell under the target gNB100B, and includes the CHO configuration including the setting information of the target candidate cell under the target gNB100C in the RRCReconfiguration.

[0218] When the terminal 200 receives RRC Reconfiguration from the source gNB100A, it immediately sends RRC Reconfiguration Complete1 (S245a) to the source gNB100A. Based on the reception of RRC Reconfiguration, the terminal 200 applies the CHO configuration including the setting information of the target candidate cell under the target gNB100C.

[0219] When the terminal 200 determines that the migration condition to the target candidate cell is met through the movement of the terminal 200, etc., it is decided to start the handover (HO) to the target candidate cell without receiving the handover command from the source gNB100A (S247). In this embodiment, the terminal 200 decides to start the HO to the target candidate cell under the target gNB100C.

[0220] When the terminal 200 decides to start HO to the target candidate cell under the target gNB100C, a random access (RA) process is performed between the target gNB100C and the terminal 200, and synchronization is established between the target gNB100C and the terminal 200 (S249). As a result, the terminal 200 is connected to the target gNB100C.

[0221] When the terminal 200 is connected to the target gNB100C, it sends RRC ReconfigurationComplete2 or RRC Setup Complete (S251) to the target gNB100C.

[0222] (3.5) HO changes during Conditional HO

[0223] Next, the HO changes in the Conditional HO process are explained. In this action, after the target gNB sends the setting information of the target candidate cell to the source gNB, the source gNB is instructed to change the setting information of the target candidate cell. In this embodiment, the target gNB100B instructs the source gNB100A to change the setting information of the target candidate cell.

[0224] (3.5.1) Action Example 1

[0225] First, the operation example 1 of HO change in the Conditional HO process is described. Fig.19 This is a diagram showing a HO change sequence (action example 1) in the Conditional HO procedure. Fig.19 S301, S303, S309 to S315 shown are Figure 4Since S11, S13, and S17 to S23 shown are the same processes, their description is omitted.

[0226] In addition, the CHO request ACK sent in S303 is also called a first message. The HO modification sent in S305 is also called a second message.

[0227] like Fig.19 As shown, after using CHO request ACK to send the setting information of the subordinate target candidate cell to the source gNB100A in S303, when it is recognized that the state of the target candidate cell has changed, the target gNB100B sends a HO change message (HO modification) (S305) to the source gNB100A.

[0228] Specifically, when the target gNB100B determines that the load status in the subordinate target candidate cell has changed and the migration conditions to the target candidate cell need to be changed, HO modification can be sent in S305.

[0229] In addition, in S305, the target gNB100B can directly send the HO modification to the source gNB100A. In this case, Xn signaling is used, for example, in sending the HO modification. Instead of this, the target gNB100B can send the HO modification to the source gNB100A via the core network. In this case, NG signaling is used, for example, in sending the HO modification.

[0230] When the source gNB100A receives the HO modification from the target gNB100B, it sends RRCReconfiguration (S307) including the CHO configuration to the terminal 200 based on the changed setting information of the target candidate cell under the target gNB100B.

[0231] (3.5.2) Action Example 2

[0232] Next, operation example 2 of HO change in the Conditional HO procedure is described. Fig. 20 This is a diagram showing the HO change sequence (action example 2) in the Conditional HO procedure. Fig. 20 S301 to S313 shown are Fig.19 Since S301 to S313 shown are the same processes, their description is omitted.

[0233] like Fig. 20As shown, when the terminal 200 receives RRC Reconfiguration from the source gNB100A, it immediately sends RRC Reconfiguration Complete1 (S307a).

[0234] When the terminal 200 is connected to the target gNB100B through the RA process of S313, RRCReconfiguration Complete2 or RRC Setup Complete (S315a) is sent to the target gNB100B.

[0235] (3.5.3) Action Example 3

[0236] Next, operation example 3 of HO change in the Conditional HO procedure is described. Fig.21 This is a diagram showing the HO change sequence (action example 3) in the Conditional HO procedure. Fig.21 S301, S303, S307, S307a, S309 shown are Fig. 20 Since S301, S303, S307, S307a, and S309 shown are the same processes, their description is omitted.

[0237] like Fig.21 As shown, when the target gNB100B recognizes that the status of the subordinate target candidate cell has changed, it sends HO modification (S331) to the source gNB100A.

[0238] When the source gNB100A receives the HO modification from the target gNB100B, after receiving RRC Reconfiguration Complete1 from the terminal 200 in S307a, RRC Reconfiguration is used to notify the terminal 200 of the change in the setting information of the target candidate cell (S333).

[0239] Specifically, the source gNB100A includes the CHO configuration after changing the setting information of the target candidate cell under the target gNB100B in the RRC Reconfiguration.

[0240] When the terminal 200 receives RRC Reconfiguration from the source gNB100A, it immediately sends RRC Reconfiguration Complete1 (S333a) to the source gNB100A. Based on the reception of RRC Reconfiguration, the terminal 200 changes the setting information of the target candidate cell under the target gNB100B.

[0241] When the terminal 200 determines that the migration condition to the target candidate cell is satisfied by the movement of the terminal 200, etc., it is decided to start the handover (HO) to the target candidate cell without receiving the handover command from the source gNB 100A (S335). In this embodiment, the terminal 200 decides to start the HO to the target candidate cell under the target gNB 100B.

[0242] When the terminal 200 decides to start HO to the target candidate cell under the target gNB100B, a random access (RA) process is performed between the target gNB100B and the terminal 200, and synchronization is established between the target gNB100B and the terminal 200 (S337). As a result, the terminal 200 is connected to the target gNB100B.

[0243] When the terminal 200 is connected to the target gNB100B, RRC ReconfigurationComplete2 or RRC Setup Complete (S339) is sent to the target gNB100B.

[0244] (3.6) Structure of RRC Reconfiguration in Conditional HO

[0245] Next, the structure of RRC Reconfiguration in the Conditional HO process is explained. In this structure, RRC Reconfiguration stores the setting information of the target candidate cells under the target gNB100B, and the setting information of the target candidate cells under the target gNB100C. In addition, "storing the setting information of multiple target candidate cells in RRC Reconfiguration" can also be expressed as "encapsulating the setting information of multiple target candidate cells in RRCReconfiguration".

[0246] First, the operation flow of encapsulating the setting information of the target candidate cell will be described. Fig. 22 FIG. 4 is a diagram showing the operation flow of encapsulating the setting information of the target candidate cell. Fig. 22As shown, the source gNB100A sends a CHO request (S350) to the target gNB100B and 100C.

[0247] When the source gNB100A receives the setting information of the target candidate cell from the target gNB100B and 100C respectively, the setting information of the target candidate cell is encapsulated in RRC Reconfiguration (S355).

[0248] When the source gNB100A encapsulates the setting information of multiple target candidate cells in RRC Reconfiguration, it sends the RRC Reconfiguration (S357) to the terminal 200.

[0249] (3.6.1) Structure example 1

[0250] Next, encapsulation of target candidate cell setting information is described in detail. Fig.23 This is a diagram for explaining the structure of RRC Reconfiguration in the Conditional HO procedure (structure example 1).

[0251] like Fig.23 As shown, the message group for the downlink dedicated control channel (DL-DCCH) includes RRC reconfiguration (RRCReconfiguration), RRC recovery message (RRC Resume), RRC release message (RRC Release), RRC reestablishment (RRC Reestablishment), security mode command (Security Mode Command), etc.

[0252] DL-DCCH is a downlink dedicated control channel used in the terminal 200 that has established an RRC connection. The terminal 200 receives the above-mentioned RRC message and the like via the DL-DCCH.

[0253] In this structural example, a new information element (IE) is set in the previous RRC Reconfiguration, and the setting information of the target candidate cell under the target gNB100B and the setting information of the target candidate cell under the target gNB100C are included in the IE.

[0254] Specifically, as a new IE, an RRC reconfiguration list (RRCReconfigurationList) is set in the conventional RRC Reconfiguration, and configuration for cell 1 (configuration for cell1) and configuration for cell 2 (configuration for cell2) are set in the RRCReconfigurationList. In addition, the number of configurations for cells (configuration for cell) is not limited to two.

[0255] In this structure, when the source gNB100A receives the setting information of the target candidate cell under the target gNB100B from the target gNB100B, the setting information of the target candidate cell is included in the configuration for cell1 in the RRCReconfigurationList. Similarly, when the source gNB100A receives the setting information of the target candidate cell under the target gNB100C from the target gNB100C, the setting information of the target candidate cell is included in the configuration for cell2 in the RRCReconfigurationList.

[0256] In addition, RRCReconfigurationList is also called CHO configuration. When the terminal 200 receives RRC Reconfiguration from the source gNB100A, it obtains the setting information of the target candidate cell under the target gNB100B and the setting information of the target candidate cell under the target gNB100C from the configuration for cell1 and configuration for cell2 in the RRC Reconfiguration.

[0257] The target candidate cell setting information may include at least one of the following information in addition to the target candidate cell information and the migration condition to the target candidate cell.

[0258] Measurement conditions

[0259] Structure of target candidate cells

[0260] Security information (e.g., security key update information)

[0261] Transaction Identifier

[0262] (3.6.2) Structure example 2

[0263] Fig.24 FIG. 2 is a diagram for explaining the structure of RRC Reconfiguration in the Conditional HO process (structure example 2). Fig.24 As shown, the message group for DL-DCCH includes RRC reconfiguration (RRC Reconfiguration), RRC resume (RRC Resume), RRC release (RRC Release), RRC reestablishment (RRC Reestablishment), security mode command (Security Mode Command), RRC reconfiguration 1 (RRC Reconfiguration1), etc.

[0264] RRC Reconfiguration1 is a new message different from the previous RRC Reconfiguration, and is an RRC reconfiguration message used in the Conditional HO process. In addition, the name of the new message is not limited to RRCReconfiguration1. In this structural example, the setting information of the target candidate cell under the target gNB100B and the setting information of the target candidate cell under the target gNB100C are included in the information element (IE) set in RRC Reconfiguration1.

[0265] Specifically, an RRC reconfiguration list (RRCReconfigurationList) is set in the new RRC Reconfiguration1, and configuration for cell1 and configuration for cell2 are set in the RRCReconfigurationList. In addition, the number of configuration for cell (configuration for cell) is not limited to two.

[0266] In this structure, when the source gNB100A receives the setting information of the target candidate cell under the target gNB100B from the target gNB100B, the setting information of the target candidate cell is included in the configuration for cell1 in the RRCReconfigurationList. Similarly, when the source gNB100A receives the setting information of the target candidate cell under the target gNB100C from the target gNB100C, the setting information of the target candidate cell is included in the configuration for cell2 in the RRCReconfigurationList.

[0267] When terminal 200 receives RRC Reconfiguration1 from source gNB100A, it obtains the setting information of the target candidate cell under target gNB100B and the setting information of the target candidate cell under target gNB100C from configuration for cell1 and configuration for cell2 in RRC Reconfiguration1.

[0268] (3.7) Transaction ID Assignment in Conditional HO Process

[0269] Next, the assignment of transaction IDs in the Conditional HO process is explained. In this action, the source gNB or the target gNB performs the assignment of transaction IDs used in the Conditional HO process.

[0270] (3.7.1) Action Example 1

[0271] First, we will explain the action example 1 of ID assignment in the Conditional HO process. In this action example, the source gNB performs the assignment of the transaction ID used in the Conditional HO process.

[0272] Fig.25 This is a diagram showing the ID assignment sequence (action example 1) in the Conditional HO process. Fig.25 S401, S403, S409 to S413 shown are Figure 4 Since S11, S13, and S17 to S21 shown are the same processes, their description is omitted.

[0273] like Fig.25 As shown, when the source gNB100A receives the CHO request ACK from the target gNB100B, 100C, the CHO configuration is included in the RRC Reconfiguration, and a transaction ID is assigned to the RRC Reconfiguration (S405).

[0274] Specifically, the source gNB100A includes the identification information of the target candidate cells under the target gNB100B and the identification information of the target candidate cells under the target gNB100C in the RRCReconfigurationList in the RRC Reconfiguration, and sets the transaction ID for the predetermined information element (IE) in the RRC Reconfiguration (refer to Fig.23). In addition, RRCReconfigurationList is also called CHO configuration.

[0275] In addition, the source gNB100A may include the identification information of the target candidate cells under the target gNB100B and the identification information of the target candidate cells under the target gNB100C in the RRC reconfiguration message used in Conditional HO, namely, RRCReconfigurationList in RRC Reconfiguration1, and set the transaction ID for the predetermined information element (IE) in RRCReconfiguration1 (refer to Fig.24 ).

[0276] The transaction ID may be a value from 0 to 3, or a fixed value of 0. In the present embodiment, the transaction ID takes a value from 0 to 3.

[0277] The source gNB100A can assign a transaction ID to the RRCReconfigurationList contained in the RRC Reconfiguration, that is, the group of setting information of the encapsulated target candidate cells, instead of assigning a transaction ID to the RRC Reconfiguration.

[0278] When the source gNB100A sets the RRC Reconfiguration, it sends the RRCReconfiguration (S407) to the terminal 200.

[0279] When the terminal 200 receives RRC Reconfiguration from the source gNB100A, it immediately obtains the setting information of the target candidate cell and sends RRC Reconfiguration Complete1 (S407a) to the source gNB100A.

[0280] In S407a, the terminal 200 includes the transaction ID assigned to the RRC Reconfiguration received from the source gNB100A in RRC Reconfiguration Complete1.

[0281] The terminal 200 monitors the CHO conditions (S409), starts HO to the target gNB100B (S411), and performs the RA process between the target gNB100B and the terminal 200 (S413), and when connected to the target gNB100B, sends RRC Reconfiguration Complete2 to the target gNB100B (S415).

[0282] (3.7.2) Action Example 2

[0283] Next, action example 2 of ID assignment in the Conditional HO process is described. In this action example, the target gNB performs the assignment of the transaction ID used in the Conditional HO process.

[0284] Fig.26 This is a diagram showing the ID assignment sequence (action example 2) in the Conditional HO procedure. Fig.26 S401, S437 to S441 shown are Figure 4 Since S11 and S17 to S21 shown are the same processes, their description is omitted.

[0285] like Fig.26 As shown, when the target gNB100B receives a CHO request from the source gNB100A, the setting information of the target candidate cell under the target gNB100B is included in the CHO request ACK, and the setting information of the target candidate cell is assigned a transaction ID (S431). Specifically, the target gNB100B includes the transaction ID in the setting information of the target candidate cell.

[0286] Similarly, when the target gNB100C receives a CHO request from the source gNB100A, the setting information of the target candidate cell under the target gNB100C is included in the CHO request ACK, and the setting information of the target candidate cell is assigned a transaction ID (S431). Specifically, the target gNB100B includes the transaction ID in the setting information of the target candidate cell.

[0287] The transaction ID may be a value from 0 to 3, or a fixed value of 0. In the present embodiment, the transaction ID takes a value from 0 to 3.

[0288] When source gNB100A receives CHO request ACK from target gNB100B and 100C, it includes CHO configuration in RRC Reconfiguration. Specifically, source gNB100A includes the identification information of the target candidate cell under target gNB100B assigned with transaction ID and the identification information of the target candidate cell under target gNB100C assigned with transaction ID in RRCReconfigurationList in RRC Reconfiguration (refer to Fig.23). In addition, RRCReconfigurationList is also called CHO configuration.

[0289] In addition, the source gNB100A can include the identification information of the target candidate cells under the target gNB100B and the identification information of the target candidate cells under the target gNB100C in the RRC reconfiguration message used in Conditional HO, namely, RRCReconfigurationList in RRC Reconfiguration1 (refer to Fig.24 ).

[0290] When the source gNB100A sets the RRC Reconfiguration, it sends the RRCReconfiguration (S435) to the terminal 200.

[0291] When the terminal 200 receives RRC Reconfiguration from the source gNB100A, it immediately obtains the setting information of the target candidate cell and sends RRC Reconfiguration Complete1 (S435a) to the source gNB100A.

[0292] The terminal 200 monitors the CHO conditions (S437), starts HO to the target gNB100B (S439), and performs the RA process between the target gNB100B and the terminal 200 (S441), and when connected to the target gNB100B, sends RRC Reconfiguration Complete2 to the target gNB100B (S443).

[0293] In S443, the terminal 200 includes the transaction ID contained in the setting information of the target candidate cell under the target gNB100B in RRC Reconfiguration Complete2.

[0294] (3.8) Recovery from HOF during Conditional HO

[0295] Next, the recovery from HOF in the Conditional HO process is described. In this action, the case where HOF occurs when the terminal 200 interrupts CHO and preferentially migrates to the target gNB after receiving the HO command (HO command) from the source gNB during the monitoring of the CHO condition is taken as the object. In this case, the terminal 200 maintains all or part of the setting information of the target candidate cell under the target gNB.

[0296] Fig. 27The figure shows the recovery sequence from HOF in the Conditional HO process. Fig. 27 S501~S507 are related to Figure 4 Since the processing of S11 to S17 is the same as that of S11 to S17, the description thereof will be omitted.

[0297] When the source gNB100A decides to preferentially migrate the terminal 200 to the target candidate cell under the target gNB100B, it sends a HO request (S509) to the target gNB100B. When the target gNB100B receives the HO request from the source gNB100A, it sends a HO request ACK (S511) to the source gNB100A.

[0298] When the source gNB100A receives the HO request ACK from the target gNB100B, it sends the HO command (S513) to the terminal 200. When the terminal 200 receives the HO command from the source gNB100A during the monitoring process of the CHO condition, it attempts the switching process between the target gNB100B and the terminal 200 (S515).

[0299] When HOF occurs during the execution of the handover process in S515 and the handover process fails, the terminal 200 reselects a target candidate cell (CHO cell) of the migration destination that meets the migration condition (S517). In this embodiment, the terminal 200 reselects a target candidate cell under the target gNB100B.

[0300] In S517, the terminal 200 maintains all or part of the setting information of the target candidate cell under the target gNB100B. In addition, "maintaining all or part of the setting information of the target candidate cell" can also be expressed as "considering that all or part of the setting information of the target candidate cell can be applied" or "considering that all or part of the setting information of the target candidate cell is valid."

[0301] In S517, the information maintained by the terminal 200 in the setting information of the target candidate cell is, for example, security information. In addition, when the target gNB100B has acquired the identification information of the terminal 200 in advance, the information maintained by the terminal 200 may be the identification information of the terminal 200.

[0302] As the identification information of the terminal 200, for example, the following information is listed.

[0303] Short Medium Access Control Identifier (short MAC-ID)

[0304] Cell-Radio Network Temporary Identifier (C-RNTI)

[0305] Implicit Radio Network Temporary Identifier (I-RNTI)

[0306] When the terminal 200 reselects the target candidate cell under the target gNB100B, a random access (RA) process is performed between the target gNB100B and the terminal 200, and synchronization is established between the target gNB100B and the terminal 200 (S519). As a result, the terminal 200 is connected to the target gNB100B.

[0307] When the terminal 200 is connected to the target gNB100B, an RRC reconfiguration completion message (RRCReconfiguration Complete) (S521) is sent to the target gNB100B.

[0308] In S521, the terminal 200 may include all or part of the target candidate cell setting information maintained in S517 in RRC Reconfiguration Complete, and send it to the target gNB100B using signaling radio bearer 1 (SRB1). Instead of SRB1, the terminal 200 may also include all or part of the target candidate cell setting information maintained in S517 in RRC Reestablishment request, and send it to the target gNB100B using signaling radio bearer 0 (SRB0).

[0309] In addition, SRB0 is a radio bearer for a common control channel (CCCH), and SRB1 is a radio bearer for a dedicated control channel (DCCH).

[0310] In addition, in S521, the terminal 200 may include all or part of the setting information indicating maintenance of the target candidate cell in the RRC Reconfiguration Complete and send it to the target gNB100B.

[0311] In addition, in S521, the terminal 200 can include information that can be converted in a one-to-one manner with the setting information of the target candidate cell maintained in S517 in the RRC Reconfiguration Complete and send it to the target gNB100B.

[0312] As a result, for example, security information or identification information of the terminal 200 is shared between the terminal 200 and the target gNB100B. Therefore, the target gNB100B can determine whether the terminal 200 is a terminal allowed to migrate to the target gNB100B.

[0313] In addition, the application of this action is not limited to the case where HOF occurs when the terminal 200 interrupts CHO and preferentially migrates to the target gNB after receiving the HO command from the source gNB during the monitoring of the CHO condition. For example, this action can also be applied to the case where the terminal 200 monitors the CHO condition, satisfies the migration condition to the target candidate cell under the target gNB, and performs HO to the target candidate cell without receiving the HO command from the source gNB, and HOF occurs.

[0314] (3.9) Radio bearer recovery after RLF in Conditional HO

[0315] Next, the recovery of the radio bearer after RLF in the Conditional HO process is described. In this action, in the Conditional HO process, when the terminal 200 reconnects with the target gNB, the radio bearer that was stopped due to the occurrence of RLF is resumed according to specific conditions.

[0316] In addition, the radio bearer includes a signaling radio bearer (SRB) and a data radio bearer (DRB). SRB is used for control plane data, and DRB is used for user plane data. In addition, SRB0, 1, 2, and 3 can be set in SRB according to the purpose.

[0317] SRB0 is a radio bearer for CCCH. SRB1 to SRB3 are radio bearers for DCCH. DRB is a radio bearer for user data.

[0318] SRB1 is used for sending and receiving RRC messages and NAS messages before the establishment of SRB2.

[0319] SRB2 is used for sending and receiving NAS messages. It has a lower priority than SRB1 and is set through the network after AS security is activated.

[0320] SRB3 is used for sending and receiving specific RRC messages in E-UTRA-NR Dual Connectivity (EN-DC).

[0321] In this embodiment, when the terminal 200 detects RLF while migrating to the target gNB100B using the setting information of the target candidate cell under the target gNB100B, all wireless bearers except SRB0 are stopped (suspended) between the target gNB100B and the terminal 200, and the target gNB100B is reconnected.

[0322] Fig.28The diagram shows the operation flow of the terminal 200 for restoring the radio bearer after the RLF in the Conditional HO procedure. Fig.29 It is a diagram for explaining the conditions for restoring a radio bearer after RLF in the Conditional HO procedure.

[0323] like Fig.28 As shown, the terminal 200 reselects the CHO cell during the Conditional HO process (S601). Specifically, the terminal 200 reselects the target candidate cell (CHO cell) of the migration destination that meets the migration condition. In this embodiment, the terminal 200 reselects the target candidate cell under the target gNB100B.

[0324] When the terminal 200 reselects a target candidate cell under the target gNB100B, it starts migrating to the target gNB100B according to the setting information of the target candidate cell (S603). In this case, all the radio bearers that were stopped between the target gNB100B and the terminal 200 can be restored ( Fig.29 Condition A).

[0325] The terminal 200 starts a random access (RA) process (S605) between the target gNB100B and the terminal 200 as it migrates to the target gNB100B. In this case, all radio bearers that were stopped between the target gNB100B and the terminal 200 can be restored ( Fig.29 Condition B).

[0326] When the terminal 200 completes the RA process (S607) between the target gNB100B and the terminal 200, synchronization is established between the target gNB100B and the terminal 200. As a result, the terminal 200 is connected to the target gNB100B. In this case, all radio bearers that were stopped between the target gNB100B and the terminal 200 can be restored ( Fig.29 Condition C).

[0327] In addition, when the terminal 200 receives an RRC message indicating the resumption of the radio bearer from the network during S601 to S607, all radio bearers that were stopped between the target gNB100B and the terminal 200 can be resumed ( Fig.29 Condition D).

[0328] In this case, terminal 200 may use an RRC resume complete message (RRC Resume Complete) to notify the network of completion of resumption of the radio bearer.

[0329] When the terminal 200 is connected to the target gNB100B, RRC ReconfigurationComplete (S609) is sent to the target gNB100B.

[0330] (4) Function / Effect

[0331] According to the above-mentioned implementation, the source gNB100A receives the setting information of the target candidate cells under each target gNB from the target gNB100B and 100C respectively. The source gNB100A includes a list of setting information of multiple target candidate cells in a specific message (RRC Reconfiguration or RRC Reconfiguration1). The source gNB100A sends a specific message (RRC Reconfiguration or RRC Reconfiguration1) to the terminal 200.

[0332] According to such a structure, the source gNB100A can use one message to notify the terminal 200 of the setting information of multiple target candidate cells.

[0333] Therefore, the source gNB100A is able to avoid a decrease in network throughput.

[0334] (5) Other Implementation Methods

[0335] As mentioned above, although the content of this invention was demonstrated based on embodiment, this invention is not limited to these descriptions, and it is obvious to a person skilled in the art that various deformation|transformation and improvement can be made.

[0336] For example, in the above-mentioned implementation, NR is used as an example, but Conditional HO can also be applied to LTE, and the same actions can be performed in LTE.

[0337] The block diagram used in the description of the above-mentioned embodiment ( Figure 2 and Figure 3 ) shows blocks in units of functions. These functional blocks (structural parts) are implemented by any combination of at least one of hardware and software. In addition, there is no particular limitation on the implementation method of each functional block. That is, each functional block can be implemented using a device that is physically or logically combined, or two or more physically or logically separated devices can be directly or indirectly connected (for example, using wires, wirelessly, etc.) and implemented using these multiple devices. The functional block can also be implemented by combining software with the above-mentioned one device or the above-mentioned multiple devices.

[0338] Functionally, it includes judging, deciding, determining, calculating, calculating, processing, deriving, investigating, searching, confirming, receiving, sending, outputting, accessing, solving, selecting, selecting, establishing, comparing, assuming, expecting, regarding, broadcasting, notifying, communicating, forwarding, configuring, reconfiguring, allocating, mapping, assigning, etc., but is not limited to these. For example, the functional block (structural part) that enables the sending function is called a transmitting unit or a transmitter. In short, as mentioned above, there is no particular limitation on the implementation method.

[0339] In addition, the above-mentioned gNB100A, 100B, 100C and terminal 200 can also function as a computer for processing the wireless communication method disclosed in the present invention. Fig.30 FIG. 1 is a diagram showing an example of the hardware structure of the device. Fig.30 As shown, the device may also be configured as a computer device including a processor 1001, a memory 1002 (memory), a storage 1003 (storage), a communication device 1004, an input device 1005, an output device 1006, and a bus 1007.

[0340] In the following description, the word "device" may be replaced by "circuit", "device", "unit", etc. The hardware structure of the device may include one or more of the devices shown in the figure, or may exclude some of the devices.

[0341] Each functional block of the device is implemented by any hardware element of the computer device or a combination of the hardware elements.

[0342] In addition, each function in the device is implemented by the following method: predetermined software (program) is read into hardware such as processor 1001 and memory 1002, so that processor 1001 performs calculations and controls the communication of communication device 1004 or controls at least one of the reading and writing of data in memory 1002 and storage 1003.

[0343] The processor 1001 controls the entire computer by, for example, running an operating system. The processor 1001 may be constituted by a central processing unit (CPU) including an interface with peripheral devices, a control device, a calculation device, a register, and the like.

[0344] In addition, the processor 1001 reads a program (program code), a software module or data, etc. from at least one of the memory 1003 and the communication device 1004 to the memory 1002, and performs various processes accordingly. As a program, a program that causes a computer to perform at least a part of the actions described in the above-mentioned embodiments is used. In addition, with respect to the above-mentioned various processes, although it is described that the above-mentioned various processes are performed by one processor 1001, the above-mentioned various processes can also be performed simultaneously or sequentially by more than two processors 1001. The processor 1001 can also be installed by more than one chip. In addition, the program can also be sent from the network via a telecommunication line.

[0345] The memory 1002 is a computer-readable recording medium, and may be composed of at least one of a ROM (Read Only Memory), an EPROM (Erasable Programmable ROM), an EEPROM (Electrically Erasable Programmable ROM), a RAM (Random Access Memory), etc. The memory 1002 may also be referred to as a register, a cache, a main memory (main storage device), etc. The memory 1002 may store a program (program code), a software module, etc. that can execute a method according to an embodiment of the present disclosure.

[0346] The memory 1003 is a computer-readable recording medium, and may be composed of at least one of an optical disk such as a CD-ROM (Compact Disc ROM), a hard disk drive, a floppy disk, a magneto-optical disk (e.g., a compressed disk, a digital versatile disk, a Blu-ray (registered trademark) disk, a smart card, a flash memory (e.g., a card, a stick, a key drive), a Floppy (registered trademark) disk, a magnetic strip, etc. For example, the memory 1003 may also be referred to as an auxiliary storage device. The above-mentioned storage medium may be, for example, other appropriate media such as a database, a server, etc. that includes at least one of the memory 1002 and the memory 1003.

[0347] The communication device 1004 is hardware (transceiver) used to communicate between computers via at least one of a wired network and a wireless network, and may also be called a network device, a network controller, a network card, a communication module, etc.

[0348] The communication device 1004 may be configured to include a high-frequency switch, a duplexer, a filter, a frequency synthesizer, and the like, for example, in order to realize at least one of frequency division duplex (FDD) and time division duplex (TDD).

[0349] The input device 1005 is an input device that receives input from the outside (e.g., a keyboard, a mouse, a microphone, a switch, a button, a sensor, etc.). The output device 1006 is an output device that implements output to the outside (e.g., a display, a speaker, an LED light, etc.). In addition, the input device 1005 and the output device 1006 may also be integrally formed (e.g., a touch panel).

[0350] In addition, the processor 1001 and the memory 1002 and other devices are connected via a bus 1007 for communicating information. The bus 1007 may be configured using a single bus or may be configured using different buses for each device.

[0351] In addition, the device may be configured to include hardware such as a microprocessor, a digital signal processor (DSP), an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), or an FPGA (Field Programmable Gate Array), and a part or all of each functional block may be implemented by the hardware. For example, the processor 1001 may also be implemented using at least one of these hardware.

[0352] In addition, the notification of information is not limited to the form / implementation method described in the present disclosure, and other methods may also be used. For example, the notification of information may be implemented through physical layer signaling (e.g., DCI (Downlink Control Information), UCI (Uplink Control Information)), high-layer signaling (e.g., RRC (Radio Resource Control) signaling, MAC (Medium Access Control) signaling, broadcast information (MIB (Master Information Block), SIB (System Information Block)), other signals or a combination thereof. In addition, RRC signaling may also be referred to as an RRC message, for example, an RRC Connection Setup message, an RRC Connection Reconfiguration message, etc.

[0353] Each form / embodiment described in the present disclosure may also be applied to at least one of LTE (Long Term Evolution), LTE-A (LTE-Advanced), 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, UWB (Ultra-WideBand), Bluetooth (registered trademark), a system using other appropriate systems, and a next-generation system extended therefrom. In addition, a combination of a plurality of systems (for example, a combination of at least one of LTE and LTE-A with 5G, etc.) may be applied.

[0354] The processing procedures, timings, processes, etc. of each form / implementation described in this disclosure may be changed in order without contradiction. For example, for the method described in this disclosure, the elements of various steps are presented in an illustrative order, but are not limited to the specific order presented.

[0355] In the present disclosure, specific actions performed by a base station are sometimes performed by its upper node depending on the situation. In a network consisting of one or more network nodes having a base station, various actions performed to communicate with a terminal can be performed by at least one of the base station and other network nodes other than the base station (for example, consider MME or S-GW, etc., but not limited to these). In the above, the case where there is one other network node other than the base station is illustrated, but the other network node may also be a combination of multiple other network nodes (for example, MME and S-GW).

[0356] Information, signals (information, etc.) can be output from a higher layer (or lower layer) to a lower layer (or higher layer), and can also be input or output via multiple network nodes.

[0357] The input or output information can be stored in a specific location (e.g., memory) or managed using a management table. The input or output information can be rewritten, updated, or appended. The output information can also be deleted. The input information can also be sent to other devices.

[0358] The determination may be made by a value represented by one bit (0 or 1), by a Boolean value (Boolean: true or false), or by comparison of numerical values ​​(for example, comparison with a predetermined value).

[0359] Each form / implementation described in the present disclosure may be used alone or in combination, and may be switched depending on the execution. In addition, notification of scheduled information is not limited to being performed explicitly (e.g., notification of "yes X"), but may also be performed implicitly (e.g., notification of the scheduled information is not performed).

[0360] Software, whether referred to as software, firmware, middleware, microcode, hardware description language, or by other names, shall be interpreted broadly to refer to commands, sets of commands, codes, code segments, program codes, programs, subroutines, software modules, applications, software applications, software packages, routines, subroutines, objects, executable files, execution threads, procedures, functions, etc.

[0361] In addition, software, commands, information, etc. may be sent and received via a transmission medium. For example, when software is sent from a web page, server, or other remote source using at least one of wired technology (coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), etc.) and wireless technology (infrared, microwave, etc.), at least one of these wired technology and wireless technology is included in the definition of transmission medium.

[0362] The information, signals, etc. described in the present disclosure may also be represented by any of a variety of different technologies. For example, data, commands, instructions, information, signals, bits, symbols, chips, etc. that may be involved in the above description as a whole may be represented by voltage, current, electromagnetic waves, magnetic fields or magnetic particles, light fields or photons, or any combination thereof.

[0363] In addition, the terms described in the present disclosure and the terms required for understanding the present disclosure may be replaced with terms having the same or similar meanings. For example, at least one of a channel and a symbol may also be a signal (signaling). In addition, a signal may also be a message. In addition, a component carrier (CC) may be referred to as a carrier frequency, a cell, a frequency carrier, etc.

[0364] As used in this disclosure, the terms "system" and "network" may be used interchangeably.

[0365] In addition, the information, parameters, etc. described in the present disclosure may be represented by absolute values, relative values ​​to predetermined values, or other corresponding information. For example, wireless resources may also be indicated by indexes.

[0366] The names used for the above parameters are not limiting in any way. Furthermore, the formulas etc. using these parameters may sometimes differ from those explicitly disclosed in this disclosure. Various channels (e.g., PUCCH, PDCCH, etc.) and information elements may be identified by appropriate names, and therefore the various names assigned to these various channels and information elements are not limiting in any way.

[0367] In the present disclosure, the terms "base station (BS)", "wireless base station", "fixed station", "NodeB", "eNodeB (eNB)", "gNodeB (gNB)", "access point", "transmission point", "reception point", "transmission / reception point", "cell", "sector", "cell group", "carrier", "component carrier" and the like are used interchangeably. Base stations are sometimes referred to as macrocells, small cells, femtocells, picocells, etc.

[0368] A base station can accommodate one or more (for example, 3) 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 also provide communication services through a base station subsystem (for example, a small base station for indoor use (RRH: Remote Radio Head)).

[0369] The terms "cell" or "sector" refer to a part or the entirety of a coverage area of ​​at least one of a base station and a base station subsystem that provide communication services within the coverage area.

[0370] In the present disclosure, terms such as “mobile station (MS)”, “user terminal (user terminal)”, “user equipment (UE)”, and “terminal” may be used interchangeably.

[0371] For mobile stations, those skilled in the art sometimes also use the following terms: 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 appropriate terms.

[0372] At least one of the base station and the mobile station may also be referred to as a transmitting device, a receiving device, a communication device, etc. In addition, at least one of the base station and the mobile station may be a device mounted on a mobile body, the mobile body itself, etc. The mobile body may be a means of transportation (e.g., a car, an airplane, etc.), a mobile body that moves in an unmanned manner (e.g., a drone, an autonomous vehicle, etc.), or a robot (manned or unmanned). In addition, at least one of the base station and the mobile station also includes 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 IoT (Internet of Things) device such as a sensor.

[0373] In addition, the base station in the present disclosure may also be replaced by a mobile station (user terminal, the same below). For example, regarding a structure in which the communication between a base station and a mobile station is replaced by communication between multiple mobile stations (for example, it may also be referred to as D2D (Device-to-Device), V2X (Vehicle-to-Everything, etc.), the various forms / implementations of the present disclosure may also be applied. In this case, it may also be a structure in which the mobile station has the functions of the base station. In addition, terms such as "uplink" and "downlink" may also be replaced by terms corresponding to communication between terminals (for example, "side"). For example, an uplink channel, a downlink channel, etc. may also be replaced by a side channel.

[0374] Likewise, the mobile station in the present disclosure may be replaced by a base station. In this case, the base station may have the same functions as the mobile station.

[0375] A radio frame may be composed of one or more frames in the time domain. In the time domain, one or more frames may be referred to as subframes.

[0376] A subframe may consist of one or more time slots in the time domain. A subframe may be a fixed time length (eg, 1 ms) that is independent of numerology.

[0377] A parameter set may be a communication parameter applied to at least one of the transmission and reception of a certain signal or channel. The parameter set may, for example, represent at least one of a subcarrier spacing (SCS), bandwidth, symbol length, cyclic prefix length, transmission time interval (TTI), number of symbols per TTI, radio frame structure, specific filtering processing performed by a transceiver in the frequency domain, specific windowing processing performed by a transceiver in the time domain, and the like.

[0378] A slot may be composed of one or more symbols (OFDM (Orthogonal Frequency Division Multiplexing) symbols, SC-FDMA (Single Carrier Frequency Division Multiple Access) symbols, etc.) in the time domain. A slot may be a time unit based on a parameter set.

[0379] A time slot may contain multiple mini-slots. Each mini-slot may be composed of one or more symbols in the time domain. In addition, a mini-slot may also be referred to as a sub-slot. A mini-slot may be composed of fewer symbols than a time slot. A PDSCH (or PUSCH) transmitted in units of time greater than a mini-slot may be referred to as a PDSCH (or PUSCH) mapping type A. A PDSCH (or PUSCH) transmitted using a mini-slot may be referred to as a PDSCH (or PUSCH) mapping type B.

[0380] A radio frame, a subframe, a time slot, a mini-time slot, and a symbol all represent time units for transmitting signals. A radio frame, a subframe, a time slot, a mini-time slot, and a symbol may be referred to by other corresponding names.

[0381] For example, 1 subframe can be called a transmission time interval (TTI), multiple consecutive subframes can also be called a TTI, and 1 time slot or 1 mini time slot can also be called a TTI. That is, at least one of the subframe and the TTI can be a subframe (1ms) in the existing LTE, or a period shorter than 1ms (for example, 1-13 code elements), or a period longer than 1ms. In addition, the unit representing TTI can be a time slot, a mini time slot, etc. instead of a subframe.

[0382] Here, TTI refers to, for example, the minimum time unit for scheduling in wireless communication. For example, in the LTE system, the base station schedules the allocation of wireless resources (frequency bandwidth, transmission power, etc. that can be used in each user terminal) to each user terminal in units of TTI. In addition, the definition of TTI is not limited to this.

[0383] TTI can be a transmission time unit for data packets (transport blocks), code blocks, code words, etc. after channel coding, or a processing unit for scheduling, link adaptation, etc. In addition, when TTI is assigned, the time interval (e.g., the number of symbols) to which the transport block, code block, code word, etc. is actually mapped can be shorter than the TTI.

[0384] In addition, when 1 time slot or 1 mini time slot is called TTI, more than one TTI (ie, more than one time slot or more than one mini time slot) can constitute the minimum time unit of scheduling. In addition, the number of time slots (mini time slots) constituting the minimum time unit of scheduling can be controlled.

[0385] A TTI having a time length of 1 ms is also called a normal TTI (TTI in LTE Rel.8-12), a normal TTI, a long TTI, a normal subframe, a normal subframe, a long subframe, a time slot, etc. A TTI shorter than a normal TTI may be called a shortened TTI, a short TTI, a partial or fractional TTI, a shortened subframe, a short subframe, a mini-time slot, a sub-time slot, a time slot, etc.

[0386] In addition, for a long TTI (for example, a normal TTI, a subframe, etc.), it can be replaced with a TTI having a time length exceeding 1ms, and for a short TTI (for example, a shortened TTI, etc.), it can be replaced with a TTI length that is smaller than the long TTI (longTTI) and has a TTI length of more than 1ms.

[0387] A resource block (RB) is a resource allocation unit in the time domain and the frequency domain. In the frequency domain, it may contain one or more consecutive subcarriers. The number of subcarriers contained in an RB may be the same regardless of the parameter set, for example, it may be 12. The number of subcarriers contained in an RB may also be determined according to the parameter set.

[0388] In addition, the time domain of an RB may include one or more symbols, and may be the length of 1 slot, 1 mini slot, 1 subframe, or 1 TTI. 1 TTI, 1 subframe, etc. may be composed of one or more resource blocks, respectively.

[0389] In addition, one or more RBs may be referred to as a physical resource block (PRB: Physical RB), a sub-carrier group (SCG: Sub-Carrier Group), a resource element group (REG: Resource Element Group), a PRB pair, an RB pair, and the like.

[0390] In addition, a resource block may be composed of one or more resource elements (REs). For example, 1 RE may be a radio resource region of 1 subcarrier and 1 symbol.

[0391] Bandwidth Part (BWP) (also called partial bandwidth, etc.) represents a subset of contiguous common RBs (common resource blocks) for a parameter set in a certain carrier. Here, the common RB can be determined by the index of the RB based on the common reference point of the carrier. PRBs are defined in a certain BWP and numbered within the BWP.

[0392] 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.

[0393] At least one of the set BWPs may be active, and it is not assumed that the UE transmits or receives a predetermined signal / channel outside the activated BWP. In addition, "cell", "carrier" and the like in the present disclosure may be replaced with "BWP".

[0394] The above structures of radio frames, subframes, time slots, mini-time slots, and symbols are only examples. For example, the number of subframes included in a radio frame, the number of time slots per subframe or radio frame, the number of mini-time slots included in a time slot, the number of symbols and RBs included in a time slot or mini-time slot, the number of subcarriers included in an RB, the number of symbols in a TTI, the symbol length, the cyclic prefix (CP: Cyclic Prefix) length, and the like can be changed in various ways.

[0395] The terms "connected", "coupled" or all variations of these terms are intended to indicate any direct or indirect connection or combination between two or more elements, and may include the situation where there is one or more intermediate elements between two elements that are "connected" or "coupled" to each other. The combination or connection between elements may be a physical combination or connection, a logical combination or connection, or a combination of these. For example, "access" may be used to replace "connection". In the context of the present disclosure, for two elements, it may be considered that they are "connected" or "coupled" to each other by using at least one of one or more wires, cables, and printed electrical connections, and as some non-limiting and non-inclusive examples, by using electromagnetic energy having wavelengths in the wireless frequency domain, microwave region, and light (including both visible and invisible) region, etc.

[0396] The reference signal may be referred to as RS (Reference Signal) for short, or may be referred to as a pilot signal according to the applied standard.

[0397] The phrase "according to" used in the present disclosure does not mean "only according to" unless otherwise expressly stated. In other words, the phrase "according to" means both "only according to" and "at least according to".

[0398] Any reference to an element using the terms "first", "second", etc. used in this disclosure does not necessarily limit the number and order of these elements. These terms are used in this disclosure as a simple method to distinguish between two or more elements. Therefore, a reference to a first and a second element does not mean that only two elements can be used here or that the first element must precede the second element in any form.

[0399] When the terms "include," "including," and variations thereof are used in the present disclosure, these terms are intended to be inclusive, as is the term "comprising." Furthermore, the term "or" used in the present disclosure does not mean an exclusive or.

[0400] In the present disclosure, when an article is added by translation, such as a, an, and the in English, for example, the present disclosure also includes the case where the noun following the article is in plural form.

[0401] The terms "determining" and "determining" used in the present disclosure sometimes also include various actions. "Determining" and "determining" may include, for example, considering matters that have been judged, calculated, calculated, processed, derived, investigated, searched (for example, searched in a table, database or other data structure), confirmed (ascertaining) as matters that have been "judged" or "determined", etc. In addition, "determining" and "determining" may include considering matters that have been received (for example, receiving information), transmitted (for example, transmitting information), input, output, accessed (for example, accessed data in memory) as matters that have been "judged" or "determined", etc. In addition, "determining" and "determining" may include considering matters that have been resolved (resolving), selected (selecting), chosen (choosing), established (establishing), compared (comparing), etc. as matters that have been "judged" or "determined". That is, "determining" and "determining" may include matters that have been "judged" or "determined" by any action. In addition, the word “determine” can also be replaced by “assuming”, “expecting”, “considering”, etc.

[0402] In the present disclosure, the phrase "A and B are different" may also mean "A and B are different from each other". In addition, the phrase may also mean "A and B are different from C, respectively". The phrases such as "separate" and "combine" may also be interpreted as "different".

[0403] The present disclosure is described in detail above, but it should be clear to those skilled in the art that the present disclosure is not limited to the embodiments described in the present disclosure. The present disclosure can be implemented as a modification and variation without departing from the subject matter and scope of the present disclosure as determined by the claims. Therefore, the purpose of the description of the present disclosure is to illustrate and not to have any limiting meaning on the present disclosure.

[0404] Industrial Applicability

[0405] According to the above-described radio base station, even when the terminal migrates to the target radio base station based on the setting information of the target candidate cell, it is possible to avoid a decrease in the throughput of the network, which is useful.

[0406] Description of symbols

[0407] 10 Wireless Communication Systems

[0408] 100A, 100B, 100C gNB

[0409] 110 Sending Department

[0410] 120 Receiving Department

[0411] 130 Holding unit

[0412] 140 Control Department

[0413] 200 Terminal

[0414] 210 Sending Department

[0415] 220 Receiving Department

[0416] 230 Holding Unit

[0417] 240 Control Department

[0418] 1001 Processor

[0419] 1002 Memory

[0420] 1003 Memory

[0421] 1004 Communication device

[0422] 1005 Input Device

[0423] 1006 Output Device

[0424] 1007 Bus

Claims

1. A terminal for performing a CHO process, i.e. a conditional handover process, comprising: a receiving unit receiving, from a source wireless base station, a message having a list, the list including information of a plurality of candidate cells and a plurality of migration conditions corresponding to the candidate cells, the information of the candidate cells having a first transaction ID, and the message having a second transaction ID; a control unit that, when one of the relocation conditions included in the list of the message is satisfied, synchronizes with a candidate cell corresponding to the one relocation condition without receiving a handover command, and performs relocation to a target wireless base station in which information of the candidate cell is set; as well as a sending unit that sends a first completion message having the second transaction ID to the source wireless base station before the synchronization starts, and sends a second completion message having the first transaction ID to the target wireless base station after the synchronization starts, After the transmission unit transmits the first completion message having the second transaction ID to the source wireless base station and before the synchronization starts, the control unit monitors the transition condition included in the list of the message.

2. The terminal according to claim 1, wherein: The message is a radio resource control message.

3. A wireless communication system for performing a CHO process, i.e. a conditional handover process, comprising a source wireless base station and a terminal, wherein: The source wireless base station has: A receiving unit, which receives information about candidate cells; as well as a sending unit, configured to send a message having a list to the terminal, wherein the list includes information of a plurality of candidate cells and a plurality of migration conditions corresponding to the candidate cells; The candidate cell information has a first transaction ID, The message has a second transaction ID; The terminal has: A receiving unit, which receives the message; a control unit that, when one of the relocation conditions included in the list of the message is satisfied, synchronizes with a candidate cell corresponding to the one relocation condition without receiving a handover command, and performs relocation to a target wireless base station in which information of the candidate cell is set; as well as a sending unit that sends a first completion message having the second transaction ID to the source wireless base station before the synchronization starts, and sends a second completion message having the first transaction ID to the target wireless base station after the synchronization starts, After the transmission unit transmits the first completion message having the second transaction ID to the source wireless base station and before the synchronization starts, the control unit monitors the transition condition included in the list of the message.

4. A wireless communication method for performing a CHO process, i.e. a conditional handover process, comprising the following steps: The source wireless base station receives information about candidate cells; The source wireless base station sends a message having a list to the terminal, wherein the list includes information of a plurality of candidate cells and a plurality of migration conditions corresponding to the candidate cells; The candidate cell information has a first transaction ID, The message has a second transaction ID; The terminal receives the message; The terminal sends a first completion message having the second transaction ID to the source wireless base station; monitoring the migration conditions contained in the list of the message; When one migration condition is met, the terminal does not receive a handover command, but synchronizes with a candidate cell corresponding to the one migration condition, and migrates to a target wireless base station in which information of the candidate cell is set; as well as The terminal transmits a second completion message having the first transaction ID to the target wireless base station.

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