Terminal device and wireless communication method

Abstract

To provide a terminal device and a wireless communication method that execute an optimal conditional handover (CHO) procedure when applied not only to a master cell group but also to a secondary cell group.SOLUTION: In a wireless communication system, a terminal device receives CHO configuration information including first cell information on a first cell belonging to a master cell group and second cell information on a second cell belonging to a secondary cell group, and evaluates the first cell and the second cell as candidate cells for CHO on the basis of the CHO configuration information. If a candidate cell satisfies CHO conditions, CHO is executed. In the case where CHO is executed for the second cell, which is the candidate cell, switching of the target cell for CHO is performed, and CHO is executed for the second cell as the first cell.SELECTED DRAWING: Figure 9

Description

[Technical field]

[0001] The present invention relates to a terminal device and a wireless communication method. [Background technology]

[0002] 3GPP (registered trademark), an international standardization organization, is studying NR (New Radio), a new radio access technology for fifth-generation (5G) cellular systems. NR is a technology that is being studied to enable a wider variety of services than LTE and LTE-Advanced, the fourth-generation (4G) cellular systems.

[0003] For example, in NR, conditional handover (CHO) is being considered, which sets cell information of the handover destination in advance, in order to improve the robustness (stability) of handover (HO) (see Non-Patent Document 1). The introduction of CHO is expected to have the effect of improving the handover success rate. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] 3GPP TS 38.300 Summary of the Invention [Problem to be solved by the invention]

[0005] As a CHO procedure, it is being considered to apply CHO not only to a master cell group (MCG) including a primary cell (PCell), but also to a cell group other than the master cell group, i.e., a secondary cell group (SCG) including a primary secondary cell (PSCell), but the conventional CHO procedure does not take such an extension into consideration. Therefore, in order to apply the CHO procedure to an SCG, the CHO procedure needs to be optimized, but such a proposal has not yet been made.

[0006] The present disclosure has been made in consideration of the above points, and aims to provide an optimal CHO procedure when applied not only to MCG but also to SCG. [Means for solving the problem]

[0007] A terminal device according to one embodiment of the present disclosure includes a receiving unit that receives conditional handover configuration information including first cell information of a first cell belonging to a master cell group and second cell information of a second cell belonging to a secondary cell group; an evaluation unit that evaluates the first cell and the second cell as candidate cells for conditional handover based on the conditional handover configuration information; and an execution unit that executes a conditional handover when the candidate cell satisfies a conditional handover condition.When executing a conditional handover to the second cell, which is a candidate cell, the execution unit switches the target cell for the conditional handover and executes the conditional handover with the second cell as the first cell.

[0008] A wireless communication method according to one embodiment of the present disclosure is a wireless communication method performed by a terminal device, and includes a receiving step of receiving conditional handover configuration information including first cell information of a first cell belonging to a master cell group and second cell information of a second cell belonging to a secondary cell group, an evaluation step of evaluating the first cell and the second cell as candidate cells for conditional handover based on the conditional handover configuration information, and an execution step of executing a conditional handover if the candidate cell satisfies a conditional handover condition.In the execution step, when a conditional handover is to be executed to the second cell, which is a candidate cell, switching of a target cell for the conditional handover is performed, and the conditional handover is executed with the second cell as the first cell. Effect of the Invention

[0009] According to the present disclosure, it is possible to provide an optimal CHO procedure when applied not only to MCG but also to SCG. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram for explaining the basic steps of the current CHO. [Diagram 2] 1 is a diagram illustrating an example of a configuration of a wireless communication system according to an embodiment of the present invention. [Diagram 3] FIG. 2 is a diagram illustrating an example of a hardware configuration of a terminal and a base station. [Figure 4] FIG. 2 is a diagram illustrating an example of a functional block configuration of a base station. [Diagram 5] FIG. 2 is a diagram illustrating an example of a functional block configuration of a terminal. [Figure 6] FIG. 13 is a diagram illustrating an example of CHO setting information related to the first strategy. [Figure 7] 13 is a flowchart showing an example of a processing procedure related to a first measure. [Figure 8] FIG. 11 is an explanatory diagram for explaining a CHO procedure according to the second strategy. [Figure 9] 13 is a flowchart illustrating an example of a processing procedure related to a second measure. [Figure 10] FIG. 11 is an explanatory diagram for explaining bearer types. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to the accompanying drawings, in which the same reference numerals denote the same or similar configurations.

[0012] A. This embodiment (Current basic procedure of CHO) First, the basic procedure of the current CHO will be described with reference to Fig. 1. In the following description, the cover area formed by each of the base stations 20-1 and 20-2 will be referred to as a cell. When there is no need to distinguish between the base station 20-1 and the base station 20-2, they will be referred to as the base station 20.

[0013] The terminal 10 measures the quality of neighboring cells, and when a measurement event (event trigger condition) that is set (specified, notified) in advance in at least one (Cell-X) of the measurement target cells (i.e., CHO candidate cells) is established (when the measurement result satisfies the measurement event), or when periodic measurement reporting is set and the set period expires, the terminal 10 starts a measurement report procedure and transmits a measurement report message (Measurement Report) including the measurement results of the related cells to the base station 20-1 (S10).

[0014] The base station 20-1 that has received the measurement report message determines whether to provide (set) the CHO candidate cell and the corresponding measurement event condition to the terminal 10 based on the received measurement result, and if it is determined that it is necessary, provides the CHO setting information to the terminal 10. Typically, the base station 20-1 requests HO preparation to the base station 20-2 to which the notified CHO candidate cell (Cell-X) belongs, and exchanges information for the terminal 10 to access the base station 20-2 between the base stations 20 (S11). Then, the base station 20-1 generates an RRC message (RRC Reconfiguration) including information (hereinafter referred to as CHO setting information) required for the terminal 10 to evaluate the cell related to CHO provided by the base station 20-2 and the measurement event condition related to CHO (hereinafter referred to as CHO condition), and transmits it to the terminal 10 (S12).

[0015] The terminal 10 decides whether to start CHO by comparing (evaluating) whether the CHO candidate cell (Cell-X) satisfies the CHO condition based on the CHO setting information and CHO condition included in the received RRC message. If the CHO candidate cell satisfies the CHO condition, the terminal 10 attempts HO to the base station 20-2 as a CHO target cell based on the notified CHO setting information (S13), and attempts to obtain downlink synchronization and random access to the base station 20-2 (S14). If the random access procedure with the base station 20-2 is successful, the base station 20-2 transmits a response message (RRC Reconfiguration Complete) corresponding to the received RRC message to the base station 20-2 (S15). Thereafter, the base station 20-2 determines that the CHO is successful, transmits a message (UE Context Release) to the base station 20-1 instructing it to delete the UE context (terminal-related information related to connection) of the terminal 10 (S16), and completes the CHO procedure.

[0016] (Measures for applying CHO to SCG) <First Measure> Since the current CHO procedure is premised on the MCG, if the current CHO procedure is applied to the SCG as it is, the terminal 10 cannot distinguish whether a cell to be evaluated as a CHO candidate cell is a PCell belonging to the MCG or a PSCell belonging to the SCG. Therefore, even if the base station 20 notifies the terminal 10 of CHO configuration information intending a PCell belonging to the MCG, the terminal 10 may execute CHO for a PSCell belonging to the SCG. That is, according to the conventional procedure, the terminal 10 cannot correctly evaluate a PCell belonging to the MCG and a PSCell belonging to the SCG, and therefore cannot configure these cells simultaneously. In addition, the base station 20 cannot simultaneously configure a PCell belonging to the MCG and a PSCell belonging to the SCG for the terminal 10. In order to solve this problem, in the first measure, the CHO configuration information is specified so that the terminal 10 regards only a PCell belonging to the MCG as a CHO candidate cell (in other words, regards a PSCell belonging to the SCG as not being a target of a CHO candidate cell).

[0017] <Second Measure> Since a PCell belonging to an SCG has the same functions as a PCell belonging to an MCG (e.g., a common search space), in the second approach, a CHO procedure is defined so that not only a PCell belonging to an MCG but also a PSCell belonging to an SCG is considered as a CHO candidate cell.

[0018] <System configuration> A wireless communication system according to this embodiment will be described. The wireless communication system according to this embodiment is for NR, but is not limited thereto. For example, it is also applicable to LTE and LTE-Advanced. It is also applicable to a wireless communication system that partially uses NR. More generally, this embodiment is applicable to any wireless communication system that includes at least a terminal and a base station, including future wireless communication systems. In the following description, LTE and LTE-Advanced are also referred to as EUTRA, but have the same meaning.

[0019] An area (coverage area) formed by a base station is called a cell. EUTRA and NR are cellular communication systems constructed by multiple cells. The wireless communication system according to this embodiment may apply either TDD (Time Division Duplex) or FDD (Frequency Division Duplex), or a different method may be applied to each cell.

[0020] FIG. 2 is a diagram showing an example of the configuration of a wireless communication system 1 according to the present embodiment. The terminal 10 is wirelessly connected to the base station 20-1 or the base station 20-2. Hereinafter, when the base station 20-1 and the base station 20-2 are not distinguished from each other, they are referred to as the base station 20. The terminal 10 can also wirelessly connect to the base station 20-1 and the base station 20-2 at the same time. The base station 20-1 and the base station 20-2 can use EUTRA or NR. For example, the base station 20-1 may use NR and the base station 20-2 may use EUTRA, or vice versa. The base station 20 in EUTRA is referred to as an eNB (evolved NodeB), and the base station 20 in NR is referred to as a gNB (g-NodeB). Hereinafter, the base station 20 includes both eNB and gNB. Also, the terminal 10 in EUTRA and NR is referred to as a UE (User Equipment). The base station 20, which is a gNB, may connect to the terminal 10 using a part of the frequency band it uses (BWP: bandwidth part). Hereinafter, the cell is referred to as including the BWP.

[0021] The terminal 10 is connected to the base station 20. The terminal 10 may be connected (carrier aggregation) to the base station 20 using a plurality of cells. When the terminal 10 is connected (dual connectivity) via a plurality of base stations 20, the base station 20 to which the terminal 10 is initially connected is called a master node (MN), and the base station 20 to which the terminal 10 is additionally connected is called a secondary node (SN). Among the plurality of cells to which the terminal 10 is connected, one or more cells provided by the master node are called a master cell group (MCG). Among the plurality of cells to which the terminal 10 is connected, one or more cells provided by the secondary node are called a secondary cell group (SCG). The master cell group (MCG) may optionally include one or more secondary cells (SCells) in addition to the primary secondary cell (PCell). Furthermore, the secondary cell group (SCG) may optionally include one or more secondary cells (SCells) in addition to the primary secondary cell (PSCell). In addition, the MCG may be referred to as a Primary Cell Group (PCG).

[0022] The base stations 20 are connected to each other via a base station interface. The base stations 20 and the core network device 40 are also connected to each other via a core network interface. The base station interface is used to exchange control signals required for handover and coordinated operations between the base stations 20. The core network device 40 has the base stations 20 under its control, and mainly handles load control between the base stations 20, calling (paging) the terminal 10, and mobility control such as location registration.

[0023] The terminal 10 and the base station 20 transmit and receive RRC messages in the Radio Resource Control (RRC) layer. The terminal 10 and the base station 20 also transmit and receive MAC Control Elements (MACCEs) in the Medium Access Control (MAC) layer. The RRC messages are transmitted as RRC Protocol Data Units (PDUs), and the logical channels to which they are mapped include a Common Control Channel (CCCH), a Dedicated Control Channel (DCCH), a Paging Control Channel (PCCH), a Broadcast Control Channel (BCCH), or a Multicast Control Channel (MCCH). The MAC CEs are transmitted as MAC PDUs (or MAC subPDUs). The MAC subPDUs are equivalent to a Service Data Unit (SDU) in the MAC layer plus an 8-bit header, and the MAC PDUs include one or more MAC subPDUs.

[0024] <Hardware configuration> 3 is a diagram showing an example of the hardware configuration of the terminal 10 and the base station 20. The terminal 10 and the base station 20 each include a processor 11, a memory 12, a storage device 13, a communication device 14 for performing wired or wireless communication, an input device 15 for accepting input operations, an output device 16 for outputting information, and an antenna 17.

[0025] The processor 11 is, for example, a CPU (Central Processing Unit), and controls the terminal 10 and the base station 20.

[0026] The memory 12 is composed of, for example, a Read Only Memory (ROM), an Erasable Programmable ROM (EPROM), an Electrically Erasable Programmable ROM (EEPROM), and / or a Random Access Memory (RAM).

[0027] The storage device 13 is configured by storage such as a hard disk drive (HDD), a solid state drive (SSD), and / or an embedded multi media card (eMMC).

[0028] The communication device 14 is a device that communicates via a wired and / or wireless network, and is, for example, a network card, a communication module, etc. The communication device 14 may also include an amplifier, an RF (Radio Frequency) device that performs processing related to wireless signals, and a BB (BaseBand) device that performs baseband signal processing.

[0029] The RF device performs, for example, D / A conversion, modulation, frequency conversion, power amplification, etc. on the digital baseband signal received from the BB device to generate a radio signal to be transmitted from the antenna 17. The RF device also performs frequency conversion, demodulation, A / D conversion, etc. on the radio signal received from the antenna 17 to generate a digital baseband signal and transmit it to the BB device. The BB device performs a process of converting the digital baseband signal into packet data (e.g., IP packets) and a process of converting the IP packets into a digital baseband signal.

[0030] The input device 15 is, for example, a keyboard, a touch panel, a mouse, and / or a microphone, etc. The output device 16 is, for example, a display and / or a speaker, etc.

[0031] <Function block configuration> (base station) FIG. 4 is a diagram showing an example of a functional block configuration of the base station 20. The base station 20 includes a transmitting unit 200, a receiving unit 201, and a control unit 202. FIG. 4 shows the main functional blocks in this embodiment. The transmitting unit 200 and the receiving unit 201 may be realized by, for example, the communication device 14, or may be realized by the processor 11 executing a program stored in the storage device 13 in addition to the communication device 14. The control unit 202 may be realized by the processor 11 executing a program stored in the storage device 13. The program can be stored in a storage medium. The storage medium storing the program may be a computer-readable non-transient storage medium. The non-transient storage medium is not particularly limited, and may be, for example, a storage medium such as a USB memory or a CD-ROM.

[0032] The transmitter 200 generates and transmits a downlink signal to be transmitted to the terminal 10.

[0033] The receiving unit 201 receives an uplink signal from the terminal 10 .

[0034] The control unit 202 performs various processes related to the RRC layer, for example. The control unit 202 also includes a generation unit 203 that generates CHO configuration information (CHO Configuration) indicating CHO conditions and measurement conditions required to start the CHO procedure. The CHO conditions and CHO configuration information generated by the generation unit 203 are included in an RRC message and transmitted from the transmission unit 200 to the terminal 10.

[0035] (Terminal) FIG. 5 is a diagram showing an example of a functional block configuration of the terminal 10. The terminal 10 includes a transmitting unit 100, a receiving unit 101, a determining unit 102, a measuring unit 103, an evaluating unit 104, and an executing unit 105. FIG. 5 shows main functional blocks in this embodiment. The transmitting unit 100 and the receiving unit 101 may be realized by, for example, the communication device 14, or may be realized by the processor 11 executing a program stored in the storage device 13 in addition to the communication device 14. The determining unit 102, the measuring unit 103, the evaluating unit 104, and the executing unit 105 may be realized by the processor 11 executing a program stored in the storage device 13. The program can be stored in a storage medium. The storage medium storing the program may be a non-transitory computer readable storage medium. The non-transitory storage medium is not particularly limited, and may be, for example, a storage medium such as a USB memory or a CD-ROM.

[0036] The transmitter 100 generates and transmits an uplink signal to be transmitted to the base station 20 .

[0037] The receiving unit 101 receives a downlink signal from the base station 20. The receiving unit 101 also receives an RRC message including a CHO condition and CHO setting information from the base station 20. The received CHO condition and CHO setting information are stored in the storage device 13.

[0038] Based on the CHO configuration information, the determining unit 102 determines a CHO candidate cell to be evaluated from among a plurality of cells.

[0039] The measurement unit 103 measures the reception quality (measurement quality, cell quality) of the determined CHO candidate cell and outputs the measurement result of the cell quality. The cell quality may be, for example, RSRP (Reference Signal Received Power), RSRQ (Reference Signal Received Quality), RSSI (received signal strength indicator), or RS-SINR (Reference Signal-Signal to Interference and Noise Ratio).

[0040] The evaluation unit 104 evaluates whether the determined CHO candidate cell satisfies the CHO condition based on time information, cell quality measurement results, etc. For example, the evaluation unit 104 determines that the CHO condition is satisfied when a predetermined cell quality measurement result is obtained within an evaluation time indicated by the time information (when a measurement event corresponding to a pre-set CHO is satisfied).

[0041] The execution unit 105 executes CHO when the CHO candidate cell satisfies the CHO condition.

[0042] <Details of the first measure> FIG. 6 is a diagram illustrating CHO configuration information (CHO configuration) IF according to the first strategy. The CHO configuration information IF is configured to include at least cell information for the terminal 10 to determine whether the terminal 10 is a CHO candidate cell. As shown in FIG. 6, the CHO configuration information IF may include either or both of first cell information (MCG configuration) C1 related to each cell belonging to the MCG and second cell information (SCG configuration) C2 related to each cell belonging to the SCG. The first cell information C1 includes at least first primary cell information (PCell configuration) PC1 related to the PCell, and the second cell information C2 includes at least second primary cell information (PSCell configuration) PC2 related to the PSCell. Note that the first cell information C1 and the second cell information C2 may each include information on the SCell (a cell that provides radio resources in addition to the PCell) and the like. In addition, the CHO configuration information IF may include, as a measurement configuration, a measurement event targeting the CHO candidate cell, related parameters (measurement object), and a measurement ID linking the measurement object and the measurement event.

[0043] At least identification information for identifying each cell is set in the first cell information C1 and the second cell information C2. For example, cell indexes for identifying the PCell and the PSCell are set in the first primary cell information PC1 and the second primary cell information PC2, respectively. As an example, a cell index "0" (fixed) is set for the PCell, and a cell index "1" (arbitrary) is set for the PSCell, but this is of course not limited to this. The base station 20 may notify the terminal 10 by omitting the cell index. When the terminal 10 receives the CHO configuration information IF in which the cell index is omitted, the terminal 10 may consider that the cell is a PCell and that the cell index "0" is specified. In addition, the identification information is not limited to the cell index, and may be, for example, bit information indicating whether the cell belongs to the MCG or the SCG, an additional identifier indicating the MCG (PCell) (information identifying the MCG), or an additional identifier indicating the SCG (PSCell) (information identifying the SCG).

[0044] 7 is a flowchart showing an example of a processing procedure related to the first measure performed by the terminal 10. It is assumed that the terminal 10 has received a CHO condition and CHO setting information from the base station 20.

[0045] The terminal 10 refers to the CHO configuration information IF and determines a CHO candidate cell from among a plurality of cells. Specifically, the terminal 10 compares identification information (here, cell index) included in each of the primary cell information PC1 and PC2 with the cell index of each cell to determine whether the cell belongs to the MCG or the SCG (S101). Alternatively, the terminal 10 determines whether the cell belongs to the MCG or the SCG based on bit information indicating whether the cell belongs to the MCG or the SCG. Alternatively, the terminal 10 determines the MCG based on an additional identifier indicating the MCG (PCell) and determines the other as the SCG. Alternatively, the terminal 10 determines the SCG based on an additional identifier indicating the SCG (PSCell) and determines the other as the MCG. The terminal 10 regards the PCell that belongs to the MCG as a CHO candidate cell (S102), while excluding the PSCell that belongs to the SCG from the targets of the CHO candidate cells (S103).

[0046] Furthermore, when an SCG is configured and the terminal 10 receives CHO configuration information IF in which the first cell information C1 and the second cell information C2 are configured, the terminal 10 may evaluate a CHO condition with a PCell (primary cell information PC1) as a CHO target cell, and at the same time, start evaluating a measurement event linked to a PSCell belonging to the original SCG and a PSCell (primary cell information PC2) indicated (configured) by the second cell information C2. When a measurement event linked to a PSCell (primary cell information PC2) is established, the terminal 10 may start a procedure related to an SCG addition or an SCG change.

[0047] Furthermore, when an SCG is configured and a CHO targeting a PCell belonging to an MCG is established, if the cell index or the frequency and the physical cell ID of the PSCell included in the second cell information C2 of the CHO configuration information IF is different from the currently configured SCG, the terminal 10 may perform a procedure related to SCG addition or SCG change. If the cell index or the frequency and the physical cell ID of the PSCell included in the second cell information C2 of the CHO configuration information IF is the same as the currently configured SCG, the terminal 10 may maintain the SCG and not start the change procedure. At this time, the terminal 10 may deactivate the SCG (SCG deactivation).

[0048] With this configuration, the terminal 10 can realize efficient CHO without evaluating whether or not a PSCell belonging to an SCG satisfies the CHO condition.

[0049] The terminal 10 may notify the base station 20 in advance of capability information (UE Capability) indicating that the terminal itself is compatible with the first measure. In this case, the capability information may be in a format that notifies support on a per-terminal basis, or on a per-frequency range (FR) basis or a per-band combination basis.

[0050] <Details of the second measure> FIG. 8 is an explanatory diagram for explaining the CHO procedure according to the second measure, in which the upper part shows the CHO setting information IF before the change, and the lower part shows the CHO setting information IF after the change. In the second measure, not only the PCell belonging to the MCG but also the PSCell belonging to the SCG are regarded as CHO candidate cells, and further, the setting of the CHO configuration information IF is changed when CHO targeting the PSCell is executed.

[0051] 9 is a flowchart showing an example of a processing procedure related to the second measure performed by the terminal 10. It is assumed that the terminal 10 has received a CHO condition and CHO setting information from the base station 20.

[0052] At least one of the MCG and the SCG, or both, are specified in the CHO configuration information IF for the terminal 10. The terminal 10 regards the PSCell and the PCell as CHO candidate cells based on the received CHO configuration information IF. The terminal 10 also measures the CHO candidate cells and performs an evaluation (CHO evaluation) on the CHO candidate cells to determine whether or not the CHO condition indicated by the measurement event of the measurement ID linked to the CHO candidate cells is satisfied (S201).

[0053] When a measurement event set based on CHO evaluation occurs, the terminal 10 determines whether to attempt (perform) CHO on the PSCell or the PCell based on the target cell on which the measurement event occurs (S202). When the terminal 10 determines that CHO should be performed on the PSCell (i.e., when the measurement event occurs on the PSCell), the terminal 10 swaps the cell index of the PSCell and the cell index of the PCell (S203; see A1 in FIG. 8), and then performs switching between the SCG and the MCG (S204; see A2 in FIG. 8). Then, the terminal 10 performs CHO by treating the PSCell belonging to the SCG as the PCell belonging to the MCG (S205). Note that swapping the cell index of the PSCell and the cell index of the PCell to switch (exchange) the SCG and the MCG is referred to as "switching of the CHO target cell".

[0054] On the other hand, when the measurement event set based on the CHO evaluation occurs and the terminal 10 determines that CHO should be performed on the PCell rather than the PSCell (i.e., when the measurement event occurs on the PCell), the terminal 10 does not switch the CHO target cell and simply performs CHO on the PCell (S206).

[0055] Furthermore, the terminal 10 may determine whether to perform switching of the CHO target cell based on parameters specified (set, notified) by the base station 20. The base station 20 may specify switching of the CHO target cell on a cell-by-cell or event-by-event basis. The terminal 10 may determine not to perform switching of the CHO target cell when the execution of switching of the CHO target cell is not explicitly specified.

[0056] When the terminal 10 does not perform switching of the CHO target cell and an SCG is configured, the terminal 10 may perform a procedure for adding an SCG or changing an SCG for the PSCell included in the second cell information C2 of the CHO configuration information IF based on the evaluation result of the configured measurement event.

[0057] With this configuration, terminal 10 can perform CHO by regarding not only a PCell belonging to an MCG but also a PSCell belonging to an SCG as a CHO target cell, thereby enabling efficient CHO to be realized.

[0058] After switching the CHO target cell, the terminal 10 may notify the base station 20 of the changed CHO setting information IF. Alternatively, the terminal 10 may notify the base station 20 of information indicating that switching has been performed.

[0059] The terminal 10 may notify the base station 20 in advance of capability information (UE Capability) indicating that the terminal itself is a terminal compatible with the second measure. In this case, the capability information may be in a format that notifies support in units of frequency ranges (FR) or band combinations, in addition to notification in units of terminals.

[0060] B. Modifications The above-described embodiment is intended to facilitate understanding of the present invention, and is not intended to limit the present invention. The flow charts, sequences, elements included in the embodiment, and their arrangements, materials, conditions, shapes, sizes, etc., described in the embodiment are not limited to those exemplified, and may be modified as appropriate.

[0061] <Variation 1> Regarding the second measure described above, after switching of the CHO target cell, the original MCG-related settings may be released. For example, when the terminal 10 switches between the SCG and the MCG, the terminal 10 may release the MCG-related settings before switching (for example, all the MCG-related settings, or part of the cell index settings, etc.). The terminal 10 may release the settings based on an instruction (setting) from the base station 20, or the terminal 10 may determine it by itself as one step in the CHO procedure. For example, the terminal 10 may determine it based on the quality of the original MCG (PCell). In addition, after switching the MCG-related settings to the SCG, all the cells included in the SCG may be deactivated (SCG deactivation). The base station 20 may instruct the terminal 10 whether to perform SCG deactivation by an RRC message at the same time as the CHO setting. The terminal 10 may perform SCG deactivation based on an instruction from the base station 20.

[0062] <Variation 2> Regarding the second approach described above, if a Radio Link Failure (RLF) occurs or an HO failure occurs while evaluating whether or not the CHO condition is satisfied (CHO evaluation), the terminal 10 may reuse the settings for the PSCell.

[0063] Specifically, when the terminal 10 detects a radio link failure or an HO failure, it selects a cell to which reconnection is attempted according to a predetermined cell selection condition. Here, when the selected cell is a target cell for CHO (i.e., a PSCell specified in the CHO setting information IF), the terminal 10 may start an RRC reconfiguration procedure to which a setting related to the PSCell is applied, instead of transmitting an RRC message (RRC re-establishment request) related to RRC reconnection. Note that, when reusing the setting related to the PSCell, the terminal 10 may perform the above-mentioned switching-related procedure, such as replacing the cell index of the PSCell with the cell index of the PCell (i.e., "0"). At this time, the same method as in the first modification may be applied to the procedure of whether to release the setting related to the MCG. Also, the terminal 10 may reuse the setting related to the PSCell as a target cell when an SCG link failure occurs. Furthermore, the terminal 10 may notify the base station 20 of the implementation of the RRC reconfiguration procedure to which the configuration related to the PSCell has been applied, by using a corresponding RRC message (RRC reconfiguration Complete). At this time, the terminal 10 transmits, in the RRC message, information capable of identifying the applied PSCell (SCG) from at least the CHO configuration information (for example, the first cell information C1 or the second cell information C2, or the first primary cell information PC1 or the second primary cell information PC2, or identification information indicating a cell group).

[0064] <Variation 3> Regarding the second measure described above, the terminal 10 may regard a PSCell belonging to an SCG as a CHO candidate cell only when a specific radio bearer is set by the base station 20 as a communication path for user data passing through the SCG. As bearer types, three types of radio bearers shown in FIG. 10 are defined, namely, an MCG bearer, an SCG bearer, and a split bearer, and the terminal 10 may regard a PSCell as a CHO candidate cell only when an SCG bearer is set. When an SCG (PSCell) for which a specific bearer is not set is notified, the terminal 10 may regard the SCG (PSCell) as a target cell in an SCG addition procedure or a target cell in a PSCell change procedure, rather than as a target cell for CHO.

[0065] <Summary> According to the present disclosure described above, it is possible to provide an optimal CHO procedure when applied not only to MCG but also to SCG. Therefore, the technology according to the present disclosure can contribute to the achievement of Goal 9 of the Sustainable Development Goals (SDGs), "Build resilient infrastructure, promote inclusive and sustainable industrialization, and promote innovation and infrastructure." [Explanation of symbols]

[0066] 1...wireless communication system, 10...terminal, 11...processor, 12...memory, 13...storage device, 14...communication device, 15...input device, 16...output device, 17...antenna, 20...base station, 100...transmitting unit, 101...receiving unit, 102...determining unit, 103...measurement unit, 104...evaluation unit, 105...executing unit, 200...transmitting unit, 201...receiving unit, 202...control unit, 203...generation unit.

Claims

1. A receiving unit that receives conditional handover configuration information including first cell information of a first cell that belongs to a master cell group and second cell information of a second cell that belongs to a secondary cell group; An evaluation unit that evaluates the first cell and the second cell as candidate cells for conditional handover based on the conditional handover configuration information; An execution unit that executes a conditional handover when the candidate cell satisfies a conditional handover condition, The execution unit is A terminal device that, when performing the conditional handover to the second cell that is the candidate cell, performs switching of a target cell for the conditional handover and performs the conditional handover with the second cell as the first cell.

2. The switching of the target cell of the conditional handover is to exchange the master cell group and the secondary cell group by exchanging indexes between the second cell and the first cell; The terminal device according to claim 1 , wherein the first cell is a primary cell and the second cell is a primary secondary cell.

3. The execution unit is The terminal device according to claim 1 or 2, wherein the conditional handover is performed using the second cell as the first cell only when a specific bearer is set.

4. A receiving unit that receives conditional handover configuration information including first cell information of a first cell that belongs to a master cell group and second cell information of a second cell that belongs to a secondary cell group; An evaluation unit that evaluates a candidate cell for conditional handover based on the conditional handover configuration information; An execution unit that executes a conditional handover when the candidate cell satisfies a conditional handover condition, The first cell information and the second cell information include identification information for identifying a cell group to which each cell belongs, The evaluation unit is A terminal device that determines whether or not the cell corresponds to the first cell by referring to the identification information, and evaluates the cell determined to be the first cell as the candidate cell.

5. The terminal device according to claim 4, wherein the evaluation unit determines whether to add the cell determined to be the second cell as a new secondary cell group in the conditional handover procedure based on the secondary cell group of the terminal device and the setting of the second cell.

6. The terminal device according to claim 5 , wherein the identification information is information for identifying a cell index or a cell group.

7. A wireless communication method performed by a terminal device, A receiving step of receiving conditional handover configuration information, the conditional handover configuration information including first cell information of a first cell belonging to a master cell group and second cell information of a second cell belonging to a secondary cell group; An evaluation step of evaluating the first cell and the second cell as candidate cells for conditional handover based on the conditional handover configuration information; and performing a conditional handover when the candidate cell satisfies a conditional handover condition; In the execution step, A wireless communication method, comprising: when executing the conditional handover to the second cell, which is the candidate cell, switching of a target cell for the conditional handover is performed, and the conditional handover is executed with the second cell as the first cell.

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