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 Art

[0002] In the 3GPP (registered trademark), which is an international standardization organization, studies are being conducted on NR (New Radio), which is a new radio access technology for the 5th generation (5G) cellular system. NR is being studied for technologies that enable a wider variety of services than LTE and LTE-Advanced, which are 4th generation (4G) cellular systems.

[0003] For example, in NR, conditional handover (CHO) that pre-sets cell information of a handover destination is being studied for the purpose of enhancing the robustness (stability) of handover (HO) (see Non-Patent Document 1). The introduction of CHO is expected to improve the handover success probability.

Prior Art Documents

Non-Patent Documents

[0004]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] As a conditional handover (CHO) procedure, it has been considered to apply CHO not only to a master cell group (MCG) including a primary cell (PCell), but also to cell groups other than the master cell group, that is, a secondary cell group (SCG) including a primary secondary cell (PSCell). However, the conventional CHO procedure does not consider such an extension. Therefore, in order to apply the CHO procedure to the SCG, it is necessary to optimize the CHO procedure, but such a proposal has not been made yet.

[0006] The present disclosure has been made in view of the above points, and an object thereof is to provide an optimal CHO procedure not only for the MCG but also when applied to the SCG.

Means for Solving the Problems

[0007] A terminal device according to an aspect of the present disclosure includes a receiving unit that receives conditional handover setting 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, and based on the conditional handover setting information, an evaluation unit that evaluates the first cell and the second cell as candidate cells for conditional handover, and an execution unit that executes conditional handover when the candidate cells satisfy the conditions for conditional handover. When executing conditional handover with respect to the second cell, which is a candidate cell, the execution unit switches the target cell of the conditional handover and executes the conditional handover with the second cell as the first cell.

[0008] A wireless communication method according to an aspect of the present disclosure is a wireless communication method performed by a terminal device, including: a receiving step of receiving conditional handover setting 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 evaluating step of evaluating the first cell and the second cell as candidate cells for conditional handover based on the conditional handover setting information; and an executing step of executing conditional handover when the candidate cells satisfy the conditions for conditional handover. In the executing step, when executing conditional handover to the second cell which is a candidate cell, switching of the target cell of conditional handover is performed, and conditional handover is executed with the second cell as the first cell.

Advantages of the Invention

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

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

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Figure 8

Figure 9

Figure 10

Embodiments for Carrying Out the Invention

[0011] Embodiments of the present invention will be described with reference to the accompanying drawings. In each figure, those denoted by the same reference numerals have the same or similar configurations.

[0012] A. This Embodiment (Basic Procedure of CHO in the Current Situation) First, the basic procedure of CHO in the current situation will be described with reference to FIG. 1. In the following description, the coverage area formed by each base station 20-1, 20-2 is referred to as a cell. Also, when the base station 20-1 and the base station 20-2 are not distinguished, they are described as the base station 20.

[0013] The terminal 10 measures the quality of surrounding cells, and when a measurement event (event trigger condition) preset (specified, notified) in at least one (Cell-X) of the measurement target cells (i.e., CHO candidate cells) is satisfied (when the measurement result satisfies the measurement event), or when a periodic measurement report is set and the set period has elapsed, the terminal 10 starts a measurement report procedure and transmits a measurement report message (Measurement Report) including the measurement results of 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 (configure) the CHO candidate cell and the corresponding measurement event conditions to the terminal 10 based on the received measurement results. If it is determined that it is necessary, the CHO configuration information is provided to the terminal 10. Typically, the base station 20-1 requests HO preparation from the base station 20-2 to which the notified CHO candidate cell (Cell-X) belongs, and exchanges information between the base stations 20 for the terminal 10 to access the base station 20-2 (S11). Then, the base station 20-1 generates an RRC message (RRC Reconfiguration) including the information necessary for the terminal 10 to evaluate the cell related to CHO provided by the base station 20-2 (hereinafter referred to as CHO configuration information) and the measurement event conditions related to CHO (hereinafter referred to as CHO conditions), and transmits it to the terminal 10 (S12).

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

[0016] (Measures for Applying CHO to SCG) <The First Measure> Since the current CHO procedure is based on MCG, if the current CHO procedure is directly applied up to SCG, the terminal 10 cannot distinguish whether the cell to be evaluated as a CHO candidate cell belongs to the PCell belonging to MCG or the PSCell belonging to SCG. For this reason, even when the base station 20 notifies the CHO configuration information intending the PCell belonging to MCG, the terminal 10 may execute CHO for the PSCell belonging to SCG. That is, according to the conventional procedure, since the terminal 10 cannot correctly evaluate the PCell belonging to MCG and the PSCell belonging to SCG, these cells cannot be set simultaneously. Also, the base station 20 cannot set the PCell belonging to MCG and the PSCell belonging to SCG for the terminal 10 simultaneously. To solve such a problem, in the first strategy, the CHO configuration information is defined so that the terminal 10 regards only the PCell belonging to MCG as a CHO candidate cell (in other words, regards the PSCell belonging to SCG as out of the scope of CHO candidate cells).

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

[0018] <System Configuration> The wireless communication system according to the present embodiment will be described. The wireless communication system according to the present embodiment targets NR, but is not limited thereto. For example, it is also applicable to LTE and LTE-Advanced. Also, it is applicable in a wireless communication system that partially uses NR. More generally, the present embodiment is applicable to any wireless communication system including 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, and they have the same meaning.

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

[0020] FIG. 2 is a diagram showing an example of the configuration of the wireless communication system 1 according to this embodiment. The terminal 10 is wirelessly connected to the base station 20-1 or the base station 20-2, respectively. Hereinafter, when the base stations 20-1 and 20-2 are not distinguished, they are described as the base station 20. Also, the terminal 10 can be wirelessly connected to the base stations 20-1 and 20-2 at the same time. The base stations 20-1 and 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 called an eNB (evolved NodeB), and the base station 20 in NR is called a gNB (g-NodeB). Hereinafter, when described as the base station 20, it includes both the meanings of eNB and gNB. Also, the terminal 10 in EUTRA and NR is called a UE (User Equipment). The base station 20, which is a gNB, may connect to the terminal 10 using a part (BWP: bandwidth part) of the frequency band it uses. Hereinafter, when described as a cell, it includes 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 initially connected base station 20 is called the master node (MN), and the additionally connected base station 20 is called the 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 the master cell group (MCG). Also, among the plurality of cells to which the terminal 10 is connected, one or more cells provided by the secondary node are called the secondary cell group (SCG). Note that the master cell group (MCG) may include, in addition to the primary cell (PCell), one or more secondary cells (SCell) optionally. Also, the secondary cell group (SCG) may include, in addition to the primary secondary cell (PSCell), one or more secondary cells (SCell) optionally. Note that the MCG may also be referred to as the primary cell group (PCG).

[0022] The base stations 20 are connected to each other by a base station interface. Also, the base station 20 and the core network device 40 are connected by a core network interface. The base station interface is used, for example, to exchange control signals necessary for handover and cooperative 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 and mobility control such as paging and location registration of the terminal 10.

[0023] The terminal 10 and the base station 20 transmit and receive RRC messages in the Radio Resource Control (RRC) layer. Also, the terminal 10 and the base station 20 transmit and receive MAC Control Elements (MACCEs) in the Medium Access Control (MAC) layer. The RRC message is transmitted as an RRC Protocol Data Unit (PDU), and as the logical channel to which it is mapped, 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) is used. The MAC CE is transmitted as a MAC PDU (or a MAC subPDU). The MAC subPDU is equal to the Service Data Unit (SDU) in the MAC layer with an 8-bit header added, and the MAC PDU contains one or more MAC subPDUs.

[0024] <Hardware Configuration> FIG. 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 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 receiving an input operation, an output device 16 for outputting information, and an antenna 17.

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

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

[0027] The storage device 13 is composed of, for example, storage such as HDD (Hard Disk Drive), SSD (Solid State Drive), and / or eMMC (embedded Multi Media Card), etc.

[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. Further, the communication device 14 may include an amplifier, an RF (Radio Frequency) device that processes wireless signals, and a BB (BaseBand) device that performs baseband signal processing.

[0029] The RF device generates a wireless signal transmitted from the antenna 17 by performing, for example, D / A conversion, modulation, frequency conversion, power amplification, etc. on the digital baseband signal received from the BB device. Further, the RF device generates a digital baseband signal by performing frequency conversion, demodulation, A / D conversion, etc. on the wireless signal received from the antenna 17 and transmits it to the BB device. The BB device performs processing to convert the digital baseband signal into packet data (for example, IP packets), and processing to convert 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] <Functional block configuration> (Base station) FIG. 4 is a diagram showing an example of the functional block configuration of the base station 20. The base station 20 includes a transmission unit 200, a reception unit 201, and a control unit 202. Note that FIG. 4 shows the main functional blocks in the present embodiment. The transmission unit 200 and the reception 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. Further, the program can be stored in a storage medium. The storage medium storing the program may be a computer-readable non-transitory 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.

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

[0033] The reception 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 measurement conditions and the like necessary to start CHO conditions and CHO procedures. The CHO conditions and CHO configuration information generated by the generation unit 203 are transmitted from the transmission unit 200 to the terminal 10 included in the RRC message.

[0035] (Terminal) FIG. 5 is a diagram showing an example of the functional block configuration of the terminal 10. The terminal 10 includes a transmission unit 100, a reception unit 101, a determination unit 102, a measurement unit 103, an evaluation unit 104, and an execution unit 105. Note that FIG. 5 shows the main functional blocks in the present embodiment. The transmission unit 100 and the reception 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 determination unit 102, the measurement unit 103, the evaluation unit 104, and the execution unit 105 may be realized by the processor 11 executing a program stored in the storage device 13. Further, the program can be stored in a storage medium. The storage medium storing the program may be a non-transitory computer readable 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 transmission unit 100 generates and transmits an uplink signal to be transmitted to the base station 20.

[0037] The reception unit 101 receives a downlink signal from the base station 20. Further, the reception unit 101 receives an RRC message including CHO conditions and CHO setting information from the base station 20. Note that the received CHO conditions and CHO setting information are stored in the storage device 13.

[0038] The determination unit 102 determines a CHO candidate cell to be evaluated from among a plurality of cells based on the CHO setting information.

[0039] The measurement unit 103 measures the received 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 the time information, the measurement result of the cell quality, and the like. For example, when the evaluation unit 104 obtains a measurement result of a predetermined cell quality within the evaluation time indicated by the time information (when the measurement event corresponding to the pre-set CHO is satisfied), it determines that the CHO condition is satisfied.

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

[0042] <Details of the First Strategy> FIG. 6 is a diagram illustrating a 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 one or both of the first cell information (MCG configuration) C1 regarding each cell belonging to the MCG and the second cell information (SCG configuration) C2 regarding each cell belonging to the SCG. The first cell information C1 includes at least the first primary cell information (PCell configuration) PC1 regarding the PCell, and the second cell information C2 includes at least the second primary cell information (PSCell configuration) PC2 regarding the PSCell. Note that the first cell information C1 and the second cell information C2 may each be configured to include information regarding an SCell (a cell that provides radio resources in addition to the PCell). Further, the CHO configuration information IF may include, as measurement settings, a measurement event targeting a CHO candidate cell, related parameters (measurement object), and a measurement ID that links 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, in the first primary cell information PC1 and the second primary cell information PC2, cell indexes for identifying the PCell and the PSCell are set respectively. As an example, for the PCell, a cell index "0" (fixed) may be set, and for the PSCell, for example, a cell index "1" (arbitrary) may be set, but of course it is 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 setting information IF with the cell index omitted, the terminal 10 may regard the cell as the PCell and assume that the cell index "0" is specified. Also, the identification information is not limited to the cell index, and may be, for example, bit information indicating whether it belongs to either the MCG or the SCG, an additional identifier indicating the MCG (PCell) (information for identifying the MCG), or an additional identifier indicating the SCG (PSCell) (information for identifying the SCG).

[0044] FIG. 7 is a flowchart showing an example of a processing procedure related to the first strategy performed by the terminal 10. As a premise, it is assumed that the terminal 10 has received CHO conditions and CHO setting information from the base station 20.

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

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

[0047] Also, when SCG is configured and CHO for the PCell belonging to MCG is established, if the cell index of the PSCell included in the second cell information C2 of the CHO configuration information IF, or the frequency and physical cell ID are different from the currently configured SCG, the terminal 10 may perform procedures related to SCG addition or SCG change. If the cell index of the PSCell included in the second cell information C2 of the CHO configuration information IF, or the frequency and physical cell ID are 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 such a configuration, the terminal 10 can efficiently implement CHO without evaluating whether the PSCell belonging to the SCG satisfies the CHO condition.

[0049] Note that the terminal 10 may notify the base station 20 in advance of the capability information (UE Capability) indicating that the terminal itself is a terminal corresponding to the first strategy. At this time, the capability information may be in a format that notifies support in units of terminals, frequency ranges (Frequency Range: FR), or band combinations in addition to unit notifications.

[0050] <Details of the second strategy> FIG. 8 is an explanatory diagram for explaining the CHO procedure according to the second strategy, showing the CHO configuration information IF before the change at the top and the CHO configuration information IF after the change at the bottom. In the second strategy, not only the PCell belonging to the MCG but also the PSCell belonging to the SCG is regarded as a CHO candidate cell, and further, setting changes of the CHO configuration information IF when CHO for the PSCell is executed are performed.

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

[0052] For the terminal 10, at least one of MCG and SCG, or both, is specified by the CHO setting information IF. Based on the received CHO setting information IF, the terminal 10 regards the PSCell and the PCell as CHO candidate cells. Also, the terminal 10 measures the CHO candidate cells and performs an evaluation (CHO evaluation) on the CHO candidate cells as to whether the CHO conditions indicated by the measurement events of the measurement IDs linked to the CHO candidate cells are satisfied (S201).

[0053] When the measurement event set based on the CHO evaluation is satisfied, the terminal 10 determines, based on the target cell for which the measurement event is satisfied, whether to attempt (execute) CHO for either the PSCell or the PCell (S202). When the terminal 10 determines that CHO should be executed for the PSCell (that is, when the measurement event is satisfied at the PSCell), after swapping the cell index of the PSCell and the cell index of the PCell (S203; see A1 shown in FIG. 8), the terminal 10 performs switching between the SCG and the MCG (S204; see A2 shown in FIG. 8). Then, the terminal 10 executes CHO with 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 and switching (exchanging) 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 is satisfied and the terminal 10 determines that CHO should be executed for the PCell instead of the PSCell (that is, when the measurement event is satisfied at the PCell), the terminal 10 executes CHO for the PCell as it is without performing switching of the CHO target cell (S206).

[0055] Alternatively, the terminal 10 may make a determination based on parameters specified (configured, notified) from the base station 20 regarding the implementation of switching of the CHO target cell. The base station 20 may specify the switching of the CHO target cell in terms of cell units or event units. When the implementation of switching of the CHO target cell is not explicitly specified, the terminal 10 may determine not to perform the switching of the CHO target cell.

[0056] When the terminal 10 does not perform the switching of the CHO target cell and the SCG is configured, the terminal 10 may perform procedures related to SCG addition or SCG change targeting 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 such a configuration, the terminal 10 can execute CHO considering not only the PCell belonging to the MCG but also the PSCell belonging to the SCG as the CHO target cell, enabling efficient realization of CHO.

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

[0059] The terminal 10 may notify the base station 20 in advance of capability information (UE Capability) indicating that the own terminal is a terminal corresponding to the second strategy. At this time, the capability information may be in a format that notifies support in terms of terminal units, frequency range (FR) units, or band combination units in addition to terminal unit notifications.

[0060] B. Modification Example The above-described embodiments are for facilitating the understanding of the present invention and are not for limiting the interpretation of the present invention. The flowcharts, sequences, each element included in the embodiments, and their arrangements, materials, conditions, shapes, sizes, etc. described in the embodiments are not limited to those exemplified and can be changed as appropriate.

[0061] <Modification Example 1> Regarding the second measure described above, after the switching of the CHO target cell, the settings related to the original MCG may be released. For example, when the terminal 10 performs the switching between the SCG and the MCG, it may release the settings related to the MCG before switching (for example, all the settings related to the MCG or a part such as the setting of the cell index). The terminal 10 may perform this based on an instruction (setting) from the base station 20 as to whether to release or may make a judgment by itself as one step in the CHO procedure. For example, it may be judged based on the quality of the original MCG (PCell). Also, after switching the settings related to the MCG 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 or not in an RRC message simultaneously with the CHO setting. The terminal 10 may perform SCG deactivation based on the instruction from the base station 20.

[0062] <Modification Example 2> Regarding the second measure described above, if a radio link failure (RLF) occurs or a handover failure (HO failure) occurs while evaluating whether the CHO conditions are satisfied (CHO evaluation), the terminal 10 may reuse the settings related to the PSCell.

[0063] Specifically, the terminal 10 that has detected a radio link failure or a HO failure selects a cell to attempt reconnection according to a predetermined cell selection condition. Here, when the selected cell is a target cell for CHO (i.e., the PSCell specified by the CHO configuration information IF), the terminal 10 may start an RRC reconfiguration procedure that applies the settings related to the PSCell instead of transmitting an RRC message (RRC re-establishment request) related to RRC reconnection. Note that when the terminal 10 reuses the settings related to the PSCell, the terminal 10 may perform the procedures related to the above-described switching, such as swapping the cell index of the PSCell with the cell index of the PCell (i.e., "0"). At this time, a method similar to that of Modification Example 1 may be applied to the procedure of whether to release the settings related to the MCG. Further, the terminal 10 may reuse the settings related to the PSCell as the target cell when an SCG link failure occurs. Further, the terminal 10 may notify the base station 20 of the execution of the RRC reconfiguration procedure that applies the settings related to the PSCell by using a corresponding RRC message (RRC reconfiguration Complete). At this time, the terminal 10 transmits, including in the RRC message, information (for example, first cell information C1, second cell information C2, or first primary cell information PC1, second primary cell information PC2, or identification information indicating a cell group) that can identify at least the PSCell (SCG) applied from the CHO configuration information.

[0064] <Modification Example 3> Regarding the second measure described above, the terminal 10 may regard the PSCell belonging to the 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 via the SCG. As bearer types, three types of radio bearers shown in FIG. 10, namely, MCG bearer, SCG bearer, and Split bearer, are defined. However, the terminal 10 may regard the PSCell as a CHO candidate cell only when the SCG bearer is set. When the terminal 10 is notified of an SCG (PSCell) for which a specific bearer is not set, the terminal 10 may regard the SCG (PSCell) not as a target cell for CHO but as a target cell in the SCG addition procedure or a target cell in the PSCell change procedure.

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

Description of Reference Numerals

[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... transmission unit, 101... reception unit, 102... determination unit, 103... measurement unit, 104... evaluation unit, 105... execution unit, 200... transmission unit, 201... reception 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 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 By referring to the identification information, it is determined whether or not the cell corresponds to the first cell, and the cell determined to be the first cell is regarded as the candidate cell and evaluated; For the first cell, evaluate a condition for conditional handover, and at the same time, for the second cell, evaluate a measurement event based on the configuration of the second cell, and if a measurement event linked to the second cell information is established, start a procedure for changing the secondary group; The execution unit is A terminal device that, when the first cell as the candidate cell belonging to the master cell group satisfies the conditions for conditional handover and the identification information included in the second cell information is different from that belonging to the currently set secondary group, performs a procedure for adding the secondary group or changing the secondary group.

2. The terminal device according to claim 1, 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.

3. The terminal device according to claim 1 or 2, wherein the identification information is information for identifying a cell index or a cell group.

4. The terminal device according to claim 1 or 2, wherein the first cell is a primary cell and the second cell is a primary secondary cell.

5. 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 a candidate cell for conditional handover based on the conditional handover configuration information; and performing 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, In the evaluation step, By referring to the identification information, it is determined whether or not the cell corresponds to the first cell, and the cell determined to be the first cell is regarded as the candidate cell and evaluated; For the first cell, evaluate a condition for conditional handover, and at the same time, for the second cell, evaluate a measurement event based on the configuration of the second cell, and if a measurement event linked to the second cell information is established, start a procedure for changing the secondary group; In the execution step, A wireless communication method, comprising: when the first cell as the candidate cell belonging to the master cell group satisfies the conditions for conditional handover and the identification information included in the second cell information is different from that belonging to the currently set secondary group, performing a procedure for adding the secondary group or changing the secondary group.

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