Terminal device and wireless communication method

Abstract

The present invention relates to a terminal device including: a reception section that receives condition switch 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 evaluation section that evaluates the first cell and the second cell as candidate cells for a condition switch based on the condition switch setting information; and an execution section that executes the condition switch when the candidate cells satisfy a condition for the condition switch, the execution section performing a handover of an object cell for the condition switch when the condition switch is executed for the second cell as the candidate cell, and executing the condition switch for the second cell as the first cell.

Description

TECHNICAL FIELD

[0001] The present application relates to a terminal device and a wireless communication method. BACKGROUND

[0002] In the 3GPP (3rd Generation Partnership Project) which is an international standardization organization, a new radio access technology, that is, NR (New Radio) for a fifth-generation (5G) cellular system is being studied. In the NR, technologies for realizing a variety of services are being studied in comparison with LTE and LTE-Advanced which are fourth-generation (4G) cellular systems.

[0003] For example, in the NR, in order to improve the robustness of handover (HO), CHO (Conditional Handover) which sets in advance the condition of cell information of a handover destination is being studied (refer to Non-Patent Literature 1). By introducing CHO, an effect of improving the handover success probability can be expected.

[0004] PRIOR ART DOCUMENTS

[0005] Non-Patent Literature: 3GPP TS 38.300 SUMMARY

[0006] As the CHO procedure, it is being studied to apply CHO not only to a master cell group (MCG) which includes a primary cell (PCell), but also to a cell group other than the master cell group, that is, a secondary cell group (SCG) which includes a primary secondary cell (PSCell), but 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 scheme has not been proposed.

[0007] The present disclosure is made in view of the above point, and an object thereof is to provide an optimal CHO procedure not only for the MCG but also for the case where the SCG is applied.

[0008] The terminal device of one embodiment of the present application includes a reception unit that receives setting information of a conditional handover, the setting information of the conditional handover 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 of the conditional handover on the basis of the setting information of the conditional handover; and an execution unit that executes the conditional handover when the candidate cells satisfy a condition of the conditional handover, the execution unit performing switching of a target cell of the conditional handover when the conditional handover is executed on the second cell as the candidate cell, and executing the conditional handover with the second cell as the first cell.

[0009] The wireless communication method of one embodiment of the present application is a wireless communication method performed by a terminal device, and includes a reception step of receiving setting information of a conditional handover, the setting information of the conditional handover 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 of the conditional handover on the basis of the setting information of the conditional handover; and an execution step of executing the conditional handover when the candidate cells satisfy a condition of the conditional handover, in the execution step, performing switching of a target cell of the conditional handover when the conditional handover is executed on the second cell as the candidate cell, and executing the conditional handover with the second cell as the first cell.

[0010] According to the present disclosure, it is possible to provide a CHO procedure that is optimal not only for an MCG but also for an SCG. BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 is a diagram for explaining a basic procedure of the present CHO.

[0012] Figure 2 is a diagram illustrating a configuration example of a wireless communication system to which the present embodiment is applied.

[0013] Figure 3 is a diagram illustrating an example of a hardware structure of a terminal and a base station.

[0014] Figure 4 is a diagram illustrating an example of a functional block configuration of a base station.

[0015] Figure 5 is a diagram illustrating an example of a functional block configuration of a terminal.

[0016] Figure 6 is a diagram illustrating CHO setting information to which the first countermeasure is applied.

[0017] Figure 7 is a flowchart illustrating an example of a processing step related to the first countermeasure.

[0018] Figure 8 is a diagram for explaining a CHO procedure involved in the second countermeasure.

[0019] Figure 9 is a flowchart showing an example of a processing step related to the second countermeasure.

[0020] Figure 10 is an explanatory diagram for explaining a bearer type. DETAILED DESCRIPTION

[0021] Embodiments of the present application will be described with reference to the accompanying drawings. In addition, portions having the same or similar structures are denoted by the same reference numerals throughout the respective drawings.

[0022] A. Embodiments

[0023] (Basic procedure of the current CHO)

[0024] First, the terminal 10 measures the quality of the surrounding cells, and starts a measurement reporting procedure to transmit a measurement report message (Measurement Report) including the measurement results of the associated cells to the base station 20-i in a case where a measurement event (event trigger condition) set (designated, notified) in advance in at least one of the measurement target cells (i.e., CHO candidate cells) (Cell-X) is satisfied (in a case where the measurement result satisfies the measurement event), or in a case where a periodic measurement report is set and the set period expires (S10). Figure 1 The basic procedure of the current CHO will be described. In addition, in the following description, the coverage area formed by each base station 20-1, 20-2 will be referred to as a cell. Furthermore, in a case where the base station 20-1 and the base station 20-2 are not distinguished, it will be described as the base station 20.

[0025] The terminal 10 measures the quality of the surrounding cells, and starts a measurement reporting procedure to transmit a measurement report message (Measurement Report) including the measurement results of the associated cells to the base station 20-i in a case where a measurement event (event trigger condition) set (designated, notified) in advance in at least one of the measurement target cells (i.e., CHO candidate cells) (Cell-X) is satisfied (in a case where the measurement result satisfies the measurement event), or in a case where a periodic measurement report is set and the set period expires (S10).

[0026] 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 results, and provides the CHO setting information to the terminal (10) in a case where it is determined that it is necessary. Typically, the base station 20-i requests the HO preparation to the base station 20-i to which the notified CHO candidate cell (Cell-X) belongs, and exchanges information for the terminal 10 to access the base station 20-i with the base station 20 (S11). Then, the base station 20-1 generates an RRC message (RRC Reconfiguration) including the information required for the terminal 10 to evaluate the cell related to the CHO provided from the base station 20-2 (hereinafter referred to as CHO setting information) and the measurement event condition related to the CHO (hereinafter referred to as CHO condition), and transmits it to the terminal 10 (S12).

[0027] The terminal 10 compares (evaluates) whether the CHO candidate cell (Cell-X) satisfies the CHO condition based on the measurement result of the downlink signal and the CHO condition according to the CHO setting information and the CHO condition included in the received RRC message, thereby determining whether to start CHO. The terminal 10, in a case where the CHO candidate cell satisfies the CHO condition, attempts HO to the base station 20-2 (S13) and attempts acquisition of downlink synchronization and random access to the base station 20-2 (S14) as a CHO target cell based on the notified CHO setting information. In a case where the random access procedure to 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 is successful, transmits a message (UE Context Release) indicating deletion of the UE context (terminal association information related to connection) of the terminal 10 to the base station 20-1 (S16), and completes the CHO procedure.

[0028] (Measures for applying CHO to SCG)

[0029] <First measure>

[0030] Since the current CHO procedure is premised on MCG, if the current CHO procedure is directly applied to SCG, the terminal 10 cannot distinguish whether a cell to be evaluated as a CHO candidate cell belongs to the PCell of MCG or the PSCell of SCG. Therefore, even in a case where the base station 20 wants to notify the CHO setting information of the PCell belonging to MCG, the terminal 10 can perform CHO on the PSCell belonging to SCG. That is, according to the conventional procedure, the terminal 10 cannot simultaneously set the PCell belonging to MCG and the PSCell belonging to SCG because it cannot correctly evaluate them. Further, the base station 20 cannot simultaneously set the PCell belonging to MCG and the PSCell belonging to SCG to the terminal 10. To solve this problem, in the first measure, the terminal 10 defines the CHO setting information in such a manner that only the PCell belonging to MCG is regarded as a CHO candidate cell (in other words, the PSCell belonging to SCG is not regarded as an object of CHO candidate cell).

[0031] <Second measure>

[0032] Since the PCell belonging to SCG has the same function as the PCell belonging to MCG (for example, common search space, etc.), in the second measure, 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.

[0033] <system configuration>

[0034] A wireless communication system according to the present embodiment will be described. The wireless communication system according to the present embodiment is targeted for NR, but is not limited thereto. For example, it can be applied to LTE and LTE-Advanced. Furthermore, it can be applied to a wireless communication system in which a part of NR is used. More generally, the present embodiment can be applied to a wireless communication system having at least a terminal and a base station, and this also includes a future wireless communication system. Note that, in the following description, LTE and LTE-Advanced are also referred to as EUTRA, but the meaning is the same.

[0035] A region (coverage area) formed by a base station is referred to as a cell. Furthermore, EUTRA and NR are cellular communication systems constructed by a plurality of cells. The wireless communication system according to the present embodiment can apply either of TDD (Time Division Duplex) and FDD (Frequency Division Duplex), and can apply different modes for each cell.

[0036] Figure 2 Fig. 1 is a diagram showing an example of a configuration of a wireless communication system 1 according to the present embodiment.

[0037] The terminal 10 is wirelessly connected to the base station 20-1 or the base station 20-2, respectively. Hereinafter, in the case where the base station 20-1 and the base station 20-2 are not distinguished, it is described as the base station 20. Furthermore, the terminal 10 can be wirelessly connected 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 can use NR and the base station 20-2 can 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, in the case where it is described as the base station 20, it includes both the eNB and the gNB. Furthermore, the terminal 10 in EUTRA and NR is referred to as a UE (User Equipment). The base station 20 as a gNB is connected to the terminal 10 using a part of a frequency band (BWP: BWP bandwidth part) used by the base station 20. Hereinafter, in the case where it is described as a cell, it includes a BWP.

[0038] The terminal 10 is connected with the base station 20. The terminal 10 can also be connected with the base station 20 using multiple cells (carrier aggregation). In a case where the terminal 10 is connected via multiple base stations 20 (dual connectivity), the base station 20 of the initial connection is referred to as a master node (MN), and the base station 20 of the additional connection is referred to as a secondary node (SN). Among the multiple cells to which the terminal 10 is connected, one or more cells provided by the master node are referred to as a master cell group (MCG). Further, among the multiple cells to which the terminal 10 is connected, one or more cells provided by the secondary node are referred to as a secondary cell group (SCG). Note that the master cell group (MCG) can selectively include one or more secondary cells (SCells) in addition to the primary cell (PCell). Further, the secondary cell group (SCG) can selectively include one or more secondary cells (SCells) in addition to the primary secondary cell (PSCell). Note that the MCG can be referred to as a primary cell group (PCG).

[0039] The base stations 20 are connected through a base station interface. Further, the base stations 20 and the core network device 40 are connected through a core network interface. The base station interface is used for control signals and the like required for handover or cooperative actions among the base stations 20. The core network device 40 has the base stations 20 under its jurisdiction, and mainly handles load control among the base stations 20, call (paging) of the terminal 10, location registration, and the like, which are mobile control.

[0040] The terminal 10 and the base station 20 transceive an RRC (Radio Resource Control) message in an RRC layer. Further, the terminal 10 and the base station 20 transceive a MAC (Medium Access Control) control element (MAC CE) in a MAC layer. The RRC message is transmitted as an RRC PDU (Protocol Data Unit) as a mapped logical channel using a CCCH (Common Control Channel), a DCCH (Dedicated Control Channel), a PCCH (Paging Control Channel), a BCCH (Broadcast Control Channel), or a MCCH (Multicast Control Channel). The MAC CE is transmitted as a MAC PDU (or a MAC subPDU). The MAC subPDU is equivalent to a 8-bit header added to a service data unit (SDU) in the MAC layer, and the MAC PDU includes one or a plurality of MAC subPDUs.

[0041] <Hardware structure>

[0042] Figure 3 Fig. 1 is a diagram showing an example of a hardware structure of the terminal 10 and the base station 20. The terminal 10 and the base station 20 have a processor 11, a memory 12, a storage device 13, a communication device 14 that performs wired or wireless communication, an input device 15 that receives an input operation, an output device 16 that performs output of information, and an antenna 17.

[0043] The processor 11 is, for example, a CPU (Central Processing Unit), and controls the terminal 10 and the base station 20.

[0044] The memory 12 is constituted by, for example, a ROM (Read Only Memory), an EPROM (Erasable Programmable ROM), an EEPROM (Electrically Erasable Programmable ROM), and / or a RAM (Random Access Memory), and the like.

[0045] The storage device 13 is constituted by, for example, a memory such as an HDD (Hard Disk Drive), an SSD (Solid State Drive), and / or an eMMC (embedded Multi Media Card), and the like.

[0046] The communication device 14 is a device that communicates via a wired or / and wireless network, such as a network card, a communication module, and the like. In addition, the communication device 14 can also include an amplifier, an RF (Radio Frequency) device that performs processing related to a wireless signal, and a BB (Base Band) device that performs baseband signal processing.

[0047] The RF device generates a wireless signal to be transmitted from the antenna 17, for example, by performing D / A conversion, modulation, frequency conversion, power amplification, and the like on a digital baseband signal received from the BB device. In addition, the RF device generates a digital baseband signal by performing frequency conversion, demodulation, A / D conversion, and the like on a wireless signal received from the antenna 17 and transmits it to the BB device. The BB device performs processing of converting a digital baseband signal into packet data (for example, an IP packet) and processing of converting an IP packet into a digital baseband signal.

[0048] The input device 15 is, for example, a keyboard, a touch panel, a mouse, and / or a microphone, and the like. The output device 16 is, for example, a display and / or a speaker, and the like.

[0049] <Function Block Configuration>

[0050] (Base Station)

[0051] Figure 4 is a diagram showing an example of a function block configuration of the base station 20. The base station 20 includes a transmission section 200, a reception section 201, and a control section 202. In addition, Figure 4 The main function blocks in the present embodiment are shown. The transmission section 200 and the reception section 201 can be realized, for example, by the communication device 14, or can be realized by the processor 11 executing a program stored in the storage device 13 in addition to the communication device 14. The control section 202 can also be realized by the processor 11 executing a program stored in the storage device 13. In addition, the program can be stored in a storage medium. The storage medium in which the program is stored can also be a non-transitory storage medium that is readable by a computer. The non-transitory storage medium is not particularly limited, and can be, for example, a USB memory or a CD-ROM, or the like.

[0052] The transmission section 200 generates and transmits a signal of a down link to be transmitted to the terminal 10.

[0053] The reception section 201 receives an uplink signal from the terminal 10.

[0054] The control section 202 performs various processes related to the RRC layer, for example. In addition, the control section 202 includes a generation section 203 that generates CHO configuration information (CHO Configuration) indicating a CHO condition, a measurement condition required to start a CHO procedure, and the like. The CHO condition and the CHO configuration information generated by the generation section 203 are included in an RRC message and transmitted from the transmission section 200 to the terminal 10.

[0055] (Terminal)

[0056] Figure 5 is a diagram showing an example of a functional block configuration of the terminal 10. The terminal 10 includes a transmission section 100, a reception section 101, a determination section 102, a measurement section 103, an evaluation section 104, and an execution section 105. In addition, Figure 5 The transmission section 100 and the reception section 101 can be implemented by the communication device 14, for example, or can be implemented by the processor 11 executing a program stored in the storage device 13 in addition to the communication device 14. The determination section 102, the measurement section 103, the evaluation section 104, and the execution section 105 can also be implemented by the processor 11 executing a program stored in the storage device 13. In addition, the program can be stored in a storage medium. The storage medium in which the program is stored can also be a non-transitory computer readable medium. The non-transitory storage medium is not particularly limited and can be a storage medium such as a USB memory or a CD-ROM, for example.

[0057] The transmission section 100 generates and transmits an uplink signal transmitted to the base station 20.

[0058] The reception section 101 receives a downlink signal from the base station 20. In addition, the reception section 101 receives an RRC message including a CHO condition and CHO configuration information from the base station 20. In addition, the received CHO condition and CHO configuration information are stored in the storage device 13.

[0059] The determination section 102 determines a CHO candidate cell to be evaluated from among a plurality of cells on the basis of the CHO configuration information.

[0060] The measurement section 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 can 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).

[0061] The evaluation section 104 evaluates whether the CHO condition is satisfied with respect to the determined CHO candidate cell, based on the time information and the measurement result of the cell quality, and so on. For example, the evaluation section 104 determines that the CHO condition is satisfied in a case where the measurement result of the prescribed cell quality is obtained within the evaluation time indicated by the time information (in a case where a measurement event corresponding to the CHO, which is set in advance, is satisfied).

[0062] The execution section 105 executes the CHO in a case where the CHO candidate cell satisfies the CHO condition.

[0063] <Details of the first countermeasure>

[0064] Figure 6 is a diagram illustrating a CHO configuration information (CHO configuration) IF involved in the first countermeasure.

[0065] The CHO configuration information IF includes at least cell information used for the terminal 10 to determine whether the terminal 10 is a CHO candidate cell. As described above, the CHO configuration information IF can include, for example, the following information. Figure 6As shown, the CHO configuration information IF can include either one or both of first cell information (MCG configuration) Cl 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 Cl 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. In addition, the first cell information Cl and the second cell information C2 can also be structures each including information related to an SCell (a cell that provides radio resources in addition to the PCell), and the like. In addition, the CHO configuration information IF can also include a measurement event, an associated parameter (measurement object), and a measurement ID linking the measurement object and the measurement event as measurement configuration for the CHO candidate cell.

[0066] In the first cell information Cl and the second cell information C2, at least identification information for identifying each cell, and the like is configured. For example, in the first primary cell information PC1 and the second primary cell information PC2, a cell index for identifying the PCell and the PSCell is configured, respectively. As an example, a manner of configuring a cell index "0" (fixed) with respect to the PCell and configuring a cell index "1" (arbitrary) with respect to the PSCell is considered, but is not limited thereto. The base station 20 can also notify the terminal 10 of omission of the cell index. The terminal 10 can regard the cell as the PCell and specify the cell index "0" in a case where the CHO configuration information IF is received with the cell index omitted. In addition, the identification information is not limited to the cell index, and can be, for example, bit information indicating which of the MCG or the SCG it belongs to, can be an additional identifier indicating the MCG (PCell) (information for identifying the MCG), or can be an additional identifier indicating the SCG (PSCell) (information for identifying the SCG).

[0067] Figure 7 is a flowchart showing an example of a process related to the first countermeasure performed by the terminal 10. As a premise, a case where the terminal 10 receives the CHO condition or the CHO configuration information from the base station 20 is assumed.

[0068] The terminal 10 determines CHO candidate cells from among the plurality of cells with reference to the CHO configuration information IF. Specifically, the terminal 10 determines which cell belongs to the MCG or the SCG by comparing the identification information (here, the cell index) included in each of the master cell information PC1, PC2 with the cell index of each cell (S101). Alternatively, the terminal 10 determines which cell belongs to the MCG or the SCG on the basis of the bit information indicating which of the MCG or the SCG. Alternatively, the terminal 10 determines the MCG on the basis of the identifier indicating addition of the MCG (PCell) and determines the other as the SCG. Alternatively, the terminal 10 determines the SCG on the basis of the identifier indicating addition of the SCG (PSCell) and determines the other as the MCG. The terminal 10 regards the PCell belonging to the MCG as a CHO candidate cell (S102), and on the other hand, excludes the PSCell belonging to the SCG from the target of the CHO candidate cell (S103).

[0069] Further, the terminal 10, in a case where the SCG is configured and in a case where the CHO configuration information IF in which the first cell information C1 and the second cell information C2 are configured is received, can start evaluating a measurement event linked with the PSCell belonging to the original SCG and the PSCell (master cell information PC2) indicated (configured) by the second cell information C2, while evaluating the CHO condition in which the PCell (master cell information PC1) is regarded as a CHO target cell. The terminal 10 can start a procedure related to SCG addition or SCG change in a case where the measurement event linked with the PSCell (master cell information PC2) is established.

[0070] Further, in a case where the SCG is configured and in a case where the CHO is established with the PCell belonging to the MCG as the target, in a case where 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 are different from the currently configured SCG, the terminal 10 can perform a procedure related to SCG addition or SCG change. In a case where 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 are the same as the currently configured SCG, the terminal 10 can maintain the SCG without starting a change procedure. At this time, the terminal 10 can deactivate the SCG (SCG deactivation).

[0071] According to this configuration, the terminal 10 can realize efficient CHO without evaluating whether the PSCell belonging to the SCG satisfies the CHO condition.

[0072] In addition, the terminal 10 can also notify the base station 20 in advance of capability information (UE Capability) indicating that this terminal is a terminal corresponding to the first countermeasure. At this time, the capability information includes a form in which support is notified in units of a frequency range (Frequency Range: FR) or a band combination in addition to notification in units of a terminal.

[0073] <Details of the second countermeasure>

[0074] Figure 8 is an explanatory diagram for explaining a CHO procedure involved in the second countermeasure, and the upper part shows the CHO configuration information IF before the change, and the lower part shows the CHO configuration information IF after the change.

[0075] In the second countermeasure, not only the PCell belonging to the MCG but also the PSCell belonging to the SCG are regarded as CHO candidate cells, and further, setting change of the CHO configuration information IF at the time of execution of CHO targeting the PSCell and the like are performed.

[0076] Figure 9 is a flowchart showing an example of a processing procedure related to the second countermeasure performed by the terminal 10. As a premise, it is assumed that the terminal 10 receives the CHO condition or the CHO configuration information from the base station 20.

[0077] The terminal 10 specifies at least one or both of the MCG and the SCG by the CHO configuration information IF. The terminal 10 regards the PSCell and the PCell as CHO candidate cells on the basis of the received CHO configuration information IF. In addition, the terminal 10 measures the CHO candidate cells, and performs evaluation (CHO evaluation) of whether the CHO condition indicated by the measurement event of the measurement ID linked to the CHO candidate cell is satisfied for the CHO candidate cell (S201).

[0078] The terminal 10 judges which of the PSCell or the PCell to attempt (execute) CHO on the basis of the cell on which the measurement event is established, in the case where the measurement event is established on the basis of the CHO evaluation (S202). In the case where the terminal 10 judges that CHO should be executed on the PSCell (i.e., in the case where the measurement event is established in the PSCell), the terminal 10 performs switching of the SCG and the MCG after alternation of the cell index of the PSCell and the cell index of the PCell (S203; refer to A1 shown in Figure 8 Figure 8 ​The A2) is illustrated. Then, the terminal 10 performs CHO with respect to the PSCell belonging to the SCG as the PCell belonging to the MCG (S205). Further, the switching (swapping) of the cell index of the alternate PSCell and the cell index of the PCell between the SCG and the MCG is referred to as "CHO object cell switching".

[0079] On the other hand, in a case where the measurement event set based on the CHO evaluation is satisfied and it is determined that CHO should be performed with respect to the PCell rather than the PSCell (i.e., in a case where the measurement event is satisfied in the PCell), the terminal 10 does not perform the CHO object cell switching and directly performs CHO with respect to the PCell (S206).

[0080] Further, the terminal 10 can determine the implementation of the CHO object cell switching based on a parameter specified (set, notified) from the base station 20. The base station 20 can specify the CHO object cell switching in units of cells and in units of events. In a case where the implementation of the CHO object cell switching is not explicitly specified, the terminal 10 can determine not to implement the CHO object cell switching.

[0081] In a case where the CHO object cell switching is not implemented and the SCG is set, the terminal 10 can implement a procedure related to SCG addition or SCG change with respect to the PSCell included in the second cell information C2 of the CHO setting information IF based on the evaluation result of the set measurement event.

[0082] According to this configuration, the terminal 10 can not only regard the PCell belonging to the MCG as the CHO object cell but also regard the PSCell belonging to the SCG as the CHO object cell to perform CHO, and thus efficient CHO can be achieved.

[0083] Further, the terminal 10 can notify the base station 20 of the changed CHO setting information IF after switching the above-described CHO object cell. Alternatively, the terminal 10 can notify the base station 20 of information indicating that the switching is implemented.

[0084] The terminal 10 can notify the base station 20 of capability information (UE Capability) indicating that the terminal is a terminal corresponding to the second countermeasure in advance. At this time, the capability information includes a form of notifying support in units of frequency ranges (Frequency Range: FR) or in units of band combinations in addition to the notification in units of terminals.

[0085] B. Modified Example

[0086] The above-described embodiments are for easy understanding of the present application and are not intended to limit the explanation of the present application. The flowcharts, timing charts, elements and their arrangement, materials, conditions, shapes, and dimensions, and the like described in the embodiments are not limited to the illustrated contents and can be appropriately changed.

[0087] <Modification 1>

[0088] With regard to the above-described second countermeasure, the setting related to the original MCG can be released after the CHO target cell is switched. For example, the terminal 10 can release the setting related to the MCG before the switching (for example, all of the settings related to the MCG, or a part of the settings such as the setting of the cell index) once the SCG and the MCG are switched. The terminal 10 can release based on the instruction (setting) from the base station 20, or can judge by itself as one step in the CHO procedure. For example, the judgment can be made based on the quality of the original MCG (PCell). Further, all of the cells included in the SCG can be deactivated (SCG deactivation) after the setting related to the MCG is switched to the SCG. The base station 20 can instruct the terminal 10 whether to perform the SCG deactivation by the RRC message at the same time as the CHO setting. The terminal 10 can perform the SCG deactivation based on the instruction from the base station 20.

[0089] <Modification 2>

[0090] With regard to the above-described second countermeasure, during the evaluation of whether the CHO condition is satisfied (CHO evaluation), in a case where a radio link failure (RLF) occurs, or in a case where a HO failure occurs, the terminal 10 can reuse the setting related to the PSCell.

[0091] Specifically, upon detecting a radio link failure or HO failure, terminal 10 selects a cell to attempt reconnection according to the prescribed cell selection criteria. Here, if the selected cell is the target cell for the CHO (i.e., the PSCell specified by the CHO setting information IF), terminal 10 can also initiate an RRC reconfiguration process applying the settings related to the PSCell instead of sending an RRC re-establishment request related to RRC reconnection. Furthermore, when reusing settings related to the PSCell, terminal 10 can also perform handover-related procedures such as alternating the cell index of the PSCell to the cell index of the PCell (i.e., "0"). In this case, the process of releasing settings related to the MCG can be performed using the same method as in Variation 1. Additionally, terminal 10 can reuse the settings related to the PSCell as the target cell when an SCG link failure occurs. In addition, terminal 10 can also use the corresponding RRC message (RRC reconfiguration Complete) to notify base station 20 of the implementation of the RRC reconfiguration process that applied the settings related to PSCell. In this case, terminal 10 will include at least the information of the applied PSCell (SCG) that can be determined according to the CHO setting information (e.g., first cell information C1, second cell information C2, or first primary cell information PC1, second primary cell information PC2, or identification information indicating the cell group) in the RRC message.

[0092] <Variation Example 3>

[0093] Regarding the second countermeasure mentioned above, terminal 10 can consider PSCells belonging to the SCG as CHO candidate cells only if base station 20 has configured a specific radio bearer as the communication path for user data via the SCG. As a bearer type, it is defined as follows: Figure 10 The diagram shows three types of radio bearers: MCG bearer, SCG bearer, and split bearer. However, terminal 10 can also consider a PSCell as a CHO candidate cell only if an SCG bearer is configured. When terminal 10 is notified that an SCG (PSCell) without a specific bearer configured, it can consider that SCG (PSCell) as the target cell in the process of adding an SCG or changing a PSCell, rather than the target cell for CHO.

[0094] <Summary>

[0095] According to the present disclosure described above, it is possible to provide an optimal CHO procedure not only for the MCG but also for the SCG case. Therefore, the technology according to the present disclosure can contribute to achieving the target 9 “Industry, innovation and infrastructure” of the sustainable development goals (SDGs).

[0096] 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 section, 101 … reception section, 102 … determination section, 103 … measurement section, 104 … evaluation section, 105 … execution section, 200 … transmission section, 201 … reception section, 202 … control section, 203 … generation section.

Claims

1. A terminal device, comprising: The receiving unit receives condition switching setting information, which includes: first cell information of the first cell belonging to the primary cell group and second cell information of the second cell belonging to the secondary cell group. The evaluation department, based on the conditional handover setting information, evaluates the first cell as a first candidate cell for conditional handover and evaluates the second cell as a second candidate cell for conditional handover; and The execution unit, for the primary cell group, executes conditional handover when the first candidate cell meets the conditions for conditional handover; for the secondary cell group, it executes conditional handover when the second candidate cell meets the conditions for conditional handover. Without performing the conditional handover on the secondary cell group, the execution unit performs the steps of adding the second cell or changing the second cell for the secondary cell group.

2. The terminal device according to claim 1, wherein, It also includes a determining unit, which determines whether to consider the second cell as the second candidate cell for evaluation. When the determining unit determines that the second cell will be considered as the second candidate cell for evaluation... The evaluation department will evaluate the second cell as the second candidate cell. The execution unit performs conditional handover for the secondary cell group when the second candidate cell meets the conditions for conditional handover.

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

4. A wireless communication method performed by a terminal device, comprising: The receiving step involves receiving conditional switching setting information, which includes: first cell information of the first cell belonging to the primary cell group and second cell information of the second cell belonging to the secondary cell group. The evaluation step involves evaluating the first cell as a first candidate cell for conditional handover and evaluating the second cell as a second candidate cell for conditional handover, based on the handover condition setting information. The execution steps are as follows: For the primary cell group, if the first candidate cell meets the conditions for conditional handover, a conditional handover is performed; for the secondary cell group, if the second candidate cell meets the conditions for conditional handover, a conditional handover is performed. In the execution steps, without performing the conditional handover on the secondary cell group, the steps of adding the second cell or changing the second cell are performed on the secondary cell group.

Images