Terminal device and wireless communication system

Abstract

A terminal device according to the present invention acquires, from a handover-origin base station device to which the terminal device is connected, first information that associates an uplink beam configuration and a configuration grant pertaining to the resource of an uplink shared channel for an LTM candidate cell and information that pertains to the LTM implementation condition associated with the LTM candidate cell. The terminal device then transmits an uplink reference signal to an LTM candidate cell handover-destination base station device in response to an instruction for transmitting an uplink reference signal and, on the basis of the result of measuring the uplink reference signal, acquires second information pertaining to an uplink beam which should be used by a terminal device that has been determined by the LTM candidate cell. Furthermore, when the LTM implementation condition is met, the terminal device, without starting a random access procedure, uses the first information and the second information to identify a configuration grant used for uplink transmission at the time of LTM implementation and uses the configuration grant to perform the uplink transmission with respect to a handover-destination candidate base station device.

Description

Terminal device and wireless communication system

[0001] The present disclosure relates to a terminal device and a wireless communication system.

[0002] In a mobile communication system, as a terminal device moves, a handover is performed to switch the cell (base station device) to which the terminal device is connected. Conventionally, after receiving a handover instruction from a base station device, the terminal device performs a process of establishing a connection by establishing synchronization and setting up in the cell to which the connection is to be switched. This process of switching the connection takes a certain amount of time, and the terminal device cannot communicate user data while this process is being performed.

[0003] In contrast, in the technique described in Non-Patent Document 1, a handover source base station provides a terminal device with communication parameters in the radio resource control (RRC) layer for connection with another handover destination base station before the actual handover is performed. Then, the handover source base station transmits a Layer 1 or Layer 2 command to the terminal device at the timing when the handover is to be performed, instructing the terminal device to switch cells. Upon receiving the command, the terminal device executes a random access procedure with the handover destination base station, thereby completing the handover without subsequent configuration processing in the RRC layer. This cell switching technology is called LTM (L1L2 Triggered Mobility) and is intended to suppress degradation of communication efficiency related to handover.

[0004] 3GPP (registered trademark) Contribution, R2-2209255

[0005] In the handover process using LTM disclosed in Non-Patent Document 1, the terminal device needs to receive a Cell Switch command from the base station device.

[0006] However, if the terminal device cannot receive the Cell Switch Command, the terminal device cannot initiate handover processing on its own, and must execute cell search processing and reconnection processing after detecting an RLF (Radio Link Failure). For this reason, the LTM technology of Non-Patent Document 1 has a problem in that it cannot shorten the communication interruption time and cannot speed up the handover processing.

[0007] In view of such circumstances, the present disclosure proposes a technology that enables a terminal device to perform LTM before receiving a Cell Switch command, thereby speeding up handover processing and shortening the interruption time.

[0008] In order to solve the above problem, the present disclosure provides, as an example, a terminal device having a conditional LTM function, which communicates with a plurality of base station devices while switching connection destinations, the terminal device comprising: a storage device for storing a program related to handover; and a processor for reading the program from the storage device and executing handover processing, wherein the processor performs the following steps from a connected handover source base station device: acquiring first information associating an uplink beam setting with a configuration grant related to resources of an uplink shared channel of an LTM candidate cell, and information on conditions for LTM implementation associated with a handover destination base station device of the LTM candidate cell; transmitting an uplink reference signal to the handover destination base station device of the LTM candidate cell in response to an uplink reference signal transmission instruction from the handover source base station device; and acquiring, from the handover source base station device, second information related to an uplink beam to be used by the terminal device, which is determined by the handover destination base station device of the LTM candidate cell based on a measurement result of the uplink reference signal; We propose a terminal device that performs the following processes: a process of determining whether the conditions for implementing LTM associated with the base station device that is a candidate for handover destination are satisfied; a process of identifying a configuration grant to be used for uplink transmission from the first information and the second information when implementing LTM, without starting a random access procedure, if the conditions for implementing LTM are satisfied; and a process of performing uplink transmission to the base station device that is a candidate for handover destination, using the configuration grant to be used for the uplink transmission.

[0009] According to the technology of the present disclosure, handover processing can be performed even when a terminal device cannot receive a Cell Switch command, thereby realizing faster processing and shorter interruption times.

[0010] Other features and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings, in which the same or similar elements are designated by the same reference numerals.

[0011] The accompanying drawings are included in and constitute a part of the specification, illustrate embodiments of the present invention, and are used together with the description to explain the principles of the present invention. Fig. 1 is a diagram showing an example of a schematic configuration of a wireless communication system according to this embodiment. Fig. 2 is a diagram showing an example of a schematic configuration of a base station device 100 according to this embodiment. Fig. 3 is a diagram showing an example of a schematic configuration of a terminal device 200 according to this embodiment. Fig. 4 is a diagram for explaining sequence example 1 of handover processing according to this embodiment. Fig. 5 is a diagram for explaining sequence example 2 of handover processing according to this embodiment. Fig. 6 is a diagram for explaining sequence example 3 of handover processing according to this embodiment.

[0012] Hereinafter, the embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the scope of the invention as claimed, and not all combinations of features described in the embodiments are necessarily essential to the invention. Two or more of the features described in the embodiments may be combined in any desired manner. Furthermore, the same reference numerals are used to designate identical or similar components, and redundant descriptions will be omitted.

[0013] This embodiment discloses a technique for performing LTM (however, RACH is not performed) to a candidate cell before a terminal device receives a Cell Switch Command from a handover source base station device. The technique according to this embodiment is not limited to this, but can be applied to, for example, wireless communication in the frequency band FR2 (24.25 GHz to 52.6 GHz).

[0014] <System Schematic Configuration Example> Fig. 1 is a diagram showing a schematic configuration example of a wireless communication system according to this embodiment. The wireless communication system is a cellular communication system configured in accordance with a cellular communication standard such as the fifth generation (5G) of the Third Generation Partnership Project (3GPP (registered trademark)) or its successor standard. The wireless communication system includes a plurality of base station devices (base station device 100_1, base station device 100_2, ...) and a terminal device 200.

[0015] In Fig. 1 , a terminal device 200 is about to move from within the range of a cell formed by a base station device (handover source base station device) 100_1 into the range of a cell formed by a base station device (handover destination base station device) 100_2. At this time, the terminal device 200 performs handover to switch the connection destination base station device from the handover source base station device 100_1 to the handover destination base station device 100_2. Note that, although Fig. 1 shows only the handover destination base station device 100_2 as a handover destination candidate, in reality, there may be multiple handover destination candidates (handover destination base station devices 100_3, 100_4, ..., 100_k, ...).

[0016] <Regarding Conditions (Events) for Implementing LTM> In the LTM according to the present embodiment, the terminal device 200 starts connection processing and cell switching processing with the handover destination base station device 100_2 or other handover destination candidate base station devices (handover destination base station device 100_k: k = 3, 4, ...) without receiving a command (cell switch command) instructing cell switching from the handover source base station device 100_1. As an example, the terminal device 200 acquires, from the handover source base station device 100_1, information on conditions (events) for starting the cell switching processing and on cell switching processing to be performed when the condition is determined to be met, and then determines whether the condition is met and performs cell switching processing according to the condition. For example, it is assumed that condition 1 is associated with cell switching processing to the handover destination base station device 100_2, and condition 2 is associated with cell switching processing to another handover destination candidate base station device (handover destination base station device 100_3). In this case, when it is determined (confirmed) that condition 1 is met, the terminal device 200 executes a cell switching process to the base station device 100_2. On the other hand, when it is determined (confirmed) that condition 2 is met, the terminal device 200 starts a cell switching process to another handover destination candidate base station device (handover destination base station device 100_3). A plurality of pieces of information regarding the conditions and the cell switching process are included in an RRC (Radio Resource Control) layer message RRC Reconfiguration, and a condition set for each candidate cell is included in condExecutionCond. In addition, communication parameters used for communication with the handover destination candidate base station device are included in condLTMReconfig. These pieces of information are provided from the handover source base station device 100_1 to the terminal device 200.

[0017] <Specific Examples of the Conditions (Events)> As conditions (events) for implementing LTM, it is conceivable to set conditions related to the radio quality of the communicating cell or candidate cell (CondEventA3, CondEventA4, CondEventA5, CondEventD1, CondEventT1), for example. In this case, for example, RRC Reconfiguration includes information such as condReconfigId (condition setting identifier) ​​= 1, condExecutionCond = condEventA4 (threshold = threshold 1), and condLTMReconfig = communication parameters for candidate cell 1, and condReconfigId = 2, condExecutionCond = condEventA4 (threshold = threshold 2), and condLTMReconfig = communication parameters for candidate cell 2, and this information is provided to the terminal device 200.

[0018] In addition, it has been considered that the base station device 100 sets information (MeasId) for setting a report of an event occurrence to the terminal device 200 in condExecutionCond. Here, MeasId is associated with an identifier measObjectId used by the terminal device to identify a measurement target of wireless quality and an identifier reportConfigId used by the terminal device to identify the timing of reporting to the base station device. The identifier measObjectId is associated with the NR or LTE frequency that the terminal device 200 should measure. The identifier reportConfigId is associated with the timing of reporting to the base station device 100, for example, the condEventA4 event and a threshold value related to that event. In this way, the terminal device 200 can recognize the wireless quality event to be determined from the MeasId set in condExecutionCond.

[0019] <Example of Internal Configuration of Base Station Device> Figure 2 is a diagram showing an example of the schematic configuration of the base station device 100. The base station device 100 includes, for example, a processor 101, a storage device 102, a ROM (Read Only Memory) 103, a RAM (Random Access Memory) 104, and a communication device 105. The processor 101 is a computer including one or more processing circuits, such as a general-purpose CPU (Central Processing Unit) or an ASIC (Application Specific Integrated Circuit), and performs overall processing of the device and each of the above-mentioned processes by reading and executing programs stored in the storage device 102 or ROM 103. The ROM 103 is a read-only memory that stores information such as programs related to the processes executed by the base station device 100 and various parameters. The RAM 104 functions as a workspace when the processor 101 executes programs and is also a random access memory that stores temporary information. The storage device 102 may be, for example, a removable external storage device. The communication device 105 may be, for example, a circuit for wireless communication of 5G or its successor standards. While FIG. 2 shows one communication device 105, the base station device 100 may include multiple communication devices. For example, the base station device 100 may have a wireless communication device for 5G and a successor standard, and a common antenna for these devices. The base station device 100 may also have separate antennas suitable for each standard. The base station device 100 may also include a wired communication device used when communicating with other base station devices or nodes in the core network. The base station device 100 may have a separate communication device 105 for each of multiple available frequency bands, or may have a common communication device 105 for at least some of these frequency bands.

[0020] The processor 101 reads a handover-related program stored in the memory device 102 or the ROM 103 and expands it into internal memory (not shown), thereby generating an RRC setting unit 1011, an RA instruction unit 1012, a handover instruction unit 1013, an inter-base station communication unit 1014, a TA maintenance and management unit 1015, a PUCCH / PDCCH communication unit 1016, and an uplink beam information determination unit 1017.

[0021] FIG. 2 illustrates only functions particularly related to this embodiment, and does not illustrate various other functions that the base station device 100 may have. For example, the base station device 100 naturally has other functions that base station devices compliant with 5G or its successor standards generally have. Furthermore, the functional blocks in FIG. 2 are illustrated schematically, and each functional block may be realized by being integrated or further subdivided. Furthermore, each function in FIG. 2 may be realized, for example, by the processor 101 executing a program stored in the ROM 103 or the storage device 102, or may be realized, for example, by a processor within the communication device 105 executing predetermined software. Note that the details of the processing performed by each functional unit will not be described here, and only their general functions will be outlined. In addition, the following describes an outline of the operation in a system consisting of a handover source base station device 100_1, one handover destination base station device 100_2 which is an LTM transition destination candidate, and a terminal device 200, but if there are multiple LTM transition destination candidates, the handover source base station device 100_1 and the terminal device 200 perform similar operations between each candidate handover destination base station device 100_k.

[0022] The RRC setting unit 1011 of the handover source base station device 100_1, for example, configures the RRC layer for the connected terminal device 200. The RRC setting unit 1011 transmits a handover request to other candidate base station devices 100 (such as the handover destination base station device 100_2 or the handover destination base station device 100_3) that provide neighboring cells, acquires communication setting information (communication parameters) therefrom, and notifies the terminal device 200 of the communication setting information and the above-mentioned LTM implementation conditions (communication parameters of each candidate cell and LTM implementation conditions) via an RRC layer message. In this case, the above-mentioned communication setting information (communication parameters) also includes information required when the terminal device 200 executes a random access procedure (such as a sequence for generating an RA preamble and information on radio resources used to transmit the RA preamble). In this embodiment, the RRC layer message is an RRC Configuration message. Then, the RRC setup section 1011 receives the RRC Configuration Complete message from the terminal device 200, and thereby performs connection processing setup between the terminal device 200 and another base station device 100 (handover destination base station device 100_2).

[0023] The RA instruction unit 1012 instructs the terminal device 200, for which the RRC layer configuration has been completed, to transmit an RA preamble to another base station device 100 (handover destination base station device 100_2) that is a candidate for the handover destination. Here, the instruction to transmit the RA preamble includes a sequence for generating an RA preamble that is unique to the terminal device 200 and a group of sequences that can also be used by other terminal devices 200 that are attempting to connect to other base station devices 100, and also includes information on radio resources used for transmitting the RA preamble. The RA instruction unit 1012 can instruct the currently connected terminal device 200 to transmit an RA preamble to the handover destination (candidate) base station device 100_2, for example, by a physical downlink control channel (PDCCH) order. In addition, the RA instruction unit 1012 can, if necessary, instruct the terminal device 200 to retransmit the RA preamble, or, if the RA preamble is configured to be transmitted repeatedly, can transmit an instruction to the terminal device 200 to stop transmitting the RA preamble.

[0024] The handover instruction unit 1013 of the handover source base station device 100_1 instructs the terminal device 200 to execute handover. The handover instruction unit 1013 of the handover source base station device 100_1 notifies (transfers) the TA value acquired from the handover destination base station device 100_2 (acquired by the inter-base station communication unit 1014 as described later) to the terminal device 200 before transmitting a Cell Switch Command.

[0025] Furthermore, the handover destination base station device 100_2 measures a sounding reference signal (SRS) directly transmitted from the terminal device 200, and the handover instruction unit 1013 of the handover source base station device 100_1 notifies the terminal device 200 of a transmission configuration indicator (TCI) designated based on the measurement result. Here, the TCI is information designating an uplink beam (UL beam) to be used by the terminal device 200.

[0026] Furthermore, the handover instruction unit 1013 of the handover source base station device 100_1 transmits, to the terminal device 200, a Cell switch command including information such as a cell identifier capable of identifying the handover destination base station device 100_2, for example.

[0027] The inter-base station communication unit 1014 of the base station device 100_1 communicates with each handover destination candidate base station device (such as the handover destination base station device 100_2 or 100_3) (for example, communication via a dedicated wired line). The inter-base station communication unit 1014 can, for example, notify the handover destination base station device 100_2, which is the destination of the RA preamble, to cause the connected terminal device 200 to transmit the RA preamble. The inter-base station communication unit 1014 is also used, for example, to receive information for the RA procedure in the handover destination candidate base station device (the handover destination base station device 100_2). The inter-base station communication unit 1014 can also receive, for example, a message (message 2 or message 4) to be transmitted from the handover destination base station device 100_2 to the terminal device 200 in the RA procedure. Furthermore, the handover source base station 100_1 can acquire the TA value calculated in the handover destination base station device 100_2 via the inter-base station communication unit 1014. Note that the signal received in the inter-base station communication unit 1014 is transferred to the terminal device 200 via, for example, the RA instruction unit 1012. Furthermore, the inter-base station communication unit 1014 of the handover source base station device 100_1 acquires uplink beam (UL Beam) information (described later) to be used by the terminal device 200, which is notified from the handover destination base station device 100_2.

[0028] The TA maintenance management unit 1015 of the handover source base station 100_1 manages the TA value to be used when the terminal device 200 transmits an uplink signal to the handover destination base station device 100_2. The TA maintenance management unit 1015 can set, for example, an expiration date and an update period for the TA value, and can instruct the terminal device 200 to retransmit an RA preamble so that the TA value is updated when the expiration date expires or the update period arrives. The TA maintenance management unit 1015 can also notify the terminal device 200 of the SRS setting in the handover destination base station device 100_2 and have the terminal device 200 transmit an SRS using the SRS setting, thereby updating the TA value. The terminal device 200 can also acquire the TA value via the TA maintenance management unit 1015 of the handover destination base station device 100_2. In this case, the base station device 100_2 can transmit an instruction to transmit an RA preamble and an instruction to transmit an SRS to the terminal device 200.

[0029] The PUCCH / PDCCH communication unit 1016 operates, for example, when the base station device 100 becomes the handover destination base station device 100_2. As described above, when the handover destination base station device 100_2 notifies the handover source base station device 100_1 of the TA value, it can start receiving the PUCCH and transmitting the PDCCH between it and the terminal device 200.

[0030] For example, when the base station device 100 becomes the handover destination base station device 100_2, the uplink beam information determination unit 1017 measures the uplink reference signal (SRS) transmitted by the terminal device 200, and based on the measurement results, identifies the uplink beam (UL Beam) information that the terminal device 200 should use.

[0031] Furthermore, for example, when the base station device 100 becomes the handover destination base station device 100_2, the uplink beam information determination unit 1017 may acquire from the handover source base station device 100_1 the measurement results of the downlink reference signal from the handover destination base station device 100_2 measured by the terminal device 200, and may identify beam (UL Beam) information that the terminal device 200 should use based on the measurement results.

[0032] <Example of Internal Configuration of Terminal Device> Fig. 3 is a diagram showing an example of the schematic configuration of the terminal device 200. The terminal device 200 includes, for example, a processor 201, a storage device 202, a ROM (Read Only Memory) 203, a RAM (Random Access Memory) 204, a communication device 205, an input device 206, and an output device 207. The processor 201 is a computer including one or more processing circuits such as a general-purpose CPU (Central Processing Unit) or an ASIC (Application Specific Integrated Circuit), and performs the overall processing of the device and each of the above-mentioned processes by reading and executing programs stored in the storage device 202 or ROM 203. The ROM 203 is a read-only memory that stores information such as programs related to the processing executed by the terminal device 200 and various parameters. The RAM 204 functions as a workspace when the processor 201 executes a program and is a random access memory that stores temporary information. The storage device 202 is, for example, a removable external storage device. The communication device 205 is, for example, a circuit for wireless communication of 5G or its successor standard. While FIG. 3 illustrates one communication device 205, the terminal device 200 may include multiple communication devices. For example, the terminal device 200 may have a wireless communication device for 5G and a successor standard, and a common antenna for these devices. The terminal device 200 may also include a communication device compliant with a wireless communication standard other than the cellular communication standard, such as a wireless local area network (LAN) or Bluetooth (registered trademark). Furthermore, the terminal device 200 may have separate antennas suitable for each standard. The terminal device 200 may have separate communication devices 205 for each of multiple available frequency bands, or a common communication device 205 for at least some of these frequency bands.

[0033] The input device 206 can be configured with, for example, a touch panel or a numeric keypad, and is used when a user performs a predetermined operation or inputs desired information. The output device 207 can be configured with, for example, a display device, and in this embodiment, displays information indicating the communication status, information indicating the success or failure of handover, etc.

[0034] The processor 201 reads a handover-related program stored in the storage device 202 or the ROM 203 and expands it in an internal memory (not shown), thereby generating an RRC setting unit 2011, an RA (random access) execution unit 2012, an LTM implementation condition determination unit 2015, a handover processing unit 2013, a timer control unit 2016, and a reference signal measurement / notification unit 2014. Note that FIG. 3 only shows functions particularly related to this embodiment, and various other functions that the terminal device 200 may have are not shown. For example, the terminal device 200 naturally has other functions that terminal devices compliant with 5G or its successor standards generally have. Furthermore, the functional blocks in FIG. 3 are shown schematically, and the respective functional blocks may be realized as an integrated unit or may be further subdivided.

[0035] The RRC setup unit 2011 performs connection setup processing with the handover destination (candidate) base station device 100_2 by receiving an RRC layer message from the connected handover source base station device 100_1. Note that the RRC setup unit 2011 holds the setting of the connected handover source base station device 100_1 and the settings of a plurality of handover destination candidate base station devices (handover destination base station devices 100_k: k=2, 3, 4, ..., n) in parallel.

[0036] The RA execution unit 2012 receives an instruction to transmit an RA preamble from the handover source base station device 100_1. The instruction to transmit the RA preamble is issued by a PDCCH order. Note that the RA execution unit 2012 can also receive, for example, an instruction to retransmit the RA preamble or an instruction to stop transmitting the RA preamble. Furthermore, in response to receiving the instruction to transmit the RA preamble, the RA execution unit 2012 transmits the RA preamble to the handover destination (candidate 1) base station device 100_2. Here, information on a sequence for generating the RA preamble and radio resources for receiving the RA preamble in the handover destination base station device (candidate 1) 100_2 is acquired from the currently connected handover source base station device 100_1. Note that the information on the sequence and radio resources may be acquired from system information transmitted by the handover destination base station device 100_2.

[0037] The handover processing unit 2013 acquires the TA value and an uplink reference signal (SRS) transmission instruction of the handover destination base station device 100_2 from the handover source base station device 100_1 (for example, received by MAC CE, downlink control information (DCI), or RAR), and directly transmits the uplink reference signal (SRS) to the handover destination (candidate 1) base station device 100_2. As described above, the handover destination base station device 100_2 measures the SRS, determines a transmission configuration indicator (TCI) based on the measurement result, and notifies the handover source base station device 100_1 of the TCI. Furthermore, the handover processing unit 2013 receives TCI (beam information) from the handover source base station device 100_1 using the MAC CE or the physical downlink control channel (PDCCH) / downlink control information (DCI). Note that the beam information is information that identifies the TCI state and spatial relationship (information that indicates the relationship between the UL beam and the DL beam, and is used when the TCI state is not supported).

[0038] Furthermore, in response to receiving a Cell Switch command from the currently connected handover source base station device 100_1, the handover processing unit 2013 changes the connection destination to the handover destination base station device 100_2. When the received Cell Switch command notifies the terminal device 200 of allocation of uplink radio resources in the handover destination base station device 100_2, the terminal device 200 can immediately transmit an uplink signal using the radio resources.

[0039] The reference signal measurement and notification unit 2014 measures a downlink reference signal from the handover destination base station device 100_2 (one of the LTM transfer target candidate cells) and notifies the handover source base station device 100_1 of the measurement result. When there are multiple LTM transfer target candidate cells, the reference signal measurement and notification unit 2014 measures downlink reference signals from all corresponding handover destination base station devices 100_k and notifies the handover source base station device 100_1 of each measurement result.

[0040] Meanwhile, the LTM implementation condition determination unit 2015 determines whether the LTM implementation conditions associated with the plurality of candidate cells notified from the handover source base station device 100_1 are satisfied. A handover destination to be executed is uniquely determined depending on whether the conditions are satisfied. For example, the LTM implementation conditions are determined such that a threshold included in the communication parameters is set low for a candidate cell in a good (uncongested) communication state, and a threshold is set high for a candidate cell in a bad (congested) communication state.

[0041] When the LTM implementation condition determination unit 2015 determines (confirms) that the LTM implementation conditions are met, the handover processing unit 2013 performs handover processing, not including RA execution processing, for a candidate cell (handover destination base station device 100_k) that satisfies the conditions (details will be described later). For example, when it is determined that the LTM implementation conditions associated with the handover destination base station device 100_2 of candidate 1 are met, the handover processing unit 2013 can autonomously execute handover processing in the same way as when the Cell Switch Command is received, even if the Cell Switch Command cannot be received. This eliminates the need to execute reconnection processing starting from cell search, enabling rapid cell switching.

[0042] When the LTM implementation condition determination unit 2015 determines that the communication situation satisfies the above-mentioned LTM implementation conditions, the handover processing unit 2013 specifies a configuration grant to be used for uplink transmission in accordance with the acquired uplink beam information at a timing based on the TA value, and transmits uplink data, for example, RRCReconfiguration Complete, to the handover destination base station device 100_2 using an uplink shared channel resource (PUSCH) according to the configuration grant. Then, the handover processing unit 2013 receives a UE Contention Resolution Identity MAC CE or a C-RNTI addressed PDCCH from the handover destination base station device 100_2.

[0043] The timer control unit 2016 controls the activation and deactivation of various timers (such as T304). For example, the timer (T304) is activated when the conditions for performing the LTM are confirmed to be met and the LTM execution is decided, and is deactivated when the UE Contention Resolution Identity MAC CE or the C-RNTI addressed PDCCH is received from the destination base station apparatus 100.

[0044] <Operation when RLF is detected> As described above, the terminal device 200 starts the cell switching process when it determines (confirms) that the conditions for performing LTM specified by the handover source base station device 100_1 are met. On the other hand, when the terminal device 200 detects an RLF (radio link failure), it may start the cell switching process even if the conditions are not met.

[0045] When providing the terminal device 200 with information (communication parameters) regarding the conditions for performing LTM and the cell switching process associated with the conditions for each candidate cell, the handover source base station device 100_1 also provides information indicating attemptCondReconfig=True / False. When detecting a radio link failure (RLF), the terminal device 200 searches for and selects a cell to be used for communication. When attemptCondReconfig, which is notified together with the information regarding the cell switching process, is True, the terminal device 200 determines whether the cell selected after the search is a handover destination candidate base station device (handover destination base station device 100_k) designated in the cell switching process. When determining that the selected cell is not the handover destination base station device designated in the cell switching process, the terminal device 200 performs reconnection processing as before. If the cell selected after the search is a handover destination base station device (one of the notified candidate cells) designated in the cell switching process, the cell switching process is initiated even if the conditions are not met. This can shorten the interruption time. Even in this case, if the cell selected after the search is a handover destination candidate base station device designated in the cell switching process, that is, an LTM candidate cell, the configuration grant (uplink resource and uplink beam information) corresponding to the selected downlink reference signal is identified based on the radio quality of the downlink reference signal (SSB or CSI-RS) of the LTM candidate cell and the UL beam information table described below, and can be used for uplink transmission when LTM is implemented. Also, if uplink beam information for the selected cell is received before RLF detection, it is possible to identify the configuration grant to be used for uplink transmission from the uplink beam information received from the base station device, rather than the radio quality of the downlink reference signal (SSB or CSI-RS) of the LTM candidate cell, and use it for uplink transmission when LTM is implemented.

[0046] <Handover Processing Sequence Example 1> FIG. 4 is a diagram illustrating sequence example 1 of handover processing according to this embodiment. The sequence illustrated in FIG. 4 is an example, and each procedure can be modified as described above. For example, FIG. 4 illustrates an example in which a unique sequence is notified to the terminal device 200 as a sequence for generating an RA preamble to be transmitted to the handover destination base station device 100_2. However, this may be replaced with the above-described procedure in which a set of sequences usable by multiple terminal devices 200 is notified. Note that in the example of FIG. 4, it is assumed that a connection is established between the handover source base station device 100_1 and the terminal device 200. Furthermore, although FIG. 4 illustrates only the handover destination base station device 100_2 as a base station device of an LTM transfer destination candidate cell, in reality, multiple handover destination base station devices 100_k of LTM transfer destination candidate cells exist.

[0047] In each step, the operation is performed by each processing unit (such as the RRC setting unit 1011), but since each processing unit is a function realized by the processor 101 or 201 of the base station device 100 or the terminal device 200, the operation may be performed by the processor 101 or 201. In the following description, the processing units of the handover source base station device 100_1 are referred to as an RRC setting unit 1011_1, an RA instruction unit 1012_1, a handover instruction unit 1013_1, an inter-base station communication unit 1014_1, a TA maintenance and management unit 1015_1, and a PUCCH / PDCCH communication unit 1016_1. Further, the respective processing units of the handover destination base station device 100_2 are denoted as an RRC setting unit 1011_2, an RA instruction unit 1012_2, a handover instruction unit 1013_2, an inter-base station communication unit 1014_2, a TA maintenance management unit 1015_2, and a PUCCH / PDCCH communication unit 1016_2. Furthermore, in the following respective steps, various communications are actually performed by the respective processing units of the base station device and the terminal device controlling the communication device 105 and the communication device 205.

[0048] (i) Step S401: The inter-base station communication unit 1014_1 of the handover source base station device 100_1 transmits a HANDOVER REQUEST message to the inter-base station communication unit 1014_2 of the handover destination base station device 100_2 forming an adjacent cell that is a candidate for the handover destination of the terminal device 200, or to another base station device (another candidate cell: the inter-base station communication unit 1014_k (k=3, 4, . . ) of the handover destination base station device 100_k).

[0049] (ii) Step S402: Upon receiving the HANDOVER REQUEST message, the inter-base station communication unit 1014_2 of the handover destination (candidate 1) base station device 100_2 returns a HANDOVER REQUEST ACK message including information on communication parameters to be used when the terminal device 200 connects to the handover source base station device 100_1. The communication parameters include CG (Configured Grant) setting information including information on beam settings, parameters for executing an RA (Random Access) procedure, radio resources (frequency and time resources) to be used, etc. in the handover destination base station device 100_2. Other candidate cell base station devices similarly provide communication parameters to the handover source base station device 100_1.

[0050] (iii) Step S403 The RRC configuration unit 1011_1 of the handover source base station device 100_1 notifies the terminal device 200 of an LTM Configuration message including the above-mentioned communication parameters and the like acquired from the handover destination base station device 100_2. At this time, the RRC configuration unit 1011_1 also provides the terminal device 200 with a condition (event: LTM implementation condition) that enables the implementation of LTM before the terminal device 200 receives a Cell Switch Command. This process eliminates the need for the terminal device 200 to perform RRC layer configuration processing after receiving a handover to the handover destination base station device 100_2 from the RA command unit 1012_1. Note that when there are multiple handover destination (candidate) base station devices, a similar configuration process is executed for each of them.

[0051] The RRC setting unit 2011 of the terminal device 200 receives, via the LTM Configuration included in the RRC Reconfiguration message, information (UL Beam information table) associating information on synchronization signal (SS) / physical broadcast channel (PBCH) blocks (SSB: Synchronization Signal Block) transmitted from a base station device of each LTM transfer target candidate cell (e.g., the handover destination base station device 100_2), information on downlink reference signals: e.g., SSB indexes, configured grant (CG) setting information (CG occasion) related to uplink resources, and uplink beam information (TCI).

[0052] For example, when the terminal device 200 receives TCI=1 from the handover destination base station device 100_2 via the handover base station device 100_1, it uses the uplink resource and uplink beam information (configuration grant) corresponding to the associated SSB index=1 and the first CG setting information (CG Occasion), and when TCI=2, it uses the uplink resource and uplink beam information (configuration grant) corresponding to the SSB index=2 and the second CG setting information to perform uplink transmission to the handover destination base station device 100_2 after performing LTM. Note that multiple TCIs may be associated with one CG setting information. In this case, for example, when TCI=1 or TCI=2 is received, it is possible to instruct the terminal device 200 to use uplink resources and uplink beam information (configuration grant) corresponding to the associated SSB index=1 and the first CG configuration information (CG Occasion), and when TCI=3 or TCI=4 is received, it is possible to instruct the terminal device 200 to use uplink resources and uplink beam information (configuration grant) corresponding to the associated SSB index=2 and the second CG configuration information. This makes it possible to reduce the CG configuration information (CG Occasion) set in the terminal device 200 and save uplink radio resources allocated to each terminal device when congestion is high, etc.

[0053] (iv) Step S404 The RA instruction unit 1012_1 of the handover source base station device 100_1 transmits a PDCCH order to the terminal device 200, instructing the terminal device 200 to transmit an RA preamble to the handover destination base station device 100_2 (specifying a base station device of any appropriate candidate cell when there are multiple candidate cells). Here, this instruction (PDCCH order) can include information specifying a sequence to be used by the terminal device 200 to generate an RA preamble and a radio resource from which the RA preamble is to be transmitted. Note that the radio resource from which the RA preamble is to be transmitted may be identified based on, for example, system information in the handover destination base station device 100_2 transmitted from the handover destination base station device 100_2 and measured by the terminal device 200. In other words, this information does not need to be acquired from the currently connected handover source base station device 100_1. Furthermore, the sequence to be used when generating the RA preamble may be identified in advance. In one example, in step S403, information on this sequence may be notified to the terminal device 200.

[0054] (v) Step S405 The RA execution unit 2012 of the terminal device 200 transmits an RA preamble to the handover destination base station device 100_2 in accordance with the instruction. The purpose of executing the RA procedure is to suppress deterioration of communication efficiency during handover. When the RA preamble is transmitted, the inter-base station communication unit 1014_1 of the handover source base station device 100_1 may notify the handover destination base station device 100_2 that the terminal device 200 plans to transmit an RA preamble. At this time, the inter-base station communication unit 1014_1 of the handover source base station device 100_1 can notify the handover destination base station device 100_2 of information on the sequence used by the terminal device 200 to generate the RA preamble. This enables the RA instruction unit 1012_2 of the handover destination base station device 100_2 to detect the RA preamble transmitted by the terminal device 200. Note that this processing is just one example, and the HANDOVER REQUEST in step S401 may implicitly notify that the terminal device 200 plans to transmit an RA preamble. Also, in this case, the handover destination base station device 100_2 may specify, in the HANDOVER REQUEST ACK in step S402, the sequence that the terminal device 200 should use to generate an RA preamble. Note that these are just one example, and information on the sequence that the terminal device 200 should use to generate an RA preamble may be shared between the handover source base station device 100_1 and the handover destination base station device 100_2 by other messages.

[0055] (vi) Step S406: The TA maintenance unit 1015_2 of the handover destination base station device 100_2 calculates a TA value based on the RA preamble transmitted from the terminal device 200. Then, the inter-base station communication unit 1014_2 notifies the handover source base station device 100_1 of the calculated TA value. Note that this TA value may be managed by both the handover source base station device 100_1 and the handover destination base station device 100_2, or may be managed by one of them. This TA value may be acquired from the handover destination base station device 100_2, for example, in response to the handover source base station device 100_1 deciding to execute handover of the terminal device 200. For example, the inter-base station communication unit 1014_1 of the handover source base station device 100_1 notifies the handover destination base station device 100_2 of the execution of handover. In response to the notification, the TA maintenance unit 1015_1 acquires the TA value from the handover destination base station device 100_2. Note that, when there are a plurality of handover destination (candidate) base station devices (the handover destination base station devices 100_2 to 100_k), the handover source base station device 100_1 may acquire the TA values ​​from all the handover destination (candidate) base station devices.

[0056] At this point, the terminal device 200 has not yet started handover to the handover destination base station device 100_2. In this state, the handover processing unit 2013 of the terminal device 200 continuously measures the radio signal from the handover destination base station device 100_2 (for example, SSB measurement) and notifies the connected handover source base station device 100_1 of the measurement result. The handover instruction unit 1013 of the handover source base station device 100_1 can determine whether to perform handover according to the measurement result.

[0057] (vii) Step S407 The handover instruction unit 1013_1 of the handover source base station device 100_1 notifies the terminal device 200 of the TA value acquired from the handover destination base station device 100_2 and transmits an uplink reference signal (SRS) transmission instruction. Note that, when there are multiple handover destination (candidate) base station devices (handover destination base station devices 100_2 to 100_k), the handover source base station device 100_1 notifies the terminal device 200 of the TA values ​​of all the handover destination (candidate) base station devices. Note that the TA value notification and the uplink reference signal (SRS) transmission instruction can also be notified to the terminal device 200 at different timings.

[0058] (viii) Step S408 The handover processing unit 2013 of the terminal device 200 transmits an uplink reference signal (SRS) to the handover destination base station device 100_2.

[0059] The uplink beam information determination unit 1017_2 of the handover destination base station device 100_2 measures the SRS transmitted by the terminal device 200 and determines (specifies) the uplink beam (UL beam) to be used when the terminal device 200 communicates with the handover destination base station device 100_2.

[0060] (ix) Step S409: The uplink beam information determination unit 1017_2 of the handover destination base station device 100_2 specifies, by a Transmission Configuration Indicator (TCI), uplink beam information to be used in the terminal device 200. Then, the inter-base station communication unit 1014_2 of the handover destination base station device 100_2 provides the TCI to the handover source base station device 100_1.

[0061] (x) Step S410: The handover instruction unit 1013 of the handover source base station device 100_1 notifies the terminal device 200 of the TCI acquired from the handover destination base station device 100_2, for example, by using a medium access control element (MAC CE) or downlink control information (DCI).

[0062] (xi) Step S411: The handover instruction unit 1013_1 of the handover source base station device 100_1 transmits a Cell Switch Command to the terminal device 200. The Cell Switch Command can be transmitted by using, for example, a medium access control element (MAC CE) or downlink control information (DCI).

[0063] When the handover processing unit 2013 of the terminal device 200 is able to receive the Cell Switch Command, PUSCH resources are allocated by the handover destination base station device 100_2, and the handover is completed. Then, the terminal device 200 becomes able to transmit user data to the handover destination base station device 100_2 using the allocated PUSCH resources. Note that the terminal device 200 has already executed the RA procedure as described above. Therefore, when the terminal device 200 is able to receive the Cell Switch Command, it is not necessary to execute the RA procedure again, and the terminal device 200 can immediately transmit user data to the handover destination base station device 100_2 using the designated radio resources.

[0064] Furthermore, when the Cell Switch Command is received, the handover processing unit 2013 of the terminal device 200 may transmit an acknowledgement (ACK) or the like to the handover source base station device 100_1. Furthermore, when the Cell Switch Command is received, the handover processing unit 2013 may switch the connection destination to the handover destination base station device 100_2 and transmit an ACK, an RRCReconfigurationComplete, or the like to the handover destination base station device 100_2 by using the allocated uplink radio resources. Then, the inter-base station communication unit 1014 of the handover destination base station device 100_2 can transfer the acknowledgement to the handover source base station device 100_1. As a result, the handover source base station device 100_1 can recognize that the terminal device 200 has switched its connection destination to the handover destination base station device 100_2, and can discard the context information of the terminal device 200, for example.

[0065] On the other hand, when the handover instruction unit 1013_1 of the handover source base station device 100_1 does not receive an Ack from the terminal device 200, the handover instruction unit 1013_1 may retransmit the Cell Switch Command to ensure that the handover is performed reliably.

[0066] (xii) Step S412: The LTM implementation condition determination unit 2015 of the terminal device 200 determines (confirms) whether the above-mentioned LTM implementation conditions are met (satisfied). Specifically, the LTM implementation condition determination unit 2015 determines whether the LTM implementation conditions corresponding to each LTM transfer target candidate cell notified from the handover source base station device 100_1 are satisfied.

[0067] (xiii) Step S413: When the LTM implementation condition determination unit 2015 of the terminal device 200 confirms that the conditions for performing LTM are met, the handover processing unit 2013 determines to perform cell switching to the handover destination base station device 100_k of the candidate cell corresponding to the met conditions. Note that, when there are multiple candidate cells that meet the conditions for performing LTM, for example, the candidate cell with the shortest distance between the terminal device 200 and each handover destination base station device 100_k may be selected as the switching destination, or the candidate cell with the lowest congestion level may be selected as the switching destination.

[0068] (xiv) Step S414 If it is confirmed that the conditions for implementing LTM are met, the timer control unit 2016 of the terminal device 200 starts a timer (T304).

[0069] (xv) Step S415: The handover processing unit 2013 of the terminal device 200 identifies, at a timing based on the TA value, the uplink beam (UL beam) specified in the TCI and a configuration grant to be used for uplink transmission from the UL beam information table, and transmits uplink data, for example, RRCReconfiguration Complete, to the handover destination base station device 100_2 using the uplink beam (UL beam) specified in the TCI by using resources of the uplink shared channel (PUSCH) according to the identified configuration grant.

[0070] (xvi) Step S416 The handover destination base station apparatus 100_2 that has received the RRCReconfigurationComplete transmits a UE Contention Resolution Identity MAC CE or a C-RNTI addressing PDCCH to the terminal apparatus 200 using the PUCCH / PDCCH communication unit 1016_2.

[0071] (xvii) Step S417 When the UE Contention Resolution Identity MAC CE or the C-RNTI addressing PDCCH is received, the timer control unit 2016 of the terminal device 200 stops the timer (T304) started in step S414.

[0072] After the cell switch, the terminal device 200 may retain information condLTMReconfig related to the cell switch process that was not executed. By retaining information related to the cell switch process that was not executed by the terminal device 200 even after the cell switch, it is possible to eliminate the need to receive new condLTMReconfig from the base station device after the cell switch. Furthermore, information related to whether or not to retain information condLTMReconfig related to the cell switch process that was not executed may be notified to the terminal device 200 from the handover source base station device 100_1 before the cell switch.

[0073] As described above, when the terminal device 200 performs handover from the handover source base station device 100_1 to the handover destination base station device 100_2, the period during which user data communication is not possible (instantaneous interruption time) can be shortened. Furthermore, since there is no need to transmit an RA preamble again to the handover destination base station device 100_2 when performing LTM, and uplink data can be transmitted using the TA value, the designated uplink beam, and the configuration grant, processing can be faster than when an RA preamble is transmitted. This makes it possible to provide, for example, communication services that require low latency and high reliability. Furthermore, shortening the period during which user data communication is not possible (instantaneous interruption time) makes it possible to suppress a decrease in wireless communication efficiency.

[0074] <Handover Processing Sequence Example 2> Fig. 5 is a diagram for explaining sequence example 2 of handover processing according to the present embodiment. In sequence example 2 of Fig. 5 as well, it is assumed that a connection is established between the handover source base station device 100_1 and the terminal device 200. Also in sequence example 2 of Fig. 5 as well, as in Fig. 4, only the handover destination base station device 100_2 is shown as a base station device of an LTM transfer target candidate cell, but in reality there are multiple handover destination base station devices 100_k of LTM transfer target candidate cells.

[0075] In sequence example 2 of Figure 5, steps S407 and S409 are partially changed from sequence example 1 of Figure 4 to steps S407' and S409', and step S408 is changed to steps S408-1 and S408-2, but the other steps are the same as those in sequence example 1 of Figure 4, so their explanation will be omitted.

[0076] (i) Step S407' The handover instruction unit 1013_1 of the handover source base station device 100_1 notifies the terminal device 200 of the TA value acquired from the handover destination base station device 100_2, and transmits a downlink reference signal (e.g., SSB or CSI-RS) measurement result transmission instruction (no uplink reference signal (SRS) transmission instruction is sent). Note that, when there are multiple handover destination (candidate) base station devices (handover destination base station devices 100_2 to 100_k), the handover source base station device 100_1 notifies the terminal device 200 of the TA values ​​of all the handover destination (candidate) base station devices.

[0077] (ii) Step S408-1: The base station device 100_k of each LTM transfer target candidate cell constantly outputs a downlink reference signal (e.g., SSB or CSI-RS) at a constant period. The handover processing unit 2013 of the terminal device 200 measures each downlink reference signal (SRS) and transmits the measurement result to the handover source base station device 100_1.

[0078] (iii) Step S408-2 The inter-base station communication unit 1014_1 of the handover source base station apparatus 100_1 transmits the downlink reference signal (SSB or CSI-RS) measurement result acquired from the terminal apparatus 200 to the handover destination base station apparatus 100_2.

[0079] The uplink beam information determination unit 1017_2 of the handover destination base station device 100_2 determines (identifies) the uplink beam (UL Beam) to be used when the terminal device 200 communicates with the handover destination base station device 100_2 based on the downlink reference signal measurement results by the terminal device 200 (downlink beam information and uplink beam information are paired (due to duality), and if the downlink beam can be identified, the uplink beam can be identified).

[0080] <Handover Processing Sequence Example 3> Fig. 6 is a diagram for explaining sequence example 3 of handover processing according to the present embodiment. In the example of Fig. 6, as in Fig. 4, it is assumed that a connection is established between the handover source base station device 100_1 and the terminal device 200. Also in Fig. 6, only the handover destination base station device 100_2 is shown as a base station device of an LTM transfer target candidate cell, but in reality, there are a plurality of handover destination base station devices 100_k of LTM transfer target candidate cells.

[0081] (i) Steps S601 to S606 The processes in steps S601 to S606 are the same as those in steps S401 to S406 in FIG.

[0082] (ii) Step S607: The handover instruction unit 1013_1 of the handover source base station device 100_1 notifies the terminal device 200 of the TA value acquired from the handover destination base station device 100_2 (unlike step S407, an uplink reference signal (SRS) transmission instruction is not transmitted). Note that, when there are multiple handover destination (candidate) base station devices (handover destination base station devices 100_2 to 100_k), the handover source base station device 100_1 notifies the terminal device 200 of the TA values ​​of all the handover destination (candidate) base station devices.

[0083] (iii) Step S608: The handover instruction unit 1013_1 of the handover source base station device 100_1 transmits a Cell Switch Command to the terminal device 200. The Cell Switch Command can be transmitted by using, for example, a medium access control element (MAC CE) or downlink control information (DCI).

[0084] (iv) Step S609 The process of step S609 is the same as step S412 in FIG.

[0085] (v) Step S610 The reference signal measurement and notification unit 2014 of the terminal device 200 detects and measures downlink reference signals (SSB or CSI-RS) output from each handover destination base station device 100_k, and selects the reference signal with the best communication quality or the reference signal found first (a signal with a predetermined quality (threshold) or higher). Then, based on the information (UL Beam information table) acquired in the LTM Configuration, the reference signal measurement and notification unit 2014 determines a configuration grant (uplink resource and uplink beam information) corresponding to the index of the selected downlink reference signal (SSB).

[0086] (vi) Step S611: When the reference signal measurement and notification unit 2014 of the terminal device 200 determines the configuration grant, the handover processing unit 2013 determines to execute cell switching processing to the handover destination base station device 100_k of the candidate cell corresponding to the condition match. Note that, when there are multiple candidate cells that match the condition for performing LTM, for example, the candidate cell with the shortest distance between the terminal device 200 and each handover destination base station device 100_k may be selected as the switching destination, or the candidate cell with the lowest congestion level may be selected as the switching destination.

[0087] (xii) Steps S612 to S615 The processes in steps S612 to S615 are the same as those in steps S414 to S417 in FIG.

[0088] <Summary of the embodiment> (i) Terminal device according to the first embodiment A terminal device having a conditional LTM function, which communicates with a plurality of base station devices while switching connection destinations, comprising: a storage device for storing a program related to handover; and a processor for reading the program from the storage device and executing handover processing, wherein the processor: acquires, from a connected handover source base station device, first information associating an uplink beam setting with a configuration grant related to resources of an uplink shared channel of an LTM candidate cell, and information on conditions for LTM implementation associated with a handover destination base station device of the LTM candidate cell; transmits an uplink reference signal to the handover destination base station device of the LTM candidate cell in response to an uplink reference signal transmission instruction from the handover source base station device; and acquires, from the handover source base station device, second information related to an uplink beam to be used by the terminal device, which is determined by the handover destination base station device of the LTM candidate cell based on a measurement result of the uplink reference signal; A terminal device that executes the following processes: a process of determining whether the conditions for implementing LTM associated with the base station device that is a handover destination candidate are satisfied; a process of identifying a configuration grant to be used for uplink transmission from the first information and the second information when implementing LTM, without starting a random access procedure, if the conditions for implementing LTM are satisfied; and a process of performing uplink transmission to the base station device that is a handover destination candidate, using the configuration grant to be used for the uplink transmission.(ii) Terminal device according to a second embodiment A terminal device having a conditional LTM function, which communicates with a plurality of base station devices while switching connection destinations, comprising: a storage device for storing a program related to handover; and a processor for reading the program from the storage device and executing handover processing, wherein the processor: acquires, from a connected handover source base station device, first information associating a configuration grant related to resources of an uplink shared channel of an LTM candidate cell with an uplink beam configuration, and information on conditions for LTM implementation associated with a handover destination base station device of the LTM candidate cell; notifies the handover source base station device of the measurement result of a downlink reference signal from the LTM candidate cell; acquires, from the handover source base station device, second information related to the uplink beam to be used by the terminal device, which is determined by the handover destination base station device of the LTM candidate cell; and determines whether the conditions for LTM implementation associated with the handover destination candidate base station device are satisfied. When the conditions for implementing LTM are satisfied, a terminal device executes the following processes when implementing LTM: identifying a configuration grant to be used for uplink transmission from the first information and the second information without starting a random access procedure; and performing uplink transmission to the base station device that is a candidate for handover destination using the configuration grant to be used for the uplink transmission.(iii) Terminal device according to a third embodiment A terminal device having a conditional LTM function, which communicates with a plurality of base station devices while switching connection destinations, comprising: a storage device for storing a program related to handover; and a processor for reading the program from the storage device and executing handover processing, wherein the processor: acquires, from the connected handover source base station device, beam setting related information relating a downlink reference signal of an LTM candidate cell to a setting grant related to an uplink shared channel resource, and information on an LTM implementation condition associated with the handover destination base station device of the LTM candidate cell; determines whether the LTM implementation condition associated with the handover destination candidate base station device is satisfied; and, if the LTM implementation condition is satisfied, specifies a setting grant related to an uplink shared channel resource to be used in the handover destination base station device of the LTM candidate cell using the measurement result of the downlink reference signal of the LTM candidate cell and the beam setting related information; and performing a process of performing uplink transmission to the base station device that is a handover destination candidate by using a configuration grant related to resources of the uplink shared channel without starting a random access procedure when LTM is implemented.

[0089] In the above-described embodiment, the handover source and handover destination base station devices are described as providing one cell, but these base station devices may provide multiple cells. Furthermore, in the above description, the term "base station device" may be read as "cell." That is, in the above description, terms such as "handover source base station device" are used, but these may be read as "handover source cell." Note, however, that the base station device providing each cell is the entity that transmits and receives signals. In the above example, the terminal device transmits an SRS. However, a separate uplink reference signal different from the SRS may be used to determine the uplink beam to be used by the terminal device. (iv) The functions of this embodiment and each example can also be realized by software program code. In this case, a storage medium on which the program code is recorded is provided to a system or device, and the computer (or CPU or MPU) of the system or device reads the program code stored in the storage medium. In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiment, and the program code itself and the storage medium on which it is stored constitute the present disclosure. Examples of storage media for supplying such program code include flexible disks, CD-ROMs, DVD-ROMs, hard disks, optical disks, magneto-optical disks, CD-Rs, magnetic tapes, non-volatile memory cards, and ROMs.

[0090] Furthermore, an operating system (OS) running on a computer may perform some or all of the actual processing based on instructions in the program code, and the functions of the above-described embodiments may be realized by this processing.Furthermore, after the program code is read from a storage medium and written to memory on the computer, a CPU of the computer may perform some or all of the actual processing based on instructions in the program code, and the functions of the above-described embodiments may be realized by this processing.

[0091] Furthermore, the program code of the software that realizes the functions of the embodiments and each example may be distributed via a network and stored in a storage means such as a hard disk or memory of the system or device, or in a storage medium such as a CD-RW or CD-R, so that when used, the computer (or CPU or MPU) of the system or device reads and executes the program code stored in the storage means or storage medium.

[0092] The processes and techniques described herein are not inherently related to any specific device and can be implemented by a combination of components. Various types of general-purpose devices can also be added. A dedicated device may be constructed to perform the functions of this embodiment and each example. Various functions can also be formed by appropriately combining multiple components disclosed in this embodiment and each example. For example, some components may be omitted from all the components shown in the embodiment and each example, or components from different examples may be appropriately combined.

[0093] Although specific examples are described in this disclosure, they are in all respects for the purpose of explanation (understanding the technology of the present disclosure) and not for the purpose of limitation. Those skilled in the art will recognize that there are many combinations of hardware, software, and firmware suitable for implementing the technology of the present disclosure. For example, the software described can be implemented in a wide variety of programming or scripting languages, such as assembler, C / C++, Perl, Shell, PHP, Java (registered trademark), etc.

[0094] Furthermore, in the above-described embodiment, the control lines and information lines are those that are considered necessary for the explanation, and not all control lines and information lines in the product are necessarily shown. All components may be interconnected.

[0095] In addition, other implementations of the present disclosure will be apparent to those skilled in the art from consideration of the present embodiments and examples. The specification and examples are exemplary only, with the scope and spirit of the present disclosure being indicated by the following claims.

[0096] This application claims priority based on Japanese Patent Application No. 2023-170293, filed on September 29, 2023, the entire contents of which are incorporated herein by reference.

Claims

1. A terminal device having an L1L2 Triggered Mobility (LTM) function and communicating with a plurality of base station devices while switching a connection destination, comprising: a storage device for storing a program related to handover; and a processor for reading the program from the storage device and executing handover processing, wherein the processor: acquires, from a connected handover source base station device, first information associating a setting grant related to resources of an uplink shared channel of an LTM candidate cell with an uplink beam setting, and information on conditions for LTM implementation associated with a handover destination base station device of the LTM candidate cell; in response to an uplink reference signal transmission instruction from the handover source base station device, transmits an uplink reference signal to the handover destination base station device of the LTM candidate cell; and acquires, from the handover source base station device, second information related to an uplink beam to be used by the terminal device, which is determined by the handover destination base station device of the LTM candidate cell based on a measurement result of the uplink reference signal. A terminal device that executes the following processes: a process of determining whether a condition for implementing LTM associated with a base station device that is a handover destination candidate is satisfied; a process of identifying a configuration grant to be used for uplink transmission from the first information and the second information when LTM is implemented, without starting a random access procedure, when the condition for implementing LTM is satisfied; and a process of performing uplink transmission to the base station device that is a handover destination candidate, using the configuration grant to be used for the uplink transmission.

2. A terminal device having an L1L2 Triggered Mobility (LTM) function and communicating with a plurality of base station devices while switching connection destinations, comprising: a storage device for storing a program related to handover; and a processor for reading the program from the storage device and executing handover processing, wherein the processor performs the following steps from a connected handover source base station device: acquiring first information associating a setting grant related to resources of an uplink shared channel of an LTM candidate cell with an uplink beam setting, and information on conditions for LTM implementation associated with a handover destination base station device of the LTM candidate cell; notifying the handover source base station device of a measurement result of a downlink reference signal from the LTM candidate cell; acquiring from the handover source base station device second information related to an uplink beam to be used by the terminal device determined by the handover destination base station device of the LTM candidate cell; and determining whether the conditions for LTM implementation associated with a handover destination candidate base station device are satisfied. A terminal device that, when the conditions for implementing the LTM are satisfied, executes a process of identifying a configuration grant to be used for uplink transmission from the first information and the second information without starting a random access procedure when implementing the LTM, and a process of performing uplink transmission to the base station device that is a candidate for the handover destination using the configuration grant to be used for the uplink transmission.

3. The terminal device according to claim 1 or 2, wherein the processor executes a process of acquiring a timing advance value of a handover destination base station device of the LTM candidate cell from the handover source base station device before performing LTM.

4. The terminal device according to claim 3, wherein the processor executes a process for determining the timing of the uplink transmission to the handover destination base station device using the timing advance value.

5. The terminal device according to claim 4, wherein the processor transmits an RRCReconfiguration Complete to the handover target candidate base station device at the determined timing using a configuration grant to be used for the uplink transmission.

6. A terminal device having a conditional L1L2 Triggered Mobility (LTM) function and communicating with a plurality of base station devices while switching connection destinations, comprising: a storage device for storing a program related to handover; and a processor for reading the program from the storage device and executing handover processing, wherein the processor: acquires, from a connected handover source base station device, beam setting related information relating a downlink reference signal of an LTM candidate cell to a setting grant related to an uplink shared channel resource, and information on an LTM implementation condition associated with a handover destination base station device of the LTM candidate cell; determines whether the LTM implementation condition associated with a handover destination candidate base station device is satisfied; and, if the LTM implementation condition is satisfied, specifies a setting grant related to an uplink shared channel resource to be used in the handover destination base station device of the LTM candidate cell using the measurement result of the downlink reference signal of the LTM candidate cell and the beam setting related information; and performing a process of performing uplink transmission to the base station device that is a handover destination candidate, using a configuration grant related to resources of the uplink shared channel, without starting a random access procedure when LTM is performed.

7. The terminal device of claim 6, wherein the processor, when detecting a radio link failure, executes a process of identifying a configuration grant for the resources of the uplink shared channel using the measurement result of the downlink reference signal and the beam setting related information, and a process of performing uplink transmission to the base station device that is a candidate for handover destination using the configuration grant for the resources of the uplink shared channel without initiating a random access procedure when LTM is implemented.

8. The terminal device according to claim 6, wherein the downlink reference signal is an SSB or a CSI-RS.

9. The terminal device of claim 6, wherein the beam setting related information is information associating the downlink reference signals of multiple LTM candidate cells with configuration grants regarding resources of multiple uplink shared channels, and the processor associates multiple downlink reference signals with one of the configuration grants and stores the beam setting related information in the memory device.

10. The terminal device according to claim 6, wherein the processor executes a process of acquiring a timing advance value of a handover destination base station device of the LTM candidate cell from the handover source base station device before performing LTM.

11. The terminal device according to claim 10, wherein the processor executes a process for determining the timing of the uplink transmission to the handover destination base station device using the timing advance value.

12. The terminal device according to claim 11, wherein the processor transmits an RRCReconfiguration Complete to the handover target candidate base station device at the determined timing, using a configuration grant related to resources of the uplink shared channel.

13. A wireless communication system comprising a plurality of base station devices and at least one terminal device having an L1L2 Triggered Mobility (LTM) function, which executes handover from a handover source base station device to a handover destination candidate base station device, wherein the handover source base station device to which the terminal device is connected executes the following processes: transmitting, to the terminal device, first information associating a setting grant related to resources of an uplink shared channel of an LTM candidate cell with an uplink beam setting, and information on conditions for LTM implementation associated with the handover destination base station device of the LTM candidate cell; transmitting an uplink reference signal transmission instruction to the terminal device; and transmitting, to the terminal device, second information related to an uplink beam to be used by the terminal device; and the terminal device executes the following processes: transmitting an uplink reference signal to the handover destination base station device of the LTM candidate cell in response to the uplink reference signal transmission instruction from the handover source base station device; A wireless communication system which performs the following processes: acquiring, from the handover source base station device, the second information determined by the handover destination base station device of the LTM candidate cell based on the measurement result of the uplink reference signal; determining whether the condition for implementing LTM associated with the handover destination candidate base station device is satisfied; identifying a configuration grant to be used for uplink transmission from the first information and the second information when implementing LTM when the condition for implementing LTM is satisfied, without starting a random access procedure; and performing uplink transmission to the handover destination candidate base station device using the configuration grant to be used for the uplink transmission.

14. A wireless communication system comprising a plurality of base station devices and at least one terminal device having an L1L2 Triggered Mobility (LTM) function, which executes handover from a handover source base station device to a handover destination candidate base station device, wherein the handover source base station device to which the terminal device is connected executes a process of transmitting to the terminal device first information associating a setting grant related to an uplink shared channel resource of an LTM candidate cell with an uplink beam setting, and information on a condition for LTM implementation associated with the handover destination base station device of the LTM candidate cell, and a process of transmitting to the terminal device second information related to an uplink beam to be used by the terminal device determined by the handover destination base station device of the LTM candidate cell, wherein the terminal device executes a process of notifying the handover source base station device of a measurement result of a downlink reference signal from the LTM candidate cell, and a process of determining whether the condition for LTM implementation associated with the handover destination candidate base station device is satisfied, When the conditions for implementing the LTM are satisfied, a process of identifying a configuration grant to be used for uplink transmission from the first information and the second information without starting a random access procedure during implementation of the LTM, and a process of performing uplink transmission to the base station device that is a candidate for the handover destination using the configuration grant to be used for the uplink transmission.

15. A wireless communication system comprising a plurality of base station devices and at least one terminal device having an L1L2 Triggered Mobility (LTM) function, which executes handover from a handover source base station device to a handover destination candidate base station device, wherein the handover source base station device to which the terminal device is connected executes a process of transmitting to the terminal device beam setting related information that associates a downlink reference signal of an LTM candidate cell with a setting grant related to an uplink shared channel resource and information on an LTM implementation condition associated with the handover destination base station device of the LTM candidate cell, the terminal device executes a process of determining whether the LTM implementation condition associated with the handover destination candidate base station device is satisfied, and if the LTM implementation condition is satisfied, a process of specifying a setting grant related to an uplink shared channel resource to be used in the handover destination base station device of the LTM candidate cell using the measurement result of the downlink reference signal of the LTM candidate cell and the beam setting related information, and performing a process of performing uplink transmission to the base station device that is a handover destination candidate, using a configuration grant related to resources of the uplink shared channel, without starting a random access procedure when LTM is performed.

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