Base station device executing handover with improved efficiency, terminal device, and control method

Abstract

To improve communication efficiency when a handover is performed.SOLUTION: A base station device notifies a terminal device in connection of a setting of a radio resource control (RRC) layer on one or more candidate cells as a switching destination of a connection destination from at least any one of one or more cells to which the terminal device is in connection, acquires a timing advance value for the one or more candidate cells, and transmits, to the terminal device, information indicating a first timing advance value used by a first cell from a plurality of cells and a second timing advance value used by a second cell from the plurality of cells so as to be included in a command as a command for instructing a change of the cell as the connection destination using the setting when the terminal device is connected to the plurality of cells after the change of the connection destination.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to handover techniques in cellular communication systems. [Background technology]

[0002] In a mobile communication system, as a terminal device moves, a cell (base station device) to which the terminal device is connected is switched (e.g., a handover is performed). Conventionally, after receiving a handover instruction from a base station device, a process is performed in which a connection is established by establishing synchronization and setting in a cell to which the connection is switched. This process for switching the connection takes a certain amount of time, and the terminal device cannot communicate user data during the period in which this process is being performed. In contrast, in the method described in Non-Patent Document 1, the handover source base station device provides the terminal device with communication parameters in a radio resource control (RRC) layer for connection with another base station device to which the handover is to be performed before the handover is actually performed. Then, the handover source base station device transmits a layer 1 or layer 2 command to the terminal device to instruct the cell to be switched at the timing when the handover should be performed. In response to receiving the command, the terminal device executes a random access procedure with the handover destination base station device, thereby completing the handover without carrying out subsequent local processing in the RRC layer. With such a technique, it is possible to suppress deterioration of communication efficiency related to the handover. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] 3GPP (registered trademark) Contribution, R2-2209255 Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention provides a technique for further improving communication efficiency when a handover is performed. [Means for solving the problem]

[0005] A base station device according to one embodiment of the present invention has a notification means for notifying a connected terminal device of radio resource control (RRC) layer settings for one or more candidate cells to which the terminal device will switch its connection destination from at least one of one or more cells to which the terminal device is connected, an acquisition means for acquiring timing advance values ​​for the one or more candidate cells, and a transmission means for transmitting a command to instruct the terminal device to change the connection destination cell using the settings, the command including information indicating a first timing advance value used by a first cell of the multiple cells and a second timing advance value used by a second cell of the multiple cells when the terminal device connects to multiple cells after the connection destination is changed.

[0006] A terminal device according to one embodiment of the present invention has an acquisition means for acquiring, from a base station device to which it is connected, radio resource control (RRC) layer settings for one or more candidate cells to which the terminal device is to switch its connection destination from at least one of one or more cells to which it is connected; a receiving means for receiving from the base station device a command instructing the terminal device to change its connection destination cell using the settings, the command including information indicating a first timing advance value used by a first cell among the plurality of cells and a second timing advance value used by a second cell among the plurality of cells when the terminal device connects to multiple cells after the connection destination is changed; a change means for changing the connection destination cell in accordance with the command; and an adjustment means for adjusting the transmission timing of an uplink signal using the first timing advance value for the first cell and the second timing advance value for the second cell after the connection destination cell is changed. Effect of the Invention

[0007] According to the present invention, it is possible to improve communication efficiency when a handover is performed. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram illustrating an example of the configuration of a wireless communication system. [Diagram 2] FIG. 2 illustrates an example of a hardware configuration of the apparatus. [Diagram 3] FIG. 2 is a diagram illustrating an example of a functional configuration of a base station device. [Figure 4] FIG. 2 is a diagram illustrating an example of a functional configuration of a terminal device. [Diagram 5] FIG. 1 is a diagram illustrating an example of a flow of processing executed in a wireless communication system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, the embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the invention according to the claims, and not all combinations of features described in the embodiments are essential to the invention. Two or more features among the multiple features described in the embodiments may be arbitrarily combined. In addition, the same reference numbers are used for the same or similar configurations, and duplicated descriptions are omitted.

[0010] (System Configuration) Fig. 1 shows an example of the configuration of a wireless communication system according to this embodiment. This 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 base station devices 101 to 104 and a terminal device 111. Note that, for simplicity of explanation, Fig. 1 shows only four base station devices and one terminal device, but it goes without saying that a large number of base station devices and terminal devices may exist.

[0011] 1, terminal device 111 is about to move from within the range of a cell formed by base station device 101 into the range of a cell formed by base station device 102. At this time, terminal device 111 will perform handover to switch the connected base station device from base station device 101 to base station device 102.

[0012] In this embodiment, a handover procedure is executed to shorten the period during which the terminal device 111 cannot communicate user data due to handover. That is, the handover source base station device 101 executes a setting in a radio resource control (RRC) layer (setting using an RRC message) before actually handing over the terminal device 111. That is, in a conventional handover, the terminal device 111 receives a handover instruction from the handover source base station device 101, and the setting in the RRC layer for the handover destination base station device 102, which is performed during the handover process, is notified to the terminal device 111 prior to the timing when the handover process should actually be performed. In this setting, communication parameters used in connection and communication with the handover destination candidate base station device 102 are notified to the terminal device 111. The communication parameters include, for example, beam settings in the handover destination candidate base station device 102, parameters when performing a random access procedure, and radio resources (frequency and time resources) to be used. Furthermore, when multiple communication parameters used for communication with the base station device 102 are notified, an identifier (e.g., RRC-TransactionIdentifier, CondReconfigId, or both) uniquely associated with each of the communication parameters may be included in an RRC message or configuration parameters in the RRC layer notified to the terminal device 111. In this case, CondReconfigId is set for each candidate base station device or combination of base station devices as the handover destination. Furthermore, an RRC-TransactionIdentifier may be set when multiple communication parameters are notified for each base station device or combination of base station devices. As an example, CondReconfigId=0 is associated with the base station device 102 that is a candidate base station as the handover destination, and further, when multiple parameters of the base station device 102 are notified, an RRC-TransactionIdentifier (e.g., 0, 1, ...) may be set for each of the parameters.Furthermore, the handover source base station device 101 may transmit to the terminal device 111 an instruction to measure a synchronization signal (SS) / physical broadcast channel (PBCH) block (SSB) transmitted from the handover destination candidate base station device 102. Note that the SSBs may be transmitted using beams directed in different directions. In this case, a measurement instruction may be transmitted so that the terminal device 111 measures each of the SSBs.

[0013] The terminal device 111 measures the SSB sent from the base station device 102, which is a candidate for the handover destination, according to a measurement instruction from the currently connected base station device 101. The terminal device 111 then notifies the currently connected base station device 101 of the measurement result. Here, the base station device 101 may notify the base station device 102, which is a candidate for the handover destination, of the measurement result. In this way, when the terminal device 111 actually performs a handover, the base station device 102 can specify the rough direction of the beam to be used in communication with the terminal device 111. Here, the base station device 102 may notify the terminal device 111 of the transmission setting of the channel state information (CSI)-reference signal (RS) in order to further specify a detailed beam to be used in the downlink (link from the base station device to the terminal device). Note that this notification is performed by the base station device 102 notifying the base station device 101 of the transmission setting of the CSI-RS, and the base station device 101 transferring the transmission setting to the currently connected terminal device 111. When the terminal device 111 receives the transmission setting, it measures the CSI-RS transmitted from the base station device 102 according to the information, and notifies the connected base station device 101 of the measurement result. Then, the base station device 101 transfers the measurement result to the base station device 102. In this way, the base station device 102 can acquire the measurement result of the CSI-RS in the terminal device 111. As a result, the base station device 102 can determine the detailed beam to be used for downlink communication after the terminal device 111 has handed over, before the handover is actually performed. This makes it possible to omit the process of determining the beam direction in detail after the handover is performed, and the period during which the efficiency of communication of user data of the terminal device 111 decreases can be shortened. As an example, the above-mentioned CSI-RS transmission configuration can be instructed to the terminal device 111 using a CSI-RS measurement configuration consisting of a CSI-RS radio resource configuration (CSI-RS-Resource) and a reporting configuration (csi-ReportConfig) for the base station device 102 that are pre-configured in the terminal device 111 as communication parameters before handover.The CSI-RS-Resource includes the time position and frequency position of the radio resource block where the CSI-RS is transmitted. For example, the terminal device 111 may be instructed to measure the radio resource of a specific CSI-RS by specifying the CSI-RS-Resource using the CSI-RS-Resource id in the medium access control element (MAC CE) or the downlink control information (DCI). Also, in the csi-ReportConfig, aperiodic or periodic CSI report timing is set. For example, the terminal device 111 may be instructed to report the measurement result of the CSI-RS at a specific timing by specifying the csi-ReportConfig using the csi-ReportConfig id in the MAC CE or the DCI. In addition, when the base station device 101 performs the above-mentioned measurement configuration on the terminal device 111, the base station device 101 may transmit, to the terminal device 111, for example, a cell identifier included in the MAC CE or DCI as information for the terminal device 111 to identify which base station device's CSI-RS transmission configuration the device has.

[0014] Furthermore, the terminal device 111 executes a random access (RA) procedure before it is determined to execute a handover to the base station device 102. That is, the terminal device 111 may execute a process for establishing synchronization of an uplink (a link from the terminal device to the base station device) before an actual handover is performed. For example, the base station device 101 to which the terminal device 111 is connected transmits an instruction to the terminal device 111 to transmit a random access preamble (RA preamble) to the base station device 102. Then, in accordance with this instruction, the terminal device 111 transmits the RA preamble in radio resources prepared for the RA procedure in the base station device 102. Note that information on the radio resources and the sequence used to generate the RA preamble may be notified to the terminal device 111 from the base station device 101 during, for example, the above-mentioned RRC layer setting process. Furthermore, these pieces of information may be notified to the terminal device 111 when the base station device 101 issues an instruction to transmit the RA preamble. Through this procedure, the RA preamble transmitted from the terminal device 111 is received by the base station device 102. Then, the base station device 102 can determine a timing advance value (TA value) to be used when the terminal device 111 transmits an uplink signal to the base station device 102.

[0015] Thereafter, the base station device 101 may notify the terminal device 111 to execute handover at a predetermined opportunity, such as when the reception quality of a radio signal from the base station device 101 in the terminal device 111 is deteriorated by a predetermined level compared to the reception quality of a radio signal from the base station device 102. This notification may be performed using a command that may be called a Cell switch command. This command may be transmitted using a media access control element (MAC CE) or downlink control information (DCI). Note that this command includes identification information of a cell formed by the base station device 102, which is the handover destination. In addition, when multiple settings in the RRC layer used for communication with the base station device 102 are set, an identifier (for example, an RRC-TransactionIdentifier, a CondReconfigId, or both) uniquely associated with each setting in the RRC layer may be included in this command. In addition, information regarding the beam determined in the base station device 102 and notified to the base station device 101 by measuring SSB or CSI-RS in advance as described above may be notified to the terminal device 111 from the base station device 101. In response to receiving a command from the base station device 101 specifying the base station device 102 as the handover destination, the terminal device 111 changes the connection destination from the base station device 101 to the base station device 102. In this case, since the RA procedure has already been executed as described above, it is not necessary to execute a new RA procedure. Also, since the CSI-RS is measured before the handover as described above, it is not necessary to newly determine a fine beam to be used in downlink communication after the handover. Therefore, the terminal device 111 can communicate user data with the base station device 102 immediately after the handover. Also, when the handover is successful after receiving the command, the terminal device 111 can notify the base station device 102 of the success in an uplink control message such as an RRC message of RRC Reconfiguration Complete or a MAC CE.In this case, the terminal device 111 may include an identifier associated with communication parameters used for communication with the base station device 102 (for example, an RRC-TransactionIdentifier or a CondReconfigId or both) in the RRC message.

[0016] Also, as described above, the base station device 102 can determine the TA value in advance. Therefore, the base station device 102 can notify the base station device 101 of the TA value in advance, and the base station device 101 can notify the terminal device 111 of the TA value by the above-mentioned command. As a result, the terminal device 111 can establish uplink synchronization with the base station device 102 at the time when the handover to the base station device 102 is instructed by the base station device 101, and therefore it becomes possible to transmit uplink user data to the base station device 102 without executing the RA procedure again.

[0017] The terminal device 111 can connect to multiple cells in parallel. For example, the terminal device 111 can connect to a cell provided by the base station device 101 and a cell provided by the base station device 103 in parallel. Here, when the terminal device 111 connects to multiple cells provided by different base station devices, separate TA values ​​are set for each cell. For example, in the terminal device 111, two TA values ​​are set: a first TA value for a cell provided by the base station device 101 and a second TA value for a cell provided by the base station device 103. Note that, when the TA value to be used is the same, for example, when multiple cells are provided by the same base station device or a base station device located at approximately the same position, the same TA value can be used for the multiple cells. In this way, a group of cells using the same TA value is called a timing advance group (TAG). A TA value is set for each TAG.

[0018] In this embodiment, a case will be considered in which the above-mentioned Cell Switch Command is used to perform handover of the terminal device 111 connected to multiple cells. When the terminal device 111 is connected to multiple cells and will be connected to multiple cells after handover, the Cell Switch Command may include identification information of the multiple cells after the handover. For example, when the terminal device 111 transitions from a state in which it is connected to a first cell formed by the base station device 101 and a second cell formed by the base station device 102 to a state in which it is connected to a second cell formed by the base station device 102 and a third cell formed by the base station device 103, for example, a Cell Switch Command including identification information of the second cell and identification information of the third cell may be transmitted to the terminal device 111. In this case, identification information of the third cell to be changed as a connection destination is notified to the terminal device 111, and identification information of the second cell does not have to be notified to the terminal device 111. However, in this case, identification information of the first cell from which the switching is performed may be notified to the terminal device 111. Note that, although an example in which only one of the two cells is changed has been shown here, two or more cells may be changed at once. In addition, an identifier associated with the setting in the RRC layer may be included in this command to indicate which cell the handover is to be performed to. For example, a setting in one RRC layer may include a setting for using multiple cells in parallel. For example, in the case where the setting for connecting to the second cell formed by the base station device 102 and the third cell formed by the base station device 103 is performed in advance in the terminal device 111, an identifier corresponding to the setting may be notified to the terminal device 111. For example, it is assumed that a first setting for using the first cell and the third cell in parallel, a second setting for using the second cell and the third cell in parallel, and a third setting for using the first cell and the fourth cell formed by the base station device 104 in parallel are notified to the terminal device 111 connected to the first cell and the second cell. It is also assumed that a first identifier is assigned to the first setting, a second identifier is assigned to the second setting, and a third identifier is assigned to the third setting.In this case, for example, the base station device 101 forming the first cell from which the connection destination is changed notifies the terminal device 111 of a Cell Switch Command specifying the second identifier, whereby the terminal device 111 can switch the connection destination cell to a combination of the second cell and the third cell. Note that the Cell Switch Command at this time may be notified to the terminal device 111 from the second base station device 102 with which the connection is maintained from before the connection destination is changed to after the change. In addition, when setting information for using multiple cells in parallel is notified to the terminal device 111 in advance, the setting information may include the setting of TAGs for each of the multiple cells. For example, it may be notified in the setting information that the second cell belongs to the first TAG and the third cell belongs to the second TAG.

[0019] In this way, assuming that multiple cells can be switched at once, it is useful to notify the terminal device 111 of the TA value to be applied to each of the multiple cells after switching in this command. That is, since the TA value is set for each TAG as described above, when multiple cells after handover belong to different TAGs, information indicating the TA value for each of these TAGs is notified to the terminal device 111, so that the terminal device 111 does not need to be notified again of the TA value to be used after switching the connection destination cell. In this embodiment, in consideration of such circumstances, it is made possible to specify multiple TA values ​​in the Cell Switch Command.

[0020] In one example, the Cell Switch Command includes the TA value itself to be used in each TAG. In addition, when a TA value already held in the terminal device 111 is used, the Cell Switch Command may include information specifying the TA value held in the terminal device 111, rather than the TA value itself. For example, when the terminal device 111 switches the connection destination cell between the second cell and the third cell formed by the base station device 103 from a state in which the terminal device 111 is connected to the first cell formed by the base station device 101 and the second cell formed by the base station device 102, the terminal device 111 can reuse the TA value of the second cell among the TA values ​​used before the connection destination is changed. Here, even if the same cell is continuously used, it may be assumed that the configuration of the TAG changes. For this reason, information indicating that the TA value used in the TAG to which the second cell belongs before the connection destination cell is changed is reused in the TAG to which the second cell belongs after the connection destination is changed may be notified in the Cell Switch Command.

[0021] It is also possible that the base station device 103 determines the TA value of the third cell to which the terminal device 111 was not connected by executing the above-mentioned advance RA procedure, and notifies the terminal device 111 in advance of the determined TA value via the base station device 101 or the base station device 102. In such a case, the terminal device 111 may be notified by a Cell Switch Command that the TA value notified in advance should be used for the TAG to which the third cell belongs. When a TA value held in the terminal device 111 in advance is used, the TA value is specified by identification information associated with the TA value. This identification information may be, for example, information (tag-id) specifying a specific TAG before switching of the connection destination cell, or information specifying a specific cell in which the TA value is set. When notifying the terminal device 111 of the TA value in advance, the base station device 101 and the base station device 102 connected to the terminal device 111 can notify the terminal device 111 of the TA value by individually attaching identification information to the TA value. This allows the base station device 101 and the base station device 102 to specify, in the Cell Switch Command, which TA value to use in a specific TAG after the connection destination is changed, using the identification information.

[0022] In addition, in the above embodiment, the case where one TAG is associated with one cell has been described, but the description according to this embodiment can also be applied to the case where one TAG is associated with multiple cells and one TA value is associated with each TAG, or different TAGs are associated with multiple TRPs (Transmission and Reception Points) belonging to the same cell, or one cell is composed of multiple TRPs. When one cell is composed of multiple TRPs, it is also assumed that each TRP is associated with a TA value. In that case, as identification information associated with a TA value for identifying a TA value to be used, in addition to information (tag-id) specifying a TAG, information for specifying a TRP may be notified in advance, or may be notified by a Cell Switch Command.

[0023] Furthermore, when the TA value previously set and held in the terminal device 111 is to be updated, the base station device 101 and the base station device 102 may include in the Cell Switch Command a differential value Ta-Tb between the updated value Ta and the pre-update value Tb. In this case, a Cell Switch Command including identification information indicating which of the pre-set TA values ​​is to be used and the differential value may be notified to the terminal device 111. The terminal device 111 can specify the TA value to be used after changing the connection destination cell by adding the differential value to the TA value corresponding to the identification information for a specific TAG.

[0024] The above-mentioned methods of notifying information indicating the TA value may be used in combination. That is, for some of the multiple TAGs set after a connection destination is changed, the TA value itself may be notified, and for the remaining part, identification information previously associated with a specific TA value (TAG identification information, TA value identification information, cell identification information, etc.) may be notified. Also, a difference value for updating may be notified only for some of the TA values. That is, the above-mentioned information indicating the TA value may be arbitrarily combined and notified to the terminal device 111.

[0025] When the terminal device 111 receives the Cell Switch Command as described above, it can specify the TA value corresponding to each TAG based on the information indicating the TA value included in the command. Then, the terminal device 111 changes the connection destination cell according to the command, and adjusts the transmission timing of the uplink signal in the cell belonging to each TAG using the specified TA value after changing the connection destination cell. Note that, when the terminal device 111 has acquired a TA value for a specific cell in advance as described above, it can store the TA value in association with specific identification information (identification information of the cell or identification information prepared for the TA value). Then, when identification information is included in the Cell Switch Command as information indicating the TA value for a specific TAG, the terminal device 111 can specify the TA value corresponding to the identification information as the TA value for the specific TAG. Also, when the TA value itself is included in the Cell Switch Command as information indicating the TA value for a specific TAG, the terminal device 111 can determine to use the value specified in the command as the TA value for the specific TAG. When the terminal device 111 receives the TA value itself, it may start a timer (timeAlignmentTimer) related to the expiration date of the TA value. This timer measures a period during which the terminal device 111 considers that the timing of uplink signal transmission is synchronized. The terminal device 111 obtains a value (timeAlignmentTimerDedicated) specific to the terminal device 111 or a value (timeAlignmentTimerCommon) common to terminal devices in the cell as the expiration date of the timer, and manages the TA value based on this value. The value of the timer (timeAlignmentTimer) related to the expiration date of the TA value may be notified together with the TAG as part of the setting in the RRC layer that is set in advance in the terminal device 111 before the notification of the Cell Switch Command, or the timer value may be set together with the TAG in the Cell Switch Command.In addition, when the terminal device 111 performs an RA procedure in advance before changing the cell to which the terminal device 111 is connected, the terminal device 111 may notify the terminal device 111 of the expiration date of the timers together with the notification. In addition, when the terminal device 111 receives a new TA value, the terminal device 111 restarts the timer. When the timer related to the above-mentioned expiration date managed for each TAG expires, the terminal device 111 holds the TA value associated with the TAG of the expired timer and stops transmitting an uplink signal using the TA value, for example, transmitting a PUCCH or an SRS. After that, when the terminal device 111 receives a TA value or a difference value from the held TA value from the base station device, the terminal device 111 updates the TA value. In addition, when the terminal device 111 is instructed to delete the TA value from the base station device, the terminal device 111 deletes the TA value.

[0026] In the above embodiment, the notification of the TA value for the cell to which the connection is switched in the Cell Switch Command has been described, but the TA value for the cell to which the terminal device 111 is not connected may be notified in this command. For example, the TA value for the fourth cell formed by the base station device 104 may be included in the Cell Switch Command that instructs the terminal device 111 to change the cell to which the terminal device 111 is connected from a state in which the terminal device 111 is connected to the first cell formed by the base station device 101 and the second cell formed by the base station device 102 to a state in which the terminal device 111 is connected to the second cell and the third cell formed by the base station device 103. In this case, the terminal device 111 must have performed an RA procedure for the fourth cell in advance, and the TA value determined by the base station device 104 must have been notified to at least one of the base station device 101 and the base station device 102, and in the pre-setting in the RRC layer before the Cell Switch Command is notified, the terminal device 111 must have been notified of information on the cell that the terminal device 111 manages as the cell to which the terminal device 111 is not connected after the handover, and the TAG to which the cell belongs. Also, at this time, information for identifying a cell managed by the terminal device 111 as a cell to which the terminal device 111 does not connect and the TAG to which the cell belongs may be notified to the terminal device 111 in the Cell Switch Command, instead of presetting in the RRC layer. In this way, by notifying the terminal device 111 of the TA value for a cell that is not directly involved in the change of the connection destination, when the cell to which the terminal device 111 connects is further changed and the terminal device 111 connects to a fourth cell, it becomes possible to establish uplink timing synchronization with the fourth base station device without the terminal device 111 executing the RA procedure again. Although the above description has been given of the fourth cell, the same process may be performed for multiple cells, such as a fifth cell or a sixth cell to which the terminal device 111 does not connect, after the terminal device 111 changes the cell connection destination.

[0027] (Device configuration) Next, the device configuration will be described. FIG. 2 shows an example of the hardware configuration of the base station device and the terminal device of this embodiment. In one example, the base station device and the terminal device are configured to include a processor 201, a ROM 202, a RAM 203, a storage device 204, and a communication circuit 205. The processor 201 is a computer configured to include one or more processing circuits such as a general-purpose CPU (Central Processing Unit) or an ASIC (Application Specific Integrated Circuit), and executes the overall processing of the device and each of the above-mentioned processes by reading and executing a program stored in the ROM 202 or the storage device 204. The ROM 202 is a read-only memory that stores information such as programs and various parameters related to the processing executed by the base station device and the terminal device. The RAM 203 functions as a workspace when the processor 201 executes a program, and is a random access memory that stores temporary information. The storage device 204 is configured, for example, by a removable external storage device. The communication circuit 205 is configured, for example, by a circuit for wireless communication of 5G or its successor standard. Although one communication circuit 205 is illustrated in FIG. 2, the base station device and the terminal device may have multiple communication circuits. For example, the base station device and the terminal device may have wireless communication circuits for 5G and its successor standard, and a common antenna for those circuits. The base station device and the terminal device may have separate antennas suitable for each standard. The base station device may further have a wired communication circuit used when communicating with other base station devices or nodes of the core network. The terminal device may further have a communication circuit conforming to a wireless communication standard other than the cellular communication standard, such as a wireless local area network (LAN) or Bluetooth (registered trademark). The base station device and the terminal device may have separate communication circuits 205 for each of a plurality of available frequency bands, or may have a common communication circuit 205 for at least a part of those frequency bands.

[0028] FIG. 3 shows an example of the functional configuration of a base station device. The base station device has, for example, an RRC setting unit 301, an RA instruction unit 302, a TA value acquisition unit 303, an inter-base station communication unit 304, and a cell switching instruction unit 305. Note that FIG. 3 mainly shows the functions of the base station device 101 or the base station device 102 to which the terminal device 111 is connected. The base station device 103 and the base station device 104 forming the candidate cell for the connection change destination are the same as conventional base station devices except that they may transmit information about the TA value to the base station device 101 or the base station device 102, and are therefore omitted from the illustration here. Note that the base station device 101 to the base station device 104 are classified only based on whether or not they are the connection destination of the terminal device 111, and all of these base station devices can have the functions of FIG. 3. That is, for example, when the base station device 103 or the base station device 104 is connected to another terminal device not shown, the base station device 101, the base station device 102, etc. can be used as a candidate for the connection change destination to perform the above-mentioned processing using the functions of FIG. 3. FIG. 3 shows only functions particularly related to this embodiment, and does not show various other functions that the base station device may have. For example, the base station device naturally has other functions that a base station device conforming to 5G or its successor standards generally has. The functional blocks in FIG. 3 are shown in a schematic manner, and each functional block may be integrated and realized, or may be further subdivided. Each function in FIG. 3 may be realized, for example, by the processor 201 executing a program stored in the ROM 202 or the storage device 204, or may be realized, for example, by a processor present in the communication circuit 205 executing a predetermined software. The details of the processing performed by each functional unit will not be described here in detail, and only the rough functions will be outlined.

[0029] The RRC setting unit 301 performs, for example, RRC layer setting for a connected terminal device. For example, the RRC setting unit 301 transmits a handover request to another base station device that provides a neighboring cell that is a candidate for a connection change destination of the terminal device, acquires communication setting information from the other base station device, and notifies the terminal device of the communication setting information by a message of the RRC layer. Here, the RRC setting unit 301 may transmit to the terminal device, in an RRC layer message, setting information on a combination of cells that the terminal device can use in parallel, based on, for example, information on frequency bands that the terminal device can use in parallel. This setting information may include, for example, information on which TAG each of the multiple cells to be combined belongs to. Here, the currently connected cell may be included as a connection destination candidate when the terminal device changes the connection destination. That is, when the terminal device is connected to the first cell and the second cell, if a combination of the second cell and the third cell is set as a combination of connection destination candidate cells for the terminal device, the connected second cell is included in the connection destination candidate. For this reason, the RRC setting unit 301 may also obtain setting information for the second cell and notify the terminal device. Note that this is an example, and as for the setting information specific to the second cell, it may be notified to the terminal device that the current setting information should be reused, and only setting information required when using the second cell in combination with the third cell. Note that, when there are multiple candidates for a combination of connection destination cells, when setting information for each of the multiple candidates is prepared, specific identification information may be assigned to each of the multiple setting information. This identification information may be, for example, an RRC-TransactionIdentifier, a CondReconfigId, or both. Note that the message of the RRC layer is an RRC Reconfiguration message. After that, the RRC setting unit 301 performs connection processing setting between the terminal device and another base station device by receiving an RRC Reconfiguration Complete message including an RRC-TransactionIdentifier, a CondReconfigId, or both from the terminal device.

[0030] The RA instruction unit 302 instructs the terminal device for which the RRC layer setting has been completed to transmit an RA preamble for each of the candidate cells to which the connection is to be made. Here, the instruction to transmit the RA preamble includes information for identifying the base station device or cell to which the RA preamble is to be transmitted, a sequence for generating an RA preamble specific to the terminal device, and a group of sequences that can also be used by other terminal devices that are attempting to connect to the candidate cell to which the connection is to be made, and may also include information on radio resources used to transmit the RA preamble. For example, the RA instruction unit 302 may instruct the currently connected terminal device to transmit an RA preamble to the candidate base station device to which the connection is to be made, by a physical downlink control channel (PDCCH) order. In addition, the RA instruction unit 302 may instruct the terminal device to retransmit the RA preamble as necessary, or, if the RA preamble is configured to be repeatedly transmitted, may transmit an instruction to stop transmitting the RA preamble to the terminal device. When the base station device or cell to which the RA preamble is to be transmitted is composed of multiple TRPs (Transmission and Reception Points), in addition to information for identifying the base station device or cell to which the RA preamble is to be transmitted, information for identifying the destination TRP may be included in the transmission instruction.

[0031] The TA value acquisition unit 303 acquires, for each of the candidate cells to which the terminal device is to be connected, a TA value determined as a result of, for example, the RA instruction unit 302 making the terminal device transmit an RA preamble. The TA value acquisition unit 303 may also acquire, not only the TA value for the candidate cell to which the terminal device is not currently connected, but also the TA value for the cell currently connected to the terminal device that is included as a candidate cell after the connection destination is changed. The TA value acquisition unit 303 does not need to acquire the TA value for the cell to which the terminal device is currently connected among the candidate cells. The inter-base station communication unit 304 communicates with the base station device that forms the candidate cell to which the terminal device is to be connected. The inter-base station communication unit 304 may, for example, notify another base station device to which the RA preamble is to be transmitted that the connected terminal device is to transmit an RA preamble. The inter-base station communication unit 304 is also used, for example, to receive information for the RA procedure in the base station device that forms the candidate cell to which the terminal device is to be connected from that base station device. The TA value acquisition unit 303 can acquire, for example, a TA value calculated in a base station device that forms a candidate cell via the inter-base station communication unit 304.

[0032] The cell switching instruction unit 305 instructs the terminal device to execute cell switching in response to the terminal device being in a state in which it should execute cell switching, such as when the reception quality of a radio signal from another base station device forming a candidate cell to which the terminal device is to be connected becomes higher than a predetermined level or more than the radio quality between the terminal device and the terminal device. The cell switching instruction unit 305 transmits to the terminal device a Cell switch command including, for example, a cell identifier capable of identifying a destination cell, and identification information such as an RRC-TransactionIdentifier and a CondReconfigId corresponding to the setting information notified by the RRC setting unit 301. Note that, when the terminal device connects to multiple cells and multiple TAGs are set for the multiple cells, the cell switching instruction unit 305 may transmit to the terminal device a command including information indicating TA values ​​for each of the multiple TAGs. That is, information indicating a first TA value to be applied in a first cell of the multiple cells and a second TA value to be applied in a second cell may be included in this command and transmitted to the terminal device. According to this, immediately after cell switching, the terminal device can transmit uplink user data signals in the multiple cells after switching by using those TA values. Note that the information indicating the TA value here may be the TA value itself, or may be identification information (e.g., tag-id or cell identifier) ​​capable of identifying the TA value held in the terminal device. Also, information indicating some TA values ​​among the multiple TA values ​​may be the TA value itself, and information indicating other TA values ​​may be identification information capable of identifying the TA value. Also, the cell switching instruction unit 305 may notify the terminal device in this command of the TA value for a candidate cell after a further cell switching after the terminal device switches the connection destination. According to this, it becomes unnecessary to execute the RA procedure again for the candidate cell when the terminal device switches the cell to which it is further connected.When notifying the terminal device of the TA value itself, the cell switching instruction unit 305 can notify the terminal device of the value of timeAlignmentTimerCommon or timeAlignmentTimerDedicated related to the TA value in the Cell Switch Command.

[0033] FIG. 4 shows an example of the functional configuration of a terminal device. The terminal device has, for example, an RRC setting unit 401, an RA processing unit 402, a TA value holding unit 403, a cell switching unit 404, and a timing adjustment unit 405. Note that FIG. 4 shows only functions particularly related to this embodiment, and various other functions that the terminal device may have are omitted from the illustration. For example, the terminal device naturally has other functions that terminal devices conforming to 5G and subsequent standards generally have. In addition, the functional blocks in FIG. 4 are shown in a schematic manner, and each functional block may be integrated and realized, or may be further subdivided. In addition, each function in FIG. 4 may be realized, for example, by the processor 201 executing a program stored in the ROM 202 or the storage device 204, or may be realized, for example, by a processor present inside the communication circuit 205 executing a predetermined software. Note that the details of the processing performed by each functional unit will not be described here in detail, and only the rough functions will be outlined.

[0034] The RRC setting unit 401 performs connection setting processing for a cell that is a connection candidate by receiving a message of the RRC layer from a connected base station device. The RRC setting unit 401 holds a setting for a connected cell and a setting for a connection candidate cell in parallel. When the RRC setting unit 401 holds a plurality of pieces of setting information, the RRC setting unit 401 may hold corresponding identification information (for example, an RRC-TransactionIdentifier, a CondReconfigId, or both) together with the setting information. The setting information for a combination of a plurality of cells may include, for example, information indicating which TAG each of the plurality of cells belongs to. The RA processing unit 402 transmits an RA preamble for a connection candidate cell in response to receiving an instruction to transmit an RA preamble from a connected base station device. Here, information on a sequence for generating an RA preamble and radio resources for receiving an RA preamble in a connection candidate cell may be received from a connected base station device. The sequence and radio resource information may be obtained from system information sent by the base station device forming the connection candidate cell. For example, after transmitting the above-mentioned RA preamble, the RA processing unit 402 may obtain the TA value determined in the destination base station device via the currently connected base station device. If there are multiple connection candidate cells that can use the same TA value at this time, the RA processing unit 402 may receive information for identifying the cell that can use the same TA value from the base station device and store the TA value in association with information for identifying the TAG, such as a tag-id.

[0035] The TA value holding unit 403 holds, for example, a TA value for adjusting the transmission timing of an uplink signal to a connected base station device, and a TA value acquired by the RA processing unit 402 or notified in a Cell Switch Command from a connected base station device. The TA value holding unit 403 may hold the TA value in association with, for example, identification information of a TAG to which the TA value is applied, or identification information of a cell to which the TA value is applied (a cell formed by the base station device that determined the TA value). Note that, when a difference value between a post-update TA value and a pre-update TA value is notified together with identification information associated with a specific TA value in order to update the specific TA value, the TA value holding unit 403 may update the TA value corresponding to the identification information using the notified difference value. Furthermore, when the TA value is acquired, the TA value holding unit 403 may start a timer (timeAlignmentTimer). The TA value is treated as valid until the timer expires.

[0036] The cell switching unit 404 changes the cell to which the terminal device is connected in response to receiving a command (cell switch command) from the connected base station device to instruct cell switching. The command may include identification information specifying which of the setting information set in the RRC setting unit 401 should be used. The terminal device can specify which cell to connect to by extracting the identification information from the command and specifying the setting information corresponding to the identification information. Note that this is an example, and the identification information of the cell specifying the connection destination cell may be included in the command. The command also includes information indicating a TA value to be used. Note that when the terminal device connects to multiple cells, the command may include information indicating a first TA value for a first cell included in the multiple cells and information indicating a second TA value for a second cell. That is, the command may include information indicating multiple TA values. Note that the information indicating the TA value may be the TA value itself, or may be identification information capable of identifying the TA value.

[0037] The timing adjustment unit 405 adjusts the transmission timing of the uplink signal based on, for example, the TA value stored in the TA value storage unit 403. Furthermore, when a connection destination cell is switched by a Cell Switch Command, the timing adjustment unit 405 adjusts the transmission timing of the uplink signal after the cell is switched based on information indicating the TA value notified in the command. This allows the terminal device to transmit the uplink signal at an appropriate timing immediately after the connection destination cell is switched, since the TA value to be used is specified based on the information included in the Cell Switch Command.

[0038] (Processing flow) Next, an example of the flow of processing executed in the wireless communication system will be described with reference to Fig. 5. Note that the flow of processing in Fig. 5 is only an example, and each step can be modified as described above.

[0039] In this processing example, for example, the terminal device initially establishes a connection with a base station device providing cell A and a base station device providing cell B, and communicates in these cells (S501). Here, cell A belongs to TAG1, cell B belongs to TAG2, T1 is used as a TA value in TAG1, and T2 is used as a TA value in TAG2. That is, the terminal device controls the transmission timing of an uplink signal to cell A so that the signal is earlier than the timing at which the signal is received by T1, and controls the transmission timing of an uplink signal to cell B so that the signal is earlier than the timing at which the signal is received by T2. After that, for example, the base station device forming cell A first transmits a HANDOVER REQUEST message to the base station device forming cell C and the base station device forming cell D, which are connection destination candidates after cell switching of the terminal device (S502). When the base station device forming cell C or cell D receives this message, it returns a HANDOVER REQUEST ACK message including setting information such as information on communication parameters to be used when the terminal device connects to the base station device forming cell A (S503). Note that the base station device forming cell A may hold in advance setting information for cell B to which the terminal device is already connected, for example. Then, the base station device forming cell A notifies the terminal device of an RRC Reconfiguration message including setting information such as communication parameters notified from another base station device (S504). The setting information notified here may include setting information for using multiple cells in parallel. In addition, identification information capable of identifying the setting information may be associated with the setting information. Here, it is assumed that setting 1 for using cell B and cell C in parallel and setting 2 for using cell A and cell D in parallel are notified to the terminal device. In addition, in setting 1, information such as that cell B belongs to TAG1 and cell C belongs to TAG2, and in setting 2, that cell A belongs to TAG1 and cell D belongs to TAG2, is notified to the terminal device.When the terminal device receives this message, it transmits an RRC Reconfiguration Complete message to the base station device of cell A and completes the configuration process using the RRC layer message (S505). This process makes it unnecessary for the terminal device to perform the RRC layer configuration process after the cell switching is instructed.

[0040] Next, the base station device of cell A instructs the terminal device to transmit an RA preamble to each cell that is a candidate for connection after cell switching (S506). Here, this instruction may include information specifying the sequence that the terminal device should use to generate the RA preamble and the radio resource to which the RA preamble should be transmitted. The radio resource to which the RA preamble should be transmitted may be specified based on system information of the cell that is transmitted in the candidate cell and measured by the terminal device, for example. That is, the terminal device does not need to obtain this information from the connected base station device. Also, the sequence to be used when generating the RA preamble may be specified in advance. In one example, the information on this sequence may be notified to the terminal device in S504. The terminal device transmits the RA preamble to the cells C and D that are not connected in accordance with the instruction (S507). At this time, the base station device of cell A may notify the base station device of cell C and the base station device of cell D that the terminal device plans to transmit the RA preamble. At this time, the base station device of cell A may notify the base station device of cell C and the base station device of cell D of information on the sequence used to generate the RA preamble that the terminal device transmits to each cell. This enables the base station device of cell C and the base station device of cell D to detect the RA preamble transmitted by the terminal device. Note that this is one example, and for example, the HANDOVER REQUEST of S502 may implicitly notify that the terminal device plans to transmit the RA preamble. In this case, the HANDOVER REQUEST ACK of S503 may specify the sequence that the terminal device should use to generate the RA preamble. Note that these are one example, and information on the sequence that the terminal device should use to generate the RA preamble may be shared between the base station device of cell A, the base station device of cell C, and the base station device of cell D by other messages. The base station device of cell C and the base station device of cell D may calculate a TA value based on the RA preamble transmitted from the terminal device, and notify the base station device of cell A of the calculated TA value (S508).

[0041] Thereafter, for example, in the terminal device, when a predetermined condition is satisfied, such as when the wireless quality of a signal from the base station device of cell C becomes higher than the wireless quality of a signal from the base station device of cell A by a predetermined level or more, a cell switching process may be performed. The base station device of cell A decides to change the cell to which the terminal device is connected, for example, from a combination of cell A and cell B to a combination of cell B and cell C. In this case, the setting to use cell B and cell C in combination has been notified to the terminal device as "setting 1" in S504. Therefore, the base station device of cell A transmits a Cell Switch Command to instruct the terminal device to switch the cell to which the terminal device is connected using "setting 1" (S509). Note that this is only an example, and any information that allows the terminal device to specify that cell B and cell C should be used in combination may be notified to the terminal device in this command. Note that this command includes information indicating a TA value. Here, in setting 1 notified in S504, it is specified that cell B belongs to TAG1 and cell C belongs to TAG2. For this reason, the command includes a plurality of TA values ​​to be used in each TAG. For example, the terminal device is connected to cell B even before switching the connection destination cell, and at that time, cell B belongs to TAG2, so it is assumed that the TA value used in TAG2 before the cell switching can be used in TAG1 after the cell switching. For this reason, information (e.g., tag-id) specifying the TA value of TAG2 before the cell switching can be included in the Cell Switch Command as information indicating the TA value of TAG1 to which cell B belongs. In addition, the terminal device is not connected to cell C before the cell switching, and the TA value for cell C has not been notified. For this reason, "T3", which is the TA value to be used in cell C, can be included in the Cell Switch Command as information indicating the TA value of TAG2 to which cell C belongs. Since this TA value has been notified from the base station device of cell C to the base station device of cell A in S508, the base station device of cell A can include this TA value (T3) in the Cell Switch Command.

[0042] When the terminal device receives the Cell Switch Command, it changes the connection destination cell to a combination of cell B and cell C in accordance with the command. Then, the terminal device can specify the TA value to be used in each cell by using the information indicating the TA value included in the command. Therefore, the terminal device can transmit an uplink signal at an appropriately adjusted transmission timing immediately after cell switching without being notified of the TA value again from the base station device of cell C or the like (S510, S511).

[0043] In this processing example, the base station device forming cell A takes the lead in controlling cell switching, but the base station device forming cell B to which the terminal device is connected may take the lead in controlling this. Also, in the example of FIG. 5, the TA value for cell D already acquired in cell A is notified to the terminal device in the Cell Switch Command. According to this, when the cell to which the terminal device is connected to cell D is switched after changing the cell to which the terminal device is connected to cell B and cell C, the terminal device does not need to execute the RA procedure again. However, this is only an example, and the TA value of cell D does not need to be included in the Cell Switch Command. Also, in the above example, the TA value of cell C is notified in the Cell Switch Command, but for example, after S508, the base station device of cell A may notify the terminal device of the TA value (T3) in association with specific identification information such as identification information of cell C. In this case, the terminal device holds the specific identification information and the notified TA value. Then, in the Cell Switch Command of S509, the specific identification information is included as information indicating the TA value of TAG2, so that the terminal device can specify that the TA value (T3) held in association with the specific identification information should be used in TAG2. Note that, although the above description has been given of the case where TAG1 and TAG2 are used, two or more TAGs such as TAG3, TAG4, and TAGn may be used.

[0044] In this way, according to the present embodiment, it is possible to significantly reduce the time from when the base station device, which is the connection destination before the cell change, decides to change the connection destination of the terminal device to another cell until the terminal device starts transmitting an uplink signal including user data in the changed cell. This makes it possible to contribute to Goal 9 of the Sustainable Development Goals (SDGs) led by the United Nations, which is to "build resilient infrastructure, promote sustainable industrialization and foster innovation."

[0045] The invention is not limited to the above-described embodiment, and various modifications and variations are possible within the scope of the gist of the invention.

Claims

1. A base station device, A notification means for notifying a connected terminal device of a radio resource control (RRC) layer configuration for one or more candidate cells to which the terminal device is to switch its connection destination from at least one of the one or more cells to which the terminal device is connected; obtaining means for obtaining a timing advance value for the one or more candidate cells; a transmission means for transmitting, to the terminal device, a command for instructing the terminal device to change a connection destination cell using the setting, the command including information indicating a first timing advance value used by a first cell among the plurality of cells and a second timing advance value used by a second cell among the plurality of cells when the terminal device connects to a plurality of cells after the connection destination is changed; A base station device comprising:

2. The base station device according to claim 1, characterized in that when the terminal device stores at least one of the first timing advance value and the second timing advance value in association with predetermined identification information, the transmitting means transmits the predetermined identification information in the command as information indicating the stored value.

3. The base station device according to claim 1, characterized in that the terminal device transmits at least one of the first timing advance value and the second timing advance value as information indicating the value by including the value in the command.

4. The base station device according to claim 1, characterized in that when the terminal device holds at least one of the first timing advance value and the second timing advance value in association with predetermined identification information, and when the held value is to be updated, the transmitting means includes the predetermined identification information in the command as information indicating at least one of the first timing advance value and the second timing advance value, and also includes in the command a differential value between the updated value and the value before the update.

5. The base station device according to claim 1, characterized in that the transmitting means transmits, in the command, a timing advance value for a cell that is one or more candidate cells and is not included in the plurality of cells to which the terminal device will connect after the connection destination is changed.

6. A terminal device, An acquisition means for acquiring, from a connected base station device, a radio resource control (RRC) layer configuration for one or more candidate cells to which the terminal device is to switch its connection destination from at least one of the one or more cells to which the terminal device is connected; a receiving means for receiving, from the base station device, a command instructing a change of a connection destination cell using the setting, the command including information indicating a first timing advance value used by a first cell among the plurality of cells and a second timing advance value used by a second cell among the plurality of cells when the terminal device connects to a plurality of cells after the change of connection destination; A change means for changing a connection destination cell in accordance with the command; an adjustment means for adjusting a transmission timing of an uplink signal by using the first timing advance value for the first cell and the second timing advance value for the second cell after a connection destination cell is changed; A terminal device comprising:

7. a storage unit for storing one or more timing advance values ​​and identification information for each of the one or more timing advance values ​​in association with each other; when at least one of the first timing advance value and the second timing advance value is stored in association with predetermined identification information, the receiving means receives the command including the predetermined identification information as information indicating the stored value, 7. The terminal device according to claim 6, wherein the adjustment means adjusts the transmission timing of the uplink signal by using the value stored in correspondence with the predetermined identification information.

8. the receiving means receives the command including at least one of the first timing advance value and the second timing advance value as information indicating the value; 7. The terminal device according to claim 6, wherein the adjusting means adjusts the transmission timing of the uplink signal by using a value included in the command.

9. a storage unit for storing one or more timing advance values ​​and identification information for each of the one or more timing advance values ​​in association with each other; when at least one of the first timing advance value and the second timing advance value is stored in association with a predetermined identification information and the stored value is to be updated, the receiving means receives a command including the predetermined identification information as information indicating the stored value and including a difference value between the updated value and the value before the update; The terminal device according to claim 6, characterized in that the adjustment means updates the value stored corresponding to the specified identification information using a difference value included in the command, and adjusts the transmission timing of the uplink signal using the updated value.

10. The terminal device according to claim 6, characterized in that the receiving means receives the command including a timing advance value for a cell that is one or more candidate cells and is not included in the plurality of cells to which the terminal device will connect after the connection destination is changed.

11. 7. The terminal device according to claim 6, further comprising a timer that is started when the timing advance value is obtained.

12. A control method executed by a base station device, comprising: Notifying a currently connected terminal device of a radio resource control (RRC) layer configuration for one or more candidate cells to which the terminal device is to switch its connection destination from at least one of the one or more cells to which the terminal device is connected; obtaining a timing advance value for the one or more candidate cells; A command for instructing the terminal device to change a connection destination cell using the setting, the command including information indicating a first timing advance value used by a first cell among the plurality of cells and a second timing advance value used by a second cell among the plurality of cells when the terminal device connects to a plurality of cells after the connection destination is changed; and A control method comprising:

13. A control method executed by a terminal device, comprising: Acquiring, from a connected base station device, a radio resource control (RRC) layer configuration for one or more candidate cells to which the terminal device is to switch its connection destination from at least one of the one or more cells to which the terminal device is connected; receiving, from the base station device, a command instructing a change of a connection destination cell using the setting, the command including information indicating a first timing advance value used by a first cell among the plurality of cells and a second timing advance value used by a second cell among the plurality of cells when the terminal device connects to the plurality of cells after the change of connection destination; changing a connection destination cell in accordance with the command; adjusting a transmission timing of an uplink signal by using the first timing advance value for the first cell and the second timing advance value for the second cell after changing a connection destination cell; A control method comprising:

14. A computer installed in the base station device notifying a connected terminal device of a radio resource control (RRC) layer configuration for one or more candidate cells to which the terminal device is to switch its connection destination from at least one of the one or more cells to which the terminal device is connected; obtaining a timing advance value for the one or more candidate cells; a command for instructing the terminal device to change a connection destination cell using the setting, the command including information indicating a first timing advance value used by a first cell among the plurality of cells and a second timing advance value used by a second cell among the plurality of cells when the terminal device connects to a plurality of cells after the connection destination is changed, the command being transmitted; Program for.

15. A computer installed in the terminal device Acquire, from a connected base station device, a radio resource control (RRC) layer configuration for one or more candidate cells to which the terminal device is to switch its connection destination from at least one of the one or more cells to which the terminal device is connected; receiving, from the base station device, a command instructing a change of a connection destination cell using the setting, the command including information indicating a first timing advance value used by a first cell among the plurality of cells and a second timing advance value used by a second cell among the plurality of cells when the terminal device connects to a plurality of cells after the change of connection destination; Change the connected cell according to the command, After changing the connection destination cell, adjusting a transmission timing of an uplink signal by using the first timing advance value for the first cell and the second timing advance value for the second cell. Program for.

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