Base station device, terminal device, and control method for performing handover with improved communication efficiency

Abstract

A base station device according to the present invention sets a radio resource control (RRC) layer, which is a radio resource control layer, for a connected terminal device with respect to another base station device which is a candidate for a handover destination of the terminal device from the base station device. The base station device instructs the terminal device to transmit a random access preamble to the other base station device by means of a physical downlink control channel (PDCCH) command without performing handover to the other base station device, and transmits a command instructing handover to the other base station device to the terminal device in response to the terminal device being in a state in which handover to the other base station device is to be performed.

Description

Technical Field

[0001] The present invention relates to a handover technique for a cellular communication system. Background Art

[0002] In a mobile communication system, as the terminal device moves, a handover is performed to switch the connection destination cell (base station device) of the terminal device. Typically, after receiving a handover instruction from the base station device, the terminal device performs a cell synchronization establishment and setting process for the connection switching destination, and performs a process to establish a connection. The process of switching the connection destination requires a certain amount of time, and while performing the process, the terminal device cannot transmit user data. In this regard, in the method described in non-patent document 1, before the actual handover, the base station device as the handover source provides the terminal device with communication parameters for connecting to the other base station device radio resource control (RRC) as the handover destination. Then, the base station device as the handover source sends a layer 1 or layer 2 instruction to the terminal device indicating that the cell is to be switched when the handover is to be performed. In response to receiving the instruction, the terminal device can perform a random access process with the base station device as the handover destination to complete the handover without subsequent ground processing on the RRC layer. Through this technology, the degradation of communication efficiency associated with the handover can be reduced.

[0003] Prior art literature

[0004] Non-patent literature

[0005] Non-patent document 1: 3GPP (registered trademark) manuscript, R2-2209255 Summary of the invention

[0006] Problems to be solved by the invention

[0007] The present invention provides techniques for further improving the efficiency of handover-related communications.

[0008] Means used to solve problems

[0009] According to one aspect of the present invention, a base station device comprises: a setting unit, which sets a wireless resource control layer, i.e., an RRC layer, of another base station device in connection with a terminal device, and the other base station device is a candidate for a handover destination of the terminal device from the base station device; an instruction unit, which instructs the terminal device not to perform a handover to the other base station device but to send a random access preamble code to the other base station device through a physical downlink control channel, i.e., a PDCCH instruction; and a sending unit, which sends a command to the terminal device to instruct a handover to the other base station device in accordance with a situation in which the terminal device is in a state in which the handover to the other base station device should be performed.

[0010] According to one aspect of the present invention, a terminal device comprises: a receiving unit, which receives settings for a wireless resource control layer, i.e., an RRC layer, of another base station device from a connected base station device, and receives a physical downlink control channel, i.e., a PDCCH instruction from the base station device, wherein the other base station device is a candidate for a handover destination of the terminal device from the base station device, and the physical downlink control channel instruction instructs the terminal device not to perform a handover to the other base station device but to send a random access preamble code to the other base station device; a sending unit, which sends the random access preamble code to the other base station device in accordance with the instruction; and an execution unit, which executes the handover to the other base station device when a command instructing the handover to the other base station device is received from the base station device.

[0011] Effects of the Invention

[0012] According to the present invention, it is possible to improve communication efficiency related to handover.

[0013] Other features and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings. Note that throughout the drawings, the same reference numerals represent the same or similar components. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

[0015] Figure 1 is a diagram illustrating a configuration example of a wireless communication system.

[0016] Figure 2 is a diagram illustrating an example of the hardware configuration of the device.

[0017] Figure 3 is a diagram illustrating an example of a functional configuration of a base station apparatus.

[0018] Figure 4 is a diagram illustrating an example of a functional configuration of a terminal device.

[0019] Figure 5 is a diagram illustrating an example of the flow of processing performed by a wireless communication system. DETAILED DESCRIPTION

[0020] Hereinafter, the embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments are not intended to limit the scope of the claimed invention, nor are they intended to limit the invention requiring the combination of all the features described in the embodiments. Two or more of the multiple features described in the embodiments may be appropriately combined. In addition, the same reference numerals are given to the same or similar configurations, and their redundant descriptions are omitted.

[0021] (System Configuration)

[0022] Figure 1 The figure shows an example of the configuration of a wireless communication system according to an embodiment of the present invention. The wireless communication system is a cellular communication system configured to comply with a cellular communication standard such as the fifth generation (5G) and subsequent standards of the Third Generation Partnership Project (3GPP (registered trademark)). The wireless communication system includes a base station device 101, a base station device 102, and a terminal device 111. Note that in Figure 1 In the example, in order to simplify the description, only two base station devices and one terminal device are shown, but naturally there may be more base station devices and terminal devices.

[0023] exist Figure 1 In this case, terminal device 111 moves from the area of ​​the cell formed by base station device 101 to the area of ​​the cell formed by base station device 102. At this time, terminal device 111 performs handover for switching the connection destination base station from base station device 101 to base station device 102.

[0024] In an embodiment of the present invention, a handover process is performed to reduce the time period during which the terminal device 111 cannot transmit user data due to the handover. In other words, before the handover is actually performed on the terminal device 111, the switching source base station device 101 performs the setting of the radio resource control (RRC) layer (setting using the RRC message). In other words, in the previous handover, the terminal device 111 received a handover indication from the base station device 101 of the handover source, and at a moment before the handover process was actually performed, the terminal device 111 was notified of the setting of the RRC layer to be performed when the handover process was started. In the setting here, the terminal device 111 is notified of the communication parameters used when connecting to and communicating with the base station device 102 as a handover destination candidate. For example, the communication parameters may include a beam setting for the base station device 102 as a handover destination candidate, parameters to be used when performing a random access procedure, or wireless resources (frequency and time resources), etc. Furthermore, the base station apparatus 101 as the handover source may transmit, to the terminal apparatus 111 , a synchronization signal (SS) / physical broadcast channel (PBCH) block (SSB) measurement command to be transmitted from the base station apparatus 102 as the handover destination candidate.

[0025] The terminal device 111 measures the SSB transmitted from the base station device 102, which is a candidate for the handover destination, according to the measurement instruction from the base station device 101 in connection. Then, the terminal device 111 notifies the base station device 101 in connection of the measurement result. Here, the base station device 101 can notify the measurement target, that is, the base station device 102, which is a candidate for the handover destination, of the measurement result. Therefore, in the case where the terminal device 111 has actually performed the handover, the base station device 102 can determine the approximate direction of the beam to be used when communicating with the terminal device 111. Here, in order to determine the detailed beam used in the downlink, the base station device 102 can notify the terminal device 111 of the transmission setting of the channel state information (CSI)-reference signal (RS). Note that the notification can be performed by sending the transmission setting of the CSI-RS from the base station device 102 to the base station device 101, and the base station device 101 sends the transmission setting to the terminal device 111 in connection. When the terminal device 111 receives the transmission setting, the CSI-RS to be transmitted from the base station device 102 is measured based on the information, and the measurement result is notified to the connected base station device 101. Then, the base station device 101 forwards the measurement result to the base station device 102. In this way, the base station device 102 can obtain the measurement result of the CSI-RS of the terminal device 111. Therefore, the base station device 102 can determine the detailed beam to be used in the downlink communication after the terminal device 111 performs the handover before the handover is actually performed. Therefore, the processing for determining the beam direction in detail after the handover has been performed can be omitted, and the time period during which the communication efficiency of the user data of the terminal device 111 deteriorates can be shortened. For example, the above-mentioned CSI-RS transmission setting can be sent to the terminal device 111 using the CSI-RS measurement setting, which is configured by the CSI-RS radio resource setting (CSI-RS-Resource) and the report setting (csi-ReportConfig) related to the base station device 102, and is pre-set as a communication parameter in the terminal device 111 before the handover. CSI-RS-Resource includes the time position and frequency position of the radio resource block used to send the CSI RS. For example, by using the CSI-RS-Resource id in the media access control / control element (MAC CE) or the downlink control information (DCI) to determine the CSI RS resource, the terminal device 111 can be instructed to measure the radio resource of a specific CSI RS. In addition, in Csi-ReportConfig, the reporting timing of aperiodic or periodic CSI reports is set. For example, by using the csi-ReportConfig id in the MAC CE or DCI to determine the csi-ReportConfig, the terminal device 111 can be instructed to report the CSI-RS measurement results at a specific time.In addition, when the above-mentioned measurement configuration is performed on the terminal device 111, as information for the terminal device 111 to determine which base station device the CSI-RS transmission configuration is for, for example, the base station device 10 may include a cell identifier in a MAC CE or DCI and send it to the terminal device 111.

[0026] In the embodiment of the present invention, in order to further reduce the degradation of communication efficiency at the time of handover, the terminal device 111 performs a random access (RA) process before determining to perform a handover to the base station device 102. In other words, before actually performing the handover, the terminal device 111 can perform a process for uplink synchronization establishment. The base station device 101 to which the terminal device 111 is connected sends an instruction to the base station device 102 for the terminal device 111 to send a random access preamble (RA preamble). Then, the terminal device 111 uses the wireless resources prepared for the RA process in the base station device 102 according to the instruction to send the RA preamble. Note that, for example, when the above-mentioned RRC layer setting process is performed, the wireless resources and the sequence information for generating the RA preamble can be sent from the base station device 101 to the terminal device 111. In addition, when the RA preamble transmission instruction is sent from the base station device 101, the information can be notified to the terminal device 111. For example, the instruction can be performed using a PDCCH instruction, which is a conventional process for sending the RA preamble from the base station device 101. Note that PDCCH is a physical downlink control channel. Note that when the uplink synchronization of the base station device 101 connected to the terminal device 111 is turned off, the RA preamble is sent from the terminal device 111 to the base station device 101 using the previous PDCCH instruction. In this regard, the embodiment of the present invention is different in that it is used to send the RA preamble to the base station device 102 that is not connected. According to this process, the RA preamble sent from the terminal device 111 is received by the base station device 102. Then, the base station device 102 can determine the timing advance value (TA value) to be used when the terminal device 111 sends an uplink signal to the base station device 102. Then, for example, the base station device 102 notifies the base station device 101 connected to the terminal device 111 of the TA value, and the base station device 101 transmits the TA value to the terminal device 111 to notify the terminal device 111 of the TA value. Therefore, when the base station device 101 instructs handover to the base station device 102, the terminal device 111 can establish uplink synchronization with the base station device 102. Therefore, uplink user data can be transmitted to the base station apparatus 102 without performing the RA process again. The RA process to be performed via the PDCCH command according to the embodiment of the present invention will be described in detail below.

[0027] Thereafter, when there is a predetermined opportunity, such as when the reception quality of the wireless signal from the base station device 101 at the terminal device 111 is lower than the reception quality of the wireless signal from the base station device 102, etc. by a predetermined level, the base station device 101 can notify the terminal device 111 to perform the handover. The notification can be performed using an instruction called a cell switching instruction. The instruction can be sent using a media access control / control element (MAC CE) or downlink control information (DCI). Note that the instruction contains identification information of the cell formed by the base station device 102 as the handover destination. In addition, in the case where multiple settings of the RRC layer for communicating with the base station device 102 are set, the instruction may include an identifier uniquely associated with each setting of the RRC layer, such as an RRC-TransactionIdentifier. In addition, at this time, as described above, the TA value determined at the base station device 102 and sent to the base station device 101 via the RA processing performed in advance can be sent from the base station device 101 to the terminal device 111. In addition, as described above, information related to the beam determined by the base station apparatus 102 by performing SSB or CSI-RS measurement in advance and transmitted to the base station apparatus 101 can be transmitted from the base station apparatus 101 to the terminal apparatus 111. In addition, the base station apparatus 102 can maintain the uplink wireless resources to be used by the terminal apparatus 111, and notify the base station apparatus 101 of the information of the maintained wireless resources. Then, the base station apparatus 101 can notify the terminal apparatus 111 of the information of the uplink wireless resources in the above-mentioned instruction. Therefore, after the terminal apparatus 111 receives the above-mentioned instruction, the terminal apparatus 111 can transmit user data without performing control communication with the base station apparatus 102 after the handover. Note that the uplink user data wireless resources can be transmitted from the base station apparatus 102 to the terminal apparatus 111 after the handover. In this case, by performing RA processing before receiving the instruction as described above, the RA processing after the instruction reception can be omitted. Therefore, the terminal apparatus 111 can immediately transmit user data using the specified wireless resources. Note that, for example, the base station apparatus 101 before the handover can obtain a buffer status report (BSR) from the terminal apparatus 111 in connection, and can notify the content to the handover destination base station apparatus 102. Therefore, the base station apparatus 102 can allocate an appropriate amount of wireless resources to the terminal apparatus 111 without receiving the BSR from the terminal apparatus 111. In addition, in response to receiving the above-mentioned instruction from the base station apparatus 101, the terminal apparatus 111 can switch the connection destination to the base station apparatus 102 and send a scheduling request (SR) to the base station apparatus 102.

[0028] Note that, in the case where the terminal device 111 receives the instruction via MAC CE as described above, the terminal device 111 may send an acknowledgment (Ack) or the like to the base station device 101. In addition, in the case where the terminal device 111 receives the above-mentioned instruction, the terminal device 111 may switch the connection destination to the base station device 102, and send an Ack or the like to the base station device 102. In this case, the terminal device 111 may send an Ack to the base station device 102 using the uplink radio resources allocated as described above. In addition, the base station device 102 may transmit the acknowledgment to the base station device 101. In this way, for example, the base station device 101 may determine that the terminal device 111 has switched the connection destination to the base station device 102, and may discard the context information of the terminal device 111. Note that, in the case where the base station device 101 has not received an Ack from the terminal device 111, the above-mentioned instruction may be resent, and handover may be ensured. In addition, in the case where the terminal device 111 receives the instruction via DCI as described above, the terminal device 111 may send a predetermined signal such as an SR or a BSR to the handover destination base station device 102 to implicitly notify the base station device 102 that the instruction has been received. Note that the uplink radio resources of the base station apparatus 102 for transmitting the SR or BSR using the DCI of the instruction can be notified to the terminal apparatus 111 via the base station apparatus 101. Note that, for example, a predetermined signal such as a BSR can be transmitted using a dedicated MAC CE indicating that a handover has been performed based on the above instruction, and can be transmitted in a manner similar to the conventional BSR. In addition, unlike SR, BSR, etc., a dedicated MAC CE indicating that a handover based on the above instruction has been performed can be notified to the base station apparatus 102.

[0029] Note that the use of a timer may be able to determine whether the handover of the terminal device 111 has been successful. When the above-mentioned instruction is received, the terminal device 111 starts measuring a predetermined time period with a first timer. Note that after the first timer starts the time measurement, the terminal device 111 may receive the PDCCH from the base station device 101 in parallel with receiving the PDCCH from the base station device 102. In other words, the terminal device 111 may be able to receive the above-mentioned instruction retransmitted from the base station device 101 and a predetermined signal transmitted from the base station device 102 at the time of successful handover. For example, the terminal device 111 may continue to observe the PDCCH from the two base station devices while switching between receiving the signal of the base station device 101 and receiving the signal of the base station device 102 in a time-division manner. In addition, for example, after receiving the instruction, the terminal device 111 may send a response signal such as the above-mentioned Ack to the base station device 102, and may start a second timer. Note that the amount of time measured by the second timer is less than the amount of time set by the first timer. In addition, the response signal may be, for example, a signal different from the Ack, such as a Cell switching instruction response. For example, in the case where a retransmission instruction or a negative acknowledgement (Nack) indicating that a response signal cannot be received from the base station apparatus 102 is not received within the time until the second timer expires, the terminal apparatus 111 can determine that the handover has succeeded. In the case of receiving a retransmission instruction or Nack, the terminal apparatus 111 can retransmit the response signal, reset the second timer, and start measuring time again. Note that in the case of receiving a retransmission instruction or Nack after the first timer expires, the terminal apparatus 111 can determine that the handover has failed.

[0030] In addition, in another example, when the second timer is not used and a predetermined signal is received from the base station device 102 when the first timer is running, the terminal device 111 can determine that the handover has been successful. In this case, the terminal device 111 can stop the first timer in response to the received predetermined signal. Here, the predetermined signal from the base station device 102 can be, for example, a signal indicating the end of the reception of the PDCCH sent from the base station device 101. In addition, the predetermined signal from the base station device 102 can be an acknowledgment (Ack) for the above-mentioned response signal. In response to receiving the predetermined signal, the terminal device 111 can end the reception of the PDCCH sent from the base station device 101 and continue the reception of the PDCCH from the base station device 102. On the other hand, in the case of receiving a retransmission request or Nack related to the response signal before the first timer ends, the terminal device 111 can retransmit the response signal to the base station device 102. In addition, when the response signal is sent, the third timer is started, and in the case of not receiving the above-mentioned predetermined signal before the third timer ends (regardless of whether the first timer exists), the terminal device 111 can determine that the base station device 102 has not successfully received the response signal. In this case, if the first timer has not ended, the terminal device 111 retransmits the response signal and resets the third timer. If the first timer has ended, the terminal device 111 may determine that the handover has failed. In addition, the terminal device 111 may limit the number of retransmissions of the above-mentioned response signal. In this case, the terminal device 111 may determine that the handover has failed in response to the number of retransmissions of the response signal reaching a predetermined number of times.

[0031] Note that, in the case where the terminal device 111 determines that the handover has failed, the terminal device 111 may end the reception of the PDCCH of the base station device 102 and continue to receive the PDCCH of the base station device 101. Furthermore, in this case, the terminal device 111 may notify the base station device 101 that the handover has failed. In the case where the base station device 102 receives a response signal from the terminal device 111, the base station device 102 may determine that the handover has succeeded, and may notify the base station device 101 that the handover has succeeded. The base station device 101 may delete the context information of the terminal device 111 based on the notification.

[0032] Furthermore, in response to receiving the cell switching instruction, the terminal device 111 may end receiving the PDCCH from the base station device 101. In this case, if the terminal device 111 determines that the handover to the base station device 102 has failed, the terminal device 111 may perform a reconnection process.

[0033] For example, when the above-mentioned RRC layer is set up for processing, the information of the duration measured by the above-mentioned timer and the maximum number of retransmissions of the response signal may be notified to the terminal device 111. Note that, in the case where there are multiple cells as candidates for handover destinations, information such as the timer value and the maximum number of retransmissions of each individual cell in the multiple cells may be notified to the terminal device 111. In addition, at least a portion of the multiple cells may be grouped, and the common setting information of each group may be notified to the terminal device 111. In addition, the common setting information of all cells may be notified to the terminal device 111. In addition, for example, the setting information may be notified to the terminal device 111 via a cell switching instruction. Note that in order to send the above-mentioned response signal, uplink wireless resource allocation is performed. However, information indicating the maximum number of retransmissions in the allocated uplink cloud may be notified to the terminal device 111.

[0034] As described above, the terminal device 111 can shorten the time period during which user data cannot be communicated when handover is performed from the base station device 101 to the base station device 102. Therefore, for example, a communication service with low latency and high reliability can be provided. In addition, by shortening the time period during which user data cannot be communicated, degradation of wireless communication efficiency can be reduced.

[0035] (RA processing based on PDCCH command)

[0036] <Processing Example 1>

[0037] The RA processing based on the PDCCH instruction performed according to an embodiment of the present invention will now be described in more detail. For example, an example will be described in which an inherent sequence is assigned to the terminal device 111 when the RA preamble is generated. First, the base station device 101 notifies the base station device 102 that the terminal device 111 is to start the RA processing. Therefore, both the base station device 101 in which the terminal device 111 is connected and the base station device 102 as a handover destination candidate can be made aware that the RA processing will be performed by the terminal device 111. Then, as described above, the base station device 101 uses the PDCCH to instruct the terminal device 111 to perform the RA processing. At this time, for example, the base station device 101 can notify the terminal device 111 of information for determining wireless resources (frequency and time resources) (such as the SS / PBCH index and PRACH mask index set by the base station device 102, for receiving the RA preamble by the base station device 102), as well as information indicating the sequence of the RA preamble to be used (random access preamble index). Note that, in the case where there are multiple cells as handover destination candidates, the base station apparatus 101 can use one PDCCH to collectively notify the terminal apparatus 111 of the information of the multiple cells. In addition, the base station apparatus 101 can use a separate PDCCH to notify the terminal apparatus 111 of the information of at least a part of the multiple cells. Note that, as described above, the sequence of the RA preamble here can be individually allocated to the terminal apparatus 111. Therefore, for each cell of the handover destination candidate, information indicating a sequence can be notified to the terminal apparatus 111. Therefore, in the case of receiving the RA preamble of the corresponding sequence, the base station apparatus as the handover destination candidate can uniquely determine that the transmission source of the RA preamble is the terminal apparatus 111. Based on the information received from the base station apparatus 101, for the cell as the handover destination candidate, the terminal apparatus 111 uses the wireless resources corresponding to the cell and uses the specified sequence to transmit the RA preamble. For example, the base station apparatus 101 notifies the terminal apparatus 111 of the wireless resources in the base station apparatus 102 that allow the transmission of the RA preamble and the sequence to be used by the terminal apparatus 111. Then, the terminal apparatus 111 transmits the RA preamble to the base station apparatus 102 using the sequence notified by the base station apparatus 101, using the wireless resources notified by the base station apparatus 101. The base station apparatus 102, which is a handover destination candidate, uses the wireless resources for RA processing, performs RA preamble detection processing using the sequence specified for the terminal apparatus 111, and determines whether the RA preamble has been received from the terminal apparatus 111.

[0038] Note that at this time, the TA value may not be notified to the terminal device 111, and contention resolution does not need to be performed by specifying the sequence of the RA preamble inherent to the terminal device 111. Therefore, the base station device 102 may not send an RA response back to the terminal device 111. However, based on the reception timing of the RA preamble, the base station device 102 may determine the TA value to be used by the terminal device 111. Then, for example, the TA value may be sent from the base station device 102 to the base station device 101. For example, the base station device 101 may notify the terminal device 111 of the information of the value together with the following instruction. Note that in the case where the RA response is not sent, the terminal device 111 cannot recognize whether the RA preamble has been received normally. Therefore, in the present processing example, in the case where the RA preamble cannot be received from the terminal device 111 within a predetermined time period, the base station device 102 may cause the terminal device 111 to resend the RA preamble via the base station device 101. For example, the base station device 102 may send a predetermined notification to the base station device 101 indicating that the RA preamble cannot be received from the terminal device 111. In the case of receiving the predetermined notification, the base station device 101 sends a PDCCH instruction to the terminal device 111 again, so that it resends the RA preamble. In the case of receiving the PDCCH instruction again, the terminal device 111 resends the RA preamble. On the other hand, in the case of not receiving the PDCCH instruction again, the terminal device 111 can be configured not to resend the RA preamble. In other words, in this processing example, the terminal device 111 can be configured not to resend the RA preamble when there is no special instruction.

[0039] Note that in the above example, the base station apparatus 102 does not send an RA response. However, the base station apparatus 102 may send an RA response. In this case, the terminal apparatus 111 may obtain a TA value via the RA response. In addition, in response to not receiving an RA response, the terminal apparatus 111 may spontaneously resend the RA preamble. Note that, in the case of receiving an RA response, the terminal apparatus 111 does not perform processing after the RA process (processing after message 3 in the RA process). In other words, the terminal apparatus 111 may obtain a TA value via the RA response, and may end the RA process without performing subsequent processing. In addition, the base station apparatus 102 does not include the allocation of wireless resources for message 3 in the RA response. In other words, in a normal RA process, an uplink wireless resource for sending message 3 is specified in the RA response. However, since there is no need to send message 3, there is no need to specify wireless resources for this.

[0040] Note that in the above-mentioned processing example, in the absence of a retransmission instruction of the RA preamble from the base station apparatus 101 or the base station apparatus 102, the terminal apparatus 111 does not retransmit the RA preamble. However, such a limitation is not intended. For example, the terminal apparatus 111 may retransmit the RA preamble at a predetermined period, and repeatedly transmit the RA preamble at a predetermined period unless an instruction to stop transmitting the RA preamble is received from the base station apparatus 101 or the base station apparatus 102. For example, in the case where the RA preamble is normally detected at the base station apparatus 102, a predetermined time period has passed, and it is determined that the terminal apparatus 111 stops transmitting the RA preamble, the base station apparatus 101 or the base station apparatus 102 may transmit an RA preamble transmission stop instruction to the terminal apparatus 111.

[0041] <Processing Example 2>

[0042] In processing example 1, a sequence of an RA preamble inherent to the terminal device 111 is specified. However, such a limitation is not intended. In another processing example, the terminal device 111 transmits an RA preamble using a sequence selected from a group of sequences used in contention-based RA processing of a cell that is a candidate for a handover destination. As described above, the base station device 101 obtains the SSB measurement result of the cell that is a candidate for a handover destination from the terminal device 111, and selects a cell based on the measurement result so that the terminal device 111 performs RA processing. For example, the base station device 101 can select a cell with a wireless quality equal to or greater than a predetermined level as a cell to be processed by RA. In addition, the base station device 101 can select a predetermined number of one or more cells in sequence starting from the best wireless quality as cells to be processed by RA. Then, the base station device 101 notifies the terminal device 111 of the SSB index corresponding to the selected cell. Based on the SSB index, the terminal device 111 can identify the wireless resources (frequency and time resources) used to send the RA preamble. Here, the base station apparatus 102 may specify a cell radio network temporary identifier (C-RNTI) for RA processing communications and post-contention resolution communications, and may notify the terminal apparatus 111 of the C-RNTI via the base station apparatus 101. In addition, instead of the C-RNTI, a temporary identifier (temporary C-RNTI (TC-RNTI)) may be notified to the terminal apparatus 111.

[0043] Thereafter, the terminal device 111 transmits an RA preamble. For example, the terminal device 111 selects a sequence from a set of sequences corresponding to the notified SSB index, generates an RA preamble, and transmits the RA preamble using the wireless resources corresponding to the SSB index. Here, the terminal device 111 selects a sequence from a set of sequences that can access the base station device 102, and uses the wireless resources used for the RA processing of the base station device 102 to transmit the RA preamble generated using the selected sequence. A set of sequences that can be used to generate the RA preamble here can also be used by other terminal devices, and the base station device 102 cannot determine whether the RA preamble has been received from the terminal device 111 only based on the detection of the RA preamble. Therefore, in the case of detecting the RA preamble, the base station device 102 transmits an RA response for subsequent contention resolution. After transmitting the RA preamble, the terminal device 111 starts a timer (ra-ResponseWindow) for measuring a specific time period for detecting the RA response. In the case of receiving an RA response within a specific time period, the terminal device 111 stops retransmitting the RA preamble. In the case where an RA response is not received within a specific time period, the terminal device 111 retransmits the RA preamble, and resets and restarts the timer. For example, the maximum number of retransmissions of the RA preamble is specified by a signal sent from the base station device 101 or the base station device 102. Note that, as described above, the identification information (C-RNTI, TC-RNTI, etc.) of the terminal device 111 can be notified from the base station device 101 to the terminal device 111. However, instead of the notification, the base station device 102 can notify the terminal device 111 of the TC-RNTI via the RA response. Note that the UE can use the random access (RA)-RNTI to determine the resource allocation of the frequency domain and time domain of the physical downlink shared channel (PDSCH) for sending the RA response. In other words, the resource allocation is specified by the DCI format 1_0 with the CRC scrambled by the base station device 102, and the terminal device 111 can obtain the information using the RA-RNTI. Note that the RA-RNTI is determined based on the position of the wireless resources used in the transmission of the RA preamble (the time position and frequency position determined by the signal, time slot or frame). Then, the terminal device 111 receives an RA response corresponding to the RA preamble transmitted by the terminal device 111 , based on the resource allocation obtained using the RA-RNTI.

[0044] When receiving the RA response, the terminal device 111 transmits a message 3 of the RACH process to the base station device 102 using the uplink radio resources specified in the RA response. Here, the terminal device 111 receives the TA value to be used with the RA response, and uses the TA value to control the transmission timing of the message 3. Note that at this point in time, it is not confirmed whether the TA value is the TA value for the terminal device 111. In other words, other terminal devices receiving the RA preamble with the same subframe and frequency position can also recognize the same RA-RNTI and receive the RA response. Therefore, it is not confirmed that the TA value obtained by the terminal device 111 is a value determined based on the RA preamble sent by the terminal device 111 at this point in time. In the case where the C-RNTI is used to resolve this situation (in other words, contention resolution), the terminal device 111 transmits the identification information (C-RNTI) of the terminal device 111 notified as described above to the base station device 102 via message 3. In addition, the terminal device 111 starts a timer (ra-ContentionResolutionTimer) for measuring a certain period of time to determine whether the contention resolution at the base station device 102 has succeeded. In the case where the terminal device 111 receives a DCI addressed to the identification information (C-RNTI) of the terminal device 111 before the end of the certain time period, the terminal device 111 can determine that the TA value has been set based on the RA preamble sent by the terminal device 111. In the case of using TC-RNTI, the terminal device 111 sends the identification information of the terminal device 111 (for example, InitialUE-Identity configured by 5G-S-TMSI and a random number) to the base station device 102 via message 3. Thereafter, the terminal device 111 starts a timer (ra-ContentionResolutionTimer) for measuring a certain time period to determine whether the contention resolution at the base station device 102 has been successful. In the case where the message 4 sent using the DCI addressed to the identification information (TC-RNTI) of the terminal device 111 before the end of the certain time period includes the identification information of the terminal device 111 (for example, InitialUE-Identity) sent to the base station device 102 via message 3, the terminal device 111 can determine that the TA value has been set based on the RA preamble sent by the terminal device 111. Note that here, only the TA value is confirmed (uplink synchronization establishment has been performed), and the connection between the terminal device 111 and the base station device 102 has not been confirmed. On the other hand, in the case where the terminal device 111 does not receive the DCI addressed to the identification information (C-RNTI or TC-RNTI) of the terminal device 111 within the above-mentioned certain period of time, the TA value obtained using the RA response is not the TA value based on the RA preamble code transmitted by the terminal device 111. Therefore, the terminal device 111 retransmits the RA preamble code.

[0045] Note that the above-mentioned signal transmitted from the base station apparatus 102 to the terminal apparatus 111 may be transmitted to the terminal apparatus 111 via the base station apparatus 101. In this case, the base station apparatus 102 transmits the contents of the message 2 (RA response) and the message 4 to the base station apparatus 101 using, for example, the inter-base station interface, and the base station apparatus 101 notifies the terminal apparatus 111 of the information corresponding to the message. As described above, in the case where the wireless signal is directly transmitted from the base station apparatus 102 to the terminal apparatus 111, the terminal apparatus 111 needs to perform the process of receiving the message 2 and the message 4 from the base station apparatus 101 while continuing to receive the PDCCH of the base station apparatus 101. In contrast, in the case where the message 2 and the message 4 are notified to the terminal apparatus 111 via the base station apparatus 101, the terminal apparatus 111 does not need to receive the wireless signal from the base station apparatus 102. Note that only one of the message 2 and the message 4 may be transmitted to the terminal apparatus 111 via the base station apparatus 101.

[0046] Note that, in the case where the terminal device 111 needs to receive a signal of a cell that is a candidate for the handover destination, the base station device 101 can notify the terminal device 111 of the timing for receiving a downlink signal (e.g., PDCCH) from the base station device of the candidate cell. For example, in the case where the above-mentioned message 2 and message 4 are directly sent from the base station device 102 to the terminal device 111, the terminal device 111 needs to receive a signal such as PDCCH from the base station device 102. In this case, the base station device 101 can notify the terminal device 111 of the timing information for sending a signal such as PDCCH at the base station device 102. Note that there are multiple candidate cells, and the base station device 101 can notify the base station devices of the candidate cells of the change in reception timing so that the timing of the PDCCH of the cells does not overlap. Note that, in the case where there are multiple candidate cells and the timing of the PDCCH of the cells overlaps, the terminal device 111 can notify the base station device 101 of the information of the cell with overlapping reception timing. For example, with the activation of the ra-ResponseWindow as an opportunity, after the transmission of the RA preamble, the terminal device 111 starts to receive the PDCCH of the cell that is the candidate for the transmission destination of the RA preamble. Note that at this time, the terminal device 111 can continue to receive the PDCCH of the base station device 101 in connection, and is in a state of receiving the PDCCH from multiple base station devices in parallel. Thereafter, for example, with the end of the ra-ResponseWindow as an opportunity, the terminal device 111 can end the reception of the PDCCH of the candidate cell. In addition, the terminal device 111 can end the reception of the PDCCH via an instruction from the candidate cell base station device (for example, the base station device 102) or the base station device 101. Note that the instruction from the candidate cell base station device can be sent directly from the base station device to the terminal device 111, or can be sent via the base station device 101.

[0047] Note that in the above processing example, the terminal device 111 stops sending the RA preamble at the end of the timer if no RA response is received. However, such a limitation is not intended. For example, in a case where the terminal device 111 repeatedly sends the RA preamble at a predetermined period and receives an RA preamble sending stop indication from the base station device 101 or the base station device 102, the sending of the RA preamble can be stopped. Note that the sending stop indication can be a signal different from the RA response. For example, in a case where the terminal device 111 determines to stop sending the RA preamble due to the lapse of a predetermined time period, etc., the base station device 101 or the base station device 102 can send an RA preamble sending stop indication to the terminal device 111. Therefore, the stopping of the sending of the RA preamble can be instructed by control on the network side.

[0048] (Processing of the obtained TA value)

[0049] Note that the TA value to be used when the terminal device 111 transmits a signal to the base station device 102 is stored in at least one of the terminal device 111 or the base station device 102 via the above-described processing. However, when a certain amount of time has passed, it can be expected that the TA value is no longer applicable to the real environment. Therefore, in this processing example, how to process the obtained TA value, for example, using a method to maintain an appropriate value of the TA value or end the maintenance of the TA value will be described.

[0050] In the first example, a timer is used to manage the effective period and update period of the TA value. For example, the terminal device 111 starts a predetermined timer in response to the TA value of the candidate cell obtained from the base station device 101 or the base station device 102 as a handover destination candidate. In addition, in response to the end of the predetermined timer, the terminal device 111 performs the above-mentioned process again to send the RA preamble code again and obtain the updated TA value. In addition, the base station device 101 to which the terminal device 111 is connected or the base station device 102 as a handover destination candidate starts a predetermined timer in response to the TA value determined in the base station device 102. Then, in response to the end of the predetermined timer, the base station device that manages the timer can instruct the terminal device 111 to perform the above-mentioned RA process. For example, in the case where the base station device 101 manages the timer, the base station device 101 can send the PDCCH instruction again, thereby performing the above-mentioned process again. In addition, in the case where the base station device 102 manages the timer, the base station device 102 can send a message to the terminal device 111 requesting the base station device 101 to send the PDCCH instruction. Furthermore, when the terminal apparatus 111 continues to receive signals from the base station apparatus 102 , the base station apparatus 102 may directly instruct the terminal apparatus 111 to perform RA processing.

[0051] Note that the terminal device 111 may not perform the RA process again, and may transmit a predetermined signal such as a sounding reference signal (SRS). In other words, by receiving a predetermined uplink wireless signal at the base station device 102, the base station device 102 may be updated to an appropriate TA value. Therefore, for example, at a predetermined timing such as when a predetermined timer managed in the terminal device 111 ends, the terminal device 111 may transmit a predetermined uplink signal using a set TA value related to the base station device 102. Note that, for example, the terminal device 111 may transmit an SR to the base station device 102 and receive an allocation of wireless resources for transmitting a predetermined signal. In addition, in response to receiving an uplink signal transmission instruction for updating the TA value from the base station device 101 or the base station device 102, the terminal device 111 may transmit a predetermined uplink signal. For example, in response to a transmission start instruction from the base station device 102, the terminal device 111 may transmit a predetermined signal such as an SRS irregularly or periodically. Note that a predetermined signal such as an SRS may be transmitted at a timing based on the TA value before the update. Furthermore, during the periodic transmission of the predetermined signal, the terminal device 111 may stop the periodic transmission of the predetermined signal in response to receiving a transmission stop indication for the predetermined signal from the base station device 102. Furthermore, in another example, in the absence of an explicit indication from the base station device 102, the terminal device 111 may periodically transmit a predetermined signal such as an SRS in response to receiving an RA response from the base station device 102. Note that in the case where the terminal device 111 needs to receive an indication from the base station device 102, after performing the above-mentioned RA processing and obtaining the TA value, the terminal device 110 may continue to receive signals such as a PDCCH from the base station device 102. Furthermore, the base station device 101 may provide a transmission and stop indication of the predetermined signal and an opportunity to transmit the predetermined signal.

[0052] Note that, in the case where the terminal device 111 continues to measure the radio quality of the cell as the handover destination candidate and the radio quality deteriorates to a predetermined level or less, for example, the maintenance of the TA value related to the cell may be terminated. Note that the termination of the maintenance of the TA value may be determined by the terminal device 111, or may be determined by the base station device 101 that receives the radio quality report and then sends an instruction to the terminal device 111. In addition, the base station device 102 may measure the radio quality of the above-mentioned predetermined signal from the terminal device 111, and may determine to terminate the maintenance of the TA value based on the result. In this case, if the terminal device 111 is maintaining the TA value, the base station device 102 may instruct the terminal device 111 to discard the TA value. In the case where the maintenance of the TA value is terminated and the above-mentioned timer for maintaining the TA value is still running, the terminal device 111 or the base station device 101 or the base station device 102 stops the timer. In addition, after the above-mentioned timer for maintaining the TA value has ended, the terminal device 111 or the base station device 101 or the base station device 102 may not restart a similar timer. In addition, when the terminal device 111 continues to receive a signal such as a PDCCH from the base station device 102 for maintaining the TA value, the terminal device 111 may end the reception of the signal. Note that the end of receiving the signal from the base station device 102 may be instructed from the base station device 101 or the base station device 102 to the terminal device 111.

[0053] Note that, as described above, the terminal device 111 can perform handover and connect to the base station device 102 in response to receiving a cell switching command from the base station device 101. In this case, the connection between the terminal device 111 and the base station device 101 is disconnected. After the connection is disconnected, the base station device 101 can be set as a base station device that is a handover destination candidate for the terminal device 111. For example, the terminal device 111 can maintain the TA value of the base station device 101 while being connected to the base station device 102. In addition, while being connected to the base station device 102, the terminal device 111 can continue to receive a predetermined signal (PDCCH, etc.) from the base station device 101, thereby maintaining the TA value of the base station device 101. Therefore, in the case where the terminal device repeatedly performs handover between a plurality of base station devices, etc., unnecessary RA processing, etc. can be prevented, thereby allowing more efficient communication.

[0054] (Device Configuration)

[0055] Next, the device configuration will be described. Figure 2is an example of the hardware configuration of a base station device and a terminal device according to an embodiment of the present invention. For example, the base station device and the terminal device 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 including one or more processing circuits, such as a general-purpose central processing unit (CPU), an application-specific integrated circuit (ASIC), and the like. The processing of the entire device and the above-mentioned processing are performed by the processor 201 reading out and executing the program stored in the ROM 202 and the storage device 204. ROM 202 is a read-only memory that stores information (such as programs related to the processing performed by the base station device and the terminal device), various parameters, and the like. RAM 203 is a random access memory that is used as a workspace and temporarily stores information when the processor 201 executes the program. For example, the storage device 204 is composed of a detachable external storage device. The communication circuit 205 is composed of, for example, a circuit for 5G wireless communication or a successor standard. Note that in Figure 2 In the figure, only a single communication circuit 205 is shown, but the base station device and the terminal device may include multiple communication circuits. For example, the base station device and the terminal device may include wireless communication circuits for 5G and for successive standards and antennas shared by the circuits. Note that the base station device and the terminal device may include antennas suitable for each standard, respectively. In addition, the base station device may also include a wired communication circuit used when communicating with other base station devices or core network nodes. In addition, the terminal device may also include communication circuits that comply with wireless communication standards other than cellular communication standards (such as wireless local area networks (LANs) and Bluetooth (registered trademark)). Note that the base station device and the terminal device may include separate communication circuits 205 for multiple available frequency bands, or may include a common communication circuit 205 shared by two or more frequency bands.

[0056] Figure 3 The figure shows an example of the functional configuration of the base station apparatus. For example, the base station apparatus includes an RRC setting unit 301, a RACH indication unit 302, an inter-base station communication unit 303, a handover indication unit 304, and a TA maintenance management unit 305. Note that Figure 3 , the main figure shows the functions of the base station device 101 to which the terminal device 111 is connected. The base station device 102 as a handover destination candidate is similar to the conventional base station device, except that a part of the signal for RA processing is not transmitted and a part of the signal is transmitted to the base station device 101. Therefore, the base station device 102 is not shown here. In addition, Figure 3 In the figure, only the functions specifically related to the embodiments of the present invention are shown, and various other functions that the base station device may include are omitted from the figure. For example, the base station device naturally includes other functions that are usually included in a base station device that complies with 5G or subsequent standards. In addition, Figure 3The functional blocks are schematically shown in the figure, and the functional blocks may be formed integrally or may be subdivided when implemented. In addition, for example, Figure 3 The functions in can be realized by the processor 201 executing a program stored in the ROM 202 or the storage device 204, or can be realized by the processor in the communication circuit 205 executing predetermined software. Note that the processing performed by the above-mentioned functional units will not be described here, and the functions are described here in a broad sense.

[0057] For example, the RRC setting unit 301 performs RRC layer settings for the terminal device in connection. For example, the RRC setting unit 301 sends a switching request to other base station devices that are candidates for handover destinations providing adjacent cells, obtains communication setting information from the other base station devices, and notifies the terminal device of the communication setting information via an RRC layer message. The RRC layer message is an RRC reconfiguration message. Then, the RRC setting unit 301 performs connection processing settings between the terminal device and other base station devices by receiving an RRC reconfiguration completion message from the terminal device. The RACH indication unit 302 indicates that the terminal device that has completed the RRC layer setting sends an RA preamble to other base station devices that are candidates for handover destinations. Here, the RA preamble transmission indication may include a sequence for generating an RA preamble inherent to the terminal device and a set of sequences that may also be used by other terminal devices that attempt to connect to other base station devices, or may include information on wireless resources for sending RA preambles. For example, the RACH indication unit 302 may instruct the terminal device in connection to send an RA preamble to a base station device that is a candidate for handover destination via a physical downlink control channel (PDCCH) command. In addition, in the case where the RACH indication unit 302 is configured to instruct the terminal device to resend the RA preamble or repeatedly send the RA preamble, the RACH indication unit 302 may send an RA preamble transmission stop indication to the terminal device as needed.

[0058] The inter-base station communication unit 303 communicates between base station devices that are candidates for handover destinations. For example, the inter-base station communication unit 303 can notify other base station devices that are the destinations for sending RA preambles, so that the terminal device in connection sends RA preambles. In addition, for example, the inter-base station communication unit 303 is used to receive information for RA processing at a base station device that is a candidate for handover destination. In addition, for example, the inter-base station communication unit 303 can receive a message (message 2 or message 4) to be sent from a base station device that is a candidate for handover destination to a terminal device in RA processing. In addition, the TA value calculated in the base station device that is a candidate for handover destination can be obtained via the inter-base station communication unit 303. Note that the signal received at the inter-base station communication unit 303 can be transmitted to the terminal device via a RACH indication unit, etc.

[0059] For example, in the case where the reception quality of the wireless signal from the other base station device as the handover destination of the terminal device is higher than the wireless quality between the present device and the terminal device by a predetermined level or more, in response to the terminal device becoming in a state where the handover should be performed, the handover instruction unit 304 instructs the terminal device to perform the handover. For example, the handover instruction unit 304 sends a cell switching command including a cell identifier to the terminal device, and the cell identifier can determine the base station device as the handover destination, etc. Note that in the case where the TA value used by the terminal device that sends the RA preamble in the uplink communication, etc. is determined, the TA value can be included in the instruction sent to the terminal device. Therefore, the terminal device can directly use the TA value to send the uplink user data signal after the handover. In addition, in the above-mentioned embodiment of the present invention, the handover instruction unit 304 sends the above-mentioned instruction after the RA processing is performed by the terminal device. However, for example, in some cases, such as in response to an uplink communication delay request for the terminal device, the above-mentioned instruction can be sent before the RA processing is performed. In other words, the RA processing can be performed before the handover instruction exchange, or the RA processing can be performed after the instruction exchange.

[0060] The TA maintenance management unit 305 manages the TA value to be used when the terminal device sends an uplink signal to the base station device that is a candidate for the handover destination. For example, the TA maintenance management unit 305 can set the valid period and update period of the TA value, and can resend the RA preamble to the terminal device, thereby updating the TA value when the valid period ends or the update period arrives. In addition, the TA maintenance management unit 305 can notify the terminal device of the SRS setting of the base station device that is the handover destination, and can update the TA value by sending the SRS to the terminal device using the SRS setting. Note that the base station device that is the handover destination may include the TA maintenance management unit 305, or the base station device may send an RA preamble sending indication or an SRS sending indication to the terminal device.

[0061] Figure 4 The figure shows an example of the functional configuration of the terminal device. For example, the terminal device includes an RRC setting unit 401, a RACH indication receiving unit 402, a RACH processing unit 403, a handover processing unit 404 and a TA maintenance management unit 405. Note that Figure 4 In the figure, only the functions specifically related to the embodiments of the present invention are illustrated, and various other functions that the terminal device may include are omitted from the figure. For example, the terminal device naturally includes other functions that are usually included in a terminal device that complies with 5G or subsequent standards. In addition, in Figure 4 The functional blocks are schematically shown in the figure, and the functional blocks may be formed integrally or may be subdivided when implemented. In addition, for example, Figure 4The functions in the embodiment can be implemented by the processor 201 executing a program stored in the ROM 202 or the storage device 204, or can be implemented by the processor in the communication circuit 205 executing predetermined software. Note that the processing performed by the above-mentioned functional units will not be described here, and the functions will be described here in a broad sense.

[0062] The RRC setting unit 401 performs connection setting processing with the base station device as the handover destination candidate by receiving an RRC layer message from the base station device as the connection destination. Note that the RRC setting unit 401 maintains the setting for the base station device being connected in parallel with the setting for the base station device as the handover destination candidate. The RACH indication receiving unit 402 receives an RA preamble transmission instruction from the base station device being connected. The RA preamble transmission instruction can be performed via a PDCCH instruction. Note that, for example, the RACH indication receiving unit 402 can also receive an RA preamble retransmission instruction, an RA preamble transmission stop instruction, etc. In response to the RACH indication receiving unit 402 receiving the instruction, the RACH processing unit 403 transmits an RA preamble to the base station device as the handover destination candidate. Here, information on the sequence for generating the RA preamble and the radio resources for receiving the RA preamble in the base station device as the handover destination candidate can be received from the base station device being connected via the RACH indication receiving unit 402. Note that the information on the sequence and the radio resources can be obtained from the system information delivered by the base station device as the handover destination candidate. The handover processing unit 404 changes the connection destination base station device in response to receiving a handover instruction (cell switching instruction) from the base station device being connected. Note that due to the setting process of the RRC setting unit 401 and the RACH process of the RACH processing unit 403, the terminal device does not need to perform special setting processing with the base station device that is a handover destination candidate. Therefore, for example, in the case where the allocation of uplink radio resources in the base station device that is a handover destination candidate is notified via the received instruction, the terminal device can immediately send an uplink signal using the radio resources.

[0063] In the case of obtaining the TA value of the base station device as a handover destination candidate, the TA maintenance management unit 405 performs TA value maintenance and management. For example, in response to the end of the TA value effective period, the TA maintenance management unit 405 may retransmit the RA preamble and update the TA value without receiving an instruction from the base station device being connected or the base station device being the handover destination candidate. In addition, via an instruction from the base station device being connected or the base station device being the handover destination candidate, the TA maintenance management unit 405 may transmit an RA preamble or a predetermined signal such as an SRS for the base station device being the handover destination candidate, and update the TA value. In addition, in the case of receiving information indicating the end of TA value maintenance from the base station device being connected, the TA maintenance management unit 405 ends the maintenance of the TA value. Here, the TA maintenance management unit 405 may immediately discard the TA value whose maintenance has ended, or may maintain it for an effective period. In addition, after the handover is performed, the TA maintenance management unit 405 may maintain and manage the TA value of the base station device being the handover source. In other words, after handover from a base station apparatus to another base station apparatus is performed, the TA maintenance management unit 405 can maintain the TA value of the base station apparatus in connection as the TA value of the base station apparatus that is a handover destination candidate.

[0064] (Processing Flow)

[0065] Figure 5 The figure shows an example of a process flow performed by a wireless communication system according to an embodiment of the present invention. Figure 5 The examples shown in are examples, and modifications such as those described above can be applied to each process. Figure 5 In the example shown in , a sequence inherent to the terminal device is notified to the terminal device as a sequence for generating an RA preamble to be transmitted to a base station device that is a handover destination candidate. However, this may be replaced by the above-described process in which a group of sequences that can be used by a plurality of terminal devices is notified. Note that in Figure 5 In the example of , a connection between the first base station device as the handover source and the terminal device is established.

[0066] First, the first base station device sends a handover request message (S501) to the second base station device that forms a neighboring cell that is a candidate for the handover destination of the terminal device. When the second base station device receives the message, the second base station device sends back a handover request ACK message (S502) containing information such as communication parameters to be used when the terminal device is connected to the first base station device. Then, the first base station device notifies the terminal device of an RRC reconfiguration message (S503) containing the communication parameters notified by the second base station device. When the terminal device receives the message, the terminal device sends an RRC reconfiguration completion message to the first base station device and ends the setting process using an RRC layer message. Through this process, after the handover indication has been sent from the first base station device to the second base station device, the terminal device does not need to perform the RRC layer setting process. Note that in Figure 5 In the example of , only one base station device as a handover destination candidate is illustrated. However, similar setting processing can be performed on a plurality of candidate base station devices.

[0067] Thereafter, the terminal device measures a wireless signal (e.g., SSB) transmitted from a second base station device that is a candidate for a handover destination (S505), and notifies the first base station device of the measurement result (S506). Here, the first base station device may notify the second base station device of the measurement result. In this case, the second base station device may determine the approximate beam used when communicating with the terminal device. The second base station device may send a CSI-RS and cause the terminal device to perform a measurement to form a more detailed beam. In this case, the second base station device may send CSI-RS setting information to the first base station device to transmit it to the terminal device. The terminal device measures the CSI-RS based on the setting information, and reports the measurement result to the first base station device in connection. The first base station device then transmits the measurement result to the second base station device. Therefore, after the terminal device performs a handover to the second base station device, the second base station device may immediately use a detailed beam to transmit a downlink signal.

[0068] Next, the first base station device instructs the terminal device to send an RA preamble to the second base station device (S507). Here, the instruction may include a sequence used by the terminal device to generate an RA preamble and information specifying a wireless resource for sending the RA preamble. Note that, for example, the wireless resource for sending the RA preamble may be determined based on system information of the second base station device sent from the second base station device and measured by the terminal device. In other words, the information may not be obtained from the base station device in connection. In addition, the sequence to be used when generating the RA preamble may be predetermined. For example, in S503, the information of the sequence may be notified to the terminal device. The terminal device sends an RA preamble to the second base station device according to the instruction (S508). At this time, the first base station device may notify the second base station device that the terminal device is going to send an RA preamble. At this time, the first base station device may notify the second base station device of the information of the sequence used by the terminal device to generate the RA preamble. Therefore, the second base station device can detect the RA preamble to be sent by the terminal device. Note that this is an example, and, for example, the handover request of S501 may be used to implicitly notify the terminal device that the RA preamble will be sent. In addition, in this case, the handover request ACK of S502 can be used by the second base station device to specify the sequence used by the terminal device to generate the RA preamble. Note that this is an example, and information about the sequence used by the terminal device to generate the RA preamble, etc. can be shared between the first base station device and the second base station device via another message. The second base station device calculates the TA value based on the RA preamble sent from the terminal device (S509). The second base station device can notify the first base station device of the calculated TA value (S510). Note that the TA value can be managed by one or both of the first base station device and the second base station device. In addition, for example, in response to the first base station device determining to perform a handover of the terminal device, the TA value can be notified from the second base station device to the first base station device. For example, the first base station device can notify the second base station device of the handover, and in response to the notification, the TA value can be sent from the second base station device to the first base station device.

[0069] At this time, the terminal device has not yet performed a handover to the second base station device. In this state, the terminal device continuously measures the wireless signal from the second base station device (S511) and notifies the first base station device in the connection of the measurement result (S512). The first base station device can determine to hand over according to the measurement result (S513). For example, when a predetermined condition is met, such as when the wireless quality of the signal from the second base station device is higher than the wireless quality of the signal from the first base station device by more than a predetermined level, the first base station device can determine to hand over the terminal device to the second base station device. The first base station device sends an instruction (S514) instructing the terminal device to hand over according to the determination. The instruction may include the TA value obtained in S510 and information on uplink resources for sending signals immediately after the handover. Note that the TA value can be transmitted to the terminal device immediately after notifying the first base station device in S510. In this case, the instruction does not need to include the TA value. In addition, the first base station device can determine the information of the uplink resource by inquiring the second base station device in advance. In addition, the first base station device can instruct the terminal device to use the reserved predetermined wireless resources that the second base station device can use without sending an inquiry. When the terminal device receives the instruction, the terminal device can change the connection destination base station device to the second base station device, and can send a response signal to the instruction to the second base station device using the resources specified by the received instruction (S515). Therefore, the second base station device can confirm that the terminal device has performed a handover to the second base station device, and thereafter, user data can be transmitted between the terminal device and the second base station device (S516). Note that in addition to or instead of the response signal of S515, the terminal device can also send user data to the second base station device.

[0070] In this way, according to an embodiment of the present invention, the base station device as the handover source determines to make the terminal device actually perform the handover to the other base station device. Thereafter, the time taken before the terminal device can start user data communication with the post-handover base station device can be greatly reduced. This contributes to the achievement of Goal 9 of the Sustainable Development Goals (SDGs) initiated by the United Nations, namely, "improving resilient infrastructure, promoting sustainable industrialization, and seeking the expansion of innovation."

[0071] The present invention is not limited to the above-described embodiments, and various changes / modifications can be made within the gist of the present invention.

[0072] This application claims the benefit of Japanese Patent Application No. 2023-019287, filed on February 10, 2023, which is hereby incorporated by reference into this application.

Claims

1. A base station device, wherein: The base station device comprises: a setting unit that performs setting of a radio resource control layer (RRC layer) of another base station device for the terminal device being connected, the other base station device being a candidate for a handover destination of the terminal device from the base station device; an instruction unit for instructing the terminal device not to perform handover to the other base station device and to instruct, through a physical downlink control channel (PDCCH) instruction, to send a random access preamble to the other base station device; as well as A transmitting unit transmits a command instructing the terminal device to hand over to the other base station device in response to the terminal device being in a state where the handover to the other base station device is required.

2. A terminal device, wherein: The terminal device comprises: a receiving unit that receives, from a base station device being connected, a setting of a radio resource control layer (RRC layer) of another base station device, and receives a physical downlink control channel (PDCCH) instruction from the base station device, the other base station device being a candidate for a handover destination of the terminal device from the base station device, the physical downlink control channel instruction instructing the terminal device not to perform a handover to the other base station device but to send a random access preamble to the other base station device; a sending unit, configured to send the random access preamble to the other base station apparatus according to the instruction; as well as An execution unit executes the handover to the other base station device when receiving a command instructing the handover to the other base station device from the base station device.

3. The terminal device according to claim 2, wherein: The receiving unit receives, through the one PDCCH, an instruction to transmit the random access preamble to the plurality of other base station devices.

4. The terminal device according to claim 2 or 3, wherein: The receiving unit receives, from the base station device, a sequence specific to the terminal device used by the terminal device when generating the random access preamble and information for specifying wireless resources that can be used when transmitting the random access preamble, The transmitting unit generates the random access preamble using the sequence specific to the terminal device, and transmits the random access preamble in the wireless resource specified by the information.

5. The terminal device according to any one of claims 2 to 4, wherein: The receiving unit receives, from the base station apparatus or the other base station apparatus, a TA value which is a value of a timing advance determined in the other base station apparatus based on the random access preamble code transmitted by the terminal apparatus.

6. The terminal device according to claim 5, wherein: The terminal device further includes a maintaining unit, the maintaining unit maintaining the TA value, The transmission unit transmits a predetermined uplink signal to the other base station device in response to the expiration of the validity period of the TA value or the arrival of an update period.

7. The terminal device according to claim 6, wherein: The transmission unit transmits the random access preamble as the predetermined uplink signal to the other base station apparatus when the base station apparatus instructs transmission of the random access preamble in response to expiration of a validity period of the TA value or arrival of an update period.

8. The terminal device according to claim 6 or 7, wherein: The transmission unit transmits the SRS as the predetermined uplink signal to the other base station apparatus at a transmission timing determined using the TA value in a predetermined cycle or in response to an instruction from the other base station apparatus to transmit the SRS.

9. The terminal device according to any one of claims 6 to 8, wherein: The maintaining unit ends maintaining the TA value when the radio quality between the terminal device and the other base station device becomes equal to or lower than a predetermined level.

10. The terminal device according to claim 4, wherein: When a signal requesting retransmission of the random access preamble is received from the base station device, the sending unit retransmits the random access preamble, and when a signal requesting retransmission of the random access preamble is not received from the base station device or the other base station device, the sending unit does not retransmit the random access preamble.

11. The terminal device according to claim 10, wherein: The terminal device also has: a timer starting unit that starts a timer when receiving a command instructing handover to the other base station device; a response transmission unit that transmits, to the other base station device as the handover destination, a confirmation response to a command instructing handover to the other base station device; as well as A timer stopping unit stops the timer in response to receiving a predetermined signal from the other base station device serving as a handover destination.

12. The terminal device according to claim 11, wherein: The receiving unit receives setting information common to all cells.

13. The terminal device according to claim 12, wherein: The command received from the base station apparatus includes a timing advance value, that is, a TA value.

14. The terminal device according to claim 13, wherein: The terminal device performs handover to the other base station device by omitting an RA procedure for the other base station device.

15. The terminal device according to claim 14, wherein: The terminal device starts the timer in response to obtaining the TA value of the candidate cell from the base station device or the other base station device.

16. The terminal device according to claim 4, wherein: The transmission unit repeatedly transmits the random access preamble at a predetermined cycle until receiving an instruction to stop transmission of the random access preamble from the base station apparatus, and stops transmission of the random access preamble in response to receipt of the transmission stop instruction.

17. The terminal device according to any one of claims 2 to 16, wherein: The receiving unit receives, from the base station device, a set of sequences that can be used when generating the random access preamble to be transmitted to the other base station device, The transmission unit generates the random access preamble using one sequence selected from the group of sequences, and transmits the random access preamble to the other base station apparatus.

18. The terminal device according to claim 17, wherein: The receiving unit receives a response to the random access preamble from the base station device or the other base station device, When receiving the response, the transmitting unit transmits a first message including identification information of the terminal device to the other base station device. The receiving unit receives, from the base station device or the other base station device, a second message including identification information of the terminal device in response to the first message.

19. The terminal device according to claim 18, wherein: The receiving unit receives, from the base station device, notification of at least one of a timing at which the response to the random access preamble of the terminal device is transmitted from the other base station device and a timing at which the second message is transmitted from the other base station device.

20. The terminal device according to any one of claims 2 to 18, wherein: The sending unit repeatedly resends the random access preamble code at a predetermined period according to the instruction of sending the random access preamble code, The receiving unit receives an instruction to stop transmitting the random access preamble from the base station device, The sending unit stops sending the random access preamble code according to the situation of receiving the sending stop instruction.

21. A control method, which is executed by a base station device, wherein: The control method comprises: The step of performing settings on a radio resource control layer (RRC layer) of another base station device for a terminal device in connection, the other base station device being a candidate for a handover destination of the terminal device from the base station device; Instructing the terminal device not to perform handover to the other base station device and to send a random access preamble to the other base station device through a physical downlink control channel (PDCCH) instruction; as well as The step of transmitting, to the terminal device, a command instructing handover to the other base station device, in response to the terminal device being in a state in which handover to the other base station device is required.

22. A control method, which is executed by a terminal device, wherein: The control method comprises: The step of receiving, from the connected base station device, a setting of a radio resource control layer (RRC layer) of another base station device, the other base station device being a candidate for a handover destination of the terminal device from the base station device; A step of receiving a physical downlink control channel (PDCCH) instruction from the base station device, the physical downlink control channel instruction instructing the terminal device not to perform a handover to the other base station device and to send a random access preamble to the other base station device; The step of sending the random access preamble code to the other base station device according to the instruction; as well as When a command instructing handover to the other base station device is received from the base station device, a step of handing over to the other base station device is executed.

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