Base station, communication device, communication method, and control program

Abstract

To solve the problem in which: relay UE cannot be appropriately selected.SOLUTION: A base station is disclosed, which comprises: acquisition means that, in a first state of executing relay communication in which communication between first user equipment (UE) and the base station is realized through second EU that relays communication, acquires first signal intensity information representing the signal intensity between the first UE and the second UE, and second signal intensity information representing the signal intensity between the first UE and third UE not connected with the first UE; and comparison means that, in the first state, compares the first signal intensity information with the second signal intensity information. The first signal intensity information with the second signal intensity information are information on the signal intensity of the same physical channel.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to a base station, a communication device, a communication method, and a control program. [Background technology]

[0002] In recent years, 3GPP (3rd Generation Partnership Project) (registered trademark) has been formulating specifications for LTE (Long Term Evolution) and 5GNR (New Radio). Among these, a standard specification called Sidelink communication (hereinafter, Sidelink) has been formulated. This specification considers the realization of direct wireless communication that does not involve a mobile communication network (core network).

[0003] Furthermore, the 3GPP is currently formulating specifications to expand the range of Sidelink communication by using a function (Sidelink relay function) to relay Sidelink communication via a relay device (Relay UE: User Equipment).The specifications also stipulate a means for a communication terminal (Remote UE) to switch from communication connecting to a base station via a relay UE (indirect path) to direct communication with a base station (direct path), and a means for switching from the direct path to the indirect path.

[0004] Patent Document 1 proposes an improvement to the problem that occurs in the procedure (discovery) when a remote UE connects to a base station via a relay UE. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2018-535594 Summary of the Invention [Problem to be solved by the invention]

[0006] Currently, 3GPP does not specify a method for determining when to switch from an indirect path to another indirect path, which means that there is a problem in that it is not possible to appropriately select a relay UE. [Means for solving the problem]

[0007] Therefore, one aspect of the present invention provides a base station comprising: an acquisition means for acquiring, in a first state in which communication between a first UE (User Equipment) and the base station is relayed communication realized via a second UE that relays the communication, first signal strength information representing a signal strength between the first UE and the second UE and second signal strength information representing a signal strength between the first UE and a third UE not connected to the first UE; and a comparison means for comparing, in the first state, the first signal strength information and the second signal strength information, wherein the first signal strength information and the second signal strength information are information on signal strength of the same physical channel. Effect of the Invention

[0008] According to one aspect of the present invention, it is possible to appropriately select a relay UE and switch to an indirect path with higher communication quality while continuing the service. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram illustrating an example of a configuration of a communication system according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a block diagram showing an example of a functional configuration of a base station in the present embodiment. [Diagram 3] 2 is a block diagram showing an example of a functional configuration of a remote UE in the present embodiment. FIG. [Figure 4] 2 is a block diagram showing an example of a functional configuration of a relay UE in the present embodiment. FIG. [Diagram 5] FIG. 1 is a schematic diagram illustrating a sidelink physical channel. [Figure 6] FIG. 4 is a sequence diagram illustrating an example of an exchange between communication devices in the first embodiment. [Figure 7] 4 is an example of a flowchart between communication devices according to the first embodiment. [Figure 8] 4 is an example of a flowchart between communication devices according to the first embodiment. [Figure 9] 4 is an example of a flowchart between communication devices according to the first embodiment. [Figure 10] FIG. 13 is a diagram illustrating an example of a configuration of a communication device according to a second embodiment. [Figure 11] 13 is an example of a sequence diagram between communication devices according to the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, the embodiments will be described in detail with reference to the attached drawings. Note that the following embodiments do not limit the invention according to the claims. Although the embodiments describe a number of features, not all of these features are essential to the invention, and the features may be combined in any manner. Furthermore, in the attached drawings, the same reference numbers are used for the same or similar configurations, and duplicated descriptions are omitted.

[0011] [First embodiment] (System Configuration) Fig. 1 is a diagram showing an example of the configuration of a system according to this embodiment. The system of this embodiment includes UEs 101 to 103, a base station gNB 104, and a core network (not shown) to which the gNB 104 is connected via fibers or the like. gNB is an abbreviation for gNodeB, which stands for next generation NodeB. UE is an abbreviation for User Equipment.

[0012] In the system of Figure 1, Remote UE-A (101), Relay UE-B (102), and Relay UE-C (103) are all within the communication area (105) of a gNB (104).

[0013] Remote UE-A (101) communicates with gNB (104) using sidelink relay communication. Relay UE-B (102) operates as a relay UE that relays communication between Remote UE-A (101) and gNB (104) using sidelink relay function. That is, Remote UE-A connects to the base station via an indirect path (indirect path shown in Figure 1) via Relay UE-B. It communicates data with base stations and devices on the core network (not shown). In addition, the Uu link described later refers to the link when Remote UE-A communicates directly with the gNB without going through a relay UE.

[0014] The Relay UE-C (103) has a sidelink relay function and can operate as a relay UE. The Relay UE-C (103) is in a connected state with the gNB (104).

[0015] The Remote UE-A 101 can transmit a discovery signal to a nearby UE (i.e., Relay UE-C 103) to search for the Relay UE-B 102 or another relay UE (candidate relay UE), and can receive a response signal to the discovery signal.

[0016] In addition, Relay UE-C 103 can respond to a discovery signal from Remote UE-A 101, and can also transmit a discovery signal to nearby UEs.

[0017] Although Relay UE-B102 is a relay UE, it can respond to a discovery signal in the same way as Relay UE-C103, and can also transmit a discovery signal to nearby UEs.

[0018] (Functional configuration of the device) Next, the functional configuration of the communication device according to the present embodiment will be described. Note that the functional block configuration described below is merely an example.

[0019] Some (possibly all) of the functional blocks described may be replaced with other functional blocks that perform similar functions, some functional blocks may be omitted, or further functional blocks may be added. In addition, one functional block described below may be divided into multiple functional blocks, or multiple functional blocks may be integrated into one functional block. Also, only some of the functional blocks may be configured with hardware, and the other functions may be configured with software. When the functional blocks are configured with software, a processor constituting the control units 201, 301, and 401 described below executes a control program for realizing the functions stored in the storage units 202, 302, and 402 described below. This provides the functions of the functional blocks.

[0020] FIG. 2 is a block diagram showing an example of the functional configuration of the gNB (104) in this embodiment. In FIG. 2, 201 is a control unit that controls the operation of the base station. 202 is a storage unit that stores information used by the control unit 201 for control and information related to communication. 203 is a management unit for UE information within the base station area, and the UE information manages the IDs of subordinate UEs and measurement results (such as the signal strength of Uu links) reported from the subordinate UEs. 204 is a processing unit that determines whether the UEs managed by 203 should be connected via an indirect path or a direct path. 205 is a generation unit for a message used to instruct path switching. 206 is a message analysis processing unit that analyzes a message received from a subordinate UE. 207 is a communication unit that transmits and receives information via wireless communication with the subordinate UEs, and performs a process of transmitting a message generated by the message generation processing unit 205 and a process of receiving a message from the subordinate UEs.

[0021] FIG. 3 is a block diagram showing an example of the functional configuration of a remote UE (101) in this embodiment. In FIG. 3, 301 is a control unit that controls the operation of the remote UE. 302 is a storage unit that stores information used by the control unit 301 for control and information related to communication. 303 is a measurement unit that measures "signal strength between relay UEs (relay link)", "signal strength between base stations (Uu link)", and "signal strength between candidate relay UEs" as seen from the remote UE. 304 is a processing unit that enables connection to a base station via the relay function of the relay UE (i.e., via an indirect path) by connecting to the relay UE via Sidelink. 305 is a generation unit that generates a discovery signal to be transmitted to nearby relay UEs, and an RRC Reconfiguration Complete message and Measurement Report to be transmitted to a base station.

[0022] Reference numeral 306 denotes a message analysis processing unit that analyzes messages such as a discovery signal or a response signal transmitted from a nearby relay UE, and an RRC Reconfiguration message transmitted from a base station. Reference numeral 307 denotes a communication unit that transmits and receives information with nearby relay UEs and base stations via wireless communication, and performs a process of transmitting messages generated by the message generation processing unit 205 and a process of receiving messages from nearby relay UEs and base stations.

[0023] Each signal strength measured by signal strength measurement section 303 is stored in storage section 302, which also stores information on discovery reference signal strength SD-RSRP, which will be described later.

[0024] FIG. 4 is a block diagram showing an example of the functional configuration of the relay UE (102, 103) in this embodiment. In FIG. 4, the description of the same functional blocks as in FIG. 3 is omitted. 403 is a functional unit that measures the "signal strength between relay UEs (relay link)" seen from the relay UE. 404 is a processing unit that performs a relay function to connect a sidelink-connected remote UE to a base station via the relay UE. 405 transmits a discovery signal to a nearby remote UE and responds to a discovery signal transmitted from the remote UE. Furthermore, 405 is a functional unit that generates an RRC Reconfiguration Complete message and a Measurement Report to be transmitted to the base station. 406 is a message analysis processing unit that analyzes a discovery signal transmitted from a remote UE, an RRC Reconfiguration message transmitted from a base station, and other messages.

[0025] 5 is a diagram showing an example of the configuration of a physical channel in sidelink communication. The vertical axis shows frequency, and the horizontal axis shows time. Note that a physical channel means a channel that is divided by physical resources such as frequency and time.

[0026] A PSCCH (Physical Sidelink Control CHannel) 501 is a physical channel for exchanging control information in sidelink communication. The control information is information indicating the frequency of data transmitted in the PSSCH (described later), allocation in resource blocks divided by time, and the like.

[0027] Reference numeral 502 denotes a PSSCH (Physical Sidelink Shared CHannel), which is a physical channel for exchanging data payload or additional control information in sidelink communication.

[0028] 503 is a PSBCH (Physical Sidelink Broadcast CHannel), which is a physical channel related to synchronization in sidelink communication. The PSBCH 503 is periodically transmitted together with a sidelink synchronization signal block (S-SSB) at a time frequency other than the slot of the resource pool.

[0029] Reference numeral 504 denotes a PSDCH (Physical Sidelink Discovery CHannel), which is a physical channel for UE search (discovery) in sidelink communication. A searching UE (searching UE) periodically transmits a discovery request signal. A UE (searched UE) that receives the discovery request signal extracts necessary information and responds to the searching UE. For example, it performs presence confirmation and signal strength measurement. Signal strength measurement is defined as SD-RSRP (Sidelink Discovery Reference Signal Received Power) in 3GPP technical specification TS36.214 5.1.22.

[0030] The method of measuring the signal strength is as follows: First, the searching UE transmits a PSDCH 504 with a valid CRC (Cyclic Redundancy Check) in discovery. The searched UE receives the reference signal of the PSDCH 504, measures the signal strength of the signal in the signal strength measuring section 403, and transmits information on the value of the signal strength to the searching UE.

[0031] (Processing example) The operation of this embodiment will be described with reference to the operation sequence diagram shown in FIG. 6 and the flowcharts shown in FIGS.

[0032] Fig. 6 is an example of a switching sequence from an indirect path to an indirect path in this embodiment. Fig. 7, Fig. 8, and Fig. 9 are flowcharts showing the contents of the sequence in Fig. 6 in this embodiment for the gNB 104 and the Remote UE-A 101.

[0033] In the gNB 104, the control unit 201 executes a control program stored in the storage unit 202 to realize each process on the gNB side shown in the flowchart. In addition, in the Remote UE-A 101, the control unit 301 executes a control program stored in the storage unit 302 to realize each process on the UE side shown in the flowchart. Note that some of the processes are realized in cooperation with the hardware and functional units described above.

[0034] In this embodiment, Remote UE-A 101 uses Sidelink Relay processing unit 304 and is connected to the base station via Sidelink relay processing unit 404 of Relay UE-B 102. Remote UE-A 101 is transmitting and receiving user data (such as streaming data) (F601, S701).

[0035] Next, during the transmission and reception of the data, the control unit 301 of the Remote UE-A101 activates the message generation processing unit 305. Then, the message generation processing unit 305 creates a discovery request signal, and transmits the discovery request signal to the Relay UE-B102 and the Relay UE-B103 through the wireless communication unit 307 (F602). Furthermore, the control unit 301 activates the message analysis processing unit 306. The control unit 301 prepares for analysis of a message to be performed when a response signal to the discovery request signal or a discovery request signal from a neighboring relay UE including the Relay UE-B102 is received through the wireless communication unit 307 (i.e., the execution of discovery is started) (S702). Furthermore, the Relay UE-B102 that has received the discovery request signal transmits a discovery response signal to the Remote UE-A101 (F603).

[0036] Next, signal strength measurement section 303, which has been started up in advance by control section 301 of Remote UE-A101, starts measuring "the signal strength between Remote UE-A101 and gNB104 (hereinafter, Uu link)" and "the signal strength between Remote UE-A101 and Relay UE-B102 (hereinafter, relay link)" (F603, S703). The signal strength of the relay link is measured by measuring SD-RSRP, which is the strength of the discovery reference signal transmitted by Relay UE-B102.

[0037] When the wireless communication unit 307 receives a discovery signal and a response signal to the discovery signal from a neighboring relay UE, the message analysis processing unit 306 analyzes the signal and stores the ID of the relay UE that transmitted the signal and the serving cell ID in the candidate relay UE list held by the storage unit 302 (S704, S705).

[0038] If there is a candidate relay UE in the candidate relay UE list, the signal strength measurement unit 303 starts measuring the signal strength between the Remote UE-A 101 and the candidate relay UE (S703). The signal strength measurement unit 303 measures the discovery reference signal strength SD-RSRP from the discovery signal of the candidate relay UE (F603).

[0039] FIG. 6 illustrates an example in which Relay UE-C is found as a candidate relay UE.

[0040] Remote UE-A101 follows the events specified in advance by the measurement configuration from gNB104.

[0041] The message generation processing unit 305 creates a Measurement report that stores information on the "Uu link signal strength", "relay link signal strength", and "signal strength between the Remote UE-A101 and the candidate relay UE in the candidate relay UE list". Then, the created Measurement report is transmitted to the gNB 104 via the wireless communication unit 307 (F604, S706).

[0042] When the wireless communication unit 207 of the gNB 104 receives the measurement report, it is sent to the message analysis processing unit 206 for analysis. The analysis result of the processing unit 206 is sent to the path switching decision processing unit 204 for confirmation (S707). That is, the processing unit 204 functions as an acquisition unit for acquiring the signal strength of the above three links.

[0043] Here, at least the "signal strength of the relay link" and the "signal strength between the remote UE-A 101 and the candidate relay UE in the candidate relay UE list" both use the discovery reference signal strength SD-RSRP. Therefore, the gNB 104 can make comparisons using the same indicator. That is, the processing unit 204 also functions as a comparison means for comparing signal strengths.

[0044] The timing at which Remote UE-A101 notifies the gNB104 of the result of discovery reference signal strength SD-RSRP may be either regular or irregular. In the case of irregular notification, for example, it may be according to an instruction from the gNB104. Also, Remote UE-A101 may detect the SD-RSRP of each Relay UE from time to time and notify when there is a change of, for example, 20 dB or more within a certain period of time. Note that 20 dB is merely an example, and it means that a certain threshold is set and notification is made when it exceeds that threshold.

[0045] A specific path switching method will be described below.

[0046] If the signal strength of the relay link in Remote UE-A 101 is equal to or greater than a threshold, the path switching decision processor 204 determines that relaying can continue and completes the decision process without taking any action (S801). If it is below the threshold, it determines that relaying cannot continue and checks the signal strength of the Uu link in Remote UE-A 101. If it is equal to or greater than the threshold, it instructs Remote UE-A 101 to switch paths from an indirect path to a direct path and has it switch paths (S802, S803).

[0047] If the signal strength of the Uu link in Remote UE-A101 is below the threshold, it is determined that it is difficult to continue relaying even if the path is switched to a direct path. Then, the candidate relay UE list is checked, and the signal strength information of the relay UE (Relay UE-C103) with the strongest signal strength that has the same serving cell ID as the Remote UE-A101 is obtained (S804).

[0048] If the signal strength between Remote UE-A 101 and Relay UE-C 103 is below the threshold, it is determined that it is difficult to continue relaying on any path, and the path switching process is completed (S805).

[0049] If the signal strength between Remote UE-A 101 and Relay UE-C 103 is equal to or greater than a threshold, the path is switched to an indirect path via Relay UE-C 103. As a result, Remote UE-A 101 determines that the currently running service (streaming, etc.) can be continued, and notifies control unit 201 that it is necessary to switch from the indirect path to an indirect path (F605, S805).

[0050] The control unit 201 performs RRC reconfiguration for the Relay UE-C103. That is, an RRC reconfiguration message is transmitted to the Relay UE-C via the message generation processing unit 205 and the wireless communication unit 207. This notifies the Relay UE-C of information required for establishing sidelink relay communication with the Remote UE-A101. The required information includes the sl-L2 Relay UE-Config. The sl-L2 Relay UE-Config includes information used in the SRAP (Sidelink Relay Adaptation Protocol) protocol required for operation as a relay UE. The control unit 201 confirms receipt of an RRC reconfiguration complete message from the Relay UE-C103 via the wireless communication unit 207 and the message analysis processing unit. This completes the RRC reconfiguration for the Relay UE-C103 (F606, S901).

[0051] Next, the control unit 201 performs RRC reconfiguration for the Remote UE-A101. That is, an RRC reconfiguration message is transmitted to the Remote UE-A101 via the message generation processing unit 205 and the wireless communication unit 207. This notifies the Remote UE-A101 of information required for establishing sidelink relay communication with the Relay UE-C103. The required information includes sl-L2RemoteUE-Config. The sl-L2RemoteUE-Config includes information used in the Sidelink Relay Adaptation Protocol (SRAP) protocol required for operation as a remote UE (F607, S903).

[0052] At this time, the message generation processing unit adds sl-PathSwitchConfig, which stores the ID of Relay UE-C 103, to ReconfigurationWithSync in the RRC reconfiguration message. This makes it possible to notify Remote UE-A 101 that the indirect path via Relay UE-B 102 has been switched to the indirect path via Relay UE-C 103 (S903).

[0053] The control unit 301 in Remote UE-A101 confirms receipt of an RRC reconfiguration message from the gNB 104 via the wireless communication unit 307 and the message analysis processing unit 306. At this time, the control unit 301 confirms the ID of Relay UE-C103 from the sl-Path Switch Config. As a result, it is determined that the indirect path via Relay UE-B102 is being switched to the indirect path via Relay UE-C103 (F607, S904).

[0054] Next, the control unit 301 stops data transmission and reception with the Relay UE-B 102 and establishes communication with the Relay UE-C 103 (F608, S905). After that, the Remote UE-A 101 and the Relay UE-B 103C can use the Sidelink relay communication based on the SRAP protocol information acquired in the RRC reconfiguration message. That is, the Remote UE-A 101 can transmit and receive data to and from the gNB 104 via the Relay UE-C 103.

[0055] After establishing communication with Relay UE-C103, the control unit 301 causes the message generation processing unit 305 to generate an RRC reconfiguration complete message. The Sidelink Relay processing unit 304 and the wireless communication unit 307 transmit the RRC reconfiguration complete message to the gNB 104 via Relay UE-C103 (F609, S906). Here, the message is not transmitted via Relay UE-B102.

[0056] The gNB 104 receives the RRC reconfiguration complete message from Remote UE-A 101 via Relay UE-C 103 through the wireless communication unit 207 and the message analysis processing unit 206. This enables the gNB 104 to determine that switching of the indirect path of Remote UE-A 101 has been completed (F609, S907).

[0057] After the indirect path switching of Remote UE-A 101 is completed, the gNB 104 performs RRC reconfiguration on the Relay UE-B 102. Then, the gNB 104 releases the sidelink relay function for the Remote UE-A 101 (F610, S908).

[0058] On the other hand, Remote UE-A 101 releases the link with Relay UE-B 102 (F611, S909).

[0059] Through the above-described process, the Remote UE-A101 transmits the discovery reference signal strengths (SD-RSRPs) of the connected Relay UE-B102 and the candidate relay UEs to the gNB104. This makes it possible to compare the signal strengths of the same physical channel and select an appropriate candidate relay UE. Furthermore, the gNB104 and the Remote UE-A101 can switch from an indirect path to an indirect path without interrupting the service.

[0060] In this embodiment, the configuration is described in which SD-RSRP is measured and compared as "signal strength between Remote UE-A101 and Relay UE-B102" and "signal strength between Remote UE-A101 and candidate relay UE". However, it is also possible to measure SL-RSRP (Sidelink Reference Signal Received Power) based on the physical channel PSBCH as the signal strength between the UEs. Therefore, the measurement results of SL-RSRP may be compared.

[0061] On the other hand, in this embodiment, control is performed so as not to compare results measured using different measurement indexes such as SD-RSRP and SL-RSRP. For example, control is not performed so as to compare the measurement result of SL-RSRP for "signal strength between Remote UE-A101 and Relay UE-B102" and the measurement result of SD-RSRP for "signal strength between Remote UE-A101 and candidate relay UE".

[0062] [Second embodiment] In the first embodiment, the flow of optimally selecting and switching one relay UE from two relay UEs connected to one base station has been described. In this embodiment, a configuration in which one relay UE is connected to each of two base stations will be described. The functional configuration (FIGS. 2, 3, and 4) of the communication device in the second embodiment is the same as that in the first embodiment.

[0063] [System configuration] Fig. 10 is a diagram showing an example of the configuration of a system according to this embodiment. Explanation of the same numbers as in Fig. 1 will be omitted. In Fig. 10, Remote UE-A 101 is transmitting and receiving data to and from a gNB-A 104 on an indirect path (Indirect Path in Fig. 10) to a Relay UE-B 102.

[0064] Relay UE-C (103) has a sidelink relay function and can operate as a relay UE. Unlike the first embodiment, Relay UE-C (103) is connected to gNB-B (1001). gNB-A 104 and gNB-B 1101 are connected by wire or wirelessly and can communicate with each other.

[0065] (Processing example) The operation of this embodiment will be described using the sequence in Fig. 11. Remote UE-A101 is using Sidelink Relay processing unit 304 to transmit and receive user data (such as streaming data) to and from the base station via Sidelink relay function 404 of Relay UE-B102 (F1101). During the transmission and reception of the data, control unit 301 of Remote UE-A101 starts message generation processing unit 305 and creates a discovery signal request. Thereafter, the discovery request is transmitted to Relay UE-B102 and Relay UE-B103 via wireless communication unit 307 (F1102). Relay UE-B102, which has received the discovery request, transmits a discovery signal to nearby UEs (F1103).

[0066] Next, the signal strength measurement unit 303, which has been started up in advance by the control unit 301 of the Remote UE-A 101, starts measuring the "Uu link signal strength" and the "relay link signal strength" (F1103, S703). The signal strength of the relay link is measured based on the discovery reference signal strength SD-RSRP transmitted by the Relay UE-B 102.

[0067] If there is a candidate relay UE in the candidate relay UE list, the signal strength measurement unit 303 starts measuring the signal strength between the Remote UE-A 101 and the candidate relay UE. The signal strength measurement unit 303 measures the discovery reference signal strength SD-RSRP from the discovery signal of the candidate relay UE (F1103).

[0068] Remote UE-A101 follows the events specified in advance by the measurement configuration from gNB-A104.

[0069] The message generation processing unit 305 creates a Measurement report that stores information on the "Uu link signal strength", the "relay link signal strength", and the "signal strength between the Remote UE-A101 and the candidate relay UE in the candidate relay UE list". Then, the created Measurement report is transmitted to the gNB-A104 via the wireless communication unit 307 (F1104, S706).

[0070] When the wireless communication unit 207 of the gNB 104 receives the measurement report, it is sent to the message analysis processing unit 206 for analysis. The analysis result of the processing unit 206 is sent to the path switching decision processing unit 204 for confirmation (S707). That is, the processing unit 204 functions as an acquisition unit that acquires the signal strength of the above three links. This allows the gNB 104 to make comparisons using the same indicators.

[0071] Here again, the "signal strength of the relay link" and the "signal strength between the remote UE-A101 and the candidate relay UE in the candidate relay UE list" use the discovery reference signal strength SD-RSRP. Therefore, the gNB-A104 can make comparisons using the same indicator. That is, the processing unit 204 also functions as a comparison means for comparing signal strengths.

[0072] Based on the SD-RSRP, the path switching determination processing unit 204 determines to switch the path to Relay UE-C103 under gNB-B1001 (F1105).

[0073] (Handover processing) The gNB-A 104 requests the gNB-B 1001 to perform a handover of the Remote UE-A 101 (F1106). This request conveys information about the Remote UE-A 101 to the gNB-B 1001, and also includes the fact that the handover is to be via the Relay UE-B 102.

[0074] Upon receiving the handover request, the gNB-B1001 notifies the gNB-A104 of a response message to the handover request if the Remote UE-A101 is capable of handover (F1107).

[0075] Control unit 201 of gNB-B 1001 performs RRC reconfiguration for Relay UE-C 103. By transmitting an RRC reconfiguration message to Relay UE-C, information necessary for establishing sidelink relay communication with Remote UE-A 101 is notified. By confirming receipt of an RRC reconfiguration complete message from Relay UE-C 103, RRC reconfiguration for Relay UE-C 103 is completed (F1108).

[0076] Next, control unit 201 of gNB-B104 performs RRC reconfiguration for Remote UE-A101. By transmitting an RRC reconfiguration message to Remote UE-A101, information necessary for establishing sidelink relay communication with Relay UE-C103 is notified. The necessary information includes sl-L2RemoteUE-Config. The sl-L2RemoteUE-Config includes information used in the Sidelink Relay Adaptation Protocol (SRAP) protocol, which is necessary for operation as a remote UE (F1109).

[0077] At this time, the message generation processing unit adds sl-PathSwitchConfig, which stores the ID of Relay UE-C 103, to ReconfigurationWithSync of the RRC reconfiguration message. This makes it possible to notify Remote UE-A 101 that there has been a switch from an indirect path via Relay UE-B 102 to an indirect path via Relay UE-C 103.

[0078] Control unit 301 in Remote UE-A 101 confirms receipt of an RRC reconfiguration message from gNB-A 104. At this time, control unit 301 confirms the ID of Relay UE-C 103 from the sl-PathSwitchConfig. As a result, control unit 301 determines that the indirect path via Relay UE-B 102 is being switched to the indirect path via Relay UE-C 103 (F1109).

[0079] Next, the control unit 301 of the Remote UE-A101 stops data transmission and reception with the Relay UE-B102 and establishes communication with the Relay UE-C103 (F1110). After that, the Remote UE-A101 and the Relay UE-B103C can use the Sidelink relay communication based on the SRAP protocol information acquired in the RRC reconfiguration message. That is, the Remote UE-A101 can transmit and receive data with the gNB-B1001 via the Relay UE-C103.

[0080] After establishing communication with Relay UE-C 103, control unit 301 causes message generation processing unit 305 to generate an RRC reconfiguration complete message. Sidelink relay processing unit 304 and wireless communication unit 307 transmit the RRC reconfiguration complete message to gNB-B 1001 via Relay UE-C 103 (F1111, F1112). At this time, the message is not transmitted via Relay UE-B 102. Furthermore, gNB-B 1101 notifies gNB-A 104 of the RRC reconfiguration complete message (F1113).

[0081] By receiving the RRC reconfiguration complete message, gNB-A104 can determine that the switching of the indirect path of Remote UE-A101 has been completed (F1111, F1112, F1113).

[0082] After the indirect path switching of Remote UE-A 101 is completed, gNB-A 104 performs RRC reconfiguration on Relay UE-B 102. Then, gNB-A 104 releases the sidelink relay function for Remote UE-A 101 (F1114).

[0083] On the other hand, Remote UE-A101 releases the link with Relay UE-B102 (F1115).

[0084] As a result, Remote UE-A 101 can select an appropriate candidate relay UE by transmitting the discovery reference signal strength (SD-RSRP) of the connected Relay UE-B 102 and the candidate relay UE to gNB-A 104. Furthermore, appropriate switching of relay UEs between different base stations can be performed.

[0085] In addition to the control of the first embodiment, the control of the second embodiment can also be configured to be performed. For example, when selecting a relay UE when two or more relay UEs are connected to each of two base stations, it is possible to simultaneously implement the first embodiment and this embodiment to select an optimal relay UE. More specifically, when the gNB-A 104 is able to find a suitable relay UE candidate by the control described in the first embodiment, it may perform a switching process to the relay UE candidate. On the other hand, when the gNB-A 104 is unable to find a suitable relay UE candidate by the control of the first embodiment and finds a suitable relay UE by the control described in the second embodiment, it may perform a switching control accompanied by a handover of the second embodiment.

[0086] As in the first embodiment, the present embodiment has been described with respect to a configuration in which SD-RSRPs are measured and compared, but it is also possible to compare the measurement results of SL-RSRPs.

[0087] In the first and second embodiments, an example is shown in which one candidate relay UE is found, but the present invention can also be applied to a case in which two or more candidate relay UEs are found. In this case, the SD-RSRPs of all the candidate relays found may be measured and the best one may be selected.

[0088] In the first and second embodiments, when the remote UE searches for candidate relay UEs, the remote UE receives a 5G ProSe UE-to-Network Relay direct discovery Announcement message or Additional Information. This executes a search process to search for surrounding candidate relay UEs. The remote UE may receive the above signal from a connected relay UE.

[0089] Furthermore, when searching for candidate relay UEs, the remote UE may be configured to perform a process of searching for candidate UEs autonomously in addition to or instead of the above-mentioned search process of receiving signals emitted by the surrounding UEs and searching for candidates.

[0090] In this case, specifically, when searching for a candidate relay UE, the remote UE transmits a 5G ProSe UE-to-Network Relay direct discovery soliciation message. If the remote UE receives a response to the soliciation message, the remote UE considers that it has discovered the candidate relay UE. Note that the remote UE may transmit the above signal to a connected relay UE and receive a response to the soliciation message from the relay UE.

[0091] [Other embodiments] The present invention provides a program for implementing one or more of the functions of the above-described embodiments to a system or device via a network or a storage medium. It can also be implemented by a process in which one or more processors in a computer of the system or device read and execute the program. It can also be implemented by a circuit (e.g., ASIC) that implements one or more functions.

[0092] The invention is not limited to the above-described embodiments, and various modifications and variations are possible without departing from the spirit and scope of the invention. Accordingly, the following claims are appended to apprise the public of the scope of the invention.

[0093] The disclosure of this specification includes the configurations described in the following items.

[0094] (Item 1) A base station, In a first state in which communication between a first UE (User Equipment) and the base station is performed via a second UE that relays the communication, an acquiring means for acquiring first signal strength information representing a signal strength between the first UE and the second UE, and second signal strength information representing a signal strength between the first UE and a third UE not connected to the first UE; a comparison means for comparing the first signal strength information with the second signal strength information in the first state, The base station, wherein the first signal strength information and the second signal strength information are information on signal strength of a same physical channel.

[0095] (Item 2) Based on the comparison result of the comparison means, 2. The base station according to claim 1, further comprising: a processing means for issuing a switching instruction from the first state to a second state in which communication with the first UE is performed via the third UE.

[0096] (Item 3) Based on the comparison result of the comparison means, From the first state, The base station according to item 1, further comprising a processing means for instructing a switching to a third state in which the first UE communicates with another base station via the third UE connected to the other base station.

[0097] (Item 4) 5. The base station according to any one of items 1 to 4, wherein the physical channel is a channel used by the first UE when searching for neighboring UEs.

[0098] (Item 5) The base station according to any one of items 1 to 4, wherein the physical channel is a PSDCH (Physical Sidelink Discovery CHannel).

[0099] (Item 6) The base station according to any one of items 1 to 5, characterized in that the first UE transmits a PSDCH (Physical Sidelink Discovery CHannel) with a valid CRC (Cyclic Redundancy Check) to the second UE and the third UE.

[0100] (Item 7) The base station according to any one of items 1 to 6, wherein the first signal strength information and the second signal strength information are measurement results of a Sidelink Discovery Reference Signal Received Power (SD-RSRP).

[0101] (Item 8) 1. A communication device, comprising: In a first state in which communication between the communication device and a base station is performed via a first UE that relays communication, A searching means for searching a second UE different from the first UE; a measuring means for measuring a first signal strength, which is a strength of a signal received from the first UE in the first state, and a second signal strength, which is a strength of a signal received from the second UE; a notification means for notifying the base station of the first signal strength information and the second signal strength information in the first state; receiving means for receiving a switching instruction from the base station that has received the information on the first signal strength and the information on the second signal strength; A communication device, characterized in that the first signal strength and the second signal strength are signal strengths of the same physical channel.

[0102] (Item 9) The communication device according to item 8, further comprising a switching means for performing a switching process from the first state to a second state in which communication with the base station is performed via the second UE based on receipt of the switching instruction.

[0103] (Item 10) The communication device according to item 8, further comprising a switching means for performing a switching process from the first state to a third state in which communication is performed with another base station via the second UE connected to the another base station based on the reception of the switching instruction.

[0104] (Item 11) 11. The communication device according to any one of items 8 to 10, wherein the physical channel is a channel used when searching for nearby UE.

[0105] (Item 12) The communication device according to any one of items 8 to 11, characterized in that the physical channel is a PSDCH (Physical Sidelink Discovery CHannel).

[0106] (Item 13) the search by the search means is performed based on a discovery procedure; The communication device according to any one of items 8 to 12, characterized in that it receives a 5G ProSe UE-to-Network Relay direct discovery Announcement message or Additional Information.

[0107] (Item 14) the search by the search means is performed based on a discovery procedure; The communication device according to any one of items 8 to 13, characterized in that it transmits a Soliciation message of 5G ProSe UE-to-Network Relay direct discovery and receives a response to the Soliciation message.

[0108] (Item 15) 15. The communication device according to any one of items 8 to 14, wherein the notification means notifies the information on the first signal strength and the information on the second signal strength in a single message.

[0109] (Item 16) 1. A method for controlling communications, comprising: In a first state in which communication between a first UE (User Equipment) and the base station is performed via a second UE that relays the communication, acquiring first signal strength information representing a signal strength between the first UE and the second UE, and second signal strength information representing a signal strength between the first UE and a third UE not connected to the first UE; a comparison step of comparing the first signal strength information with the second signal strength information in the first state; and a processing step of issuing a switching instruction from the first state to a second state in which the third UE communicates with the first UE via the third UE; The control method, characterized in that the first signal strength and the second signal strength are signal strengths of the same physical channel.

[0110] (Item 17) On the computer, In a first state in which communication between a first UE (User Equipment) and the base station is performed via a second UE that relays the communication, acquiring first signal strength information representing a signal strength between the first UE and the second UE, and second signal strength information representing a signal strength between the first UE and a third UE not connected to the first UE; a comparison step of comparing the first signal strength information with the second signal strength information in the first state; and executing a processing step of issuing a switching instruction from the first state to a second state in which the first UE communicates with the third UE via the third UE; The program, characterized in that the first signal strength and the second signal strength are signal strengths of the same physical channel. [Explanation of symbols]

[0111] 101 Remote UE-A 102 Relay UE-B 103 Relay UE-C 104 gNB 105 gNB coverage

Claims

1. A base station capable of communication compliant with the 3GPP (3rd Generation Partnership Project) standard, In a first state in which communication between a remote UE and the base station is performed via a first relay UE (User Equipment), Receiving means for receiving a MeasurementReport message including first information representing the signal strength between the remote UE and the first relay UE, and second information representing the signal strength between the remote UE and a second relay UE not connected to the remote UE, The system includes a determination means that, after receiving the MeasurementReport message, determines a switch from the first state to a second state in which communication with the remote UE is made via a second relay UE different from the first relay UE, A base station characterized in that both the first information and the second information are signal strength information of a signal associated with a predetermined physical channel.

2. The base station according to claim 1, characterized in that the determination means determines switching from the first state to the second state when the signal strength between the remote UE and the first relay UE falls below a first threshold.

3. The base station according to claim 1, further comprising a transmission means for transmitting an RRC Reconfiguration message to the remote UE via the first relay UE after deciding to switch from the first state to the second state.

4. The base station according to claim 1, characterized in that the predetermined physical channel is a channel used by the remote UE when searching for a neighboring UE.

5. The base station according to claim 1, characterized in that the predetermined physical channel is a PSDCH (Physical Sidelink Discovery Channel).

6. The base station according to claim 1, characterized in that the remote UE transmits a PSDCH (Physical Sidelink Discovery Channel) with CRC (Cyclic Redundancy Check) enabled to the first relay UE and the second relay UE.

7. The base station according to claim 1, characterized in that the first information and the second information are information indicating the value of SD-RSRP (Sidelink Discovery Reference Signal Received Power).

8. A communication device capable of communication in accordance with the 3GPP (3rd Generation Partnership Project) standard, In a first state where communication with the base station is performed via the first relay UE, A search means for searching for at least one candidate relay UE different from the first relay UE, A measuring means for measuring a first signal strength, which is the strength of the signal received from the first relay UE in the first state, and a second signal strength, which is the strength of the signal received from at least one candidate relay UE, In the first state, the information of the first signal strength and the information of the second signal strength are included. A transmission means for transmitting a MeasurementReport message to the base station, A receiving means for receiving an RRCreconfiguration message from the base station that received the MeasurementReport message, The system includes a switching means that, after receiving the RRCreconfiguration message, performs a switching process from the first state to a second state in which communication with the base station is performed via a second relay UE, which is one of the at least one candidate relay UEs. A communication device characterized in that both the first signal strength and the second signal strength are signal strengths of signals associated with a predetermined physical channel.

9. The communication device according to claim 8, characterized in that the second relay UE is determined by the base station from among the at least one candidate relay UE.

10. The communication device according to claim 8, characterized in that the second relay UE is a communication device connected to another base station.

11. The communication device according to claim 8, characterized in that the predetermined physical channel is a channel used when searching for a neighboring UE.

12. The communication device according to claim 8, characterized in that the predetermined physical channel is PSDCH (Physical Sidelink Discovery Channel).

13. The search by the aforementioned search means is performed based on the discovery procedure specified in the 3GPP standard. The communication device according to claim 8, characterized in that the discovery procedure is a procedure for discovering at least one candidate relay UE by receiving a 5G ProSe UE-to-Network Relay direct discovery Announcement message or Additional Information.

14. The search by the aforementioned search means is performed based on the discovery procedure specified in the 3GPP standard. The communication device according to claim 8, characterized in that the discovery procedure is a procedure for discovering at least one candidate relay UE by transmitting a 5G ProSe UE-to-Network Relay direct discovery message and receiving a response to the solution message.

15. The communication device according to claim 8, characterized in that the RRCreconfiguration message includes ReconfigWithSync which includes sl-pathSwitchConfig.

16. The communication terminal according to claim 15, wherein the switching process includes establishing a PC5 connection with a UE having an ID obtained from the sl-pathSwitchConfig as the second relay UE.

17. The user terminal according to claim 16, wherein the switching process further includes transmitting the RRCreconfigurationcomplete message to the base station via the second relay UE after the establishment of the PC5 connection.

18. The communication device according to claim 8, characterized in that the information of the first signal strength and the information of the second signal strength are information indicating the value of SD-RSRP (Sidelink Discovery Reference Signal Received Power).

19. A method of controlling communication, In a first state where communication between a remote UE (User Equipment) and a base station is performed as relay communication via a first relay UE that relays the communication, A receiving step of receiving a MeasurementReport message which includes first information representing the signal strength between the remote UE and the first relay UE, and second information representing the signal strength between the remote UE and a second relay UE that is not connected to the remote UE, The system includes a decision step of deciding to switch from the first state to a second state in which communication is made with the remote UE via the second relay UE, A control method characterized in that both the first information and the second information are signal intensity information of a signal associated with a predetermined physical channel.

20. A program for a computer to operate the communication control method described in Claim 19.

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