Communication device, base station, control method, and program

Abstract

Provided is a communication device for relaying communication between a User Equipment (UE) and a base station, the communication device characterized by comprising: a measurement means for measuring the signal strength of communication performed with the UE; and a notification means for notifying the base station of a measurement result by the measurement means, wherein the notification means notifies the base station of a measurement result pertaining to the relay UE in a relay state in which communication between the UE and the base station is being relayed.

Description

Communication device, base station, control method, and program

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

[0002] In recent years, the 3GPP (registered trademark) (3rd Generation Partnership Project) has been formulating specifications for LTE (Long Term Evolution) and 5G NR (5th Generation New Radio). Among these, a standard specification called Sidelink communication (hereinafter also referred to as "Sidelink") has been formulated. This specification realizes direct wireless communication between devices using an interface called PC5 without going through a mobile communication network (core network).

[0003] Furthermore, 3GPP is currently developing specifications to expand the Sidelink communication range by using a Sidelink relay function that relays Sidelink communications via a relay device (relay UE). 3GPP specifies a means for a communication terminal (remote UE) with the function of connecting to a base station through a Sidelink function relay to switch from an indirect path to a direct path and a means for switching from a direct path to an indirect path. Note that the indirect path here corresponds to a communication path that connects to a base station via a relay UE, and the direct path corresponds to a communication path that connects to a base station without going through a relay UE. In this case, switching from an indirect path to a direct path or from a direct path to an indirect path can be achieved without interrupting the ongoing service.

[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.

[0005] Special table 2018-535594 publication

[0006] Currently, 3GPP does not specify a method for determining when to switch from an indirect path to another indirect path, which poses a problem that a relay UE cannot be appropriately selected.

[0007] The present invention has been made in consideration of at least one of the above-described problems, and an object of one aspect of the present invention is to provide a mechanism that enables appropriate selection of a relay UE.

[0008] A communication device according to one aspect of the present invention is a communication device that relays communication between a UE (User Equipment) and a base station, and includes: a measurement means for measuring the signal strength of communication between the UE; and a notification means for notifying the base station of the measurement result by the measurement means, wherein the notification means, in a relay state in which communication between the UE and the base station is being relayed, notifies the base station of the measurement result regarding the UE being relayed.

[0009] According to one aspect of the present invention, it is possible to appropriately select a relay UE.

[0010] 7B is a diagram showing an example of the configuration of a communication system in the present embodiment. FIG. 7C is a block diagram showing an example of the functional configuration of a base station in the present embodiment. FIG. 7D is a block diagram showing an example of the functional configuration of a remote UE in the present embodiment. FIG. 7E is a block diagram showing an example of the functional configuration of a relay UE in the present embodiment. FIG. 7F is a sequence diagram showing an example of exchange between communication devices in the first embodiment. FIG. 7G is an example of a flowchart between communication devices in the first embodiment. FIG. 7H is an example of a flowchart between communication devices in the first embodiment. FIG. 7H is an example of a flowchart between communication devices in the first embodiment. FIG. 7H is an example of a flowchart related to a modified example of FIG. 7B. FIG. 7I is a sequence diagram showing an example of exchange between communication devices in the second embodiment.

[0011] Each embodiment will be described in detail below with reference to the accompanying drawings. In the following description, the "number ***" in TS*** represents the number of the technical specification in the 3GPP standard.

[0012] [First embodiment] Figure 1 is a diagram showing an example of the configuration of a communication system according to this embodiment. The system of this embodiment consists of UEs 101 to 103, a gNB 104 which is a base station, and a core network (not shown) to which the gNB 104 is connected via fiber or the like. gNB is an abbreviation for gNodeB, which stands for next generation NodeB. UE is an abbreviation for User Equipment.

[0013] 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 gNB (104).

[0014] The remote UE-A (101) communicates with the gNB (104) using Sidelink relay communication. The relay UE-B (102) operates as a relay UE that relays communication between the remote UE-A (101) and the gNB (104) using the Sidelink relay function. That is, the remote UE-A (101) connects to the base station via an indirect path (Indirect Path shown in FIG. 1) via the relay UE-B (102). Note that data is communicated with base stations and devices on the core network (not shown). The Uu link described later refers to a link when the remote UE-A (101) communicates directly with the gNB (104) without going through a relay UE.

[0015] The relay UE-C (103) has a Sidelink relay function and can operate as a relay UE. The relay UE-C (103) is connected to the gNB (104).

[0016] The remote UE-A (101) can transmit a discovery signal to a nearby UE (i.e., a relay UE-C (103)) to search for a relay UE-B (102) or another relay UE (candidate relay UE). The remote UE-A (101) can also receive a response signal from the nearby UE (i.e., a relay UE-C (103)) in response to the transmitted discovery signal.

[0017] The discovery signal may be a Solicitation Message for 5G ProSe direct discovery or 5G ProSe UE-to-Network Relay Discovery. ProSe is an abbreviation for Proximity-based Services. The response signal may be a Response Message to the Solicitation Message.

[0018] Furthermore, the discovery signal transmitted from the neighboring UE may be a 5G ProSe UE-to-Network Relay direct discovery Announcement message, or may be Additional Information. Furthermore, the discovery procedure may be based on the remote UE-A (101) receiving the 5G ProSe UE-to-Network Relay direct discovery Announcement message, or may be based on the remote UE-A (101) receiving the Additional Information.

[0019] The relay UE-C (103) can also respond to a discovery signal from the remote UE-A (101) and can also transmit a discovery signal to nearby UEs.

[0020] Although the relay UE-B (102) is a relay UE, it can respond to discovery signals in the same way as the relay UE-C (103) and can also transmit discovery signals to nearby UEs.

[0021] 2 is a block diagram showing an example of the functional configuration of the base station 104 in this embodiment. Note that some or all of the functional blocks described below with reference to FIGS. 2 and 3 may be replaced with other functional blocks that perform similar functions, some functional blocks may be omitted, or additional functional blocks may be added. Furthermore, one functional block described below may be divided into multiple functional blocks, or multiple functional blocks may be integrated into one functional block.

[0022] In the example shown in FIG. 2, the base station 104 includes a control unit 201, a storage unit 202, a UE management unit 203, a path switching determination processing unit 204, a message generation processing unit 205, a message analysis processing unit 206, and a wireless communication unit 207.

[0023] The control unit 201 controls the operation of the base station 104. The control unit 201 is configured with one or more processors such as a CPU or an MPU, and controls the entire communication device by executing a control program read into the RAM, which is the storage unit 202. Note that each process performed by the control unit 201, which will be described in the flowcharts below, can also be realized using a hardware circuit such as an ASIC or an FPGA (Field Programmable Gate Array). ASIC is an abbreviation for Application Specific Integrated Circuit. Furthermore, the processes described in the flowcharts below can also be realized by using a hardware circuit in cooperation with a processor such as a CPU or an MPU.

[0024] The memory unit 202 stores information used by the control unit 201 for control and information related to communication. The memory unit 202 may include a main memory unit and an auxiliary memory unit. The main memory unit may be, for example, a read-only memory (ROM) or a random access memory (RAM). The main memory unit may store or temporarily store programs and data such as an operating system (OS), which is basic software executed by the control unit 201, and application software. The auxiliary memory unit may be, for example, a hard disk drive (HDD) or a solid state drive (SSD), and may store data related to application software. For example, a control program stored in a non-volatile memory area is expanded into RAM and executed by a processor constituting the control unit 201. In this way, the control unit 201 and the memory unit 202 may function as a so-called computer.

[0025] The storage unit 202 may include a recording medium that stores a predetermined program. The program stored in this recording medium may be installed via a drive device or the like, and the installed predetermined program may be executable by the control unit 201. Various types of recording media can be used as the recording medium. For example, the recording medium may be a recording medium that records information optically, electrically, or magnetically, such as a CD (Compact Disc)-ROM, a flexible disk, or a magneto-optical disk. The recording medium may also be a semiconductor memory that records information electrically, such as a ROM or a flash memory.

[0026] The recording medium does not include a carrier wave.

[0027] The UE management unit 203 manages UE information within the base station area. The UE management unit 203 manages UE information including the IDs of subordinate UEs and measurement results reported from subordinate UEs (such as the signal strength of the Uu link, which will be described later). The path switching determination processing unit 204 determines whether to connect the UEs under its management via an indirect path or a direct path, based on the UE information managed by the UE management unit 203. The message generation processing unit 205 generates a message used to instruct path switching. The message analysis processing unit 206 analyzes messages received from subordinate UEs.

[0028] The functions corresponding to the UE management unit 203, the path switching determination processing unit 204 and / or the message generation processing unit 205 may be realized as software modules implemented by the control unit 201.

[0029] The wireless communication unit 207 transmits and receives information to and from the subordinate UEs via wireless communication. For example, the wireless communication unit 207 transmits messages generated by the message generation processing unit 205 and receives messages from the subordinate UEs.

[0030] FIG. 3 is a block diagram showing an example of the functional configuration of a remote UE (for example, remote UE-A (101)) in this embodiment.

[0031] In the example shown in FIG. 3 , the remote UE includes a control unit 301 , a storage unit 302 , a signal strength measurement unit 303 , a Sidelink Relay processing unit 304 , a message generation processing unit 305 , a message analysis processing unit 306 , and a wireless communication unit 307 .

[0032] The control unit 301 controls the operation of the remote UE. The control unit 301 is configured with one or more processors such as a CPU or an MPU, and controls the entire communication device by executing a control program read into the RAM, which is the storage unit 302. Note that each process performed by the control unit 301, which will be described in the flowcharts below, can also be realized using a hardware circuit such as an ASIC or an FPGA. Furthermore, the processes described in the flowcharts below can also be realized by having the hardware circuit cooperate with a processor such as a CPU or an MPU.

[0033] The storage unit 302 stores information used by the control unit 301 for control and information related to communication.

[0034] The signal strength measurement unit 303 measures the "signal strength between relay UEs (relay links, PC5 links)", "signal strength between base stations (Uu links)", and "signal strength between candidate relay UEs" as seen from the remote UE. Note that each signal strength measured by the signal strength measurement unit 303 is stored in the memory unit 302. The information stored in the memory unit 302 may be information on measurement values ​​of signal strength such as SL-RSRP and SD-RSRP. SL-RSRP is an abbreviation for Sidelink Reference Signal Received Power. SD-RSRP is an abbreviation for Sidelink Discovery Reference Signal Received Power.

[0035] The Sidelink Relay processing unit 304 enables connection to the base station 104 via the relay function of the relay UE (i.e., via an indirect path) by establishing a Sidelink connection with the relay UE.

[0036] The message generation processing unit 305 generates various messages, including a discovery signal to be transmitted to nearby relay UEs, and an RRC Reconfiguration Complete message and a Measurement Report to be transmitted to the base station 104.

[0037] The message analysis processing unit 306 analyzes messages such as discovery signals and response signals transmitted from nearby relay UEs, and RRC Reconfiguration messages transmitted from the base station 104 .

[0038] The wireless communication unit 307 transmits and receives information via wireless communication with nearby relay UEs and the base station 104. The wireless communication unit 307 performs processing for transmitting messages generated by the message generation processing unit 305 and processing for receiving messages from nearby relay UEs and the base station 104.

[0039] FIG. 4 is a block diagram showing an example of the functional configuration of the relay UEs (102, 103) in this embodiment.

[0040] In Figure 4, the description of the same functional blocks as in Figure 3 will be omitted. The signal strength measurement unit 403 measures "signal strength between relay UEs (relay links, PC5 links)," "signal strength of remote UEs connected to other relay UEs via relay links," and "signal strength between base stations (Uu links)" as seen from the relay UE. The Sidelink Relay processing unit 404 performs a relay function to connect a Sidelink-connected remote UE to the base station 104 via the relay UE. The message generation processing unit 405 transmits discovery signals to nearby remote UEs and responds to discovery signals transmitted from the remote UEs. Furthermore, the message generation processing unit 405 generates an RRC Reconfiguration Complete message and a Measurement Report to be transmitted to the base station 104. The message analysis processing unit 406 analyzes messages such as discovery signals transmitted from remote UEs and RRC Reconfiguration messages transmitted from the base station 104 .

[0041] Next, an example of the operation of this embodiment will be described with reference to FIGS.

[0042] Figure 5 is an example of a switching sequence from an indirect path to an indirect path in this embodiment. Figures 6, 7A, 7B, and 8 are flowcharts of the sequence of Figure 5 in this embodiment, divided into processing on the gNB104 side and processing on the remote UE-A (101) side.

[0043] In the gNB 104, the control unit 201 executes the control program stored in the memory unit 202 to realize each of the gNB-side processes shown in this flowchart. In addition, in the remote UE-A (101), the control unit 301 executes the control program stored in the memory unit 302 to realize each of the UE-side processes shown in this flowchart. Note that some of the processes are realized in cooperation with the hardware and functional units described above.

[0044] In this embodiment, the remote UE-A (101) uses the Sidelink Relay processing unit 304 and is connected to the base station 104 via the Sidelink Relay processing unit 404 of the relay UE-B (102). The remote UE-A (101) is currently transmitting and receiving user data (such as streaming data) via this connection with the base station 104 (F501, S601).

[0045] Next, while transmitting and receiving user data, the control unit 301 of the remote UE-A (101) activates the message generation processing unit 305. The message generation processing unit 305 then creates a discovery request signal and transmits the discovery request signal to the relay UE-B (102) and the relay UE-C (103) via the wireless communication unit 307. The control unit 301 also activates the message analysis processing unit 306. The control unit 301 prepares for message analysis 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-B (102), is received via the wireless communication unit 307 (i.e., discovery execution is started) (S602).

[0046] Next, the signal strength measurement unit 303, which has been started in advance by the control unit 301 of the remote UE-A (101), starts measuring the signal strength. Specifically, the signal strength measurement unit 303 starts measuring the "signal strength between the remote UE-A (101) and the gNB 104" and the "signal strength between the remote UE-A (101) and the relay UE-B (102)" (F502, S603). Note that the link between the remote UE-A (101) and the gNB 104 is also referred to as the Uu link hereinafter. Also, the link between the remote UE-A (101) and the relay UE-B (102) is also referred to as the relay link hereinafter.

[0047] Similarly, the signal strength measurement unit 403 of the relay UE-B (102) also starts measuring the "signal strength between the relay UE-B (102) and the remote UE-A (101)" (F503). Similarly, the signal strength measurement unit 403 of the relay UE-C (103) also starts measuring various signal strengths (F504). At this stage, the relay UE-C (103) is operating as a relay, but may not be connected to any UE. In this state, the relay UE-C (103) does not issue any signal related to Sidelink.

[0048] 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 response signal. The ID of the relay UE that transmitted the signal and the serving cell ID are stored in a candidate relay UE list held by the storage unit 302 (S604, S605). Note that in the flowchart shown in FIG. 6 , the determination of "NO" in step S604 may be made possible after a predetermined time has elapsed since the start of the processing of step S602. For example, the control unit 301 may determine "NO" in step S604 if it has not received a response signal to the discovery request signal even after a predetermined time has elapsed since transmitting the discovery request signal.

[0049] 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 (S603). Here, FIG. 6 illustrates a case where the relay UE-C (103) is found as a candidate relay UE. At this stage, the relay UE-C (103) is in a relay preparation state and is not connected to the remote UE-A (101). However, the relay UE-C (103) transmits a response to the 5G ProSe UE-to-Network Relay direct discovery Announcement message. Alternatively, the relay UE-C (103) transmits a response to the Additional Information or Solicitation message. The signal strength measurement unit 303 of the remote UE-A may measure the signal strength of the relay UE-C (103) based on the reception result of the response from the relay UE-C (103).

[0050] The remote UE-A (101) follows the events previously specified by the measurement configuration from the gNB 104.

[0051] 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-A (101) and the candidate relay UE in the candidate relay UE list." The created Measurement report is then transmitted to the gNB 104 via the wireless communication unit 307 (F502, S606).

[0052] When the wireless communication unit 207 of the gNB104 receives a Measurement Report from the remote UE-A (101), it is sent to the message analysis processing unit 206, which analyzes it. The result of the analysis by the message analysis processing unit 206 is sent to the path switching judgment processing unit 204, which confirms it (S607). In this case, the path switching judgment processing unit 204 functions as an acquisition unit for acquiring the signal strength of the above three types of links.

[0053] A specific path switching method will be described below.

[0054] If the signal strength of the relay link at the remote UE-A (101) is equal to or greater than the first threshold, the path switching determination processing unit 204 determines that relaying can be continued and completes the determination processing without taking any action (S701). If the signal strength is below the first threshold, it determines that relaying cannot be continued and checks the signal strength of the Uu link at the remote UE-A (101) (an example of third signal strength information). If the signal strength of the Uu link is equal to or greater than the second threshold, the path switching determination processing unit 204 instructs the remote UE-A (101) to switch paths from the indirect path to the direct path and causes the path switching to be performed (S702, S703). The second threshold may be the same as or different from the first threshold used in step S701.

[0055] If the signal strength of the Uu link at the remote UE-A (101) is below the second threshold, the path switching determination processor 204 determines that it is difficult to continue relaying even if the path is switched to the direct path. Then, the path switching determination processor 204 checks the candidate relay UE list and acquires various signal strength information measured by the relay UE having the same serving cell ID as the remote UE-A (101) (or communicating with the base station 104). Specifically, the relay UE-C (103) requests signal strength information (an example of second signal strength information) of the remote UE-A (101) measured by the relay UE-C (103) (F504, S704). Furthermore, the relay UE-B (102) requests signal strength information (an example of first signal strength information) of the remote UE-A (101) measured by the relay UE-B (102) for strength comparison (F503, S704).

[0056] Here, the signal strength of the remote UE-A (101) measured by the relay UE-C (103) and the signal strength of the remote UE-A (101) measured by the relay UE-B (102) are preferably the signal strengths of the same physical channel, which may be PSBCH or PSDCH.

[0057] PSBCH is an abbreviation for Physical Sidelink Broadcast Channel. PSBCH is a physical channel related to synchronization in Sidelink communication. PSBCH is periodically transmitted together with a Sidelink Synchronization Signal Block (S-SSB) at a time frequency that is not a slot in the resource pool. The above-mentioned signal strength SL-RSRP is the signal strength based on the physical channel PSBCH.

[0058] PSDCH is an abbreviation for Physical Sidelink Discovery Channel. PSDCH is a physical channel used for UE discovery in Sidelink communication. The signal strength SD-RSRP mentioned above is the signal strength based on the physical channel PSDCH (defined in 3GPP technical specification TS36.214 5.1.22).

[0059] With reference to the flowchart of Figure 7B, the operation when the relay UE-C (103) receives a request for signal strength information at S704 of Figure 7A will be described, and the operation of the gNB 104 following S704 of Figure 7A will be described. Note that with reference to Figure 7B, the operation when the relay UE-C (103) receives a request for signal strength information at S704 of Figure 7A will be described, but the operation when the relay UE-B (102) receives a request for signal strength information at S704 of Figure 7A may be similar.

[0060] When the relay UE-C (103) receives a request for signal strength information from the gNB 104 (S752) in a relay preparation state (S751) in which the relay UE-C (103) is not connected to the remote UE-A (101), etc., it starts measurement. That is, the signal strength measurement unit 403 of the relay UE-C (103) starts measuring the "signal strength between the relay UE-C (103) and the remote UE-A (101)" (F504, S753). In a modified example, the signal strength measurement unit 403 of the relay UE-C (103) may periodically measure the "signal strength between the relay UE-C (103) and the remote UE-A (101)". In this case, the processing of S704 in FIG. 7A may be omitted.

[0061] The message generation processing unit 405 of the relay UE-C (103) creates a Measurement report that stores information on the "signal strength between the relay UE-C (103) and the remote UE-A (101)" (S754). Then, the created Measurement report is transmitted to the gNB 104 via the wireless communication unit 407 (F504, S754). Similarly, the relay UE-B (102) transmits the created Measurement report to the gNB 104 via the wireless communication unit 407 (F503).

[0062] When the wireless communication unit 207 of the gNB 104 receives a Measurement Report from the relay UE-C (103) (and the relay UE-B (102)), it sends it to the message analysis processing unit 206 (S782, S783). Then, the message analysis processing unit 206 performs an analysis. The result of the analysis by the message analysis processing unit 206 is sent to the path switching judgment processing unit 204, which confirms it (S784).

[0063] If the signal strength measured by the relay UE-C (103) is lower than the signal strength measured by the relay UE-B (102), the path switching decision processing unit 204 determines that it is difficult to continue relaying on any path. In this case, the path switching decision processing unit 204 completes the path switching process ("NO" in S784).

[0064] If the signal strength measured by the relay UE-C (103) is equal to or greater than the signal strength measured by the relay UE-B (102), the path switching judgment processing unit 204 determines that switching to the indirect path related to the relay UE-C (103) is necessary. That is, it determines that the service (streaming, etc.) currently being executed by the remote UE-A (101) can be continued by switching to the indirect path via the relay UE-C (103). Then, the path switching judgment processing unit 204 notifies the control unit 201 that switching from the indirect path to the indirect path is necessary (F505, "YES" in S784).

[0065] In this case, the path switching determination processor 204 may further determine whether the signal strength measured by the relay UE-C (103) is equal to or greater than a third threshold (S783A), as in the modified example shown in Fig. 9. The third threshold may be the same as the first threshold used in S701. If the signal strength measured by the relay UE-C (103) is equal to or greater than the third threshold, the path switching determination processor 204 may notify the controller 201 that switching from an indirect path to an indirect path is necessary (F505, "YES" in S784).

[0066] However, the values ​​measured on the remote UE-A (101) side and the values ​​measured on the relay UE side such as relay UE-C (103) do not necessarily match depending on the measurement timing, for example, when both are moving, such as when they are mounted on a vehicle.

[0067] In this regard, according to the examples shown in FIGS. 7B and 9, the measurement values ​​obtained in steps S782 and S783 are used in the determination in step S784. This allows the signal strengths obtained by two relay UEs at approximately the same time to be compared. That is, when comparing the signal strength measured by the relay UE-C (103) with the signal strength measured by the relay UE-B (102), the results of measurements taken at approximately the same time can be used. In this case, since the value measured by the remote UE-A (101) is not used, the measurements related to the candidate relay UEs in steps S603 and S605 may be omitted. Alternatively, in another modification, the measurement values ​​obtained in step S607, along with the measurement values ​​obtained in steps S782 and S783, may be used in the determination in step S784.

[0068] The control unit 201 performs RRC reconfiguration for the relay UE-C (103). That is, an RRC reconfiguration message is transmitted to the relay UE-C (103) via the message generation processing unit 205 and the wireless communication unit 207. This notifies the relay UE-C (103) of information necessary for establishing sidelink relay communication with the remote UE-A (101). The necessary information includes sl-L2Relay UE-Config. The sl-L2Relay 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 the reception of the RRC reconfiguration complete message from the relay UE-C (103) via the wireless communication unit 207 and the message analysis processing unit 206. This completes the RRC reconfiguration for the relay UE-C (103) (F506, S801).

[0069] Next, the control unit 201 performs RRC reconfiguration to the remote UE-A (101). That is, an RRC reconfiguration message is transmitted to the remote UE-A (101) via the message generation processing unit 205 and the wireless communication unit 207. This notifies the remote UE-A (101) of information necessary for establishing Sidelink relay communication with the relay UE-C (103). The necessary information includes sl-L2RemoteUE-Config. The sl-L2RemoteUE-Config includes information used in the SRAP protocol necessary for operation as a remote UE (F507, S803).

[0070] At this time, the message generation processing unit 205 adds the following information to the RRC reconfiguration message. That is, the message generation processing unit 205 adds sl-pathSwitchConfig, which stores the ID of the relay UE-C (103), to ReconfigurationWithSync (S802). This allows the remote UE-A (101) to be notified that the indirect path via the relay UE-B (102) has been switched to the indirect path via the relay UE-C (103) (S803).

[0071] The control unit 301 in the remote UE-A (101) 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 ID of the relay UE-C (103) is confirmed from the sl-Path Switch Config. As a result, it is determined that the indirect path via the relay UE-B (102) is being switched to the indirect path via the relay UE-C (103) (F507, S804).

[0072] 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) (F508, S805). After that, the remote UE-A (101) and the relay UE-C (103) can use Sidelink relay communication based on the SRAP protocol information acquired in the RRC reconfiguration message. That is, the remote UE-A (101) can send and receive data with the gNB 104 via the relay UE-C (103).

[0073] After establishing communication with the relay UE-C (103), 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 the relay UE-C (103) (F509, S806). Here, the message is not transmitted via the relay UE-B (102).

[0074] The gNB 104 receives an RRC reconfiguration complete message from the remote UE-A (101) via the relay UE-C (103) through the wireless communication unit 207 and the message analysis processing unit 206. This allows it to determine that the switching of the indirect path of the remote UE-A (101) has been completed (F509, S807).

[0075] After completing the indirect path switching of the remote UE-A (101), the gNB 104 performs RRC reconfiguration on the relay UE-B (102) and releases the Sidelink relay function for the remote UE-A (101) (F510, S808).

[0076] On the other hand, the remote UE-A (101) releases the link with the relay UE-B (102) (F511, S809).

[0077] By the processing described above, gNB104 and remote UE-A (101) can switch from an indirect path to an indirect path without disconnecting the service.

[0078] [Other Embodiments] In the above-described embodiments, signal strength measurements such as SL-RSRP and SD-RSRP (Sidelink Discovery Reference Signal Received Power) are used for comparison. SL-RSRP is an abbreviation for Sidelink Reference Signal Received Power. Figure 10 shows an example of a switching sequence from an indirect path to an indirect path when SD-RSRP is used as the signal strength. In the figure, F901 is a discovery signal sent from the remote UE-A (101), and F902 is a discovery response signal from the relay UE-B (102) and the relay UE-C (103) in response to the discovery signal. F903 is a notification of a measurement report including signal strength information of a discovery response signal measured by the remote UE-A (101). F904 is a notification of a measurement report including signal strength information of a discovery signal measured by the relay UE-B (102). F905 is a notification of a measurement report including signal strength information of a discovery signal measured by the relay UE-C (103).

[0079] Although the present embodiment has been described as an example in which one candidate relay UE is found, it is also possible to apply the present invention to a case in which two or more candidate relay UEs are found. In this case, it is sufficient to acquire signal strength measurements from all the candidate relay UEs found and select the best one.

[0080] In this embodiment, when a remote UE searches for a candidate relay UE, the remote UE receives the following. That is, the remote UE receives a 5G ProSe UE-to-Network Relay direct discovery Announcement message or Additional Information. This causes the remote UE to perform a search process to search for surrounding candidate relay UEs. The remote UE may also receive the above signal from a connected relay UE.

[0081] 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.

[0082] In this case, specifically, when searching for a candidate relay UE, the remote UE transmits a 5G ProSe UE-to-Network Relay direct discovery Solicitation message. Then, if the remote UE receives a response to the Solicitation message, it is deemed to have discovered a candidate relay UE. Note that the remote UE may transmit the above signal to the currently connected relay UE and receive a response to the Solicitation message from the relay UE.

[0083] The present invention can also be realized by supplying a program that realizes one or more of the functions of each of the above-described embodiments to a system or device via a network or a storage medium, and having one or more processors in the computer of the system or device read and execute the program.The present invention can also be realized by a circuit (e.g., an ASIC or FPGA) that realizes one or more of the functions.

[0084] Although each embodiment has been described in detail above, it is not limited to the specific embodiment, and various modifications and changes are possible within the scope of the claims. It is also possible to combine all or a plurality of components of the above-described embodiments.

[0085] The present invention is not limited to the above-described embodiments, and various modifications and variations can be made without departing from the spirit and scope of the present invention. Therefore, the following claims are appended to apprise the public of the scope of the present invention.

[0086] This application claims priority based on Japanese Patent Application No. 2023-221346, filed on December 27, 2023, the entire contents of which are incorporated herein by reference.

Claims

1. A communication device that relays communication between a UE (User Equipment) and a base station, comprising: a measuring means for measuring the signal strength of communication performed with the UE; and a notifying means for notifying the base station of the measurement result obtained by the measuring means, wherein the notifying means notifies the base station of the measurement result regarding the UE being relayed in a relaying state where communication between the UE and the base station is relayed.

2. The communication device according to claim 1, wherein the relaying state includes a state in which the UE being relayed is connected by Sidelink communication and is connected to the base station by Uu communication.

3. The communication device according to claim 1 or 2, wherein the signal strength related to the measurement result includes at least one of SL-RSRP (Sidelink Reference Signal Received Power) and SD-RSRP (Sidelink Discovery Reference Signal Received Power).

4. The communication device according to any one of claims 1 to 3, wherein the notifying means notifies the measurement result by means of a Measurement report.

5. In a first state where communication with a first UE (User Equipment) is performed via a second UE, an acquisition means for acquiring first signal strength information representing the signal strength between the first UE and the second UE from the second UE; an acquisition means for acquiring second signal strength information representing the signal strength between the first UE and a third UE not connected to the first UE from the third UE in the first state; and a comparison means for comparing the first signal strength information and the second signal strength information in the first state. A base station characterized by comprising.

6. The base station according to claim 5, 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 based on the comparison result of the comparison means.

7. The base station according to claim 5 or 6, wherein the third UE includes a UE connected to another base station.

8. The base station according to any one of claims 5 to 7, wherein the first signal strength information and the second signal strength information are measurement results of SL-RSRP or measurement results of SD-RSRP.

9. The base station according to claim 6, wherein the processing means gives the switching instruction to the second state when the signal strength represented by the first signal strength information is lower than a first threshold value.

10. The acquisition means further acquires third signal strength information representing the signal strength between the first UE and the base station, and the processing means gives the switching instruction to the second state when the signal strength represented by the third signal strength information is lower than a second threshold value. The base station according to claim 6.

11. The base station according to claim 6, wherein the processing means gives the switching instruction to the second state when the signal strength represented by the second signal strength information is higher than the signal strength represented by the first signal strength information.

12. The base station according to claim 6, wherein the processing means gives the switching instruction to the second state when the signal strength represented by the second signal strength information is equal to or higher than a third threshold value.

13. The base station according to any one of claims 6, 9 to 12, wherein the process of giving the switching instruction includes notifying the information related to the first UE to the first UE by an RRC (Radio Resource Control) reconfiguration message to the third UE, and notifying the information related to the third UE to the first UE by an RRC reconfiguration message.

14. A control method for controlling communication, comprising: an acquisition step of acquiring, in a first state where communication between a first UE (User Equipment) and a base station is executed via a second UE, 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 and the second signal strength information in the first state; and a processing step of giving a switching instruction from the first state to a second state where communication between the first UE and the base station is executed via the third UE based on a comparison result of the comparison step.

15. The control method according to claim 14, wherein the first signal strength information and the second signal strength information are signal strengths of the same physical channel.

16. A program causing a computer to execute, in a first state where communication between a first UE (User Equipment) and a base station is performed via a second UE, an acquisition step of 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 and the second signal strength information in the first state; and a processing step of giving an instruction to switch from the first state to a second state where communication between the first UE and the base station is performed via the third UE based on a comparison result of the comparison step.

17. The program according to claim 16, wherein the first signal strength information and the second signal strength information are signal strengths of the same physical channel.

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