BASE STATION, USER EQUIPMENT, CONTROL METHOD, AND PROGRAM

Description

1 / 24 “BASE STATION, USER EQUIPMENT, CONTROL METHOD, AND PROGRAM” FIELD OF THE INVENTION

[0001] The present description refers to a base station, a user device, a control method, and a program. FUNDAMENTALS OF THE INVENTION

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

[0003] In addition, in 3GPP, a specification was developed to extend the communication range of Sidelink with a Sidelink relay function that relays Sidelink communication through a relay device (relay UE). 3GPP defines means for a communication terminal (remote UE) with the function of connecting to a base station via a Sidelink function relay to switch from an indirect path to a direct path, and means for the communication terminal to switch from the direct path to the indirect path. The indirect path, in this case, corresponds to a communication path to connect to the base station via the relay UE, and the direct path corresponds to a communication path to connect to the base station without going through the relay UE.In this case, switching from the indirect path to the direct path, or from the direct path to the indirect path, can be performed without disconnecting the running service.

[0004] PTL 1 suggests improvements for the inconveniences that arise during the procedure when a remote UE connects to a base station via a relay UE (discovery). Petition 870250083685, dated 09 / 17 / 2025, page 52 / 90 2 / 24 List of Citations Patent Literature

[0005] PTL 1: Patent Publication PCT Japanese Translation No. 2018-535594 SUMMARY OF THE INVENTION Technical Problem

[0006] Incidentally, in a first state where the remote UE communicates with the base station via the relay UE, it is highly convenient to be able to switch to a second state where the remote UE communicates with the base station via another relay UE when, for example, the communication condition becomes poor. This is because, for example, the services in use in the first state can be used continuously in the second state.

[0007] However, the existing technologies described above have the drawback that such switching cannot be performed.

[0008] The present invention aims to solve at least one of the above drawbacks. One aspect of the present invention is to provide a mechanism for flexibly performing the switching of relay UEs. Solution to the Problem

[0009] One aspect of the present invention provides a base station. The base station includes a first acquisition unit configured to acquire the first signal strength information in a first communication relay state with a remote user equipment, UE, via a relay UE, wherein the first signal strength information indicates a first signal strength between the remote UE and the relay UE, and a processing unit configured to, based on the first signal strength information, issue a switching instruction to the remote UE to switch from the first relay state to a second communication relay state with the remote UE via a relay UE different from the relay UE, wherein the remote UE that may be in the first relay state is a remote UE that supports the transmission of a message of Petition 870250083685, dated 09 / 17 / 2025, page 53 / 90 3 / 24 discovery related to 5G. ADVANTAGEOUS EFFECTS OF THE INVENTION

[0010] According to one aspect of the present invention, it is possible to provide a mechanism that flexibly performs the switching of relay UEs. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 is a diagram showing an example of the configuration of communication devices in a first mode.

[0012] Figure 2 is a block diagram showing an example of the functional configuration of a base station in the first mode.

[0013] Figure 3 is a block diagram showing an example of the functional configuration of a remote UE in the first mode.

[0014] Figure 4 is a diagram showing an example of a sequence between communication devices in the first mode.

[0015] Figure 5 is an example of a flowchart between communication devices in the first mode.

[0016] Figure 6 is an example of a flowchart between communication devices in the first mode.

[0017] Figure 7 is an example of a flowchart between communication devices in the first mode.

[0018] Figure 8 is an example of a flowchart between the devices of communication in a second mode.

[0019] Figure 9 is an example of a flowchart between communication devices in a third mode. DETAILED DESCRIPTION

[0020] The modalities will be described in detail below with reference to the attached drawings. <Primeira Modalidade>

[0021] Figure 1 is a diagram showing an example of a system configuration according to the present embodiment. In Figure 1, a UE A 101, a UE B 102 and a UE C 103 are located within a communication area 105 of Petition 870250083685, dated 09 / 17 / 2025, page 54 / 90 4 / 24 a base station 104.

[0022] In this embodiment, a user device (UD) is considered a terminal that supports Sidelink relay communication. Specifically, the UD is assumed to be a smartphone or similar; however, the UD is not limited to this. The UD may be, for example, a communication terminal such as a tablet terminal and a PC, a wearable terminal such as a smartwatch and virtual reality glasses, and a vehicle navigation system installed in a car, or similar.

[0023] UE A 101 operates as a remote UE that communicates with base station 104 using Sidelink relay communication. UE B 102 operates as a relay UE that relays the communication between UE A 101 and base station 104 using a Sidelink relay function. In other words, UE A 101 shown in Figure 1 transmits and receives data to / from base station 104 via an indirect path, i.e., through UE B 102.

[0024] The UE C 103 has a Sidelink relay function and is capable of operating as a UE relay. Figure 1 illustrates a state where the UE C 103 is connected to base station 104; however, the UE C 103 has not yet started operating as a UE relay.

[0025] UE A 101 is capable of transmitting a discovery signal (discovery request signal) for the purpose of searching for a UE that is different from UE B 102 and that could become a relay UE (hereinafter referred to as the “candidate relay UE”). For example, UE A 101 is capable of transmitting a discovery signal to a UE located near UE A 101 (hereinafter referred to as the “neighboring UE”), for example, UE C 103. UE A 101 is capable of receiving a reply signal from a neighboring UE to such a discovery signal.

[0026] The discovery signal may be a Request Message for direct 5G ProSe discovery or UE-Network 5G ProSe Relay Discovery. ProSe is short for Proximity Based Services. The response signal may be a Response Message to a Petition 870250083685, dated 09 / 17 / 2025, pp. 55 / 90 5 / 24 Request Message. The UE A 101 is capable of receiving discovery signals transmitted by candidate relay UEs for the purpose of searching for candidate relay UEs. The discovery signal transmitted by a candidate relay UE may be a Direct UE-5G ProSe Network Discovery Announcement message or Additional Information. The discovery procedure may be based on the fact that the remote UE receives a Direct UE-5G ProSe Network Discovery Announcement message or receives Additional Information.

[0027] UE C 103 is capable of responding to a discovery signal from UE A 101 and is capable of transmitting a discovery signal to neighboring UEs on its own.

[0028] Figure 2 is a block diagram showing an example of the functional configuration of base station 104 in the present embodiment. One, some, or all of the functional blocks described with reference to Figures 2 and 3 may be replaced by other functional blocks that perform similar functions, one or some of the functional blocks may be omitted, or additional functional blocks may be added. A functional block described in the following description may be divided into a plurality of functional blocks, or a plurality of functional blocks may be integrated into a functional block.

[0029] In the example shown in Figure 2, 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.

[0030] Control unit 201 controls the operation of base station 104. Control unit 201 is composed, for example, of one or more processors, such as a CPU and an MPU, and controls the entire communication apparatus by executing a control program read from a RAM, which is storage unit 202. The processes to be executed by control unit 201, described with reference to the flowchart (described later), can also be performed using a hardware circuit, such as a circuit Petition 870250083685, dated 09 / 17 / 2025, pp. 56 / 90 6 / 24 application-specific integrated circuit (ASIC) and a field-programmable gate array (FPGA). By collaborating a hardware circuit with a processor, such as a CPU and an MPU, it is also possible to perform the processes described in the flowchart (described later).

[0031] Storage unit 202 stores information that control unit 201 uses for control and communication-related information. Storage unit 202 may include a primary storage unit and an auxiliary storage unit. Examples of primary storage units include read-only memory (ROM) and random-access memory (RAM). The primary storage unit may temporarily store or save programs and data from an operating system (OS), which is basic software, and application software, executed by control unit 201. Examples of auxiliary storage units include a hard disk drive (HDD) and a solid-state drive (SSD). The auxiliary storage unit may store data related to application software and similar data.For example, control programs stored in a non-volatile storage area are deployed to random access memory (RAM) and executed by the processor that makes up control unit 201. In this way, control unit 201 and storage unit 202 can function as a single computer.

[0032] Storage unit 202 may include a recording medium that stores a pre-determined program. The program stored on the recording medium may be installed by means of a drive device or similar, and the installed pre-determined program may be executable by control unit 201. Various types of recording media may be used as the recording medium. The recording medium may be a recording medium that records information optically, electrically, or magnetically, such as a compact disc (CD-ROM), a floppy disk, a magneto-optical disc, or similar. The recording medium may be, for example, a semiconductor memory that records information electrically, such as a ROM, a flash memory, or similar. A Petition 870250083685, dated 09 / 17 / 2025, pp. 57 / 90 7 / 24 carrier is not included with the recording support.

[0033] UE Management Unit 203 manages UE information within a base station area. UE Management Unit 203 manages UE information which includes the IDs of subordinate UEs and measurement results (signal strengths of UE links (described later) and similar) reported by subordinate UEs. Path Switching Determination Processing Unit 204 determines whether the UE under management should be connected via an indirect or direct path based on the UE information managed by UE Management Unit 203. Message Generation Processing Unit 205 generates a message used to issue a path switching instruction. Message Analysis Processing Unit 206 analyzes messages received from subordinate UEs.

[0034] The functions corresponding to the UE management unit 203, the path switching determination processing unit 204 and / or the message generation processing unit 205 can be implemented as software modules implemented by the control unit 101.

[0035] Wireless communication unit 207 transmits and receives information via wireless communication to / from subordinate UEs. For example, wireless communication unit 207 performs a message transmission process for messages generated by message generation processing unit 205 and a message reception process for messages from subordinate UEs.

[0036] Figure 3 is a block diagram showing an example of the functional configuration of the remote UE (e.g., UE A 101 or UE C 103) in this embodiment.

[0037] In the example shown in Figure 3, the remote UE includes a control unit 301, a storage unit 302, a signal strength measurement unit 303, a Sidelink retransmission processing unit 304, a message generation processing unit 305, a message analysis processing unit 306, and a unit of Petition 870250083685, dated 09 / 17 / 2025, pp. 58 / 90 8 / 24 wireless communication 307.

[0038] Control unit 301 controls the operation of the remote UE. Control unit 301 consists, for example, of one or more processors, such as a CPU and an MPU, and controls the entire communication device by executing a control program read from RAM, which is storage unit 302. The processes to be executed by control unit 301, described with reference to the flowchart (described later), can also be performed using hardware circuits, such as an ASIC and an FPGA. By combining a hardware circuit with a processor, such as a CPU and an MPU, it is also possible to perform the processes described in the flowchart (described later).

[0039] Storage unit 302 saves information that control unit 301 uses for control and communication-related information. Signal strength measurement unit 303 measures the “signal strength with the relay UE (relay link)”, the “signal strength with the base station (Uu link)”, and the “signal strength with the candidate relay UE” from the remote UE. Sidelink relay processing unit 304 establishes the Sidelink connection with a relay UE to enable connection to base station 104 via the relay UE’s relay function (i.e., via an indirect path). Message generation processing unit 305 generates various messages. Various messages include a discovery signal transmitted to neighboring relay UEs, a RRC Reconfiguration Completed message, and a Measurement Report transmitted to base station 104.Message analysis processing unit 306 analyzes discovery signals and response signals transmitted from neighboring relay UEs and messages, such as an RRC Reconfiguration message, transmitted from base station 104. Wireless communication unit 307 transmits and receives information via wireless communication to / from neighboring relay UEs and base station 104. Wireless communication unit 307 performs a message transmission process for messages generated by message generation processing unit 205 and a message reception process. Petition 870250083685, dated 09 / 17 / 2025, pp. 59 / 90 9 / 24 messages from neighboring relay UEs and base station 104.

[0040] Next, the operation of this modality will be described with reference to the operation sequence diagram shown in Figure 4 and the flowcharts shown in Figures 5, 6 and 7.

[0041] Figure 4 is an example of a switching sequence from one indirect path to another indirect path in the present embodiment. Figures 5, 6, and 7 are flowcharts in which the content of the sequence in Figure 4 in the present embodiment is separated for base station 104 and UE A 101. The processes shown in each flowchart can be implemented by control unit 201 executing the control program stored in storage unit 202 at base station 104. The computation and information processing and the control of hardware components can be implemented by control unit 301 executing the control program stored in storage unit 302 at UE A 101.

[0042] A switching procedure for switching the connection of a first indirect path using UE B 102 to a second indirect path using UE C 103 will be described with reference to the sequence diagram and flowcharts.

[0043] UE A 101 transmits and receives user data via UE B 102.

[0044] Initially, communication via an indirect path A will be described. UE A 101 transmits and receives user data to / from base station 104 through the Sidelink relay function of UE B 102 (F401, S501). In other words, UE A 101 is transmitting and receiving user data (streaming data or similar) to / from base station 104 using the Sidelink relay processing unit 304. In Figure 4, to clearly indicate the process in which the relay UE is relaying communication between the remote UE and the base station, the points where the relay UE is performing the relay process are indicated by circular marks. The dashed lines in Figure 4 indicate the transmission and reception of user data, and the solid lines indicate the transmission and reception of data. Petition 870250083685, dated 09 / 17 / 2025, pages 60 / 90 10 / 24 control data reception.

[0045] During the transmission and reception of user data to / from base station 104, control unit 301 of UE A 101 activates message generation processing unit 305. Then, control unit 301 generates a discovery signal. Subsequently, control unit 301 of UE A 101 transmits the generated discovery signal to neighboring UEs via wireless communication unit 307. Control unit 301 activates message analysis processing unit 306 to prepare the message analysis to be conducted upon receipt of a response signal to the discovery signal or a discovery signal from a neighboring UE via wireless communication unit 307. In other words, control unit 301 of UE A 101 initiates a discovery process to search for candidate relay UEs (S502).

[0046] Subsequently, the signal strength measurement unit 303, previously activated by the control unit 301 of UE A 101, begins measuring the “signal strength between UE A 101 and base station 104” and the “signal strength between UE A 101 and UE B 102”, in collaboration with the wireless communication unit 307 (F402, S503). The link between UE A 101 and base station 104 is then referred to as the “Uu link”, and the link between UE A 101 and UE B 102 is referred to as the “relay link”.

[0047] When wireless communication unit 307 receives a discovery signal from a neighboring UE or a response signal to a discovery signal, message analysis processing unit 306 analyzes the received signal. Then, message analysis processing unit 306 stores the ID or service cell ID of the neighboring UE that transmitted the signal in a list of candidate relay UEs (“SIM” in S504, S505). The list of candidate relay UEs can be stored in storage unit 302.

[0048] When there is a candidate relay UE in the list of candidate relay UEs, the signal strength measurement unit 303 Petition 870250083685, dated 09 / 17 / 2025, pp. 61 / 90 11 / 24 starts measuring the “signal strength between UE A 101 and the UE candidate relay” (S503).

[0049] When UE A 101 stops receiving a discovery signal and a response signal to a discovery signal from neighboring UEs (“NO” in S504), UE A 101 creates a Measurement Report (S506). In other words, UE A 101 creates a measurement report according to an event previously designated by a measurement configuration from base station 104. Negative determination in step S504 may be allowed after a predetermined time from the start of the S502 step process. More specifically, the process needs to proceed to step S506 only when it is determined that the predetermined time has elapsed since the start of the S502 step process; whereas, when it is not determined that the predetermined time has elapsed, the reception of a signal is awaited, and a list update process needs to be executed whenever a discovery signal is received.

[0050] The process of transmitting the search results will be described next. UE A 101 then transmits the measurement report to base station 104 via UE B 102 (F402, S506). This measurement report includes the measurement results (various signal strengths) from signal strength measurement unit 303 and the list of candidate relay UEs in storage unit 302.

[0051] The control of base station 104, which receives the measurement report, will be described below. When the wireless communication unit 207 of base station 104 receives the measurement report, the path switching determination processing unit 204 checks various signal strengths on UE A 101, which are analyzed by the message analysis processing unit 206 (S507). In this case, the various signal strengths include the “Uu link signal strength”, the “relay link signal strength”, and the “signal strength between UE A 101 and the candidate relay UE in the list of candidate relay UEs”.

[0052] When the signal strength of the relay link in UE A 101 is Petition 870250083685, dated 09 / 17 / 2025, pp. 62 / 90 If 12 / 24 is greater than or equal to a Th1 limit (an example of a first limit) (“YES” in S601), the path switching determination processing unit 204 determines that retransmission can be continued and concludes the determination without executing anything. The Th1 limit corresponds to the lower limit value of the signal strength range that allows stable continuation of retransmission. Th1 is assumed to be a limit set by the base station supplier 104; however, Th1 is not limited to this. Th1 may be a limit set by a communications operator using base station 104. In this case, Th1 can be configured to be changed via a settings screen (not shown) or similar as an operational parameter of base station 104.The Th1 limit can be a limit defined as a reference value to be changed in a connection test or similar between the base station and the UE, or it can be a limit defined as a reference value to be changed in a communication standard. On the other hand, when the signal strength of the relay link on UE A 101 is less than the Th1 limit (“NO” in S601), the path switching determination processing unit 204 determines that the relay is difficult to continue, and checks the signal strength of the Uu link on UE A 101. Then, when the “Uu link signal strength” is greater than or equal to a Th2 limit (an example of a second limit) (“YES” in S602), the path switching determination processing unit 204 issues an instruction to UE A 101 to switch from an indirect path to a direct path, causing UE A 101 to switch the path (S603).In this case, the Th2 limit can be equal to the Th1 limit or it can be different from the Th1 limit. For example, the Th2 limit can be a value greater than the Th1 limit. Similarly to Th1, Th2 can be a value defined by the base station 104 provider or it can be a limit defined by a communication carrier. Similarly to Th1, Th2 can be a limit defined by a connection test or a limit defined by a communication standard. By running the S603 process, it is possible to switch the connection state from a state where UE A 101 uses the first indirect path to connect to base station 104 using UE B 102 to a state where UE A 101 uses the direct path. Petition 870250083685, dated 09 / 17 / 2025, pp. 63 / 90 13 / 24 connect directly to base station 104.

[0053] When the link signal strength Uu in UE A 101 is less than the Th2 threshold (“NO” in S602), the path switching determination processing unit 204 determines that retransmission is difficult to continue, even when the path is switched to the forward path, and checks the list of candidate relay UEs. From the list of candidate relay UEs, the path switching determination processing unit 204 identifies the candidate relay UE with the same service cell ID (i.e., within the base station cell 104) and the highest signal strength (S604). For descriptive purposes, an example is given where a candidate relay UE present in the base station cell 104 and with the highest signal strength is UE C 103.

[0054] In this case, the path switching determination processing unit 204 compares the signal strength between UE A 101 and UE C 103, which is the candidate relay UE, with the Th1 threshold. At this point, when the signal strength between UE A 101 and UE C 103 is less than the Th1 threshold (“NO” in S605), the path switching determination processing unit 204 determines that it is difficult to continue the relay and concludes the path switching process.

[0055] On the other hand, when the signal strength between UE A 10 and UE C 103 is greater than or equal to the Th1 threshold (“YES” in S605), the path switching determination processing unit 204 determines that the running service can be continued. In other words, the path switching determination processing unit 204 determines that UE A 101 can continue the running service through UE C 103, switching from the indirect path through UE B 102 to the indirect path through UE C 103. In this case, the path switching determination processing unit 204 proceeds to step S701 in Figure 7 and notifies the control unit 201 of a switching instruction to switch from an indirect path to an indirect path (F403). The running service is optional and can be, for example, a Petition 870250083685, dated 09 / 17 / 2025, pp. 64 / 90 14 / 24 video streaming service, a video conferencing service, a voice calling service or similar.

[0056] Control unit 201 performs RRC reconfiguration for UE C 103 via wireless communication unit 207 (F404, S701). In other words, message generation processing unit 205 notifies UE C 103 of the information needed to establish Sidelink relay communication with UE A 101 via wireless communication unit 207. The required information includes sl-L2RelayUE-Config (S702). The slL2RelayUE-Config contains information used for the Sidelink Relay Adaptation Protocol (SRAP), necessary for operation as a relay UE. Control unit 201 verifies receipt of a completed RRC reconfiguration message from UE C 103 via wireless communication unit 207 and message analysis processing unit 206. Upon confirming receipt of the relevant message, control unit 201 completes the RRC reconfiguration for UE C 103.

[0057] Subsequently, control unit 201 performs RRC reconfiguration for UE A 101 via wireless communication unit 207 (F405, S703). In other words, message generation processing unit 205 notifies UE A 101 of the information needed to establish Sidelink relay communication with UE C 103 via wireless communication unit 207. The required information includes sl-L2RemoteUEConfig. The sl-L2RemoteUE-Config contains information used for the Sidelink Relay Adaptation Protocol (SRAP) required for operation as a remote UE.

[0058] In addition, message generation processing unit 205 adds sl-PathSwitchConfig to ReconfigurationWithSync in the RRC reconfiguration message. At this time, the sl-PathSwitchConfig that stores the ID of UE C 103 is used. As a result, message generation processing unit 205 can notify UE A 101 about switching from an indirect path via UE B 102 to an indirect path via UE C 103 (S702). Petition 870250083685, dated 09 / 17 / 2025, pp. 65 / 90 15 / 24

[0059] Control unit 301 in UE A 101 verifies receipt of the RRC reconfiguration message from base station 104 via wireless communication unit 307 and message analysis processing unit 306. At this time, control unit 301 determines that it is a switching from the indirect path via UE B 102 to the indirect path via UE C 103, checking the UE C ID from sl-PathSwitchConfig (F405, S704).

[0060] Subsequently, control unit 301 of UE A 101 interrupts data transmission and reception to / from UE B 102 and establishes PC5 communication (PC5 Connection) with UE C 103 (F406, S705). UE A 101 and UE C 103 can then utilize Sidelink relay communication based on SRAP information acquired from the RRC reconfiguration message. In other words, UE A 101 can transmit and receive data to / from base station 104 via UE C 103.

[0061] After communication with UE C 103 is established, control unit 301 causes message generation processing unit 205 to generate a completed RRC reconfiguration message. Sidelink retransmission processing unit 304 and wireless communication unit 307 transmit the completed RRC reconfiguration message to base station 104 via UE C 103 (F407, S706). In other words, Sidelink retransmission processing unit 304 and wireless communication unit 307 transmit the completed RRC reconfiguration message to base station 104 via UE C 103 instead of UE B 102.

[0062] Base station 104 receives the completed RRC reconfiguration message from UE A 101 via UE C 103, through wireless communication unit 307 and message analysis processing unit 306. Base station 104 can determine that the indirect path switching to UE A 101 has been completed, based on receiving the relevant message (F407, S707).

[0063] After the indirect route switching to UE A 101 is completed, the Petition 870250083685, dated 09 / 17 / 2025, pp. 66 / 90 16 / 24 base station 104 performs RRC reconfiguration for UE B 102, causing UE B 102 to release the Sidelink relay function to UE A 101 (F408, S708).

[0064] On the other hand, UE A 101 releases the PC5 link with UE B 102 (F409, S709).

[0065] Next, UE A 101 continues to transmit and receive user data to / from base station 104 via the UE C 103 Sidelink relay function (F410). In other words, UE A 101 continues to transmit and receive user data (such as streaming data) to / from base station 104 using the Sidelink relay processing unit 304. When there are undelivered packets being processed by UE B 102, these undelivered packets are transferred to UE C 103 as needed and transmitted to the destination by UE C 103. These undelivered packets can be configured to be transferred directly from UE B 102 to UE C 103, or they can be configured to be transferred from UE B 102 to base station 104 and then transferred again from base station 104 to UE C 103.When the latter case, that is, a method of transferring undelivered packets via base station 104, is adopted, the transfer to UE C 103 can be omitted when the destination of the user data is not UE A 101, but the central network for communication on the uplink.

[0066] Incidentally, switching from an indirect path to a direct path and switching from a direct path to an indirect path are defined in 3GPP; however, switching from an indirect path to an indirect path is not defined at this time. For this reason, when the signal strengths of both the indirect and direct paths are low for a remote UE connected via an indirect path, the path needs to perform path switching with a different UE after switching once to a direct path, therefore the procedure is redundant. Due to the redundant procedure, when either connection is disconnected during the switching procedure, there is a possibility that the running service will be interrupted. Petition 870250083685, dated 09 / 17 / 2025, pp. 67 / 90 17 / 24

[0067] In contrast, in the present embodiment, a switching mechanism is defined from one indirect path to another indirect path with a simpler procedure than the existing procedure, which makes it possible to switch from one indirect path to another indirect path with a simpler procedure than the existing procedure. According to this procedure, base station 104 and UE A 101 can flexibly switch from one indirect path to another indirect path. At this time, it is possible to switch to another indirect path without disconnecting a running service.

[0068] Next, other alternative modalities (a second modality and a third modality) to the first modality will be described. In the description of the other modalities below, similar reference symbols are assigned to components similar to those of the modality described above, and the description of these may be omitted. <Segunda Modalidade>

[0069] In the first embodiment described above, the example was given in which UE A 101 constantly performs discovery while connected to base station 104 via an indirect path through UE B 102. With this method, it is possible to constantly monitor, for example, the presence or absence of a candidate relay UE; however, resources, such as electrical power related to discovery, are constantly consumed. Therefore, in the second embodiment, the need for UE A to perform discovery of candidate relay UEs is determined based on the measured signal strength.

[0070] The configuration (Figure 1) of the communication devices in the second mode and the functional configuration (Figures 2 and 3) of the communication devices may be the same as in the first mode described above, therefore, the description is omitted.

[0071] Next, the operation of the second mode will be described with reference to the flowchart shown in Figure 8. The flowchart shown in Figure 8 refers to F401 and F402 in the sequence shown in Figure 4, described with reference to the first mode. Petition 870250083685, dated 09 / 17 / 2025, pp. 68 / 90 18 / 24

[0072] In this embodiment, UE A 101 is transmitting and receiving user data (such as streaming data) to / from base station 104 via the Sidelink relay function of UE B 102, using the Sidelink relay processing unit 304 (S801).

[0073] Subsequently, the signal strength measurement unit 303, previously activated by the control unit 301 of UE A 101, starts measuring the “signal strength of link Uu” and the “signal strength of the relay link” (S802).

[0074] Here, in the present embodiment, when the “relay link signal strength” is less than the Th1 threshold or when the “Uu link signal strength” is less than the Th2 threshold, UE A 101 initiates the transmission and reception of a discovery signal (S803, S804). In a modification, when the “relay link signal strength” is less than the Th1 threshold and the “Uu link signal strength” is less than the Th2 threshold, UE A 101 may initiate the transmission and reception of a discovery signal.

[0075] When a discovery signal or a response signal is received from a candidate relay UE (“SIM” in S805), the message analysis processing unit 306 stores information about the candidate relay UE, acquired from the signal, in the list of candidate relay UEs. The signal strength measurement unit 303 starts measuring the “signal strength between UE A 101 and the candidate relay UE added to the list” (S806).

[0076] UE A 101 creates a measurement report based on an event designated by the measurement configuration previously from base station 104 and transmits the measurement report to base station 104 (S807). UE A 101 transmits the measurement report to base station 104 via UE B 102.

[0077] When the wireless communication unit 207 of base station 104 receives the measurement report, the path switching determination processing unit 204 checks the various signal strengths (S807). The various signal strengths may include the “Uu link signal strength”, the Petition 870250083685, dated 09 / 17 / 2025, pp. 69 / 90 19 / 24 “relay link signal strength” and the “signal strength between UE A 101 and the candidate relay UE in the list of candidate relay UEs” on UE A 101, analyzed by message analysis processing unit 206. The UE A 101 processes from S807 may be similar to the processes shown in Figure 7 (and to the F403 processes in Figure 4), therefore, the description is omitted.

[0078] When the wireless communication unit 207 of base station 104 receives the measurement report, the path switching determination processing unit 204 checks several signal strengths on UE A 101, analyzed by the message analysis processing unit 206 (S808). In this case, several signal strengths include the “Uu link signal strength”, the “relay link signal strength”, and the “signal strength between UE A 101 and the candidate relay UE in the list of candidate relay UEs”. The processes of base station 104 from S808 may be similar to the processes of F403 in Figures 4, 6 and 7 (and to the processes of F403 in Figure 4), the description being omitted.

[0079] According to the present embodiment, a similar advantageous effect is also obtained as in the first embodiment. According to the present embodiment, UE A 101 can reduce discovery-related resources when communication quality is high, determining the discovery opportunity of a candidate relay UE based on the signal strength being measured.<Terceira Modalidade>

[0080] The third mode differs primarily from the first mode described above, in that, when base station 104 determines a candidate relay UE, base station 104 uses the “signal strength between the candidate relay UE and base station 104” reported by the candidate relay UE.

[0081] The configuration (Figure 1) of the communication devices in the third mode and the functional configuration (Figures 2 and 3) of the communication devices may be the same as in the first mode described above, Petition 870250083685, dated 09 / 17 / 2025, pp. 70 / 90 20 / 24 therefore, the description is omitted.

[0082] Next, the operation of the third mode will be described with reference to the flowchart shown in Figure 9. The operation of the third mode differs mainly in that the flowchart in Figure 6, described with reference to the first mode, is changed to the flowchart shown in Figure 9.

[0083] Specifically, when the signal strength of the relay link on UE A 101 is greater than or equal to the Th1 threshold (“YES” in S901), the path switching determination processing unit 204 determines that the relay can be continued, and concludes the determination process without executing anything. When the signal strength is less than the Th1 threshold (“NO” in S901), the path switching determination processing unit 204 determines that the relay is difficult to continue and checks the signal strength of the Uu link on UE A 101. In this case, when the signal strength of the Uu link on UE A 101 is greater than or equal to the Th2 threshold (“YES” in S902), the path switching determination processing unit 204 issues an instruction to UE A 101 to switch from an indirect path to a direct path (S903).

[0084] When the signal strength of link Uu in UE A 101 is less than the Th2 threshold (“NO” in S902), the path switching determination processing unit 204 determines that retransmission is difficult to continue, even when the path is switched to the forward path, and checks the list of candidate relay UEs. At this point, the path switching determination processing unit 204 removes UEs that do not have their own service cell IDs (i.e., UEs that are not within the base station cell 104) from the list of candidate relay UEs (S904).The path switching determination processing unit 204 acquires the link signal strength Uu of the candidate relay UE (between the candidate relay UE and base station 104) from the UE management unit 203 and removes (masks) the candidate relay UEs with signal strength lower than the Th2 threshold from the list of candidate relay UEs (S904). Petition 870250083685, dated 09 / 17 / 2025, pp. 71 / 90 21 / 24 When there are no UEs without their own service cell ID or no candidate relay UEs with a signal strength lower than the Th2 threshold, the list of candidate relay UEs remains unchanged.

[0085] Subsequently, the path switching determination processing unit 204 acquires the signal strength of the relay UE with the highest signal strength from the list of candidate relay UEs (S905). In this embodiment, in one example, the relay UE with the highest signal strength is UE C 103.

[0086] In this case, the path switching determination processing unit 204 compares the signal strength between UE A 101 and UE C 103 with the Th1 threshold. At this point, when the signal strength between UE A 101 and UE C 103 is less than the Th1 threshold (“NO” in S906), the path switching determination processing unit 204 determines that retransmission is difficult to continue and concludes the path switching process.

[0087] On the other hand, when the signal strength between UE A 101 and UE C 103 is greater than or equal to the Th1 threshold (“YES” in S906), the path switching determination processing unit 204 determines that the running service can be continued. In other words, the path switching determination processing unit 204 determines that UE A 101 can continue the running service through UE C 103 by switching to the indirect path through UE C 103. In this case, the path switching determination processing unit 204 proceeds to step S701 in Figure 7, as in the first embodiment, and notifies the control unit 201 of a switching instruction to switch from an indirect path to an indirect path (F403). The flow of subsequent processes is the same as in Figures 4 and 7, described in the first embodiment.

[0088] Here, in the first mode, base station 104 identifies the candidate relay UE with the highest signal strength from the list of candidate relay UEs received from UE A 101 and attempts to switch to an indirect path via UE C 103 (S604 in Figure 6). However, in this case, if Petition 870250083685, dated 09 / 17 / 2025, pp. 72 / 90 22 / 24 The signal strength between UE C 103 and base station 104 is lower than the Th2 limit, there is a possibility that stable Sidelink relay communication cannot be continued after switching to the indirect path.

[0089] In contrast, in the present embodiment, as described above, candidate relay UEs whose signal strength between UE C 103 and base station 104 is less than the Th2 threshold are removed from the list of candidate relay UEs in advance. In other words, in the present embodiment, as described above, before base station 104 identifies the candidate relay UE with the highest signal strength from the list of candidate relay UEs, the candidate relay UEs are reduced based on the “signal strength with the base station (Uu link)”. Therefore, according to the present embodiment, it is possible to select the candidate relay UEs that can continue the most stable Sidelink relay communication and issue a path switching instruction.

[0090] In the present embodiment, as an equivalent configuration, in step S604 of Figure 6, candidate relay UEs whose signal strength between UE A 101 and the candidate relay UE is less than the Th1 threshold can be removed from the list of candidate relay UEs in advance.

[0091] In a modification, from a similar point of view, a candidate relay UE involved with path switching can be determined from among the candidate relay UEs by considering both the signal strength between UE A 101 and the candidate relay UE and the signal strength between the candidate relay UE and base station 104. For example, it is assumed that there are two or more candidate relay UEs whose signal strength between UE A 101 and the candidate relay UE is greater than or equal to the Th1 threshold and the signal strength between the candidate relay UE and base station 104 is greater than or equal to the Th2 threshold. In this case, among the two or more candidate relay UEs, the candidate relay UE with the highest composite value of the signal strength between UE A 101 and the candidate relay UE and the signal strength between the candidate relay UE and base station 104 Petition 870250083685, dated 09 / 17 / 2025, pp. 73 / 90 23 / 24 can be determined as a candidate UE relay involved with path switching. In this case, the composite value can be calculated so that the signal strength between UE A 101 and the candidate UE relay and the signal strength between the candidate UE relay and base station 104 receive greater importance than the other.

[0092] The embodiments have been described in detail above; however, they are not limited to these specific embodiments. Various modifications and alterations are possible within the scope of the appended claims. It is also possible to combine all or some of the components of the embodiments described above.

[0093] The present invention is not limited to the embodiments described above. Various alterations and modifications are applicable without departing from the character and scope of the present invention. Therefore, the following claims are appended to demonstrate the scope of the present invention.

[0094] This application claims the benefit of Japanese Patent Application No. 2023-061970, filed on April 6, 2023, which is incorporated herein by reference in its entirety. List of Reference Symbols

[0095] 101 EU A

[0096] 102 UEB

[0097] 103 UEC

[0098] 104 Base Station

[0099] 105 Communication Area

[0100] 201 Control unit (processing unit)

[0101] 202 Storage unit

[0102] 203 Management Unit

[0103] 204 Path switching determination processing unit (processing unit)

[0104] 205 Message generation processing unit

[0105] 206 Message analysis processing unit

[0106] 207 Wireless communication unit (first acquisition unit, Petition 870250083685, dated 09 / 17 / 2025, pp. 74 / 90 24 / 24 second acquisition unit and third acquisition unit)

[0107] 301 Control unit (switching processing unit)

[0108] 302 Storage unit

[0109] 303 Signal strength measurement unit (first signal strength measurement unit and second signal strength measurement unit)

[0110] 304 Sidelink Relay Processing Unit

[0111] 305 Message generation processing unit (fetch processing unit)

[0112] 306 Message analysis processing unit

[0113] 307 Wireless communication unit (first notification unit and second notification unit) Petition 870250083685, dated 09 / 17 / 2025, pp. 75 / 90

Claims

1 / 5 CLAIMS 1. Base station capable of performing communication compatible with the 3rd Generation Partnership Project standard, 3GPP, characterized in that it comprises: a receiving means configured to receive a Measurement Report message including the first signal strength information in a first communication retransmission state with a remote user equipment, UE, via a first retransmitting UE, the first signal strength information indicating a first signal strength between the remote UE and the first retransmitting UE; a determination means configured to, after receiving the Measurement Report message, determine to switch from the first retransmission state to a second communication retransmission state with the remote UE via a second retransmitting UE different from the first retransmitting UE;and the transmission medium is configured to, after determining the switch from the first retransmission state to the second retransmission state, transmit an RRC Reconfiguration message to the remote UE via the first retransmitting UE.

2. Base station, according to claim 1, characterized in that the determination means is configured to determine switching from the first retransmission state to the second retransmission state in a case where the first signal strength is less than a first threshold.

3. Base station, according to claim 1 or 2, characterized in that the receiving medium is configured so that, for at least one candidate relay EU that may become the second relay EU, it receives the Measurement Report message including the second signal strength information, indicating a second signal strength between the remote EU and the candidate relay EU.

4. Base station, according to claim 3, characterized in that the means of determination is configured to determine switching from the first retransmission state to the second retransmission state additionally based on the second signal strength information.

5. Base station, according to claim 3, characterized in that the determination means is configured to determine switching from the first retransmission state to the second retransmission state in a case where the second signal strength is greater than or equal to the first threshold.

6. Base station, according to any one of claims 3 to 5, characterized in that the means of determination is configured to, in a case where there is a plurality of candidate relay UEs, determine any one of a plurality of candidate relay UEs having the second highest signal strength as the second relay UE, based on the second signal strength information.

7. Base station, according to any one of claims 1 to 6, characterized in that the remote UE that may be in the first relay state is a remote UE that supports transmission of a discovery message compliant with the 3GPP standard.

8. Base station, according to any one of claims 3 to 6, characterized in that the second signal strength information between the remote UE and the second relay UE is the signal strength information related to a discovery message.

9. Base station, according to any one of claims 1 to 8, characterized in that the RRC Reconfiguration message to be transmitted to the remote UE via the transmission medium includes ReconfigurationWithSync including sl-pathSwitchConfig.

10. Base station, according to any one of claims 1 to 9, characterized in that the transmission medium is configured to, before transmitting the RRC Reconfiguration message, transmit information related to the remote UE using another RRC Reconfiguration message to the second relay UE.

11. User equipment capable of performing communication compatible with the 3rd Generation Partnership Project standard, 3GPP, characterized in that it comprises: a search medium configured to, in an initial communication connection state with a base station via a first relay UE, search for at least one candidate relay UE other than the first relay UE; a measurement medium configured to measure an initial signal strength of a signal received from the first relay UE; a transmission medium configured to transmit, to the base station, a Measurement Report message including information related to the initial signal strength measured by the measurement medium; a receiving medium configured to receive an RRC Reconfiguration message from the base station that received the Measurement Report message;and the switching medium is configured to, after receiving the RRC Reconfiguration message, execute a switching process to switch from the first connection state to a second communication connection state with the base station via a second UE relay different from the first UE relay.

12. User equipment according to claim 11, characterized in that the measuring means is configured to additionally measure a second signal strength of a signal received from at least one candidate relay UE found by the search means, and the Measurement Report message additionally includes information relating to the second signal strength measured by the measuring means.

13. User Equipment, according to claim 11, characterized in that the second relay UE is determined by the base station from among at least one candidate relay UE.

14. User equipment, according to any of the claims 11 to 13 in Petition 870250083685, dated 09 / 17 / 2025, pp. 78 / 90 4 / 5, characterized in that the search medium is configured to, in a discovery procedure related to the 3GPP standard, perform at least one of the following: receiving an Advertisement message for direct discovery of UE-5G ProSe Network, receiving Additional Information and transmitting a Request message for direct discovery of UE-5G ProSe Network, and receiving a response to the Request message.

15. User equipment, according to any one of claims 11 to 14, characterized in that the RRC Reconfiguration message includes ReconfigurationWithSync including slpathSwitch Config.

16. User equipment, according to claim 15, characterized in that the switching process includes establishing a PC5 connection with a UE that has an ID acquired from slpathSwitchConfig as the second relay UE.

17. User equipment according to claim 16, characterized in that the switching process additionally includes transmitting a completed RRC reconfiguration message to the base station via a second UE relay after the PC5 connection has been established.

18. User equipment, according to any one of claims 11 to 17, characterized in that the search for the search medium is initiated at any of the following times: to initiate a connection with the base station via the first relay UE, at which time the first signal strength is less than a first threshold in the first connection state, and at which time the signal strength with the base station is less than a second threshold in the first connection state.

19. Control method for controlling the communication of a user device capable of performing communication compatible with the standard of Petition Project 870250083685, dated 09 / 17 / 2025, page 1.79 / 90 5 / 5 Third-Generation Partnership, 3GPP, characterized in that it comprises: searching for at least one user equipment, UE, candidate relay other than a first UE relay in a first communication connection state with a base station via the first UE relay; measuring a first signal strength of a signal received from the first UE relay; transmitting to the base station a Measurement Report message including information related to the first measured signal strength; receiving a RRC Reconfiguration message from the base station that received the Measurement Report message; and after receiving the RRC Reconfiguration message, executing a switching process to switch from the first connection state to a second communication connection state with the base station via a second UE relay other than the first UE relay.

20. Non-transient recording media, characterized by the fact that it records a program to make a computer function as follows: search for at least one first user equipment, UE, candidate relay other than a first UE relay in a first communication connection state with a base station via the first UE relay; measure a first signal strength of a signal received from the first UE relay; transmit, to the base station, a Measurement Report message including information related to the first measured signal strength; receive an RRC Reconfiguration message from the base station that received the Measurement Report message; and after receiving the RRC Reconfiguration message, execute a switching process to switch from the first connection state to a second communication connection state with the base station via a second UE relay other than the first UE relay.Petition 870250083685, dated 09 / 17 / 2025, pp. 80 / 90.

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