Communication device, base station, control method, and program

Abstract

To provide a mechanism that makes it possible to select a relay UE appropriately.SOLUTION: A communication device for relaying communication between a UE (user equipment) and a base station includes measurement means for measuring the signal strength of communication performed with the UE and notification means for notifying the base station of a measurement result obtained by the measuring means. The notification means, in a state of relaying communication between the UE and the base station, notifies the base station of the measurement result concerning the UE being relayed.SELECTED DRAWING: Figure 6

Description

Technical Field

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

Background Art

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

[0003] Furthermore, in 3GPP, the development of a specification to expand the communication range of Sidelink by a Sidelink relay function that relays Sidelink communication via a relay device (relay UE) is in progress. In 3GPP, a communication terminal (remote UE) having a function of connecting to a base station through Sidelink function relay is defined with means for switching from an indirect path to a direct path and means for switching from a direct path to an indirect path. Here, the indirect path corresponds to a communication path connecting to a base station via a relay UE, and the direct path corresponds to a communication path connecting to a base station without going through a relay UE. In this case, the switching from an indirect path to a direct path and the switching from a direct path to an indirect path can be realized without disconnecting the service being executed.

[0004] Patent Document 1 proposes an improvement in problems that occur in the procedure (discovery) when a remote UE connects to a base station via a relay UE.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Currently, 3GPP does not stipulate a determination method when switching from an indirect path to an indirect path. Therefore, there is a problem that a relay UE cannot be appropriately selected.

[0007] The present invention has been made in view of at least one of the above problems. One aspect of the present invention aims to provide a mechanism that enables appropriate selection of a relay UE.

Means for Solving the Problems

[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, measurement means for measuring the signal strength of communication performed with the UE, notification means for notifying the base station of the measurement result by the measurement means, In a relay state where the notification means relays communication between the UE and the base station, the notification means is characterized by notifying the base station of the measurement result regarding the relayed UE.

Effects of the Invention

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

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 7A

Figure 8

Figure 9

Figure 10

Mode for Carrying Out the Invention

[0011] Hereinafter, each embodiment will be described in detail with reference to the accompanying drawings. In the following description, "number ***" in TS*** represents the number of the technical specification (Technical Specification) in the 3GPP standard.

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

[0013] In the system of FIG. 1, the remote UE-A (101), relay UE-B (102), and relay UE-C (103) are all within the communication area (105) of the 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 the 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) passing through the relay UE-B (102). Note that data is communicated with the base station and devices on the core network (not shown in the figure). Also, the Uu link, which will be described later, means the link when the remote UE-A (101) communicates directly with the gNB (104) without going through the relay UE.

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

[0016] The remote UE-A (101) can transmit a discovery signal to neighboring UEs (i.e., the relay UE-C (103)) for searching for the relay UE-B (102) or another relay UE (candidate relay UE). Also, the remote UE-A (101) can receive a response signal to the transmitted discovery signal, which is a response signal from a neighboring UE (i.e., the relay UE-C (103)).

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

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

[0019] Also, the relay UE-C (103) can respond to the discovery signal from the remote UE-A (101). Also, the relay UE-C (103) can itself transmit a discovery signal to neighboring UEs.

[0020] The relay UE-B (102) is a relay UE, but like the relay UE-C (103), it can respond to the discovery signal and can itself transmit a discovery signal to neighboring UEs.

[0021] FIG. 2 is a block diagram showing an example of the functional configuration of the base station 104 in the present embodiment. Hereinafter, some or all of the functional blocks described with reference to FIGS. 2 and 3 may be replaced with other functional blocks that perform the same functions, some functional blocks may be omitted, or additional functional blocks may be added. Also, one functional block shown in the following description may be divided into a plurality of functional blocks, or a plurality of 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 composed of one or more processors such as a CPU or an MPU, for example, and controls the entire communication device by executing a control program read into a RAM which is the storage unit 202. Note that each process performed by the control unit 201 described in the flowchart to be described later 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. Also, by having the hardware circuit cooperate with a processor such as a CPU or an MPU, the processes described in the flowchart to be described later can be realized.

[0024] The storage unit 202 stores information used by the control unit 201 for control and information related to communication. The storage unit 202 may include a main storage unit and an auxiliary storage unit. The main storage unit is, for example, a ROM (Read Only Memory) or a RAM (Random Access Memory). The main storage unit may store or temporarily store programs and data such as an OS (Operating System) which is basic software executed by the control unit 201 and application software. The auxiliary storage unit is, for example, an HDD (Hard Disk Drive) or an SSD (Solid State Drive), and may store data related to application software. For example, a control program stored in a non-volatile storage area is expanded into a RAM and executed by a processor constituting the control unit 201. In this way, the control unit 201 and the storage unit 202 may function as a so-called computer.

[0025] The memory unit 202 may include a recording medium that stores a predetermined program. The program stored in this recording medium is installed via a drive device or the like, and the installed predetermined program may be made 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 optically, electrically, or magnetically records information, such as a CD (Compact Disc)-ROM, a flexible disk, a magneto-optical disk, etc. Also, the recording medium may be a semiconductor memory or the like that electrically records information, such as a ROM or a flash memory. Note that the recording medium does not include a carrier wave.

[0026] 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 described later). Based on the UE information managed by the UE management unit 203, the path switching determination processing unit 204 determines whether to connect the managed UEs via an indirect path or a direct path. The message generation processing unit 205 generates a message used for an instruction to switch the path. The message analysis processing unit 206 analyzes the message received from a subordinate UE.

[0027] Note that 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 implemented as software modules realized by the control unit 201.

[0028] The wireless communication unit 207 transmits and receives information in wireless communication with subordinate UEs. For example, the wireless communication unit 207 performs transmission processing of the message generated by the message generation processing unit 205 and reception processing of the message from a subordinate UE.

[0029] FIG. 3 is a block diagram showing a functional configuration example of a remote UE (for example, remote UE-A (101)) in the present embodiment.

[0030] 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.

[0031] The control unit 301 controls the operation of the remote UE. The control unit 301 is composed of one or more processors such as a CPU or an MPU, for example, and controls the entire communication device by executing a control program read into the RAM which is the storage unit 302. Each process performed by the control unit 301 described in the flowchart to be described later can also be realized using a hardware circuit such as an ASIC or an FPGA. Further, by the cooperation of the hardware circuit and a processor such as a CPU or an MPU, the processes described in the flowchart to be described later can also be realized.

[0032] The storage unit 302 stores information used by the control unit 301 for control and information related to communication.

[0033] The signal strength measurement unit 303 measures the "signal strength between relay UEs (relay link, PC5 link)", the "signal strength between base stations (Uu link)", and the "signal strength between candidate relay UEs" as seen from the remote UE. Each signal strength measured by the signal strength measurement unit 303 is stored in the storage unit 302. The information stored in the storage unit 302 may be information on measurement values of signal strengths 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.

[0034] The Sidelink Relay processing unit 304 enables connection to the base station 104 via the relay function of the relay UE (that is, via an indirect path) by connecting to the relay UE through Sidelink.

[0035] The message generation processing unit 305 generates various messages. The various messages include a discovery signal to be transmitted to neighboring relay UEs, an RRC Reconfiguration Complete message and a Measurement Report to be transmitted to the base station 104.

[0036] The message analysis processing unit 306 analyzes messages such as a discovery signal, a response signal transmitted from a neighboring relay UE, and an RRC Reconfiguration message transmitted from the base station 104.

[0037] The wireless communication unit 307 transmits and receives information through wireless communication with neighboring relay UEs and the base station 104. The wireless communication unit 307 performs transmission processing of the messages generated by the message generation processing unit 305 and reception processing of the messages from neighboring relay UEs and the base station 104.

[0038] FIG. 4 is a block diagram showing a functional configuration example of the relay UEs (102, 103) in the present embodiment.

[0039] In FIG. 4, the description of the same functional blocks as in FIG. 3 is omitted. The signal strength measurement unit 403 measures the "signal strength between relay UEs (relay link, PC5 link)", the "signal strength of a remote UE connected by a relay link to other relay UEs", and the "signal strength between base stations (Uu link)" as seen from the relay UE. The Sidelink Relay processing unit 404 performs a relay function to connect a remote UE connected by Sidelink to the base station 104 via the relay UE. The message generation processing unit 405 transmits a discovery signal to a neighboring remote UE and responds to the discovery signal sent from the remote UE. Further, 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 a discovery signal transmitted from a remote UE and an RRC Reconfiguration message transmitted from the base station 104.

[0040] Next, with reference to FIGS. 5 to 8, an operation example of this embodiment will be described.

[0041] FIG. 5 is an example of a switching sequence from an indirect path to an indirect path in this embodiment. FIGS. 6, 7, and 8 are flowcharts divided into the processing on the gNB104 side and the processing on the remote UE-A (101) side among the sequences of FIG. 5 in this embodiment.

[0042] In gNB104, by executing the control program stored in the storage unit 202 by the control unit 201, each process on the gNB side shown in this flowchart is realized. In the remote UE-A (101), by executing the control program stored in the storage unit 302 by the control unit 301, each process on the UE side shown in this flowchart is realized. Note that some processes are realized in cooperation with the above-described hardware and functional units.

[0043] 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 transmitting and receiving user data (such as streaming data) via such a connection to the base station 104 (F501, S601).

[0044] Next, during the transmission and reception of user data, the control unit 301 of the remote UE-A (101) activates the message generation processing unit 305. Then, the message generation processing unit 305 creates a discovery request signal and transmits the discovery request signal to the relay UE-B (102) and the relay UE-C (103) through the wireless communication unit 307. Further, the control unit 301 activates the message analysis processing unit 306. It prepares for the analysis of the message to be performed when receiving a response signal of the discovery request signal or a discovery request signal from a neighboring relay UE including the relay UE-B (102) through the wireless communication unit 307 (that is, starts the execution of discovery.) (S602).

[0045] Next, the signal strength measurement unit 303 that has been pre-activated 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). Hereinafter, the link between the remote UE-A (101) and the gNB 104 is also referred to as the Uu link. Also, hereinafter, the link between the remote UE-A (101) and the relay UE-B (102) is also referred to as the relay link.

[0046] Regarding the signal strength measurement unit 403 of the relay UE-B (102) as well, similarly, measurements such as the "signal strength between the relay UE-B (102) and the remote UE-A (101)" are started (F503). Also, regarding the signal strength measurement unit 403 of the relay UE-C (103) as well, various signal strength measurements are started similarly (F504). At this stage, the relay UE-C (103) may be operating as a relay but not connected to a UE. In such a state, the relay UE-C (103) does not emit signals related to Sidelink.

[0047] 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 storage unit 302 stores the ID of the relay UE that transmitted the signal and the serving cell ID in the candidate relay UE list (S604, S605). In the flowchart shown in FIG. 6, the determination of "NO" in step S604 may be possible after a predetermined time from the start of the process in step S602. For example, if the control unit 301 does not receive a response signal to the discovery request signal even after a predetermined time has elapsed since transmitting the discovery request signal, step S604 may be determined to be "NO".

[0048] When 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 the case where the relay UE-C (103) is found as the candidate relay UE. At this stage, the relay UE-C (103) is in the 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, it transmits a response to the Additional Information or Soliciatioin message. The signal strength measurement unit 303 of the remote UE-A may measure the radio wave strength of the relay UE-C (103) based on the reception result of the response from the relay UE-C (103).

[0049] The remote UE-A (101) follows the events specified in advance by the Measurement configuration from the gNB104.

[0050] The message generation processing unit 305 creates a Measurement report storing information on the "signal strength of the Uu link", the "signal strength of the relay link", and the "signal strength between the remote UE-A (101) and the candidate relay UE in the candidate relay UE list". Then, the created Measurement report is transmitted to the gNB104 via the wireless communication unit 307 (F502, S606).

[0051] When the wireless communication unit 207 of the gNB104 receives the Measurement report from the remote UE-A (101), it is sent to the message analysis processing unit 206, and the message analysis processing unit 206 performs the analysis. The result analyzed by the message analysis processing unit 206 is sent to the path switching determination processing unit 204, and the path switching determination processing unit 204 confirms it (S607). In this case, the path switching determination processing unit 204 functions as an acquisition means for acquiring the signal strengths of the above three types of links.

[0052] A specific path switching method will be described below.

[0053] If the signal strength of the relay link in the remote UE-A (101) is equal to or greater than the first threshold, the path switching determination processing unit 204 determines that relay is possible and completes the determination process without performing anything (S701). If it is below the first threshold, it is determined that relay is difficult, and the signal strength of the Uu link (an example of the third signal strength information) in the remote UE-A (101) is confirmed. If the signal strength of the Uu link is equal to or greater than the second threshold, the remote UE-A (101) is instructed to switch the path from the indirect path to the direct path and to perform the switch (S702, S703). Note that the second threshold may be the same as or different from the first threshold used in step S701.

[0054] If the signal strength of the Uu link in the remote UE-A (101) is below the second threshold, the path switching determination processing unit 204 determines that relay will still be difficult even if the path is switched to the direct path. Then, the candidate relay UE list is checked, and various signal strength information measured by a relay UE that is the same as its own serving cell ID (or is communicating with the base station 104) is acquired. Specifically, the signal strength information (an example of the second signal strength information) of the remote UE-A (101) measured by the relay UE-C (103) is requested (F504, S704). Furthermore, the signal strength information (an example of the first signal strength information) of the remote UE-A (101) measured by the relay UE-B (102) is requested for intensity comparison (F503, S704).

[0055] 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. In this case, the same physical channel may be the PSBCH or PSDCH.

[0056] PSBCH is the abbreviation of Physical Sidelink Broadcast CHannel. PSBCH is a physical channel related to synchronization in Sidelink communication. PSBCH is periodically transmitted at time frequencies that are not slots of the resource pool, together with the Sidelink synchronization signal block S-SSB (Sidelink-Synchronization Signal Block). The above-mentioned signal strength SL-RSRP is the signal strength based on the physical channel PSBCH.

[0057] PSDCH is the abbreviation of Physical Sidelink Discovery CHannel. PSDCH is a physical channel for UE search (discovery) in Sidelink communication. The above-mentioned signal strength SD-RSRP is the signal strength based on the physical channel PSDCH (defined in 3GPP technical specification TS36.214 5.1.22).

[0058] Referring to the flowchart of FIG. 7A, the operation when the relay UE-C (103) receives a request for signal strength information at S704 in FIG. 7 will be described, and the operation of gNB104 following S704 in FIG. 7 will be described. Note that, referring to FIG. 7A, the operation when the relay UE-C (103) receives a request for signal strength information at S704 in FIG. 7 will be described, but the operation when the relay UE-B (102) receives a request for signal strength information at S704 in FIG. 7 may be the same.

[0059] In the relay preparation state (S751) where the relay UE-C (103) is not connected to the remote UE-A (101) or the like, when the relay UE-C (103) receives a request for signal strength information from the gNB104 (S752), 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). Note that in a modification, the signal strength measurement unit 403 of the relay UE-C (103) may periodically execute the measurement of the "signal strength between the relay UE-C (103) and the remote UE-A (101)". In this case, the process of S704 in FIG. 7 may be omitted. The message generation processing unit 405 of relay UE-C (103) creates a Measurement report storing information on "signal strength between relay UE-C (103) and remote UE-A (101)" (S754). Then, the created Measurement report is transmitted to gNB104 via the wireless communication unit 407 (F504, S754). Similarly, relay UE-B (102) transmits the created Measurement report to gNB104 via the wireless communication unit 407 (F503).

[0060] When the wireless communication unit 207 of gNB104 receives a Measurement report from relay UE-C (103) (and relay UE-B (102)), it sends it to the message analysis processing unit 206 (S782, S783). Then, the message analysis processing unit 206 performs analysis. The result analyzed by the message analysis processing unit 206 is sent to the path switching determination processing unit 204, and the path switching determination processing unit 204 confirms it (S784).

[0061] If the signal strength measured by relay UE-C (103) is lower than the signal strength measured by relay UE-B (102), the path switching determination processing unit 204 determines that it is difficult to continue relaying on any path. In this case, the path switching determination processing unit 204 completes the path switching process ("NO" in S784).

[0062] If the signal strength measured by relay UE-C (103) is equal to or greater than the signal strength measured by relay UE-B (102), the path switching determination processing unit 204 determines that it is necessary to switch to the indirect path related to relay UE-C (103). That is, by switching to the indirect path via relay UE-C (103), it is determined that the service (such as streaming) being executed by remote UE-A (101) can be continued. Then, the path switching determination processing unit 204 notifies the control unit 201 that it is necessary to switch from the indirect path to the indirect path (F505, "YES" in S784).

[0063] In this case, the path switching determination processing unit 204 may further determine whether the signal strength measured by the relay UE-C (103) is equal to or greater than a third threshold value, as in the modification example shown in FIG. 9 (S783A). The third threshold value may be the same as the first threshold value used in S701. When the signal strength measured by the relay UE-C (103) is equal to or greater than the third threshold value, the path switching determination processing unit 204 may notify the control unit 201 that it is necessary to switch from the indirect path to the indirect path (F505, "YES" in S784).

[0064] By the way, the values measured on the remote UE-A (101) side and the values measured on the relay UE side such as the relay UE-C (103) do not always match depending on the measurement timing, for example, when both are moving in a vehicle-mounted manner or the like.

[0065] In this regard, according to the examples shown in FIGS. 7A and 9, the measurement values obtained in step S782 and step S783 are used for the determination in step S784. Thereby, the signal strengths obtained at substantially the same timing by the two relay UEs can 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 measured at substantially the same timing can be used. In this case, since the value measured on the remote UE-A (101) side is not used, the measurement related to the candidate relay UE in step S603 and step S605 may be omitted. Alternatively, in another modification example, the measurement value obtained in step S607 may be used for the determination in step S784 together with the measurement values obtained via step S782 and step S783.

[0066] The control unit 201 performs RRC reconfiguration on the relay UE-C (103). That is, it transmits an RRC reconfiguration message to the relay UE-C (103) via the message generation processing unit 205 and the radio communication unit 207. Thereby, it notifies the 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 the information used in the SRAP (Sidelink Relay Adaptation Protocol) protocol necessary for the operation as a relay UE. The control unit 201 confirms the reception of an RRC reconfiguration complete message from the relay UE-C (103) via the radio communication unit 207 and the message analysis processing unit 206. Thereby, the RRC reconfiguration for the relay UE-C (103) is completed (F506, S801).

[0067] Next, the control unit 201 performs RRC reconfiguration on the remote UE-A (101). That is, it transmits an RRC reconfiguration message to the remote UE-A (101) via the message generation processing unit 205 and the radio communication unit 207. Thereby, it notifies the 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 the information used in the SRAP protocol necessary for the operation as a remote UE (F507, S803).

[0068] At this time, the message generation processing unit 205 adds the following information in the RRC reconfiguration message. That is, the message generation processing unit 205 adds a sl-pathSwitchConfig storing the ID of the relay UE-C (103) in ReconfigurationWithSync (S802). Thereby, it is possible to notify the remote UE-A (101) that this is a switch from the indirect path via the relay UE-B (102) to the indirect path via the relay UE-C (103) (S803).

[0069] The control unit 301 in the remote UE-A (101) confirms the reception of the 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. Thereby, it is determined that this is a switch from the indirect path via the relay UE-B (102) to the indirect path via the relay UE-C (103) (F507, S804).

[0070] 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). Thereafter, the remote UE-A (101) and the relay UE-C (103) can use sidelink relay communication based on the SRAP protocol information obtained in the RRC reconfiguration message. That is, the remote UE-A (101) can transmit and receive data with the gNB 104 via the relay UE-C (103).

[0071] After establishing communication with 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 gNB104 via relay UE-C (103) (F509, S806). Here, it is not transmitted via relay UE-B (102).

[0072] gNB104 receives the RRC reconfiguration complete message from remote UE-A (101) via relay UE-C (103) through the wireless communication unit 207 and the message analysis processing unit 206. Thereby, it can be determined that the switching of the indirect path of remote UE-A (101) is completed (F509, S807).

[0073] After the indirect path switching of remote UE-A (101) is completed, gNB104 performs RRC reconfiguration on relay UE-B (102). Then, the sidelink relay function for remote UE-A (101) is released (F510, S808).

[0074] On the other hand, remote UE-A (101) releases the link with relay UE-B (102) (F511, S809).

[0075] Through the processes described above, gNB104 and remote UE-A (101) can switch from an indirect path to an indirect path without disconnecting the service.

[0076] [Other Embodiments] In the above-described embodiment, measurement values of signal strengths such as SL-RSRP and SD-RSRP (Sidelink Discovery Reference Signal Received Power) are used for comparison. Note that SL-RSRP is an abbreviation for Sidelink Reference Signal Received Power. FIG. 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 transmitted 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) for the discovery signal. F903 is a notification of a Measurement report including signal strength information of the discovery response signal measured by the remote UE-A (101). F904 is a notification of a Measurement report including signal strength information of the discovery signal measured by the relay UE-B (102). F905 is a notification of a Measurement report including signal strength information of the discovery signal measured by the relay UE-C (103).

[0077] Also, in this embodiment, an example in which one candidate relay UE is found is shown, but it can also be naturally applied when two or more candidate relay UEs are found. In this case, measurement values of signal strengths may be acquired from all the found candidate relay UEs, and the best one may be selected.

[0078] Note that, in this embodiment, when the 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. Thereby, a search process for searching for surrounding candidate relay UEs is executed. Note that the remote UE may receive the above signal from a relay UE with which the remote UE is connected.

[0079] Furthermore, when searching for candidate relay UEs, the remote UE may be configured to perform a process of spontaneously searching for candidate UEs in addition to or instead of the above-described search process of receiving signals transmitted by the surrounding UEs to search for candidates.

[0080] In this case, specifically, when searching for candidate relay UEs, the remote UE transmits a Soliciation message of 5G ProSe UE-to-Network Relay direct discovery. Then, when the remote UE can receive a response to the Soliciatioin message, it is regarded as having discovered a candidate relay UE. Note that the remote UE may transmit the above signal to the relay UE with which it is connected and receive a response to the Soliciatioin message from the relay UE.

[0081] The present invention can also be realized by supplying a program that realizes one or more 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 a computer of the system or device read and execute the program. Further, it can also be realized by a circuit (for example, ASIC or FPGA) that realizes one or more functions.

[0082] As described above in detail for each embodiment, the present invention is not limited to a specific embodiment, and various modifications and changes are possible within the scope described in the claims. Also, it is possible to combine all or a plurality of the components of the above-described embodiments.

[0083] Note that the following supplementary notes are disclosed regarding the above embodiments.

[0084] [Supplementary Note 1] A communication device that relays communication between a UE (User Equipment) and a base station, measurement means for measuring the signal strength of communication performed with the UE, notification means for notifying the base station of the measurement result by the measurement means. The notification means is characterized in that, in a relay state where communication between a UE and a base station is relayed, the measurement result regarding the relayed UE is notified to the base station. A communication device. [Appendix 2] The relay state according to claim 1, characterized in that it includes a state in which the relayed UE is connected by sidelink communication and is connected to the base station by Uu communication. The communication device according to claim 1. [Appendix 3] The signal strength related to the measurement result is characterized in that it includes at least one of SL-RSRP (Sidelink Reference Signal Received Power) and SD-RSRP (Sidelink Discovery Reference Signal Received Power). The communication device according to claim 1 or 2. [Appendix 4] The notification means is characterized in that the measurement result is notified by a Measurement report. The communication device according to any one of claims 1 to 3. [Appendix 5] In a first state where communication with a first UE (User Equipment) is executed via a second UE, acquisition means for acquiring first signal strength information representing the signal strength between the first UE and the second UE from the second UE; In the first state, 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; A base station comprising comparison means for comparing the first signal strength information and the second signal strength information in the first state. [Appendix 6] The base station according to claim 5, further comprising processing means for issuing a switching instruction from the first state to a second state where communication is performed between the first UE via the third UE based on the comparison result of the comparison means. [Appendix 7] The third UE according to claim 5 or 6, including a UE connected to another base station. The base station according to claim 5 or 6. [Appendix 8] The base station according to any one of Appendices 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. [Appendix 9] The base station according to any one of Appendices 6 to 8, 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. [Appendix 10] The acquisition means further acquires third signal strength information representing the signal strength between the base station and the first UE. The base station according to any one of Appendices 6 to 9, wherein 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. [Appendix 11] The base station according to any one of Appendices 6 to 10, 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. [Appendix 12] The base station according to any one of Appendices 6 to 11, 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. [Appendix 13] The base station according to any one of Appendices 6, 9 to 12, wherein the process of giving the switching instruction includes notifying the third UE of information related to the first UE by an RRC (Radio Resource Control) reconfiguration message and notifying the first UE of information related to the third UE by an RRC reconfiguration message.

Explanation of Signs

[0085] 101 Remote UE-A (an example of the first UE) 102 Relay UE-B (an example of the second UE) 103 Relay UE-C (an example of a third UE) 104 Base station 105 Communication area 201 Control unit 202 Memory unit 203 UE management unit 204 Path switching determination processing unit (an example of comparison means and processing means) 205 Message generation processing unit 206 Message analysis processing unit 207 Wireless communication unit (an example of acquisition means) 301 Control unit 302 Memory unit 303 Signal strength measurement unit (an example of measurement means) 304 Relay processing unit 305 Message generation processing unit 306 Message analysis processing unit 307 Wireless communication unit (an example of notification means) 403 Signal strength measurement unit (an example of measurement means) 404 Relay processing unit 405 Message generation processing unit 406 Message analysis processing unit 407 Wireless communication unit (an example of notification means)

Claims

1. A communication device that relays communication between a UE (User Equipment) and a base station, comprising: measuring means for measuring the signal strength of communication performed with the UE; notification means for notifying the base station of the measurement result by the measuring means; The notification means is characterized in that, in a relay state in which communication between the UE and the base station is relayed, the measurement result regarding the relayed UE is notified to the base station.

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

3. The signal strength related to the measurement result according to claim 1 is characterized by 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 notification means notifies the measurement result by a Measurement report.

5. In a first state where communication with a first UE (User Equipment) is executed via a second UE, acquisition means for acquiring first signal strength information representing the signal strength between the first UE and the second UE from the second UE; In the first state, 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; A base station comprising comparison means for comparing the first signal strength information and the second signal strength information in the first state.

6. The base station according to claim 5, further comprising processing means for giving an instruction to switch from the first state to a second state in which communication is performed between the first UE via the third UE based on the comparison result of the comparison means.

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

8. The first signal strength information and the second signal strength information according to claim 5 are characterized by the measurement result of SL-RSRP or the measurement result 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 obtaining means further obtains third signal strength information representing a signal strength between the first UE and the base station, 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 third signal strength information is lower than a second threshold value.

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

14. A method for controlling communication, comprising: In a first state where communication between a first UE (User Equipment) and a base station is executed via a second UE, An obtaining step of obtaining 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 comparing step of comparing the first signal strength information and the second signal strength information in the first state; A control method, characterized by comprising a processing step of giving a switching instruction from the first state to a second state in which communication between the first UE and the base station is executed via a third UE based on a comparison result of the comparing 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. On a computer 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; A program characterized by executing a processing step of giving an instruction to switch from the first state to a second state in which communication between the first UE and the base station is performed via a 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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