Relay device, control method, and program

Abstract

This invention provides technology for properly performing relay communication using relay devices. [Solution] A relay device that communicates with a first communication device and a second communication device and relays terminal-to-terminal communication includes a receiving means for receiving a Link Modification Request from the first communication device, and a transmitting means for sending a Link Modification Accept to the first communication device at different timings depending on whether the message type of the Link Modification Request is of a first type or a second type.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a relay apparatus, a control method, and a program.

BACKGROUND ART

[0002] Cellular communication standards (also referred to as 3GPP standards) are being formulated in the 3rd Generation Partnership Project (3GPP (registered trademark): The 3rd Generation Partnership Project). In recent years, specification development for LTE (Long Term Evolution) and NR (New Radio) under 3GPP has been advancing. Among these, a standard specification called sidelink communication (hereinafter also simply referred to as sidelink) has been formulated. This specification realizes direct wireless communication between communication terminals using an interface called PC5. A communication terminal is also referred to as a terminal device, a terminal, a user apparatus, UE (User Equipment), or the like.

[0003] In ProSe (Proximity based Services), which is the sidelink communication standard for NR, standardization for 5G ProSe UE-to-UE Relay is in progress. UE-to-UE Relay is a mechanism in which a relay apparatus (also described as a Relay) relays communication between wireless terminals in sidelink communication where two communication terminals (End UEs) perform direct communication without going through a base station. By relaying communication, the communication distance between communication terminals can be extended.

[0004] The UE-to-UE Relay standard is described in Non-Patent Literature 1. By 3GPP Release 18 (Rel-18), link release and link changes for single-hop UE-to-UE Relay using one relay device have been standardized. Discussions are now underway for Release 19 (Rel-19) regarding functional enhancements to single-hop UE-to-UE Relay using one relay device, and for UE-to-UE Relay using multiple relay devices (also called multi-hop UE-to-UE Relay). In this specification and drawings, release may be replaced with disconnection. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] 3GPP TS 23.304, Proximity based Services (ProSe) in the 5G System (5GS) [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] Link modification processing in UE-to-UE Relay is achieved by the following processes A and B. Process A is the process of relaying a Link Modification Request message from the source End UE to the target End UE. Process B is the process of relaying a Link Modification Accept message from the target End UE to the source End UE. In the case of multi-hop UE-to-UE Relay, since multiple relay devices are connected between the End UEs, the time from sending the Link Modification Request message to receiving the Link Modification Accept message may be long. When link release is performed using a Link Modification Request message, the link release process is performed after receiving the Link Modification Accept message. Therefore, when link release is performed using a Link Modification Request message in a multi-hop UE-to-UE Relay, the time until link release becomes long. Thus, there is room for consideration regarding relay communication using relay devices. In this specification and drawings, Link Modification Request and Link Modification Request message are used interchangeably. The same applies to other messages.

[0007] One aspect of this disclosure, in view of the above, aims to provide a technology for appropriately performing relay communication using a relay device. [Means for solving the problem]

[0008] A relay device according to one aspect of the present disclosure is a relay device that communicates with a first communication device and a second communication device and relays terminal-to-terminal communication, comprising: receiving means for receiving a Link Modification Request from the first communication device; and transmitting means for transmitting a Link Modification Accept to the first communication device at different timings depending on whether the message type of the Link Modification Request is of a first type or a second type. [Effects of the Invention]

[0009] According to one aspect of this disclosure, relay communication using a relay device can be performed appropriately. [Brief explanation of the drawing]

[0010] [Figure 1] This is a block diagram showing an example of the hardware configuration of a relay device according to an embodiment. [Figure 2] This is a block diagram showing an example of the functional configuration of a relay device according to an embodiment. [Figure 3] This is a diagram showing an example configuration of a communication system according to the embodiment. [Figure 4] This is a sequence diagram showing an example of link change processing for a multi-hop UE-to-UE Relay according to the first embodiment. [Figure 5] This figure shows an example of processing by the relay device according to the first embodiment. [Figure 6] This figure shows an example of processing by a relay device according to the second embodiment. [Figure 7] This figure shows an example of processing by a relay device according to the third embodiment. [Modes for carrying out the invention]

[0011] The embodiments will be described in detail below with reference to the attached drawings. Note that the following embodiments do not limit the scope of the claims. While the embodiments describe multiple features, not all of these features are essential to this disclosure, and the features may be combined in any way. Furthermore, in the attached drawings, the same or similar configurations may be given the same reference numeral, and redundant descriptions may be omitted. Also, the technical scope of this disclosure is determined by the claims and is not limited by the following individual embodiments.

[0012] [First Embodiment] This embodiment describes the message transmission process of a relay device in the link change sequence of a multi-hop UE-to-UE Relay.

[0013] (Configuration of the relay device) Figure 1 is a block diagram showing an example of the hardware configuration of the relay device according to this embodiment. The relay device according to this embodiment is a relay device (relay terminal) that relays sidelink communication between terminals to extend the coverage of sidelink communication.

[0014] As shown in Figure 1, the hardware configuration 101 of the relay device includes, for example, a control unit 102, a storage unit 103, a wireless communication unit 104, a communication antenna control unit 105, a GPS communication unit 106, and a GPS antenna control unit 107.

[0015] The control unit 102 is composed of one or more processors, such as a CPU (Central Processing Unit) and an MPU (Micro Processing Unit). The control unit 102 controls the entire relay device by executing a control program stored in the memory unit 103 (a control program read from RAM (Random Access Memory)). Note that each process performed by the control unit 102, which will be explained later using a flowchart, can also be implemented using hardware circuits such as ASICs and FPGAs. ASIC is an abbreviation for Application Specific Integrated Circuit, and FPGA is an abbreviation for Field Programmable Gate Array. Furthermore, the processes explained later using a flowchart can also be implemented by the cooperation of hardware circuits and processors such as a CPU and MPU.

[0016] The storage unit 103 stores a control program executed by the control unit 102, and various types of information such as cell information and connected terminal information. The storage unit 103 may include a main storage unit and an auxiliary storage unit. The main storage unit is, for example, a ROM (Read Only Memory), a RAM, or the like. 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 102, and application software. The auxiliary storage unit is, for example, an HDD (Hard Disk Drive), an SSD (Solid State Drive), or the like, and may store data related to application software and the like. For example, the control program stored in the non-volatile storage area is loaded into the RAM and executed by the processor constituting the control unit 102. In this way, the control unit 102 and the storage unit 103 may function as a so-called computer.

[0017] The wireless communication unit 104 performs cellular communication such as LTE (Long Term Evolution) and 5G (NR) conforming to the 3GPP standards. Note that, while 5G will be described in various embodiments including the present embodiment, the present disclosure is also applicable to systems other than 5G (for example, next-generation mobile communication systems such as 5G Advanced and 6G, LTE, LTE-Advanced, combinations thereof, etc.).

[0018] The communication antenna control unit 105 controls antennas for wireless communication performed by the wireless communication unit 104. For example, the communication antenna control unit 105 controls the antennas so as to switch the directivity direction of the antennas.

[0019] The GPS communication unit 106 receives satellite signals from GPS (Global Positioning System) satellites, and acquires position information of the current position including position specifying information such as longitude and latitude information, current time information, and the like. Note that the GPS communication unit 106 may have a function of measuring (positioning) the current position based on the satellite signals. Note that other GNSS (Global Navigation Satellite System) may be used instead of or in addition to GPS.

[0020] The GPS antenna control unit 107 controls the antenna for GPS communication performed by the GPS communication unit 106.

[0021] Figure 2 is a block diagram illustrating an example of the functional configuration of the relay apparatus according to the present embodiment. The functional blocks illustrated in Figure 2 are implemented by software.

[0022] The software function 200 illustrated in Figure 2 includes a signal transmission unit 201, a signal reception unit 202, a data storage unit 203, a connection control unit 204, a message type determination unit 205, a transmission timing determination unit 206, a link usage status determination unit 207, and a communication device count confirmation unit 208.

[0023] The signal transmission unit 201 (an example of a transmission unit or transmission means) and the signal reception unit 202 (an example of a reception unit or reception means) perform cellular communication such as LTE and 5G (NR) conforming to the 3GPP standard with communication apparatuses. Note that a link change request message, a link change response message, a disconnection request message, and a disconnection response message, which will be described later, are transmitted and received by the signal transmission unit 201 and the signal reception unit 202. The signal transmission unit 201 and the signal reception unit 202 may also be referred to as a (signal) transmission / reception unit or transmission / reception means, a (signal) communication unit or communication means, or the like.

[0024] The data storage unit 203 stores and holds the software (program) and information related to connected terminals, etc.

[0025] The connection control unit 204 controls sidelink connections, relay connections, and the like with other communication apparatuses.

[0026] The message type determination unit 205 (an example of a determination unit or determination means) determines the message type of a link change request message received from a communication apparatus forming a UE-to-UE Relay.

[0027] The transmission timing determination unit 206 (an example of a determination unit or determination means) determines the timing for sending a link change response message to the communication device that sent the link change request message. For example, the transmission timing determination unit 206 determines the timing for sending the link change request message to the next communication device (another relay device or End UE) based on the determined message type. More specifically, the transmission timing determination unit 206 determines, based on the determined message type, whether to send the message to the next communication device first or to send the message to the communication device that sent the link change request message first. The message sent to the next communication device is either a link change request message or a disconnect request message, and the message sent to the communication device that sent the link change request message is a link change response message. Details of the method for determining the transmission timing will be described later.

[0028] The link usage determination unit 207 (an example of a determination unit or determination means) determines the usage status of the link (in other words, the communication path) with the communication device forming the UE-to-UE Relay. The method for determining this link usage status will be described in the second embodiment.

[0029] The communication device count confirmation unit 208 (an example of a determination unit or determination means) confirms (determines) the number of relay devices forming a UE-to-UE Relay (i.e., the number of relay devices relaying terminal-to-terminal communication) when the relay device receives a link change request message. This confirmation method will be explained in the third embodiment.

[0030] Furthermore, some (or sometimes all) of the described functional blocks may be replaced with other functional blocks that perform similar functions, some functional blocks may be omitted, or further functional blocks may be added. Also, one functional block may be divided into multiple functional blocks, or multiple functional blocks may be integrated into one functional block. In addition, only some of the functional blocks may be configured in hardware, with the remaining functions configured in software. When a functional block is configured in software, the processor constituting the control unit 102 shown in Figure 1 executes a control program to realize the function stored in the storage unit 103 shown in Figure 1. This provides the function of that functional block.

[0031] Figure 3 shows an example configuration of the communication system according to this embodiment. In the example shown in Figure 3, two End UEs and N relay devices form a UE-to-UE Relay.

[0032] End UE301 is connected to the first relay device 303, and End UE302 is connected to the Nth relay device 304. Between the first relay device 303 and the Nth relay device 304, one or more ((N-2)) relay devices are connected in series (if N is 3 or more). Alternatively, there is no relay device between the first relay device 303 and the Nth relay device 304, and the first relay device 303 and the Nth relay device 304 are connected (if N is 2). This UE-to-UE Relay is connected by one or more QoS (Quality of Service) flows. A QoS flow is a virtual transmission path generated per QoS unit. A QoS flow is identified by identification information or an identifier called a QFI (QoS Flow Identifier). The link modification process allows you to control the QoS included in a link, such as adding a QoS flow to an existing link, changing the settings of a QoS flow included in an existing link, or removing a QoS flow from an existing link.

[0033] In this embodiment, the number of relay devices is set to two (N=2), and the UE-to-UE Relay is assumed to be connected by a single QoS flow.

[0034] Next, we will describe the Link Modification Request message. In this specification and the drawings, the Link Modification Request message is an example of a message that requests a change in the communication path.

[0035] The Link Modification Request message format used in this embodiment is the message format specified in TS 24.554. Specifically, the Link Modification Request includes a Link modification operation code information element, a PC5 QoS flow descriptions information element, and the like.

[0036] A Link Modification Request is used to add a QoS flow to an existing link, change the settings of a QoS flow included in an existing link, or remove a QoS flow from an existing link. These additions, changes, and deletions are distinguished by specifying the message type. The message type is specified in the Link modification operation code field of the Link modification operation code information element. For example, when End UE deletes a QoS flow, it specifies a value indicating the deletion of a QoS flow (5 (decimal):0101 (binary)) as the message type. Then, End UE stores the QFI of the QoS flow to be deleted in the PQFI field of the PC5 QoS flow description in the PC5 QoS flow descriptions information element. PQFI is an abbreviation for PC5 QoS Flow Identifier. A relay device that receives a Link Modification Request message can determine from the message type and PQFI included in the message that a deletion of a QoS flow is being requested and which QFI to delete.

[0037] Next, we will describe how the relay device determines the timing for sending a Link Modification Accept message. In this embodiment, the relay device determines this transmission timing based on the message type of the received Link Modification Request message. A Link Modification Accept message may also be called a Link Modification Acceptance message, and examples include a message that accepts a change in the communication path, or a response message to a message requesting a change in the communication path.

[0038] Upon receiving a link change request message, the relay device (message type determination unit 205) checks the Link modification operation code field of the received message and obtains and determines the message type.

[0039] When the message type indicates QoS flow deletion, the relay device (transmission timing determination unit 206) operates as follows: The relay device decides to send a link change response message to the communication device that sent the link change request message before sending the link change request message to the next communication device (relay device or End UE). Then, the relay device sends the link change response message to the communication device that sent the link change request message before sending the link change request message to the next communication device. Sending the link change response message before sending the link change request message is done to advance the timing of link disconnection (release).

[0040] Alternatively, another method for releasing a link is to use a Disconnect Request message. When a relay device receives this Disconnect Request message, it may also send a Disconnect Response message to the communication device that sent the Disconnect Request message before sending a message to the next communication device. This allows for the timing of sending response messages when two different messages aimed at releasing a link are received. A Disconnect Request message is an example of a message that requests the disconnection of a communication path. A Disconnect Response message may also be called a Disconnect Acceptance message, and is an example of a message that accepts the disconnection of a communication path, or a response message to a message requesting the disconnection of a communication path.

[0041] On the other hand, if the message type indicates something other than QoS flow deletion, the relay device (transmission timing determination unit 206) operates as before. That is, the relay device decides to send a link change request message to the next communication device (relay device or End UE) before sending a link change response message to the communication device that sent the link change request message. More specifically, the relay device decides to send a link change response message to the communication device that sent the link change request message after sending the link change request message to the next communication device and receiving a link change response message from the next communication device. Then, the relay device sends a link change response message to the communication device that sent the link change request message after sending the link change request message to the next communication device and receiving a link change response message from the next communication device.

[0042] (Operation of communication device) Figure 4 is a sequence diagram showing an example of the link change process for a multi-hop UE-to-UE Relay according to this embodiment.

[0043] End UE301 and relay device 303 form a unicast link (400a). Relay device 303 and relay device 304 form a unicast link (400b). Relay device 304 and End UE302 form a unicast link (400c).

[0044] End UE301 sends a Link Modification Request message to relay device 303 (S401). When relay device 303 receives the Link Modification Request from End UE301, it obtains and determines the message type of the Link Modification Request. If the message type indicates QoS flow deletion, relay device 303 operates as follows in S402a: That is, relay device 303 responds with a Link Modification Accept message, releases (deletes) the QoS flow to be deleted, and deletes all context data associated with the QoS flow.

[0045] Next, relay device 303 sends a Link Modification Request to relay device 304, with a message type indicating QoS flow deletion (S403a).

[0046] When relay device 304 receives a Link Modification Request from relay device 303, it obtains and determines the message type. If the message type indicates QoS flow deletion (in this example, the message type indicates QoS flow deletion), relay device 304 operates as follows: relay device 304 responds with Link Modification Accept, releases (deletes) the QoS flow to be deleted, and deletes all context data associated with the QoS flow (S404a).

[0047] Next, the relay device 304 sends a Link Modification Request to the End UE 302, with a message type indicating QoS flow deletion (S405a).

[0048] When End UE302 receives a Link Modification Request from relay device 304, it obtains and determines the message type. If the message type indicates QoS flow deletion (in this example, the message type indicates QoS flow deletion), End UE302 operates as follows: End UE302 responds with Link Modification Accept, releases (deletes) the QoS flow to be deleted, and deletes all context data associated with the QoS flow (S406a).

[0049] If, in S401, the Link Modification Request message type transmitted by End UE301 and received by relay device 303 indicates something other than QoS flow deletion, relay device 303 operates as follows: relay device 303 sends a Link Modification Request of the same message type to relay device 304 (S403b).

[0050] When relay device 304 receives a Link Modification Request from relay device 303, it obtains and determines the message type. If the message type is anything other than QoS flow deletion (in this example, the message type is anything other than QoS flow deletion), relay device 304 operates as follows: relay device 304 sends a Link Modification Request of the same type to End UE 302 (S405b).

[0051] When End UE302 receives a Link Modification Request from relay device 304, it responds with Link Modification Accept and performs processing according to the message type (S406b).

[0052] When relay device 304 receives a Link Modification Accept from End UE 302, it sends a Link Modification Accept to relay device 303 and performs processing according to the message type (S404b).

[0053] When relay device 303 receives a Link Modification Accept from relay device 304, it sends a Link Modification Accept to End UE 301 and performs processing according to the message type (S402b).

[0054] Finally, when End UE301 receives a Link Modification Accept from relay device 303, it performs processing according to the message type.

[0055] Next, we will describe an example of a processing flow in which a relay device controls the timing of sending a Link Modification Accept based on the message type when it receives a Link Modification Request.

[0056] Figure 5 shows an example of processing by a relay device according to this embodiment. More specifically, Figure 5 shows an example of processing in which the relay device receives a Link Modification Request from the first communication device and changes the transmission timing (and the message to be transmitted) based on the message type. In this embodiment, it is assumed that the first communication device is an End UE and the second communication device is a relay device, or that the first communication device is a relay device and the second communication device is either a relay device or an End UE.

[0057] First, the relay device receives a Link Modification Request from the first communication device (S501) and determines the message type of the Link Modification Request (S502).

[0058] If the message type indicates QoS flow deletion (Yes in S502), the relay device sends a Link Modification Accept to the first communication device (S503). Next, the relay device sends a Link Modification Request to the second communication device (S504), receives a Link Modification Accept from the second communication device (S505), and completes the process.

[0059] In addition, the message that the relay device sends to the second communication device in S504 may be a Disconnect Request instead of a Link Modification Request. In this case, the message received from the second communication device in S505 (the response message to the message sent in S504) may be a Disconnect Response. For example, if only the QoS flow that was requested to be deleted in the link modification request message received by the relay device exists on the link, it can be determined that the link will be released after the QoS flow is deleted (see the second embodiment). Therefore, in this case, the relay device may send a Disconnect Request to the second communication device instead of a Link Modification Request (S504).

[0060] In S502, if the message type does not indicate QoS flow deletion (No in S502), the relay device sends a Link Modification Request to the second communication device (S506). Subsequently, when the relay device receives a Link Modification Accept from the second communication device (S507), it sends a Link Modification Accept to the first communication device (S508) and completes the process.

[0061] In this embodiment, the processing when a relay device forming a UE-to-UE Relay receives a Link Modification Request has been described. In this embodiment, the relay device changes the transmission timing (and the message to be transmitted) based on the message type of the received message. Specifically, if the message type indicates QoS flow deletion, the relay device sends a Link Modification Accept to the source of the received message before sending a Link Modification Request to the next communication device. In this way, in the link release process using a link change message, the timing of sending the link change response message can be changed based on the message type of the link change request message received by the relay device, thereby making it possible to accelerate the timing of link release. Therefore, relay communication using the relay device can be performed appropriately.

[0062] [Second Embodiment] In the first embodiment, an example was described in which the timing of sending a link change response message when a relay device forming a UE-to-UE Relay receives a link change request message is changed based on the message type of the received message.

[0063] More specifically, in the first embodiment, it was explained that if the message type indicates QoS flow deletion, the timing of sending Link Modification Accept is advanced. However, there are cases where it is not necessary to advance the sending timing even if the message type indicates QoS flow deletion. For example, if a link contains QoS flows other than the QoS flow to be deleted, only the QoS flow to be deleted will be deleted, and the link will not be released. In this case, the connection with the communication device is maintained, so it is not necessarily necessary to advance the timing of sending Link Modification Accept.

[0064] Therefore, in this embodiment, we will describe an example in which the timing of sending a link change response message when a relay device forming a UE-to-UE Relay receives a link change request message is changed based on the message type and link usage status.

[0065] In the following, we will omit descriptions of configurations and processes that are the same as or similar to those in the first embodiment, and will focus on describing configurations and processes that differ from those in the first embodiment.

[0066] First, we will explain how the relay device determines the link usage status and the timing for sending Link Modification Accept.

[0067] The link usage status is determined (or judged) by the link usage status determination unit 207 based on the QoS flow included in the link and the QFI to be deleted specified in the link change request message.

[0068] If only the QoS flow requested for deletion exists on the link in the link modification request message, it can be determined that the link will be released after the QoS flow is deleted. In this case, the relay device (transmission timing determination unit 206) decides to send a Link Modification Accept before a Link Modification Request in order to expedite the timing of link release.

[0069] On the other hand, if the link contains both the QoS flow requested for deletion in the link change request message and other QoS flows, it can be determined that the link will not be released even after the QoS flow is deleted. In this case, since there is no need to accelerate the timing of link release, the relay device (transmission timing determination unit 206) decides to send the Link Modification Accept message after communication with the relay destination communication device.

[0070] In summary, the transmission timing determination unit 206 determines the timing for transmitting the link change request message to the next communication device based on the message type and link usage status of the received link change request message. More specifically, the transmission timing determination unit 206 determines, based on the message type and link usage status, whether to transmit the message to the next communication device first or to transmit the message to the communication device that sent the link change request message first.

[0071] Next, we will describe an example of a processing flow in which a relay device controls the timing of sending a Link Modification Accept based on the message type and link usage status when it receives a Link Modification Request.

[0072] Figure 6 shows an example of processing by a relay device according to this embodiment. More specifically, Figure 6 shows an example of processing in which the relay device receives a Link Modification Request from the first communication device and changes the transmission timing (and the message to be transmitted) based on the message type and link usage status. In this embodiment, it is assumed that the first communication device is an End UE and the second communication device is a relay device, or that the first communication device is a relay device and the second communication device is either a relay device or an End UE.

[0073] First, the relay device receives a Link Modification Request from the first communication device (S501) and determines the message type of the Link Modification Request (S502).

[0074] If the message type indicates QoS flow deletion (Yes in S502), the relay device obtains the identifier of the QoS flow to be deleted (S601). Then, the relay device 304 confirms the link it forms with the second communication device (more specifically, the QoS flow included in that link) (S602).

[0075] Next, the relay device determines the link usage status based on the QoS flow included in the link. Specifically, the relay device determines whether the link contains QoS flows other than those to be deleted (S603).

[0076] If the link does not contain any QoS flows other than those to be deleted (No in S603), the relay device operates as follows: The relay device determines that the link will be released after the QoS flow is deleted, and in order to expedite the timing of the link release, it decides to send a Link Modification Accept to the first communication device first, and proceeds to S503. The processing from S503 onward is the same as in the first embodiment, so the explanation is omitted.

[0077] On the other hand, if the link contains QoS flows other than those to be deleted (Yes in S603), the relay device operates as follows: The relay device determines that the link will not be released after the QoS flow is deleted, and decides to communicate with the second communication device first, and then send a Link Modification Accept to the first communication device, proceeding to S506. The processing from S506 onward is the same as in the first embodiment, so the explanation is omitted.

[0078] If the message type in S502 does not indicate QoS flow deletion (No in S502), the relay device proceeds to S506. The processing from S506 onward is the same as in the first embodiment, so the explanation is omitted.

[0079] In this embodiment, the processing when a relay device forming a UE-to-UE Relay receives a Link Modification Request has been described. In this embodiment, the relay device changes the transmission timing (and the message to be sent) based on the message type and link usage status of the received message. Specifically, if the message type indicates QoS flow deletion and no QoS flows other than those to be deleted are included in the link, the relay device operates as follows: That is, the relay device sends a Link Modification Accept to the source of the received message before sending a Link Modification Request to the next communication device. On the other hand, if the message type indicates QoS flow deletion and QoS flows other than those to be deleted are included in the link, the relay device operates as follows: That is, the relay device sends a Link Modification Accept to the source of the received message after communicating with the next communication device. In this way, in the link release process, by changing the transmission timing of the link change response message based on the message type and link usage status of the link change request message received by the relay device, it is possible to speed up the link release timing. On the other hand, if it is not necessary to speed up the link release timing, messages can be sent and received according to the conventional procedure. Therefore, relay communication using the relay device can be performed appropriately.

[0080] [Third Embodiment] In the first and second embodiments, examples were described of controlling the timing of sending a Link Modification Accept based on the message type and, optionally, the link usage status.

[0081] However, if the number of relay devices in a multi-hop UE-to-UE Relay (i.e., the number of hops in terminal-to-terminal communication) is not large, it is expected that the time until the link is released will not be very long. In this case, it can be said that there is no need to speed up the timing of link release. Therefore, the relay device may obtain the number of relay devices forming the UE-to-UE Relay and perform the above control only if the number of relay devices is above a threshold.

[0082] The number of relay devices forming a UE-to-UE Relay can be obtained from the "List of candidates U2U relay UE info" field included in the Link Modification Request. Specifically, the "List of candidates U2U relay UE info" field contains a list of User Info IDs for the relay devices. The relay device (communication device count confirmation unit 208) can obtain and determine the number of relay devices from the number of User Info IDs included in this list.

[0083] Therefore, in this embodiment, we will describe an example in which the timing of sending a link change response message when a relay device forming a UE-to-UE Relay receives a link change request message is changed based on the message type and the number of relay devices.

[0084] In the following, descriptions of configurations and processes that are the same as or similar to those in the first or second embodiment will be omitted, and the focus will be on configurations and processes that differ from those in the first or second embodiment.

[0085] In this embodiment, the transmission timing determination unit 206 determines the timing for transmitting the link change request message to the next communication device based on the message type of the received link change request message and the number of relay devices forming the UE-to-UE Relay. More specifically, the transmission timing determination unit 206 determines, based on the message type and the number of relay devices, whether to transmit the message to the next communication device first or to transmit the message to the communication device that sent the link change request message first.

[0086] Figure 7 shows an example of processing by a relay device according to this embodiment. More specifically, Figure 7 shows an example of processing in which a relay device receives a Link Modification Request from a first communication device and changes the transmission timing (and the message to be transmitted) based on the message type and the number of relay devices. In this embodiment, it is assumed that the first communication device is an End UE and the second communication device is a relay device, or that the first communication device is a relay device and the second communication device is either a relay device or an End UE.

[0087] First, the relay device receives a Link Modification Request from the first communication device (S501) and determines the message type of the Link Modification Request (S502).

[0088] If the message type indicates QoS flow deletion (Yes in S502), the relay device obtains the number of relay devices forming the UE-to-UE Relay and determines whether the number of relay devices is equal to or greater than a threshold (S701).

[0089] If the number of relay devices is greater than or equal to the threshold (Yes in S701), the relay device decides to perform a process to accelerate the timing of link release and proceeds to S503. The processes from S503 onward are the same as in the first embodiment, so the explanation is omitted.

[0090] On the other hand, if the number of relay devices is below the threshold (Yes in S701), the relay device decides not to perform the process to accelerate the timing of link release and proceeds to S506. The processing from S506 onward is the same as in the first embodiment, so the explanation is omitted.

[0091] If the message type in S502 does not indicate QoS flow deletion (No in S502), the relay device proceeds to S506. The processing from S506 onward is the same as in the first embodiment, so the explanation is omitted.

[0092] In this embodiment, the processing when a relay device forming a UE-to-UE Relay receives a Link Modification Request has been described. In this embodiment, the relay device changes the transmission timing (and the message to be transmitted) based on the message type of the received message and the number of relay devices. Specifically, if the message type indicates QoS flow deletion and the number of relay devices is greater than or equal to a threshold, the relay device operates as follows: That is, the relay device sends a Link Modification Accept to the source of the received message before sending a Link Modification Request to the next communication device. On the other hand, if the message type indicates QoS flow deletion and the number of relay devices is less than a threshold, the relay device operates as follows: That is, the relay device sends a Link Modification Accept to the source of the received message after communicating with the next communication device. In this way, in the link release process, by changing the transmission timing of the link change response message based on the message type of the link change request message received by the relay device and the number of relay devices, it is possible to speed up the link release timing. On the other hand, if it is not necessary to speed up the link release timing, messages can be sent and received according to the conventional procedure. Therefore, relay communication using relay devices can be performed appropriately.

[0093] [Other embodiments] Although a multi-hop UE-to-UE relay has been described above, this disclosure may also be applied to a single-hop UE-to-UE relay. That is, both the first communication device and the second communication device described using Figures 5 to 7 may be End UEs.

[0094] This disclosure can also be implemented by supplying a program that implements one or more of the functions of the embodiments described above to a system or device via a network or storage medium, and by having one or more processors in the computer of that system or device read and execute the program. Furthermore, this disclosure can also be implemented by a circuit (e.g., an ASIC or FPGA) that implements one or more functions.

[0095] This disclosure is not limited to the embodiments described above, and various modifications and variations are possible without departing from the spirit and scope of this disclosure.

[0096] The names of the functional units, messages, parameters, fields, etc., described in the embodiments described above are examples and may be changed to other names.

[0097] The matters described in the above embodiments may be incorporated into other embodiments, provided they do not contradict each other. For example, Link Modification Accept may be sent to the first communication device first if the message type indicates QoS flow deletion, no QoS flows other than those to be deleted are included in the link, and the number of relay devices is greater than or equal to a threshold.

[0098] Furthermore, the following additional information is disclosed regarding the above embodiments.

[0099] [Note 1] A relay device that communicates with the first communication device and the second communication device and relays terminal-to-terminal communication, Receiving means for receiving a Link Modification Request from the first communication device, A transmission means that transmits a Link Modification Accept to the first communication device at different timings depending on whether the message type of the Link Modification Request is of the first type or the second type, A relay device having the following features.

[0100] [Note 2] The first type mentioned above is a Link Modification Request indicating the deletion of a QoS flow. The relay device according to Appendix 1, wherein, when the message type is the first type, the transmitting means transmits the Link Modification Accept to the first communication device before transmitting a predetermined message to the second communication device.

[0101] [Note 3] The second type mentioned above is a Link Modification Request that does not indicate the deletion of a QoS flow. The relay device according to Appendix 1, wherein, when the message type is of the second type, the transmitting means transmits a predetermined message to the second communication device, and after receiving a response message for the predetermined message from the second communication device, transmits the Link Modification Accept to the first communication device.

[0102] [Note 4] Based on the Link Modification Request, it has a first determination means for determining the usage status of the communication path between the relay device and the second communication device, The transmission means is a relay device as described in Appendix 1, which transmits the Link Modification Accept to the first communication device based on the message type and the usage status.

[0103] [Note 5] The relay device described in Appendix 4, wherein the first determination means determines the usage status based on the first QoS flow included in the communication path.

[0104] [Note 6] The relay device according to Appendix 5, wherein, if the message type is the first type and the communication path includes only the first QoS flow, the transmitting means transmits the Link Modification Accept to the first communication device before transmitting a predetermined message to the second communication device.

[0105] [Note 7] The relay device according to Appendix 5, wherein, if the message type is the second type and the communication path includes the first QoS flow and a second QoS flow other than the first QoS flow, the transmitting means transmits a predetermined message to the second communication device, and after receiving a response message for the predetermined message from the second communication device, transmits the Link Modification Accept to the first communication device.

[0106] [Note 8] It has a second determination means for determining the number of relay devices that relay the aforementioned inter-terminal communication, The transmission means is a relay device as described in Appendix 1, which transmits the Link Modification Accept to the first communication device based on the message type and the number of devices.

[0107] [Note 9] The relay device according to Appendix 8, wherein, if the message type is the first type and the number of units is equal to or greater than a threshold, the transmitting means transmits the Link Modification Accept to the first communication device before transmitting a predetermined message to the second communication device.

[0108] [Note 10] The relay device according to Appendix 8, wherein, if the message type is the first type and the number of units is less than a threshold, the transmitting means transmits a predetermined message to the second communication device, and after receiving a response message for the predetermined message from the second communication device, transmits the Link Modification Accept to the first communication device.

[0109] [Note 11] The relay device as described in Appendix 2, 6, or 9, wherein the predetermined message is a Disconnect Request or a Link Modification Request.

[0110] [Note 12] The relay device described in Appendix 3, 7, or 10, wherein the predetermined message is a Link Modification Request.

[0111] [Note 13] A control method for a relay device that communicates with a first communication device and a second communication device and relays terminal-to-terminal communication, The process involves receiving a Link Modification Request from the aforementioned first communication device, The process involves sending a Link Modification Accept to the first communication device at different timings depending on whether the Link Modification Request message type is of the first type or the second type. A control method including

[0112] [Note 14] A program to cause the relay device's computer to execute the control method described in Appendix 13. [Explanation of Symbols]

[0113] 102 Control Unit 103 Storage section 201 Signal Transmission Unit 202 Signal Receiving Unit 203 Data Storage Unit 205 Message Type Determination Unit 206 Transmission timing determination unit 207 Link Usage Determination Unit 208 Communication Device Count Verification Unit 301, 302 End UE 303, 304 Relay (relay device)

Claims

1. A relay device that communicates with the first communication device and the second communication device and relays terminal-to-terminal communication, Receiving means for receiving a Link Modification Request from the first communication device, A transmission means that transmits a Link Modification Accept to the first communication device at different timings depending on whether the message type of the Link Modification Request is of the first type or the second type, A relay device having the following features.

2. The first type mentioned above is a Link Modification Request indicating the deletion of a QoS flow. The relay device according to claim 1, wherein, if the message type is of the first type, the transmitting means transmits the Link Modification Accept to the first communication device before transmitting a predetermined message to the second communication device.

3. The second type is a Link Modification Request that does not indicate the deletion of a QoS flow. The relay device according to claim 1, wherein, when the message type is of the second type, the transmitting means transmits a predetermined message to the second communication device, and after receiving a response message for the predetermined message from the second communication device, transmits the Link Modification Accept to the first communication device.

4. The system has a first determination means for determining the usage status of the communication path between the relay device and the second communication device based on the Link Modification Request, The relay device according to claim 1, wherein the transmitting means transmits the Link Modification Accept to the first communication device based on the message type and the usage status.

5. The relay device according to claim 4, wherein the first determination means determines the usage status based on the first QoS flow included in the communication path.

6. The relay device according to claim 5, wherein if the message type is the first type and the communication path includes only the first QoS flow, the transmitting means transmits the Link Modification Accept to the first communication device before transmitting a predetermined message to the second communication device.

7. The relay device according to claim 5, wherein if the message type is the second type and the communication path includes the first QoS flow and a second QoS flow other than the first QoS flow, the transmitting means transmits a predetermined message to the second communication device, and after receiving a response message for the predetermined message from the second communication device, transmits the Link Modification Accept to the first communication device.

8. It has a second determination means for determining the number of relay devices that relay the aforementioned inter-terminal communication, The relay device according to claim 1, wherein the transmitting means transmits the Link Modification Accept to the first communication device based on the message type and the number of devices.

9. The relay device according to claim 8, wherein if the message type is the first type and the number of units is equal to or greater than a threshold, the transmitting means transmits the Link Modification Accept to the first communication device before transmitting a predetermined message to the second communication device.

10. The relay device according to claim 8, wherein if the message type is the first type and the number of units is less than a threshold, the transmitting means transmits a predetermined message to the second communication device, and after receiving a response message for the predetermined message from the second communication device, transmits the Link Modification Accept to the first communication device.

11. The relay device according to claim 2, 6, or 9, wherein the predetermined message is a Disconnect Request or a Link Modification Request.

12. The relay device according to claim 3, 7, or 10, wherein the predetermined message is a Link Modification Request.

13. A control method for a relay device that communicates with a first communication device and a second communication device and relays terminal-to-terminal communication, The process of receiving a Link Modification Request from the first communication device, The process of sending a Link Modification Accept to the first communication device at different timings depending on whether the message type of the Link Modification Request is of the first type or the second type, A control method including

14. A program for causing the computer of a relay device to execute the control method described in claim 13.

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