Communication device, control method, and program

Abstract

A communication device according to one aspect of the present disclosure operates as a relay device in User Equipment (UE)-to-UE Relay, generates mobility information relating to the movement of the communication device, and transmits the mobility information to an End UE.

Description

Communication device, control method, and program

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

[0002] In the 3rd Generation Partnership Project (3GPP (registered trademark): 3rd Generation Partnership Project), a cellular communication standard (also referred to as the 3GPP standard) has been established. In recent years, the specifications of 3GPP's LTE (Long Term Evolution) and NR (New Radio) have been in progress. Among these, a standard specification called sidelink communication has been established. This specification realizes direct wireless communication between wireless terminals using an interface called PC5 without going through a mobile communication network (core network).

[0003] In 3GPP, the standardization of 5G ProSe (Proximity-based services) UE-to-UE Relay is in progress. UE-to-UE Relay is a mechanism in sidelink communication where two wireless terminals (End UE) communicate directly without going through a base station, and the communication between the wireless terminals is relayed by a relay device (also described as Relay). By relaying the communication, it becomes possible to extend the communication distance between wireless terminals. Note that UE is an abbreviation for User Equipment and may also be called a terminal device or simply a terminal.

[0004] The standard for UE-to-UE Relay is described in TS (Technical Specification) 23.304. Up to 3GPP Release 18, the following have been standardized. ・ Detection of the relay device (UE-to-UE Relay Discovery). ・ Establishment (also referred to as construction) of UE-to-UE Relay. ・ Reselection of the relay device in an established UE-to-UE Relay (Reselection).

[0005] In establishing and re-selecting a UE-to-UE relay, the selection of the relay device is performed by the End UE. Generally, the signal strength (radio wave strength) between devices is used as the selection criterion. The End UE measures the radio wave strength with multiple relay device candidates in the vicinity and selects the relay device candidate with the highest radio wave strength as the relay device.

[0006] Patent Document 1 describes a technique in which End UE selects a communication path (relay device) based on path selection information that includes at least one of channel quality information, load information, and device capability information.

[0007] Special Publication No. 2023-515299

[0008] Incidentally, if the relative movements (speed, direction, etc.) of the End UE and the relay device are different, there is a high possibility that relay communication will be interrupted. For example, in such a case, the End UE is a moving vehicle and the relay device is a vehicle traveling in the opposite lane. Depending on the timing of the measurement of radio wave strength, such as at the moment they pass each other, the radio wave strength may become high, and the selection criteria for the relay device may be met. Even if relay communication is established using a relay device selected in this way, the distance between the devices will increase in a relatively short time, and communication will be interrupted.

[0009] One possible solution is for the End UE to obtain information about the movement of the relay device (referred to as mobility information) from the relay device. For example, based on the acquired mobility information, the End UE can select a relay device whose relative movement is similar to that of the End UE, thereby establishing a less interrupted communication. Similarly, a method can be considered for the relay device to obtain the End UE's mobility information from the End UE. However, the method for obtaining mobility information in UE-to-UE Relay is not clearly defined. If the method for obtaining mobility information is not clearly defined, it may not be possible to use the mobility information of other devices, and relay communication may not be performed properly.

[0010] One aspect of this disclosure, in view of the above, aims to provide a technology for appropriately performing relay communication.

[0011] A communication device according to one aspect of the present disclosure is a communication device that operates as a relay device in a UE (User Equipment)-to-UE Relay, and comprises a generating means for generating mobility information relating to the movement of the communication device, and a transmitting means for transmitting the mobility information toward the End UE.

[0012] According to one aspect of this disclosure, relay communication can be performed appropriately.

[0013] Figure 1 is a block diagram showing an example of the hardware configuration of the End UE and relay device according to the embodiment. Figure 2A is a block diagram showing an example of the functional configuration of the End UE and relay device according to the embodiment. Figure 2B is a block diagram showing an example of the functional configuration of the End UE and relay device according to the embodiment. Figure 3A is a diagram showing an example of the configuration of the communication system according to the embodiment. Figure 3B is a diagram showing an example of the configuration of the communication system according to the embodiment. Figure 4 is a diagram showing an example of the data format of mobility information according to the embodiment. Figure 5 is a sequence diagram showing an example of the UE-to-UE Relay establishment process according to the first embodiment. Figure 6 is a flowchart showing an example of the relay device (or relay device candidate) selection process according to the first embodiment. Figure 7 is a sequence diagram showing an example of the UE-to-UE Relay establishment process according to the second embodiment. Figure 8 is a sequence diagram showing an example of the UE-to-UE Relay re-selection process according to the third embodiment. Figure 9 is a flowchart showing an example of the UE-to-UE Relay re-selection implementation decision process according to the third embodiment. Figure 10 is a sequence diagram showing an example of the UE-to-UE Relay reselection process according to the fourth embodiment.

[0014] 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 the invention, 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.

[0015] <First Embodiment> In this embodiment, an example of using mobility information in the sequence for establishing a UEto-UE Relay using UEto-UE Relay Discovery will be described.

[0016] Figure 1 is a block diagram showing an example of the hardware configuration of the End UE and relay device according to this embodiment. In various embodiments, including this embodiment, the End and relay device may have, for example, the hardware configuration 101 shown in Figure 1.

[0017] The hardware configuration 101 includes 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. GPS is an abbreviation for Global Positioning System.

[0018] 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 device by executing a control program stored in the memory unit 103 (a control program read from the 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.

[0019] The storage unit 103 stores control programs executed by the control unit 102, as well as various types of information such as cell information, connected terminal information, and mobility information. The storage unit 103 may include a main memory unit and an auxiliary memory unit. The main memory unit is, for example, ROM (Read Only Memory), RAM, etc. The main memory unit may store or temporarily store programs and data such as the OS (Operating System), which is the basic software executed by the control unit 102, and application software. The auxiliary memory unit is, for example, an HDD (Hard Disk Drive), SSD (Solid State Drive), etc. The auxiliary memory unit may store data related to application software, etc. For example, a control program stored in a non-volatile memory area is loaded into 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.

[0020] The wireless communication unit 104 performs cellular communication such as LTE (Long Term Evolution) and 5G (NR) in accordance with the 3GPP standard. In various embodiments, including this embodiment, 5G will be described, but this disclosure is also applicable to other next-generation mobile communication systems such as 5G Advanced and 6G, LTE, LTE-Advanced, and combinations thereof.

[0021] The communication antenna control unit 105 controls the antenna used for wireless communication performed by the wireless communication unit 104.

[0022] The GPS communication unit 106 receives satellite signals from GPS satellites and acquires current location information, including position identification information such as latitude and longitude, and current time information. The GPS communication unit 106 may also have a function to measure (position) the current location based on satellite signals. In place of or in addition to GPS, other GNSS (Global Navigation Satellite System) may be used.

[0023] The GPS antenna control unit 107 controls the antenna used for GPS communication performed by the GPS communication unit 106.

[0024] Figures 2A and 2B are block diagrams showing examples of the functional configuration of the End UE and relay device according to this embodiment. Functions other than the data storage unit shown in Figures 2A and 2B may be implemented by software of the End UE and relay device that executes communication control functions. In various embodiments, including this embodiment, the End UE and relay device may each have, for example, the software function 200 and software function 201 shown in Figures 2A and 2B.

[0025] Figure 2A is a block diagram showing an example of the functional configuration of End UE according to an embodiment. The software function 200 includes a signal transmission unit 202, a signal reception unit 203, a data storage unit 204, a connection control unit 205, a mobility information generation unit 206, a connection strength evaluation unit 207, a relay device selection unit 208, a relay device candidate selection unit 209, and a re-selection execution decision unit 210.

[0026] The signal transmitting unit 202 and the signal receiving unit 203 perform cellular communication such as LTE and 5G in accordance with the 3GPP standard with other communication devices. Messages containing mobility information, which will be described later, are transmitted and received by the signal transmitting unit 202 and the signal receiving unit 203. The signal transmitting unit 202 is an example of a transmitting means, the signal receiving unit 203 is an example of a receiving means, and the signal transmitting unit 202 and the signal receiving unit 203 are examples of a communication means or a transmitting and receiving means.

[0027] The data storage unit 204 stores and retains the software itself, information about the connected terminal, mobility information, and the like. Mobility information will be described later.

[0028] The connection control unit 205 controls side link connections, relay connections, etc., with other communication devices.

[0029] The mobility information generation unit 206 generates mobility information to be notified to surrounding communication devices. For example, the mobility information generation unit 206 generates mobility information for End UE based on location information, acceleration information, etc., acquired or calculated by the GPS communication unit 106, or by inertial sensors, acceleration sensors (not shown), etc., built into End UE. Alternatively, for example, the mobility information generation unit 206 generates mobility information for End UE based on user input. The mobility information generation unit 206 is an example of a generation means.

[0030] The connection strength evaluation unit 207 evaluates the connection strength between the surrounding communication devices and the device itself based on mobility information received from surrounding communication devices and the mobility information of the device itself. In various embodiments, including this embodiment, the connection strength evaluation unit 207 evaluates the connection strength based on the similarity of the movement or physical position changes of the two communication devices. The method for evaluating the connection strength will be described later. Note that "evaluate the connection strength" may be read as "determine the connection strength". The connection strength evaluation unit 207 is an example of a determination means or an evaluation means.

[0031] The relay device selection unit 208 selects a relay device based on the connection strength evaluated based on mobility information. In various embodiments, including this embodiment, the relay device selection unit 208 selects the communication device with the highest connection strength as the relay device. The relay device selection unit 208 is an example of a selection means.

[0032] The relay device candidate selection unit 209 selects a relay device candidate based on the connection strength evaluated based on mobility information. In various embodiments, including this embodiment, the relay device candidate selection unit 209 selects a communication device whose connection strength is above a threshold as a relay device candidate. The relay device candidate selection unit 209 is an example of a selection means.

[0033] The re-selection decision unit 210 decides whether or not to perform re-selection of the relay device. In this embodiment, the re-selection decision unit 210 periodically checks the connection strength between its own device and the relay device. If the connection strength exceeds a threshold, it decides not to perform re-selection. If the connection strength falls below the threshold, it decides to perform re-selection. The re-selection decision unit 210 is an example of a decision means.

[0034] Figure 2B is a block diagram showing an example of the functional configuration of a relay device according to an embodiment. The software function 201 includes a signal transmission unit 202, a signal reception unit 203, a data storage unit 204, a connection control unit 205, a mobility information generation unit 206, a connection strength evaluation unit 207, and a message relay determination unit 211.

[0035] The signal transmitting unit 202 and the signal receiving unit 203 perform cellular communication such as LTE and 5G in accordance with the 3GPP standard with other communication devices. Messages containing mobility information, which will be described later, are transmitted and received by the signal transmitting unit 202 and the signal receiving unit 203. The signal transmitting unit 202 is an example of a transmitting means, the signal receiving unit 203 is an example of a receiving means, and the signal transmitting unit 202 and the signal receiving unit 203 are examples of a communication means or a transmitting and receiving means.

[0036] The data storage unit 204 stores and retains the software itself, information about the connected terminal, mobility information, and the like. Mobility information will be described later.

[0037] The connection control unit 205 controls side link connections, relay connections, etc., with other communication devices.

[0038] The mobility information generation unit 206 generates mobility information to be notified to surrounding communication devices. For example, the mobility information generation unit 206 generates mobility information for the relay device based on location information, acceleration information, etc., acquired or calculated by the GPS communication unit 106, or by inertial sensors, acceleration sensors (not shown), etc., built into the relay device. Alternatively, for example, the mobility information generation unit 206 generates mobility information for the relay device based on user input. The mobility information generation unit 206 is an example of a generation means.

[0039] The connection strength evaluation unit 207 evaluates the connection strength between the surrounding communication devices and the device itself based on mobility information received from surrounding communication devices and the mobility information of the device itself. In various embodiments, including this embodiment, the connection strength evaluation unit 207 evaluates the connection strength based on the similarity of the movement or physical position changes of the two communication devices. The method for evaluating the connection strength will be described later. The connection strength evaluation unit 207 is an example of a determination means or an evaluation means.

[0040] The message relay decision unit 211 decides whether or not to relay a message based on the connection strength evaluated based on mobility information. In various embodiments, including this embodiment, the message relay decision unit 211 decides to relay the message if the connection strength is above a threshold, and decides not to relay the message if the connection strength is below the threshold. The message relay decision unit 211 makes a decision on whether or not to relay a message when the signal receiving unit 203 receives a message containing a relay instruction (triggered by the signal receiving unit 203 receiving a message containing a relay instruction). Here, the relay instruction is the Relay_Indication described later. The message relay decision unit 211 is an example of a decision means.

[0041] Figures 3A and 3B show examples of the configuration of a communication system according to an embodiment.

[0042] Figure 3A shows a configuration example of a communication system when the connection strength is high. End UE301 and End UE302 establish UE-to-UE Relay via relay device 303. These communication devices are moving in the same direction at the same speed. Therefore, there is a high possibility that the relay connection will continue for a long time. In this case, the connection strength of UE-to-UE Relay is evaluated as high.

[0043] Figure 3B shows a configuration example of a communication system when the connection strength is low. End UE301 and End UE302 establish UE-to-UE Relay via relay device 304. In this relay, while End UE301 and End UE302 are moving in the right direction of the drawing, relay device 304 is moving in the opposite direction (left direction of the drawing). Therefore, there is a high possibility that the relay connection will be interrupted. In this case, the connection strength of UE-to-UE Relay is evaluated as low.

[0044] Next, mobility information used when evaluating the connection strength will be described.

[0045] Figure 4 is a diagram showing an example of the data format of mobility information according to the embodiment.

[0046] MobilityInfo400 indicating the entire mobility information is added to several messages used in the communication between the End UE and the relay device described later.

[0047] MobilityInfo400 includes Device identificationinformation401, Mobility-StatusInfo402, and Mobility-Profile405.

[0048] Device identification information 401 is the identification information of the communication device. Since mobility information of a plurality of communication devices may be added to the message, the Device identification information 401 is used to identify which communication device's mobility information it is. As the identification information of the communication device, for example, User Info ID may be used.

[0049] Mobility-StatusInfo402 is simple mobility information. When there is a limit to the data size that can be added to the message, the data size can be reduced by adding only simple mobility information. Mobility-StatusInfo402 includes a Mobility-StatusIndicator403 indicating the moving state of the communication device (whether the communication device is moving or stopped). Mobility-StatusInfo402 also includes a GuaranteedStaticTime404 indicating the stop time of the communication device.

[0050] Mobility-Profile405 is detailed mobility information. By adding detailed mobility information to the message, although the data size becomes larger, a more accurate connection strength can be evaluated.

[0051] Mobility-Profile 405 includes Speed-Info 406, which provides information regarding the mobile speed of the communication device, and Mobility-Area-Info 407, which provides information regarding the mobile area of ​​the communication device. The information regarding the mobile speed of the communication device may include, for example, at least one of the maximum speed, minimum speed, and average speed over a recent predetermined period. The information regarding the mobile area of ​​the communication device may include, for example, information identifying the cell in which the communication device is located (e.g., cell ID, base station name, etc.). Mobility-Profile 405 also includes StaticDuration-Info 408, which provides detailed information regarding the downtime, such as the elapsed downtime and the scheduled downtime (scheduled start time and scheduled end time). Mobility-Profile 405 also includes Geolocation-Info 409, which provides information regarding the physical location (e.g., latitude and longitude) and direction of movement of the communication device.

[0052] Next, we will explain the processing flow for establishing a UE-to-UE Relay based on mobility information.

[0053] Figure 5 is a sequence diagram showing an example of the UE-to-UE Relay establishment process according to the first embodiment. The sequence shown in Figure 5 is equivalent to the sequence of the UE-to-UE Relay establishment process described in Section 6.7.1 of TS23.304.

[0054] In this embodiment, the mobility information of the relay device is notified to the End UE by adding the mobility information of the relay device to the Discovery message used in the existing sequence. In addition, in this embodiment, the process by which the End UE selects a relay device is modified so that the relay device is selected based on mobility information rather than radio wave strength.

[0055] First, Source End UE301, Target End UE302, and Relay303 perform service authentication and provisioning (S501).

[0056] Next, Source End UE301 performs a 5G ProSe UE-to-UE Relay Discovery (S502). There are two types of 5G ProSe UE-to-UE Relay Discovery: Model A and Model B. The 5G ProSe UE-to-UE Relay Discovery is defined in Section 6.3.2.4 of TS23.304.

[0057] Model A is implemented by the relay device notifying surrounding communication devices of an announcement message (UE-to-UE Relay Discovery Announcement message) (see Section 6.3.2.4.2 of TS23.304). In this embodiment, the relay device (Relay 303) adds its own mobility information to the announcement message and notifies surrounding communication devices of this announcement message. The End UE (Source End UE 301 and Target End UE 302) obtains the mobility information of the relay device from the received announcement message. According to TS23.304 and TS24.554, a UE-to-UE Relay Discovery Announcement message is a type of 5G ProSe direct discovery message.

[0058] Model B is implemented by the following two notifications (see Section 6.3.2.4.3 of TS23.304): (1) Notification of a discovery request message (UE-to-UE Relay Discovery Solicitation message) from the Source End UE to the Target End UE. According to TS23.304 and TS24.554, the UE-to-UE Relay Discovery Solicitation message is a type of 5G ProSe direct discovery message. (2) Notification of a discovery response message (UE-to-UE Relay Discovery Response message) from the Target End UE that received the discovery request message to the Source End UE. According to TS23.304 and TS24.554, the UE-to-UE Relay Discovery Response message is a type of 5G ProSe direct discovery message.

[0059] In the case of UE-to-UE Relay, the detection request message and detection response message are transmitted via surrounding relay devices.

[0060] In this embodiment, when the relay device (Relay 303) forwards a detection request message, it adds its own mobility information to the detection request message and notifies the End UE (Target End UE 302) of the detection request message. Also in this embodiment, when the relay device (Relay 303) forwards a detection response message, it adds its own mobility information to the detection response message and notifies the End UE (Source End UE 301) of the detection response message. The End UE obtains the mobility information of the relay device from the received detection response message.

[0061] In the case of Model B, the End UEs (Source End UE301 and Target End UE302) may also add their own mobility information to the message. In this case, the destination End UE can know the mobility information of the source End UE and the mobility information of the relay device. The destination End UE can then comprehensively evaluate the connection strength from the mobility information of the entire UE-to-UE Relay, including its own mobility information. In addition, the relay device can also evaluate the connection strength from the mobility information of the source End UE and its own mobility information. The relay device may decide (or determine) whether or not to relay the message based on the connection strength.

[0062] Next, the Source End UE 301 selects a relay device based on the connection strength evaluated based on the received mobility information (S503). Details of the process flow by which the End UE selects a relay device will be described later.

[0063] The subsequent processing follows the existing sequence, so I will briefly explain it.

[0064] Source End UE301 notifies Relay303 of a Direct Communication Request message in order to establish a unicast Layer 2 link with Relay303 (S504).

[0065] Relay303 and Source End UE301 establish security (S505).

[0066] After security is established, Relay 303 notifies Target End UE 302 of a Direct Communication Request to establish a unicast Layer 2 link with Target End UE 302 (S506).

[0067] Target End UE302 and Relay303 establish security (S507).

[0068] After security is established, Target End UE302 notifies Relay303 of the Direct Communication Accept message (S508).

[0069] For IP traffic, Relay 303 assigns an IP (Internet Protocol) v4 address or an IPv6 prefix to Target End UE 302 (S509).

[0070] Relay 303 notifies Source End UE 301 of the Direct Communication Accept message (S510).

[0071] For IP traffic, Relay303 assigns an IPv4 address or IPv6 prefix to Source End UE301 (S511).

[0072] In the case of IP traffic, Relay 303 functions as a DNS server. Therefore, in response to a request from Source End UE301, Relay 303 notifies Source End UE301 of the IPv4 address or IPv6 prefix of Target End UE302 (S512).

[0073] Finally, Source End UE301 communicates with Target End UE302 via Relay303 (S513).

[0074] Next, we will explain the processing flow by which End UE selects a relay device based on mobility information.

[0075] Figure 6 is a flowchart showing an example of the relay device (or relay device candidate) selection process according to the first embodiment. In the processing flow shown in Figure 6, End UE selects a relay device (or relay device candidate) from the received mobility information. In this embodiment, the mobility information is used by Source End UE 301 to select a relay device at S503 in Figure 5. The selection of relay device candidates will be described later in the third embodiment.

[0076] First, the Source End UE301 receives a message from a nearby communication device (S601). Then, the Source End UE301 obtains mobility information from the received message (S602).

[0077] Next, Source End UE301 evaluates the connection strength based on the acquired mobility information (S603). Details of the connection strength evaluation will be described later.

[0078] Next, Source End UE301 determines whether the evaluated connection strength is above a threshold (S604).

[0079] If the connection strength is not above the threshold (No in S604), Source End UE301 terminates the process.

[0080] On the other hand, if the connection strength is above the threshold (Yes in S604), Source End UE301 selects the device (the device that sent the message) as the relay device (S605). Then, Source End UE301 terminates processing.

[0081] In this embodiment, the threshold value is the maximum value of the most recently evaluated connection strength. In other words, the communication device with the highest connection strength in the most recent instance is selected as the relay device.

[0082] Next, we will describe an example of a method for evaluating connection strength based on mobility information.

[0083] One example of a method for evaluating connection strength is to use relative speed. When the relative speed is low, the distance between devices can be kept constant for a relatively long time, making communication less likely to be interrupted. In this case, the connection strength between devices is judged to be high. Conversely, when the relative speed is high, the distance between devices widens relatively quickly, increasing the likelihood of connection interruption, so the connection strength between devices is judged to be low.

[0084] To calculate the relative velocity, information indicating the movement speed contained in Speed-Info 406 within MobilityInfo 400 and information indicating the direction of movement contained in Geolocation-Info 409 within MobilityInfo 400 are used. As the movement speed, any of the maximum speed, minimum speed, or average speed may be used. The communication device may periodically observe the latitude and longitude information contained in Geolocation-Info 409 within GeolocationMobilityInfo 400 to determine the movement speed and direction of movement. The communication device calculates a relative velocity vector from the velocity vector of the notifying communication device calculated from the determined movement speed and direction of movement, and from the velocity vector obtained based on its own generated mobility information. Then, the communication device evaluates the connection strength in N stages (N is an integer of 2 or more) based on a comparison of the magnitude (V) of the calculated relative velocity vector with one or more thresholds. For example, when evaluating connection strength in two stages (high or low), one threshold (T) is set. In this case, for example, the communication device may evaluate the connection strength as "2" (high) if V ≤ T, and as "1" (low) if T < V. Also, in this case, for example, the threshold compared with the connection strength in S604 for the selection of a relay device candidate in the third embodiment described later is set to an arbitrary value such as "2". Also, for example, when evaluating connection strength in four stages, three thresholds (T1 < T2 < T3) are set. In this case, for example, the communication device may evaluate the connection strength as "4" (high) if V ≤ T1, "3" (slightly high) if T1 < V < ≤ 2, "2" (slightly low) if T2 < V ≤ T3, and "1" (low) if T3 < V. Also, in this case, for example, the threshold compared with the connection strength in S604 for the selection of a relay device candidate in the third embodiment described later is set to an arbitrary value such as "3" or "4". Alternatively, the communication device may evaluate the connection strength as the reciprocal of the magnitude (V) of the calculated relative velocity vector.

[0085] Other possible methods for evaluating connection strength include the following:

[0086] For example, a communication device may determine that the connection strength between devices is high if the mobility area information included in the notified Mobility-Area-Info 407 is the same as the mobility area information in its own generated mobility information. In this case, the communication device may evaluate the connection strength as "2". On the other hand, if this is not the case, the communication device may determine that the connection strength between devices is low (for example, it may evaluate the connection strength as "1").

[0087] Furthermore, if the latitude and longitude information contained in the notified Geolocation-Info 409 is close to the latitude and longitude information in its own generated mobility information, the communication device may determine that the connection strength between devices is high. In this case, the communication device may evaluate the connection strength as "2," for example. On the other hand, if this is not the case, the communication device may determine that the connection strength between devices is low (for example, it may evaluate the connection strength as "1"). Here, "close" may mean that the distance between communication devices calculated from this latitude and longitude information is less than or equal to a predetermined value.

[0088] Furthermore, if the period during which the stop scale included in StaticDuration-Info408 matches the stop scale in its generated mobility information is long, the communication device may determine that the connection strength between devices is high. In this case, the communication device may evaluate the connection strength as "2," for example. On the other hand, if this is not the case, the communication device may determine that the connection strength between devices is low (for example, it may evaluate the connection strength as "1"). Here, the stop scale refers to the period from the scheduled stop start time to the scheduled stop end time, and "long" may mean that the period during which these stop scales match is greater than or equal to a predetermined value.

[0089] Alternatively, the communication device may simply determine that the connection strength between devices is high if the movement status (moving or stopped) included in the Mobility-StatusIndication 403 matches the movement status in its generated mobility information. In this case, the communication device may evaluate the connection strength as "2," for example. On the other hand, if this is not the case, the communication device may determine that the connection strength between devices is low (for example, it may evaluate the connection strength as "1").

[0090] Furthermore, the communication device may evaluate the connection strength using any combination of the above methods (for example, by taking the average or weighted average of the above connection strength values).

[0091] Furthermore, the communication device may evaluate the connection strength by considering both mobility information and radio wave strength.

[0092] Which information in the mobility information is used for connection strength evaluation (which evaluation method is used) may be determined by the base station, by End UE, or by the relay device.

[0093] In this way, communication devices can establish relay communication that is less prone to interruptions by selecting devices with high connection strength (in other words, devices with similar relative movements) as relay devices based on mobility information.

[0094] According to this embodiment, the relay device adds its mobility information to the announcement message or detection request message and detection response message, and notifies the End UE of these messages. The End UE evaluates the connection strength based on the notified mobility information (and its own mobility information) and selects a relay device based on the connection strength. As a result, a relay device with a high connection strength is selected based on the mobility information, which reduces or prevents communication interruptions in relay communication and ensures communication stability. Therefore, relay communication can be performed appropriately.

[0095] <Second Embodiment> In the first embodiment, an example of using mobility information in the sequence for establishing a UE-to-UE Relay using UE-to-UE Relay Discovery was described. In this embodiment, an example of using mobility information in the sequence for establishing a UE-to-UE Relay using integrated Discovery will be described. Note that in the second embodiment, the same configuration and processing as in the first embodiment will not be described.

[0096] Figure 7 is a sequence diagram showing an example of the UE-to-UE Relay establishment process according to the second embodiment. The sequence shown in Figure 7 is equivalent to the sequence of the UE-to-UE Relay establishment process described in Section 6.7.3 of TS23.304. As described above, the process shown in Figure 7 uses integrated Discovery.

[0097] In this embodiment, the mobility information of the relay device is notified to the End UE by adding the mobility information of the relay device to the Direct Communication Request message used in the existing sequence. In addition, in this embodiment, the process by which the End UE selects a relay device is modified so that the relay device is selected based on mobility information rather than radio wave strength. According to TS23.304 and TS24.554, the Direct Communication Request message can be said to be a type of 5G ProSe direct communication message.

[0098] First, the Source End UE301, Target End UE302, and relay devices (Relay-1 and Relay-2) perform service authentication and provisioning (S701).

[0099] Next, Source End UE301 broadcasts a Direct Communication Request message to Target End UE302, allowing relaying by the relay device (S702). Relaying permission is controlled by the Relay_Indication included in the Direct Communication Request message (see Section 11.3.56 of TS24.554, etc.). If the Direct Communication Request message includes a Relay_Indication, relaying of the Direct Communication Request message is permitted. On the other hand, if the Direct Communication Request message does not include Relay_Indication, relaying of the Direct Communication Request message is not permitted. In this embodiment, Source End UE301 includes Relay_Indication in the Direct Communication Request message and broadcasts the message.

[0100] When the relay devices (Relay-1 and Relay-2) receive a Direct Communication Request message from Source End UE301, they perform the following operation in S703. Specifically, the relay devices (Relay-1 and Relay-2) broadcast the Direct Communication Request message destined for Target End UE302 without allowing relaying by the relay devices (S703). In other words, the relay devices (Relay-1 and Relay-2) broadcast the Direct Communication Request message without including Relay_Indication. In addition, in this embodiment, the relay devices (Relay-1 and Relay-2) add the mobility information of the relay device to the Direct Communication Request message and broadcast this message.

[0101] When Target End UE302 receives a Direct Communication Request message from one or more relay devices, it performs the following operation in S704. Specifically, Target End UE302 evaluates the connection strength based on the mobility information contained in the Direct Communication Request message and selects a relay device based on the evaluated connection strength (S704). The processing flow for selecting a relay device and the method for evaluating the connection strength are the same as in the first embodiment, so a description is omitted. Note that in S704, the selection of a relay device and the evaluation of the connection strength are performed by Target End UE302, not Source End UE.

[0102] Here, at S701, the Source End UE 301 may also add its own mobility information to the Direct Communication Request message. In this case, the Target End UE can know the mobility information of the Source End UE and the mobility information of the relay device. The Target End UE can then comprehensively evaluate the connection strength from the mobility information of the entire UE-to-UE Relay, including its own mobility information. In addition, the relay device can also evaluate the connection strength from the mobility information of the Source End UE and its own mobility information. Based on the connection strength, the relay device may decide (or determine) whether or not to relay the Direct Communication Request message.

[0103] The subsequent processing follows the existing sequence, so a brief explanation will be given. In this embodiment, the case where Relay-1 is selected as the relay device will be used as an example.

[0104] Relay-1 and Target End UE302 establish security (S705).

[0105] Target End UE302 sends a Direct CommunicationAccept message to Relay-1 (S706).

[0106] For IP traffic, Relay-1 assigns an IPv4 address or IPv6 prefix to Target End UE302 (S707).

[0107] Source End UE301 and Relay-1 establish security (S708).

[0108] Relay-1 receives QoS (Quality of Service) information from Source End UE301. After receiving the QoS information, Relay-1 notifies Target End UE302 of the QoS information using a Link Modification Request message (S709).

[0109] When Target End UE302 receives a Link Modification Request from Relay-1, it responds to Relay-1 with a Link Modification Accept message (S710).

[0110] Relay-1 responds to Source End UE301 with a Direct Communication Accept message (S711).

[0111] For IP traffic, Relay-1 assigns an IPv4 address or IPv6 prefix to Source End UES301 (S712).

[0112] In the case of IP traffic, Relay-1 functions as a DNS server. Therefore, in response to a request from Source End UE301, Relay-1 notifies Source End UE301 of the IPv4 address or IPv6 prefix of Target End UE302 (S713).

[0113] Finally, Source End UE301 communicates with Target End UE302 via Relay-1 (S714).

[0114] According to this embodiment, the relay device adds its mobility information to the Direct Communication Request message and notifies the End UE of this message. The End UE evaluates the connection strength based on the notified mobility information (and its own mobility information) and selects a relay device based on the evaluated connection strength. As a result, a relay device with a high connection strength is selected based on the mobility information, which reduces or prevents communication interruptions in relay communication and ensures communication stability. Therefore, relay communication can be performed appropriately.

[0115] <Third Embodiment> In the first and second embodiments, an example of using mobility information in the sequence for establishing a UE-to-UE Relay was described. In this embodiment, an example of using mobility information in the sequence for re-selecting a relay device after establishing a UE-to-UE Relay will be described. Note that in the third embodiment, the same configurations and processes as in the first or second embodiment will not be described.

[0116] Figure 8 is a sequence diagram showing an example of the UE-to-UE Relay reselection process according to the third embodiment. The reselection of the relay device by the UE-to-UE Relay reselection process is performed after the UE-to-UE Relay is established. Figure 8 shows the process flow for changing the relay device from Relay-1 to Relay-2. The sequence shown in Figure 8 is equivalent to the sequence of the UE-to-UE Relay reselection process described in Section 6.7.4 of TS 23.304.

[0117] In this embodiment, mobility information of candidate relay devices is notified to the End UE by adding mobility information to periodically notified messages and Link Modification Request messages. In addition, in this embodiment, the process by which the End UE decides to re-select a relay device and the process of selecting a relay device are modified to be based on mobility information rather than radio wave strength. According to TS23.304 and TS24.554, the Link Modification Request message can be said to be a type of 5G ProSe direct communication message.

[0118] Source End UE301 and Target End UE302 are configured to establish a Relay-1 and PC5 unicast link (S801).

[0119] Source End UE301 and Target End UE302 are configured to establish a Relay-2 and PC5 unicast link (S802).

[0120] Source End UE301 and Target End UE302 forward traffic via Relay-1 (S803).

[0121] The relay devices (Relay-1 and Relay-2) add the relay device's mobility information to the message they send from the relay device to the Source End UE301 and send the message to the Source End UE301 (S804). The message sent from the relay device to the Source End UE301 is a message that is notified periodically. Examples of messages that are notified periodically include announcement messages (UE-to-UE Relay Discovery Announcement message) and PC5 RRC messages (measurement report). The Source End UE301 can periodically evaluate the connection strength with the relay device by obtaining mobility information from the messages that are notified periodically. The connection strength with Relay-1 can be used to determine whether to re-select the relay device, and the connection strength with Relay-2 can be used to select a candidate relay device when re-selecting the relay device.

[0122] Next, Source End UE301 decides to perform a reselection of the relay device (S805).

[0123] The following describes the processing flow for deciding whether to re-select the relay device.

[0124] Figure 9 is a sequence diagram showing an example of the UE-to-UE Relay re-selection decision process according to the third embodiment. Figure 9 shows the processing flow in which the End UE decides to perform re-selection of the relay device based on the mobility information it receives.

[0125] First, Source End UE301 receives a message from the relay device (S901). Then, Source End UE301 obtains mobility information from the received message (S902).

[0126] Next, Source End UE301 evaluates the connection strength based on the acquired mobility information (S903). The details of the connection strength evaluation are the same as in the first embodiment, so the explanation is omitted.

[0127] Next, Source End UE301 determines whether the evaluated connection strength is below a threshold (S904).

[0128] If the connection strength is not below the threshold (No in S904), Source End UE301 returns to S901 and waits for the next message to be received.

[0129] On the other hand, if the connection strength is below the threshold (Yes in S904), Source End UE301 decides to re-select the relay device (S905). Then, Source End UE301 terminates the process.

[0130] Returning to the explanation of Figure 8, the Source End UE301 then selects a relay device candidate (S806). The relay device candidate is also selected based on mobility information, similar to the relay device. The Source End UE301 may select multiple relay device candidates. The Source End UE301 may obtain mobility information to be used for selecting the relay device candidate from the message notified in S804, or it may obtain (receive) mobility information again from surrounding communication devices after the decision to perform re-selection. If mobility information is obtained again, a 5G ProSe UE-to-UE Relay Discovery is performed as in the first embodiment. When using Model B, if the Direct Discovery set is not set in the detection request message, the surrounding communication device that received the message will return a detection response message instead of the Target End UE. As described above, the detection request message is a UE-to-UE Relay Discovery Solution message. The detection response message is a UE-to-UE Relay Discovery Response message. Surrounding communication devices can notify the End UE of their mobility information by adding their own mobility information to the detection response message and sending the detection response message.

[0131] Next, we will explain the processing flow by which End UE selects relay device candidates based on mobility information.

[0132] The selection of relay device candidates is processed according to the processing flow shown in Figure 6, similar to the selection of relay devices described in the first embodiment. Therefore, a detailed explanation of the selection of relay device candidates is omitted. The difference from the first embodiment is that, in the selection of relay device candidates, an arbitrary value is used as the connection strength threshold in S604, as described above, and communication devices whose connection strength is equal to or greater than the threshold are selected as relay device candidates. As described above, multiple relay device candidates may be selected.

[0133] Returning to the explanation of Figure 8, the Source End UE301 then sends a Link Modification Request message to the Target End UE302 via the relay device (Relay-1) (S807, S808). This message contains a relay reselection instruction. In addition, the Source End UE301 adds mobility information of the selected relay device candidate to this message.

[0134] The Target End UE302 selects a relay device from the relay device candidates in accordance with the relay reselection instruction included in the received Link Modification Request (S809). The relay device is selected based on mobility information according to the processing flow shown in Figure 6, similar to the first embodiment. Selecting a relay device may be considered as selecting or determining the communication path between the Source End UE301 and the Target End UE302.

[0135] Here, in S807, Source End UE301 may also add its own mobility information to the Link Modification Request message. In this case, Target End UE can know the mobility information of Source End UE and the mobility information of the relay device candidate. Then, Target End UE can comprehensively evaluate the connection strength from the mobility information of the entire UE-to-UE Relay, including its own mobility information.

[0136] The subsequent processing follows the existing sequence, so I will briefly explain it.

[0137] The Target End UE302 sends a Link Modification Accept message to the Source End UE301 via the relay device (Relay-1) (S810, S811). This message contains the user information ID of the new relay device (Relay-2) selected by the Target End UE302.

[0138] Source End UE301 transmits Link Modification Ack to Target End UE302 via Relay-1 (S812, S813).

[0139] Finally, Source End UE301 communicates with Target End UE302 via the new relay device (Relay-2) (S814).

[0140] According to this embodiment, a relay device candidate adds its mobility information to a message (such as a periodically notified message) and notifies the End UE of this message. The Source End UE evaluates the connection strength based on the notified mobility information (and its own mobility information) and selects a relay device candidate based on the connection strength. The Source End UE adds the relay device candidate's mobility information to a Link Modification Request message and notifies the Target End UE of this message. The Target End UE evaluates the connection strength based on the notified mobility information (and its own mobility information) and re-selects a relay device based on the connection strength. As a result, a relay device with high connection strength is re-selected based on the mobility information, which reduces or prevents communication interruptions in relay communication, ensures communication stability, and reduces the load associated with re-selecting a relay device. Therefore, relay communication can be performed appropriately.

[0141] <Fourth Embodiment> In the third embodiment, an example of using mobility information in the sequence for re-selecting a relay device was described. In this embodiment, an example of using mobility information in the sequence for re-selecting a relay device using integrated Discovery will be described. Furthermore, in the integrated Discovery of the second embodiment, a single-hop UE-to-UE Relay involving one relay device was described. In this embodiment, in addition to the above, a multi-hop UE-to-UE Relay involving multiple relay devices will be described. Note that in the fourth embodiment, the same configurations and processes as in the first, second, or third embodiments will not be described.

[0142] Figure 10 is a sequence diagram showing an example of the UE-to-UE Relay reselection process according to the fourth embodiment. The reselection of the relay device by the UE-to-UE Relay reselection process is performed after the UE-to-UE Relay is established. Figure 10 shows the processing flow for changing the relay devices from Relay-1 and Relay-2 to Candidate Relay-1 and Candidate Relay-2, respectively. As described above, the process shown in Figure 10 uses integrated Discovery.

[0143] Source End UE301 and Target End UE302 forward traffic via Relay-1 and Relay-2 (S1001).

[0144] The relay devices (Relay-1 and Relay-2) add the relay device's mobility information to the message they send from the relay device to the Source End UE301 and send the message to the Source End UE301 (S1002). The process in S1002 is the same as the process in S804 in Figure 8 of the third embodiment, so the explanation is omitted. The Source End UE301 obtains mobility information from the messages that are notified periodically.

[0145] Next, Source End UE301 decides to perform a re-selection of the relay device (S1003). The decision to perform the re-selection is carried out according to the processing flow shown in Figure 9, similar to the third embodiment. Therefore, the explanation of the decision to perform the re-selection is omitted.

[0146] When Source End UE301 decides to perform a reselection, it performs the following operation in S1004. That is, Source End UE301 broadcasts a Direct Communication Request message to Target End UE302, allowing relaying by the relay device (S1004). Here, the permission for relaying is controlled by Relay_Indication included in the message. In this embodiment, the way Relay_Indication is used changes to support multi-hop. In single-hop, Relay_Indication is used like a flag, and message relaying is included in the message only if permitted. In contrast, in multi-hop, Relay_Indication is used as a parameter representing the number of times relaying is permitted. When establishing a multi-hop UE-to-UE relay using two relay devices, Source End UE301 stores "2" in Relay_Indication. When a surrounding communication device receives a message containing Relay_Indication, it decrements the value of Relay_Indication by 1 before notifying the next communication device of the message. If the value of Relay_Indication becomes 0, relaying of that message is not permitted. In this embodiment, Source End UE301 includes Relay_Indication as 2 in a Direct Communication Request message and broadcasts this message in order to permit relaying twice.

[0147] When Candidate Relay-1 receives a Direct Communication Request message from Source End UE301, it performs the following operation in S1005. Specifically, Candidate Relay-1 decrements Relay_Indication by 1 to 1 and includes this in the Direct Communication Request message, and broadcasts this message to the surrounding area (S1005). In addition, in this embodiment, Candidate Relay-1 adds its mobility information to the Direct Communication Request message and broadcasts this message.

[0148] When Candidate Relay-2 receives a Direct Communication Request message from Candidate Relay-1, it performs the following operation in S1006. Specifically, Candidate Relay-2 includes 0 (Relay_Indication decremented by 1) in the Direct Communication Request message and broadcasts this message to the surrounding area (S1006). In addition, in this embodiment, Candidate Relay-2 adds its mobility information to the Direct Communication Request message and broadcasts this message.

[0149] The Target End UE302 receives a Direct Communication Request message from one or more relay devices (S1006). The Target End UE302 then evaluates the connection strength based on the mobility information contained in the Direct Communication Request message and selects a relay device based on the evaluated connection strength (S1007). The processing flow for selecting a relay device and the method for evaluating the connection strength are the same as in the first embodiment, so a description is omitted. In this way, the Target End UE302 can select or determine the communication path between the relay devices, i.e., the Source End UE301 and the Target End UE302, based on the evaluated connection strength.

[0150] Here, in S1004, the Source End UE 301 may also add its own mobility information to the Direct Communication Request message. In this case, the Target End UE can know the mobility information of the Source End UE and the mobility information of the relay device candidate. The Target End UE can then comprehensively evaluate the connection strength from the mobility information of the entire UE-to-UE Relay, including its own mobility information. In addition, the relay device candidate can also evaluate the connection strength from the mobility information of the Source End UE and its own mobility information. The (first) relay device candidate may decide (or determine) whether or not to relay the Direct Communication Request message based on the connection strength. Furthermore, in the case of multi-hop, the second and subsequent relay device candidates can also evaluate the connection strength with the previous relay device candidate based on the received Direct Communication Request message. Similarly, the second and subsequent relay device candidates may decide (or determine) whether or not to relay the Direct Communication Request message based on the connection strength.

[0151] In the sequence following the selection of a relay device, processing is carried out in the same manner as in a single hop. Specifically, security establishment, sending of Direct Communication Accept messages, and assignment of IPv4 addresses or IPv6 prefixes are repeatedly performed in each section of the selected relay device. Therefore, a detailed explanation is omitted. Information about the relay device selected by Target End UE is included in the Direct Communication Accept message and notified to the next relay device.

[0152] According to this embodiment, a candidate relay device adds its mobility information to a Direct Communication Request message and notifies the End UE of this message. The End UE evaluates the connection strength based on the notified mobility information (and its own mobility information) and re-selects a relay device based on the connection strength. As a result, a relay device with a high connection strength is selected based on the mobility information, which reduces or prevents communication interruptions in relay communication, ensures communication stability, and reduces the load associated with re-selecting a relay device. Furthermore, in this embodiment, communication interruptions can be reduced or prevented in multi-hop relay communication, ensures communication stability, and reduces the load associated with re-selecting a relay device. Therefore, relay communication can be performed appropriately.

[0153] <Other Embodiments> This disclosure can also be implemented by supplying a program that implements one or more of the functions of each 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 (for example, an ASIC or FPGA) that implements one or more functions.

[0154] 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.

[0155] 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.

[0156] Furthermore, some (or in some cases all) of the above-mentioned functional blocks may be replaced with other functional blocks that perform similar functions, some functional blocks may be omitted, or additional functional blocks may be added.

[0157] Furthermore, one functional block as described above may be divided into multiple functional blocks, or multiple functional blocks may be integrated into a single functional block.

[0158] The order of the processing procedures, sequences, flowcharts, etc., in the embodiments described above is not limited to the specific order presented, and may be rearranged or additional steps may be added, as long as they do not contradict each other.

[0159] The matters described in the above embodiments may be incorporated into other embodiments, insofar as they do not contradict each other.

[0160] The present invention is not limited to the embodiments described above, and various modifications and variations are possible without departing from the spirit and scope of the invention. Accordingly, the following claims are attached to make the scope of the invention public.

[0161] This application claims priority based on Japanese Patent Application No. 2024-180746, filed on 16 October 2024, and all of its contents are incorporated herein by reference.

[0162] 101 Hardware configuration 102 Control unit 103 Storage unit 104 Wireless communication unit 105 Communication antenna control unit 106 GPS communication unit 107 GPS antenna control unit 200 Software functions 201 Software functions 202 Signal transmission unit 203 Signal reception unit 204 Data storage unit 205 Connection control unit 206 Mobility information generation unit 207 Connection strength evaluation unit 208 Relay device selection unit 209 Relay device candidate selection unit 210 Re-selection execution decision unit 211 Message relay decision unit 301 End UE 302 End UE 303 Relay device 304 Relay device

Claims

1. A communication device that operates as a relay device in a UE (User Equipment)-to-UE Relay, comprising: a generation means for generating mobility information relating to the movement of the communication device; and a transmission means for transmitting the mobility information toward the End UE.

2. The communication device according to claim 1, wherein the mobility information includes information indicating at least one of the following: the movement state of the communication device, the movement speed of the communication device, the stop time of the communication device, the movement area of ​​the communication device, the position of the communication device, and the direction of movement of the communication device.

3. The communication device according to claim 1 or 2, wherein the transmitting means transmits the mobility information to the End UE, including it in a 5G ProSe direct discovery message.

4. The communication device according to claim 1 or 2, wherein the transmitting means transmits the mobility information to the End UE, including it in a 5G ProSe direct communication message.

5. A communication device that operates as an End UE in a UE-to-UE Relay, comprising: receiving means for receiving first mobility information relating to the movement of a relay device from a relay device; generating means for generating second mobility information relating to the movement of the communication device; and first determining means for determining the connection strength between the communication device and the relay device based on the first mobility information and the second mobility information.

6. The communication device according to claim 5, wherein the first mobility information includes first information indicating at least one of the following: the movement state of the relay device, the movement speed of the relay device, the stopping time of the relay device, the movement area of ​​the relay device, the position of the relay device, and the direction of movement of the relay device, and the second mobility information includes second information indicating at least one of the following: the movement state of the communication device, the movement speed of the communication device, the stopping time of the communication device, the movement area of ​​the communication device, the position of the communication device, and the direction of movement of the communication device.

7. The communication device according to claim 6, wherein the determination means calculates the relative speed between the relay device and the communication device from the moving speed and direction of the relay device and the moving speed and direction of the communication device based on the first information and the second information, and determines the connection strength based on the relative speed.

8. The communication device according to claim 6, wherein the determination means determines the connection strength by comparing the movement state of the relay device and the movement state of the communication device based on the first information and the second information.

9. The communication device according to claim 6, wherein the determination means calculates the distance between the relay device and the communication device from the position of the relay device and the position of the communication device based on the first information and the second information, and determines the connection strength based on the distance.

10. The communication device according to claim 6, wherein the determination means compares the moving area of ​​the relay device and the moving area of ​​the communication device based on the first information and the second information to determine the connection strength.

11. The communication device according to claim 5, wherein, when establishing or re-selecting a UE-to-UE Relay, the receiving means receives the respective mobility information from one or more relay devices, the determining means determines the respective connection strength between one or more relay devices and the communication device based on the respective mobility information, and the communication device further has a first selection means that selects the relay device with the highest connection strength among the respective connection strengths as the relay device in the UE-to-UE Relay.

12. The communication device according to claim 5, wherein, when establishing or re-selecting a UE-to-UE Relay, the receiving means receives the respective mobility information from one or more relay devices, the determining means determines the respective connection strength between one or more relay devices and the communication device based on the respective mobility information, and the communication device further has a second selection means for selecting the relay devices whose connection strength is equal to or greater than a first threshold as candidates for relay devices in the UE-to-UE Relay.

13. The communication device according to claim 5, wherein the receiving means receives the first mobility information during a UE-to-UE Relay connection, and the communication device further comprises a second determination means that determines to perform a UE-to-UE Relay reselection when the connection strength falls below a second threshold.

14. A communication device that operates as a relay device in a UE-to-UE Relay, comprising: generation means for generating mobility information relating to the movement of the communication device; and transmission means for periodically transmitting the mobility information toward the End UE during a UE-to-UE Relay connection.

15. The communication device according to claim 14, wherein the transmitting means transmits the mobility information to the End UE, including it in a 5G ProSe direct discovery message.

16. The communication device according to claim 14, wherein the transmitting means transmits the mobility information to the End UE, including it in the PC5 RRC message.

17. A communication device that operates as an End UE in a UE-to-UE Relay, comprising: a generating means for generating mobility information relating to the movement of the communication device; and a transmitting means for transmitting the mobility information to a relay device.

18. A communication device that operates as a relay device in a UE-to-UE relay, comprising: receiving means for receiving first mobility information relating to the movement of an End UE from an End UE; generating means for generating second mobility information relating to the movement of the communication device; and first determining means for determining the connection strength between the communication device and the End UE based on the first mobility information and the second mobility information.

19. The communication device according to claim 18, further comprising a second determination means for determining whether or not to relay a message based on the connection strength.

20. The communication device according to claim 19, wherein the second determination means determines to relay the message if the connection strength is equal to or greater than a threshold, and determines not to relay the message if the connection strength is less than a threshold.

21. The communication device according to claim 19, wherein the second determination means determines whether or not to relay the message when the receiving means receives the message which includes a relay instruction.

22. The communication device according to any one of claims 19 to 21, further comprising a transmission means for transmitting the second mobility information in the message when the second determination means decides to relay the message.

23. A communication device that operates as an End UE in a UE-to-UE Relay, comprising: receiving means for receiving first mobility information relating to the movement of the relay device and second mobility information relating to the movement of the other End UE from the relay device and another End UE, respectively; generating means for generating third mobility information relating to the movement of the communication device; and selecting means for selecting a communication path between the communication device and the other End UE based on the first mobility information, the second mobility information and the third mobility information.

24. A control method performed by a communication device operating as a relay device in a UE-to-UE Relay, comprising the steps of: generating mobility information relating to the movement of the communication device; and transmitting the mobility information toward the End UE.

25. A control method performed by a communication device operating as an End UE in a UE-to-UE Relay, comprising: receiving first mobility information relating to the movement of a relay device from a relay device; generating second mobility information relating to the movement of the communication device; and determining the connection strength between the communication device and the relay device based on the first mobility information and the second mobility information.

26. A control method performed by a communication device operating as a relay device in a UE-to-UE Relay, comprising the steps of: generating mobility information relating to the movement of the communication device; and periodically transmitting the mobility information toward the End UE during the UE-to-UE Relay connection.

27. A control method performed by a communication device operating as an End UE in a UE-to-UE Relay, comprising the steps of: generating mobility information relating to the movement of the communication device; and transmitting the mobility information to a relay device.

28. A control method performed by a communication device operating as a relay device in a UE-to-UE Relay, comprising: receiving first mobility information relating to the movement of an End UE from an End UE; generating second mobility information relating to the movement of the communication device; and determining the connection strength between the communication device and the End UE based on the first mobility information and the second mobility information.

29. A control method performed by a communication device operating as an End UE in a UE-to-UE Relay, comprising: receiving first mobility information relating to the movement of the relay device and second mobility information relating to the movement of the other End UE from the relay device and another End UE, respectively; generating third mobility information relating to the movement of the communication device; and selecting a communication path between the communication device and the other End UE based on the first mobility information, the second mobility information, and the third mobility information.

30. A program for causing a computer to execute the control method described in any one of claims 24 to 29.

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