U2U relay reselection

Abstract

The apparatus, systems, and methods described herein relate to a scenario in which a candidate relay UE device may have prior knowledge of a source UE device's interest in connecting to a particular target UE device based on a prior request from the source UE device. If the candidate relay UE device determines that the sidelink connection between the candidate relay UE device and the target UE device meets the criteria for establishing a U2U relay connection between the source UE device and the target UE device, the candidate relay UE device should notify the source UE device without waiting for the next scheduled Model A transmission period.

Description

Priority claims

[0001] This application claims priority to U.S. Provisional Application No. 63 / 428,513, entitled "U2U RELAY RESELECTION," filed November 29, 2022, with Docket No. TPRO 00379 US, which is expressly incorporated herein by reference in its entirety. [Technical Field]

[0002] The present invention relates generally to wireless communications, and more particularly to relay reselection. [Background technology]

[0003] The sidelink relay function allows a user equipment (UE) device to connect with another UE device via a relay UE device. Summary of the Invention

[0004] The apparatus, systems, and methods described herein relate to a scenario in which a candidate relay UE device may have prior knowledge of a source UE device's interest in connecting to a particular target UE device based on a prior request from the source UE device. If the candidate relay UE device determines that the sidelink connection between the candidate relay UE device and the target UE device meets the criteria for establishing a U2U relay connection between the source UE device and the target UE device, the candidate relay UE device notifies the source UE device without waiting for the next scheduled Model A transmission period. [Brief explanation of the drawings]

[0005] [Figure 1A] 1 is a block diagram of an example system in which a source user equipment (UE) device establishes a UE-to-UE (U2U) relayed connection to a target UE device via a first relay UE device, and the second relay UE device refrains from sending a response to the U2U establishment request. [Figure 1B]1B is a block diagram of an example of the system of FIG. 1A in which the source UE device re-establishes a U2U relay connection with the target UE device via a second relay UE device. [Figure 2] FIG. 1B is a block diagram of an example of the user equipment device of FIGS. 1A, 1B, 3A, and 3B. [Figure 3A] 1 is a block diagram of an example system in which a source UE device establishes a first U2U relay connection to a first target UE device via a first relay UE device and establishes a second U2U relay connection to a second target UE device via a second relay UE device. [Figure 3B] 1 is a block diagram of an example system in which a source UE device establishes a U2U relay connection with a first target UE device and a second target UE device via a second relay UE device. [Figure 4] 10 is a flowchart of an example of a method performed in a relay UE device. DETAILED DESCRIPTION OF THE INVENTION

[0006] Many wireless communication systems employing several base stations providing wireless services to user equipment (UE) devices enable sidelink communication between two or more UE devices, allowing UE devices to communicate directly with other UE devices. In sidelink communication, the UE devices transmit data signals to each other over a communication link using cellular resources instead of through a base station. Such proximity services (ProSe) communication is sometimes referred to as device-to-device (D2D).

[0007] Additionally, one or more UE devices can be used as relay devices between the UE devices and a destination, where the relay devices forward data between the UE devices and the destination. The destination may be a communication network or another UE device (e.g., a destination UE device or a target UE device). When the destination device is another UE device, the relay function is typically referred to as UE-to-UE (U2U) relay.

[0008] The purpose of the sidelink U2U relay function is primarily to enable two remote UE devices (e.g., a source UE device and a destination UE device) to (1) connect directly when the two remote UE devices are in close proximity, or (2) establish an indirect connection via a U2U relay UE device. When two UE devices are directly connected via a U2U connection, deterioration of the radio conditions (e.g., quality) of the direct path may be indicated by the detection of a sidelink radio link failure (SL-RLF) or when the sidelink reference signal received power (SL-RSRP) measurement falls below a configured sidelink (SL) threshold. When the radio conditions of the direct path deteriorate, the source UE device may frequently require discovery of an alternative route to connect to the target UE device, with the assistance of a relay UE device. To select a relay UE device that may be used as an alternative route to the target UE device, the source UE device needs to know whether both the source UE device and the target UE device are reachable by candidate relay UE devices.

[0009] Typically, decisions for relay selection and reselection are based on discovery messages transmitted according to either a Model A discovery procedure or a Model B discovery procedure. In Model A discovery, either a source UE device or a relay UE device can announce its presence by transmitting a discovery message indicating "I'm here," and the transmitting UE device does not expect a response to the message. In some examples, Model A discovery is used by a relay UE device to periodically broadcast its availability to function as a U2U relay UE device. In a further example, the relay UE device also includes a neighbor list (NL) in the discovery message, which includes a list of UE devices that the relay UE device can reach.

[0010] In Model B discovery, either a source UE device or a relay UE device transmits a discovery message requesting "Are you there?", and a UE device that receives the discovery message containing the request may respond by transmitting a message indicating the presence of the UE device that received the discovery message. In some examples, Model B discovery is used by a source UE device to inquire of nearby relay UE devices whether it can reach a target UE device of interest. In some examples, if the relay UE device can reach the target UE device, the relay UE device is considered a candidate relay UE device for U2U relaying. In some cases, none of the relay UE devices may currently be able to reach the target UE device of interest. However, because the source UE device, target UE device, and candidate relay UE devices can all move relative to one another, this does not mean that the relay UE device will be unable to reach the target UE device at a later point in time.

[0011] While the devices, systems, and methods described herein may be utilized in any suitable relay selection and reselection scenario, there are at least two scenarios in particular that should be considered. First, after a source UE device establishes an indirect path with a target UE device via a first relay UE device, another relay UE device may better serve as an indirect path toward the target UE device due to the relative mobility of all UE devices. Second, a source UE device may be interested in connecting to two target UE devices. In such a situation, the source UE device typically utilizes two separate indirect paths to each of the respective target UE devices. The first scenario is described in more detail below with reference to FIGS. 1A-1B. The second scenario is described in more detail below with reference to FIGS. 3A-3B.

[0012] While the techniques described herein may be applied to various types of systems and communication specifications, the devices described herein operate in accordance with at least one revision of the 3rd Generation Partnership Project (3GPP) New Radio (NR) V2X communication specification. Thus, while the techniques described herein may be adopted by one or more future revisions of the communication specification, these techniques may also be applied to other communication specifications in which sidelink or D2D is employed. More specifically, the techniques may be applied to current and future releases of the 3GPP NR specification. For example, these techniques may also be applied to 3GPP NR (3GPP Rel-17) and 3GPP Rel-18.

[0013] The apparatus, systems, and methods described herein relate to a scenario in which a candidate relay UE device may have prior knowledge of a source UE device's interest in connecting to a particular target UE device based on a prior request from the source UE device. If the candidate relay UE device determines that the sidelink connection between the candidate relay UE device and the target UE device meets the criteria for establishing a U2U relay connection between the source UE device and the target UE device, the candidate relay UE device notifies the source UE device without waiting for the next scheduled Model A transmission period.

[0014] Although different examples described herein may be described separately, any of the features of any example may be added to, omitted from, or combined with any other example. Similarly, any feature of any example may be performed in parallel or in a different manner / order than described or shown herein.

[0015] As noted above, the apparatus, systems, and methods described herein are generally applicable to relay selection and reselection, but are particularly relevant to two specific scenarios. The system illustrated in Figures 1A-1B addresses a first scenario in which a source UE device establishes an indirect path with a target UE device through a first relay UE device. At a later point in time, due to changing conditions that may be based on the relative mobility of all UE devices, it is determined that another relay UE device would better serve as an indirect path toward the target UE device.

[0016] FIG. 2 is a block diagram of an example UE device 200 suitable for use as any one of the UE devices described herein. Accordingly, the UE device 200 is an example of a source UE device 102, a first relay UE device (Relay UE1) 104, a second relay UE device (Relay UE2) 106, a first target UE device (Target UE1) 108, and a second target UE device (Target UE2) 302. As shown in FIG. 2, the user equipment (UE) device 200 includes a controller 216, a transmitter 218, a receiver 214, and an antenna 212, as well as other electronics, hardware, and software code. The UE device 200 may wirelessly connect to a radio access network via a base station (not shown) that provides various radio services to the UE 200. In the example shown in FIG. 1A, the UE 104 operates in accordance with at least one revision of the 3rd Generation Partnership Project 5G New Radio (3GPP 5G NR) communication specification. In other examples, the UE 104 may operate in accordance with other communication specifications. For the examples shown in Figures 1A, 1B, 3A, and 3B, all UE devices have the same components, circuitry, and configuration as UE 200 of Figure 2. However, any of the UE devices of Figure 1A may have different components, circuitry, and configuration than UE 200 in other examples.

[0017] UE 200 is any fixed, mobile, or portable device that performs the functions described herein. The various functions and operations of the blocks described with reference to UE 200 may be implemented in any number of devices, circuits, or elements. Two or more functional blocks may be integrated into a single device, and functions described as being performed in any single device may be implemented across several devices.

[0018] The controller 216 includes any combination of hardware, software, and / or firmware for performing the functions described herein and facilitating the overall functionality of the user equipment device. An example of a suitable controller 216 includes software code running on a microprocessor or processor configuration coupled to memory. The transmitter 218 includes electronics configured to transmit wireless signals. In some situations, the transmitter 218 may include multiple transmitters. The receiver 214 includes electronics configured to receive wireless signals. In some situations, the receiver 214 may include multiple receivers. The receiver 214 and the transmitter 218 each transmit and receive signals via an antenna 212. The antenna 212 may include separate transmit and receive antennas. In some situations, the antenna 212 may include multiple transmit and receive antennas.

[0019] The transmitter 218 and receiver 214 in the example of FIG. 2 perform radio frequency (RF) processing, including modulation and demodulation. Accordingly, the receiver 214 may include components such as a low noise amplifier (LNA) and a filter. The transmitter 218 may include a filter and an amplifier. Other components may include an isolator, a matching circuit, and other RF components. These components, in combination with or in cooperation with other components, perform user equipment device functions. The required components may depend on the specific functions required by the user equipment device.

[0020] The transmitter 218 includes a modulator (not shown), and the receiver 214 includes a demodulator (not shown). The modulator can apply any one of a plurality of modulation orders to modulate the signal transmitted by the transmitter 218. The demodulator demodulates the received signal according to one of a plurality of modulation orders.

[0021] 1A is a block diagram of an example system in which a source user equipment (UE) device establishes a UE-to-UE (U2U) relay connection to a target UE device through a first relay UE device, and the second relay UE device refrains from responding to requests from the source UE device. For simplicity, FIG. 1A shows only one source UE device 102, two relay UE devices 104 and 106, and one target UE device 108. However, other examples may utilize any number of source, relay, and target UE devices.

[0022] The source UE device 102 may also be referred to herein as a source UE, a source wireless communication device (WCD), or a source remote UE device. The relay UE devices 104 and 106 may also be referred to herein as relay UEs or relay WCDs. The target UE device 108 may also be referred to herein as a target UE, a target WCD, a destination UE device, a destination UE, or a destination WCD. Additionally, any of the UE devices herein may be described as D2D devices if they transmit data signals to each other over a communication link using cellular resources instead of communicating via a base station.

[0023] 1A, a source UE 102 in the system 100 sends a request message 109 to a target UE 108 indicating a request to establish a UE-to-UE (U2U) relay connection. Relay UE1 104 receives the request message over a sidelink connection 110. Relay UE2 106 receives the request message over a sidelink connection 112.

[0024] In some examples, the request message 109 is a direct communication request message. In other examples, the request message 109 is a Model B discovery request message. In examples in which the request message 109 is a Model B discovery request message, a relay UE device that receives a Model B query from a source UE device transmits its own discovery message to a target UE device identified in the Model B discovery request message received from the source UE device. If the target UE device responds to the discovery message transmitted by the relay UE device, the relay UE device is considered to be "reachable" for the target UE device. In conventional systems, the relay UE device transmits a discovery message response to the source UE device indicating that the relay UE device is reachable for the target UE device.

[0025] In the example shown in FIG. 1A , the controller 216 of relay UE1 104 determines, based on the signal 113 received from the target UE 108, that the sidelink connection 114 from relay UE1 104 to the target UE 108 meets the criteria for establishing a U2U relayed connection. As described above, in some examples, the signal that relay UE1 104 receives from the target UE 108 is a Model B discovery response message. In other examples, the signal 113 that relay UE1 104 receives from the target UE 108 is a sidelink reference signal or a discovery message (e.g., a Model A discovery message) transmitted from the target UE 108. After making the determination, relay UE1 104 transmits, via its transmitter 218 and antenna 212, a response message 115 to the source UE 102 indicating that relay UE1 104 is capable of facilitating the U2U relayed connection to the target UE 108. In this way, relay UE1 104 informs source UE 102 that relay UE1 104 can "reach" target UE 108. Thus, in this example, if link 114 meets the criteria, the target is considered reachable.

[0026] In the example shown in FIG. 1A, the controller 216 of the relay UE2 106 determines that the sidelink connection 118 from the relay UE2 106 to the target UE 108 does not meet the criteria for establishing a U2U relay connection based on a measurement of the signal 116 received from the target UE 108. In some examples, the measurement of the signal received from the target UE 108 is either a sidelink discovery reference signal received power (SD-RSRP) level measurement or a sidelink reference signal received power (SL-RSRP) level measurement. In further examples, the minimum sidelink quality threshold level is configured or pre-configured in the relay UE device. In some of these examples, the minimum sidelink quality threshold level is a minimum SD-RSRP level or a minimum SL-RSRP level. In further examples, the relay UE device may receive sidelink threshold configuration information indicating the minimum sidelink quality threshold level. In still further examples, the sidelink threshold configuration information is transmitted to the relay UE device by another UE device or a base station (not shown). In some examples, the relay UE device uses the minimum sidelink quality threshold level to determine whether the relay UE device is reachable by the target UE device. More specifically, in these examples, a minimum sidelink quality threshold level needs to be met before "reachability" is assumed.

[0027] In response to determining that the sidelink connection from Relay UE2 106 to the target UE 108 does not meet the criteria for establishing a U2U relay connection, Relay UE2 106 does not respond to the request message received from the source UE 102. Thus, for the example of FIG. 1A , a Model B discovery response 120 (or any other signal indicating reachability to the target UE 106) is not sent to the source UE 102.

[0028] The source UE 102 evaluates the response message received from the relay UE1 104 (and any other response messages received from other relay UE devices). Based on the response messages received from the relay UE devices, the source UE 102 utilizes its controller 216 to select / reselect a relay UE device to establish a U2U relayed connection to the target UE 108. In the example shown in FIG. 1A, the source UE 102 selects / reselects the relay UE1 104 and establishes a U2U relayed connection to the target UE 108 via the relay UE1 104. In the example shown in FIG. 1A, the U2U relayed connection between the source UE 102 and the target UE 108 includes a sidelink connection 110 and a sidelink connection 114. In some examples, the sidelink connection 110 and the sidelink connection 114 are both PC5 connections.

[0029] While the relay UE2 106 previously refrained from responding to the request message received from the source UE 102, the relay UE2 106, using its controller 216, (1) monitors the sidelink connection from the relay UE2 106 to the target UE 108 and (2) determines that the sidelink connection from the relay UE2 106 to the target UE 108 has changed such that the sidelink connection meets the criteria for establishing a U2U relay connection. In some examples, the sidelink connection from the relay UE2 106 to the target UE 108 changes due to the movement of one or more UE devices relative to one another. In other examples, the sidelink connection from the relay UE2 106 to the target UE 108 changes based on the movement of one or more obstacles and / or interference sources that affect the transmission / reception of signals by the UE devices.

[0030] FIG. 1B is a block diagram of an example of the system of FIG. 1A in which the source UE device re-establishes a U2U relayed connection with the target UE device via a second relay UE device, or otherwise switches to a U2U relayed connection via a second relay UE device. For example, conditions change such that the quality of the sidelink 118 improves to meet a criterion. In the example shown in FIG. 1B, the UE devices are moving relative to each other such that relay UE2 106 is "reachable" to target UE 108. The receiver 214 of the relay UE receives a signal 122 from the target UE 108, which is used to determine that the quality of the sidelink 118 meets a criterion. In response to determining that the sidelink connection 118 from relay UE2 106 to the target UE 108 meets the criteria, relay UE2 106 utilizes its transmitter 218 and antenna 212 to transmit a notification message 124 to the source UE 102 prior to the next scheduled Model A discovery message, indicating that the sidelink connection 118 from relay UE2 106 to the target UE 108 meets the criteria.

[0031] In some examples, the notification message is a Model A discovery message. In examples where the notification message is a Model A discovery message, the Model A discovery message may include the target UE 108 in a neighbor list, which is a list of one or more target UE devices each having a communication link with the relay UE2 106 whose quality level meets or exceeds a minimum sidelink quality threshold level. In still further examples, the discovery message sent from the relay UE2 106 to the source UE 102 may also include sidelink quality measurements of each of the reachable target UE devices. In some of these examples, the sidelink measurements may be SD-RSRP measurements or SL-RSRP measurements.

[0032] In some examples, whether a relay UE device is already PC5 connected to a target UE device may affect relay selection / reselection. This situation may occur if another source UE device also desires to connect to the same target UE device through one of the candidate relay UE devices, which is why a PC5 connection to the target UE device may already be established. Thus, in some examples, if two candidate relay UE devices can reach the target UE device (e.g., as indicated by the contents of their respective neighbor lists), the source UE device should select the relay UE device that is already PC5 connected to the target UE device. Thus, in other examples, the notification message sent from relay UE2 106 to source UE 102 also includes an indication that relay UE2 106 is connected to target UE 108 via a PC5 connection. In a further example, the notification message is a discovery message (e.g., either a Model A Response or a Model B Response) that includes a flag (e.g., a bit indicator) indicating whether relay UE2 106 is connected to target UE 108 via a PC5 connection.

[0033] In yet another example, if it is determined that the sidelink connection 118 from relay UE2 106 to the target UE 108 meets the criteria for establishing a U2U relayed connection between the source UE 102 and the target UE 108, the relay UE2 106 may already be facilitating another U2U relayed connection from the source UE 102 to another target UE device (not explicitly shown in FIGS. 1A-1B). In these examples, while the relay UE2 106 is facilitating another U2U relayed connection from the source UE 102 to the other target UE device, the relay UE2 106 sends a notification message to the source UE 102 (indicating that the sidelink connection 118 from relay UE2 106 to the target UE 108 meets the criteria). Furthermore, in some of these examples, the notification message may be a PC5 radio resource control (PC5-RRC) message sent from relay UE2 106 to the source UE 102 rather than a discovery message.

[0034] In response to receiving the notification message from relay UE2 106, source UE 102 utilizes its controller 216 to re-establish a U2U relayed connection with target UE 108 via relay UE2 106. In the example shown in FIG. 1B , the U2U relayed connection between source UE 102 and target UE 108 includes sidelink connection 112 and sidelink connection 118. In some examples, both sidelink connection 112 and sidelink connection 118 are PC5 connections.

[0035] 1A-1B, when a source UE device selects / reselects a relay UE device for an indirect path (e.g., a U2U relay connection) to a target UE device, it may still be advantageous for other, non-selected candidate relay UE devices to transmit discovery messages. For example, even if the source UE device has not transmitted a Model B discovery query, another, non-selected candidate relay UE device may be closer to the target UE device than the previously selected relay UE device. Because a candidate relay UE device may have prior knowledge of a source UE device's interest in connecting to a particular target UE device based on a previous Model B discovery query from the source UE device, in some examples, the candidate relay UE device should transmit a Model A discovery message as soon as the interested target UE device exceeds the SD-RSRP / SL-RSRP threshold, without waiting for the next scheduled Model A transmission period.

[0036] 3A is a block diagram of an example system 100 in which a source UE device 102 establishes a first U2U relayed connection to a first target UE device 108 via a first relay UE device and a second U2U relayed connection to a second target UE device 302 via a second relay UE device 106. The source UE device 102 transmits one or more request messages 304 requesting to establish a UE-to-UE (U2U) relayed connection to the target UE 108 and a UE-to-UE (U2U) relayed connection to the target UE 302. Relay UE1 104 receives the request messages via a sidelink connection 110. Relay UE2 106 receives the request messages via a sidelink connection 112.

[0037] 3A , relay UE1 104 determines that the sidelink 114 to the first target UE (UE1) 108 meets the criteria, but the sidelink (not shown) to the second target UE (target UE2) 302 does not. Also, relay UE2 106 determines that the sidelink 306 to the second target UE (UE2) 302 meets the criteria, but the sidelink 118 to the first target UE (UE1) 308 does not. Consequently, according to the techniques described above, a first U2U relayed connection is established to the first target UE device (target UE1) 108 via the first relay UE device (relay UE1), and a second U2U relayed connection is established to the second target UE device (target UE2) 302 via the second relay UE device (relay UE2) 106. Because the sidelink 118 did not meet the criteria, the second relay UE device (relay UE2) does not send a response to the source UE 102 for the request 304 to establish a U2U connection to the first target device (target UE1) 108. However, the second relay UE device (relay UE2) 106 retains information related to the request 304 while refraining from sending a response.

[0038] Although the source has established connections to target UE devices 108 and 302, as well as UE2 302, having two separate indirect paths to each of the target UE devices (e.g., target UE1 108 and target UE2 302) can be disadvantageous. For example, in some cases, the complexity of handling two relay UE devices may be higher than handling one relay UE device. More specifically, when handling two relay UE devices, the increased complexity may be associated with monitoring four hops (e.g., two indirect paths, each with two hops). In comparison, when handling one relay UE device, only three hops need to be monitored (e.g., one hop from the source UE to the relay UE and one hop from the relay UE to each of the two target UEs). In other cases, the number of relay UEs to which the source UE may connect may be limited. Therefore, there are advantages to a source UE device utilizing a single relay UE device to establish U2U relay connections with multiple target UE devices. In the examples herein, the relay UE device maintains information regarding the request 304 and facilitates connection to both target UE devices via a single relay device if conditions allow for such establishment.

[0039] 3A-3B illustrate an example where it is preferable to have a single relay UE device facilitating U2U relay connections to multiple target UE devices, and where a candidate relay UE device maintains knowledge of a source UE device's interest in establishing relay connections to one or more target UE devices. For example, after a source UE device establishes one or more U2U relay connections (either via a single relay UE device or via multiple relay UE devices), if a single candidate relay UE device is within range of both target UE devices, another candidate relay UE device (e.g., either a new or existing relay UE device) may be better suited to connect to the target UE device.

[0040] In the example of FIG. 3A, the source UE 102 transmits request messages indicating a request to establish a first UE-to-UE (U2U) relayed connection to target UE1 108 and a request to establish a second U2U relayed connection to target UE2 302. Relay UE1 104 receives the request messages over the sidelink connection 110. Relay UE2 106 receives the request messages over the sidelink connection 112. The request 304 may be transmitted in a single request message or in two different request messages. If two request messages are transmitted, the messages may be transmitted simultaneously or at different times. The requests are received by both the relay UE device 104 and the relay UE device 106.

[0041] Using its controller 216, the relay UE2 106, in response to determining that the sidelink connection from relay UE2 106 to target UE1 108 does not meet the criteria for establishing a U2U relay connection, refrains from responding to a request message to establish a U2U connection to the first target UE device (target UE1) 108, but responds to a request to establish a U2U connection to the second relay UE device (relay UE2) 302. In this example, the relay UE2 106 evaluates the signal 308 from target UE2 302 and determines that the sidelink 306 meets the criteria. The relay UE2 106 further uses its controller 216 to monitor the sidelink connection 118 from relay UE2 106 to target UE1 108. In other circumstances, the relay UE2 106 also determines that the sidelink 306 does not meet the criteria and does not respond to any requests from the source UE 102. In such a situation, relay UE2 106 further uses its control unit 216 to monitor (1) the sidelink connection from relay UE2 106 to target UE1 108 and (2) the sidelink connection from relay UE2 106 to target UE2 302.

[0042] 3B, the conditions have changed such that the sidelink 306 meets the criteria, causing relay UE2 106 to send a notification 124 to the source UE 102. Based on measurements of the signal 122 from target UE1 108, a controller within relay UE2 determines that the sidelink 118 meets the criteria. In response to determining that the sidelink connection 118 from relay UE2 106 to the target UE 108 meets the criteria, relay UE2 106 utilizes its transmitter 218 and antenna 212 to send a notification message 124 to the source UE 102 prior to the next scheduled Model A discovery message, indicating that the sidelink connection 118 from relay UE2 106 to the target UE 108 meets the criteria.

[0043] In some examples, the notification message is a Model A discovery message. In examples where the notification message is a Model A discovery message, the Model A discovery message may include the target UE 108 in a neighbor list, which is a list of one or more target UE devices each having a communication link with the relay UE2 106 whose quality level meets or exceeds a minimum sidelink quality threshold level. In still further examples, the discovery message sent from the relay UE2 106 to the source UE 102 may also include sidelink quality measurements of each of the reachable target UE devices. In some of these examples, the sidelink measurements may be SD-RSRP measurements or SL-RSRP measurements.

[0044] In some circumstances, as described above, relay UE2 106 may determine that the sidelink to both target UE device 108 and target UE device 302 does not meet the criteria. In such circumstances, relay UE2 106 refrains from responding to the request message in response to (1) determining that the sidelink connection from relay UE2 106 to target UE1 108 does not meet the criteria for establishing a U2U relay connection and (2) determining that another sidelink connection 306 to target UE2 302 does not meet the criteria for establishing a U2U relay connection. The relay UE2 106 further uses its control unit 216 to (1) monitor the sidelink connection from relay UE2 106 to target UE1 108, (2) monitor the sidelink connection from relay UE2 106 to target UE2 302, and (3) determine that the sidelink connection from relay UE2 106 to target UE1 108 and the sidelink connection from relay UE2 106 to target UE2 302 have changed such that the sidelink connection from relay UE2 106 to target UE1 108 and the sidelink connection from relay UE2 106 to target UE2 302 meet the criteria for establishing the requested U2U relay connection.

[0045] In response to determining that the sidelink connection from relay UE2 106 to target UE1 108 and from relay UE2 106 to target UE2 302 meets the criteria, relay UE2 106 sends a notification message indicating that the sidelink connection from relay UE2 106 to target UE1 108 and from relay UE2 106 to target UE2 302 meets the criteria. In response to receiving the notification message from relay UE2 106, source UE 102, utilizing its controller 216, re-establishes the U2U relayed connection with target UE1 108 via relay UE2 106. Source UE 102 also, utilizing its controller 216, establishes a U2U relayed connection with target UE2 302 via relay UE2 106. In the example shown in FIG. 3B, the U2U relay connection between source UE 102 and target UE 1 108 includes sidelink connection 112 and sidelink connection 118, and the U2U relay connection between source UE 102 and target UE 2 302 includes sidelink connection 112 and sidelink connection 306.

[0046] Thus, in some examples, if a single candidate relay UE device can reach both the target UE 108 and the target UE 308, the candidate relay UE device should send a notification message (e.g., a Model A Discovery message) to the source UE device. If the candidate relay UE device can reach both target UE devices is already one of the source UE device's existing relay UE devices, the candidate relay UE device may also notify the source UE device via a PC5-RRC message rather than via a Discovery message.

[0047] 4 is a flowchart of an example of a method performed in a relay UE device. In this example, the method may be performed by relay UE 1 104.

[0048] In step 402, the relay UE device receives a request message from the source UE device indicating a request to establish a U2U relayed connection to the target UE device. In step 404, the relay UE device refrains from responding to the request message in response to determining that the sidelink connection from the relay UE device to the target UE device does not meet the criteria for establishing a U2U relayed connection. In step 406, the relay UE device monitors the sidelink connection from the relay UE device to the target UE device and determines that the sidelink connection has changed such that the sidelink connection meets the criteria. In step 408, the relay UE device transmits a notification message to the source UE device indicating that the sidelink connection meets the criteria, prior to the next scheduled Model A Discovery message, in response to determining that the sidelink connection meets the criteria.

[0049] In other examples, one or more steps of method 400 may be omitted, combined, performed in parallel, or performed in a different order than described herein or illustrated in Figure 4. In still further examples, additional steps may be added to method 400 that are not explicitly described in connection with the example illustrated in Figure 4.

[0050] Clearly, other embodiments and modifications of the present invention will occur readily to those skilled in the art in view of these teachings. The foregoing description is illustrative, not limiting. The present invention is to be limited only by the scope of the following claims, which include all such embodiments and modifications when viewed in conjunction with the above specification and accompanying drawings. The scope of the present invention should, therefore, be determined not with reference to the above description, but should instead be determined with reference to the appended claims along with their full scope of equivalents.

Claims

1. A relay user equipment (UE) device, comprising: a receiver configured to receive a request message from a source UE device, the request message indicating a request to establish a UE-to-UE (U2U) relay connection to a target UE device; a controller configured to refrain from responding to the request message in response to determining that a sidelink connection from the relay UE device to the target UE device does not meet a criterion for establishing the U2U relay connection, the controller being configured to monitor the sidelink connection and determine that the sidelink connection has changed such that it meets the criterion; and a transmitter configured to, in response to the determination that the sidelink connection satisfies the criteria, send a notification message to the source UE device indicating that the sidelink connection satisfies the criteria, before a next scheduled Model A discovery message; A relay user equipment (UE) device comprising:

2. The relay UE device of claim 1 , wherein the transmitter is configured to transmit the notification message while facilitating another U2U relay connection from the source UE device to another target UE device.

3. The relay UE device of claim 1 , wherein the notification message is a Model A discovery message.

4. The relay UE device of claim 3 , wherein the Model A discovery message includes the target UE device in a neighbor list.

5. The relay UE device of claim 1 , wherein the request message is a direct communication request message.

6. The relay UE device of claim 1 , wherein the request message is a Model B discovery request message.

7. the request message further indicates a request to establish another U2U relay connection to another target UE device; the controller is configured to refrain from responding to the request message in response to a determination that the sidelink connection from the relay UE device to the target UE device does not satisfy a criterion for establishing the U2U relay connection and a determination that another sidelink connection to another target UE device does not satisfy a criterion for establishing the another U2U relay connection; and the controller is configured to monitor the sidelink connection and the another sidelink connection and determine that the sidelink connection and the another sidelink connection have changed such that the sidelink connection and the another sidelink connection satisfy the criterion. the transmitter is configured to, in response to determining that the sidelink connection and the further sidelink connection satisfy the criteria, transmit the notification message indicating that the sidelink connection and the further sidelink connection satisfy the criteria. The relay UE device of claim 1 .

8. 2. The relay UE device of claim 1, wherein the receiver is configured to receive a signal transmitted from the target UE device, and the controller is configured to determine, based on measurements of the signal, that the sidelink connection from the target UE device to the relay UE device does not meet the criterion.

9. 9. The relay UE apparatus of claim 8, wherein the measurement of the signal is either a Sidelink Discovery Reference Signal Received Power (SD-RSRP) level measurement or a Sidelink Reference Signal Received Power (SL-RSRP) level measurement.

10. The relay UE device of claim 1 , wherein the notification message includes an indication that the relay UE device is connected to the target UE device via a PC5 connection.

11. The relay UE device of claim 1 , wherein the notification message is a PC5 Radio Resource Control (PC5-RRC) message sent to the source UE device.

12. A source user equipment (UE) device, comprising: a transmitter configured to transmit a request message to a first relay UE device and a second relay UE device, the request message indicating a request to establish a UE-to-UE (U2U) relay connection to a target UE device; a receiver configured to receive a response message from the first relay UE device indicating that the first relay UE device is able to facilitate the U2U relay connection to the target UE device; a controller configured to establish the U2U relay connection with the target UE device via the first relay UE device; Equipped with the receiving unit is further configured to receive a notification message from the second relay UE device indicating that a sidelink connection between the second relay UE device and the target UE device satisfies a criterion for establishing the U2U relay connection; and the controller is further configured to re-establish the U2U relay connection with the target UE device via the second relay UE device in response to the notification message. A source user equipment (UE) device.

13. 13. The source UE device of claim 12, wherein the receiver is configured to receive the notification message before a next scheduled Model A discovery message is transmitted by the second relay UE device.

14. 13. The source UE device of claim 12, wherein the receiver is configured to receive the notification message while the second relay UE device is facilitating another U2U relay connection from the source UE device to another target UE device.

15. The source UE device of claim 12 , wherein the notification message is a Model A discovery message.

16. The source UE device of claim 15 , wherein the Model A discovery message includes the target UE device in a neighbor list.

17. The source UE device of claim 12 , wherein the request message is a direct communication request message.

18. The source UE device of claim 12 , wherein the request message is a Model B discovery request message.

19. the request message further indicates a request to establish another U2U relay connection to another target UE device; the receiver is configured to receive, from the second relay UE device, a notification message indicating that the sidelink connection and another sidelink connection between the second relay UE device and the other target UE device satisfy the criteria, the notification message being transmitted in response to a determination that the sidelink connection and the other sidelink connection satisfy the criteria. The source UE device of claim 12.

20. The source UE device of claim 12 , wherein the notification message includes an indication that the second relay UE device is connected to the target UE device via a PC5 connection.

21. The source UE device of claim 12 , wherein the notification message is a PC5 Radio Resource Control (PC5-RRC) message sent to the source UE device.

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