Relay device management using neighbor lists

Abstract

To provide a source user equipment (UE) device that identifies a UE device that can provide relay functionality, either alone and / or with the assistance of a network.SOLUTION: In a communication system, a source UE device receives a neighbor list from each of a plurality of neighbor UE devices where each neighbor list identifies proximate UE devices that are within communication range of the neighbor UE device transmitting the neighbor list. The source UE device selects, from the plurality of neighbor UE devices, at least one candidate relay device for relaying destination device data to a destination UE device. The selection is at least partially based on the received neighbor lists. The destination device data and a relay indicator are transmitted to the at least one candidate relay device. The relay indicator indicates that the at least one candidate device is to transmit the destination device data to the destination UE device.SELECTED DRAWING: Figure 1B

Description

Claiming priority

[0001] This application claims the benefit of priority to Provisional Application No. 63 / 066601, "Device-to-Device Relaying based on Neighbor List Broadcast," filed on August 17, 2020, Docket No. TPRO 00350 US, which is assigned to the assignee of this application and is expressly incorporated by reference in its entirety. [Technical field]

[0002] The present invention relates generally to wireless communications, and more particularly to wireless communications links that use relay devices.

[0003] This application is related to patent application serial no. TUTL 00350B PC, entitled "RELAY DEVICE MANAGEMENT BASED ON DATA PRIORITY LEVEL," and patent application serial no. TUTL 00350C PC, entitled "RELAY DEVICE MANAGEMENT USING NEIGHBOR LISTS WITH LINK QUALITY INDICATION," which are filed concurrently herewith and are hereby incorporated by reference in their entireties. [Background technology]

[0004] Many wireless communication systems using several base stations providing wireless services to user equipment (UE) devices enable sidelink communication between two or more UE devices, where the UE devices can directly communicate with other UE devices. In addition, one or more UE devices can be used as relay devices between a source UE device and a destination UE device. The relay device forwards data received from the source UE device to the destination UE device. Some conventional systems facilitating device-to-device transmission employ ad-hoc networks in which wireless devices autonomously select communication resources for transmission. For example, in the current NR V2X (5G NR Rel-16 V2X) Mode 2 communication standard, each vehicle-to-vehicle wireless communication device autonomously selects a time slot / frequency sub-band resource for data transmission. Such techniques can be used in time division multiple access (TDMA) schemes, as well as other access schemes such as orthogonal frequency division multiple access (OFDMA)-TDMA-based 5G NR V2X. In TDMA-based vehicular ad-hoc networks (VANETs), the autonomous selection of time slots for data transmission causes collisions when two or more devices select the same time slot for transmission. Collisions are reduced by sensing and / or decoding of the control channel based on energy sensing. Summary of the Invention

[0005] A source user equipment (UE) device receives a neighbor list from each of a plurality of neighboring UE devices. Each neighbor list identifies nearby UE devices that are within communication range of the neighboring UE device transmitting the neighbor list. The source UE device selects at least one candidate relay device from the plurality of neighboring UE devices for relaying destination device data to the destination UE device. The selection is based at least in part on the received neighbor list. The destination device data and a relay indicator are transmitted to the at least one candidate relay device. The indicator indicates that the at least one candidate device transmits the destination device data to the destination UE device. [Brief description of the drawings]

[0006] [Figure 1A]FIG. 1A is a block diagram of an example of a communication system including multiple user equipment (UE) devices and two base stations.

[0007] [Figure 1B] FIG. 1B is a block diagram of the communication system for the example of FIG. 1A after the neighbor list message has been received at the source UE device.

[0008] [Figure 1C] FIG. 1C is a block diagram of an example communication system in which a candidate has previously reserved communication resources.

[0009] [Diagram 2] FIG. 2 is a block diagram of an example of a base station suitable for use as each base station.

[0010] [Diagram 3] FIG. 3 is a block diagram of an example of a UE device suitable for use as each of the UE devices.

[0011] [Figure 4A] 4A is a message flow diagram of an example in which a source UE device selects a candidate relay device based at least in part on a neighbor list received from a UE device, the relay UE device being configured with distance-based HARQ feedback (NACK only) by the source UE device.

[0012] [Figure 4B] 4B is a message flow diagram of an example in which a source UE device selects a candidate relay device based at least in part on a neighbor list received from a UE device, the relay UE device being configured with HARQ feedback of ACK / NACK by the source UE device.

[0013] [Diagram 5] FIG. 5 is a flow diagram of an example method for managing relay transmissions at candidate relay devices.

[0014] [Figure 6] FIG. 6 is a flow chart of a method for sending relay transmissions at a candidate relay device.

[0015] [Figure 7] FIG. 7 is a flow chart of an example method for managing relay transmissions at a source UE device.

[0016] [Figure 8] FIG. 8 is a block diagram of an example geographical deployment of a UE device and a corresponding neighbor list containing link quality information associated with the deployment.

[0017] [Figure 9] FIG. 9 is a block diagram of a system for an example neighbor list that includes communication link quality information.

[0018] [Figure 10] FIG. 10 is a flow chart of an example of a method performed in a source UE device for selecting candidate relay devices based on a ranked neighbor list. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] As described above, a relay device relays data and control information between a source UE device and a destination UE device. In conventional systems, a relay device self-declares relay capability and / or a communication network identifies UE devices that can provide relay capability. However, in the examples herein, the source UE, alone and / or with the assistance of the network, identifies candidate relay devices and transmits destination device data and an indicator to at least one candidate relay device. The indicator indicates that the candidate relay device forwards destination device data to the destination device. In some circumstances, the indicator may also reserve communication resources for transmission of destination device data from the candidate relay device. For at least some of the examples described herein, the source UE device selects a candidate relay device based on a neighbor list provided by the UE device. In at least one example, the neighbor list includes link information to nearby UE devices in the list from which the source UE device selects a candidate relay device based at least in part on the link information. The link information may include information related to link quality, such as link quality and distance to the nearby device. In some circumstances, each of the device identifiers in the neighbor list is associated with one rank of a plurality of ranks indicative of the link information.

[0020] FIG. 1A is a block diagram of an example of a communication system 100 including multiple user equipment (UE) devices 101-107 and two base stations 108, 110. While the techniques described herein may be applied to various types of systems and communication specifications, the example devices described above operate in accordance with at least one revision of the 3GPP (registered trademark) 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 be applied to other communication specifications in which sidelink or D2D (Device to Device) are adopted. More specifically, these 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 (Release 17). For example, the UE devices 101-107 may be any type of device capable of receiving signals from and transmitting signals to base stations and other UE devices. The UE devices operate in a communication system including multiple base stations 108, 110. Each of a number of base stations 108, 110 provides wireless service within a service area. As shown in FIG. 1, UE devices 101-107 may be served by any of the base stations and may pass between base stations according to known handover techniques. Thus, even though two or more UE devices are communicating with each other using a sidelink connection, each of the UE devices 101-107 may be served by a different base station. In some circumstances, the UE devices may be in IDLE mode with respect to the base station when communicating using the sidelink.

[0021] For example, the source UE device 101 transmits destination device data to the destination UE device 102 via at least one relay UE device. As described in more detail below, the source UE device 101 selects candidate relay devices 103, 104, 105 from the nearby UE devices 103-107 based on neighbor list messages 112, 114, 116, 118 received from at least some of the nearby UE devices or from the network. In one scenario, the UE device periodically broadcasts a neighbor list message that includes a list of identifiers (IDs) of nearby UE devices from which the UE device has successfully received a broadcast transmission, such as a discovery message. For example, the neighbor list includes device identifiers (IDs) of UE devices whose broadcast transmissions have been successfully received within the previous S time slots, where S is a network-wide parameter known to all devices. In some situations where a PC5 connection is established between the UE device and the source UE device, the neighbor list is transmitted to the source UE device via a unicast link. Thus, the UE device is able to transmit broadcast transmissions and The neighboring UE devices may be notified by a unicast transmission or / and the neighbor list may include the ID of the UE device transmitting the neighbor list. In a situation where half-duplex is used for communication, each UE device broadcasts the neighbor list if there are no other neighboring devices transmitting using the same resource. In one example, each UE device first finds an unused time slot and then broadcasts the neighbor list message. After the broadcasted neighbor list is received, the neighboring UE devices assume that the same device periodically rebroadcasts in the same time slot. In the example of FIG. 1A, the neighbor lists 112, 114, 116 from the UE devices 103-105 include the device identifier (ID2) of the destination UE device 102. However, the neighbor list 118 broadcast from the UE device 106 does not include ID2. Such a situation may occur, for example, when the signal strength of the broadcast detection signal or neighbor list message transmitted from the UE device 106 is below a minimum threshold. Using the neighbor list, the source UE device 101 can identify all of its immediate neighbors (approaching UE devices) and the immediate neighbors of its immediate neighbors (nearby UE devices). When an updated neighbor list is received, the source UE device updates the maintained information with new additions or deletions of neighbor UE device IDs and neighbor UE device IDs of neighbors. As described herein, a "UE device" refers to any UE device. A "potential candidate relay device" refers to a UE device that may be considered by the source UE device to be a candidate relay device. A "candidate relay device" is a UE device selected by the source UE device to perform the function of a relay between the source UE device and the destination device. A "relay UE device" is a UE device that is at least attempting to perform the relay function. An approaching UE device is a neighbor UE device of a UE device that generates a neighbor list that includes that neighbor UE device in the neighbor list. Thus, any particular UE device may be referred to by different terms depending on the stage of the relay device selection and transmission process and the neighbor list generation and transmission process.

[0022] As described herein, neighbor list transmissions also include transmissions containing sensing data collected by a UE device and provided to nearby UE devices. Such transmissions may be in response to requests from nearby UE devices. For example, each UE device may "sense" their neighbors using energy detection and / or decoding of control information and then broadcast the results and / or provide the results directly to a requesting UE device in response to a request from the requesting UE device.

[0023] In some situations, the neighbor list, or at least some information related to the neighbor list, is provided by the network to a UE device, such as a source UE device. In one scenario, the network maintains location information for each UE device and creates a neighbor list for a particular UE based on the location information. The network then forwards the neighbor list to the UE device via a transmission from the base station. A network-generated neighbor list 119 is illustrated in FIG. 1A. The neighbor list 119 is indicated by a dashed line as being optional. In another scenario, the network periodically broadcasts a list of UE devices detected in the area to all UE devices located in the same area. In one example, the network neighbor list 119 includes a list of neighbor UE devices for the source UE device and neighbor UE devices. The neighbor UE devices are for each UE device listed in the neighbor list. Thus, the source UE device can determine which neighbor UE devices have the destination UE device as a neighbor from such neighbor list. In another example, the network neighbor list identifies possible candidate relay devices, and the source UE device requests neighbor lists from these possible candidate relay devices. In one such example, the network may identify suitable possible candidate relay devices in response to a request from a source UE device. After receiving neighbor lists from the possible candidate relay devices, the source identifies a neighbor list that includes the destination UE device as a neighbor UE device and selects a candidate relay device.

[0024] FIG. 1B is a block diagram of the example communication system 100 of FIG. 1A after the source UE device 101 receives the neighbor list messages 112, 114, 116, 118. The source UE device 101 evaluates the information provided by the neighbor list messages 112, 114, 116, 118 and selects candidate relay devices. In FIGS. 1A and 1B, the source UE device selects the three UE devices 103, 104, 105 as candidate relay devices. Because the three neighbor list messages 112, 114, 116 sent from the three UE devices 103, 104, 105 included the ID of the destination device (ID2), the source UE device determines that the three base stations 103, 104, 105 will relay (forward) the destination device data 120 to the destination UE device 102. ) are suitable candidates for a relay. As described below, additional criteria may be used by the source UE device 101 in selecting a candidate relay. In some situations, for example, information related to the proximity of the destination UE device to each UE device may be provided in a neighbor list from which the source UE device selects candidate relays based on proximity. Other criteria may also be evaluated.

[0025] The source UE device transmits a transmission 122 including destination device data 120 and control information 124. The destination device data 120 is data that the source UE device intends to be delivered to the destination UE device 102. The control information 124 includes at least a relay indicator that indicates to each candidate relay device that the destination device data 120 should be relayed to the destination UE device. In some circumstances, the transmission 122 includes multiple transmissions. For example, at least some of the control information 124 is transmitted in a transmission other than the transmission including the destination device data. The relay indicator may be communicated to the candidate relay devices during establishment of a unicast (PC5) connection prior to the transmission of the destination device data. The relay indicator may be transmitted in a direct communication request message (PC5-S) that initiates the unicast link establishment procedure. The relay indicator may include at least an ID of the destination UE device and may include some information indicating that the candidate relay device should transmit the destination device data to the destination UE device. The relay indicator may be implicit in some circumstances. An example of a suitable technique for transmitting the relay indicator includes techniques used in conventional systems, except that the relay indicator indicates to the candidate relay device that it has been selected as a relay device. An example of a suitable technique includes using a one-bit control field where the presence of a flag indicates that the candidate relay device will relay the destination device data. The indicator can also be implicit. In some scenarios, for example, the inclusion of a destination device ID in a source transmission indicates that the destination device data will be relayed. Thus, the presence of a destination UE device ID in a transmission received at a candidate relay device can form a relay indicator in some situations.

[0026] In some situations, the control information 124 also includes a reservation of communication resources. In an example of such a situation, the reservation of communication resources and the relay indicator are directed to the candidate relay devices 103, 104, 105, while the reservation of communication resources is directed to all nearby UE devices. The nearby UE devices include UE devices that can receive the transmission of the control information 124 and may include UE devices that provided a neighbor list but were not selected as a candidate relay device. The nearby devices may also include other UE devices, such as devices that have recently entered an area near the source UE device and UE devices that did not transmit a neighbor list message. In some situations, for example, the UE device refrains from transmitting a neighbor list message but instead broadcasts a discovery signal or message to all neighbor devices. The other UE devices receive the broadcast and detect the presence of the broadcasting UE device. A device that is interested in becoming a relay device detects the discovery message, compiles the information in the message, and broadcasts a neighbor list message. Thus, in the example of FIG. 1B, the reservation of communication resources is directed to the UE device from which the neighbor list was received, but also to any other UE devices that are within range of the control signal.

[0027] The reservation of communication resources reserves communication resources 126, which may be, for example, one or more time slots in a particular channel or a particular frequency. For example, the reservation of communication resources is performed according to the techniques for reserving resources defined in the 5G NR V2X Mode-2 communication specification, except that the reservation is not for future transmissions from the UE device transmitting the reservation (the source UE device), but rather for one or more other UE devices (the relay devices), which are for transmission to the destination UE device. For example, when applying the NR V2X physical layer design, the reservation of the relayed data is transmitted as part of the second stage sidelink control information (SCI). The second stage SCI consists of the location of the reserved resource, the destination device ID, the priority, and the MCS of the relayed transmission (if different from the source to relay transmission). In some situations, the reservation of communication resources is omitted. In other situations, the reservation of communication resources is dynamically determined by the source UE device. In yet another situation, the network may dynamically determine when a reservation transmission of communications resources is permitted. When the determination is made dynamically, the determination may be based on current conditions in the area. In one example, the determination is based at least in part on the level of communications traffic or communications congestion in the area, where the determination that a reservation of communications resources should be transmitted decreases as the level of traffic and / or congestion increases.

[0028] After identifying the candidate relay devices, the source UE device decides whether to transmit traffic 122 in a broadcast or unicast transmission. As is known, the same data can be transmitted to multiple UE devices using different transmission techniques, often referred to as cast types. Cast types include at least unicast, groupcast, and broadcast. A unicast transmission can only be received by a single UE device that is the intended recipient of the data. Thus, multiple transmissions are required to transmit the same data to multiple UE devices using unicast. A broadcast transmission can typically be received by all UE devices within range of the transmission. A groupcast transmission can only be received by UE devices that are members of the group. In the examples herein, the broadcast transmission to the candidate relay devices includes UE device identification information. Although the broadcast can be received by all UE devices in the area, the broadcast transmission is directed to the selected relay candidate device. Thus, for at least some of the examples herein, the candidate relay devices select the candidate relay devices based on the identification information included in the broadcast transmission. The source UE device 101 determines that the selected candidate relay device is selected as a relay device. This is an example of a case where the suitable identification information includes a UE ID. Thus, by way of example, the source UE device 101 may transmit the transmission 122 together with the destination device data 120 in a single transmission using a broadcast to two or more candidate relay devices in the group, or may transmit the same data to the candidate relay devices in multiple unicast transmissions. In the example of unicast transmission, a unicast connection between the source UE device and each selected candidate relay device is established before transmitting the destination device data. For clarity and brevity, although FIG. 1B and FIG. 1C show a single arrow and box representing the transmission 122, the transmission 122 may include multiple transmissions in some situations. Thus, the transmission from the source UE device 101 to multiple candidate relay devices may be facilitated by multiple unicast connections or broadcast connections. In some situations, a groupcast connection may be used for the connection between the source UE device and multiple candidate relay devices. Such a technique is different from a groupcast transmission to multiple destination UE devices. For example, a source UE device may use one or more relay devices to relay a groupcast transmission to multiple destination UE devices, where the connection between the source UE device and the candidate relay devices may be unicast or broadcast.

[0029] Each candidate relay device 103-105 receives the transmission 122 and evaluates the control information 124 to determine that the source UE device 101 is requesting the candidate relay device to relay destination device data 120 to the destination UE device 102. For example, the candidate relay device identifies the destination UE device 102 based on an identifier (ID2) included in the control information 124. The candidate relay device determines whether to perform relay functions for the source UE device and the destination UE device. In some circumstances, the decision may be based on the availability of resources at the candidate relay device, such as memory, battery life, available bandwidth, and / or channel conditions. As discussed below, the decision may be based on the relative priority of data, including the destination device data 120, data for the relay device's own communication, and data for other destination device data included in the relay request transmission from the other source UE device.

[0030] If a candidate relay device determines that it can relay the destination device data 120, it becomes a relay UE device and transmits the destination device data 120 to the destination UE device in a relay transmission. For example, two candidate relay devices 103, 104 transmit relay transmissions 128, 130 including the destination device data, respectively, while the third candidate relay device 105 refrains from transmitting. For example, the relay transmissions 128, 130 are the same signal and are transmitted on the reserved communication resource 126. Thus, the relay transmissions 128, 130 appear as a single transmission signal that experiences multipath at the destination UE device 102 and can be received by a conventional receiver component. One or more UE devices may be selected as candidate relay devices, and any number of candidate relay devices may be relay UE devices. As described below, in the examples herein, a hybrid automatic repeat request (HARQ) message is transmitted in response to the transmission 122 and / or the relay transmissions 128, 130.

[0031] FIG. 1C is a block diagram of the communication system 100 for an example where the candidate has previously reserved the communication resource 132. For example, the source UE device 101 has received the neighbor list messages 112, 114, 116, 118 as described with reference to FIG. 1A. The source UE device 101 has also obtained information identifying the communication resources reserved by one or more nearby UE devices 103-107. In some situations, the source UE device 101 obtains the information identifying the communication resources reserved by other UE devices based on control signals broadcast from the other UE devices. For example, conventional techniques provide mechanisms for UE devices to reserve future communication resources, and the source UE device 101 detects such control signals. As mentioned above, examples of communication resource reservation techniques are defined in the 5G NR V2X Mode-2 communication specifications. In other situations, nearby UE devices or UE-based roadside units (RSUs) can act as schedulers for sidelink communications between UE devices in the nearby area of ​​the scheduling UE device. Thus, the scheduling UE device reserves communication resources for one or more other UE devices in the area, and the source UE device identifies the reserved communication resources based on a scheduling signal received from the scheduling UE device. In some situations, one of the candidate relay devices is a scheduling device, which periodically announces the reservation of a set of resources to neighboring UE devices, including the source UE device. In one scenario, the source UE device transmits a source transmission including destination device data to the candidate relay device using the resources reserved by the scheduling device. In another scenario, the source UE device 101 transmits a source transmission to the candidate relay device before the time of the reserved resources, and the one or more candidate relay devices transmit a relay transmission to the destination device using the resources reserved by the scheduling device.

[0032] As shown in the example of FIG. 1C, the source UE device 101 evaluates the neighbor list message and the reserved communication resources to identify candidate relay devices. In some situations, the source UE device may identify several potential candidate relay devices based on the neighbor list and the reserved resources, but only one candidate relay device is selected. The source UE device may apply additional criteria in selecting a candidate relay device. The source UE device may, for example, evaluate the proximity of the potential candidate relay devices to the destination UE device.

[0033] The source UE device 101 transmits a transmission 122 including destination device data 120 and control information 124 including a communications resource preemption indicator. The communications resource preemption indicator indicates to the candidate relay device 103 that the source UE device is requesting that the candidate relay device use the communications resource 132 to transmit destination device data for which the communications resource 132 was previously reserved by the candidate relay device 103 (or reserved by another device, such as a scheduling UE device, for the candidate relay device). Thus, in the example of FIG. 1C, the source UE device 101 does not transmit a communications resource reservation, as described with reference to FIG. 1B. In some situations, the source UE device 101 may transmit both a communications resource reservation and a communications resource preemption indicator. In other situations, the source UE device 101 may dynamically determine whether to transmit a communications resource reservation or a communications resource preemption indicator. For example, if the source UE device is sending a source transmission to multiple candidate relay devices via broadcast, a reservation of communications resources may be sent, and if the source UE device is sending a source transmission to candidate relay devices via unicast, a preemption indicator of communications resources may be sent.

[0034] The candidate relay device 103 receives the transmission 122 and evaluates the control information 124 to determine that the source UE device 101 is requesting the candidate relay device to relay the destination device data 120 to the destination UE device 102 by using communication resources 103 previously reserved by the candidate relay device 103. For example, the candidate relay device identifies the destination UE device 102 based on an identifier (ID2) included in the control information 124. The candidate relay device 102 determines whether to perform relay functions for the source UE device 101 and the destination UE device 102. In some circumstances, the decision may be based on the availability of resources at the candidate relay device 103, such as memory, battery life, available bandwidth, and / or channel conditions. As discussed below, the decision may be based on the relative priority of data, including the destination device data 120, data for the relay device's own communication, and data for other destination device data included in the relay request transmission from other source UE devices.

[0035] If the candidate relay device 103 determines that it can relay the destination device data 120, it becomes a relay UE device and transmits the destination device data 120 in a relay transmission 134 to the destination UE device. As described below, a hybrid automatic repeat request (HARQ) message is transmitted in response to the transmission 122 and / or the relay transmissions 128, 130 illustrated herein. In some circumstances, it is up to the destination UE device to determine whether the candidate relay device can function as a relay UE device. For example, after receiving a source transmission, the candidate relay attempts to establish an RD communication link in which the destination UE device accepts the candidate relay device as a relay UE device. After the establishment of the RD communication link, the candidate relay device becomes a relay UE device. If the destination UE device does not accept the candidate as a relay, the candidate relay device does not become a relay UE device.

[0036] In the case where multiple candidate relay devices are selected by the source UE device, the destination UE device may select which candidate relay device to accept (with the response) as a relay UE device according to one or more factors. Examples of factors and criteria for downselection by the destination UE device include signal strength, link quality, local policy, and combinations thereof. Other criteria may also be used.

[0037] As mentioned above, the source transmission may be sent to one or more candidate relay devices using unicast or broadcast, respectively. In the case of unicast transmission, the candidate relay device is selected after the source UE device and the relay UE device establish a unicast link. In a typical scenario, the first step of unicast link establishment includes sending a direct communication request message (application layer message) with a relay indication field set. In the situation where more than one candidate relay device is selected, the source UE device may establish multiple unicast links or broadcast with relay UE identification information to the selected candidate relay devices. The establishment of the unicast link is usually preceded by a discovery protocol including model A or model B discovery with neighbor lists. Establishing a sidelink (SL) unicast connection or PC5-RRC allows the two UE devices to share capabilities and use a common RLC configuration (such as RLC-UM or RLC-AM with RLC ACK / NACK).

[0038] FIG. 2 is a block diagram of an example of a base station 200 suitable for use as each of the base stations 108, 110. The base station 200 includes a control unit 204, a transmission unit 206, and a reception unit 208, as well as other electronics, hardware, and code. The base station 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 the base stations 108, 110 may be implemented in any number of devices, circuits, or elements. Two or more functional blocks may be integrated into a single device, and the functions described as being performed in any single device may be implemented in several devices. The base station 200 may be a fixed device or device that is installed in a specific location during system deployment. Examples of such devices include a fixed base station or a fixed transceiver station. Although base stations may be referred to by different terms, base stations are typically referred to as gNodeBs or gNBs when operating in accordance with one or more communication specifications for 3GPP V2X operation. In some circumstances, the base station 200 may be a mobile device that is temporarily installed in a specific location. Some examples of such equipment include mobile transceiver stations that may include power generation equipment such as generators, solar panels, and / or batteries. Larger and heavier versions of such equipment may be transported on trailers. In yet other situations, the base station 200 may be a portable device that is not fixed to a particular location.

[0039] The controller 204 includes any combination of hardware, software, and / or firmware for performing the functions described herein as well as facilitating the overall functionality of the base station 200. Examples of suitable controllers 204 include a microprocessor or code running on a processor arrangement coupled to a memory. The transmitter 206 includes electronics configured to transmit wireless signals. In some circumstances, the transmitter 206 may include multiple transmitters. The receiver 208 includes electronics configured to receive wireless signals. In some circumstances, the receiver 208 may include multiple receivers. The receiver 208 and the transmitter 206 receive and transmit signals, respectively, via an antenna 210. The antenna 210 may include separate transmit and receive antennas. In some circumstances, the antenna 210 may include multiple transmit and receive antennas.

[0040] The transmitter 206 and receiver 208 in the example of FIG. 2 perform radio frequency (RF) processing, including modulation and demodulation. Thus, the receiver 208 may include components such as a low noise amplifier (LNA) and a filter. The transmitter 206 may include a filter and an amplifier. Other components may include isolators, matching circuits, and other RF components. These components perform base station functions in combination or cooperation with other components. The components required will depend on the particular functionality required by the base station.

[0041] The transmitter 206 includes a modulator (not shown) and the receiver 208 includes a demodulator (not shown). The modulator modulates the signal to be transmitted as part of the downlink signal and may apply any one of a number of modulation orders. The demodulator demodulates the uplink signal received at the base station 200 according to one of a number of modulation orders.

[0042] The base station 200 includes a communication interface 212 for sending and receiving messages to and from other base stations. The communication interface 212 may be connected to a backhaul or network that enables communication with other base stations. In some circumstances, the link between base stations may include at least some wireless portions. Thus, the communication interface 212 may include wireless communication capabilities and may utilize some of the components of the transmitter 206 and / or receiver 208.

[0043] FIG. 3 is a block diagram of an example of a UE device 300 suitable for use as each of the UE devices 101-107, 801-807. In some examples, the UE device 300 is any wireless communication device, such as a mobile phone, a walkie-talkie modem, a personal digital assistant (PDA), a tablet, or a smartphone. In other examples, the UE device 300 is a machine type communication (MTC) communication device or an Internet of Things (IOT) device. Thus, the UE device 300 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 the UE device 300 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 in multiple devices.

[0044] The UE device 300 includes at least a controller 302, a transmitter 304, and a receiver 306. The controller 302 includes any combination of hardware, software, and / or firmware to perform the functions described herein and facilitate the overall functionality of the communication device. An example of a suitable controller 302 includes a microprocessor or code executed on a processor arrangement coupled to a memory. The transmitter 304 includes electronics configured to transmit wireless signals. In some circumstances, the transmitter 304 may include multiple transmitters. The receiver 306 includes electronics configured to receive wireless signals. In some circumstances, the receiver 306 may include multiple receivers. The receiver 304 and the transmitter 306 receive and transmit signals, respectively, via an antenna 308. The antenna 308 may include separate transmit and receive antennas. In some circumstances, the antenna 308 may include multiple transmit and receive antennas.

[0045] The transmitter 304 and receiver 306 in the example of FIG. 3 perform radio frequency (RF) processing including modulation and demodulation. Thus, the receiver 304 may include components such as a low noise amplifier (LNA) and a filter. The transmitter 306 may include a filter and an amplifier. Other components may include isolators, matching circuits, and other RF components. These components perform the functions of the communication device in combination or cooperation with other components. The components required may depend on the particular functions required by the communication device.

[0046] The transmitter 306 includes a modulator (not shown) and the receiver 304 includes a demodulator (not shown). The modulator can apply any of a number of modulation orders to modulate a signal that is transmitted as part of the uplink signal. The demodulator demodulates the downlink signal according to one of a number of modulation orders.

[0047] 4A is an example message flow diagram 400 in which the source UE device 101 selects candidate relay devices based at least in part on a neighbor list received from the UE device, and the relay UE device is configured with distance-based HARQ feedback (NACK only) by the source UE device 101. The message flow of FIG. 4A is an example of a message flow scenario for the communication system 100 described above with reference to FIGS. 1A, 1B, and 1C. The destination UE device 102 broadcasts its neighbor list message in a transmission 402. Nearby UE devices within communication range of the destination device, including UE devices 103, 104, receive the neighbor list message. In some circumstances, the destination UE device may broadcast a discovery message rather than a neighbor list message that allows all neighbor devices to detect the presence of the destination UE device 102.

[0048] In transmission 404, the UE device 103 transmits a neighbor list message including the IDs of the UE devices that it has detected through either the received neighbor list message or the discovery message. The neighbor list message also includes the IDs of the UE devices included in the received neighbor list message. In transmission 406, the UE device 104 transmits a neighbor list message. Because both UE devices 103, 104 received neighbor list messages from the destination UE device 102, the identifier (ID2) of the destination UE device 102 is included in the neighbor list messages received by the source UE device 101 in transmissions 404, 406 from the UE devices 103, 104.

[0049] The source UE device evaluates the neighbor list message and selects a candidate relay, at event 408. The selection of the candidate relay can be based on criteria in addition to the neighbor list.

[0050] As described herein, transmission from the source UE device 101 to the multiple candidate relay devices 103, 104 can be via multiple unicast connections or broadcast. If unicast is used, a unicast connection is established prior to the transmission of destination device data. Transmissions 409 and 410 establish unicast connections with the candidate relay device 104 and the candidate relay device 103, respectively. The arrows representing transmissions 109, 110 are shown as dashed lines, indicating that transmissions 109, 110 are omitted if broadcast techniques are used. Transmissions 109, 110 convey a relay indicator, since the unicast establishment includes information identifying the UE device 103, 104 as a candidate relay device.

[0051] In transmission 411, the source UE device 101 transmits destination device data and control information to the candidate relay devices. Thus, transmission 411 is an example of a source transmission 122 as described above for a broadcast transmission, and transmissions 409, 410, 411 are examples of source transmissions 122 where unicast is used. In the case of a broadcast transmission, transmission 411 indicates to the candidate relay devices 103, 104 that they will relay the destination device data to the destination device. Two relay UE devices 103, 104 are shown in FIG. 4A. However, transmission 411 could have been sent to additional candidate relay devices, such as, for example, UE device 105. In the example of FIG. 4A, transmission 411 can be a broadcast transmission directed to a group of candidate relay devices where UE devices 103, 104 are identified in the broadcast transmission. According to known techniques, the source UE device (transmitting UE device) provides HARQ feedback configurations to the candidate relay devices (receiving UE devices). In the example of FIG. 4A, the HARQ feedback configuration is a distance-based HARQ configuration, where the receiving device sends NACK feedback only if it is within a maximum distance.

[0052] In transmission 412, the relay UE device 103 transmits destination device data to the destination UE device 102. In transmission 414, the relay UE device 104 transmits destination device data to the destination UE device 102. For example, the two transmissions are the same and are transmitted using the same communication resources. Thus, at the destination UE device 102, the two transmissions 412, 414 resemble a single transmission that has experienced multipath propagation and can therefore be received by the destination UE device 102 using conventional reception techniques. In one scenario, the relay transmission 412 and the relay transmission 414 are broadcast. In another scenario, the relay transmission 412 and the relay transmission 414 are transmitted via a unicast connection. If unicast is used, the unicast connection is established before transmitting the destination device data in the relay transmission 412, 414. However, the destination device data can still be transmitted via the same communication resources by using the same radio bearer for the unicast transmission of the destination device data.

[0053] At transmission 416, HARQ feedback is transmitted from the destination UE device 102. For example, the HARQ feedback is a broadcast transmission that may be received by all of the relay UE devices 103, 104 that transmitted the destination device data. The HARQ feedback may be an ACK / NACK or NACK only, depending on the HARQ feedback configuration.

[0054] In transmission 418, the relay UE device 103 transmits HARQ feedback to the source UE device 101. In transmission 420, the relay UE device 104 transmits HARQ feedback to the source UE device 101. Since the HARQ configuration established by the source UE device 101 is distance-based HARQ, only NACK feedback is provided. Thus, the arrows representing the transmissions 418, 420 in FIG. 4 are shown in dashed lines in FIG. 4A to indicate that the transmissions 418, 420 are performed only if a NACK is required. For example, the same communication resources are used to transmit the NACK feedback to the source UE device. Since the transmission 418 from the relay UE device 403 is the same as the transmission 420 from the relay UE device 404, the signals appear as a single transmission that experiences multipath propagation. The NACK transmissions 418, 420 may be transmitted in response to a NACK feedback received from the destination UE device 102 or in response to a failed reception of the transmission 410. Thus, in some circumstances, only one of the relay UE devices may send a NACK feedback to the source UE device 101 .

[0055] Figure 4B is an example message flow diagram 450 in which the source UE device 101 selects candidate relay devices based at least in part on a neighbor list received from the UE device, and the relay UE device is configured with ACK / NACK HARQ feedback by the source UE device 101. The message flow of Figure 4B is an example of a message flow scenario for the communications system 100 described above with reference to Figures 1A, 1B, and 1C. Transmissions 402, 404, 406, 409, 410, 411, 412, 414 and event 408 are performed as described above with reference to Figure 4, except that the HARQ configuration for the HARQ feedback from the candidate relay devices is ACK / NACK and not distance-based HARQ.

[0056] At transmission 452, the relay UE device 103 transmits an ACK HARQ feedback to inform the source UE device 101 that the source transmission 410 was successfully received by the relay UE device 103. At transmission 454, the relay UE device 104 transmits an ACK HARQ feedback to inform the source UE device 101 that the source transmission 410 was successfully received by the relay UE device 104. In the example of Figure 4B, therefore, the HARQ feedback transmitted from the relay device is not transmitted over the same communications resources.

[0057] At transmission 456, the destination UE device 102 broadcasts HARQ feedback to the relay UE devices 103, 104 indicating whether the relay transmissions 412, 144 were successfully received at the destination UE device 102. Since the relay transmissions are the same, an ACK is sent if at least one relay transmission is successfully received. In the example of FIG. 4B, the HARQ feedback from the relay UE device to the source UE device 101 is therefore independent of the HARQ feedback from the destination UE device 102 to the relay UE device 103, 104. In other words, the relay UE device only provides feedback regarding signals transmitted to it and does not forward or communicate the results of the HARQ feedback received from the destination UE device 102 for the example of FIG. 4B.

[0058] At event 458, if a NACK feedback is received from the destination UE device 102, the relay device performs a retransmission. If a NACK feedback is received, each relay UE device retransmits the destination device data in a relay transmission. In some situations, the relay transmissions from the relay device use the same communication resources and transmit the same signal. In some cases, if the relay device does not receive either an ACK or a NACK (i.e., HARQ-DTX), the relay UE device performs a retransmission of the destination device data.

[0059] 5 is a flow chart of an example method 500 for managing relay transmissions at a candidate relay device. By way of example, the method may be performed by a UE device operating in a system compliant with at least one revision of the NR V2X specification, such as the system 100 described above. Thus, the method may be performed by relay UE devices 103-105.

[0060] In step 502, it is determined whether a source transmission with destination device data is received from a source UE device with an indication that the destination device data should be relayed to the destination UE device. In a situation where the source transmission is a broadcast transmission with relay identification information, the source transmission may include both the destination device data and a relay indicator that requests that the candidate relay devices relay the destination device data to the destination device. If the source transmission is a unicast transmission, the source transmission typically includes the destination device data and some identification information that allows the relay UE device to determine that the transmission is intended for the relay UE device. Such identification information may include a UE ID of the relay UE device. In another example, the identification information includes a UE ID of the destination UE device. In a case where the identification information does not include a relay UE ID but includes a UE ID of the destination UE device, the identification information may also include a UE ID of the source UE device. In some situations, information other than a UE ID may be used. An example of a suitable mechanism for transmitting the identification information includes transmitting the identification information in a side control information (SCI). As mentioned above, the relay request indicator is transmitted during the establishment of the PC5-RRC connection, for example in a direct communication request message (PC5-S). Thus, in some scenarios, the relay request indicator may not be transmitted with the destination device data in the source transmission. However, in some other scenarios, the relay request indicator may be included in the source transmission and may contain sufficient information to provide the identification information. If a source transmission has not been received, the method proceeds to step 504, where the UE device continues direct UE device to UE device communications, and returns to step 502. If a source transmission has been received, the method continues to step 506.

[0061] At step 506, it is determined whether the communication link to the destination UE device is still above a minimum threshold for communication with the candidate relay device. As an example, the candidate relay device determines whether an updated neighbor list has been received from the destination UE device identified in the source transmission. In some circumstances, the candidate relay device determines whether a recent discovery signal has been received from the destination UE device in determining whether the destination UE device meets the minimum threshold for communication. If the source transmission is unicast, the determination of whether the minimum threshold is met is typically performed during establishment of a PC5-RRC connection between the source UE device and the candidate relay device and is performed prior to receipt of destination device data. In other cases, receipt of a discovery message from the relay UE device may be used to determine whether the minimum threshold is met. If the destination UE device is within communication range, the method continues to step 508. If not, the method proceeds to step 510. Step 506 provides a mechanism for dealing with the situation where the source UE device has not yet received an updated neighbor list from the candidate relay device when initiating the source transmission.

[0062] At step 510, an undeliverable feedback message is sent to the source UE device. In one example, the undeliverable feedback message is a PC5-RRC message indicating that the candidate relay device is unable to deliver the destination device data. In another example, the undeliverable feedback message indicates why the destination device data cannot be delivered and indicates that the destination UE device no longer meets the minimum link threshold. In some circumstances, a NACK feedback message can be sent as the undeliverable feedback message, but such feedback is of little value to the source UE device because the source UE cannot determine from the NACK whether the source transmission was not received by the candidate relay device or the relay transmission failed.

[0063] In step 512, the neighbor list is updated to exclude the destination UE device that is no longer in communication range. In step 514, the neighbor list is broadcast at the next scheduled neighbor list broadcast time. After the updated neighbor list is broadcast, the method returns to step 502. Although not shown in Figure 5, the relay UE device will send an updated neighbor list that includes the destination UE device if the destination UE device returns to being in communication range.

[0064] In step 508, it is determined whether communication data other than destination device data is available for transmission. The other communication data may include direct communication data, which is data that the candidate relay device transmits to another UE device as a direct UE device to UE device communication. That is, the direct communication data is data related to the relay candidate device's own communication. As shown in FIG. 5, the communication data may also include other destination device data that the candidate relay device is requested to relay. In some situations, the candidate relay device may be functioning as a relay UE device for some source UE devices. If other communication data is available, the method continues to step 516. If not, the method proceeds to step 518.

[0065] In step 516, the destination device data is transmitted to the destination UE device in a relay transmission. In some situations, the communication resources used for the relay transmission may be communication resources previously reserved by the candidate relay device. For example, the communication resources may have been reserved for a direct communication data transmission from the candidate relay device to another UE device. In other situations, the communication resources used for the relay transmission may have been reserved by the source UE device, as described above with reference to FIG. 1.

[0066] In step 518, it is determined whether the priority level of the destination device data is greater than the priority levels of the other communication data. A priority level is established for each of the data communications, and the candidate relay devices evaluate the priority level. In accordance with NR V2X, the QoS requirements of the physical (PHY) layer are indicated in the priority field of the first stage SCI (3 bits representing 8 QoS levels that are mapped to higher layers). Thus, at least one factor that can be applied to different data includes the QoS level. However, the QoS level does not necessarily correspond to a one-to-one comparison by the candidate relay devices where the highest QoS leads to the highest priority assignment. In one example, the serving base station (gNB) configures the UE device (including the candidate relay UE device) to prioritize data based on whether the data is relayed data or direct communication data. Thus, if the direct communication data is prioritized, the candidate relay device assigns the priority of the direct communication data higher than the priority of the relayed data. The base station can pre-configure the UE device for a situation where the UE device is out of coverage (OoC).

[0067] In another example, the candidate relay device determines the prioritization of data based on at least the QoS level provided by the source UE device for the destination device's data. The assigned priority can be based on other factors and algorithms in addition to or instead of the QoS level. Other factors for assigning priority levels to various data include application type and packet delay budget of the data. For example, public safety applications may be assigned the highest priority.

[0068] In some circumstances, a candidate relay device informs the source UE device during a discovery or relay reselection procedure whether the candidate relay device has the capability to handle relaying of high priority data. With such techniques, the source UE device can apply the information to better select or reselect a candidate relay device.

[0069] For example, if the priorities are the same, the candidate relay device determines that the destination device data priority is less than or equal to the direct communication data priority level. If the destination device data priority level is greater than the direct communication data priority level, the method continues to step 519. If not, the method proceeds to step 520.

[0070] The destination device data is transmitted with higher priority than other data in step 519. As will be described below with reference to step 522, the other data may be transmitted in accordance with prioritized bit rate (PBR) techniques.

[0071] In step 520, the candidate relay device transmits a prioritization indication message to the source UE device informing the source UE device that the destination device data has been prioritized below other data. In some circumstances, the prioritization indication message may indicate additional information regarding the prioritization and other data. For example, the priority of the other data and / or the amount of the other data may be provided. In other circumstances, a NACK HARQ feedback to the source UE device may be sent in response to the prioritization message. Such a technique may be advantageous when the priority of the destination device data is prioritized below a minimum threshold.

[0072] In step 522, the destination device data is transmitted with a lower priority. In accordance with known techniques, the candidate relay device assigns different logical channel IDs (LCIDs) and applies logical channel prioritization (LCP) at the MAC layer to determine which data is transmitted next. Typically, the highest priority logical channel is processed first in the MAC PDU, followed by data from the next higher priority logical channel, and so on until the MAC PDU space is exhausted. In an absolute priority based method, data from the higher priority logical channel occupies all the MAC PDU space, so data from the lower priority logical channel may be starved if data from the lower priority logical channel cannot be transmitted. A Prioritized Bit Rate (PBR) is defined for each logical channel to avoid starvation of low priority data as well as to transmit data in order of importance. The PBR is the minimum data rate guaranteed on a logical channel. Even if a logical channel has a low priority, at least a small amount of MAC PDU space is allocated to guarantee the PBR. Thus, by using the PBR, the starvation problem can be avoided. Thus, the destination device's data is still transmitted to the destination device, but perhaps at a slower rate than is preferred or with more delay than is acceptable. Thus, the sending of the prioritization indication at step 520 allows the source UE device to evaluate the current relay device and priority level to determine whether relay reselection should be invoked.

[0073] In some circumstances, instead of transmitting the destination device with a low priority, the destination device's data may not be transmitted by the candidate relay device if its priority level is lower than the priority of other data. In such circumstances, the prioritization indication in step 520 indicates that the destination device data will not be relayed.

[0074] 6 is a flow chart of a method 600 of transmitting relay transmissions including retransmissions at candidate relay devices. For example, the method may be performed by a UE device operating in a system in accordance with at least one revision of the NR V2X specification, such as the system 100 described above. Thus, the method may be performed by relay UE devices 103-105.

[0075] In step 602, the destination device data is transmitted to the destination UE device 102. The relay UE device transmits a relay transmission including the destination device data. In some situations, the communication resources used for the relay transmission may be communication resources previously reserved by the candidate relay device. For example, the communication resources may have been reserved for a direct communication data transmission from the relay UE device to another UE device. In other situations, the communication resources used for the relay transmission may have been reserved by the source UE device, as described above with reference to FIG. 1. In FIG. 1B, the HARQ feedback timer is started at the time of the relay transmission. For example, the retransmission counter is incremented after the transmission. Thus, after the first transmission of the destination device data, the retransmission counter is set to "1" and incremented for each retransmission of the same destination device data.

[0076] In step 604, it is determined whether an ACK HARQ feedback has been received from the destination UE device. If an ACK is received, the method continues with normal operation. For example, the method continues with step 502 of the example of FIG. 5. If an ACK is not received, the method proceeds to step 606 where it is determined whether a NACK HARQ feedback has been received. If a NACK has not been received, the method continues with step 608. If a NACK is received, the method continues with step 610.

[0077] In some situations, the relay UE device transmits a NACK immediately after receiving a NACK from the destination UE device. The source UE device can then take immediate action in response to the failed relay transmission. The source UE device can, for example, notify the relay UE device to perform a retransmission. In another example, the source UE device can immediately resume the relay process by evaluating the neighbor list and selecting a candidate relay device. Also, the relay UE device can transmit an ACK to the source UE device as an alternative or in addition to continuing normal operation instead of receiving an ACK in step 604. As described below, in some situations where the HARQ feedback includes an ACK, the source UE device can take action in response to not receiving an ACK from the relay UE device within a threshold period. For example, the source UE device can reserve communication resources for the retransmission and instruct the relay UE device to perform a retransmission. In one technique, the source UE device transmits the reserved communication resources to the relay UE device but does not transmit the destination data. In another technique, the source UE device uses PC5-S messaging (for groupcast) or PC5-RRC signaling (for unicast) to instruct the relay UE device whether it should perform a retransmission when it receives a NACK from the destination UE device. In this case, the instruction is valid for the entire session of the groupcast or unicast connection until the source UE device changes the instruction to stop autonomous retransmissions at the relay UE device. One advantage of such a scheme is that it allows retransmissions before the HARQ timer expires.

[0078] In step 608, it is determined whether the HARQ feedback timer for the relay transmission has expired. If the timer has expired, the method continues at step 610. If not, the method returns to step 604.

[0079] In step 610, it is determined whether the retransmission counter exceeds a threshold. If the number of retransmissions of the destination device data is greater than the threshold, the method continues to step 612. If not, the method returns to step 602, where the destination device data is retransmitted, the retransmission counter is incremented, and the HARQ feedback timer is reset. In some circumstances, the number of retransmissions may be configurable and may vary depending on the QoS of the communication service.

[0080] In step 612, the source UE device is notified that the relay transmission to the destination UE device has failed. For example, the relay UE device sends a message to notify the source UE device via the PC5-RRC link or the PC5-S layer. As is known, the upper layer PC5 signaling (PC5-S) layer is located above the Packet Data Convergence Protocol (PDCP), Radio Link Control (RLC), Medium Access Control (MAC) sublayer, and the physical layer, as well as the control plane layers of the PC5 interface. As described below, the source UE device can re-evaluate the neighbor list and restart the relay process, including the candidate relay selection process.

[0081] 7 is a flow chart of an example method 700 for managing relay transmissions at a source UE device. By way of example, the method may be performed by a UE device operating in a system compliant with at least one revision of the NR V2X specification, such as the system 100 described above. Thus, the method may be performed by a source UE device 101.

[0082] At step 702, neighbor lists from nearby UE devices are received and stored. In accordance with known techniques, the source UE device receives neighbor lists from the UE devices, with each neighbor list identifying neighbor UE devices of the UE device sending the neighbor list and neighbor UE devices of the listed neighbors. The information in each list is stored in memory and is updated upon receiving updated neighbor lists. As described in more detail below, the neighbor list may include information indicative of the link quality of each neighbor UE device in some circumstances.

[0083] At step 704, it is determined whether a relay transmission is pending. The source UE device determines whether destination device data should be transmitted to the destination UE device using the relay UE device. If no transmission is available for potential relay transmission, the method returns to step 702 and the neighbor list is received and updated. The UE device may continue with direct UE device-to-UE device communications and / or communications with the base station. If a transmission via a relay UE device is available, the method continues to step 706.

[0084] At step 706, a candidate relay is selected. The source UE device selects at least one candidate relay and may select multiple candidate relays based on information in the neighbor list. In some situations, the selection of a candidate relay may be based simply on the inclusion of the destination device in the neighbor list of the UE device providing the neighbor list. In other situations, the selection may be based on additional criteria. For example, as described below, the selection may be based on the quality of the communication link between the potential candidate relay and the destination device.

[0085] At step 708, a source transmission including the destination device data is transmitted to the candidate relay device. If multiple candidate relay devices are selected, the source transmission is transmitted via broadcast in an example. In some circumstances, unicast may be used for the source transmission. For example, the source transmission includes an indicator indicating that the candidate relay device will forward the destination device data to the destination device. In some circumstances, the indicator may also reserve communication resources for the transmission of the destination device data from the candidate relay device. In some examples, as described above, the source UE device also transmits a communication resource reservation to reserve communication resources for the relay transmission from the candidate relay device to the destination UE device. In other examples, the source transmission includes a request to transmit the relay transmission using the communication resources received by the candidate relay device for its own transmission. As described above, the relay indicator may be part of a unicast connection establishment procedure in which multiple unicast links are used with multiple candidate relay devices.

[0086] In step 710, it is determined whether a forwarded ACK has been received. In an example where ACK / NACK HARQ feedback from destination device to relay UE device is forwarded by the relay UE device to the source UE device, the source UE device receives the forwarded ACK when the destination UE device successfully receives the destination device data. If a forwarded ACK has been received in the relay transmission, the method returns to step 702. Otherwise, the method continues to step 712.

[0087] In step 712, it is determined whether a forwarded NACK is received. In an example where the NACK HARQ feedback from the destination device to the relay UE device is forwarded by the relay UE device to the source UE device, if the destination UE device does not successfully receive the destination device's data, the source UE device receives a forwarded NACK. If a forwarded NACK is not received, the method continues to step 714. Otherwise, the method continues to step 716.

[0088] At step 714, it is determined whether the HARQ feedback timer for the source transmission has expired. If the timer has not expired, the method returns to step 710. If the timer has expired, the method returns to step 702 and restarts the process. The updated neighbor list information is applied to select a candidate relay device, which may be different from the one previously selected.

[0089] In step 716, it is determined whether the retransmission counter exceeds a threshold. If the number of retransmissions of the destination device data is greater than the threshold, the method returns to step 702 to restart the process. If not, the method proceeds to step 718, where the relay UE device is instructed to retransmit the destination device data, and then returns to step 710 to monitor HARQ feedback for the new transmission. The retransmission counter is incremented and the HARQ feedback timer is reset.

[0090] FIG. 8 is a block diagram of an example of a geographical arrangement 800 of UE devices 801-807 and a corresponding neighbor list 810 including link quality information associated with the arrangement 800. For example, the neighbor list 810 is provided by a first UE device 801 having a unique identification of "ID10". The neighbor list 810 includes a number of rankings 811-815, each ranking being associated with a range of received signal strengths of signals received from the UE device. The signals received and measured at the first UE device 801 may be discovery signals or neighbor list signals conveying neighbor lists from nearby UE devices 102-107. In some situations, other signals may be used. In some situations, the ranks are based directly on the geographical location of the UE devices. For example, in one scenario, the UE devices share their locations with other nearby UE devices, and the neighbor list is generated based on the distance between the locations.

[0091] The rankings are at least partially related to the distance between the first UE device and the UE device transmitting the signal, since the received signal strength of the signal depends at least in part on the distance to the transmitter transmitting the signal. The received signal strength is also related to the quality of the communication link between the transmitting UE device and the first UE device. Thus, each of the multiple rankings also indicates the quality of the communication link between the first UE device 801 and the UE device associated with the particular rank. In other words, the UE device associated with the ranking is expected to have a communication link to the first UE device having a quality level associated with that ranking. The rankings are organized such that a lower ranking indicates a higher quality of the communication link. A rank of 1 represents a higher quality (shorter distance) communication link than a rank of 2.

[0092] For example, the rankings are associated with the distances 817-820 between the UE devices 802-807 and the first UE device 801. As shown in FIG. 8, the area between the largest circle representing the longest distance 820 and the second largest circle representing the second longest distance 819 is associated with a rank of 4 815. The area between the second largest circle representing the second longest distance 819 and the third largest circle representing the third longest distance 818 is associated with a rank of 3 814. The area between the smallest circle representing the shortest distance 817 and the next largest circle representing the next longest distance 818 is associated with a rank of 2 813. The area within the smallest circle is associated with a rank of 1 812. In this example, the rankings are associated with the distances between the UE devices 802-807 and the first UE device 801, but in some circumstances, the rankings of the UE devices may not correspond to the distances between the UE devices and the first UE device. This may occur, for example, when the communication path between the two UE devices is obstructed. However, the rankings still indicate the quality of the communication link. Thus, the techniques described herein are based on selecting relay devices based on the quality of the communication link, where one factor in determining the quality of the link may be based on distance. As discussed above, distance may be determined by the UE devices exchanging information regarding their locations. However, distance is an indirect mechanism for ranking the quality of the links, and in some circumstances, techniques that more directly determine the quality of the links may be used for ranking purposes.

[0093] The neighbor list 810 includes information identifying neighboring devices of a first UE device and associating a ranking with each UE device. However, the information may be represented in any format or structure. FIG. 8 illustrates the information in tabular form, where each rank 811-815 uniquely corresponds to a UE device set of a plurality of UE device sets 821-825. For example, a first UE device 801 is associated with rank 0. Thus, an identification ID10 of the first UE device is listed in the UE device set 821 associated with rank 0 811. An identification ID21 of a second UE device is listed in the UE device set 822 associated with rank 1 812. The UE device ID is not included in the UE device set 823 associated with rank 2813 because no neighboring UE devices are within the region of rank 2823. Continuing with the example, the UE device identifiers, ID15, ID17, of the third UE device 803 and the fourth UE device 804 are included in the UE device set 824 associated with rank 3814, and the fifth UE device 805 and the sixth UE device 806 are included in the UE device set 825 associated with rank 4815. UE device identifier ID22 is not included in the neighbor list as it is outside rank 4815, the lowest quality ranking.

[0094] Figure 9 is a block diagram of system 100 for an example where neighbor lists 112, 114, 116, 118 include communication link quality information. The neighbor lists in the example of Figure 3 are as follows: Figure 9 is therefore an example of neighbor list 810 discussed with reference to Figure 8. The operation of system 100 is the same as that of system 100 described above, except for aspects relating to neighbor lists, relay candidate selection, and signal modulation and coding management based on link quality information.

[0095] In the example of FIG. 9, neighbor lists 112, 114, 116, 118 from four UE devices 103-106 are received at the source UE device 101. Each neighbor list includes an identifier of the UE device associated with a ranking. As an example, the identifier (ID2) of the destination UE device 102 is included in each of the four neighbor lists associated with the identifier: rank 2 of the neighbor list 112 from the UE device 103, rank 1 of the neighbor list 114, rank 1 of the neighbor lists 114, 116 from the UE devices 104, 105, and rank 4 of the neighbor list 118 from the UE device 106. The source UE device 101 evaluates the lists and selects a candidate relay device based on the ranking of the identifier (ID2) of the destination UE device 102. In one scenario, the source UE device 101 receives three candidate relay devices 103-105 including the UE device 103 with rank 2 and the UE devices 104, 105 with rank 1 of ID2. In another scenario, the source UE device 101 selects only UE devices 104, 105 with rank 1 for ID2. Although UE device 106 includes ID2 as rank 4, the source may select UE device 106 as a candidate relay device in some circumstances.

[0096] In another example, the source UE device 101 selects a candidate relay device based further on the quality of the communication link between the source UE device 101 and the potential candidate relay device. A suitable technique includes selecting a candidate relay device based on the sum of the ranks of the destination UE device and the source UE device listed in the neighbor list. Potential candidate devices with a lower total rank sum are selected more than candidate devices with a higher total rank sum. Applying the scenario shown in FIG. 1. In FIG. 9, for example, the sum of the ranks of UE device 103 is the rank (1) of ID1 plus the rank (2) of ID2, which is equal to 3. The sum of the ranks of UE device 104 is the rank (2) of ID1 plus the rank (1), which is also equal to 3. Thus, the selection of candidate devices may include both UE device 103 and UE device 104, even though the destination UE device has a higher rank (e.g., rank 1) in the neighbor list 114 of UE device 104.

[0097] In some situations, the source UE device 101 may select a single candidate relay device with the lowest rank or the lowest total path rank. In other situations, the source UE device 101 may select a set of candidate relay devices with the same total path rank. In the situation of FIG. 2, for example, in FIG. 9, the source UE device 101 selects UE devices 103-105 as candidate relay devices because all three have a total path rank of 3, which is the lowest of the potential candidate relay devices 103-106. In other examples, the source UE device 101 selects a set of candidate relay devices whose total path rank is less than the threshold but may have different total path ranks. In such a situation, the UE device 106 may be selected in addition to the UE devices 103-105, even though the UE device 106 has a total path rank of 5.

[0098] In addition to providing criteria for selecting potential candidate relay devices, the neighbor list including link quality information can provide criteria for managing modulation and coding of source and relay transmissions. In one example, the source UE device 101 selects a modulation and coding scheme (MCS) based on the neighbor list. The MCS can be based at least in part on the rank of the UE device in the neighbor list, since the rank of the UE device is a function of the link quality between the UE devices. In an example, the source UE device 101 applies a more robust MCS to lower ranks.

[0099] In one example, the source UE device selects an MCS based on the lowest rank of the destination UE device that appears in the neighbor list of the candidate relay devices. In the scenario of Figure 2, and therefore in Figure 9, the MCS is based on rank 1 since the destination UE device has rank 1 in the neighbor list 114, 116. Such a technique may be advantageous if the relay UE device applies the same MCS to the relay transmission as was used in the source transmission.

[0100] In another example, the source UE device 101 selects a different MCS for the relay transmission from the MCS of the source transmission. Such a technique may be more efficient than using the same MCS for both transmissions. The source UE device 101 indicates the MCS in the control information of the source transmission that applies to the relay transmission. The selection of the MCS for the relay transmission is based at least in part on the lowest rank assigned to the destination device in the neighbor list. A more robust MCS is selected for a lower rank and a less robust MCS is selected for a higher rank. In some circumstances, the MCS of the source transmission is based at least in part on the rank of the identity of the source UE device 101 in the neighbor list of the candidate relay devices.

[0101] FIG. 10 is a flow chart of an example of a method 1000 performed in a source UE device for selecting a candidate relay device based on a neighbor list having a rank. By way of example, the method is performed by a UE device operating in a system compliant with at least one revision of the NR V2X specification, such as the system 100 described above. Thus, the method may be performed by the source UE device 101. The example of FIG. 10 may be performed as part of the example described above with reference to FIG. 7. For example, steps 1002, 1004, 1006, and 1008 may be performed as part of step 706, and step 1010 is an example of performing step 708. Although this example describes the selection of a relay based on a neighbor list and rankings, in some circumstances the selection is based on other criteria. Other criteria include: These may include higher layer criteria such as relaying policy, security, supported application criteria, etc. In this case, some applications may be approved by the network and not all relaying UE devices may be able to support the intended application. Thus, the examples described herein may be performed in conjunction with other selection mechanisms.

[0102] Also, in some circumstances, the final decision of the candidate relay devices capable of performing the functions of the relay UE device may include involvement from the destination UE device. For example, in some scenarios, the source UE may select a small number of candidate relay devices, which then inform the destination UE device regarding the request from the source UE, and the destination UE device finalizes the selection of which device to use as a relay from among the candidate relay devices selected by the source UE device. As a result, in some circumstances, the example of FIG. 10 may include additional steps not shown in FIG. 10, where these steps involve actions, feedback, or other intervention by the destination UE device.

[0103] In step 1002, the link rank from the source to the destination is calculated. For each neighbor list, the source UE device calculates the sum of the destination UE device's rank and the source UE device's rank.

[0104] At least one candidate relay device is selected at step 1004 based at least in part on the calculated source-to-destination link rank. For example, the UE device with the neighbor list having the lowest rank sum is the preferred candidate and is selected. In some cases, only the UE device with the lowest rank sum is selected. In other situations, the UE device with the lowest rank sum is selected, and other UE devices with lower rank sum values ​​are selected, even though their values ​​are not the lowest.

[0105] In step 1006, a destination MCS for the relay transmission is selected based at least in part on the rank value of the destination UE device 102. For example, the lowest rank (best link) is used to determine the destination MCS. Thus, if multiple candidate relay devices are selected, the source UE device evaluates the neighbor lists of the selected candidate relay devices to identify the lowest rank associated with the destination UE device's ID and determines the MCS for the relay transmission.

[0106] At step 1008, a source MCS for the source transmission is determined. In one example, the source MCS for the source transmission is the same as the destination MCS for the relay transmission. In another example, the source MCS is different from the destination MCS. In one technique, the source MCS and relay MCS are determined based at least in part on the highest rank (lowest quality) of the communication links of all SR links associated with the ID of the source UE device. Thus, in such an example, if multiple relay UE devices are selected, the highest ranked SR communication link determines the source MCS for the source transmission and the highest ranked RD communication link determines the relay MCS for the relay transmission. Thus, the most robust MSC as dictated by the lowest quality link is used for each segment of the relay path, respectively.

[0107] The management of the MCS depends at least in part on the particular example cast type and communication resource scenario. In the example described below with multiple candidate relays, each segment of the relay path (SR link and RD link) are either unicast or broadcast with relay instruction information.

[0108] If the source transmission is broadcast with a relay identification and the relay transmission is broadcast with a destination device identification, the source MSC may be the same for the two path segments, or the source MCS may be different from the relay MCS. If the source MCS is the same as the relay MCS, the MCS is selected based on the highest ranked (lowest quality) link, which in one example may be either the SR link or the RD link. If the source MCS is In one MCS management approach that is different from the relay MCS, the source MCS is based on the highest ranked (lowest quality) SR link of all SR links of the selected relay, and the relay MCS is based on the highest ranked (lowest quality) RD link of all RD links of the selected relay.

[0109] In other scenarios where the source transmissions are multiple unicast transmissions (one for each selected relay device) on different communication resources and the relay transmissions are broadcast using the destination device identity, the source MCS of each source unicast transmission may be different from the other source unicast transmissions. Each source MCS is based on the quality of a particular link to the relay UE device. A single relay MSC may be used for all RD links of the selected relay device and is selected based on the highest ranked (lowest quality) RD link.

[0110] In some scenarios where the source transmission consists of multiple unicast transmissions (one for each selected relay device) on the same communication resource, a unicast is established for each selected relay device, but the source transmission of the destination data is made over the same resource (radio bearer). The selected relay UE device and the relay transmission consists of multiple unicast transmissions (from each selected relay device to the destination device) on the same communication resource. A unicast connection is established from each selected relay UE device to the destination device, but the relay transmission of the destination data is made over the same resource (radio bearer) to the selected destination UE device. In such scenarios where the source MCS is the same as the relay MCS, the MCS is selected based on the highest ranked (lowest quality) link, which can be either an SR link or an RD link. If the source MCS is different from the relay MCS, the source MCS is based on the highest ranked (lowest quality) SR link of all SR links of the selected relays, and the relay MCS is based on the highest ranked (lowest quality) RD link of all RD links of the selected relays.

[0111] In step 1010, a source transmission is transmitted to the candidate relay devices. The source transmission includes destination device data and control information as described above. In some situations, the source transmission also includes control information identifying the destination MCS to be used for the relay transmission. In implementations where the relay UE device applies the same MCS to the relay transmission as was used to transmit the source transmission, the control information identifying the destination MCS is omitted. In situations where the source and destination MCS are different, the control information identified the destination MCS.

[0112] Clearly, other embodiments and modifications of the present invention will be readily apparent to those skilled in the art in light of these teachings. The above description is illustrative and not limiting. The present invention is to be limited only by the scope of the following claims, which claims include all such embodiments and modifications, when taken 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 source user equipment (UE) device, comprising: a receiver for receiving a UE list directly from a relay UE device, the UE list identifying a plurality of nearby UE devices within communication range of the relay UE device; a transmitter configured to transmit a direct communication request message to the relay UE device for establishing a unicast link with the relay UE device; The transmitter transmits data addressed to the target UE device directly to the relay UE device via the unicast link. Source UE device.

2. A processor for controlling a source user equipment (UE) device, comprising: receiving, directly from a relay UE device, a UE list identifying a number of nearby UE devices within communication range of the relay UE device; sending a direct communication request message to the relay UE device for establishing a unicast link with the relay UE device; and transmitting data destined for the target UE device directly to the relay UE device via the unicast link. Processor.

3. receiving, by a source user equipment (UE) device directly from the relay UE device, a UE list identifying a plurality of nearby UE devices that are within communication range of the relay UE device; the source UE device sending a direct communication request message to the relay UE device for establishing a unicast link with the relay UE device; the source UE device transmitting data destined for the target UE device directly to the relay UE device via the unicast link. method.

4. receiving, by a source user equipment (UE) device directly from the relay UE device, a UE list identifying a plurality of nearby UE devices that are within communication range of the relay UE device; the source UE device sending a direct communication request message to the relay UE device for establishing a unicast link with the relay UE device; and causing the source UE device to transmit data destined for the target UE device directly to the relay UE device via the unicast link. program.

5. a relay user equipment (UE) device transmitting, directly to a source UE device, a UE list identifying a plurality of nearby UE devices within communication range of the relay UE device; receiving, from the source UE device from which the relay UE device has received the UE list, a direct communication request message for establishing a unicast link between the source UE device and the relay UE device; receiving, by the relay UE device, via the unicast link, destination device data from the source UE device intended for target UE devices identified by the UE list; the relay UE device directly transmits the destination device data to the target UE device. program.

6. A mobile communication system comprising a source user equipment (UE) device and a relay UE device, The source UE device: receiving directly from the relay UE device a UE list identifying a plurality of nearby UE devices within communication range of the relay UE device; sending a direct communication request message to the relay UE device to establish a unicast link with the relay UE device; The relay UE device, receiving, via the unicast link, destination device data from the source UE device intended for target UE devices identified by the UE list; Transmitting the destination device data directly to the target UE device. Mobile communication system.

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