Patent Description:
In communications systems having user equipment (UE) and network nodes, relays such as UE-to-network relay UE (U2N relay) and UE-to-UE relay UE (U2U relay) may enhance network coverage and reliability. In a network employing relays by UEs, a transmitting UE needs to discover and select a relay before starting its transmissions to a remote UE. For a single-hop U2N relay, two possible models, may specified for discovery and relay selection or re-selection. In a first model (hereinafter model A), a U2N relay sends discovery announcement messages to remote UEs. In a second model (hereinafter model B), remote UEs send solicitation messages to ask for a relay service from another relay UE. The U2N relays may then respond to the solicitation messages from the remote UEs. In contrast to a single hop relay, for a multi-hop relay, it is possible for one relay (e.g., U2U relay) to be within in network coverage or out of coverage. In a scenario where it is possible for every UE to transmit discovery and become a U2U relay, allowing every UE to do can waste resources and create congestion to the discovery resource pool. Thus, methods and apparatus that determine which UEs or wireless transmit/receive unit (WTRUs) transmit discovery messages and/or what information the discovery messages should include are needed. Other methods and devices for multi-hop relays in a mesh network are disclosed in the patent publications <CIT> and <CIT>.

This invention is defined by the appended claims. Methods and apparatuses are described herein for multiple hop discovery and relay selection. For example, a network node may determine configuration information for transmission of a discovery message. The configuration information may comprise a Uu reference signal received power (RSRP) condition and a distance to base station (BS) condition. The Uu RSRP condition may include a range of Uu RSRP per hop to the BS and a range of Uu RSRP per Quality of Service (QoS) of a relay service. The distance to BS condition may include a range of distance to the BS per number of hops to the BS and a range of distance to the BS per QoS of a relay service. The network node may then transmit, to one or more child network nodes, the discovery message based on the configuration information.

For example, the communications systems <NUM> may employ one or more channel access methods, such as code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), orthogonal FDMA (OFDMA), singlecarrier FDMA (SC-FDMA), zero-tail unique-word discrete Fourier transform Spread OFDM (ZT-UW-DFT-S-OFDM), unique word OFDM (UW-OFDM), resource block-filtered OFDM, filter bank multicarrier (FBMC), and the like.

As shown in <FIG>, the communications system <NUM> may include wireless transmit/receive units (WTRUs) 102a, 102b, 102c, 102d, a radio access network (RAN) <NUM>, a core network (CN) <NUM>, a public switched telephone network (PSTN) <NUM>, the Internet <NUM>, and other networks <NUM>, though it will be appreciated that the disclosed embodiments contemplate any number of WTRUs, base stations, networks, and/or network elements. By way of example, the WTRUs 102a, 102b, 102c, 102d, any of which may be referred to as a station (STA), may be configured to transmit and/or receive wireless signals and may include a user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a subscription-based unit, a pager, a cellular telephone, a personal digital assistant (PDA), a smartphone, a laptop, a netbook, a personal computer, a wireless sensor, a hotspot or Mi-Fi device, an Internet of Things (IoT) device, a watch or other wearable, a head-mounted display (HMD), a vehicle, a drone, a medical device and applications (e.g., remote surgery), an industrial device and applications (e.g., a robot and/or other wireless devices operating in an industrial and/or an automated processing chain contexts), a consumer electronics device, a device operating on commercial and/or industrial wireless networks, and the like.

Each of the base stations 114a, 114b may be any type of device configured to wirelessly interface with at least one of the WTRUs 102a, 102b, 102c, 102d to facilitate access to one or more communication networks, such as the CN <NUM>, the Internet <NUM>, and/or the other networks <NUM>. By way of example, the base stations 114a, 114b may be a base transceiver station (BTS), a NodeB, an eNode B (eNB), a Home Node B, a Home eNode B, a next generation NodeB, such as a gNode B (gNB), a new radio (NR) NodeB, a site controller, an access point (AP), a wireless router, and the like.

In an embodiment, the base station 114a and the WTRUs 102a, 102b, 102c may implement a radio technology such as NR Radio Access , which may establish the air interface <NUM> using NR.

For example, the power source <NUM> may include one or more dry cell batteries (e.g., nickel-cadmium (NiCd), nickel-zinc (NiZn), nickel metal hydride (NiMH), lithium-ion (Liion), etc.), solar cells, fuel cells, and the like.

The WTRU <NUM> may include a full duplex radio for which transmission and reception of some or all of the signals (e.g., associated with particular subframes for both the UL (e.g., for transmission) and DL (e.g., for reception) may be concurrent and/or simultaneous. In an embodiment, the WTRU <NUM> may include a half-duplex radio for which transmission and reception of some or all of the signals (e.g., associated with particular subframes for either the UL (e.g., for transmission) or the DL (e.g., for reception)).

The AP may have access or an interface to a Distribution System (DS) or another type of wired/wireless network that carries traffic in to and/or out of the BSS. 11e DLS or an <NUM>.

The primary channel may be a fixed width (e.g., <NUM> wide bandwidth) or a dynamically set width. In certain representative embodiments, Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) may be implemented, for example in <NUM> systems.

A <NUM> channel may be formed by combining <NUM> contiguous <NUM> channels, or by combining two noncontiguous <NUM> channels, which may be referred to as an <NUM>+<NUM> configuration.

11af and <NUM>. 11af and <NUM>. 11n, and <NUM>. 11af supports <NUM>, <NUM>, and <NUM> bandwidths in the TV White Space (TVWS) spectrum, and <NUM>. 11ah may support Meter Type Control/Machine-Type Communications (MTC), such as MTC devices in a macro coverage area.

11n, <NUM>. 11ac, <NUM>. 11af, and <NUM>. If the primary channel is busy, for example, due to a STA (which supports only a <NUM> operating mode) transmitting to the AP, all available frequency bands may be considered busy even though a majority of the available frequency bands remains idle.

The WTRUs 102a, 102b, 102c may communicate with gNBs 180a, 180b, 180c using subframe or transmission time intervals (TTls) of various or scalable lengths (e.g., containing a varying number of OFDM symbols and/or lasting varying lengths of absolute time).

For example, the AMF 182a, 182b may be responsible for authenticating users of the WTRUs 102a, 102b, 102c, support for network slicing (e.g., handling of different protocol data unit (PDU) sessions with different requirements), selecting a particular SMF 183a, 183b, management of the registration area, termination of non-access stratum (NAS) signaling, mobility management, and the like. For example, different network slices may be established for different use cases such as services relying on ultra-reliable low latency (URLLC) access, services relying on enhanced massive mobile broadband (eMBB) access, services for MTC access, and the like. The AMF 182a, 182b may provide a control plane function for switching between the RAN <NUM> and other RANs (not shown) that employ other radio technologies, such as LTE, LTE-A, LTE-A Pro, and/or non-3GPP access technologies such as WiFi.

The following terminologies may be used throughout this disclosure:.

The terms UE-to-UE (U2) relay and WTRU-to-WTRU relay may be used interchangeably throughout this disclosure. The terms UE-to-UE (U2U) and WTRU-to-WTRU may be used interchangeably throughout this disclosure. The terms UE-to-Network (U2N) relay and WTRU-to-Network relay may be used interchangeably throughout this disclosure. The terms UE-to-Network (U2N) and WTRU-to-Network may be used interchangeably throughout this disclosure.

Current <NUM> wireless communications systems operate primarily on network to device communications links wherein data flows directly between a base station (Network) and a wireless user device (UE or WTRU). In order to extend coverage range from the base station, sidelink relaying may be used, which refers to the use of both WTRU-to-Network relays and WTRU-to-WTRU relays.

<FIG> is a diagram of an exemplary wireless communications system for implementing sidelink relaying.

An exemplary system comprises a network node or gNB, <NUM>. The network node <NUM> is configured to communicate wirelessly with mobile user equipment (UE). Three signal level thresholds are shown at increasing distances from the node <NUM>. A plurality of user devices (UE) are shown. User equipment (UE) (<NUM>, <NUM>, <NUM>) are shown located between Threshold <NUM> and Threshold <NUM>. User equipment (UE) (<NUM>, <NUM>) are shown located between Threshold <NUM> and Threshold <NUM>. User equipment (UE) (<NUM>, <NUM>, <NUM>) are shown located beyond Threshold <NUM>. As shown, UE <NUM>, <NUM>, and <NUM> communicate directly with the node <NUM>. These direct UE-node links (210a, 210b, 210c) are is labeled Uu. UE <NUM> and <NUM> are shown transmitting U2N discovery messages, i.e. announcing to other UE that they are available to relay from another UE (e.g. <NUM>, <NUM>) directly back to the node <NUM>. UE <NUM>, <NUM> and <NUM> are shown transmitting U2U discovery messages (230a. 233a, 240a), i.e. announcing to other UE that they are available to relay from that other UE to another UE closer to the node <NUM>. UE <NUM> and <NUM> are shown as remote UE that are incapable of direct communication with the node <NUM>, but can communicate with the node via relays 232a and 240a with US <NUM> and <NUM>, respectively.

In discovery model A, a U2N relay sends discovery announcement messages to remote UEs. In discovery model B, remote UEs send solicitation messages to ask for a relay service from another relay UE. The U2N relays may then respond to the solicitation messages from the remote UEs. <FIG> illustrates an example system employing discovery model A.

In contrast to a single hop relay, for a multi-hop relay (e.g. as shown in <FIG> by UE <NUM>, <NUM>, <NUM>), it is possible for one relay (e.g., U2U relay) to be within in network coverage or out of coverage (e. g UE <NUM>). In a scenario where it is possible for every UE to transmit discovery and become a U2U relay, allowing every UE to do so can waste resources and create congestion to the discovery resource pool. Described below are methods for determining which UEs or wireless transmit/receive unit (WTRUs) transmit discovery messages and/or what information the discovery messages should include are needed.

For model A discovery, the WTRU may be (pre-)configured multiple (e.g., two) Uu RSRP ranges, in which the first range may be used when the WTRU transmit a discovery message to be an WTRU-to-Network relay (e.g., directly connect to the gNB), and the second range may be used when the WTRU transmits a discovery message to be an WTRU-to-WTRU relay (e.g., not directly connect to the gNB). The WTRU may then determine whether to transmit a discovery message based on whether the WTRU targets to be an WTRU-to-WTRU relay or WTRU-to-Network relay and whether the measured Uu RSRP is within the associated range. Specifically, if the Uu RSRP is within the first range (e.g., Thres2<Uu RSRP< Thres1), the WTRU may transmit a discovery message to serve as an WTRU-to-Network relay. Otherwise, if the Uu RSRP is within the second range (e.g., Thres3<Uu RSRP< Thres2), the WTRU may transmit a discovery message to serve as an WTRU-to-WTRU relay. The WTRU may additionally determine whether to transmit a discovery message to serve as an WTRU-to-WTRU based on whether it detects a WTRU-to-Network relay. Specifically, it may transmit a discovery message to serve as an WTRU-to-WTRU if it detects a WTRU-to-Network relay; otherwise, it may not transmit the discovery message.

<FIG> illustrates an example WTRU-to-Network relay discovery with Model A. In Model A, WTRU-to-Network relay may send announcement messages. A UE <NUM> announcing availability as a UE-network relay sends a discovery announcement message <NUM>, <NUM>, <NUM>, which is received by remote UE1 (<NUM>), UE2 (<NUM>) and UE <NUM>(<NUM>). In embodiments, the UE announcing availability as a UE-Network relay can also send additional information (<NUM>, <NUM>, <NUM>) to the remote UE (<NUM>, <NUM>, <NUM>), respectively.

<FIG> illustrates an example WTRU-to-Network relay discovery with Model B. In model B, a remote WTRU (e.g. <NUM>) may send solicitation messages (<NUM>, <NUM>, <NUM>) to ask for a relay service from another relay WTRU (e.g. <NUM>, <NUM>, <NUM>. Then WTRU-to-Network relays may respond to the solicitation message from the remote WTRU. In this example, UE-Network Relay <NUM> (<NUM>) and UE-Network Relay <NUM> (<NUM>) respond to the remote UE <NUM> with discovery response messages <NUM> and <NUM>, respectively.

The coverage extension for sidelink-based communication may include WTRU-to-Network coverage extension and WTRU-to-WTRU coverage extension. For WTRU-to-Network coverage extension, Uu coverage reachability may be necessary for WTRUs to reach a server in PDN network or counterpart WTRU out of proximity area.

For the WTRU-to-WTRU coverage extension, proximity reachability may be limited to single-hop sidelink link, either via EUTRA-based or NR-based sidelink technology. However, that may not be sufficient in the scenario where there is no Uu coverage, considering the limited single-hop sidelink coverage. Overall, sidelink connectivity may be further extended in NR framework, in order to support the enhanced QoS requirements.

Mechanisms with minimum specification impact to support the SA requirements for sidelink-based WTRU-to-network and WTRU-to-WTRU relay may focus on the following aspects (if applicable) for layer-<NUM> relay and layer-<NUM> relay [RAN2]; relay (re-)selection criterion and procedure; relay/remote WTRU authorization; QoS for relaying functionality; service continuity; security of relayed connection after SA3 has provided its conclusions; and impact on user plane protocol stack and control plane procedure (e.g., connection management of relayed connection).

Mechanisms to support upper layer operations of discovery model/procedure for sidelink relaying may assume no new physical layer channel / signal [RAN2]. WTRU-to-network relays and WTRU-to-WTRU relays may use the same relaying embodiment. For layer-<NUM> WTRU-to-network relay, the architecture of end-to-end PDCP and hop-by-hop RLC may be taken as starting point.

Relaying via ProSe WTRU-to-Network relays can extend network coverage to an out of coverage WTRU by using PC5 (D2D) between an out of coverage WTRU and a WTRU-to-Network relay. A ProSe WTRU-to-Network relay may provide a generic L3 forwarding function that can relay any type of IP traffic between the remote WTRU and the network. One-to-one and one-to-many sidelink communications are used between the remote WTRU(s) and the ProSe WTRU-to-Network relay. For both remote WTRU and relay WTRU, only one single carrier (i.e., Public Safety ProSe Carrier) operation may be supported (i.e., Uu and PC5 may be the same carrier for relay/remote WTRU). The remote WTRU may be authorized by upper layers and can be in-coverage of the Public Safety ProSe Carrier or out-of-coverage on any supported carriers including Public Safety ProSe Carrier for WTRU-to-Network relay discovery, (re)selection and communication. The ProSe WTRU-to-Network relay may be always in-coverage of EUTRAN. The ProSe WTRU-to-Network relay and the remote WTRU may perform sidelink communication and sidelink discovery.

Relay selection/reselection for ProSe WTRU-to-Network relays may be performed based on combination of a AS layer quality measurements (e.g., RSRP) and upper layer criteria. Specifically, a base station (BS) (e.g., eNB) may control whether the WTRU can act as a ProSe WTRU-to-Network relay. If the BS (e.g., eNB) broadcast any information associated to ProSe WTRU-to-Network relay operation, then ProSe WTRU-to-Network relay operation may be supported in the cell.

The BS (e.g., eNB) may provide transmission resources for ProSe WTRU-to-Network relay discovery using broadcast signaling for RRC_IDLE state and dedicated signaling for RRC_CONNECTED state. The BS (e.g., eNB) may provide reception resources for ProSe WTRU-to-Network relay discovery using broadcast signaling. The BS (e.g., eNB) may broadcast a minimum and/or a maximum Uu link quality (e.g., RSRP) threshold(s) that the ProSe WTRU-to-Network relay needs to respect before it can initiate a WTRU-to-Network relay discovery procedure. In RRC_IDLE, when the BS (e.g., eNB) broadcasts transmission resource pools, the WTRU may use the threshold(s) to autonomously start or stop the WTRU-to-Network relay discovery procedure. In RRC_CONNECTED, the WTRU may use the threshold(s) to determine if it can indicate to BS (e.g., eNB) that it is a relay WTRU and wants to start ProSe WTRU-to-Network relay discovery.

If the BS (e.g., eNB) does not broadcast transmission resource pools for ProSe-WTRU-to-Network relay discovery, then a WTRU can initiate a request for ProSe-WTRU-to-Network relay discovery resources by dedicated signaling, respecting these broadcasted threshold(s).

If the ProSe-WTRU-to-Network relay is initiated by broadcast signaling, it can perform ProSe WTRU-to-Network relay discovery when in RRC_IDLE. If the ProSe WTRU-to-Network relay is initiated by dedicated signaling, it can perform relay discovery as long as it is in RRC_CONNECTED.

A ProSe WTRU-to-Network relay performing sidelink communication for ProSe WTRU-to-Network relay operation has to be in RRC_CONNECTED. After receiving a layer-<NUM> link establishment request or TMGI monitoring request (e.g., upper layer message) from the remote WTRU, the ProSe WTRU-to-Network relay may indicate to the BS (e.g., eNB) that it is a ProSe WTRU-to-Network relay and intends to perform ProSe WTRU-to-Network relay sidelink communication. The BS (e.g., eNB) may provide resources for ProSe WTRU-to-Network relay communication.

The remote WTRU can decide when to start monitoring for ProSe WTRU-to-Network relay discovery. The remote WTRU can transmit ProSe WTRU-to-Network relay discovery solicitation messages while in RRC_IDLE or in RRC_CONNECTED depending on the configuration of resources for ProSe WTRU-to-Network relay discovery. The BS (e.g., eNB) may broadcast a threshold, which is used by the remote WTRU to determine if it can transmit ProSe WTRU-to-Network relay discovery solicitation messages, to connect or communicate with ProSe WTRU-to-Network relay WTRU. The RRC_CONNECTED remote WTRU, may use the broadcasted threshold to determine if it can indicate to BS (e.g., eNB) that it is a remote WTRU and wants to participate in ProSe WTRU-to-Network relay discovery and/or communication. The BS (e.g., eNB) may provide, transmission resources using broadcast or dedicated signaling and reception resources using broadcast signaling for ProSe WTRU-to-Network relay operation. The remote WTRU may stop using ProSe WTRU-to-Network relay discovery and communication resources when RSRP goes above the broadcasted threshold.

Exact time of traffic switching from Uu to PC5 or vice versa is up to a higher layer.

The remote WTRU may perform radio measurements at PC5 interface and use them for ProSe WTRU-to-Network relay selection and reselection along with higher layer criterion. A ProSe WTRU-to-Network relay may be considered suitable in terms of radio criteria if the PC5 link quality exceeds configured threshold (e.g., pre-configured or provided by BS such as eNB). The remote WTRU may select the ProSe WTRU-to-Network relay, which satisfies higher layer criterion and has best PC5 link quality among all suitable ProSe WTRU-to-Network relays.

The remote WTRU triggers ProSe WTRU-to-Network Relay reselection when PC5 signal strength of current ProSe WTRU-to-Network relay is below configured signal strength threshold. The remote WTRU triggers ProSe WTRU-to-Network Relay reselection when it receives a layer-<NUM> link release message (e.g., upper layer message) from ProSe WTRU-to-Network relay.

<FIG> illustrates an example user plane radio protocol stack for layer <NUM> evolved User Equipment (UE)-to-Network relay (PC5), between a remote WTRU <NUM>, a relay WTRU <NUM>, an eNB <NUM> and core network <NUM>. Communication between the remote WTRU <NUM> and the relay WTRU is at the physical layer PC5 (<NUM>). Communication between the relay WTRU <NUM> and the eNB <NUM> is the physical layer Uu (<NUM>). Communication between the eNB and the CN is by S1-U/S5/S8 (<NUM>). <FIG> illustrates an example control plane radio protocol stack for layer <NUM> evolved UE-to-Network relay (PC5). WTRU-to-Network relays for commercial use cases tailored to wearables and loT devices may be performed in RAN. Contrary to ProSe WTRU-to-Network relays which uses a L3 (e.g., IP layer) relaying approach, the WTRU-to-Network relays for wearables may use a L2 relay (<NUM>, <NUM>) based on the protocol stacks as illustrated in <FIG> and <FIG>.

Relay embodiments may be based on a one to one communication link established at upper layers (ProSe layer) between two WTRUs (e.g., the remote WTRU and WTRU-to-Network relay). Such connection may be transparent to the AS layer and connection management signaling and procedures performed at the upper layers may be carried by AS layer data channels. The AS layer may be unaware of such a one to one connection.

In NR V2X the AS layer may support the notion of a unicast link between two WTRUs. Such unicast link may be initiated by upper layers (as in the ProSe one-to-one connection). However, the AS layer may be informed of the presence of such unicast link, and any data that may be transmitted in unicast fashion between the peer WTRUs. With such knowledge, the AS layer can support HARQ-feedback, CQI feedback, and power control schemes which are specific to unicast.

A unicast link at the AS layer may be supported via a PC5-RRC connection. The PC5-RRC connection may be defined as follows: The PC5-RRC connection is a logical connection between a pair of a Source Layer-<NUM> ID and a Destination Layer-<NUM> ID in the AS. One PC5-RRC connection is corresponding to one PC5 unicast link. The PC5-RRC signaling can be initiated after its corresponding PC5 unicast link establishment. The PC5-RRC connection and the corresponding sidelink SRBs and sidelink DRBs are released when the PC5 unicast link is released as indicated by upper layers. For each PC5-RRC connection of unicast, one sidelink SRB is used to transmit the PC5-S messages before the PC5-S security has been established. One sidelink SRB is used to transmit the PC5-S messages to establish the PC5-S security. One sidelink SRB is used to transmit the PC5-S messages after the PC5-S security has been established, which is protected. One sidelink SRB is used to transmit the PC5-RRC signaling, which is protected and only sent after the PC5-S security has been established.

PC5-RRC signaling may include a sidelink configuration message (e.g., RRCReconfigurationSidelink) where one WTRU configures the RX-related parameters of each sideling radio bearer (SLRB) in the peer WTRU. Such reconfiguration message can configure the parameters of each protocol in the L2 stack (e.g., SDAP, PDCP, etc.). The receiving WTRU can confirm or reject such configuration, depending on whether it can support the configuration suggested by the peer WTRU.

In embodiments, a WTRU (e.g., WTRU-to-WTRU relay WTRU) is (pre-)configured with some or all of the following conditions to transmit/forward a discovery message:.

In embodiments, if the WTRU does not satisfy condition(s) to become a WTRU-to-Network relay (e.g., it can be WTRU-to-WTRU relay only). The following actions are performed:.

In further embodiments, a WTRU (e.g., WTRU-to-WTRU relay WTRU) is (pre-)configured with the following conditions to forward a discovery message:.

In further embodiments, a WTRU (e.g., WTRU-to-WTRU relay WTRU) monitors a discovery solicitation message from child WTRUs (e.g., remote WTRU) and a discovery announcement message from a parent node (e.g., WTRU-to-Network relay).

If the WTRU has on going connection with the gNB, for each detected discovery solicitation message, the WTRU determines the number of remaining hops to reach the gNB based on the indication in the message. The WTRU forwards the path information of the detected discovery message to the parent node using PC5-RRC if the number of hops to the gNB is smaller than the remaining hops in the discovery solicitation message.

Otherwise, if the WTRU does not have on going connection with the gNB, the WTRU determines the shortest path to gNB based on the detected discovery announcement message from parent nodes and forwards the path information of the detected discovery message using discovery solicitation message if the conditions to transmit discovery solicitation message as a function of the number of hops in the shortest path are satisfied (e.g., Uu RSRP condition if the WTRU is in coverage and distance to gNB condition if the WTRU is out of network coverage).

Embodiments for discovery transmission are described herein.

In embodiments, a WTR performs discovery monitoring. In one embodiment, the WTRU determines whether to monitor discovery transmissions from other WTRUs for multi-hop relay. For example, for model A discovery, the WTRU determines to monitor discovery resource pool if the WTRU does not satisfy the condition to be a WTRU-to-Network relay. Specifically, if Uu RSRP becomes smaller than a (pre-)configured threshold, the WTRU triggers discovery monitoring to monitor discovery transmission from a WTRU-to-Network to offer WTRU-to-WTRU relay service to remote WTRUs.

In embodiments, a first WTRU decodes discovery messages from other WTRUs. The first WTRU performs one or any combination of the trigger discovery transmission procedure and trigger relay (re)selection procedure upon reception of discovery messages from the other WTRUs.

In embodiments, the first WTRU performs a trigger discovery transmission procedure, for example, the first WTRU (e.g., WTRU-to-WTRU relay) monitors discovery messages from the child/parent node (e.g., WTRU-to-Network relay) to transmit a discovery message and conveys the child/parent node information to the remote WTRUs to offer the WTRU-to-WTRU relay service to the remote WTRUs.

In embodiments, the first WTRU performs a trigger relay (re)selection procedure, for example, the WTRU (e.g., remote WTRU) has an on-going connection with a WTRU-to-WTUR relay connecting directly to a WTRU-to-Network relay. The WTRU monitors discovery messages from other WTRUs. The WTRU triggers relay (re)selection if it detects a discovery message from a WTRU-to-Network relay. The WTRU triggers relay (re)selection by switching from the existing path to the new path if the discovery messages from the WTUR-to-Network relay satisfies a set of condition(s) (e.g., SL-RSRP is greater than a threshold).

In embodiments, a WTRU determines the QoS of the relay service. In embodiments, the QoS of the relay service includes each hop QoS (hop-by-hop QoS) and the QoS from the source to the destination (i.e., end-to-end QoS). The QoS parameters include one or any combination of the priority associated with the relay service, the latency associated with the relay service, and the reliability associated with the relay service. In embodiments, the priority associated with the relay service is determined based on the priority of the established SLRB/LCH from tone or multiple nodes in the relay path. In embodiments, the latency associated with the relay service is determined based on the latency associated with one hop and the maximum number of hops allowed from the source to the destination. In embodiments, the reliability associated with the relay service is determined based on the reliability associated with one hop and the maximum number of hops allowed from the source to the destination.

In embodiments, a WTRU determines the QoS of the discovery message. In one embodiment, the QoS of the discovery message includes one or any combination of the parameters such as the priority of the message, the reliability of the message, and the latency requirement of the message.

In embodiments, a WTRU indicates the relay type in the discovery message. In one embodiment, the WTRU transmits a discovery message. In embodiments, the WTRU indicates its relay type (e.g., WTRU-to-WTRU relay, WTRU-to-Network relay, the number of hops to the source/destination, etc.) in the discovery message to offer relay service to another WTRU. In embodiments, the WTRU indicates whether it is a WTRU-to-WTRU relay and/or WTRU-to-Network relay. In one embodiment, the WTRU transmits a discovery message to indicate that it can be an WTRU-to-Network relay. In another embodiment, the WTRU transmits a discovery message to indicate it can be a WTRU-to-WTRU relay. In another embodiment, the WTRU transmits a discovery message to indicate that it can be either a WTRU-to-WTRU relay or an WTRU-to-Network relay. In embodiments, the indication is implicitly or explicitly indicated in the discovery message.

In embodiments, a WTRU determines its relay type. In one embodiment, the WTRU determines its relay type (e.g., WTRU-to-WTRU relay, WTRU-to-Network relay) based on one or any combination of the following:.

In embodiments, a WTRU determines whether to transmit a discovery message. In one embodiment, the WTRU determines whether to transmit a discovery message based on one or any combination of the following: the (pre-)configured number of hops to the gNB; the remaining number of hops and/or the remaining delay to reach the source/destination node; the availability of the parent/child node; the measured Uu RSRP; the measured SL RSRP; the distance to the parent/child node and/or the distance to the source/destination node; the distance to gNB; the coverage status of the WTRU; QoS of the relay service; indication from the child/parent node; the connection status to a child/parent node; the load of the WTRU; the cell ID; and/or the PLMN ID.

In embodiments, a WTRU determines whether to transmit a discovery message based on the (pre-)configured number of hops to the gNB. In one embodiment, the WTRU determines whether to transmit a discovery message based on the (pre-)configured relay type. In embodiments, the WTRU is (pre-)configured to be a WTRU-to-Network relay only. The WTRU then determines whether to transmit a discovery message based on the conditions to be a WTRU-to-Network relay. In embodiments, the WTRU is (pre-)configured to be a WTRU-to-WTRU relay WTRU. The WTRU then determines whether to transmit a discovery message based on the conditions to be a WTRU-to-WTRU relay. The conditions include some or all of: the availability of a source/destination node, the Uu RSRP, etc. In embodiments, the WTRU is (pre-) configured to be a relay regardless of whether it is a WTRU-to-WTRU or WTRU-to-Network relay. The WTRU then determines whether to transmit a discovery message based on the conditions to transmit a discovery to be a WTRU-to-Network relay or the conditions to transmit a discovery to be a WTRU-to-WTRU relay.

In embodiments, a WTRU determines whether to transmit a discovery message based on the remaining number of hops and/or the remaining delay to reach the source/destination node. In embodiments, the WTRU receives a discovery message from a parent/child node, the WTRU determines whether to transmit a discovery message to forward the discovery information for the parent/child node based on the number of remaining hops and/or the remaining delay for the discovery message, which is indicated in the discovery message received from the parent/child node. In embodiments, the WTRU determines the remaining delay and/or the remaining number of hops for a discovery message based on the discovery message received from the parent/child node. In embodiments, if the remaining delay and/or the remaining number of hops is smaller than a threshold, the WTRU does not transmit the discovery message; otherwise, if the remaining delay and/or the remaining number of hops is greater than the threshold, the WTRU transmits the discovery message.

For example, the WTRU receives a discovery message from an WTRU-to-Network relay. The WTRU determines whether to transmit a discovery message to forward the discovery information from the WTRU-to-Network relay based on the maximum number of hops the WTRU-to-Network relay wants to reach the destination/source WTRU, which is implicitly or explicitly indicated in the discovery message from the WTRU-to-Network relay. If the discovery message indicates that WTRU-to-WTRU relay is disabled (i.e., WTRU-to-Network relay only serve remote WTRUs), the WTRU will not transmit a discovery message to forward the discovery information from the WTRU-to-Network relay; otherwise, the WTRU will transmit the discovery message to forward the discovery information from the WTRU-to-Network relay.

In embodiments, the WTRU determine whether to transmit a discovery message based on the availability of the parent/child node. In embodiments, if the WTRU determines that it is not allowed to be an WTRU-to-Network relay, the WTRU determines whether it can be an WTRU-to-WTRU relay to relay message from/to another WTRU-to-Network relay based on the availability of one or multiple parent/child nodes. In embodiments, for a model A discovery procedure, the WTRU determines to transmit a discovery message if it detects a suitable WTRU-to-Network relay; otherwise, the WTRU will not transmit a discovery message. In embodiments, the WTRU determines whether it detects a suitable WTRU-to-Network relay by decoding the discovery messages from an WTRU-to-Network relay. In embodiments, for a model B discovery procedure, the WTRU determines to transmit a discovery message if it detects a suitable remote WTRU; otherwise, if the WTRU does not detect a remote WTRU, the WTRU will not transmit a discovery message. In another embodiment, the WTRU determines to transmit a discovery message if it detects one suitable child WTRU and another suitable parent WTRU; otherwise, the WTRU will not transmit a discovery message.

In embodiments, a WTRU determines whether to transmit a discovery message based on its measured Uu RSRP. In embodiments, the WTRU is (pre-)configured with multiple Uu RSRP ranges, in which each range is associated with one type of the discovery message, the number of hops to the gNB, the QoS of the relay service, and/or the number of hops to the source/destination node. The WTRU determines which Uu RSRP range to apply based on the number of hops to the gNB, and/or the number of hops to the source/destination nodes. The WTRU transmits the discovery message if the measured Uu RSRP is within the range. Otherwise, the WTRU will not transmit the discovery message.

In one example, as illustrated in <FIG>, for model A discovery, WTRUs are (pre-)configured with multiple (e.g., two) Uu RSRP ranges, in which the first range (<NUM>-<NUM>) is used when the WTRU transmits a discovery message to be an WTRU-to-Network relay (e.g., directly connect to the gNB), and the second range (<NUM>-<NUM>) is used when the WTRU transmits a discovery message to be an WTRU-to-WTRU relay (e.g., the WTRU is not directly connect to the gNB). The WTRU then determines whether to transmit a discovery message based on whether the WTRU targets to be an WTRU-to-WTRU relay or WTRU-to-Network relay and whether the measured Uu RSRP is within the associated range. Specifically, if the Uu RSRP is within the first range (e.g., Thres2<Uu RSRP< Thres1), the WTRU (e.g. <NUM>, <NUM>) transmits a discovery message (e.g. 220a, 222a) to serve as an WTRU-to-Network relay. Otherwise, if the Uu RSRP is within the second range (e.g., Thres3<Uu RSRP< Thres2), the WTRU (e.g. <NUM>, <NUM>) transmits a discovery message (e.g. 230a 232a) to serve as an WTRU-to-WTRU relay.

An example of the foregoing embodiment is described in flow diagram <FIG> as follows: Instep <NUM> one example, a WTRU is (pre-)configured with multiple (e.g., two) Uu RSRP ranges, in which Range <NUM> is used when the WTRU transmits a discovery message to be an WTRU-to-Network relay (e.g., directly connect to the gNB), and Range <NUM> is used when the WTRU transmits a discovery message to be an WTRU-to-WTRU relay (e.g., the WTRU is not directly connect to the gNB). , At Step <NUM>, the WTRU determines whether the Uu RSRP is within the first range (e.g., Thres2<Uu RSRP< Thres1). IF the answer is yes, then at step <NUM>, the WTRU transmits a discovery message to serve as an WTRU-to-Network relay. If the answer is no, then at step <NUM>, the WTRU determines whether the Uu RSRP is within the second range (e.g., Thres3<Uu RSRP< Thres2). If the answer is yes, then at step <NUM>, the WTRU transmits a discovery message to serve as an WTRU-to-WTRU relay. In embodiments, as shown for example at step <NUM>, the WTRU additionally determines whether to transmit a discovery message to serve as an WTRU-to-WTRU based on whether it detects a WTRU-to-Network relay. If the answer is yes, at step <NUM>, the WTRU transmits a discovery message to serve as an WTRU-to-WTRU if it detects a WTRU-to-Network relay; otherwise, it will not transmit the discovery message.

In another embodiment, a WTRU determines whether to transmit a discovery based on the SL RSRP of the sidelink channel between the WTRU and the child node and/or the sidelink channel between the WTRU and the parent node. Specifically, the WTRU transmits the discovery message if the SL RSRP of the slidelink channel between the WTRU and the child node and/or the sidelink channel between the WTRU and the parent node is greater than a threshold. In embodiments, the SL RSRP threshold is (pre-)configured per sidelink hop.

In another embodiment, the WTRU determines whether to transmit a discovery message based on the distance to the parent/child node and/or the distance to the source/destination node. In embodiments, the WTRU is (pre-)configured a distance range to the parent/child node and/or a distance range to the source/destination node to be a relay. The WTRU then determines whether to transmit a discovery message to offer service to the remote WTRU based on the distance between the WTRU and the child/parent node and/or based on the distance between the WTRU and the source/destination node. In embodiments, the WTRU transmits the discovery message and in embodiments conveys the information about the source/destination node and/or the parent/child node if the distance between the WTRU and the source/destination node and/or the distance between the WTRU and the parent/child node is within a (pre-)configured range.

In another embodiment, the WTRU determines whether to transmit a discovery message based on the distance to the gNB. Specifically, the WTRU is be (pre-)configured one or multiple ranges of distance to the gNB to determine whether it is allowed to transmit a discovery message. Each range of distances is a function of the number of hops to the gNB, the QoS of the relay service, and/or the QoS of the discovery message. The WTRU then determines whether to transmit a discovery message based on the distance to the gNB, the number of hops to the gNB, the QoS of the relay service, and/or the QoS of the discovery message.

In embodiments, for one QoS of a relay service, the WTRU is (pre-)configured for two ranges of distances, in which the first range is used when the WTRU is a WTRU-to-Network relay, and the second range is used when the WTRU is a WTRU-to-WTRU relay connecting directly to a WTRU-to-Network relay. The WTRU then determines whether to transmit a discovery message based on the distance to the gNB and the number of hops to gNB (e.g., whether the WTRU is a WTRU-to-Network relay or a WTRU-to-WTRU relay connection directly to a WTRU-to-Network relay). For example, the WTRU transmit a discovery message to become a WTRU-to-Network relay if the distance to the gNB is within the first range.

In another embodiment, the WTRU determines whether to transmit a discovery message based on the coverage status of the WTRU. For example, the WTRU transmits a discovery message to be a WTRU-to-WTRU relay if the WTRU is out of network coverage; however, if the WTRU is within the network coverage, the WTRU transmits a discovery message to be a WTRU-to-Network relay. If the WTRU is be (pre-)configured to be a WTRU-to-WTRU relay, the WTRU is allowed to transmit a discovery message if it is out of network coverage; otherwise, if the WTRU is in network coverage, the WTRU is not allowed to transmit discovery message to be a WTRU-to-WTRU relay.

In another embodiment, an example of which is illustrated in <FIG>, the WTRU determines whether to transmit a discovery message based on the QoS of the relay service. At step <NUM>, the WTRU receives the discovery message from a WTRU-to-Network relay. At step <NUM>, the WTRU determines whether to transmit a discovery message to be a WTRU-to-WTRU relay of the WTRU-to-Network relay based on the QoS of the relay service indicated in the discovery message. In embodiments, the WTRU determines to transmit the discovery message if the QoS of the relay service is within one range at step <NUM>; otherwise, at step <NUM> the WTRU determines not to transmit the discovery message to be a WTRU-to-WTRU relay of the WTRU-to-Network relay. In embodiments, the QoS range is further (pre-)configured based on other parameters such as SL-RSRP, the load of the WTRU, etc..

In another embodiment, the WTRU determines whether to transmit a discovery message based on the indication from the child/parent node. The WTRU can have an on-going connection with the child/parent node. The WTRU then receives an indication from the child/parent node to transmit a discovery message. The indication is conveyed to the WTRU via SCI, MAC CE, or PC5 RRC. The WTRU then triggers discovery transmission based on the indication from the child/parent node.

In another embodiment, the WTRU determines whether to transmit a discovery message based on the connection status to a child/parent node. The WTRU may have an on-going connection with the child/parent node. The WTRU may then receive an indication from the child/parent node to transmit discovery message. The indication may be conveyed to the WTRU via SCI, MAC CE, or PC5 RRC. The WTRU may then trigger discovery transmission based on the indication from the child/parent node. The discovery message may include the information about the child/parent node such as the ID information of the source/destination node (e.g., WTRU ID, cell ID, or PLMN ID).

In another embodiment, an example if which is illustrated in <FIG>, the WTRU determines whether to transmit a discovery message based on the load of the WTRU. In embodiments, at step <NUM>, the WTRU is (pre-)configured with one or multiple load thresholds, in which each of the thresholds is associated with one type of relay. The WTRU then determines whether to transmit a discovery message or not based on its relay type and its load. In embodiments, the WTRU is (pre-)configured with three load thresholds, in which the load level between a first threshold (Thresh <NUM>) and a second threshold (Thresh <NUM>) is associated with WTRU-to-Network relay, and the load level between a second threshold (Thresh <NUM>) and a third threshold (Thresh <NUM>) is associated with WTRU-to-WTRU relay. At step <NUM>, the WTRU determines whether the load is between the first and second thresholds. If the answer is yes, then at step <NUM>, the WTRU transmits a discovery message indicating availability as a WTRU-to-Network relay). If the answer is no, then at step <NUM>, the WTRU determines whether the load is between the second threshold and a third threshold. If the answer is yes, then at step <NUM>, the WTRU transmits a discovery message indicating availability as a WTRU-to-WTRU relay. While not shown, in <FIG>, if the load level is above the third threshold, in embodiments, the WTRU does not send a discovery message. In embodiments, the WTRU is (pre-)configured with two load thresholds. For loads between a first threshold and a second threshold, the WTRU sends a discovery message indicating availability as a WTRU-Network relay and for loads above the second threshold the WTRU sends a discovery message indicating availability as a WTRU-WTRU relay. In embodiments, the WTRU is (pre-)configured with one load threshold. For loads below a first threshold, the WTRU sends a discovery message indicating availability as a WTRU-Network relay and for loads above the first threshold the WTRU sends a discovery message indicating availability as a WTRU-WTRU relay.

In embodiments, an WTRU determines which conditions to check before discovery transmission based on the coverage status of the WTRU. In one embodiment, the WTRU is (pre-)configured with multiple sets of conditions to perform discovery transmission, each set of conditions is determined based on one or any combination of the coverage status of the WTRU and the Uu RRC status of the WTRU.

For the coverage status of the WTRU, the WTRU is (pre-)configured two set of conditions to transmit discovery, in which the first set of conditions may be required if the WTRU is in the network coverage and the another set of conditions is required when the WTRU is out of network coverage. The WTRU determines which set of conditions to transmit discovery message based on the coverage status of the WTRU. If the WTRU is in the network coverage, the WTRU checks the first set of conditions, and if the WTRU is out of network coverage, the WTRU checks the second set of conditions. For example, for in network coverage scenario, in embodiments, the WTRU is required to check the Uu RSRP conditions (e.g., Uu RSRP should be within a (pre-)configured range). The WTRU then determines whether to transmit discovery message based on the Uu RSRP. However, when the WTRU is out of network coverage, the WTRU is required to check the distance to the gNB (e.g., distance to the gNB is within a (pre-)configured range). The WTRU then determines whether to transmit discovery message based on the distance to the gNB.

For the Uu RRC status of the WTRU, for example, the WTRU is (pre-)configured with two set of conditions to check in which the first set of conditions i required if the WTRU is in RRC connected mode and the second set of conditions is required if the WTRU is in RRC idle/inactive mode. The WTRU then determines which set of conditions to check based on the RRC status of the WTRU.

In an embodiment, the WTRU is (pre-)configured to be either a WTRU-to-Network or a WTRU-to-WTRU relay. The WTRU is (pre-)configured with two ranges of Uu RSRP in which the first range of Uu RSRP is the condition to be a WTRU-to-Network relay and the second range of Uu RSRP is the condition to be a WTRU-to-WTRU relay. The WTRU first determines whether it can be a WTRU-to-Network relay or not based on the Uu RSRP. Specifically, if Uu RSRP is within the first Uu RSRP range, the WTRU determines to be a WTRU-to-Network relay, and it transmits the discovery message to offer WTRU-to-Network relay service to other remote WTRUs. Otherwise, if Uu RSRP is not within the first range, the WTRU determines that it is not able to be an WTRU-to-Network relay. The WTRU then checks if Uu RSRP is within the second range or not. If the Uu RSRP is not within the second range, the WTRU determines that it is not able to be either WTRU-to-Network relay or WTRU-to-WTRU relay. Otherwise, if Uu RSRP is within the second range, the WTRU determines that it can be a WTRU-to-WTRU relay. In embodiments, the WTRU performs discovery monitoring to detect the availability of a WTRU-to-Network relay. If the WTRU detects a WTRU-to-Network relay, the WTRU determines to transmit a discovery message to be an WTRU-to-WTRU relay connecting to the WTRU-to-Network relay. In embodiments, the WTRU includes the information of the detected WTRU-to-Network relay in the discovery message.

In another exemplary embodiment, the WTRU is (pre-)configured to be either a WTRU-to-Network or a WTRU-to-WTRU relay. The WTRU is (pre-)configured with one range of Uu RSRP as a condition to be a WTRU-to-Network relay. The WTRU is further (pre-)configured with the one range of distance to gNB as a condition to be a WTRU-to-WTRU relay. The WTRU first determines whether it can be a WTRU-to-Network relay or not based on the Uu RSRP. If Uu RSRP is within the first Uu RSRP range, the WTRU determines to be a WTRU-to-Network relay, and it transmits the discovery message to offer WTRU-to-Network relay service to other remote WTRU. If the WTRU does not satisfy the condition to be a WTRU-to-Network relay, the WTRU then monitors discovery to detect the availability of a WTRU-to-Network relay. The WTRU then receives the location information of the source/destination node (e.g., gNB) from a discovery message transmitted from a WTRU-to-Network relay. The WTRU may then determine whether to be a WTRU-to-WTRU relay connecting directly to the WTRU-to-Network relay based on the distance between the WTRU and the gNB. Specifically, if the distance is within the (pre-)configured range, the WTRU may be a WTRU-to-WTRU relay; otherwise, the WTRU may not be a WTRU-to-Network relay. The WTRU may then transmit discovery message and may include the information about the gNB and the WTRU-to-Network relay in the discovery message to offer the relay service to the remote WTRU.

In embodiments, a WTRU determines the information to include in a discovery message. In embodiments, a WTRU includes one or any combination of the following information in the discovery message:.

In embodiments, the WTRU determines which information to include in the discovery message. In embodiments, the WTRU determines which information to include in the discovery message based on one or any combination of the following:.

In embodiments, a WTRU determines whether to include one child/parent node in the discovery message. In embodiments, the WTRU determines whether to include one child/parent node in the discovery message based on one or any combination of the following:.

In embodiments, a WTRU determines the QoS of the relay service. In embodiments, the WTRU determines the hop-by-hop QoS of the relay service. The WTRU determines the QoS of the relay service in the next hop based on the required QoS in the current hop, the maximum number of hops and/or the end-to-end QoS of the relay service. In embodiments, the WTRU is a WTRU-to-WTRU relay, which connects directly to the WTRU-to-Network relay and a remote WTRU. The WTRU receives a discovery message from a remote WTRU for model B discovery. The WTRU then determines the required QoS of the relay service in the hop between itself and the WTRU-to-Network relay based on the end-to-end required QoS, the required QoS in the hop between the WTRU and the remote WTRU and the <NUM>-hop relay service. In embodiments, the WTRU may equally split end-to-end latency among each hop.

In embodiments, an example of which is shown in <FIG>, at step <NUM>, a first WTRU (WTRU1) receives, from a second WTRU (WTRU2), a discovery message that includes a number of hops to a base station (BS) from the second WTRU, a location of the BS, and quality of service (QoS) parameters of the second WTRU. At step <NUM>, based on the location of the BS, a distance to the BS from the first WTRU is determined. In embodiments, the determined distance to the BS is within a preconfigured allowed range of distances, wherein the preconfigured allowed range of distances is associated with a number of hops from the first WTRU; At step <NUM>, based on the QoS parameters of the second WTRU, a relay load of the first WTRU, and side link (SL) reference signal received power (SL RSRP) of the received discovery message QoS parameters of the first WTRU for a relay service provided by the first WTRU are determined. At step <NUM>, WTRU1 determines whether the QoS parameters of the first WTRU and the determined distance to the BS are within preconfigured limits. If the answer is yes, then at step <NUM>, WTRU1 transmits to a third WTRU (WTRU3) a discovery message, which is a WTRU-WTRU discovery message. If the answer is no, at step <NUM>, WTRU1 does not transmit the discovery message. In further embodiments, the discovery message includes some or all of: a relay type of the first WTRU, a number of hops to the BS from the first WTRU, and the QoS parameters of the first WTRU, and a location of the BS. In further embodiments, the QoS parameters of the first WTRU include some or all of: priority information associated with the relay service, latency information associated with the relay service, and reliability information associated with the relay service.

Embodiments for relay selection and re-selection are described herein.

In embodiments, the WTRU (e.g., remote WTRU) determines the transmission latency of a packet. Specifically, the WTRU receives a timestamp in the packet the time, in which the packet is originally transmitted. The WTRU then determines the latency associated with one packet based on the time it decodes the message and the timestamp indicated in the packet. In embodiments, the WTRU indicates the timestamp in a packet. The source/destination node then determines the latency associated with the packet.

In embodiments, the WTRU determines the quality of the path based on one or any combination of: the number of hops in the path; the minimum RSRP (SL-RSRP or Uu RSRP) of all hops; and/or the average RSRP of all hops.

In embodiments, the WTRU performs the path shorten procedure by doing one or any combination of: monitoring discovery message; transmitting discovery message; triggering relay (re)selection; and/or performing connection establishment with the newly selected node.

In embodiments, the WTRU triggers the path shorten procedure based on one or any combination of the following events:.

Claim 1:
A method for use in a first wireless transmit / receive unit, WTRU, the method comprising:
receiving (<NUM>), from a second WTRU, a first discovery message that includes an indication of a number of hops to a base station, BS, from the second WTRU, an indication of a location of the BS, and quality of service, QoS, parameters of the second WTRU;
determining (<NUM>), based on the location of the BS, a distance to the BS from the first WTRU, wherein the determined distance to the BS is within a preconfigured allowed range, wherein the preconfigured allowed range is associated with a number of hops from the first WTRU;
determining (<NUM>), based on the QoS parameters of the second WTRU, a relay load of the first WTRU, and side link, SL, reference signal received power, SL RSRP, of the received first discovery message, QoS parameters of the first WTRU for a relay service provided by the first WTRU;
transmitting (<NUM>), based on the QoS parameters of the first WTRU and the determined distance to the BS, to a third WTRU, a second discovery message.