Method of determining relay selection behavior in wireless transmit / receive unit

Abstract

A wireless transmit / receive unit (WTRU) may determine an identifier of a first WTRU and / or an identifier of a second WTRU. The first WTRU and / or the second WTRU may be configured to communicate via a PC5 connection. The first WTRU may receive configuration information. The configuration information may include an indication of a time period associated with the relay selection procedure. The first WTRU may determine satisfaction of a trigger condition. The trigger condition may be associated with a channel condition of a PC5 connection with the second WTRU. The first WTRU may determine whether to initiate a discovery and / or link modification procedure and / or wait for a time period associated with a relay selection procedure based on satisfaction of a trigger condition. The WTRU may make a decision based on a comparison between the identifier of the first WTRU and the identifier of the second WTRU.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 445,362, filed February 14, 2023, which is incorporated herein by reference in its entirety. Background Art

[0003] Release 17 has specified SL-based wireless transmit / receive unit (WTRU)-to-network relay. Sidelink relays may be introduced to support 5G ProSe WTRU-to-network relay (U2N relay) functionality to provide connectivity to the network for (one or more) U2N remote WTRUs. Both Layer 2 (L2) and / or Layer 3 (L3) U2N relay architectures may be supported. Aside from controlling sidelink resources, the L3 U2N relay architecture may be transparent to the serving RAN of the U2N relay WTRU.

[0004] A U2N relay WTRU may be in RRC_CONNECTED to perform relaying of unicast data. L2 U2N relay operation may support several RRC state combinations. A U2N relay WTRU and a U2N remote WTRU may both be in RRC CONNECTED to perform transmission and / or reception of relayed unicast data. A U2N relay WTRU may be in RRC_IDLE, RRC_INACTIVE, and / or RRC_CONNECTED if the U2N remote WTRU(s) connected to the U2N relay WTRU are in RRC_INACTIVE and / or RRC_IDLE.

[0005] For L2 U2N relay, the U2N remote WTRU may be configured to use resource allocation mode 2 only for data to be relayed. A single unicast link may be established between one L2 U2N relay WTRU and / or one L2 U2N remote WTRU. Traffic of the U2N remote WTRU and / or traffic of the U2N relay WTRU via a given U2N relay WTRU may be separated in different Uu radio link control (RLC) channels on the Uu. Summary of the Invention

[0006] A first wireless transmit / receive unit (WTRU) may determine an identifier of a first WTRU and / or an identifier of a second WTRU. The first WTRU and / or the second WTRU may be configured to communicate via a PC5 connection. The first WTRU may receive configuration information. The configuration information may include an indication of a time period associated with a relay selection procedure. The first WTRU may determine that a trigger condition is satisfied. The trigger condition may be associated with a channel condition of the PC5 connection with the second WTRU. The first WTRU may determine whether to initiate a discovery and / or link modification procedure and / or wait for a time period associated with the relay selection procedure based on the satisfaction of the trigger condition. The WTRU may make this determination based on a comparison between the identifier of the first WTRU and the identifier of the second WTRU.

[0007] The triggering conditions may include a radio link failure (RLF) of the PC5 connection and / or a sidelink reference signal received power (SL-RSRP) measurement of the PC5 connection falling below a threshold.

[0008] The first WTRU may send a discovery and / or link modification message to initiate the discovery and / or link modification procedure. The first WTRU may make this determination based on a determination that the identifier of the first WTRU is less than the identifier of the second WTRU.

[0009] The first WTRU may start a timer for the time period based on a determination that the identifier of the first WTRU is greater than the identifier of the second WTRU.

[0010] If the time period lapses and / or the first WTRU does not receive an indication of relay selection, the first WTRU may initiate a discovery and / or link modification procedure.

[0011] The identifier of the first WTRU may include a first layer 2 ID and / or a local ID. The identifier of the second WTRU may include a layer 2 ID and / or a local ID.

[0012] The first WTRU may be designated as a master WTRU. If the first WTRU sends a request for the configuration information and a higher layer designates the first WTRU as the master WTRU without requiring configuration information and / or based on rules associated with the access stratum (AS) layer, the first WTRU may perform relay selection.

[0013] The rules associated with the AS layer include rules associated with quality of service (QoS) flows, channel state information (CSI) associated with the PC5 connection, and / or rules based on an identifier of the first WTRU and / or an identifier of the second WTRU.

[0014] The first WTRU may receive a release message from the second WTRU and / or trigger the relay selection procedure in response to receiving the release message. The first WTRU may stop a timer associated with the time period based on receiving a discovery solicitation message indicating that the second WTRU has completed relay selection and / or based on determining that channel conditions for the PC5 communication have changed. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1A is a system diagram illustrating an example communication system in which one or more disclosed embodiments may be implemented;

[0016] Figure 1B is a diagram illustrating that according to one embodiment, Figure 1A A system diagram of an example wireless transmit / receive unit (WTRU) used in the illustrated communication system;

[0017] Figure 1C is a diagram illustrating that according to one embodiment, Figure 1A a system diagram of an example radio access network (RAN) and an example core network (CN) used in the illustrated communication system;

[0018] Figure 1D is a diagram illustrating that according to one embodiment, Figure 1A a system diagram of yet another example RAN and yet another example CN used in the illustrated communication system;

[0019] Figure 2 Depicts the user plane protocol stack for Layer 2 (L2) WTRU to network relay;

[0020] Figure 3 Depicts the control plane protocol stack for L2 WTRU to network relay;

[0021] Figure 4 Describes the protocol stack for WTRU-to-network relay discovery messages;

[0022] Figure 5 Depicted is WTRU-to-WTRU relay discovery utilizing Model A;

[0023] Figure 6 WTRU-to-WTRU relay discovery utilizing Model B is depicted. DETAILED DESCRIPTION

[0024] Figure 1A The present invention is a schematic diagram illustrating an example communication system 100 in which one or more disclosed embodiments may be implemented. The communication system 100 may be a multi-access system that provides content, such as voice, data, video, messaging, broadcast, etc., to multiple wireless users. The communication system 100 may enable multiple wireless users to access such content by sharing system resources, including wireless bandwidth. For example, the communication system 100 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), single-carrier FDMA (SC-FDMA), zero-tail unique word DFT spread OFDM (ZT UWDTS-s OFDM), unique word OFDM (UW-OFDM), resource block filtered OFDM, filter bank multi-carrier (FBMC), etc.

[0025] like Figure 1A As shown, the communication system 100 may include wireless transmit / receive units (WTRUs) 102a, 102b, 102c, 102d, RAN 104 / 113, CN 106 / 115, public switched telephone network (PSTN) 108, the Internet 110, and other networks 112. However, it will be appreciated that the disclosed embodiments contemplate any number of WTRUs, base stations, networks, and / or network elements. Each of the WTRUs 102a, 102b, 102c, 102d may be any type of device configured to operate and / or communicate in a wireless environment. By way of example, the WTRUs 102a, 102b, 102c, 102d (any of which may be referred to as a “station” and / or “STA”) may be configured to transmit and / or receive wireless signals and may include user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a subscription-based unit, a pager, a cellular phone, 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 device, a head-mounted display (HMD), a vehicle, a drone, medical equipment and applications (e.g., remote surgery), industrial equipment and applications (e.g., robots and / or other wireless devices operating in industrial and / or automated process chain environments), consumer electronic devices, devices operating on commercial and / or industrial wireless networks, etc. Any of the WTRUs 102a, 102b, 102c, and 102d may be interchangeably referred to as WTRUs.

[0026] The communication system 100 may also include a base station 114a and / or a base station 114b. 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 106 / 115, the Internet 110, and / or other networks 112. By way of example, the base stations 114a, 114b may be a base transceiver station (BTS), a Node B, an eNode B, a Home Node B, a Home eNode B, a gNB, an NR Node B, a site controller, an access point (AP), a wireless router, and the like. While the base stations 114a, 114b are each depicted as a single element, it will be appreciated that the base stations 114a, 114b may include any number of interconnected base stations and / or network elements.

[0027] Base station 114a may be part of RAN 104 / 113, which may also include other base stations and / or network elements (not shown), such as a base station controller (BSC), a radio network controller (RNC), relay nodes, etc. Base station 114a and / or base station 114b may be configured to transmit and / or receive wireless signals on one or more carrier frequencies, which may be referred to as cells (not shown). These frequencies may be in licensed spectrum, unlicensed spectrum, or a combination of licensed and unlicensed spectrum. A cell may provide wireless service coverage to a specific geographic area, which may be relatively fixed or may change over time. The cell may be further divided into cell sectors. For example, the cell associated with base station 114a may be divided into three sectors. Thus, in one embodiment, base station 114a may include three transceivers, one for each sector of the cell. In one embodiment, base station 114a may employ multiple-input multiple-output (MIMO) technology and may use multiple transceivers for each sector of the cell. For example, beamforming may be used to transmit and / or receive signals in desired spatial directions.

[0028] The base stations 114a, 114b may communicate with one or more of the WTRUs 102a, 102b, 102c, 102d over an air interface 116, which may be any suitable wireless communication link (e.g., radio frequency (RF), microwave, centimeter wave, micrometer wave, infrared (IR), ultraviolet (UV), visible light, etc.). The air interface 116 may be established using any suitable radio access technology (RAT).

[0029] More specifically, as described above, the communication system 100 may be a multiple access system and may employ one or more channel access schemes such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and the like. For example, the base station 114a in the RAN 104 / 113 and the WTRUs 102a, 102b, 102c may implement a radio technology such as Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA), which may establish the air interface 115 / 116 / 117 using Wideband CDMA (WCDMA). WCDMA may include communication protocols such as High Speed ​​Packet Access (HSPA) and / or Evolved HSPA (HSPA+). HSPA may include High Speed ​​Downlink (DL) Packet Access (HSDPA) and / or High Speed ​​UL Packet Access (HSUPA).

[0030] In one embodiment, the base station 114a and the WTRUs 102a, 102b, 102c may implement a radio technology such as Evolved UMTS Terrestrial Radio Access (E-UTRA), which may establish the air interface 116 using Long Term Evolution (LTE) and / or LTE-Advanced (LTE-A) and / or LTE-Advanced Pro (LTE-A Pro).

[0031] In one embodiment, the base station 114a and the WTRUs 102a, 102b, 102c may implement a radio technology such as NR wireless access, which may establish the air interface 116 using New Radio (NR).

[0032] In one embodiment, the base station 114a and the WTRUs 102a, 102b, 102c may implement multiple radio access technologies. For example, the base station 114a and the WTRUs 102a, 102b, 102c may jointly implement LTE radio access and NR radio access, e.g., using dual connectivity (DC) principles. Thus, the air interface used by the WTRUs 102a, 102b, 102c may be characterized by multiple types of radio access technologies and / or transmissions to / from multiple types of base stations (e.g., eNBs and gNBs).

[0033] In other embodiments, the base station 114a and the WTRUs 102a, 102b, 102c may implement a radio technology such as IEEE 802.11 (i.e., Wireless Fidelity (WiFi)), IEEE 802.16 (i.e., Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000, CDMA2000 1X, CDMA2000 EV-DO, Interim Standard 2000 (IS-2000), Interim Standard 95 (IS-95), Interim Standard 856 (IS-856), Global System for Mobile communications (GSM), Enhanced Data rates for GSM Evolution (EDGE), GSM EDGE (GERAN), and the like.

[0034] For example, Figure 1A The base station 114b in the WLAN may be a wireless router, a Home NodeB, a Home eNodeB, or an access point, and may utilize any suitable RAT to facilitate wireless connectivity in a local area, such as a business, a home, a vehicle, a campus, an industrial facility, an air corridor (e.g., for use by drones), a road, and the like. In one embodiment, the base station 114b and the WTRUs 102c, 102d may implement a radio technology such as IEEE 802.11 to establish a wireless local area network (WLAN). In one embodiment, the base station 114b and the WTRUs 102c, 102d may implement a radio technology such as IEEE 802.15 to establish a wireless personal area network (WPAN). In another embodiment, the base station 114b and the WTRUs 102c, 102d may utilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE, LTE-A, LTE-A Pro, NR, etc.) to establish a microcell or a femtocell. Figure 1A As shown, base station 114b may be directly connected to Internet 110. Therefore, base station 114b may not need to access Internet 110 via CN 106 / 115.

[0035] The RAN 104 / 113 may be in communication with the CN 106 / 115, which may be any type of network configured to provide voice, data, applications, and / or Voice over Internet Protocol (VoIP) services to one or more of the WTRUs 102a, 102b, 102c, 102d. The data may have different quality of service (QoS) requirements, such as different throughput requirements, latency requirements, fault tolerance requirements, reliability requirements, data throughput requirements, mobility requirements, etc. The CN 106 / 115 may provide call control, billing services, mobile location-based services, prepaid calling, Internet connectivity, video distribution, etc., and / or perform advanced security functions, such as user authentication. Although in Figure 1AAlthough not shown, it will be appreciated that the RAN 104 / 113 and / or the CN 106 / 115 may be in direct or indirect communication with other RANs that employ the same RAT as the RAN 104 / 113 or a different RAT. For example, in addition to being connected to the RAN 104 / 113, which may utilize NR radio technology, the CN 106 / 115 may also be in communication with another RAN (not shown) that employs GSM, UMTS, CDMA2000, WiMAX, E-UTRA, or WiFi radio technology.

[0036] The CN 106 / 115 may also serve as a gateway for the WTRUs 102a, 102b, 102c, 102d to access the PSTN 108, the Internet 110, and / or other networks 112. The PSTN 108 may include a circuit-switched telephone network that provides plain old telephone service (POTS). The Internet 110 may include a global system of interconnected computer networks and devices that use common communication protocols, such as the Transmission Control Protocol (TCP), the User Datagram Protocol (UDP), and / or the Internet Protocol (IP) from the TCP / IP Internet protocol suite. The networks 112 may include wired and / or wireless communication networks owned and / or operated by other service providers. For example, the networks 112 may include another CN connected to one or more RANs, which may employ the same RAT as the RAN 104 / 113 or a different RAT.

[0037] Some or all of the WTRUs 102a, 102b, 102c, 102d in the communication system 100 may include multi-mode capabilities (e.g., the WTRUs 102a, 102b, 102c, 102d may include multiple transceivers for communicating with different wireless networks via different wireless links). Figure 1A The WTRU 102c shown in FIG. 1 may be configured to communicate with the base station 114a, which may employ a cellular-based radio technology, and with the base station 114b, which may employ an IEEE 802 radio technology.

[0038] Figure 1B is a system diagram illustrating an example WTRU 102. Figure 1B As shown, the WTRU 102 may include, among other things, a processor 118, a transceiver 120, a transmit / receive element 122, a speaker / microphone 124, a keypad 126, a display / touchpad 128, non-removable memory 130, removable memory 132, a power supply 134, a global positioning system (GPS) chipset 136, and / or other peripherals 138. It will be appreciated that the WTRU 102 may include any subcombination of the foregoing elements while remaining consistent with an embodiment.

[0039] The processor 118 may be a general purpose processor, a special purpose processor, a conventional processor, a digital signal processor (DSP), a plurality of microprocessors, one or more microprocessors associated with a DSP core, a controller, a microcontroller, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) circuit, any other type of integrated circuit (IC), a state machine, etc. The processor 118 may perform signal coding, data processing, power control, input / output processing, and / or any other functionality that enables the WTRU 102 to operate in a wireless environment. The processor 118 may be coupled to the transceiver 120, which may be coupled to the transmit / receive element 122. Although Figure 1B The processor 118 and the transceiver 120 are depicted as separate components, but it is understood that the processor 118 and the transceiver 120 may be integrated together in an electronic package or chip.

[0040] The transmit / receive element 122 may be configured to transmit signals to or receive signals from a base station (e.g., base station 114a) over the air interface 116. For example, in one embodiment, the transmit / receive element 122 may be an antenna configured to transmit and / or receive RF signals. In one embodiment, the transmit / receive element 122 may be, for example, an emitter / detector configured to transmit and / or receive IR, UV, or visible light signals. In yet another embodiment, the transmit / receive element 122 may be configured to transmit and / or receive both RF and light signals. It should be understood that the transmit / receive element 122 may be configured to transmit and / or receive any combination of wireless signals.

[0041] Although the transmit / receive element 122 is Figure 1B Although depicted as a single element in FIG1 , the WTRU 102 may include any number of transmit / receive elements 122. More specifically, the WTRU 102 may employ MIMO technology. Thus, in one embodiment, the WTRU 102 may include two or more transmit / receive elements 122 (e.g., multiple antennas) for transmitting and receiving wireless signals over the air interface 116.

[0042] The transceiver 120 may be configured to modulate signals to be transmitted by the transmit / receive element 122 and demodulate signals received by the transmit / receive element 122. As described above, the WTRU 102 may have multi-mode capabilities. Thus, for example, the transceiver 120 may include multiple transceivers to enable the WTRU 102 to communicate via multiple RATs, such as NR and IEEE 802.11.

[0043] The processor 118 of the WTRU 102 may be coupled to, and may receive user input data from, a speaker / microphone 124, a keypad 126, and / or a display / touchpad 128 (e.g., a liquid crystal display (LCD) display unit or an organic light emitting diode (OLED) display unit). The processor 118 may also output user data to the speaker / microphone 124, the keypad 126, and / or the display / touchpad 128. Furthermore, the processor 118 may access information from and store data in any type of suitable memory, such as non-removable memory 130 and / or removable memory 132. The non-removable memory 130 may include random access memory (RAM), read-only memory (ROM), a hard disk, or any other type of memory storage device. The removable memory 132 may include a subscriber identity module (SIM) card, a memory stick, a secure digital (SD) memory card, and the like. In other embodiments, the processor 118 may access information from and store data in memory that is not physically located on the WTRU 102, such as on a server or a home computer (not shown).

[0044] The processor 118 may receive power from the power source 134 and may be configured to distribute and / or control power to the other components in the WTRU 102. The power source 134 may be any suitable device for powering the WTRU 102. For example, the power source 134 may include one or more dry cell batteries (e.g., nickel-cadmium (NiCd), nickel-zinc (NiZn), nickel-metal hydride (NiMH), lithium-ion (Li-ion), etc.), solar cells, fuel cells, etc.

[0045] The processor 118 may also be coupled to the GPS chipset 136, which may be configured to provide location information (e.g., longitude and latitude) regarding the current location of the WTRU 102. In addition to or in lieu of information from the GPS chipset 136, the WTRU 102 may receive location information from a base station (e.g., base stations 114a, 114b) over the air interface 116 and / or determine its location based on the timing of signals received from two or more nearby base stations. It will be appreciated that the WTRU 102 may acquire location information by any suitable location-determination method while remaining consistent with an embodiment.

[0046] The processor 118 may be further coupled to other peripherals 138, which may include one or more software and / or hardware modules that provide additional features, functionality, and / or wired or wireless connectivity. For example, the peripherals 138 may include an accelerometer, an electronic compass, a satellite transceiver, a digital camera (for photos and / or video), a universal serial bus (USB) port, a vibration device, a television transceiver, a hands-free headset, Module, frequency modulation (FM) radio unit, digital music player, media player, electronic game player module, Internet browser, virtual reality and / or augmented reality (VR / AR) device, activity tracker, etc. The peripheral device 138 may include one or more sensors, which may be one or more of a gyroscope, an accelerometer, a Hall effect sensor, a magnetometer, an orientation sensor, a proximity sensor, a temperature sensor, a time sensor, a geographic location sensor, an altimeter, a light sensor, a touch sensor, a magnetometer, a barometer, a posture sensor, a biometric sensor, and / or a humidity sensor, etc.

[0047] The WTRU 102 may include a full-duplex radio for which transmission and reception of some or all signals (e.g., signals associated with particular subframes used for UL (e.g., for transmission) and downlink (e.g., for reception)) may be concurrent and / or simultaneous. The full-duplex radio may include an interference management unit 139 to reduce and or substantially eliminate self-interference via hardware (e.g., a choke) or via signal processing by a processor (e.g., a separate processor (not shown) or via the processor 118). In one embodiment, the WTRU 102 may include a half-duplex radio for which transmission and reception of some or all signals (e.g., signals associated with particular subframes used for UL (e.g., for transmission) or downlink (e.g., for reception)) may be concurrent and / or simultaneous.

[0048] Figure 1C 1 is a system diagram illustrating the RAN 104 and the CN 106 according to an embodiment. As described above, the RAN 104 may employ an E-UTRA radio technology to communicate with the WTRUs 102a, 102b, 102c over the air interface 116. The RAN 104 may also be in communication with the CN 106.

[0049] The RAN 104 may include eNode-Bs 160a, 160b, 160c, though it will be appreciated that the RAN 104 may include any number of eNode-Bs while remaining consistent with an embodiment. The eNode-Bs 160a, 160b, 160c may each include one or more transceivers for communicating with the WTRUs 102a, 102b, 102c over the air interface 116. In one embodiment, the eNode-Bs 160a, 160b, 160c may implement MIMO technology. Thus, for example, the eNode-B 160a may use multiple antennas to transmit wireless signals to and / or receive wireless signals from the WTRU 102a.

[0050] Each of the eNode-Bs 160a, 160b, 160c may be associated with a particular cell (not shown) and may be configured to handle radio resource management decisions, handover decisions, user scheduling in UL and / or DL, etc. Figure 1C As shown, eNode-Bs 160a, 160b, 160c may communicate with each other over an X2 interface.

[0051] Figure 1C The CN 106 shown in FIG may include a mobility management entity (MME) 162, a serving gateway (SGW) 164, and a packet data network (PDN) gateway (or PGW) 166. While each of the foregoing elements is depicted as part of the CN 106, it should be understood that any of these elements may be owned and / or operated by an entity other than the CN operator.

[0052] The MME 162 may be connected to each of the eNode-Bs 162a, 162b, 162c in the RAN 104 via an S1 interface and may serve as a control node. For example, the MME 162 may be responsible for authenticating users of the WTRUs 102a, 102b, 102c, bearer activation / deactivation, selecting a particular serving gateway during an initial attach of the WTRUs 102a, 102b, 102c, and the like. The MME 162 may also provide a control plane function for switching between the RAN 104 and other RANs (not shown) that employ other radio technologies, such as GSM and / or WCDMA.

[0053] The SGW 164 may be connected to each of the eNode Bs 160a, 160b, 160c in the RAN 104 via an S1 interface. The SGW 164 may generally route and forward user data packets to and from the WTRUs 102a, 102b, 102c. The SGW 164 may also perform other functions, such as anchoring the user plane during inter-eNode B handovers, triggering paging when downlink data is available for the WTRUs 102a, 102b, 102c, managing and storing the context of the WTRUs 102a, 102b, 102c, and the like.

[0054] The SGW 164 may be connected to the PGW 166, which may provide the WTRUs 102a, 102b, 102c with access to packet-switched networks, such as the Internet 110, to facilitate communications between the WTRUs 102a, 102b, 102c and IP-enabled devices.

[0055] The CN 106 may facilitate communications with other networks. For example, the CN 106 may provide the WTRUs 102a, 102b, 102c with access to circuit-switched networks, such as the PSTN 108, to facilitate communications between the WTRUs 102a, 102b, 102c and traditional land-line communications devices. For example, the CN 106 may include, or may communicate with, an IP gateway (e.g., an IP Multimedia Subsystem (IMS) server) that acts as an interface between the CN 106 and the PSTN 108. In addition, the CN 106 may provide the WTRUs 102a, 102b, 102c with access to other networks 112, which may include other wired and / or wireless networks owned and / or operated by other service providers.

[0056] Even though the WTRU Figures 1A-1D Although described as a wireless terminal, it is contemplated that in certain representative embodiments such a terminal may employ (eg, temporarily or permanently) a wired communication interface with a communication network.

[0057] In a representative embodiment, the other network 112 may be a WLAN.

[0058] A WLAN in infrastructure basic service set (BSS) mode may have an access point (AP) for the BSS and one or more stations (STAs) associated with the AP. The AP may access or be connected to a distributed system (DS) or another type of wired / wireless network that transmits traffic to and / or out of the BSS. Traffic originating from outside the BSS and destined for a STA may arrive through the AP and be delivered to the STA. Traffic originating from a STA to a destination outside the BSS may be sent to the AP for delivery to the corresponding destination. For example, traffic between STAs within a BSS may be sent through the AP, where the source STA may send traffic to the AP, and the AP may deliver the traffic to the destination STA. Traffic between STAs within a BSS may be considered and / or referred to as peer-to-peer traffic. Peer-to-peer traffic may be transmitted between the source and destination STAs (e.g., directly between them) using direct link setup (DLS). In certain representative embodiments, the DLS may use 802.11e DLS or 802.11z tunneled DLS (TDLS). A WLAN using an independent BSS (IBSS) mode may not have an AP, and STAs (eg, all STAs) within or using the IBSS may communicate directly with each other. The IBSS communication mode is sometimes referred to herein as an "ad hoc" communication mode.

[0059] When using 802.11ac infrastructure operation mode or a similar operation mode, the AP can transmit beacons on a fixed channel (such as a primary channel). The primary channel can be a fixed width (e.g., a wide bandwidth of 20 MHz) or a width dynamically set via signaling. The primary channel can be the operating channel of the BSS and can be used by STAs to establish a connection with the AP. In certain representative embodiments, such as in an 802.11 system, carrier sense multiple access with collision avoidance (CSMA / CA) can be implemented. For CSMA / CA, STAs (e.g., each STA), including the AP, can sense the primary channel. If a particular STA senses / detects and / or determines that the primary channel is busy, the particular STA can back off. One STA (e.g., only one station) can transmit at any given time in a given BSS.

[0060] High throughput (HT) STAs may communicate using a 40 MHz wide channel, for example, via a combination of a primary 20 MHz channel and adjacent or non-adjacent 20 MHz channels to form a 40 MHz wide channel.

[0061] Very high throughput (VHT) STAs can support 20 MHz, 40 MHz, 80 MHz, and / or 160 MHz wide channels. 40 MHz and / or 80 MHz channels can be formed by combining consecutive 20 MHz channels. A 160 MHz channel can be formed by combining eight consecutive 20 MHz channels, or by combining two discontinuous 80 MHz channels, which can be referred to as an 80+80 configuration. For the 80+80 configuration, after channel coding, the data can pass through a segment parser that can separate the data into two streams. Each stream can be subjected to inverse fast Fourier transform (IFFT) processing and time domain processing separately. These streams can be mapped onto two 80 MHz channels, and the data can be transmitted by the transmitting STA. At the receiver of the receiving STA, the operations of the above-mentioned 80+80 configuration can be reversed, and the combined data can be sent to the media access control (MAC).

[0062] 802.11af and 802.11ah support operating modes below 1 GHz. The channel operating bandwidth and carrier in 802.11af and 802.11ah are reduced relative to the channel operating bandwidth and carrier used in 802.11n and 802.11ac. 802.11af supports 5 MHz, 10 MHz, and 20 MHz bandwidths in the TV White Space (TVWS) spectrum, and 802.11ah supports 1 MHz, 2 MHz, 4 MHz, 8 MHz, and 16 MHz bandwidths using non-TVWS spectrum. According to a representative embodiment, 802.11ah may support metered type control / machine type communications, such as MTC devices in macro coverage areas. MTC devices may have certain capabilities, for example, limited capabilities, including support for (e.g., only support for) certain and / or limited bandwidths. MTC devices may include batteries with battery life above a threshold (e.g., in order to maintain very long battery life).

[0063] WLAN systems that can support multiple channels and channel bandwidths, such as 802.11n, 802.11ac, 802.11af, and 802.11ah, include a channel that can be designated as a primary channel. The bandwidth of the primary channel can be equal to the maximum common operating bandwidth supported by all STAs in the BSS. The bandwidth of the primary channel can be set and / or limited by one STA among all STAs operating in the BSS that supports the minimum bandwidth operating mode. In the example of 802.11ah, for a STA that supports (e.g., only supports) 1 MHz mode (e.g., an MTC-type device), the primary channel can be 1 MHz wide, even if the AP and other STAs in the BSS support 2 MHz, 4 MHz, 8 MHz, 16 MHz, and / or other channel bandwidth operating modes. Carrier sensing and / or network allocation vector (NAV) settings may depend on the status of the primary channel. If the primary channel is busy, for example, due to a STA (which only supports 1 MHz operating mode) transmitting to the AP, all available frequency bands can be considered busy, even if most of the available frequency bands remain idle and can be used.

[0064] In the United States, 802.11ah can be used in the available frequency band from 902MHz to 928MHz. In South Korea, the available frequency band is from 917.5MHz to 923.5MHz. In Japan, the available frequency band is from 916.5MHz to 927.5MHz. The total available bandwidth for 802.11ah ranges from 6MHz to 26MHz, depending on the country code.

[0065] Figure 1D1 is a system diagram illustrating the RAN 113 and the CN 115 according to one embodiment. As described above, the RAN 113 may employ NR radio technology to communicate with the WTRUs 102a, 102b, 102c over the air interface 116. The RAN 113 may also be in communication with the CN 115.

[0066] The RAN 113 may include gNBs 180a, 180b, and 180c, though it will be appreciated that the RAN 113 may include any number of gNBs while remaining consistent with an embodiment. The gNBs 180a, 180b, and 180c may each include one or more transceivers for communicating with the WTRUs 102a, 102b, and 102c over the air interface 116. In one embodiment, the gNBs 180a, 180b, and 180c may implement MIMO technology. For example, the gNBs 180a and 180b may utilize beamforming to transmit signals to and / or receive signals from the gNBs 180a, 180b, and 180c. Thus, for example, the gNB 180a may use multiple antennas to transmit wireless signals to and / or receive wireless signals from the WTRU 102a. In one embodiment, the gNBs 180a, 180b, and 180c may implement carrier aggregation technology. For example, the gNB 180a may transmit multiple component carriers (not shown) to the WTRU 102a. A subset of these component carriers may be on unlicensed spectrum, while the remaining component carriers may be on licensed spectrum. In one embodiment, the gNBs 180a, 180b, and 180c may implement coordinated multi-point (CoMP) technology. For example, the WTRU 102a may receive coordinated transmissions from the gNB 180a and gNB 180b (and / or gNB 180c).

[0067] The WTRUs 102a, 102b, 102c may communicate with the gNBs 180a, 180b, 180c using transmissions associated with scalable numerology. For example, the OFDM symbol spacing and / or OFDM subcarrier spacing may be different for different transmissions, different cells, and / or different portions of the wireless transmission spectrum. The WTRUs 102a, 102b, 102c may communicate with the gNBs 180a, 180b, 180c using subframes or transmission time intervals (TTIs) of varying or scalable lengths (e.g., containing a variable number of OFDM symbols and / or lasting a variable length of absolute time).

[0068] The gNBs 180a, 180b, 180c may be configured to communicate with the WTRUs 102a, 102b, 102c in a standalone configuration and / or a non-standalone configuration. In a standalone configuration, the WTRUs 102a, 102b, 102c may communicate with the gNBs 180a, 180b, 180c without accessing other RANs (e.g., such as the eNode-Bs 160a, 160b, 160c). In a standalone configuration, the WTRUs 102a, 102b, 102c may utilize one or more of the gNBs 180a, 180b, 180c as mobility anchors. In a standalone configuration, the WTRUs 102a, 102b, 102c may communicate with the gNBs 180a, 180b, 180c using signals in an unlicensed frequency band. In a non-standalone configuration, the WTRUs 102a, 102b, 102c may communicate / connect with the gNBs 180a, 180b, 180c while also communicating / connecting with another RAN, such as the eNode-Bs 160a, 160b, 160c. For example, the WTRUs 102a, 102b, 102c may implement DC principles to communicate with one or more gNBs 180a, 180b, 180c and one or more eNode-Bs 160a, 160b, 160c substantially simultaneously. In a non-standalone configuration, the eNode-Bs 160a, 160b, 160c may serve as mobility anchors for the WTRUs 102a, 102b, 102c, and the gNBs 180a, 180b, 180c may provide additional coverage and / or throughput for the serving WTRUs 102a, 102b, 102c.

[0069] Each of the gNBs 180a, 180b, 180c may be associated with a specific cell (not shown) and may be configured to handle radio resource management decisions, handover decisions, user scheduling in UL and / or DL, network slicing support, dual connectivity, interworking between NR and E-UTRA, routing user plane data to a user plane function (UPF) 184a, 184b, routing control plane information to an access and mobility management function (AMF) 182a, 182b, etc. Figure 1D As shown, gNBs 180a, 180b, and 180c can communicate with each other on the Xn interface.

[0070] Figure 1DThe illustrated CN 115 may include at least one AMF 182a, 182b, at least one UPF 184a, 184b, at least one Session Management Function (SMF) 183a, 183b, and possibly a Data Network (DN) 185a, 185b. While each of the aforementioned elements is depicted as part of the CN 115, it should be understood that any of these elements may be owned and / or operated by an entity other than the CN operator.

[0071] The AMF 182a, 182b may be connected to one or more of the gNBs 180a, 180b, 180c in the RAN 113 via the N2 interface and may act as a control node. For example, the AMF 182a, 182b may be responsible for authenticating users of the WTRU 102a, 102b, 102c, supporting network slicing (e.g., handling different PDU sessions with different requirements), selecting a specific SMF 183a, 183b, managing registration areas, terminating NAS signaling, mobility management, and the like. The AMF 182a, 182b may use network slicing to customize CN support for the WTRU 102a, 102b, 102c based on the type of service being used by the WTRU 102a, 102b, 102c. 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 machine-type communication (MTC) access, and / or the like. The AMF 162 may provide a control plane function for switching between the RAN 113 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.

[0072] The SMF 183a, 183b may connect to the AMF 182a, 182b in the CN 115 via the N11 interface. The SMF 183a, 183b may also connect to the UPF 184a, 184b in the CN 115 via the N4 interface. The SMF 183a, 183b may select and control the UPF 184a, 184b and configure the routing of traffic through the UPF 184a, 184b. The SMF 183a, 183b may perform other functions, such as managing and allocating WTRU IP addresses, managing PDU sessions, controlling policy enforcement and QoS, providing downlink data notification, etc. The PDU session type may be IP-based, non-IP-based, Ethernet-based, etc.

[0073] The UPF 184a, 184b may be connected to one or more gNBs 180a, 180b, 180c in the RAN 113 via an N3 interface, which may provide the WTRUs 102a, 102b, 102c with access to packet-switched networks, such as the Internet 110, to facilitate communications between the WTRUs 102a, 102b, 102c and IP-enabled devices. The UPF 184, 184b may perform other functions, such as routing and forwarding packets, enforcing user plane policies, supporting multi-homed PDU sessions, handling user plane QoS, buffering downlink packets, providing mobility anchoring, etc.

[0074] The CN 115 may facilitate communications with other networks. For example, the CN 115 may include, or may communicate with, an IP gateway (e.g., an IP Multimedia Subsystem (IMS) server) that acts as an interface between the CN 115 and the PSTN 108. Furthermore, the CN 115 may provide the WTRUs 102a, 102b, 102c with access to other networks 112, which may include other wired and / or wireless networks owned and / or operated by other service providers. In one embodiment, the WTRUs 102a, 102b, 102c may be connected to a local data network (DN) 185a, 185b through the UPF 184a, 184b via the N3 interface to the UPF 184a, 184b and the N6 interface between the UPF 184a, 184b and the DN 185a, 185b.

[0075] Given that Figures 1A-1D as well as Figures 1A-1D

[0015] As described herein, one or more or all of the functionality described herein with respect to one or more of the following may be performed by one or more emulated devices (not shown): the WTRUs 102a-d, base stations 114a-b, eNode-Bs 160a-c, MMEs 162, SGWs 164, PGWs 166, gNBs 180a-c, AMFs 182a-ab, UPFs 184a-b, SMFs 183a-b, DNs 185a-b, and / or any other device(s) described herein. An emulated device may be one or more devices configured to emulate one or more or all of the functionality described herein. For example, an emulated device may be used to test other devices and / or simulate network and / or WTRU functionality.

[0076] Emulated devices can be designed to implement one or more tests of other devices in a laboratory environment and / or in a carrier network environment. For example, one or more emulated devices can perform one or more or all functions while being fully or partially implemented and / or deployed as part of a wired and / or wireless communication network in order to test other devices within the communication network. One or more emulated devices can perform one or more or all functions while being temporarily implemented / deployed as part of a wired and / or wireless communication network. The emulated device can be directly coupled to another device for testing purposes and / or can perform tests using over-the-air wireless communications.

[0077] One or more emulated devices can perform one or more functions, including all functions, without being implemented / deployed as part of a wired and / or wireless communication network. For example, the emulated device can be used in a test lab and / or a test scenario in a non-deployed (e.g., testing) wired and / or wireless communication network to enable testing of one or more components. The one or more emulated devices can be test devices. The emulated device can transmit and / or receive data using direct RF coupling and / or wireless communication via RF circuitry (e.g., which can include one or more antennas).

[0078] The following Figure 2 and Figure 3 The protocol stacks for the user plane (UP) and control plane (CP) of the Layer 2 (L2) U2N relay architecture are described separately. For both the UP and / or CP at both the PC5 interface 220 and / or the Uu interface 240, the sidelink relay adaptation protocol (SRAP) sublayer 206 can be placed above the radio link control (RLC) sublayer 208. The Uu service data adaptation protocol (SDAP) 202, the packet data convergence protocol (PDCP) 204 and / or the radio resource control (RRC) 302 (e.g., Figure 3 2N remote WTRU 250 and / or the network gNB 260. The SRAP sublayer 206, the RLC sublayer 208, the medium access control (MAC) sublayer 210, and the physical layer (PHY) 212 may terminate at each hop (e.g., PC5 hop 230 and / or Uu hop 240). The PC5 hop 230 refers to the link between the L2 U2N remote WTRU 250 and / or the L2 U2N relay WTRU 260. The Uu hop 240 refers to the link between the L2 U2N relay WTRU 260 and / or the gNB 270.

[0079] For L2 U2N relaying, the SRAP sublayer 206 on the PC5 hop 230 may only be used for bearer mapping purposes. The SRAP sublayer 206 may not be present on the PC5 hop 230 for relaying messages on the Broadcast Control Channel (BCCH) and the Paging Control Channel (PCCH) for the L2 U2N remote WTRU 250. The SRAP sublayer 206 may not be present on the PC5 hop 220 for messages on the Signaling Radio Bearer (SRBO) for the L2 U2N remote WTRU 240. However, the SRAP sublayer 206 may be present on the Uu hop 230 for both the downlink (DL) and uplink (UL).

[0080] With respect to the L2 U2N relay 250 for uplink, the Uu SRAP sublayer 214 may support UL bearer mapping between the ingress PC5 relay RLC channel 280 and / or the egress Uu relay RLC channel 290 for relaying via the L2 U2N relay WTRU 260 Uu interface. For uplink relay traffic, different end-to-end resource blocks (RBs) (e.g., SRBs and / or data radio bearers (DRBs)) of the same remote WTRU 250 and / or different remote WTRUs may be multiplexed on the same Uu relay RLC channel 290.

[0081] The Uu SRAP sublayer 214 may support identification of the L2 U2N remote WTRU 250 for UL traffic. The Uu SRAP header may include identity information of the L2 U2N remote WTRU 250 Uu radio bearer and / or a local remote WTRU identifier (ID). The Uu SRAP header may include this information at the UL so that the gNB 270 can correlate received packets for a specific PDCP entity associated with the correct Uu radio bearer of the remote WTRU 250. The PC5 SRAP sublayer 206 at the L2 U2N remote WTRU 250 may support UL bearer mapping between the remote WTRU 250 Uu radio bearers and / or the egress PC5 relay RLC channel 280.

[0082] With respect to L2 U2N relay for the downlink, the Uu SRAP sublayer 214 may support DL bearer mapping at the gNB 270 to map the end-to-end radio bearers (e.g., SRBs and / or DRBs) of the remote WTRU 250 to the Uu relay RLC channel 290 over the relay WTRUUu interface. The Uu SRAP sublayer 214 may support DL bearer mapping and / or data multiplexing between multiple end-to-end radio bearers (e.g., SRBs and / or DRBs) of the L2 U2N remote WTRU 250 and / or different L2 U2N remote WTRUs and / or one Uu relay RLC channel 290 over the relay WTRUUu interface.

[0083] The Uu SRAP sublayer 214 may support identification of the remote WTRU 250 for DL ​​traffic. On the DL, the gNB 270 may include the identity information of the remote WTRU Uu radio bearer and / or the local remote WTRU ID in the Uu SRAP header. The gNB 270 may do this for the relay WTRU 250 to map packets received from the remote WTRU Uu radio bearer to its associated PC5 relay RLC channel 280.

[0084] The PC5 SRAP sublayer 206 at the relay WTRU 250 may support DL bearer mapping between the ingress Uu relay RLC channel 290 and / or the egress PC5 relay RLC channel 280 .

[0085] The PC5 SRAP sublayer 206 at the remote WTRU 250 may be associated with packets received for a specific PDCP entity associated with the right Uu radio bearer. The remote WTRU 250 may identify the remote WTRU based on the identity information included in the Uu SRAP header. The PC5 SRAP sublayer 206 may be responsible for mapping the WTRU ID and / or Uu radio bearer ID to the RLC channel 280 for data transmission.

[0086] The Local Remote WTRU ID may be included in both the PC5 SRAP header and / or the Uu SRAP header. The gNB 270 may configure the L2 U2N relay WTRU 260 with the Local Remote WTRU ID. The Local Remote WTRU ID may be used in the SRAP header. The Remote WTRU 250 may obtain the Local Remote ID from the gNB via Uu RRC messages including RRCSetup, RRCReconfiguration, RRCResume, and / or RRCReestablishment. The UuDRB(s) and / or Uu SRB(s) may be mapped to different PC5 relay RLC channels 280 and / or Uu relay RLC channels 290 in both the PC5 hop 230 and / or the Uu hop 240.

[0087] The gNB 270 may be responsible for avoiding conflicts regarding the use of the local remote WTRU ID. The gNB 270 may update the local remote WTRU ID by sending the updated local remote ID to the relay WTRU 250 via an RRCReconfiguration message. The serving gNB 270 may perform the local remote WTRU ID update independently of the PC5 unicast link identifier (e.g., L2 ID) update procedure. The identifiers of the remote WTRU and / or the relay WTRU may include a Layer 1 identifier and / or a local identifier.

[0088] Model A and / or Model B discovery models may be supported for U2N relay discovery. Figure 4 A protocol stack for WTRU-to-network relay discovery messages is depicted.

[0089] When the U2N remote WTRU 450 is in RRC_IDLE, RRC_INACTIVE, and / or RRC_CONNECTED, the U2N remote WTRU 450 may perform relay discovery message transmission and may monitor the sidelink for relay discovery messages. The network may broadcast a threshold. The U2N remote WTRU 450 uses this threshold to determine whether the U2N remote WTRU 450 can transmit a relay discovery solicitation message to the U2N relay WTRU(s) 460.

[0090] The U2N relay WTRU 460 may perform relay discovery message transmission. While the U2N relay WTRU 460 is in RRC_IDLE, RRC_INACTIVE, and / or RRC_CONNECTED, the U2N relay WTRU 460 may monitor the sidelink for relay discovery messages. The network may broadcast a maximum Uu reference signal received power (RSRP) threshold and / or a minimum Uu RSRP threshold. The U2N relay WTRU 460 may use the maximum Uu RSRP threshold and / or the minimum Uu RSRP threshold to determine whether the U2N relay WTRU 460 can transmit a relay discovery message to the U2N remote WTRU(s) 450.

[0091] The network may provide relay discovery configuration using broadcast and / or dedicated signaling for relay discovery. Additionally or alternatively, the U2N remote WTRU 450 and / or the U2N relay WTRU 460 may use pre-configuration for relay discovery.

[0092] The resource pool(s) used for NR sidelink communication may be used for relay discovery and / or the network may configure resource pool(s) dedicated to relay discovery. The resource pool(s) dedicated to relay discovery may be configured simultaneously with the resource pool(s) used for NR sidelink communication in system information, dedicated signaling, and / or pre-configuration.

[0093] Relay discovery can be based on its dedicated resource pool(s) on the network implementation. In an example, if resource pool(s) dedicated to relay discovery are configured, then those resource pool(s) dedicated to relay discovery can be used for relay discovery. If resource pool(s) for NR sidelink communication are configured, then all configured transport resource pool(s) can be used for relay discovery and / or sidelink communication.

[0094] For a U2N remote WTRU 450 connected to the network via a U2N relay WTRU 460 (both in-coverage and out-of-coverage), only resource allocation Mode 2 may be used for discovery message transmission. For Mode 1 operation, the gNB may allocate resources for the WTRU to use. For Mode 2 operation, the WTRU may autonomously select from a pool of resources.

[0095] The WTRU may support two different discovery procedures to discover and / or ultimately select a WTRU to a network relay. Figure 5 The first such procedure, referred to as Model A discovery, is depicted. In this Model A procedure, a WTRU-to-WTRU relay WTRU 520 may discover other WTRUs in its vicinity. The WTRU-to-WTRU relay WTRU 520 may send and / or broadcast announcement messages 502a-b to a source WTRU 510 (e.g., a remote WTRU) and / or a target WTRU 530 (e.g., another remote WTRU). As depicted at 540, the WTRU-to-WTRU relay WTRU 520 may discover other WTRUs in its vicinity via a direct discovery and / or direct communication procedure.

[0096] The announcement messages 502a-b may include the type of discovery message, the relay's user information ID, the relay service code, the neighboring WTRU's user information ID, and / or other potential information available to the relay WTRU (e.g., relay load, etc.). The remote WTRUs (e.g., the source WTRU 510 and / or the target WTRU 530) may then use this information to select the relay WTRU 520.

[0097] In a second procedure, a source WTRU 610 (eg, a remote WTRU) that desires to communicate with a target WTRU 630 (eg, another remote WTRU) may broadcast a solicitation message 602a-b to one or more candidate relay WTRUs 620a-b. Figure 6 6. This second such procedure, referred to as Model B Discovery, is depicted. The solicitation messages 602a-b may include the type of discovery message, the user information ID of the source WTRU 610, the user information ID of the target WTRU 630, and / or the relay service. When one or more candidate relays 620a-b receive the solicitation message(s) 602a-b, the one or more candidate relays 620a-b may then rebroadcast the solicitation message(s) 604a-b. The target WTRU 630 may select a relay from the received candidate relays 620a-b. The target WTRU 630 may receive the forwarded solicitation message(s) 602a-b based on various parameters, such as signal strength. At 606, the target WTRU 630 may respond to the relay WTRU 620a-b. At 608, the relay WTRU 630 may then respond to the source WTRU 610. For WTRU-to-WTRU relaying, Release 18 SA2 concludes that Model A and / or Model B discovery is supported.

[0098] The U2N remote WTRU may perform radio measurements at the PC5 interface. The U2N remote WTRU may use the measurements along with higher layer criteria for U2N relay selection and / or reselection. In the absence of a unicast PC5 connection between the U2N relay WTRU and / or the U2N remote WTRU, the U2N remote WTRU may use Sidelink Discovery Reference Signal Received Power (SD-RSRP) measurements to assess whether the PC5 link quality with the U2N relay WTRU meets the relay selection criteria.

[0099] Regarding relay reselection, the U2N remote WTRU may use SL-RSRP measurements for the serving U2N relay WTRU for relay reselection trigger evaluation. The U2N remote WTRU may use SL-RSRP measurements when the U2N relay WTRU transmits data to the U2N remote WTRU. In the absence of data transmission from the U2N relay WTRU to the U2N remote WTRU, the WTRU implementation may determine whether to use SL-RSRP and / or SD-RSRP for relay reselection trigger evaluation.

[0100] If the PC5 link quality measured by the U2N remote WTRU for the U2N relay WTRU exceeds a configured threshold, the U2N remote WTRU may consider the U2N relay WTRU according to the radio criteria. The threshold may be pre-configured and / or provided by the gNB. The U2N remote WTRU may search for suitable U2N relay WTRU candidates that meet all AS layer and higher layer criteria. The U2N remote WTRU implementation may select one U2N relay WTRU among multiple suitable U2N relay WTRUs. For L2 U2N relay (re)selection, PLMNID and / or cell ID may be used as additional AS criteria. Additionally or alternatively, higher layers may designate the remote WTRU as the master WTRU without the need for configuration information and / or rules associated with the AS layer.

[0101] The U2N remote WTRU may trigger U2N relay selection when: the direct Uu signal strength of the current serving cell of the U2N remote WTRU drops below a signal strength threshold indicated and / or configured by the upper layers of the U2N remote WTRU; the PC5 signal strength of the current U2N relay WTRU drops below a pre-configured signal strength threshold; cell (re)selection; handover via PC5-RRC signaling and / or U2N relay WTRU indication of Uu RLF; when the remote WTRU receives a PC5-S link release message from the U2N relay WTRU; and / or when the U2N remote WTRU detects a PC5 RLF indicated by the upper layers.

[0102] For an L2 U2N remote WTRU and / or an L3 U2N remote WTRU in RRC_IDLE / INACTIVE, the cell (re)selection procedure and / or the relay (re)selection procedure may be run independently. If a suitable cell and / or a suitable U2N relay WTRU are both available, the WTRU implementation may select the cell and / or U2N relay WTRU. An L3 U2N remote WTRU implementation may select the cell and / or U2N relay WTRU simultaneously.

[0103] For both L2 and / or L3 U2N relay WTRUs that are in RRC_IDLE / INACTIVE, PC5-RRC message(s) may be used to notify their connected remote WTRU(s) when the U2N relay WTRU selects a new cell. PC5-RRC message(s) may also be used to notify their connected L2 and / or L3 U2N remote WTRU(s) when the L2 / L3 U2N relay WTRU performs a handover and / or detects a Uu RLF. Upon receiving the PC5 RRC message for notification, the U2N remote WTRU implementation may determine whether to release or maintain the unicast PC5 link. If the U2N remote WTRU decides to release the unicast PC5 link, the U2N remote WTRU may trigger an L2 release procedure and / or may perform relay reselection.

[0104] A U2N relay may have a very simple connection architecture and / or network coverage. Specifically, it may be assumed that the remote WTRU is out of coverage, while the relay WTRU may be assumed to be in coverage. It may be assumed that the remote WTRU has a single unicast link with the relay WTRU. The relay WTRU may have a traditional RRC connection with the network. Finally, the remote WTRU always performs the relay selection and / or reselection procedure, so that one WTRU performs the operation.

[0105] U2U relays may have more variations in topology and / or coverage conditions, such as one, two, and / or all WTRUs being in coverage or out of coverage. U2U relays may include the same or different relays operating in Mode 1 / Mode 2, resource pooling configurations, and / or serving a single source WTRU with multiple connections to different destinations, and vice versa. In addition, any remote WTRU may initiate a relay discovery or (re)selection procedure.

[0106] With respect to U2U relays specifically, a remote WTRU that has a direct PC5 connection and / or an indirect connection (e.g., via a U2U relay) with another remote WTRU may need to select a relay (for direct to indirect) and / or a different relay (for indirect). In the event of a problem with the existing direct and / or indirect link, the remote WTRU may need to select and / or reselect a relay to continue communicating with the remote WTRU.

[0107] Two remote WTRUs may independently trigger relay selection because there is no way to determine with certainty that the other WTRU has also triggered relay selection. Two remote WTRUs independently triggering relay selection may result in the two WTRUs sending direct communication request (DCR) messages to potentially different relays. WTRUs independently sending DCR messages to different relays may result in unnecessary messages on the SL and / or potentially selecting different relays for communication in different directions. To address these issues, new conditions and / or criteria for discovery message transmission may be considered, including selecting an appropriate discovery model and / or means to synchronize relay (re)selection between source and / or destination remote WTRUs.

[0108] The WTRU may determine whether to initiate (re)selection immediately upon AS triggering and / or to initiate (re)selection after a period of time based on a certain relationship between the WTRU's own identifier (e.g., L2 ID) and the identifier of the peer WTRU (e.g., L2 ID). The relationship may be that one identifier is greater than or less than the other identifier. The WTRU and / or (one or more) peer WTRUs may communicate via a PC5 connection. The WTRU may determine that a triggering condition is satisfied. The triggering condition may depend on the channel conditions associated with the (one or more) peer WTRUs. The first WTRU may then determine whether to initiate discovery and / or link modification procedures and / or wait for a time period associated with reselection based on the satisfaction of the triggering condition. The WTRU may make this decision based on a comparison between the WTRU's identifier (e.g., L2 ID) and the identifier (e.g., L2 ID) of the peer WTRU(').

[0109] Specifically, the WTRU may perform a unicast link establishment with a peer WTRU. The WTRU may determine a source and / or destination identifier (e.g., L2 ID) for the unicast link. The WTRU may receive a configuration for a timer associated with a relay (re)selection trigger from the network. The WTRU may monitor the PC5 connection link for potential selection triggering events (e.g., the remote WTRU detects RLF and / or SL-RSRP drops below a predefined threshold). Upon detecting a selection triggering event, the WTRU may initiate a discovery and / or link modification procedure if the WTRU's source identifier (e.g., L2 ID) is less than the peer WTRU's source identifier (e.g., L2 ID). The discovery and / or link modification procedure may include a discovery and / or link modification message. The discovery and / or link modification message may include an indication of relay selection.

[0110] If the WTRU's source identifier (e.g., L2 ID) is not less than the peer WTRU's source identifier (e.g., L2 ID), the WTRU may wait for a configured time period. After the configured time period has elapsed, and if the WTRU has not received a discovery solicitation and / or link modification that includes an indication of relay selection due to a link failure, the WTRU may initiate a discovery and / or link modification procedure. The WTRU may make the decision to send a discovery and / or link modification message based on the WTRU's identifier (e.g., L2 ID) being less than the peer WTRU's identifier (e.g., L2 ID).

[0111] The WTRU may determine which discovery model procedure to use based on the AS layer triggering conditions that trigger relay selection (eg, RLF versus SL-RSRP threshold).

[0112] Specifically, the WTRU may be configured with a PC5 connection to another remote WTRU.The WTRU may be configured with an SL-RSRP threshold for acceptable link quality and / or a timer associated with the WTRU triggering a discovery solicitation.

[0113] If the WTRU detects RLF, the WTRU may transmit a link modification message and / or a Model B solicitation message including an indication of RLF detection. The WTRU may wait for a response from the relay WTRU indicating that the target has received the solicitation and / or link modification and selected the relay.

[0114] If the WTRU detects that the RSRP has dropped below a configured threshold, the WTRU may initiate relay selection based on the received Model A Announcement message. The WTRU may select a relay WTRU to communicate with a target WTRU (e.g., a remote WTRU). The WTRU may send a Release message to the WTRU (e.g., the target WTRU). The Release message may notify the WTRU to release the PC5-RRC connection and / or notify the remote WTRU that the WTRU has performed relay selection. If, after a configured duration, the WTRU has not selected a new relay, the WTRU may transmit a Model B Solicitation message and / or a Link Modification message to initiate relay selection.

[0115] A remote WTRU that communicates directly (e.g., using a direct PC5 link) or indirectly (e.g., via a WTRU-to-WTRU relay) may be designated as a primary WTRU or a secondary WTRU. This designation may serve as a means of identifying which remote WTRU is primarily responsible for triggering the relay (re)selection procedure.

[0116] Relay selection may be triggered based on detecting PC5-RLF and / or PC5 RSRP falling below a threshold for the direct link between the remote WTRUs. For the relay (re)selection example, the same AS layer triggers may apply, but based on the link between the remote WTRU and / or the relay WTRU. In both cases, either remote WTRU may trigger the (re)selection.

[0117] The two AS layer trigger conditions may have an impact on how relay selection triggering and / or discovery needs to be performed. In RLF, a remote WTRU may not be able to communicate with its peer WTRU. In an example, a method to avoid redundant relay selection by two WTRUs may require the first WTRU that detects the problem to initiate a Model B procedure. The first remote WTRU may send a solicitation to initiate relay selection. The peer remote WTRU may then send a response. When the SL-RSRP drops below a threshold, communication may still be possible to coordinate which WTRU to reselect and / or which WTRU to make Model A feasible without the need for redundant relay selection and / or link establishment procedures.

[0118] The WTRU may determine whether to initiate (re)selection immediately upon AS triggering and / or after a period of time based on a certain relationship between its own identifier (e.g., L2 ID) and / or the identifier of a peer WTRU (e.g., L2 ID). The relationship may be that one identifier is greater than or less than the other.

[0119] Specifically, the WTRU may perform unicast link establishment with a peer WTRU and / or determine source and / or destination identifiers (e.g., L2 IDs) for the unicast link. The WTRU may receive configurations for timers associated with relay (re)selection triggers from the network. The WTRU may monitor the PC5 connection link for potential selection triggering events (e.g., the remote WTRU detects RLF and / or SL-RSRP drops below a predefined threshold).

[0120] Upon detecting a selection triggering event, a WTRU (e.g., a remote WTRU) may initiate a discovery and / or link modification procedure if the WTRU's source identifier (e.g., L2 ID) is less than the peer WTRU's source identifier (e.g., L2 ID). The discovery and / or link modification procedure may include a discovery and / or link modification message. The discovery and / or link modification message may include an indication of relay selection.

[0121] If the WTRU's source identifier (e.g., L2 ID) is not less than the peer WTRU's source identifier (e.g., L2 ID), the WTRU may wait for a configured time period. After the configured time period has elapsed, and if the WTRU has not received a discovery solicitation and / or link modification (the discovery solicitation and / or link modification including an indication of relay selection due to a link failure), the WTRU may initiate a discovery and / or link modification procedure.

[0122] The relay selection behavior may be based on the master WTRU (e.g., primary) or secondary WTRU designation. The relay selection procedure may be triggered under any of the following conditions: RSRP of the direct (e.g., PC5) or indirect (e.g., relay) link is below a threshold, CBR is above a threshold, CR is above a threshold, the remote WTRU detects SL-RLF, data-related conditions (such as the age of the data, the priority of the data, the rate at which the data is consumed and / or the amount of data in the buffer, the duration of time the link is inactive (e.g., due to no data transmission), relay-related conditions (such as the data rate supported by the relay, the data rate required by the remote WTRU, the supported QoS / reliability / latency and / or relay capabilities, a change in the availability and / or quality of channel state information (CSI) information (e.g., a change in the quality of the channel state information / channel quality indicator (CSI / CQI) reports for the WTRU-relay WTRU and / or remote WTRU link), a change in the availability and / or quality of hybrid automatic repeat request (HARQ) reports (e.g., if the remote WTRU fails to receive a HARQ response).

[0123] Some of the triggered relay selection solutions herein may be applicable to certain trigger conditions (e.g., RSRP below a threshold and / or SL-RLF). In an example, a remote WTRU communicating using a direct (e.g., PC5) link may be designated as primary or secondary based on certain criteria. These criteria may include, but are not limited to, the direction of data transmission, the priority of the data, upper layer criteria, and / or which remote WTRU is able to detect the AS layer triggering condition for triggering relay selection. Under such a primary / primary designation, this primary / primary WTRU may be responsible for performing relay (re)selection. The AS layer triggering conditions may include QoS flows, CSI associated with the PC5 connection, and / or identifiers of the remote WTRU and / or peer WTRU(s).

[0124] The master / primary role may be defined based on different criteria. Specifically, the WTRU may negotiate in PC5-RRC. The WTRU may determine which of two remote WTRUs sends a request to the other WTRU (e.g., the first WTRU to request). In an example, the WTRU may determine the master / primary role based on the message transmission (e.g., which remote WTRU was the last WTRU to send the PC5-RRC configuration). The master / primary role may be assigned by upper layers without the need for PC5-RRC.

[0125] Specific rules in the AS layer may be based on unicast link setup via PC5-RRC messages (eg, the first WTRU to configure a remote WTRU may become the primary / master WTRU).

[0126] The master / primary role may be based on rules associated with QoS and / or QoS flows, including the number of QoS flows for each remote WTRU and the type of QoS flow (e.g., GBR vs. non-GBR vs. delay critical). In an example, a remote WTRU that is the receiver or target of a high priority QoS flow may be configured as the primary because the remote WTRU will be the first to potentially detect a link problem. If both peer remote WTRUs are transmitting critical or high QoS data (e.g., delay critical), there may be no master / primary WTRU configured, and either WTRU may trigger (re)election as needed.

[0127] The master / primary role may be based on other criteria associated with QoS and / or QoS flows, including the WTRU with the greater bit rate requirement, the WTRU with the most critical latency requirement, changes in data characteristics (e.g., a new LCG / DRB with a higher priority level triggered by application layer data), and / or changes in the buffer status of one or both remote WTRUs. The increase and / or decrease in buffered data at the remote WTRU, the age of packets in the buffer, the rate at which the buffer is consumed, and / or the increase / decrease in the amount of data from the DRB / LCG cluster / group may contribute to the master / primary role selection.

[0128] The remote WTRU may ensure that the above information is available at the peer remote WTRU via discovery transmissions (e.g., solicitation message transmissions). The discovery transmissions may be periodic. Additionally or alternatively, this information may be available to nearby relay WTRUs. These relay WTRUs may broadcast information that may be useful to convey to the remote WTRU.

[0129] The master / primary role may be based on CSI information between the remote WTRUs (if available). The receiving (Rx) remote WTRU may report the quality of the CSI. In an example, two remote WTRUs may have bidirectional data and / or CSI reporting available. In this case, the direction of the lower / higher CSI (e.g., CQI and / or rank indicator (RI)) report may determine which remote WTRU is configured (possibly via negotiation) as the master / secondary WTRU for relay selection triggering purposes. This CSI may be based on a certain time and / or transmission window and / or CSI reporting window average. The CSI may be reconfigured based on the CQI and / or RI falling below a certain threshold and / or exceeding a certain threshold in one or both directions.

[0130] The master / primary role may be based on the remote WTRU's channel busy rate (CBR) and / or channel occupancy rate (CR). The remote WTRUs may exchange this CBR and / or CR information. In this case, the pair of remote WTRUs may know which one will assume the master / primary role. The master / primary role may be based on the identifier (e.g., L2 ID) of the remote WTRU (e.g., the remote WTRU with a larger or smaller identifier (e.g., L2 ID) may be designated as the master / primary WTRU). The WTRU that sends the DCR message that initiates the unicast link may be designated as the master / primary WTRU.

[0131] The remote WTRU may be configured with a timer associated with a relay (re)selection trigger. A timer associated with a relay (eg, an indication trigger) may indicate to the remote WTRU that it is not the master WTRU for the purpose of a relay (re)selection trigger.

[0132] Based on its configuration, the network may explicitly configure one of the remote WTRUs as the master / primary WTRU in Uu RRC messaging. The master / primary role designation may be changed and / or determined based on conditions such as the duration of transmission and / or reception between the remote WTRUs; the duration of transmission in one direction and / or both directions; the frequency and / or resource usage of the transmission (e.g., bandwidth requirements of the transmission); and / or power consumption and / or usage, etc.

[0133] The master / primary role designation may be changed and / or determined based on: the direction of traffic between remote WTRUs; a time period; and / or consideration of the remote WTRU with the majority of traffic. In an example, if a remote WTRU 'x' transmits to another remote WTRU 'y', the receiving remote WTRU 'y' may be the primary WTRU and / or the WTRU responsible for triggering relay selection.

[0134] The master / primary role designation may be changed and / or determined based on a switch and / or change in the transmission direction between two remote WTRUs. For example, remote WTRU 'x' may be transmitting to remote WTRU 'y', and at some point in time the transmission direction may change. This transmission direction may change such that WTRU 'y' becomes the transmitter and WTRU 'x' becomes the receiver. In this case, the master / secondary designation may change such that WTRU 'x' becomes the master / primary WTRU and / or the WTRU responsible for triggering relay selection.

[0135] The master / primary role designation associated with data transmission may be based on a timer and a transmitter / receiver direction. The designation may be based on a switch from WTRU 'x' to WTRU 'y' where WTRU 'y' has been transmitting as a transmitter for some minimum amount of time. This designation may prevent frequent ping-pong back and forth of the master / secondary designation for reselection triggers. The designation may change based on a change in traffic direction. For example, a switch in traffic direction from WTRU 'x' transmitting to WTRU 'y' (where 'y' was designated as the master WTRU) to WTRU 'y' now transmitting to WTRU 'x' may result in WTRU 'x' now being designated as the master WTRU. Furthermore, the switch in traffic direction may include an additional provision to maintain this designation for some minimum amount of time in order to prevent frequent ping-pong back and forth of the master / secondary designation.

[0136] In an example, a WTRU with a higher transmission bandwidth requirement and / or power requirement may determine which of the two WTRUs is designated as the master / primary WTRU. This designation may be inferred based on the CRs exchanged between the remote WTRUs. For example, the WTRU with the higher CR may indicate a higher transmission bandwidth requirement. Another remote WTRU, being aware of the higher CR status of the initial WTRU, may utilize this information to indicate that the other remote WTRU should be the master / primary remote WTRU for (re)selection purposes.

[0137] In an example, if both remote WTRUs are transmitting, previously negotiated designations (e.g., PC5-RRC negotiated designations, and / or AS layer specific designations, etc.) may be used. If neither remote WTRU transmits for a certain period of time, one or both remote WTRUs may transmit a discovery solicitation (e.g., Model B) and / or a dedicated message (e.g., RSRP report and / or CQI report). This transmission may allow the other remote WTRU to measure SD-RSRP (in the case of discovery) and / or SL-RSRP based on a dedicated message trigger and / or triggered relay selection (if necessary).

[0138] The remote WTRU may be configured with an inactivity timer. This inactivity timer may be reset with each data transmission. The inactivity timer may then trigger the need to reconfigure the primary / secondary designation. The reconfiguration may be accomplished via any of the mechanisms described herein.

[0139] The secondary WTRU may send a release message to the primary / master WTRU. The release message may include some indication of the triggering cause. In an example, the secondary WTRU may detect that the RSRP is below a threshold. When sending the release message, the secondary WTRU may indicate this to the primary / master WTRU. The primary / master WTRU may then trigger relay selection based on this release.

[0140] The remote WTRU may choose to trigger relay (re)selection immediately and / or may postpone triggering (re)selection. The remote WTRU may make this choice based on the AS triggering condition and / or remote WTRU designation. In an example, if a remote WTRU has a unicast link established with another remote WTRU, and both remote WTRUs are configured with relay (re)selection thresholds indicating acceptable link quality, then either remote WTRU may trigger (re)selection when the (peer) remote WTRU detects SL-RLF and / or SL-RSRP drops below a certain threshold.

[0141] One or both remote WTRUs may be configured with a timer associated with a relay (re)selection trigger. The remote WTRU may detect that the SL-RLF and / or RSRP is less than a threshold for the link to the (peer) remote WTRU. In this case, the remote WTRU may first check whether the remote WTRU is acting as the master WTRU for the purpose of relay (re)selection triggering. This master / primary designation may be based on any of the criteria described herein (e.g., AS layer conditions, and / or L2 ID of the remote WTRU after link establishment, etc.). If the remote WTRU is the master / primary WTRU, the remote WTRU may trigger relay (re)selection immediately. If the remote WTRU is not the master / primary WTRU, the remote WTRU may use an associated timer. The remote WTRU may start an associated counter under RLF / RSRP conditions. (Re)selection may be triggered upon expiration of this timer.

[0142] If the remote WTRU receives a discovery solicitation indicating that the (peer) remote WTRU has completed relay selection, the timer may be stopped. In an example, if conditions at either remote WTRU (eg, conditions for PC5 communication) change, the timer may be stopped.

[0143] The master / primary WTRU may be designated based on the remote WTRU being the transmitter and the peer (target) remote WTRU being the master WTRU. Traffic conditions for either WTRU may change (e.g., higher priority data arriving at the peer remote WTRU). The remote WTRU may use this information to indicate that the remote WTRU may be designated as the master / primary WTRU and / or to reduce data from this transmitter (e.g., the current secondary WTRU).

[0144] Multiple timer expiration may result in a change in the timer duration (e.g., increase or decrease). Multiple timer-based triggering may result in a reassignment of the primary / secondary designation, where the WTRU is now designated as the primary WTRU. This reassignment of designation may provide the primary / primary remote WTRU with an opportunity to initiate relay (re)selection. This reassignment of designation may be provided to a peer remote WTRU to receive a discovery solicitation indicating relay selection. If the peer remote WTRU does not receive a discovery solicitation, it may initiate its own relay (re)selection.

[0145] Both peer remote WTRUs may be configured with associated timers for relay (re)selection triggers. In this case, the two timer values ​​may be different (e.g., one timer value is greater than the other timer value), thereby allowing staggering of relay (re)selection triggers from the remote WTRUs.

[0146] From a relay selection perspective, the timer value selected may depend on whether the associated remote WTRU is a primary or secondary WTRU. The secondary WTRU may always choose the larger timer to allow the primary WTRU to complete the relay selection process. A remote WTRU (e.g., a secondary remote WTRU) may use both timer values. One timer value may be associated with a default and / or fallback mode of operation, while another timer value (e.g., a smaller one) may be used by the remote WTRU based on certain criteria (e.g., a change in data priority such as high QoS and / or low latency).

[0147] The timer value may be associated with the remote WTRU designation. A remote WTRU that is aware of its designation as a master / primary WTRU may know to select one of the timer values ​​(e.g., a larger or smaller one). A secondary remote WTRU may select a timer value that is not selected by the master / primary WTRU. In this case, the remote WTRU configured with the lower (possibly zero) timer value may be considered the master / primary WTRU from the perspective of a relay (re)selection trigger.

[0148] The primary / primary designated remote WTRU may need to be notified of the need to trigger selection. For example, the primary / primary WTRU may need to be notified based on a situation where the primary WTRU may not be able to detect, but the secondary remote WTRU may be able to detect. In this case, remote WTRU 'x' is the primary / primary WTRU and may transmit to WTRU 'y'. WTRU 'y' may detect that the RSRP is less than a threshold. In this case, the secondary WTRU may trigger a message transmission (e.g., PC5-RRC configuration, discovery message transmission) to WTRU 'x'. This message transmission may then cause this remote WTRU to realize that the RSRP is less than the threshold, thereby triggering reselection.

[0149] Additionally or alternatively, the remote WTRU 'y' may choose to stop responding to WTRU 'x' (e.g., not sending HARQ feedback, terminating or suspending transmissions (e.g., RSRP reports and / or CSI reports, etc.) to inform upper layers that transmissions will be suspended). WTRU 'y' choosing to stop responding to WTRU 'x' may result in WTRU 'x' detecting an RLF and triggering (re)selection.

[0150] The relay WTRU may participate in determining the master / slave role and / or informing which remote WTRU should trigger relay (re)selection. In an example, the relay WTRU may modify and / or reconfigure the remote WTRU designation as master / primary WTRU versus slave WTRU for relay (re)selection triggering purposes. This determination may be based on information available to the relay (including information from other relays); the number of remote WTRUs connected to the relay (including whether multiple source remote WTRUs are communicating with multiple target remote WTRUs via the same relay); and / or the direction of the traffic, including the frequency of the traffic (e.g., whether there is more ingress data versus egress data, whether this is fluctuating or constant, etc.).

[0151] A relay with many bidirectional connections (e.g., a source and / or target remote WTRU pair with bidirectional data) may notice a change in traffic direction. This change in direction may be based on a switch in direction between these source and target WTRU pairs. This change in direction may indicate a change in the primary / secondary designation to the remote WTRU pair to reflect this switch.

[0152] A source (e.g., remote) WTRU may be connected to multiple remote target WTRUs via the same relay. If the relay detects a problem with the source WTRU link, the relay may indicate to the target (e.g., remote) WTRU that the target WTRU needs to trigger (re)selection. The relay may be aware of the status of other relay WTRUs that have the source WTRU. The relay may be aware of one or more target WTRUs in the reachable WTRU list that are communicating with the source WTRU (e.g., via a previous announcement message). The relay WTRU may provide this information to the target WTRU via an announcement and / or if the target WTRU solicits it itself (e.g., via a Mode 'B' solicitation request).

[0153] The relay WTRU may detect a problem with the source WTRU link and / or one or more of the target WTRUs communicating with the source WTRU (e.g., via the same relay). If the relay detects a problem, the relay may indicate to the source remote WTRU that the source remote WTRU should trigger (re)selection because multiple links on both the source-relay hop and the relay-target hop may be affected. The relay WTRU may provide additional information to the source WTRU (e.g., other relays in the vicinity and other relays in the list of WTRUs reachable by these relays) to aid in (re)selection.

[0154] A source (e.g., remote) WTRU may be connected to multiple remote target (e.g., remote) WTRUs via the same relay. The relay may detect a problem with one or more of the links to the target WTRUs. The relay WTRU may indicate the problem to the source remote WTRU so that the remote WTRU triggers (re)selection, rather than each individual target WTRU triggering (re)selection.

[0155] The target (e.g., remote) WTRUs may be part of a coordinated or cooperative group of WTRUs communicating with the same single source (e.g., remote) WTRU. One or more of the target WTRU links to the relay may be affected (e.g., SL-RSRP below a threshold, and / or RLF, etc.). This group of target WTRUs (individually or via a primary anchor WTRU) may need to trigger relay (re)selection.

[0156] A relay serving two remote WTRUs 'x' and 'y' may notify remote WTRU 'y' of an SL-RLF on the WTRU 'x' to relay hop. This information may be based on which remote WTRU is designated as the master / primary WTRU for reselection triggering purposes. In an example, if the relay knows that an RLF occurred on the link with remote WTRU 'x', and WTRU 'y' is the master / primary WTRU, the relay WTRU may indicate the SL-RLF to WTRU 'y'. Remote WTRU 'y' may then trigger (re)selection.

[0157] The relay WTRU may detect the RLF of WTRU 'y'. The relay WTRU may notify WTRU 'x' of this indication. This indication may cause WTRU 'x' to start a timer. WTRU 'x' may then use this timer to trigger its own (re)selection procedure if a new relay has not yet been selected.

[0158] The relay WTRU may be aware of other relay WTRUs on the list of neighboring and / or reachable remote WTRUs (e.g., based on the SD-RSRP and / or SL-RSRP for these relays and / or whether these relays already have a link (e.g., PC5-RRC connection) with these remote WTRUs. The relay WTRU may send this information to the remote WTRU(s). The information may be sent using an explicit indication (e.g., via a flag in discovery and / or MAC CE) or an implicit indication (e.g., using SL-RSRP and / or SD-RSRP when a link exists). The remote WTRU may use this indication to perform relay (re)selection.

[0159] In an example, a remote WTRU may choose to perform relay (re)selection only if a certain minimum number of relays have existing links with the peer remote WTRU with which the peer remote WTRU is attempting to communicate. This information may be made available to the remote WTRU via a previous announcement message. SL-RSRP and / or SD-RSRP measurements for these relay WTRU-remote WTRU links may also be used as criteria for whether to perform relay selection.

[0160] If the remote WTRU 'x' detects that the RSRP for the relay link is below a threshold, the remote WTRU 'x' may send a release message to the relay. The remote WTRU 'x' may also send an indication of the cause of the release. The relay may then initiate a release to the other remote WTRU 'y' hop. The release may then indicate to the remote WTRU 'y' that relay selection has been triggered.

[0161] A remote WTRU that detects a problem with a relay (e.g., RSRP below a threshold) may start a timer upon such detection. Starting the timer may be done to allow other remote WTRUs (e.g., source or target WTRUs on other relay hops) to trigger relay (re)selection (e.g., based on some previous configuration and / or indication of the relay). This remote WTRU may then trigger relay (re)selection upon expiration of this timer.

[0162] A relay WTRU may indicate which of two remote WTRUs it is acting as a relay for. This indication may trigger relay (re)selection. This indication may be based on any of the conditions described herein (e.g., direction and / or duration of traffic, etc.) and information available to the relay WTRU (e.g., status of other relays in the vicinity, and / or connectivity with other remote WTRUs, etc.).

[0163] The WTRU may determine which discovery model procedure to use based on the AS layer triggering conditions (eg, RLF and SL-RSRP thresholds) that trigger relay selection.

[0164] Specifically, a WTRU (eg, a remote WTRU) may be configured with a PC5 connection with another remote WTRU. The WTRU may be configured with an SL-RSRP threshold for acceptable link quality and / or a timer associated with the remote WTRU that triggers a discovery solicitation.

[0165] The WTRU may detect an RLF. If the WTRU detects an RLF, the WTRU may transmit a Link Modification message and / or a Model B Solicitation message including an indication of the RLF detection. Additionally, the WTRU may wait for a response from the relay WTRU indicating that the target has received the solicitation and / or Link Modification and has selected the relay.

[0166] The WTRU may detect that the RSRP has dropped below a configured threshold. If the WTRU detects that the RSRP has dropped below a certain threshold, the WTRU may initiate relay selection based on the received Model A Announcement message. In addition, the WTRU may select a relay WTRU to communicate with a target (e.g., remote) WTRU. The WTRU may send a Release message to the target WTRU to release the PC5-RRC connection and / or notify the remote WTRU that it has performed relay selection.

[0167] If after the configured time duration, the WTRU has not selected a new relay, the WTRU may transmit a Model B Solicitation message and / or a Link Modification message to initiate relay selection.

[0168] The remote WTRU may choose which model to select based on the reselection cause and / or AS layer conditions. In an example, the WTRU may choose whether to listen and / or wait for announcement messages and use these announcement messages to perform relay selection (e.g., Model A) or send a solicitation to initiate relay selection requiring the other remote WTRU to respond (e.g., Model B). Choosing an option may depend on which of the two remote WTRUs needs to trigger relay selection and / or the conditions that trigger (re)selection at the remote WTRU.

[0169] If the remote WTRU triggers (re)selection but does not see any Model A advertisements for relay selection, the remote WTRU may transmit a Model B solicitation message to elicit a U2U relay response. If the remote WTRU triggers (re)selection and the frequency and / or periodicity of the Model A advertisements indicate potentially outdated advertisements and / or a need for updated Model A discovery, the remote WTRU may transmit a Model B solicitation message to elicit a U2U relay response.

[0170] The remote WTRU may choose which model to select based on the reselection cause. If the remote WTRU detects RLF, the remote WTRU may use Model B based solicitation for relay selection. Model B based solicitation may allow the remote WTRU to notify other remote WTRUs of the problem.

[0171] If the remote WTRU detects that the RSRP is below a threshold, the remote WTRU may utilize the existing announcement message to perform relay (re)selection and / or send a release to the (peer) remote WTRU. The release may inform the peer remote WTRU that the remote WTRU is performing (re)selection. In this case, the remote WTRU may not be able to select a new relay (e.g., due to not hearing any announcement). The remote WTRU may trigger a solicitation to initiate relay selection. This trigger may be based on a timer associated with triggering the discovery solicitation (e.g., a preconfigured timer). The timer may be started at the moment the remote WTRU detects that the RSRP is below an acceptable link threshold (e.g., the remote WTRU may start the timer based on a determination that the remote WTRU's identifier (e.g., L2 ID) may be greater than the peer WTRU's identifier (e.g., L2 ID)).

[0172] The remote WTRU may choose which model to select based on RSRP. In an example, (re)selection may be triggered and an RSRP threshold may be configured (e.g., for acceptable link quality). If the observed RSRP is less than this threshold, the remote WTRU may use a solicitation based on Model B. Model B may be used as an additional redundancy measure in the relay selection procedure.

[0173] If selection is triggered and / or RSRP exceeds a configured threshold, the remote WTRU may use Model A based solicitation.

[0174] If selection is triggered and / or RSRP is below a configured threshold, the remote WTRU may use a solicitation to notify the peer remote WTRU of the reselection. Notifying the peer remote WTRU of the (re)selection may ensure that the two remote WTRUs do not perform the (re)selection independently.

[0175] The remote WTRU may choose which model to select based on whether the remote WTRU is a primary / master WTRU. If the primary / master remote WTRU triggers (re)selection, the remote (WTRU) may perform relay selection using an announcement message. The designated remote WTRU for selection and / or the peer (e.g., secondary) remote WTRU may not trigger selection itself.

[0176] If the remote WTRU is not the master / primary WTRU but needs to perform relay selection (e.g., timer expiration and / or high QoS data arrival, etc.), the remote WTRU may trigger a solicitation for relay selection. In this case, the remote WTRU may indicate the reason for triggering relay selection in the solicitation message.

[0177] Initial relay selection may always be performed using a Model B solicitation. When using a Model B solicitation, the remote WTRU may indicate to the peer remote WTRU the conditions associated with triggering the initial selection. This indication may allow coordination of the initial selection and / or establish a relationship between the two remote WTRUs (e.g., establishing a primary / secondary designation for future (re)selection).

[0178] The remote WTRU may utilize two types of solicitation messages to initiate relay selection. First, if the remote WTRU is the master / primary WTRU, the remote WTRU may utilize a default message configuration to initiate relay selection using a solicitation (e.g., Model B). The remote WTRU may utilize this configuration because the remote WTRU may be the only remote WTRU triggering reselection. If the remote WTRU triggering the (re)selection is not the master / primary WTRU, the remote WTRU may utilize an enhanced solicitation message. This enhanced solicitation message may indicate and / or include additional information in the model solicitation (e.g., the reason for triggering the reselection, such as high QoS data, etc.). This additional information may indicate and / or inform the master / primary WTRU that the master / primary WTRU should defer triggering its own (re)selection.

[0179] The conditions for triggering reselection, the remote WTRU designation (e.g., primary / secondary WTRU for triggering purposes), and / or information obtained from other relays available to the remote WTRU may be used to determine which remote WTRU performs relay (re)selection. These factors may also determine the decision to wait for an announcement message and / or perform relay selection or to send a solicitation to initiate relay selection.

[0180] The remote WTRU may utilize the current relay to detect SL-RLF. The remote WTRU may trigger relay (re)selection and / or listen for announcement messages for relay selection. If the remote WTRU does not see any announcement messages (e.g., based on a timer), the remote WTRU may initiate a solicitation to initiate an announcement response to the U2U relay. The remote WTRU may indicate certain information in the solicitation. For the purpose of relay (re)selection triggering, this information may be based on whether the remote WTRU is the primary / master WTRU.

[0181] An indication from a relay WTRU to a remote WTRU to perform relay (re)selection (e.g., based on a problem detected on the link between the relay and / or other remote WTRUs (e.g., source and / or target)) may be viewed as an implicit indication to always perform relay (re)selection using solicitation (e.g., Model B). This indication may be interpreted in this manner even in the presence of announcement messages (e.g., Model A) that the remote WTRU may hear.

[0182] If a relay detects a problem with a hop (e.g., source and / or destination hop), the relay WTRU may temporarily suspend announcement messages. The relay may temporarily suspend announcement messages to ensure that the remote WTRU (e.g., the remote WTRU relay link with the problem or other relay-remote WTRU hop) initiates relay (re)selection using a solicitation-based procedure. In this case, the relay WTRU may choose not to forward(one or more) announcement messages (e.g., its own announcement messages or announcement messages from other relay WTRUs) and / or notify other relay WTRUs to stop Model A announcements for a certain amount of time.

[0183] The link modification procedure may replace the Model B discovery mode (eg, solicitation) to trigger a relay (re)selection procedure and / or relay selection by a remote WTRU receiving a link modification request message.

Claims

1. A first wireless transmit / receive unit (WTRU), comprising: A processor configured to: determining an identifier of the first WTRU and an identifier of a second WTRU, wherein the first WTRU and the second WTRU are configured to communicate via a PC5 connection; receiving configuration information, wherein the configuration information includes an indication of a time period associated with a relay selection procedure; determining that a trigger condition has been met, wherein the trigger condition is associated with a channel condition of a PC5 connection with the second WTRU; and Based on the trigger condition being met, a determination is made based on a comparison between an identifier of the first WTRU and an identifier of the second WTRU whether to initiate a discovery or link modification procedure or to wait for a time period associated with the relay selection procedure.

2. The first WTRU of claim 1 , wherein: The trigger condition includes a radio link failure (RLF) of the PC5 connection or a sidelink reference signal received power (SL-RSRP) measurement of the PC5 connection falling below a threshold.

3. The first WTRU of claim 1 , wherein: The processor is configured to send a discovery or link modification message to initiate the discovery or link modification procedure based on a determination that the identifier of the first WTRU is less than the identifier of the second WTRU.

4. The first WTRU of claim 1 , wherein: The processor is configured to start a timer for the time period based on a determination that the identifier of the first WTRU is greater than the identifier of the second WTRU.

5. The first WTRU of claim 4, wherein: The processor is configured to initiate a discovery or link modification procedure if the time period elapses without receiving an indication of relay selection.

6. The first WTRU of claim 1 , wherein: The identifier of the first WTRU comprises a first layer 2 ID or a local ID, and wherein the identifier of the second WTRU comprises a layer 2 ID or a local ID.

7. The first WTRU of claim 1 , wherein: The first WTRU is designated as a master WTRU, and wherein the processor is configured to perform relay selection if the first WTRU sends a request for the configuration information and a higher layer designates the first WTRU as the master WTRU without requiring configuration information or based on rules associated with an access stratum (AS) layer.

8. The first WTRU of claim 7, wherein: The rules associated with the AS layer include rules associated with quality of service (QoS) flows, channel state information (CSI) associated with the PC5 connection, or rules based on an identifier of the first WTRU and an identifier of the second WTRU.

9. The first WTRU of claim 1 , wherein: The processor is configured to: receiving a release message from the second WTRU; and The relay selection procedure is triggered in response to receiving the release message.

10. The first WTRU of claim 1 , wherein: The processor is configured to: A timer associated with the time period is stopped based on receiving a discovery solicitation message indicating that the second WTRU has completed relay selection or based on a determination that channel conditions for the PC5 communication have changed.

11. A method performed by a wireless transmit / receive unit (WTRU), the method comprising: determining an identifier of a first WTRU and an identifier of a second WTRU, wherein the first WTRU and the second WTRU are configured to communicate via a PC5 connection; receiving configuration information, wherein the configuration information includes an indication of a time period associated with a relay selection procedure; determining that a trigger condition has been met, wherein the trigger condition is associated with a channel condition of a PC5 connection with the second WTRU; and Based on the trigger condition being met, a determination is made based on a comparison between an identifier of the first WTRU and an identifier of the second WTRU whether to initiate a discovery or link modification procedure or to wait for a time period associated with the relay selection procedure.

12. The method according to claim 11, wherein The trigger condition includes a radio link failure (RLF) of the PC5 connection or a sidelink reference signal received power (SL-RSRP) measurement of the PC5 connection falling below a threshold.

13. The method according to claim 11, further comprising: Based on a determination that the identifier of the first WTRU is less than the identifier of the second WTRU, a discovery or link modification message is sent to initiate the discovery or link modification procedure.

14. The method according to claim 11, further comprising: A timer for the time period is started based on a determination that the identifier of the first WTRU is greater than the identifier of the second WTRU.

15. The method according to claim 14, further comprising: If the time period elapses without receiving an indication of relay selection, a discovery or link modification procedure is initiated.

16. The method according to claim 11, wherein The identifier of the first WTRU comprises a first layer 2 ID or a local ID, and wherein the identifier of the second WTRU comprises a layer 2 ID or a local ID.

17. The method according to claim 11, wherein The first WTRU is designated as a master WTRU, and wherein the processor is configured to perform relay selection if the first WTRU sends a request for the configuration information and a higher layer designates the first WTRU as the master WTRU without requiring configuration information or based on rules associated with an access stratum (AS) layer.

18. The method according to claim 17, wherein The rules associated with the AS layer include rules associated with quality of service (QoS) flows, channel state information (CSI) associated with the PC5 connection, or rules based on an identifier of the first WTRU and an identifier of the second WTRU.

19. The method of claim 11, further comprising: receiving a release message from the second WTRU; as well as The relay selection procedure is triggered in response to receiving the release message.

20. The method of claim 11, further comprising: A timer associated with the time period is stopped based on receiving a discovery solicitation message indicating that the second WTRU has completed relay selection or based on a determination that channel conditions for the PC5 communication have changed.

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