Relay selection associated with WTRU-to-WTRU relay

Abstract

Systems, methods, and instrumentalities are described herein for relay selection associated with a WTRU to WTRU relay. A wireless transmit / receive unit (WTRU) may be configured to perform a relay selection associated with a WTRU-to-WTRU relay. The WTRU may perform relay (re) selection, e.g., based on active traffic and / or measurements performed (e.g., Reference Signal Received Power (RSRP) measurements). The WTRU may perform a network assisted relay (re) selection. The WTRU (e.g., a WTRU within coverage) may initiate a connection (e.g., an RRC connection) or trigger a message (e.g., an RRC message), for example, based on a WTRU-to-WTRU relay standard. The WTRU may report measurement results to the network, for example, based on multiple hops.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Provisional Application No. 63 / 359,949, filed on July 11, 2022, the entire contents of which are incorporated herein by reference. Background Art

[0003] Mobile communications using wireless communications continue to evolve. The fifth generation of mobile communications radio access technology (RAT) may be referred to as 5G New Radio (NR). The previous generation (legacy) mobile communications RAT may be, for example, fourth generation (4G) Long Term Evolution (LTE). Summary of the invention

[0004] Systems, methods, and means for relay selection associated with WTRU to WTRU relaying are described herein. A wireless transmit / receive unit (WTRU) may be configured to perform relay selection associated with WTRU to WTRU relaying. The WTRU may (e.g., determine) to perform relay (re)selection, for example, based on active traffic and / or measurements performed (e.g., reference signal received power (RSRP) measurements). The WTRU may perform network-assisted relay (re)selection. The WTRU (e.g., a WTRU within coverage) may initiate a connection (e.g., an RRC connection) or trigger a message (e.g., an RRC message), for example, based on WTRU to WTRU relay criteria. The WTRU may report measurement results to the network, for example, based on multi-hop.

[0005] The WTRU may determine a relay reselection behavior based on a measurement result and an active data determination associated with a first relay (e.g., whether there is a gap between active data transmissions). A WTRU (e.g., a remote WTRU used as an example) may be associated with a first relay WTRU (e.g., a WTRU-to-WTRU relay). The remote WTRU may receive configuration information indicating thresholds (e.g., a first threshold and a second threshold) associated with a sidelink (SL) RSRP (e.g., a first SL RSRP threshold and a second SL RSRP threshold, wherein the first SL RSRP threshold is higher than the second SL RSRP threshold). The configuration information may indicate data transmission gap information (e.g., a data gap transmission parameter). The remote WTRU may transmit a first transmission to the first relay. The remote WTRU may determine a SL RSRP measurement result associated with the first relay WTRU. The remote WTRU may determine that the SL RSRP measurement result associated with the first relay WTRU is lower than the first threshold and higher than the second threshold (e.g., between the first threshold and the second threshold). The remote WTRU may determine to perform an active data determination (e.g., for relay reselection) (e.g., based on determining that the SL RSRP measurement result is below the first threshold and above the second threshold). For example, the remote WTRU may initiate discovery (e.g., send or receive a discovery transmission). The remote WTRU may determine a duration associated with a data transmission time gap (e.g., associated with the initiated discovery). The remote WTRU may determine whether the duration associated with the data transmission time gap exceeds a data transmission gap threshold. The remote WTRU may perform relay reselection to a second relay, for example, based on determining that the duration associated with the data transmission time gap exceeds the data transmission gap threshold. The remote WTRU may transmit a second transmission to the second relay.

[0006] The remote WTRU may perform relay reselection based on the SL RSRP measurement result (e.g., only the SL RSRP measurement result). For example, the remote WTRU may determine that the SL RSRP measurement result is below the second (e.g., lower) threshold (e.g., below both the first threshold and the second threshold). Based on determining that the SL RSRP measurement result is below the second threshold, the remote WTRU may initiate discovery. For example, the remote WTRU may perform relay reselection to a different relay without considering the data transmission gap information.

[0007] A WTRU (e.g., a remote WTRU used as an example) may be associated with a current relay WTRU (e.g., a first relay WTRU). The remote WTRU may determine and / or preselect a second relay or a set of candidates for a reselected relay, for example, based on a first condition / initial trigger (e.g., a drop in link quality of the current relay below a preselected threshold, a change in condition of the current relay, or information from another relay). For example, based on a second condition (e.g., condition, trigger) being satisfied, the WTRU may switch to one of the determined / preselected candidates. The remote WTRU may receive (e.g., via dedicated RRC messaging or SIB) a first condition for determining / preselecting a second relay and / or a set of candidate relays for reselection. The first condition may include one or more of the following: a first (e.g., minimum) PC5 RSRP for relay selection; a second (e.g., different) PC5 RSRP associated with triggering a two-step relay candidate selection process; a time associated with completing a reselection process after an initial preselection. The remote WTRU may be configured to pre-select one or more candidates for reselection (e.g., if initial conditions for pre-selection are met). The remote WTRU may complete the reselection process (e.g., select a pre-selected relay) (e.g., if secondary conditions are met, such as expiration of a time indicating no active data transmission, additional PC5 RSRP link quality measurement results, etc.).

[0008] In an example, for example, when (e.g., when) a remote WTRU reselects to a relay WTRU and the selected relay WTRU is connected to a cell different from the remote WTRU, the remote WTRU may trigger a connection establishment. The remote WTRU may receive configuration information indicating a set of allowable relay WTRUs to which the remote WTRU may perform reselection. The remote WTRU may receive a release message. The remote WTRU may move to RRC IDLE / RRC INACTIVE. The remote WTRU may perform relay reselection. For example, if the selected relay WTRU is connected to a cell different from the remote WTRU's serving cell, the remote WTRU may initiate a connection procedure (e.g., an RRC connection procedure). BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1A is a system diagram illustrating an example communication system in which one or more disclosed embodiments may be implemented.

[0010] Figure 1B is an example of a method that can be used according to an embodiment of the present invention. Figure 1A A system diagram of an example wireless transmit / receive unit (WTRU) for use within an illustrated communication system.

[0011] Figure 1C is an example of a method that can be used according to an embodiment of the present invention. Figure 1A System diagram of an example Radio Access Network (RAN) and an example Core Network (CN) for use within an illustrated communication system.

[0012] Figure 1D is an example of a method that can be used according to an embodiment of the present invention. Figure 1A System diagram of another example RAN and another example CN for use within the illustrated communication system.

[0013] Figure 2 An example user plane protocol stack for L2 WTRU to network relay is illustrated.

[0014] Figure 3 An example control plane protocol stack for an L2 WTRU to network relay is illustrated.

[0015] Figure 4 An example protocol stack for WTRU-to-network relay discovery messages is illustrated.

[0016] Figure 5 An example of relay selection determined based on RSRP and activity data is illustrated. DETAILED DESCRIPTION

[0017] Figure 1A 1 is a diagram illustrating an example communication system 100 in which one or more disclosed embodiments may be implemented. The communication system 100 may be a multiple 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 through sharing of 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 UW DTS-s OFDM), unique word OFDM (UW-OFDM), resource block filtered OFDM, and filter bank multi-carrier (FBMC), etc.

[0018] like Figure 1AAs 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, Internet 110 and other networks 112, but it should be understood 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 send 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 smart phone, 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 devices and applications (e.g., remote surgery), industrial devices and applications (e.g., robots and / or other wireless devices operating in an industrial and / or automated process chain environment), a consumer electronic device, a device operating on a commercial and / or industrial wireless network, etc. Any of the WTRUs 102a, 102b, 102c, and 102d may be interchangeably referred to as a UE.

[0019] 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 that is 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. Although the base stations 114a, 114b are each depicted as a single element, it should be appreciated that the base stations 114a, 114b may include any number of interconnected base stations and / or network elements.

[0020] The base station 114a may be part of the 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), a relay node, etc. The base station 114a and / or the base station 114b may be configured to send 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 a licensed spectrum, an unlicensed spectrum, or a combination of licensed and unlicensed spectrums. A cell may provide coverage of wireless services 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, a cell associated with the base station 114a may be divided into three sectors. Therefore, in one embodiment, the base station 114a may include three transceivers, i.e., one transceiver for each sector of the cell. In one embodiment, the base station 114a may employ multiple-input multiple-output (MIMO) technology and may utilize multiple transceivers for each sector of the cell. For example, beamforming may be used to send and / or receive signals in a desired spatial direction.

[0021] 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).

[0022] More specifically, as noted 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, and SC-FDMA. 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 use Wideband CDMA (WCDMA) to establish the air interface 115 / 116 / 117. 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).

[0023] 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) that may establish the air interface 116 using Long Term Evolution (LTE) and / or Advanced LTE (LTE-A) and / or Advanced LTE Pro (LTE-A Pro).

[0024] In one embodiment, the base station 114a and the WTRUs 102a, 102b, 102c may implement a radio technology such as NR radio access, which may establish the air interface 116 using New Radio (NR).

[0025] 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 together implement LTE radio access and NR radio access, for example using dual connectivity (DC) principles. Thus, the air interface utilized by the WTRUs 102a, 102b, 102c may be characterized by multiple types of radio access technologies and / or transmissions transmitted to / from multiple types of base stations (e.g., eNBs and gNBs).

[0026] In other embodiments, the base station 114a and the WTRUs 102a, 102b, 102c may implement radio technologies 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), and GSM EDGE (GERAN).

[0027] Figure 1AThe base station 114b in may be, for example, a wireless router, a Home NodeB, a Home eNodeB, or an access point, and may utilize any suitable RAT to facilitate wireless connectivity in local areas such as commercial venues, homes, vehicles, campuses, industrial facilities, sky corridors (e.g., for use by drones), and roads. 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 micro-micro cell base station or a femto cell base station. As Figure 1A As shown, base station 114b may have a direct connection to Internet 110. Therefore, base station 114b may not need to access Internet 110 via CN 106 / 115.

[0028] 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, error 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 high-level security functions, such as user authentication. Although not described in detail in the text and video, the CN 106 / 115 may be 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, error 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 high-level security functions, such as user authentication. Figure 1A Although not shown in the figure, 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.

[0029] The CN 106 / 115 may also act 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) in the TCP / IP Internet protocol suite. The networks 112 may include wired communication networks 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.

[0030] 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 illustrated WTRU 102c 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.

[0031] 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 source 134, a global positioning system (GPS) chipset 136, and / or other peripherals 138. It will be appreciated that the WTRU 102 may include any sub-combination of the foregoing elements while remaining consistent with an embodiment.

[0032] 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) and state machine, etc. The processor 118 may perform signal decoding, 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.

[0033] The send / receive element 122 may be configured to send a signal to a base station (e.g., base station 114a) or receive a signal from the base station via an air interface 116. For example, in one embodiment, the send / receive element 122 may be an antenna configured to send and / or receive an RF signal. In one embodiment, the send / receive element 122 may be a transmitter / detector configured to send and / or receive, for example, an IR, UV or visible light signal. In another embodiment, the send / receive element 122 may be configured to send and / or receive both an RF signal and an optical signal. It should be understood that the send / receive element 122 may be configured to send and / or receive any combination of wireless signals.

[0034] Although the transmit / receive element 122 Figure 1B Although depicted as a single element in the figure, 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.

[0035] The transceiver 120 may be configured to modulate signals to be transmitted by the transmit / receive element 122 and to demodulate signals received by the transmit / receive element 122. As noted above, the WTRU 102 may have multi-mode capabilities. For example, the transceiver 120 may include multiple transceivers for enabling the WTRU 102 to communicate via multiple RATs, such as NR and IEEE 802.11.

[0036] 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. In addition, the processor 118 may access information from and store data in any type of suitable memory, such as a non-removable memory 130 and / or a removable memory 132. The non-removable memory 130 may include a random access memory (RAM), a 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, and a secure digital (SD) memory card, among others. In other embodiments, the processor 118 may access information from and store data in a memory that is not physically located on the WTRU 102, such as on a server or a home computer (not shown).

[0037] 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.

[0038] 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 the 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.

[0039] The processor 118 may also be coupled to other peripherals 138, which may include one or more software modules 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, FM radio unit, digital music player, media player, video game player module, Internet browser, virtual reality and / or augmented reality (VR / AR) device and activity tracker, etc. Peripheral device 138 may include one or more sensors, which may be one or more of the following: gyroscope, accelerometer, Hall effect sensor, magnetometer, orientation sensor, proximity sensor, temperature sensor, time sensor; geolocation sensor; altimeter, light sensor, touch sensor, magnetometer, barometer, gesture sensor, biometric sensor and / or humidity sensor.

[0040] The WTRU 102 may include a full-duplex radio for which transmission and reception of some or all signals (e.g., associated with specific subframes for both 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 for reducing and / or substantially eliminating self-interference via hardware (e.g., a choke) or via signal processing performed by a processor (e.g., a separate processor (not shown) or via the processor 118). In one embodiment, the WRTU 102 may include a half-duplex radio for which transmission and reception of some or all signals (e.g., associated with specific subframes for both UL (e.g., for transmission) or downlink (e.g., for reception)) may be concurrent and / or simultaneous.

[0041] Figure 1C 1 is a system diagram illustrating the RAN 104 and the CN 106 in accordance with an embodiment. As noted 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.

[0042] The RAN 104 may include evolved Node-Bs 160a, 160b, 160c, though it will be appreciated that the RAN 104 may include any number of evolved Node-Bs while remaining consistent with an embodiment. The evolved Node-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 evolved Node-Bs 160a, 160b, 160c may implement MIMO technology. Thus, the evolved Node-B 160a, for example, may use multiple antennas to transmit wireless signals to and / or receive wireless signals from the WTRU 102a.

[0043] Each of the evolved Node 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, scheduling of users in the UL and / or DL, etc. Figure 1C As shown, the eNode-Bs 160a, 160b, 160c may communicate with one another via an X2 interface.

[0044] Figure 1C The illustrated CN 106 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 being 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.

[0045] The MME 162 may be connected to each of the evolved Node-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, and selecting a particular serving gateway during an initial attach of the WTRUs 102a, 102b, 102c. The MME 162 may 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.

[0046] The SGW 164 may be connected to each of the evolved Node-Bs 160a, 160b, 160c in the RAN 104 via an S1 interface. The SGW 164 may generally route and forward user data packets to / from the WTRUs 102a, 102b, 102c. The SGW 164 may perform other functions, such as anchoring the user plane during an inter-evolved Node-B handover, triggering paging when DL data is available for the WTRUs 102a, 102b, 102c, and managing and storing the context of the WTRUs 102a, 102b, 102c.

[0047] 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.

[0048] 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 be in communication 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 networks and / or wireless networks owned and / or operated by other service providers.

[0049] Although the WTRU Figures 1A to 1D Although described as wireless terminals, it is contemplated that in certain representative embodiments, such terminals may (eg, temporarily or permanently) use a wired communications interface with a communications network.

[0050] In a representative embodiment, the other network 112 may be a WLAN.

[0051] 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 have access or an interface to a distribution system (DS) or another type of wired / wireless network that carries traffic to and / or out of the BSS. Traffic originating from outside the BSS and destined for the STA may be reached by the AP and may be delivered to the STA. Traffic originating from the STA and destined for a target outside the BSS may be transmitted to the AP to be delivered to the corresponding target. Traffic between STAs within the BSS may be transmitted by the AP, for example, wherein the source STA may transmit traffic to the AP, and the AP may deliver traffic to the target STA. Traffic between STAs within the BSS may be considered and / or referred to as point-to-point traffic. Direct link establishment (DLS) may be utilized to transmit point-to-point traffic between the source STA and the target STA (e.g., directly between them). In certain representative embodiments, the DLS may use 802.11e DLS or 802.11z tunnel DLS (TDLS). A WLAN using an independent BSS (IBSS) mode may not have an AP, and STAs within or using the IBSS (eg, all STAs in the STA) may communicate directly with each other. The IBSS communication mode may sometimes be referred to herein as an "ad-hoc" communication mode.

[0052] When using the 802.11ac infrastructure operation mode or a similar operation mode, the AP may send a beacon on a fixed channel (such as a primary channel). The primary channel may be a fixed width (e.g., a 20MHz wide bandwidth) or a width dynamically set via signaling. The primary channel may be a working channel of the BSS and may be used by the STA to establish a connection with the AP. In certain representative embodiments, carrier sense multiple access / collision avoidance (CSMA / CA) may be implemented, for example, in an 802.11 system. For CSMA / CA, a STA (e.g., each STA) (including the AP) may sense the primary channel. If the primary channel is sensed / detected and / or determined to be busy by a particular STA, the particular STA may back off. One STA (e.g., only one station) may transmit at any given time in a given BSS.

[0053] 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.

[0054] Very high throughput (VHT) STA can support 20MHz, 40MHz, 80MHz and / or 160MHz wide channels. 40MHz channels and / or 80MHz channels can be formed by combining continuous 20MHz channels. 160MHz channels can be formed by combining 8 continuous 20MHz channels, or by combining two non-continuous 80MHz channels (this can be called 80+80 configuration). For 80+80 configuration, after channel coding, the data can pass through a segment parser that can divide the data into two streams. Each stream can be processed by inverse fast Fourier transform (IFFT) and time domain processing separately. These streams can be mapped to two 80MHz channels, and the data can be sent by the transmitter STA. At the receiver of the receiver STA, the above-mentioned operation for the 80+80 configuration can be reversed, and the combined data can be transmitted to the medium access control (MAC).

[0055] 802.11af and 802.11ah support operating modes below 1GHz. Channel operating bandwidths and carriers are reduced in 802.11af and 802.11ah relative to those used in 802.11n and 802.11ac. 802.11af supports 5MHz, 10MHz, and 20MHz bandwidths in the TV White Space (TVWS) spectrum, and 802.11ah supports 1MHz, 2MHz, 4MHz, 8MHz, and 16MHz bandwidths using non-TVWS spectrum. According to a representative embodiment, 802.11ah may support instrument type control / machine type communications, such as MTC devices in macro coverage areas. MTC devices may have certain capabilities, such as limited capabilities, including support for (e.g., only support for) certain bandwidths and / or limited bandwidths. MTC devices may include batteries with battery life above a threshold (e.g., to maintain very long battery life).

[0056] WLAN systems that can support multiple channels and channel bandwidths (such as 802.11n, 802.11ac, 802.11af, and 802.11ah) include channels that can be designated as primary channels. The primary channel may have a bandwidth equal to the maximum common operating bandwidth supported by all STAs in the BSS. The bandwidth of the primary channel may be set and / or limited by a STA (which supports the minimum bandwidth operation mode) from all STAs operating in the BSS. In the example of 802.11ah, for STAs (e.g., MTC-type devices) that support (e.g., only support) a 1MHz mode, the primary channel may be 1MHz wide, even if the AP and other STAs in the BSS support 2MHz, 4MHz, 8MHz, 16MHz, and / or other channel bandwidth operation modes. Carrier sensing and / or network allocation vector (NAV) settings may depend on the state of the primary channel. If the primary channel is busy, for example, because a STA (supporting only a 1MHz operation mode) is sending to the AP, the entire available band may be considered busy even if most of the band remains idle and may be available.

[0057] In the United States, the available frequency band for 802.11ah is 902MHz to 928MHz. In South Korea, the available frequency band is 917.5MHz to 923.5MHz. In Japan, the available frequency band is 916.5MHz to 927.5MHz. The total bandwidth available for 802.11ah is 6MHz to 26MHz, depending on the country code.

[0058] Figure 1D 1 is a system diagram illustrating the RAN 113 and the CN 115 in accordance with an embodiment. As noted 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.

[0059] The RAN 113 may include gNBs 180a, 180b, 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, 180c may each include one or more transceivers for communicating with the WTRUs 102a, 102b, 102c over the air interface 116. In one embodiment, the gNBs 180a, 180b, 180c may implement MIMO technology. For example, the gNBs 180a, 180b may utilize beamforming to send signals to and / or receive signals from the gNBs 180a, 180b, 180c. Thus, the gNB 180a may, for example, use multiple antennas to send wireless signals to and / or receive wireless signals from the WTRU 102a. In one embodiment, the gNBs 180a, 180b, 180c may implement carrier aggregation technology. For example, the gNB 180a may transmit multiple component carriers to the WTRU 102a (not shown). A subset of these component carriers may be on an unlicensed spectrum, while the remaining component carriers may be on a licensed spectrum. In one embodiment, the gNBs 180a, 180b, 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).

[0060] The WTRUs 102a, 102b, 102c may communicate with the gNBs 180a, 180b, 180c using transmissions associated with parameter sets that may be scalable. For example, OFDM symbol spacing and / or OFDM subcarrier spacing may vary 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 transmit time intervals (TTIs) of varying or scalable lengths (e.g., containing different numbers of OFDM symbols and / or continuously varying absolute time lengths).

[0061] 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 while not accessing other RANs (e.g., such as the eNodeBs 160a, 160b, 160c). In a standalone configuration, the WTRUs 102a, 102b, 102c may use one or more of the gNBs 180a, 180b, 180c as mobility anchor points. In a standalone configuration, the WTRUs 102a, 102b, 102c may communicate with the gNBs 180a, 180b, 180c using signals in an unlicensed band. In a non-standalone configuration, the WTRUs 102a, 102b, 102c may communicate / connect with the gNB 180a, 180b, 180c while also communicating / connecting with another RAN, such as the eNodeB 160a, 160b, 160c. For example, the WTRUs 102a, 102b, 102c may implement the DC principle to communicate with one or more gNBs 180a, 180b, 180c and one or more eNodeBs 160a, 160b, 160c substantially simultaneously. In a non-standalone configuration, the eNodeB 160a, 160b, 160c may act as a mobility anchor for the WTRUs 102a, 102b, 102c, and the gNB 180a, 180b, 180c may provide additional coverage and / or throughput for serving the WTRUs 102a, 102b, 102c.

[0062] 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, scheduling of users in UL and / or DL, support of network slicing, dual connectivity, interworking between NR and E-UTRA, routing of user plane data towards a user plane function (UPF) 184a, 184b and routing of control plane information towards an access and mobility management function (AMF) 182a, 182b, etc. Figure 1D As shown, gNBs 180a, 180b, and 180c may communicate with each other via an Xn interface.

[0063] 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 possible data networks (DNs) 185a, 185b. Although each of the foregoing 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.

[0064] 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, support of network slicing (e.g., handling of different PDU sessions with different requirements), selecting a specific SMF 183a, 183b, management of registration areas, termination of NAS signaling and mobility management, etc. The AMF 182a, 182b may use network slicing to customize CN support for the WTRU 102a, 102b, 102c based on the type of services utilized 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 mobile broadband (eMBB) access, and / or services for machine type communication (MTC) access, etc. 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.

[0065] The SMF 183a, 183b may be connected to the AMF 182a, 182b in the CN 115 via the N11 interface. The SMF 183a, 183b may also be connected 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 service routing performed by the UPF 184a, 184b. The SMF 183a, 183b may perform other functions, such as managing and allocating UE IP addresses, managing PDU sessions, controlling policy implementation and QoS, and providing downlink data notifications. The PDU session type may be IP-based, non-IP-based, Ethernet-based, etc.

[0066] The UPF 184a, 184b may be connected to one or more of the gNBs 180a, 180b, 180c in the RAN 113 via the 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, and providing mobility anchoring, etc.

[0067] 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. In addition, the CN 115 may provide the WTRUs 102a, 102b, 102c with access to other networks 112, which may include other wired networks and / or wireless networks owned and / or operated by other service providers. In one embodiment, the WTRUs 102a, 102b, 102c may be connected to local data networks (DNs) 185a, 185b via 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.

[0068] Given that Figures 1A to 1D as well as Figures 1A to 1D Corresponding to the description of the present invention, one or more or all of the functions described herein with reference to one or more of the following items may be performed by one or more simulation devices (not shown): WTRU102a to WTRU102d, base station 114a to base station 114b, evolved Node B 160a to evolved Node B 160c, MME 162, SGW164, PGW 166, gNB 180a to ggNB 180c, AMF 182a to AMF 182b, UPF 184a to UPF 184b, SMF 183a to SMF 183b, DN 185a to DN 185b and / or any other device described herein. The simulation device may be one or more devices configured to simulate one or more or all of the functions described herein. For example, the simulation device can be used to test other devices and / or simulate network and / or WTRU functions.

[0069] The simulation device may be designed to implement one or more tests of other devices in a laboratory environment and / or in an operator network environment. For example, one or more simulation devices may perform one or more functions 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 simulation devices may perform one or more functions or all functions while being temporarily implemented / deployed as part of a wired and / or wireless communication network. The simulation device may be directly coupled to another device for testing purposes and / or may use over-the-air wireless communications to perform testing.

[0070] One or more simulation devices can perform one or more (including all) functions without being implemented / deployed as part of a wired and / or wireless communication network. For example, the simulation device can be utilized in a test scenario in a test lab and / or a non-deployed (e.g., testing) wired and / or wireless communication network to implement testing of one or more components. One or more simulation devices can be test equipment. Direct RF coupling and / or wireless communication via an RF circuit system (e.g., which can include one or more antennas) can be used by the simulation device to send and / or receive data.

[0071] Systems, methods, and means for relay selection in WTRU to WTRU relaying are described herein. A wireless transmit / receive unit (WTRU) may be configured to perform relay selection associated with WTRU to WTRU relaying. The WTRU may (e.g., determine) to perform relay (re)selection, for example, based on active traffic and / or measurements performed (e.g., reference signal received power (RSRP) measurements). The WTRU may perform network-assisted relay (re)selection. The WTRU (e.g., a WTRU within coverage) may initiate (e.g., RRC) connection or trigger (e.g., RRC) message, for example, based on WTRU to WTRU relay criteria. The WTRU may report measurement results to the network, for example, based on (e.g., multiple) hops.

[0072] The WTRU may determine a relay reselection behavior based on a measurement result and an active data determination associated with a first relay (e.g., whether there is a gap between active data transmissions). A WTRU (e.g., a remote WTRU) may be associated with a first relay WTRU (e.g., a WTRU-to-WTRU relay). The remote WTRU may receive configuration information indicating thresholds (e.g., a first threshold and a second threshold) associated with a sidelink (SL) RSRP (e.g., a first SLRSRP threshold and a second SLRSRP threshold, wherein the first SL RSRP threshold is higher than the second SL RSRP threshold). The configuration information may indicate data transmission gap information (e.g., data gap transmission parameters). The remote WTRU may determine a SL RSRP measurement result associated with the first relay WTRU. The remote WTRU may determine that the SL RSRP measurement result associated with the first relay WTRU is lower than the first threshold and higher than the second threshold (e.g., between the first threshold and the second threshold). The remote WTRU may determine to perform an active data determination (e.g., for relay reselection) (e.g., based on determining that the SL RSRP measurement result is lower than the first threshold and higher than the second threshold). For example, the remote WTRU may initiate discovery (e.g., send or receive a discovery transmission). The remote WTRU may determine a duration associated with a data transmission time gap (e.g., associated with the initiated discovery). The remote WTRU may determine whether the duration associated with the data transmission time gap exceeds a data transmission gap threshold. The remote WTRU may perform relay reselection to a second relay, for example, based on determining that the duration associated with the data transmission time gap exceeds the data transmission gap threshold.

[0073] The remote WTRU may perform relay reselection based on the SL RSRP measurement result (e.g., only the SL RSRP measurement result). For example, the remote WTRU may determine that the SL RSRP measurement result is below the second (e.g., lower) threshold (e.g., below both the first threshold and the second threshold). Based on determining that the SL RSRP measurement result is below the second threshold, the remote WTRU may initiate discovery. For example, the remote WTRU may perform relay reselection to a different relay without considering the data transmission gap information.

[0074] A WTRU (e.g., a remote WTRU used as an example) may be associated with a current relay WTRU (e.g., a first relay WTRU). The remote WTRU may determine and / or preselect a second relay or a set of candidates for a reselected relay, for example, based on a first condition / initial trigger (e.g., a drop in link quality of the current relay below a preselected threshold, a change in condition of the current relay, or information from another relay). For example, based on a second condition (e.g., condition, trigger) being satisfied, the WTRU may switch to one of the determined / preselected candidates. The remote WTRU may receive (e.g., via dedicated RRC messaging or SIB) a first condition for determining / preselecting a second relay and / or a set of candidate relays for reselection. The first condition may include one or more of the following: a first (e.g., minimum) PC5 RSRP for relay selection; a second (e.g., different) PC5 RSRP associated with triggering a two-step relay candidate selection process; a time associated with completing a reselection process after an initial preselection. The remote WTRU may be configured to pre-select one or more candidates for reselection (e.g., if initial conditions for pre-selection are met). The remote WTRU may complete the reselection process (e.g., select a pre-selected relay) (e.g., if secondary conditions are met, such as expiration of a time indicating no active data transmission, additional PC5 RSRP link quality measurement results, etc.).

[0075] In an example, for example, when (e.g., when) a remote WTRU reselects to a relay WTRU and the selected relay WTRU is connected to a cell different from the remote WTRU, the remote WTRU may trigger a connection establishment. The remote WTRU may receive configuration information indicating a set of allowable relay WTRUs to which the remote WTRU may perform reselection. The remote WTRU may receive a release message. The remote WTRU may move to RRC IDLE / RRC INACTIVE. The remote WTRU may perform relay reselection. For example, if the selected relay WTRU is connected to a cell different from the remote WTRU's serving cell, the remote WTRU may initiate a connection procedure (e.g., an RRC connection procedure).

[0076] A WTRU (e.g., a remote WTRU used as an example) may be associated with a current relay WTRU (e.g., a first relay WTRU). The remote WTRU may determine and / or preselect a second relay or a set of candidates for a reselected relay, for example, based on a first condition / initial trigger (e.g., a drop in link quality of the current relay below a preselected threshold, a change in condition of the current relay, or information from another relay). For example, based on a second condition (e.g., condition, trigger) being satisfied, the WTRU may switch to one of the determined (e.g., preselected) candidates. The remote WTRU may receive (e.g., via dedicated RRC messaging or SIB) a first condition for determining (e.g., preselecting) a second relay and / or a set of candidate relays for reselection. The first condition may include one or more of the following: a first (e.g., minimum) PC5 RSRP for relay selection; a second (e.g., different) PC5 RSRP associated with triggering a two-step relay candidate selection process; a time associated with completing a reselection process after an initial preselection. The remote WTRU may be configured to pre-select one or more candidates for reselection (e.g., if initial conditions for pre-selection are met). The remote WTRU may complete the reselection process (e.g., select a pre-selected relay) (e.g., if secondary conditions are met, such as expiration of a time indicating no active data transmission, additional PC5 RSRP link quality measurement results, etc.).

[0077] In an example, for example, when (for example, when) a remote WTRU selects (for example, reselects to) a relay WTRU and the selected relay WTRU is connected to a cell different from the remote WTRU, the remote WTRU may trigger a connection establishment. The remote WTRU may receive configuration information indicating a set of allowable relay WTRUs to which the remote WTRU may perform reselection. The remote WTRU may receive a release message. The remote WTRU may change state to, for example, an idle state or an inactive state (for example, move to RRC IDLE / RRC INACTIVE). The remote WTRU may perform relay reselection. For example, if the selected relay WTRU is connected to a cell different from the remote WTRU's serving cell, the remote WTRU may initiate a connection procedure (for example, an RRC connection procedure).

[0078] Sidelink (SL) based WTRU to network relay may be enabled and / or used. Sidelink relay may support (e.g., 5G) ProSe WTRU to network relay (U2N relay) functionality, for example, to provide connectivity to a U2N remote WTRU to a network. L2 and / or L3 U2N relay architectures may be supported. For example, in addition to controlling sidelink resources, the L3 U2N relay architecture may be transparent to the serving RAN of the U2N relay WTRU.

[0079] A U2N relay WTRU may use (eg, be in) RRC CONNECTED to perform relaying (eg, of unicast data).

[0080] For L2 U2N relay operation, one or more of the following items (e.g., the following RRC state combinations) may be supported: both the U2N relay WTRU and the U2N remote WTRU may use (e.g., be in) RRC CONNECTED to perform transmission / reception of relayed unicast data; and / or; for example, if (e.g., as long as) (e.g., all) U2N remote WTRUs connected to the U2N relay WTRU are in RRC INACTIVE or in RRC IDLE, the U2N relay WTRU may be in RRC IDLE, RRC INACTIVE, or RRC CONNECTED.

[0081] For L2 U2N relay, the U2N remote WTRU may (eg, only) use (eg, be configured to use) the resource allocation pattern for data to be relayed (eg, resource allocation pattern 2).

[0082] A (e.g., single) unicast link may be established between (e.g., one) L2 U2N relay WTRU and (e.g., one) L2 U2N remote WTRU. Traffic of the U2N remote WTRU (e.g., via a given U2N relay WTRU) and traffic of the U2N relay WTRU may be separated in different Uu RLC channels (e.g., over Uu).

[0083] A L2 U2N relay protocol architecture may be provided and / or used.

[0084] Example protocol stacks for the user plane and control plane of the L2 U2N relay architecture are shown in the figures of this document. Figure 2 An example user plane protocol stack for L2 WTRU to network relay is illustrated. Figure 3 An example control plane protocol stack for L2 WTRU to network relay is illustrated. For both CP and UP at both PC5 interface and Uu interface, the SRAP sublayer may be placed above the RLC sublayer (e.g., as Figure 2 and Figure 3). Uu SDAP, PDCP and RRC may terminate between the L2 U2N remote WTRU and a base station (e.g., gNB), for example, as shown in Figure 2 and Figure 3 SRAP, RLC, MAC, and PHY may be terminated in (e.g., each) hop (e.g., a link between an L2 U2N remote WTRU and an L2 U2N relay WTRU and a link between an L2 U2N relay WTRU and a gNB), for example, as shown in Figure 2 and Figure 3 shown.

[0085] In an example (e.g., for L2 U2N relay), the SRAP sublayer on the PC5 hop may be used (e.g., only for) bearer mapping. For example, for messages relaying the L2U2N remote WTRU on BCCH and PCCH, the SRAP sublayer may not be present on the PC5 hop. In an example, in messages (e.g., of the L2 U2N remote WTRU) on SRB0, the SRAP sublayer may not be present on the PC5 hop. The SRAP sublayer may be present on the Uu hop (e.g., for both DL and UL).

[0086] In an example (e.g., for L2 U2N relay for uplink), the Uu SRAP sublayer may support (e.g., UL) bearer mapping (between the ingress PC5 relay RLC channel and the egress Uu relay RLC channel for relaying through the L2 U2N relay WTRU Uu interface). End-to-end RBs (e.g., SRBs or DRBs) of the same remote WTRU and / or different remote WTRUs may be multiplexed (e.g., through the same Uu relay RLC channel), e.g., for uplink relay traffic.

[0087] In an example (e.g., for L2 U2N relay for uplink), the Uu SRAP sublayer may support L2 U2N remote WTRU identification (e.g., for UL traffic). Identity information (e.g., of the L2 U2N remote WTRU Uu radio bearer and / or the local remote WTRU ID) may be included in the Uu SRAP header at the UL, for example, so that a base station (e.g., gNB) can associate received packets of a (e.g., specific) PDCP entity associated with the associated Uu radio bearer of the remote WTRU. For example, the PC5 SRAP sublayer (e.g., at the L2U2N remote WTRU) may support (e.g., UL) bearer mapping between the remote WTRU Uu radio bearer and the egress PC5 relay RLC channel.

[0088] In an example (e.g., for L2 U2N relay for downlink), the Uu SRAP sublayer may support DL bearer mapping at a base station (e.g., gNB) to map end-to-end radio bearers (e.g., SRBs, DRBs) of a remote WTRU into a Uu relay RLC channel over the relay WTRU Uu interface. The Uu SRAP sublayer may support DL bearer mapping and data multiplexing between multiple end-to-end radio bearers (e.g., SRBs or DRBs) of a L2U2N remote WTRU and / or different L2 U2N remote WTRUs and / or (e.g., one) Uu relay RLC channel over the relay WTRU Uu interface.

[0089] In an example (e.g., for L2 U2N relay for downlink), the Uu SRAP sublayer may support remote WTRU identification (e.g., for DL ​​traffic). Identity information (e.g., of the remote WTRU Uu radio bearer and the local remote WTRU ID) may be included in the Uu SRAP header (e.g., by the gNB at the DL), for example, so that the relay WTRU maps packets received from the remote WTRU Uu radio bearer to its associated PC5 relay RLC channel.

[0090] In an example (eg, for L2 U2N relay for downlink), the PC5 SRAP sublayer (eg, at the relay WTRU) may support DL bearer mapping between, for example, an ingress Uu relay RLC channel and an egress PC5 relay RLC channel.

[0091] In an example (e.g., for L2 U2N relay for the downlink), the PC5 SRAP sublayer (e.g., at the remote WTRU) may associate received packets for a specific PDCP entity associated with an associated Uu radio bearer of the remote WTRU, for example based on identity information included in the Uu SRAP header.

[0092] The local remote WTRU ID may be included in a header (e.g., a PC5 SRAP header and / or a Uu SRAP header). A relay WTRU (e.g., a L2 U2N relay WTRU) may be configured with a local remote WTRU ID by a base station (e.g., a gNB), for example, for use in a SRAP header. The remote WTRU may obtain the local remote ID from a base station (e.g., a gNB), for example, via a Uu RRC message (e.g., including RRCSetup, RRCReconfiguration, RRCResume, and / or RRCReestablishment). The Uu DRBs and / or Uu SRBs may be mapped to different PC5 relay RLC channels and Uu relay RLC channels (e.g., in both a PC5 hop and a Uu hop).

[0093] The base station (e.g., gNB) may be responsible for avoiding conflicts in the use of the local remote WTRU ID. The base station (e.g., gNB) may update the local remote WTRU ID by transmitting the updated local remote ID to the relay WTRU (e.g., via a message (e.g., RRCReconfiguration message)). The serving base station (e.g., gNB) may perform the local remote WTRU ID update, for example, independently of the PC5 unicast link L2 ID update procedure.

[0094] Discovery may be enabled and / or performed.

[0095] Discovery models may be supported for U2N relay discovery. For example, Model A and Model B discovery models may be supported for U2N relay discovery. Figure 4 An example protocol stack for WTRU to network relay discovery messages is illustrated. Figure 4 As shown, a protocol stack for discovery may be provided.

[0096] The U2N remote WTRU may perform relay discovery messaging. For example, while in RRC IDLE, RRC INACTIVE, or RRC CONNECTED, the U2N remote WTRU may monitor the sidelink for relay discovery messages. The network may broadcast a threshold. The threshold may be used (e.g., by the U2N remote WTRU) to determine whether it may send a relay discovery request message (e.g., to a U2N relay WTRU).

[0097] While in RRC IDLE, RRC INACTIVE, or RRC CONNECTED, a U2N relay WTRU may perform relay discovery messaging and / or may monitor the sidelink for relay discovery messages. The network may broadcast RSRP thresholds (e.g., maximum Uu RSRP threshold, minimum Uu RSRP threshold, or both), which may be used by the U2N relay WTRU (e.g., to determine whether it may send a relay discovery message to a U2N remote WTRU).

[0098] The network may provide the relay discovery configuration information, for example, using broadcast or dedicated signaling for relay discovery.The U2N remote WTRU and / or the U2N relay WTRU may use the configuration information (eg, pre-configuration) for relay discovery.

[0099] A resource pool (e.g., for NR side link communication) may be used for relay discovery. The network may configure a resource pool dedicated to relay discovery. The resource pool dedicated to relay discovery may be configured with a resource pool for NR side link communication, for example, in system information, dedicated signaling and / or pre-configuration (e.g., simultaneously). Whether to configure a dedicated pool for relay discovery may be based on network specific implementation. For example, if a resource pool dedicated to relay discovery is configured, a resource pool dedicated to relay discovery (e.g., a resource pool dedicated only to relay discovery) may be used for relay discovery. For example, if a resource pool for (e.g., NR) side link communication is configured (e.g., only), the configured transmit resource pool (e.g., all configured transmit resource pools) may be used for relay discovery and side link communication.

[0100] In an example, for a U2N remote WTRU (eg, which may include both in coverage and out of coverage) that is connected to the network (eg, via a U2N relay WTRU), (eg, only) resource allocation mode 2 may be used for discovery messaging.

[0101] Relay selection (eg, reselection) may be performed.

[0102] A remote WTRU (e.g., a U2N remote WTRU) may perform measurements (e.g., radio measurements, such as RSRP measurements). A (e.g., U2N) remote WTRU may perform radio measurements at a PC5 interface. The remote WTRU may use the measurement results (e.g., together with higher layer criteria), for example, for U2N relay selection and reselection. The remote WTRU (e.g., a U2N remote WTRU) may use the SD-RSRP measurement results to evaluate whether the link quality (e.g., PC5 link quality) towards the U2N relay WTRU meets the relay selection criteria as discussed herein. For example, when (e.g., when) there is no unicast PC5 connection between the U2N relay WTRU and the U2N remote WTRU.

[0103] In an example (e.g., for relay reselection), a remote WTRU (e.g., a U2N remote WTRU) may use measurements (e.g., SL-RSRP) of a serving WTRU (e.g., a U2N relay WTRU) to perform relay reselection trigger evaluation, for example, when (e.g., when) there is data transmission from the (e.g., U2N) relay WTRU to the (e.g., U2N) remote WTRU. For example, in the absence of data transmission from the U2N relay WTRU to the U2N remote WTRU, it may be WTRU-specific to decide whether to use SL-RSRP or SD-RSRP for relay reselection trigger evaluation.

[0104] For example, if the PC5 link quality measured by the U2N remote WTRU towards the U2N relay WTRU exceeds a configured threshold (e.g., preconfigured or provided by the gNB), the relay (e.g., U2N relay) WTRU may be considered suitable in terms of radio criteria (e.g., by the U2N remote WTRU). The U2N remote WTRU may search for suitable U2N relay WTRU candidates that meet the (e.g., all AS layers and higher layers) criteria. For example, if there are multiple such suitable U2N relay WTRUs, it may be implemented by the U2N remote WTRU to select (e.g., one) U2N relay WTRU among them. For (e.g., L2 U2N relay) (re)selection, PLM[N ID and cell ID may be used as additional (e.g., AS) criteria.

[0105] A remote WTRU (e.g., a U2N remote WTRU) may trigger (e.g., U2N) relay selection based on one or more of the following: the (e.g., direct Uu) signal strength of the (e.g., U2N) remote WTRU's current serving cell being lower than a configured signal strength threshold; and / or an indication (e.g., made by an upper layer of the U2N remote WTRU), etc.

[0106] The (e.g., U2N) remote WTRU may trigger a (e.g., U2N) relay reselection based on one or more of the following: the (e.g., PC5) signal strength of the (e.g., current U2N) relay WTRU is lower than a (pre-)configured signal strength threshold; a cell (re)selection, handover or (e.g., Uu)RLF has been indicated (e.g., via PC5-RRC signaling) by the (e.g., U2N) relay WTRU; when (e.g., when) the remote WTRU receives a (e.g., PC5-S) link release message from the (e.g., U2N) relay WTRU; when (e.g., when) the (e.g., U2N) remote WTRU detects a (e.g., PC5)RLF; an indication (e.g., made by an upper layer).

[0107] For a L2 U2N remote WTRU and / or a L3 U2N remote WTRU (e.g., in RRC IDLE / INACTIVE), the cell (re)selection process and the relay (re)selection process may run independently. For example, if there are both a suitable cell and a suitable U2N relay WTRU, it may be up to the WTRU specific implementation to select the cell or the U2N relay WTRU. For example, a L3 U2N remote WTRU may select both a cell and a U2N relay WTRU (e.g., simultaneously), which may depend on the specific implementation of the L3 U2N remote WTRU.

[0108] For L2 and L3 U2N relay WTRUs (e.g., in RRC IDLE / INACTIVE), for example, when (e.g., when) the U2N relay WTRU selects a (e.g., new) cell, a (e.g., PC5-RRC) message may be used to notify their associated (e.g., connected) remote WTRUs. For example, when (e.g., when) the L2 / L3 U2N relay WTRU performs a handover or detects a (e.g., Uu) RLF, a (e.g., PC5-RRC) message may be used to notify its associated (e.g., connected) L2 or L3 U2N remote WTRU. The decision of whether to release or maintain a unicast (e.g., PC5) link may be specifically implemented by the (e.g., U2N) remote WTRU, for example, based on the reception of a PC5 RRC message for notification. For example, if the U2N remote WTRU determines (e.g., decides) to release a unicast PC5 link, the U2N remote WTRU may trigger an L2 release procedure and may perform relay reselection.

[0109] Relay selection / reselection rules may be specified, provided and / or used (e.g., for WTRU to NW relays). These rules may be based (e.g., primarily) on consideration of RSRP measurements on the sidelink for the remote WTRU (e.g., to determine which relay to select). WTRU to WTRU relays may be specified and relay selection rules may (e.g., need to) be considered. There may be a number of differences between U2N and U2U, which may, for example, make existing U2N relay (re)selection rules not directly applicable to U2U relays.

[0110] For example, WTRU-based relay selection for U2N relay may be used when (e.g., when) the remote WTRU is in RRC IDLE / RRC INACTIVE. In this case (e.g., the remote WTRU is in RRC IDLE / RRC INACTIVE), the remote WTRU may not have active data to send. For the remote WTRU (e.g., in RRC CONNECTED), the mobility may be controlled by the base station (e.g., gNB). For U2U relay (e.g., particularly for out of coverage scenarios), the gNB may not be involved in the mobility decision. The relay (re)selection decision (e.g., particularly when it is performed frequently) may affect the latency associated with the ongoing data transmission. (e.g., alone) RSRP-based (re)selection decision may not be appropriate in this case.

[0111] WTRU based relay selection (e.g. for U2N relay) may use (e.g. only) the quality of the SL hop. This may be based on the assumption that the relay operation threshold (e.g. configured to the U2N relay) may be guaranteed to be acceptable for the Uu hop quality. In the example (e.g. for U2U relay), the relay selection / reselection rules may take two hops into account. Measurements for both hops may not be available at the deciding WTRU and / or may also be unavailable due to the fact that different mechanisms (e.g. SL-RSRP vs. SD-RSRP) may be used on each link to make such measurements.

[0112] A U2N relay may have a (e.g., very simple) connectivity architecture and network coverage. Specifically, for example, a remote WTRU may be assumed to be out of coverage, while a relay WTRU may be assumed to be within coverage. A remote WTRU may be assumed to have a (e.g., single) unicast link with a relay WTRU. A relay WTRU may have a (e.g., traditional RRC) connection with the network. A U2U relay may have (e.g., more) variations in topology and coverage situations, for example, such as one or more (e.g., two or all) of the WTRUs being within coverage or out of coverage, and / or operating in mode 1 / mode 2, and the same relay or different relays utilizing (e.g., multiple) connections to different destinations to serve a (e.g., single) source WTRU, and vice versa. A WTRU may use both U2N relays and U2U relays. The factors described herein may be considered when selecting an appropriate relay.

[0113] The WTRU may determine to perform and / or perform relay reselection, for example, based on active traffic.

[0114] In an example, the WTRU may determine (e.g., any of the following): a relay selection rule, a relay selection criterion, whether (e.g., when / whether) relay reselection is triggered, a (e.g., a specific) relay selection procedure to follow, or similar behavior related to relay selection (e.g., based on the presence and / or type of active traffic sent / received from the relay). An advantage may be avoiding frequent relay (re)selection procedures (e.g., which may involve loss or delay of sidelink data of the relay) that may occur, for example, when (e.g., when) the WTRU performs active data transmission.

[0115] Detection of activity data and / or data types may be performed and / or enabled.

[0116] The WTRU may determine the presence / type of active data. The WTRU may determine the presence / type of active data based on, for example, one or more of: the presence of an end-to-end unicast link; the amount of data sent via the unicast link, the amount of time since the last data transmission (e.g., the data transmission time gap), and / or the QoS associated with the data, etc.

[0117] The WTRU may determine the presence / type of active data, for example, based on the presence of an end-to-end unicast link. For example, the remote WTRU may determine that active data exists when (e.g., when) the remote WTRU is configured with an adaptation layer. For example, the remote WTRU may determine that active data exists when (e.g., when) the remote WTRU is configured with an end-to-end source / destination L2 ID, a unicast link, or the like (e.g., which may be associated with transmission via a relay).

[0118] The WTRU may determine the presence / type of active data, for example, based on the amount of data sent via the unicast link. In an example, the remote WTRU may consider an increase (e.g., a sudden increase) in data intended for the target WTRU. This may be based on an increase in buffered data at the WTRU or a (e.g., sudden) increase in throughput on the unicast link. For example, if the increase in buffered data is above a threshold, the remote WTRU may consider that there is active data. In an example, the remote WTRU may consider changes (e.g., large changes) in the amount of data over a certain time (e.g., average) window on the unicast link. This may be based on a configured threshold. For example, if the amount of data over a preconfigured time window is above a threshold, the remote WTRU may consider that there is active data on the link.

[0119] The WTRU may determine the presence / type of active data, for example, based on the amount of time since the last data transmission. The status of the buffer state at the remote WTRU (e.g., if the buffer is growing / depleting, the rate of depletion, how long the packets have been in the system, etc.) may be used to infer the time since the last data transmission. A duration (e.g., tracked via a timer) that may be configured to be reset after each transmission or reception (e.g., data transmission, discovery transmission, discovery reception) may be used to track the time since the last data transmission, how long the link has been alive, etc. In an example, the remote WTRU may utilize (e.g., SL-RSRP) measurement state (e.g., measuring the time of the last SL-RSRP) to track the last data transmission / time since the last data transmission on the unicast link.

[0120] The WTRU may determine the presence / type of active data, for example, based on the QoS associated with the data. The remote WTRU may consider changes in data characteristics (e.g., a new LCG / DRB with a different / higher priority triggered by application layer data) as activity. The QoS of the data sent on the relay link may be used to determine the parameters used for activity state determination. For example, the type of QoS data may be used to determine the measurement window and / or measurement parameters used for selection. For example, lower latency data may use (e.g., require) a smaller measurement window to select a relay faster and / or also prioritize paths with lower hop counts (e.g., paths with fewer hops between the source and the target). CSI / CQI may also be used as a selection criterion. For example, in addition to considering the RSRP of the hop (e.g., per hop), CSI / CQI may also be used as a selection criterion. If the data has higher bandwidth requirements, CSI / CQI may also be used as a selection criterion in addition to the RSRP of the hop (e.g., per hop), for example, if the source has multiple paths that meet the PC5 link quality, it may use the CSI quality to make decisions between these links.

[0121] Relay selection behavior may depend on a determination of the presence and / or type of data (eg, activity data).

[0122] The WTRU may determine (e.g., select) a relay selection behavior to be performed, for example, based on a determination of the presence / type of activity data (e.g., based on a transmit time gap). For example, the relay selection behavior may be determined based on a determination of activity data (e.g., as described herein, such as based on a transmit time gap). For example, in addition to the determination of activity data, the WTRU may also consider other criteria (e.g., RSRP measurement results). For example, (e.g., in addition to the determination of activity data) the WTRU may consider one or more of the following: determining criteria for triggering relay (re)selection; determining criteria for acceptable relays; determining whether to perform a discovery process (e.g., sending and / or receiving or discovery) and / or a discovery resource pool to use; determining whether to delay relay (re)selection (e.g., delaying to a later time); and / or determining whether to perform (re)selection of a second relay and / or potential relays, etc.

[0123] The WTRU may determine (e.g., select) a relay selection action to be performed, for example, based on a determination of criteria for triggering relay (re)selection. For example, the criteria for triggering relay (re)selection may be associated with the age of data in the WTRU buffer. For example, if the age of data in the WTRU buffer exceeds (e.g., is above) a certain threshold, relay reselection may be triggered. A WTRU configured with an inactivity time (e.g., where the inactivity time may be reset at the end of the last data transmission) may trigger a relay selection event, for example, based on expiration (e.g., based on the inactivity time). The inactivity time may be tracked (e.g., via a timer).

[0124] For example, the criteria for triggering relay (re)selection may be associated with CSI information (e.g., if the information is available to the remote WTRU, e.g., from a WTRU-WTRU relay). In an example, the quality of the CSI report provided by the relay WTRU upon (e.g., when) requested by the remote WTRU may trigger a reselection event. For example, if the remote WTRU does not receive a CSI report (e.g., within a time duration (e.g., a maximum amount of time)), then expiration of time (e.g., via a timer) may trigger a relay reselection event.

[0125] The WTRU may determine (e.g., select) a relay selection behavior to be performed, for example, based on determining criteria for acceptable relays. For example, the criteria for acceptable relays may be associated with data rates supported by the WTRU-WTRU relay (e.g., current / instantaneous and / or minimum / maximum data rates). The criteria for acceptable relays may be associated with data rates used by the remote WTRU (e.g., required data rates, such as, for example, instantaneous data rates, peak data rates, average data rates, etc.). For example, if the capabilities (e.g., supported QoS / reliability / latency capabilities) of the relay WTRU are available to the remote WTRU (e.g., via a discovery message), the criteria for acceptable relays may be associated with the capabilities. The criteria for acceptable relays may be associated with measurement results (e.g., SL-RSRP) for WTRU-WTRU relays, for example, which may include RSRP for both the relay-source and relay-target directions (e.g., if available, such as based on previous / most recent transmissions). The criteria for acceptable relays may be associated with the quality of CSI reports for the relay WTRU (e.g., if available).

[0126] The WTRU may determine (e.g., select) a relay selection behavior to be performed, for example, based on determining whether to perform a discovery process (e.g., sending and / or receiving discovery) and / or a discovery resource pool to be used. For example, if the SL-RSRP or SD-RSRP is above a certain threshold, the (e.g., relay) WTRU may decide to send and / or forward a discovery message. The threshold may be based on QoS requirements. A certain SL-RSRP value / range may be able to support (e.g., only support) a certain QoS. Higher or more stringent QoS requirements may use (e.g., require) different SL-RSRP / SD-RSRP. The WTRU may decide to use a specific resource pool, for example, based on the characteristics of the data being served. This may be based on the QoS of the data (e.g., priority, reliability, latency / PDB, etc.), the amount of data being served, etc. For example, a WTRU configured with both a dedicated resource pool and a shared resource pool may choose to use a dedicated pool for data with a high QoS value, while lower QoS data may result in the shared resource pool being used for discovery messages. For example, the WTRU may use information bound to a received discovery message to determine whether to forward a discovery message. This information may be information such as the resource pool on which the message was received, the number of subchannels occupied by the discovery message, the CBR of the resource pool, the RSRP of the received discovery message, the hop count of the discovery message (e.g., if available), the hop count to the target WTRU (e.g., if available), the potential for success of a successful relay between the source / remote WTRU and the target WTRU (e.g., this may be based on the number of WTRUs currently being served by the relay WTRU, the load of the relay, and / or the SL-RSRP / SD-RSRP levels to neighboring WTRUs based on some historical context, etc.). For example, the relay may decide to send and / or forward the message based on the resource pool on which the data discovery message was received and / or if there is a (e.g., pre-configured) mapping between the resource and the sending resource pool (e.g., the mapping may indicate an automatic forwarding configuration for the discovery message).

[0127] The WTRU may determine (e.g., select) a relay selection behavior to perform, for example, based on determining whether to delay relay (re)selection to a later time. The WTRU may start reselection and decide on a set of relay candidates for reselection. The WTRU may track the duration (e.g., start a timer) or wait for another triggering event (e.g., it had an ongoing data transmission that is now completed). The WTRU may detect a (e.g., new) discovery message from a relay WTRU (e.g., in the same set or a new candidate that may provide additional information that may assist the WTRU in making the selection). If the WTRU has detected the auxiliary trigger or if the duration has expired (e.g., via a timer), the WTRU may initiate reselection of a (e.g., new) relay. The information (e.g., new information) may include information associated with the relay WTRU capabilities (e.g., load, data rate, supported QoS, SL-RSRP / SD-RSRP, etc.). The WTRU may utilize information obtained in this time window (e.g., between the first trigger and the second trigger), for example, to collect additional data and / or perform some time averaging (e.g., of RSRP, load, etc.) to consider in deciding which relay to switch to.

[0128] Figure 5 An example of relay selection behavior determined based on, for example, measurement results (e.g., RSRP) and activity data as discussed herein is illustrated. The WTRU may determine (e.g., select) a relay selection behavior to be performed, for example, based on determining whether to perform (re)selection for a second relay / potential relay. The WTRU may trigger (re)selection of a secondary relay, for example, as a means of reducing handover time between relays. This may be based on (e.g., as discussed herein and as Figure 5 As shown, configuration information indicating conditions and / or thresholds (e.g., a first (e.g., higher) threshold and a second (e.g., lower) threshold) associated with SLRSRP and / or data gap transmission parameters, and triggered by, for example, one or more of the following events: (e.g., current) relay link quality drops below (e.g., less than) a threshold (e.g., within a certain margin / difference of an RSRP threshold or a second SL-RSRP threshold, the second SL-RSRP threshold may be within a certain margin of a minimum RSRP for reselection); a change in the (e.g., remote) WTRU buffer status, which may indicate that the current relay is running out of steam, etc.; a type of QoS that the relay may or may not support, etc. For example, in the case where the priority of the data sent via the relay is higher than the threshold, when (e.g., when) the measurement result (e.g., RSRP) of the (e.g., current) relay is lower than the threshold (e.g., such as Figure 5The remote WTRU may trigger relay selection for the second relay if the measurement result (e.g., RSRP) of the (e.g., current) relay drops below a second threshold (e.g., the lower of the two thresholds, e.g., as shown in FIG. 2 ). For example, if the measurement result (e.g., RSRP) of the (e.g., current) relay drops below a second threshold (e.g., the lower of the two thresholds, e.g., as shown in FIG. Figure 5 2) as shown, the remote WTRU may change the relay to a second relay using a reselection procedure that takes into account the selected relay (eg, any potential relay) (eg, having a higher priority).

[0129] Relay selection criteria (e.g., SL RSRP measurement results, such as Figure 5 ) and activity data determination (e.g., as Figure 5 The combination shown in (shown) may include one or more of the following items: for example, when (for example, only when) the relay selection condition satisfies the condition (for example, see Figure 5 ), an activity data determination (e.g., whether there is activity data, e.g., whether a data transmission gap threshold is reached) may be used as a condition for triggering reselection. Otherwise, reselection may be skipped (e.g., not used). Parameters or conditions for determining activity data may be configured based on measurement results (e.g., SL RSRP measurement results).

[0130] The combination of the relay selection criteria (e.g., SL RSRP measurement result) and the activity data determination may include the following forms: the activity data determination (e.g., whether there is activity data, for example, whether a data transmission gap threshold is reached) may be used as a relay selection criterion for selecting a relay when (e.g., only when) a conventional relay selection condition satisfies (e.g., a certain) condition (e.g., if the SL RSRP measurement result is above / below a threshold, if the SL RSRP measurement result is between two thresholds, etc., such as Figure 5 Otherwise, the combination may not be used. For example, if the measurement result (e.g., SL RSRP) is measured to be within a first range (e.g., greater than a first threshold and less than a second threshold, as shown in FIG. 1 ), the condition for triggering relay reselection is triggered. Otherwise, the combination may not be used. Figure 5 ), the remote WTRU may use the activity data to determine whether to trigger relay reselection. For example, if the SL RSRP is below a first threshold or above a second threshold (e.g., Figure 5 As shown), the WTRU may consider (e.g., only consider) the measurement result (e.g., SL RSRP measurement result) condition to trigger relay reselection (e.g., initiate discovery (e.g., discovery transmission / reception) and perform relay selection, such as Figure 5 shown).

[0131] The combination of relay selection criteria (e.g., SL RSRP measurement results) and active data determination may include using parameters or conditions for determining active data (e.g., data gap transmission parameters, such as Figure 5 As shown), for example, the parameter or condition may be configured based on (e.g., SL RSRP) measurement results (e.g., the data transmission time gap threshold may be determined based on the SL RSRP measurement results, for example, where a higher SL RSRP measurement result may be associated with a higher data transmission time gap threshold and a lower SL RSRP measurement result may be associated with a lower data transmission time gap threshold). The threshold time period (e.g., for triggering reselection) during which no active data transmission is observed may depend on the measurement results (e.g., SL RSRP). When (e.g., when) the measured SL RSRP is high, the WTRU may receive configuration information indicating (e.g., configured with) a first (e.g., larger) time period without active data before triggering relay reselection, and when (e.g., when) the measured SL RSRP is low, the WTRU may receive configuration information indicating (e.g., configured with) a second (e.g., smaller) time period without active data before triggering relay reselection. The remote WTRU may, for example, determine the time period based on the absence of active data (e.g., based on tracking the time after the WTRU initiated discovery transmission / reception, as Figure 5 The remote WTRU may determine whether a data transmission time gap is detected based on a threshold time period (as shown in the example). Based on determining that a data transmission time gap is detected, the remote WTRU may (e.g., opportunistically) perform relay selection to a second U2U relay. The remote WTRU may receive configuration information indicating (e.g., configured with) an inhibit time (e.g., an inhibit timer) between triggering of relay reselection (e.g., after a first reselection, the remote WTRU may refrain from triggering (e.g., not triggering) a second relay reselection for a time period given by the inhibit time). The WTRU may determine the value of the inhibit time (e.g., the inhibit timer), for example, based on the measured RSRP.

[0132] The WTRU may perform network assisted relay (re)selection.

[0133] In an example, relay selection by the remote WTRU may be controlled by conditions and / or constraints (e.g., provided by the network). Examples of network control may include one or more of the following: the remote WTRU may restrict relay selection to a list of relays that are allowed or not allowed as relay reselection targets; the remote WTRU may be allowed to perform relay reselection, or may use (e.g., require) relay reselection performed by the network and indicated to the remote WTRU, for example, where if performed by the network, the remote WTRU may receive a specific relay WTRU to which relay reselection should be performed; after the remote WTRU reports the selected relay to the network, the remote WTRU may receive an acceptance or rejection of the selected relay, etc.

[0134] For a remote WTRU that is within coverage and / or RRC CONNECTED, network control may be enabled and / or used (eg, is possible).

[0135] In an example, for a WTRU that does not have any candidates that meet the criteria, a base station (e.g., a gNB) may provide a temporary candidate to the WTRU, or provide a temporary candidate that the base station knows may meet the needs of the remote WTRU temporarily or before the WTRU can select a candidate on its own (e.g., a candidate that meets the reselection criteria).

[0136] The WTRU may be configured with a set of relays by the network. The WTRU may exclude WTRUs (eg, relays) that may not be in the set as potential candidates for relay selection. This may be beneficial from a WTRU processing and latency perspective.

[0137] In an example, the WTRU may be inhibited (e.g., prohibited) from performing relay selection. For example, the network may sense that the WTRU is performing (e.g., frequent) relay (re)selection and ping-pong switching between relays (e.g., which may result in (e.g., excessive) signaling and / or impact other WTRUs). Such scenarios may indicate that the WTRU is missing information (e.g., some critical information) and / or is experiencing poor channel conditions. The base station (e.g., gNB) or the network may take over and provide the WTRU with a relay WTRU or (e.g., alternatively) suspend relay selection, for example, until some later time when a reselection event may be triggered (e.g., via a reconfiguration message or time expiration, etc.).

[0138] In an example, the WTRU may receive an indication and / or trigger from the network for relay selection. This may be in addition to (e.g., any) pre-configuration (e.g., RSRP thresholds, resource pools, etc.) that the network may provide to the WTRU for relay discovery, for example, where the WTRU may refrain from initiating (e.g., being unable to initiate) a discovery process (e.g., even if it is preconfigured for relay discovery), for example, until it receives the explicit indication or trigger from the network. The indication may be associated with a time (e.g., a timer), for example, where upon expiration of the time, the WTRU may have to wait for another indication or trigger before the WTRU may initiate the discovery process.

[0139] In an example, the WTRU may be prohibited from performing (e.g., any) discovery and relay selection. The network may provide the WTRU with a (e.g., specific) relay that the WTRU will (e.g., need to) select. This may be temporary and may be triggered by factors such as, for example, measurements made by a remote WTRU, excessive load on the relay WTRU, WTRU ping-pong handovers between relays (e.g., occurring due to triggering excessive reselection), etc. In an example, the WTRU may provide the network or gNB with assistance information about active relays / connected relays and / or candidate relays, for example, including active connections and discovery related measurement results (e.g., SL-RSRP, SD-RSRP, etc.). The network may use this assistance information in conjunction with any additional information that the network may be aware of (e.g., relay load, relay hop counts from / to the source and target WTRUs, WTRU resource pool configuration, etc.) to assist the WTRU in relay selection, for example by providing updated configuration information (e.g., such as a candidate set of relays for relay selection or, alternatively, specific relays that the WTRU should use temporarily or for some fixed time duration after which the WTRU may revert to selection).

[0140] The WTRU may determine its relay selection behavior (e.g., constraints) and / or network interactions. The WTRU may determine its relay selection behavior (e.g., constraints) and / or network interactions based on one or more of the following factors: the RRC state of the remote WTRU; resource allocation; and / or QoS of the data, etc.

[0141] The WTRU may determine its relay selection behavior (e.g., constraints) and / or network interactions based on the RRC state of the remote WTRU. A WTRU that is in RRC IDLE / INACTIVE and out of coverage (OOC) may select (e.g., based on certain preconfigured parameters) from (e.g., any) relay WTRU that meets the selection criteria. The WTRU may have a (e.g., preconfigured) list of relays that it may (e.g., be allowed to) select from. For example, if there is no such list, the WTRU may (e.g., alternatively) select from any available relay WTRU that meets (e.g., PC5) link quality.

[0142] In an example, a WTRU (e.g., in RRC CONNECTED) may be preconfigured with (e.g., different) behaviors for relay selection. The WTRU may be configured with a subset of relay WTRUs from which it may select. This additional information may be provided by the network and / or the gNB. For example, the WTRU may use (e.g., be restricted to) this set while in the RRC connected phase or for a fixed duration after the connection is established. The link quality to the relay WTRU and / or the Uu link quality may be used to determine which behavior to follow. For example, if the Uu link quality is above a certain threshold, the WTRU may select from the preconfigured set. For example, if the Uu link quality drops below a (e.g., certain) threshold, the WTRU may (e.g., freely) select (e.g., any) relay WTRU.

[0143] The WTRU may determine its relay selection behavior (e.g., constraints) and / or network interactions based on resource allocation. In an example, a WTRU that is within coverage and operating in Mode 1 may wait for the network to provide it with a relay WTRU and may start the selection process (e.g., only) based on an indication (e.g., explicit) from the network to start the selection process or after expiration of a time (e.g., via a timer) that may be preconfigured by a base station (e.g., gNB). A WTRU that is within coverage and operating in Mode 1 may start the selection process by performing measurements and (e.g., potentially) finally picking and / or reporting a set of candidates. For example, if the WTRU does not receive a relay WTRU from the network (e.g., within a certain time, e.g., via expiration of a timer), the WTRU may (e.g., only) select a relay WTRU, or if the WTRU receives a trigger (e.g., explicit) from the network / gNB to select a relay WTRU, the WTRU may select a relay WTRU. In an example, a WTRU that is within coverage may refrain from participating in (e.g., not participating in) discovery (e.g., unless instructed by the network). The WTRU may choose to refrain from participating in (e.g., not participating in) the discovery process (e.g., forwarding messages), for example, based on one or more of the following: CBR, QoS requirements, relay load, distance / hop count to the source and / or target WTRU, etc. For example, if the WTRU senses other relay WTRUs that may be in close proximity to the source / target WTRU, the WTRU may (e.g., choose to) refrain from forwarding (e.g., not forwarding) any discovery-related messages, and may also use additional information as mentioned above (e.g., CBR, relay load, etc.).

[0144] The WTRU may determine its relay selection behavior (e.g., constraints) and / or network interactions based on the QoS of the data. The WTRU may determine the relay selection behavior based on the QoS of the data being served. The WTRU may receive configuration information indicating (e.g., configured with) a set of (e.g., specific) relays to select from (e.g., when / when serving high QoS data). The WTRU may receive configuration information indicating (e.g., configured with) a different set or alternatively without constraints and may select from (e.g., all) other relays for lower QoS data.

[0145] A WTRU within coverage may initiate a (eg, RRC) connection or trigger a (eg, RRC) message, for example, based on WTRU-to-WTRU relay criteria.

[0146] WTRU to WTRU relay criteria, connection failure to a relay WTRU, and / or other events related to WTRU to WTRU relaying may initiate (e.g., additional) signaling at the remote WTRU and / or initiate a connection establishment procedure for a remote WTRU (e.g., in IDLE / INACTIVE). Such messaging / connection may be performed conditioned on the remote WTRU having received a selected relay WTRU from the network. For example, the remote WTRU may receive a relay for U2U relay from dedicated (e.g., NW) signaling (e.g., in RRC CONNECTED). The remote WTRU may be moved to RRC CONNECTED. For example, based on (e.g., some) conditions related to the U2U relay WTRU, the remote WTRU may initiate RRC CONNECTED and notify the network of such conditions. Such conditions may include one or more of the following: the SL RSRP of the relay WTRU drops below a threshold; the remote WTRU initiates / triggers relay reselection; the remote WTRU detects SL-RLF with the relay WTRU; the remote WTRU is unable to successfully initiate a unicast link with the relay or a unicast link with the target WTRU via the relay; and / or the measurement results of the alternative relay WTRU are better than the current relay WTRU (e.g., a threshold), etc.

[0147] The WTRU may be preconfigured to provide a report to the network, for example, if the WTRU is unable to connect to any of the configured relays. The WTRU may (e.g., attempt to) connect to another (e.g., any) set of available relays and provide another report, for example, if the WTRU is (e.g., still) unable to connect to (e.g., all) available relays. The network / gNB may provide the WTRU with a (e.g., new) set of relays or indicate to the WTRU that the WTRU may (e.g., attempt to) connect to (e.g., any) relay (e.g., if the WTRU has not been enabled to make such a connection).

[0148] A WTRU that is unable to connect to (e.g., any) relay and transmits an indication to the network may, for example, wait for a response (e.g., an explicit response) from the network before taking (e.g., any additional) action, or may take the action (e.g., only) after a certain duration (e.g., via a timer). The network may inform the WTRU to refrain from attempting (e.g., not attempting any) additional discovery and / or selection, for example, until instructed (e.g., explicitly) to make such an attempt.

[0149] The network may indicate to the WTRU (e.g., configure to the WTRU) a default or fallback relay, e.g., that may be utilized in the event that the WTRU is unable to connect to (e.g., any) relay. The network may provide the WTRU with a relay that the WTRU may use for this purpose. The gNB may explicitly indicate to the WTRU whether (e.g., when) the WTRU should utilize the relay (e.g., based on a Uu RSRP threshold dropping below a certain value, etc.). The gNB may indicate the duration (e.g., for how long) the WTRU should utilize the relay, e.g., explicitly via an indication, or implicitly in the event that the WTRU exits the fallback behavior upon expiration of the time (e.g., via a timer), or after the WTRU is able to select a candidate on its own.

[0150] A remote WTRU that triggers relay (re)selection (eg, PC5 link quality) may trigger an RRC connection.

[0151] The WTRU may receive configuration information indicating (e.g., configured with) a threshold (e.g., potentially different from the PC5 quality for WTRU reselection) that may trigger a (e.g., RRC) establishment / connection initiation message. For example, if the measured RSRP of the relay drops below the threshold, the remote WTRU in IDLE / INACTIVE may initiate an RRC connection and send a (e.g., RRC) message to the network to indicate such a situation.

[0152] A WTRU that may not be able to find a relay for selection (e.g., due to unsatisfactory PC5 link quality of any available relay or the fact that the WTRU has been configured with a set of allowable relays but cannot select any of these relays due to unsatisfactory link quality) may trigger an RRC connection.

[0153] A WTRU with (e.g., multiple) candidates that meet the reselection criteria may trigger a (e.g., RRC) message from the base station (e.g., gNB), for example, to provide some additional information about which relay the WTRU should select. The gNB may be able to provide this information, for example, based on any additional information it may perceive about the state of the relays (e.g., relay load, number of active connections, etc.).

[0154] The WTRU location (e.g., relative to the relay WTRU candidate) may result in a (e.g., RRC) connection request. For example, if there is a mismatch between the WTRU location and the location of the relay WTRU candidate (e.g., based on the WTRU grid or area ID, etc.), or if the distance between the WTRU and the relay WTRU is above a (e.g., certain) threshold, then a (e.g., RRC) connection request may be triggered.

[0155] For example, if the unicast link establishment between the WTRU and the network-selected relay is unsuccessful, the WTRU may initiate a (e.g., RRC) connection from the gNB / network.

[0156] A WTRU that has refrained from performing (e.g., not performing) a transmission (e.g., any transmission) or has received (e.g., any) reception from a WTRU (e.g., a relay WTRU) may trigger relay reselection (e.g., based on a period of inactivity, e.g., via a timer), which may then cause the WTRU to request (e.g., RRC) a connection.

[0157] The U2U relay WTRU may, for example, send a request for a (e.g., RRC) connection based on the relay status (e.g., if the relay load increases or decreases below a certain threshold; the number of active relay connections that the relay is maintaining exceeds a certain set threshold; the data rate of the relay's service exceeds a certain threshold; the QoS of the data that the relay is relaying; the hop count to the source / destination, etc.).

[0158] Coverage scenarios of the WTRU may result in a relay WTRU requesting (e.g., RRC) connection. A relay WTRU that is in an IDLE / INACTIVE state and senses the cell ID of another WTRU (e.g., via a PC5-RRC message) may request (e.g., RRC) connection, for example, if the cell ID is different from its own cell ID. The remote WTRU may receive configuration information indicating (e.g., configured with) a list of relay WTRUs to which reselection may be enabled (e.g., allowed). For example, if the remote WTRU performs relay reselection to a relay that falls outside of the list, or if the remote WTRU performs relay reselection to a relay WTRU that is connected / camped to a different cell than the remote WTRU, the remote WTRU may trigger (e.g., RRC) connection.

[0159] The WTRU that triggers reselection events may report these events to the network.

[0160] The WTRU performing the reselection may finally select a primary relay and a secondary relay. The secondary relay may be a backup relay, for example, which may remain available at any time in the event of a failure of the primary relay. The WTRU may report the secondary relay to the network. The WTRU may receive configuration information indicating (e.g., configured by the network to), for example, explicitly report the situation (e.g., configuration of multiple RSRP thresholds for the WTRU) or implicitly report the situation (e.g., additional distinguishing factors regarding the primary relay and the secondary relay. Both meet the PC5 link quality requirements, but additional factors such as relay load, supported QoS, hop count / distance to the target, etc. are split across relay candidates).

[0161] A WTRU (e.g., a relay WTRU) may refrain from forwarding (e.g., choose not to forward) a discovery message (e.g., based on required traffic QoS, CBR, CR, relay load, distance to source / destination, hop count, etc.). The relay WTRU may report / indicate this to the network.

[0162] A remote WTRU performing (e.g., PC5) link quality measurements (e.g., SD-RSRP or SL-RSRP) may provide an indication that may indicate (e.g., the fact that different links may have different transmission frequencies, which may, for example, imply different age durations of (e.g., each) PC5 link quality measurement. For example, if the WTRU selects a relay that does not (e.g., not necessarily) have the strongest RSRP measurement (e.g., because the measurement is based on older information than another PC5 relay link), the WTRU may report, for example, whether its selection of the relay was influenced by this information.

[0163] For example, if the measurement results of the WTRU (e.g., the remote WTRU) indicate that no relay link quality is above a (e.g., minimum) link quality threshold, the WTRU may report to the network. If the number of relays that have reached the (e.g., minimum) threshold is below the threshold (e.g., only one relay WTRU is eligible for selection), the WTRU may indicate this to the network and wait for a response (e.g., an explicit indication by the network to continue operation or an implicit indication based on a time expiration), for example, before selecting the relay for reselection.

[0164] The WTRU may report measurements to the network, for example, based on (eg, multiple) hops.

[0165] The WTRU may receive configuration information indicating (eg, configured to) report (eg, certain) measurement results to the network.

[0166] A remote or relay WTRU may receive configuration information indicating (e.g., configured to) report measurements over (e.g., more than one) hops / links (e.g., source to U2U relay and U2U relay to target / destination WTRU hops). The link quality from the relay to the destination may be based on a direct link to the target or a path via (e.g., multiple) U2U relays. Measurements between the relay and the destination / destination WTRU may be received (e.g., via PC5-RRC messages) and may include measurements over (e.g., all additional) U2U relay hops (e.g., if there are multiple U2U relays in the path). In this case, the reported measurements may be based on a combination of measurements over (e.g., all) intermediate hops (e.g., from the relay to the destination WTRU) (e.g., maximum / minimum / average measurements). The source may combine the measurements to the relay and the measurements from the relay to the destination (e.g., in any manner, such as, for example, maximum / minimum / average, etc.), just as the relay WTRU does.

[0167] Receiving link-related measurements from a relay WTRU (eg, relay WTRU to target WTRU side link measurements as described herein) may trigger a measurement report from the source WTRU.

[0168] The relay WTRU may receive configuration information instructing (e.g., configuring the relay WTRU) to report measurement results to the network. The relay WTRU may report the measurement results to the network (e.g., based on the configuration information). The measurement results may be triggered by (e.g., certain) conditions, for example, at any hop.

[0169] The measured link quality (eg, SL-RSRP / SD-RSRP) on either hop (eg, remote WTRU-relay WTRU and / or relay WTRU-target WTRU RSRP is below a configured threshold) may trigger a measurement report to the network.

[0170] For example, if the SL measurement results at the relay WTRU provide the relay WTRU with information about the location of the source and destination WTRUs (e.g., the absolute distance between the source and destination or possibly the relative distance with respect to themselves) or the area ID, and if this information exceeds a certain threshold (e.g., this may indicate the availability of a better path), a measurement report to the network may be triggered. The distance may be inferred from the sidelink measurement messages between the WTRUs (e.g., the timestamps placed at (e.g., each) originating path (such as source-relay path, relay-destination path)).

[0171] The resource pool usage measurement results at the relay (eg, CBR of the resource pool, CR for the relay WTRU) may trigger measurement reports to the network.

[0172] The QoS of various links may trigger the relay WTRU to provide measurement reports to the network. For example, if the relay WTRU observes a degradation in link quality that affects QoS on either or both hops based on a certain metric (e.g., RSRP, CSI / CQI, latency, etc.) falling below a configured threshold, the relay WTRU may be triggered to provide a measurement report. The relay may be able to observe this change, for example, via a change (e.g., an increase) in a buffer associated with a particular LCG.

[0173] The WTRU may perform relay selection, for example, based on (eg, existing) unicast links and / or relay needs.

[0174] The WTRU may use the existence of a (eg, existing) unicast link with the relay and / or between the relay and the destination WTRU as criteria for relay selection (eg, in addition to other criteria such as RSRP, load, etc.).

[0175] For example, when (e.g., when) performing reselection, a source WTRU that may be (e.g., already) connected to a destination / target WTRU may prioritize the relay path. This may be done, for example, by hysteresis or biasing in favor of the path (e.g., relative to another candidate path) unless the relay link quality has dropped below some preconfigured threshold (e.g., which may be different from the reselection threshold).

[0176] The source WTRU may give preference to a relay WTRU (e.g., to reach a particular destination) with which a unicast link is established (e.g., already exists). For example, the source WTRU may apply a measurement offset to give preference to a relay WTRU with an established (e.g., existing) unicast link over a relay WTRU with which a unicast link is not established (not yet exists).

[0177] For example, the source WTRU may also give preference to a relay WTRU that provides U2N relay service in addition to U2U relay service. For example, the source WTRU may perform such preference in the case where the source WTRU (eg, already) has ongoing or planned Uu service.

[0178] Although the above features and elements are described in particular combinations, each feature or element may be used alone without the other features and elements of the preferred embodiments, or in various combinations with or without the other features and elements.

[0179] Although the implementation described herein may consider 3GPP specific protocols, it should be understood that the implementation described herein is not limited to such scenarios and is applicable to other wireless systems. For example, although the solution described herein considers LTE, LTE-A, New Radio (NR) or 5G specific protocols, it should be understood that the solution described herein is not limited to such scenarios and is also applicable to other wireless systems.

[0180] The processes described above may be implemented in a computer program, software, and / or firmware incorporated in a computer-readable medium for execution by a computer and / or processor. Examples of computer-readable media include, but are not limited to, electronic signals (sent via wired and / or wireless connections) and / or computer-readable storage media. Examples of computer-readable storage media include, but are not limited to, read-only memory (ROM), random access memory (RAM), registers, cache memory, semiconductor memory devices, magnetic media (such as, but not limited to, built-in hard disks and removable disks), magneto-optical media, and / or optical media (such as compact disk (CD)-ROM disks and / or digital versatile disks (DVDs)). A processor associated with the software may be used to implement a radio frequency transceiver for a WTRU, terminal, base station, RNC, and / or any host computer.

Claims

1. A wireless transmit / receive unit (WTRU), the wireless transmit / receive unit (WTRU) comprising: A processor, the processor being configured to: receiving configuration information indicating a first threshold, a second threshold, and data transmission gap information; transmitting a first transmission to a first relay; determining a reference signal received power (RSRP) associated with the first relay; determining that the RSRP associated with the first relay is below the first threshold and above the second threshold; Based on determining that the RSRP associated with the first relay is below the first threshold and above the second threshold: Initiate discovery, determining that a data transmission time gap threshold is reached, wherein the data transmission time gap threshold is associated with the data transmission gap information, and Based on determining that the data transmission gap threshold is reached, performing relay reselection to a second relay; and A second transmission is transmitted to the second relay.

2. The WTRU of claim 1 , wherein the processor is further configured to: determining that the RSRP associated with the second relay is below the second threshold; and Based on determining that the RSRP associated with the second relay is below the second threshold: Initiate discovery, performing relay reselection to a third relay, and A third transmission is transmitted to the third relay.

3. The WTRU of claim 1 , wherein determining that the data transmission time gap threshold is reached comprises: determining the data transmission time gap threshold based on the data transmission gap information and the RSRP associated with the first relay; determining a duration associated with a data transmission time gap after initiating discovery; as well as It is determined that the duration is greater than the data transmission time gap threshold.

4. The WTRU of claim 3, wherein a first RSRP is associated with a first data transmission time gap threshold, wherein a second RSRP is associated with a second data transmission time gap threshold, wherein the first RSRP is greater than the second RSRP, and wherein the first data transmission time gap threshold is greater than the second data transmission time gap threshold.

5. The WTRU of claim 3, wherein the duration associated with a data transmission time gap is a duration during which no transmission is scheduled.

6. The WTRU of claim 1 , wherein the first threshold is a first RSRP threshold, wherein the second threshold is a second RSRP threshold, and wherein the first threshold is higher than the second threshold.

7. The WTRU of claim 1, wherein the first relay is a first WTRU-to-WTRU relay, and wherein the second relay is a second WTRU-to-WTRU relay.

8. The WTRU of claim 1, wherein the initiating discovery comprises sending a discovery transmission or receiving a discovery transmission.

9. A method comprising: receiving configuration information indicating a first threshold, a second threshold, and data transmission gap information; transmitting a first transmission to a first relay; determining a reference signal received power (RSRP) associated with the first relay; determining that the RSRP associated with the first relay is below the first threshold and above the second threshold; Based on determining that the RSRP associated with the first relay is below the first threshold and above the second threshold: Initiate discovery, determining that a data transmission time gap threshold is reached, wherein the data transmission time gap threshold is associated with the data transmission gap information, and Based on determining that the data transmission gap threshold is reached, performing relay reselection to a second relay; and A second transmission is transmitted to the second relay.

10. The method according to claim 9, wherein the method further comprises: determining that an RSRP associated with the second relay is below the second threshold; as well as Based on determining that the RSRP associated with the second relay is below the second threshold: Initiate discovery, performing relay reselection to a third relay, and A third transmission is transmitted to the third relay.

11. The method according to claim 9, wherein determining that the data transmission time gap threshold is reached comprises: determining the data transmission time gap threshold based on the data transmission gap information and the RSRP associated with the first relay; determining a duration associated with a data transmission time gap after initiating discovery; as well as It is determined that the duration is greater than the data transmission time gap threshold.

12. The method of claim 11, wherein a first RSRP is associated with a first data transmission time gap threshold, wherein a second RSRP is associated with a second data transmission time gap threshold, wherein the first RSRP is greater than the second RSRP, and wherein the first data transmission time gap threshold is greater than the second data transmission time gap threshold.

13. The method of claim 11, wherein the duration associated with a data transmission time slot is a duration during which no transmission is scheduled.

14. The method of claim 9, wherein the first threshold is a first RSRP threshold, wherein the second threshold is a second RSRP threshold, and wherein the first threshold is higher than the second threshold.

15. The method of claim 9, wherein the first relay is a first WTRU-to-WTRU relay, and wherein the second relay is a second WTRU-to-WTRU relay. The method of claim 9 , wherein the initiating discovery comprises sending a discovery transmission or receiving a discovery transmission.

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