Enhanced radio link failure recovery in UE-to-UE relays

Abstract

Methods, systems, and devices for wireless communication are described. A first user equipment (UE) may establish a first end-to-end (E2E) link between the first UE and a second UE, the E2E link including a second link between the first UE and a third UE configured for relay communication and a third link between the third UE and the second UE. The first UE may determine a link failure on one of the links and perform a recovery procedure including maintaining the first link. The recovery procedure may include reselecting the third UE for relay communication based on maintaining the first link and reestablishing the second link between the first UE and the third UE via one or more connection messages. The recovery procedure may include selecting a fourth UE for relay communication and releasing the second link.

Description

Technical Field

[0001] The following relates to radio link failure (RLF) recovery in wireless communications, including sidelink relaying between user equipments (UEs). Background Art

[0002] Wireless communication systems are widely deployed to provide various types of communication content, such as voice, video, packet data, messaging, broadcast, and the like. These systems may be able to support communication with multiple users by sharing available system resources (e.g., time, frequency, and power). Examples of such multiple access systems include fourth generation (4G) systems (such as long term evolution (LTE) systems, advanced LTE (LTE-A) systems, or LTE-A Pro systems) and fifth generation (5G) systems (which may be referred to as new radio (NR) systems). These systems may employ techniques such as code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), orthogonal FDMA (OFDMA), or discrete Fourier transform spread orthogonal frequency division multiplexing (DFT-S-OFDM). A wireless multiple access communication system may include one or more base stations, each of which supports wireless communications for communication devices, which may be referred to as user equipment (UE). Summary of the invention

[0003] The described technology relates to improved methods, systems, devices, and apparatuses for supporting radio link failure (RLF) recovery in sidelink relay between user equipment (UEs). For example, the described technology provides an updated link recovery process that maintains one or more links of sidelink communication, thereby reducing the overhead associated with the communication failure and reducing the recovery time associated with the communication failure. A first UE may establish a first end-to-end (E2E) link between the first UE and a second UE, the E2E link including a second link between the first UE and a third UE configured for relay communication and a third link between the third UE and the second UE. The first UE may determine a link failure on one of the links and perform a recovery process including maintaining the first link (e.g., maintaining one or more parameters associated with the first link). In some specific implementations, the recovery process may include reselecting a third UE for relay communication based on maintaining the first link and reestablishing a second link between the first UE and the third UE via one or more connection messages (e.g., resetting one or more parameters associated with the second link). In some cases, the recovery process may include selecting a fourth UE for relay communication and releasing the second link. In some examples, the link failure may be associated with the first E2E link, and the first UE may reestablish the first link. Reestablishing the first link may include resetting at least one parameter of the first link.

[0004] A method for wireless communication at a first UE is described. The method may include: establishing a first E2E link between the first UE and a second UE, wherein establishing the first link includes establishing a second link between the first UE and a third UE, the third UE being configured to relay communications between the first UE and the second UE; performing a recovery process based on an indication of a link failure, wherein the recovery process includes maintaining the first link; and communicating with the second UE based on maintaining the first link.

[0005] An apparatus for wireless communication at a first UE is described. The apparatus may include a processor, a memory coupled to the processor, and instructions stored in the memory. The instructions may be executed by the processor to cause the apparatus to: establish a first E2E link between the first UE and the second UE, wherein establishing the first link includes establishing a second link between the first UE and a third UE, the third UE being configured to relay communications between the first UE and the second UE; perform a recovery process based on an indication of a link failure, wherein the recovery process includes maintaining the first link; and communicate with the second UE based on maintaining the first link.

[0006] Another apparatus for wireless communication at a first UE is described. The apparatus may include: a component for establishing a first E2E link between the first UE and a second UE, wherein establishing the first link includes establishing a second link between the first UE and a third UE, the third UE being configured to relay communications between the first UE and the second UE; a component for performing a recovery process based on an indication of a link failure, wherein the recovery process includes maintaining the first link; and a component for communicating with the second UE based on maintaining the first link.

[0007] A non-transitory computer-readable medium storing code for wireless communication at a first UE is described. The code may include instructions that can be executed by a processor to: establish a first E2E link between the first UE and a second UE, wherein establishing the first link includes establishing a second link between the first UE and a third UE, the third UE being configured to relay communications between the first UE and the second UE; perform a recovery process based on an indication of a link failure, wherein the recovery process includes maintaining the first link; and communicate with the second UE based on maintaining the first link.

[0008] In some examples of the methods, apparatus, and non-transitory computer-readable media described herein, performing a recovery process may include operations, features, components, or instructions for reselecting a third UE for relaying communications to the second UE based on maintaining the first link and relay discovery operations.

[0009] Some examples of the methods, apparatus, and non-transitory computer-readable media described herein may also include operations, features, components, or instructions for reestablishing the second link based on reselecting a third UE for relaying communications of the first link, wherein reestablishing the second link includes utilizing at least one parameter associated with the second link before performing a recovery process.

[0010] In some examples of the methods, apparatus, and non-transitory computer-readable media described herein, reestablishing the second link may include operations, features, components, or instructions for the following actions: communicating one or more connection messages with the third UE based on reselecting the third UE, the one or more connection messages comprising a PC5 side link message, a PC5 radio resource control message, a connection setup message, or any combination thereof.

[0011] In some examples of the methods, apparatus, and non-transitory computer-readable media described herein, reestablishing the second link may include operations, features, components, or instructions for sending a message indicating failure recovery to the third UE based on reselecting the third UE.

[0012] In some examples of the methods, apparatus, and non-transitory computer-readable media described herein, reestablishing the second link may include operations, features, components, or instructions for the following actions: resetting one or more media access control parameters to initial values, the at least one parameter including the one or more media access control parameters.

[0013] Some examples of the methods, apparatus, and non-transitory computer-readable media described herein may also include operations, features, components, or instructions for releasing the second link based on the link failure, wherein the link failure may be associated with the second link.

[0014] In some examples of the methods, apparatus, and non-transitory computer-readable media described herein, performing a recovery process may include operations, features, components, or instructions for selecting a fourth UE for relaying communications of the first link based on maintaining the first link.

[0015] Some examples of the methods, apparatus, and non-transitory computer-readable media described herein may also include operations, features, components, or instructions for receiving a message from a third UE indicating that the link failure may be associated with a third link between the second UE and the third UE.

[0016] Some examples of the methods, apparatus, and non-transitory computer-readable media described herein may also include operations, features, components, or instructions for establishing a third link between the first UE and a fourth UE based on selecting a fourth UE for relaying communications of the first link, wherein communicating with the second UE may also be based on establishing the third link.

[0017] In some examples of the methods, apparatus, and non-transitory computer-readable media described herein, establishing a third link may include operations, features, components, or instructions for the following actions: communicating one or more connection messages with a fourth UE based on selecting a fourth UE, the one or more connection messages comprising a PC5 side link message, a PC5 radio resource control message, a link setup message, or any combination thereof.

[0018] A method for wireless communication at a first UE is described. The method may include: establishing a first E2E link between the first UE and a second UE, wherein establishing the first link includes establishing a second link between the first UE and a third UE, the third UE being configured to relay communications between the first UE and the second UE; reestablishing the first link based on an indication of a failure associated with the first link, wherein reestablishing the first link includes resetting at least one parameter associated with flow control on the second link; and communicating with the second UE based on maintaining the first link.

[0019] An apparatus for wireless communication at a first UE is described. The apparatus may include a processor, a memory coupled to the processor, and instructions stored in the memory. The instructions may be executed by the processor to cause the apparatus to: establish a first E2E link between the first UE and the second UE, wherein establishing the first link includes establishing a second link between the first UE and a third UE, the third UE being configured to relay communications between the first UE and the second UE; reestablish the first link based on an indication of a failure associated with the first link, wherein reestablishing the first link includes resetting at least one parameter associated with flow control on the second link; and communicate with the second UE based on maintaining the first link.

[0020] Another apparatus for wireless communication at a first UE is described. The apparatus may include: means for establishing a first E2E link between the first UE and a second UE, wherein establishing the first link includes establishing a second link between the first UE and a third UE, the third UE being configured to relay communications between the first UE and the second UE; means for reestablishing the first link based on an indication of a failure associated with the first link, wherein reestablishing the first link includes resetting at least one parameter associated with flow control on the second link; and means for communicating with the second UE based on maintaining the first link.

[0021] A non-transitory computer-readable medium storing code for wireless communication at a first UE is described. The code may include instructions that can be executed by a processor to: establish a first E2E link between the first UE and a second UE, wherein establishing the first link includes establishing a second link between the first UE and a third UE, the third UE being configured to relay communications between the first UE and the second UE; reestablishing the first link based on an indication of a failure associated with the first link, wherein reestablishing the first link includes resetting at least one parameter associated with flow control on the second link; and communicating with the second UE based on maintaining the first link.

[0022] In some examples of the methods, apparatus, and non-transitory computer-readable media described herein, reestablishing the first link may include operations, features, components, or instructions for the following actions: sending a first message to reestablish the second link based on selecting a third UE for relaying communications between the first UE and the second UE, and sending a second message to the second UE via the first link.

[0023] In some examples of the methods, apparatus, and non-transitory computer-readable media described herein, the first message includes an indication to reset at least one parameter associated with flow control on the second link.

[0024] In some examples of the methods, apparatus, and non-transitory computer-readable media described herein, the second message includes an indication to re-establish the protocol layer.

[0025] In some examples of the methods, apparatus, and non-transitory computer-readable media described herein, the second message may be an E2E PC5 radio resource control message, and the protocol layer may be a packet data convergence protocol (PDCP) entity.

[0026] Some examples of the methods, apparatus, and non-transitory computer-readable media described herein may also include operations, features, components, or instructions for resetting at least one parameter associated with flow control on the second link including resetting one or more medium access control parameters to initial values. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 and Figure 2 An example of a wireless communication system supporting radio link failure (RLF) recovery in sidelink relay between user equipments (UEs) according to one or more aspects of the present disclosure is illustrated.

[0028] Figures 3 to 5 An example of a process flow for supporting RLF recovery in a sidelink relay between UEs according to one or more aspects of the present disclosure is illustrated.

[0029] Figure 6 and Figure 7 A block diagram of an apparatus supporting RLF recovery in a sidelink relay between UEs according to one or more aspects of the present disclosure is shown.

[0030] Figure 8 A block diagram of a communication manager supporting RLF recovery in a sidelink relay between UEs is shown in accordance with one or more aspects of the present disclosure.

[0031] Fig. 9 A diagram of a system including a device supporting RLF recovery in sidelink relay between UEs according to one or more aspects of the present disclosure is shown.

[0032] Figures 10 to 13 A flow chart illustrating a method of supporting RLF recovery in a sidelink relay between UEs according to one or more aspects of the present disclosure is shown. DETAILED DESCRIPTION

[0033] Some wireless communication systems may support sidelink communications. The sidelink communications may include a first user equipment (UE) (e.g., a source UE), a second UE (e.g., a destination UE), and a third UE (e.g., a relay UE), which is configured to relay communications between the first UE and the second UE. The communication link between the first UE and the second UE may be an end-to-end (E2E) link, which includes a first hop (e.g., a second link) between the first UE and the third UE and a second hop (e.g., a third link) between the third UE and the second UE. Some sidelink communications may include a recovery process for communication failures on one or more of these links. For example, one type of communication failure may be a radio link failure (RLF) on a first link, a second link, or a third link. However, the recovery process may include releasing all links associated with the sidelink communications regardless of where the RLF is detected, thereby generating overhead when reestablishing each link and increasing the RLF recovery time.

[0034] The technology described herein provides an updated link recovery process that maintains one or more links of side link communication, thereby reducing the overhead associated with communication failures and reducing the recovery time associated with communication failures. For example, a first UE may establish a first E2E link between the first UE and the second UE, the E2E link including a second link between the first UE and a third UE configured for relay communication and a third link between the third UE and the second UE. The first UE may determine a link failure on one of the links and perform a recovery process including maintaining the first link (e.g., maintaining one or more parameters associated with the first link). In some specific implementations, the recovery process may include reselecting a third UE for relay communication based on maintaining the first link and reestablishing a second link between the first UE and the third UE via one or more connection messages (e.g., resetting one or more parameters associated with the second link). In some cases, the recovery process may include selecting a fourth UE for relay communication and releasing the second link. In some examples, the link failure may be associated with the first E2E link, and the first UE may reestablish the first link. Reestablishing the first link may include resetting at least one parameter of the first link.

[0035] Various aspects of the disclosure are first described in the context of a wireless communication system. Various aspects of the disclosure are then described in the context of a process flow. Various aspects of the disclosure are further illustrated by and described with reference to apparatus diagrams, system diagrams, and flow diagrams relating to RLF recovery in a sidelink relay between UEs.

[0036] Figure 1 An example of a wireless communication system 100 that supports RLF recovery in sidelink relay between UEs according to one or more aspects of the present disclosure is illustrated. The wireless communication system 100 may include one or more network entities 105, one or more UEs 115, and a core network 130. In some examples, the wireless communication system 100 may be a long term evolution (LTE) network, an advanced LTE (LTE-A) network, an LTE-A Pro network, a new radio (NR) network, or a network operating according to other systems and radio technologies, including future systems and radio technologies not explicitly mentioned herein.

[0037] The network entities 105 may be dispersed throughout a geographic area to form the wireless communication system 100, and may include devices in different forms or with different capabilities. In various examples, the network entities 105 may be referred to as network elements, mobility elements, radio access network (RAN) nodes, or network equipment, among other nomenclature. In some examples, the network entities 105 and the UE 115 may communicate wirelessly via one or more communication links 125 (e.g., radio frequency (RF) access links). For example, the network entity 105 may support a coverage area 110 (e.g., a geographic coverage area) within which the UE 115 and the network entity 105 may establish one or more communication links 125. The coverage area 110 may be an example of a geographic area within which the network entity 105 and the UE 115 may support signal communications according to one or more radio access technologies (RATs).

[0038] The UEs 115 may be dispersed throughout the coverage area 110 of the wireless communication system 100, and each UE 115 may be stationary or mobile or both stationary and mobile at different times. The UEs 115 may be devices in different forms or with different capabilities. Figure 1 Some example UEs 115 are illustrated in FIG. 1. The UEs 115 described herein may be capable of supporting communications with various types of devices, such as Figure 1 Other UEs 115 or network entities 105 are shown.

[0039] As described herein, a node of the wireless communication system 100 (which may be referred to as a network node or a wireless node) may be a network entity 105 (e.g., any network entity described herein), a UE 115 (e.g., any UE described herein), a network controller, an apparatus, a device, a computing system, one or more components, or another suitable processing entity configured to perform any of the techniques described herein. For example, the node may be a UE 115. As another example, the node may be a network entity 105. As another example, a first node may be configured to communicate with a second node or a third node. In one aspect of this example, the first node may be a UE 115, the second node may be a network entity 105, and the third node may be a UE 115. In another aspect of this example, the first node may be a UE 115, the second node may be a network entity 105, and the third node may be a network entity 105. In other aspects of this example, the first node, the second node, and the third node may be different relative to these examples. Similarly, references to UE 115, network entity 105, apparatus, device, computing system, etc. may include disclosure of UE 115, network entity 105, apparatus, device, computing system, etc. as nodes. For example, a disclosure that UE 115 is configured to receive information from network entity 105 also discloses that the first node is configured to receive information from a second node.

[0040] In some examples, the network entities 105 may communicate with the core network 130 or with each other or both. For example, the network entities 105 may communicate with the core network 130 via one or more backhaul communication links 120 (e.g., according to S1, N2, N3, or other interface protocols). In some examples, the network entities 105 may communicate with each other via the backhaul communication links 120 (e.g., according to X2, Xn, or other interface protocols) directly (e.g., directly between the network entities 105) or indirectly (e.g., via the core network 130). In some examples, the network entities 105 may communicate with each other via the midhaul communication links 162 (e.g., according to the midhaul interface protocol) or the fronthaul communication links 168 (e.g., according to the fronthaul interface protocol) or any combination thereof. The backhaul communication links 120, the midhaul communication links 162, or the fronthaul communication links 168 may be or include one or more wired links (e.g., electrical links, optical fiber links), one or more wireless links (e.g., radio links, wireless optical links), etc. or various combinations thereof. UE 115 may communicate with core network 130 via communication link 155 .

[0041] One or more of the network entities 105 described herein may include or may be referred to as a base station 140 (e.g., a transceiver base station, a radio base station, a NR base station, an access point, a radio transceiver, a Node B, an evolved Node B (eNB), a next generation Node B, or a Gigabit Node B (any of which may be referred to as a gNB), a 5G NB, a next generation eNB (ng-eNB), a Home Node B, a Home Evolved Node B, or other suitable terminology). In some examples, the network entity 105 (e.g., a base station 140) may be implemented in a clustered (e.g., monolithic, stand-alone) base station architecture, which may be configured to utilize a protocol stack that is physically or logically integrated within a single network entity 105 (e.g., a single RAN node, such as a base station 140).

[0042] In some examples, the network entity 105 may be implemented in a disaggregated architecture (e.g., a disaggregated base station architecture, a disaggregated RAN architecture) that may be configured to utilize a protocol stack that is physically or logically distributed between two or more network entities 105, such as an integrated access backhaul (IAB) network, an open RAN (O-RAN) (e.g., a network configuration sponsored by the O-RAN Alliance), or a virtualized RAN (vRAN) (e.g., a cloud RAN (C-RAN)). For example, the network entity 105 may include one or more of the following: a central unit (CU) 160, a distributed unit (DU) 165, a radio unit (RU) 170, a RAN intelligent controller (RIC) 175 (e.g., a near real-time RIC (near RT RIC), a non-real-time RIC (non-RT RIC)), a service management and orchestration (SMO) 180 system, or any combination thereof. The RU 170 may also be referred to as a radio head, a smart radio head, a remote radio head (RRH), a remote radio unit (RRU), or a transmit receive point (TRP). One or more components of the network entity 105 in the decomposed RAN architecture may be co-located, or one or more components of the network entity 105 may be located in distributed locations (e.g., separate physical locations). In some examples, one or more network entities 105 of the decomposed RAN architecture may be implemented as virtual units (e.g., virtual CU (VCU), virtual DU (VDU), virtual RU (VRU)).

[0043] The functional split between CU 160, DU 165, and RU 170 is flexible and can support different functions, depending on which functions (e.g., network layer functions, protocol layer functions, baseband functions, RF functions, and any combination thereof) are performed at CU 160, DU 165, or RU 170. For example, a functional split of a protocol stack can be employed between CU 160 and DU 165, such that CU 160 can support one or more layers of a protocol stack and DU 165 can support one or more different layers of a protocol stack. In some examples, CU 160 can host higher protocol layer (e.g., Layer 3 (L3), Layer 2 (L2)) functions and signaling (e.g., Radio Resource Control (RRC), Service Data Adaptation Protocol (SDAP), Packet Data Convergence Protocol (PDCP)). The CU 160 may be connected to one or more DUs 165 or RUs 170, and the one or more DUs 165 or RUs 170 may host lower protocol layers, such as layer 1 (L1) (e.g., physical (PHY) layer) or L2 (e.g., radio link control (RLC) layer, medium access control (MAC) layer) functions and signaling, and may each be at least partially controlled by the CU 160. Additionally or alternatively, a functional split of the protocol stack may be employed between the DU 165 and the RU 170, such that the DU 165 may support one or more layers of the protocol stack, and the RU 170 may support one or more different layers of the protocol stack. The DU 165 may support one or more different cells (e.g., via one or more RUs 170). In some cases, the functional split between CU 160 and DU 165 or between DU 165 and RU 170 may be within a protocol layer (e.g., some functions of a protocol layer may be performed by one of CU 160, DU 165, or RU 170, while other functions of the protocol layer are performed by a different one of CU 160, DU 165, or RU 170). CU 160 may be further functionally split into CU control plane (CU-CP) and CU user plane (CU-UP) functions. CU 160 may be connected to one or more DUs 165 via midhaul communication links 162 (e.g., F1, F1-c, F1-u), and DU 165 may be connected to one or more RUs 170 via fronthaul communication links 168 (e.g., an open fronthaul (FH) interface). In some examples, midhaul communication link 162 or fronthaul communication link 168 may be implemented according to an interface (eg, a channel) between layers of a protocol stack supported by respective network entities 105 that communicate via such communication links.

[0044] In some wireless communication systems (e.g., wireless communication system 100), infrastructure and spectrum resources for radio access may support wireless backhaul link capabilities to supplement wired backhaul connections, thereby providing an IAB network architecture (e.g., to core network 130). In some cases, in an IAB network, one or more network entities 105 (e.g., IAB nodes 104) may be partially controlled by each other. One or more IAB nodes 104 may be referred to as donor entities or IAB donors. One or more DUs 165 or one or more RUs 170 may be controlled in part by one or more CUs 160 associated with a donor network entity 105 (e.g., donor base station 140). One or more donor network entities 105 (e.g., IAB donors) may communicate with one or more additional network entities 105 (e.g., IAB nodes 104) via supported access and backhaul links (e.g., backhaul communication links 120). The IAB node 104 may include an IAB mobile terminal (IAB-MT) controlled (e.g., scheduled) by a coupled IAB donor's DU 165. The IAB-MT may include an independent set of antennas for relaying communications with the UE 115, or may share the same antennas (e.g., of the RU 170) of the IAB node 104 for access via the DU 165 of the IAB node 104 (e.g., referred to as a virtual IAB-MT (vIAB-MT)). In some examples, the IAB node 104 may include a DU 165 that supports communication links with additional entities (e.g., IAB node 104, UE 115) within a relay chain or configuration (e.g., downstream) of the access network. In such cases, one or more components of the decomposed RAN architecture (e.g., one or more IAB nodes 104 or components of the IAB node 104) may be configured to operate according to the techniques described herein.

[0045] In the case where the techniques described herein are applied to the context of a decomposed RAN architecture, one or more components of the decomposed RAN architecture may be configured to support RLF recovery in a sidelink relay between UEs as described herein. For example, some operations described as being performed by a UE 115 or a network entity 105 (e.g., a base station 140) may additionally or alternatively be performed by one or more components of the decomposed RAN architecture (e.g., an IAB node 104, a DU 165, a CU 160, a RU 170, a RIC 175, a SMO 180).

[0046] UE 115 may include or may be referred to as a mobile device, a wireless device, a remote device, a handheld device, or a subscriber device, or some other suitable term, where a "device" may also be referred to as a unit, a station, a terminal, or a client, etc. UE 115 may also include or may be referred to as a personal electronic device, such as a cellular phone, a personal digital assistant (PDA), a tablet computer, a laptop computer, or a personal computer. In some examples, UE 115 may include or may be referred to as a wireless local loop (WLL) station, an Internet of Things (IoT) device, an Internet of Everything (IoE) device, or a machine type communication (MTC) device, etc., which may be implemented in various objects such as appliances or vehicles, meters, etc.

[0047] The UE 115 described herein may be capable of communicating with various types of devices such as other UEs 115 which may sometimes act as relays, as well as network entities 105 and network equipment including macro eNBs or gNBs, small cell eNBs or gNBs, or relay base stations, etc. Figure 1 shown.

[0048] The UE 115 and the network entity 105 may wirelessly communicate with each other via one or more communication links 125 (e.g., access links) using resources associated with one or more carriers. The term "carrier" may refer to a collection of RF spectrum resources having a physical layer structure defined for supporting the communication link 125. For example, a carrier for the communication link 125 may include a portion of an RF spectrum band (e.g., a bandwidth portion (BWP)) that operates according to one or more physical layer channels for a given radio access technology (e.g., LTE, LTE-A, LTE-A Pro, NR). Each physical layer channel may carry acquisition signaling (e.g., synchronization signals, system information), control signaling for coordinating carrier operations, user data, or other signaling. The wireless communication system 100 may support communications with the UE 115 using carrier aggregation or multi-carrier operation. Depending on the carrier aggregation configuration, the UE 115 may be configured with multiple downlink component carriers and one or more uplink component carriers. Carrier aggregation may be used for both frequency division duplex (FDD) and time division duplex (TDD) component carriers. Communication between the network entity 105 and other devices may refer to communication between these devices and any portion (e.g., entity, sub-entity) of the network entity 105. For example, the terms "send," "receive," or "communicate" when referring to the network entity 105 may refer to any portion of a network entity 105 (e.g., base station 140, CU 160, DU 165, RU 170) of a RAN communicating with another device (e.g., directly or via one or more other network entities 105).

[0049] The signal waveform transmitted via the carrier may include multiple subcarriers (e.g., using multi-carrier modulation (MCM) techniques, such as orthogonal frequency division multiplexing (OFDM) or discrete Fourier transform spread OFDM (DFT-S-OFDM)). In a system using MCM technology, a resource element may refer to a symbol period (e.g., the duration of a modulation symbol) and a resource of a subcarrier, in which case the symbol period and the subcarrier spacing may be inversely related. The number of bits carried by each resource element may depend on the modulation scheme (e.g., the order of the modulation scheme, the coding rate of the modulation scheme, or both), so that a relatively high number of resource elements (e.g., in the transmission duration) and a relatively high order modulation scheme may correspond to a relatively high rate of communication. Wireless communication resources may refer to a combination of RF spectrum resources, time resources, and spatial resources (e.g., spatial layers or beams), and the use of multiple spatial resources may increase the data rate or data integrity used for communication with UE 115.

[0050] The time interval for the network entity 105 or the UE 115 may be expressed as a multiple of a basic time unit, which may be, for example, a sampling period. Seconds, for this It can represent the supported subcarrier spacing, and N f The supported discrete Fourier transform (DFT) size may be indicated. The time intervals of the communication resources may be organized according to radio frames, each having a specified duration (e.g., 10 milliseconds (ms)). Each radio frame may be identified by a system frame number (SFN) (e.g., ranging from 0 to 1023).

[0051] Each frame may include a plurality of consecutively numbered subframes or time slots, and each subframe or time slot may have the same duration. In some examples, a frame may be divided into subframes (e.g., in the time domain), and each subframe may be further divided into a certain number of time slots. Alternatively, each frame may include a variable number of time slots, and the number of time slots may depend on the subcarrier spacing. Each time slot may include a certain number of symbol periods (e.g., depending on the length of the cyclic prefix appended in front of each symbol period). In some wireless communication systems 100, a time slot may be further divided into a plurality of mini-time slots associated with one or more symbols. Excluding the cyclic prefix, each symbol period may be associated with one or more (e.g., N f The duration of a symbol period may depend on the subcarrier spacing or the operating frequency band.

[0052] A subframe, a slot, a mini-slot, or a symbol may be the smallest scheduling unit (e.g., in the time domain) of the wireless communication system 100 and may be referred to as a transmission time interval (TTI). In some examples, the TTI duration (e.g., the number of symbol periods in a TTI) may be variable. Additionally or alternatively, the smallest scheduling unit of the wireless communication system 100 may be dynamically selected (e.g., in a burst of a shortened TTI (sTTI)).

[0053] According to various techniques, physical channels may be multiplexed using carriers for communication. Physical control channels and physical data channels may be multiplexed for signaling via downlink carriers, for example, using one or more of a time division multiplexing (TDM) technique, a frequency division multiplexing (FDM) technique, or a hybrid TDM-FDM technique. A control region (e.g., a control resource set (CORESET)) of a physical control channel may be defined by a set of symbol periods and may extend across a system bandwidth of a carrier or a subset of that system bandwidth. One or more control regions (e.g., CORESETs) may be configured for a set of UEs 115. For example, one or more UEs in UE 115 may monitor or search a control region for control information according to one or more search space sets, and each search space set may include one or more control channel candidates in one or more aggregation levels arranged in a cascaded manner. The aggregation level of a control channel candidate may refer to the amount of control channel resources (e.g., control channel elements (CCEs)) associated with coded information for a control information format having a given payload size. The search space sets may include a common search space set configured for transmitting control information to multiple UEs 115 , and a UE-specific search space set for transmitting control information to a specific UE 115 .

[0054] In some examples, the network entities 105 (e.g., base stations 140, RUs 170) may be mobile and thus provide communication coverage for mobile coverage areas 110. In some examples, different coverage areas 110 associated with different technologies may overlap, but the different coverage areas 110 may be supported by the same network entity 105. In some other examples, overlapping coverage areas 110 associated with different technologies may be supported by different network entities 105. The wireless communication system 100 may include, for example, a heterogeneous network in which different types of network entities 105 provide coverage for various coverage areas 110 using the same or different radio access technologies.

[0055] The wireless communication system 100 may be configured to support ultra-reliable communication or low-latency communication or various combinations thereof. For example, the wireless communication system 100 may be configured to support ultra-reliable low-latency communication (URLLC). The UE 115 may be designed to support ultra-reliable or low-latency or critical functions. Ultra-reliable communications may include private communications or group communications and may be supported by one or more services such as push-to-talk, video, or data. Support for ultra-reliable, low-latency functions may include prioritization of services, and such services may be used for public safety or general commercial applications. The terms ultra-reliable, low-latency, and ultra-reliable low-latency may be used interchangeably herein.

[0056] In some examples, the UE 115 may be configured to support communication directly with other UEs 115 via a device-to-device (D2D) communication link 135 (e.g., according to a peer-to-peer (P2P), D2D, or sidelink protocol). In some examples, one or more UEs 115 in a group that are performing D2D communication may be within a coverage area 110 of a network entity 105 (e.g., a base station 140, a RU 170), which may support aspects of such D2D communication configured (e.g., scheduled) by the network entity 105. In some examples, one or more UEs 115 in such a group may be outside the coverage area 110 of the network entity 105, or may otherwise be unable or not configured to receive transmissions from the network entity 105. In some examples, a group of UEs 115 communicating via D2D communication may support a one-to-many (1:M) system, in which each UE 115 transmits to each of the other UEs 115 in the group. In some examples, the network entity 105 may facilitate scheduling of resources for D2D communication. In some other examples, D2D communications may be performed between UEs 115 without involving network entity 105 .

[0057] In some systems, the D2D communication link 135 can be an example of a communication channel (such as a sidelink communication channel) between vehicles (e.g., UE 115). In some examples, the vehicles can communicate using vehicle-to-everything (V2X) communication, vehicle-to-vehicle (V2V) communication, or some combination of these items. The vehicles can signal information related to traffic conditions, signal scheduling, weather, safety, emergency situations, or any other information related to the V2X system. In some examples, vehicles in the V2X system can communicate with roadside infrastructure (such as roadside units), or communicate with the network via one or more network nodes (e.g., network entity 105, base station 140, RU 170) using vehicle-to-network (V2N) communication, or both.

[0058] The core network 130 may provide user authentication, access authorization, tracking, Internet Protocol (IP) connectivity, and other access, routing, or mobility functions. The core network 130 may be an evolved packet core (EPC) or a 5G core (5GC), which may include at least one control plane entity (e.g., a mobility management entity (MME), an access and mobility management function (AMF)) for managing access and mobility and at least one user plane entity (e.g., a serving gateway (S-GW), a packet data network (PDN) gateway (P-GW), or a user plane function (UPF)) for routing packets or interconnecting to an external network. The control plane entity may manage non-access stratum (NAS) functions such as mobility, authentication, and bearer management of UEs 115 served by network entities 105 (e.g., base stations 140) associated with the core network 130. User IP packets may be delivered through the user plane entity, which may provide IP address allocation and other functions. The user plane entity may be connected to the IP services 150 of one or more network operators. IP services 150 may include access to the Internet, an intranet, an IP Multimedia Subsystem (IMS), or packet-switched streaming services.

[0059] The wireless communication system 100 may operate using one or more frequency bands that may be in the range of 300 megahertz (MHz) to 300 gigahertz (GHz). Generally speaking, the region from 300 MHz to 3 GHz is referred to as the ultra-high frequency (UHF) region or decimeter band because the wavelength ranges from about one decimeter to one meter in length. UHF waves may be blocked or redirected by buildings and environmental features (which may be referred to as clusters), but these waves may be sufficient to penetrate structures so that macro cells provide services to UEs 115 located indoors. Communications using UHF waves may be associated with smaller antennas and shorter ranges (e.g., less than 100 kilometers) compared to communications using smaller frequencies and longer waves in the high frequency (HF) or very high frequency (VHF) portions of the spectrum below 300 MHz.

[0060] The wireless communication system 100 can utilize licensed and unlicensed RF spectrum bands. For example, the wireless communication system 100 can use unlicensed bands (such as the 5 GHz Industrial, Scientific, and Medical (ISM) band) to employ License Assisted Access (LAA), LTE Unlicensed (LTE-U) radio access technology, or NR technology. When operating using unlicensed RF spectrum bands, devices such as network entity 105 and UE 115 can employ carrier sensing for conflict detection and avoidance. In some examples, operations using unlicensed bands can be based on carrier aggregation configuration (e.g., LAA) in combination with component carriers operating using licensed bands. Operations using unlicensed spectrum can include downlink transmissions, uplink transmissions, P2P transmissions, or D2D transmissions, among others.

[0061] The network entity 105 (e.g., base station 140, RU 170) or UE 115 may be equipped with multiple antennas that can be used to employ technologies such as transmit diversity, receive diversity, multiple-input multiple-output (MIMO) communication, or beamforming. The antennas of the network entity 105 or UE 115 may be located in one or more antenna arrays or antenna panels, which may support MIMO operations or transmit or receive beamforming. For example, one or more base station antennas or antenna arrays may be co-located at an antenna assembly, such as an antenna tower. In some examples, antennas or antenna arrays associated with the network entity 105 may be located at different geographical locations. The network entity 105 may include an antenna array having a set of antenna ports of multiple rows and columns that the network entity 105 can use to support beamforming for communications with the UE 115. Similarly, the UE 115 may include one or more antenna arrays that may support various MIMO or beamforming operations. Additionally or alternatively, the antenna panel may support RF beamforming for signals sent via the antenna ports.

[0062] Beamforming (which may also be referred to as spatial filtering, directional transmission, or directional reception) is a signal processing technique that may be used at a transmitting device or a receiving device (e.g., a network entity 105, a UE 115) to shape or steer an antenna beam (e.g., a transmit beam, a receive beam) along a spatial path between the transmitting device and the receiving device. Beamforming may be achieved by combining signals communicated via antenna elements of an antenna array so that some signals propagating along a particular direction relative to the antenna array experience constructive interference, while other signals experience destructive interference. Adjustments to signals communicated via antenna elements may include the transmitting device or the receiving device applying an amplitude offset, a phase offset, or both to signals carried via antenna elements associated with the device. Adjustments associated with each of these antenna elements may be defined by a set of beamforming weights associated with a particular direction (e.g., relative to the antenna array of the transmitting device or the receiving device or relative to some other direction).

[0063] The wireless communication system 100 may be a packet-based network that operates according to a layered protocol stack. In the user plane, communications at the bearer or PDCP layer may be IP-based. The RLC layer may perform packet segmentation and reassembly to communicate via logical channels. The MAC layer may perform priority processing and multiplexing of logical channels into transport channels. The MAC layer may also implement error detection techniques, error correction techniques, or both to support retransmission to improve link efficiency. In the control plane, the RRC layer may provide the establishment, configuration, and maintenance of an RRC connection that supports a radio bearer for user plane data between the UE 115 and the network entity 105 or the core network 130. The PHY layer may map a transport channel to a physical channel.

[0064] In some cases, as part of a UE-to-UE (U2U) relay operation, the first UE 115 may communicate with the second UE 115 via a third UE 115 (e.g., relay UE 115). The third UE 115 may relay traffic between the first UE 115 and the second UE 115. In some cases, the first UE 115 may be the originator of the relayed traffic (e.g., source UE 115), and the second UE 115 may be the destination of the relayed traffic (e.g., destination UE 115), but the traffic may also flow from the second UE 115 to the first UE 115 via the third UE 115. To facilitate the relay communication, the first UE 115 may establish a first hop (e.g., second link, communication link 135) with the third UE 115, and the third UE 115 may establish a second hop (e.g., third link) with the second UE 115 so that the second UE 115 communicates with the third UE 115. In some examples, the second link and the third link may be examples of single-hop relay, where a single relay UE 115 relays communications between a source UE 115 and a destination UE 115. In some other examples, the second link and the third link may represent multiple links as part of a multi-hop relay, where multiple relay UEs 115 are connected to each other to support relaying communications between a second UE 115 and a third UE 115 (e.g., a source UE 115 is linked to a first relay UE 115, which is linked to one or more second relay UEs 115). A link between two remote UEs (e.g., a first UE and a second UE) may constitute an E2E link.

[0065] In some examples, the first UE 115 may perform a relay connection process (e.g., setup). For example, the first UE 115 may determine to perform a relay process associated with an L3 relay or an L2 relay. The first UE 115 may perform a relay discovery operation to discover a potential (e.g., candidate) relay UE. The first UE 115 may select a third UE 115 and perform a route discovery operation. The first UE 115 may then communicate a setup message (e.g., a unicast link setup message) with the third UE 115 to set up a second link, and the third UE 115 may communicate a setup message with the second UE 115 to set up a third link. In some cases, for an L3 relay, the first UE 115 may communicate a message indicating a quality of service (QoS) associated with the L3 relay with the third UE 115 to set up the second link, and the third UE 115 may communicate a message indicating the QoS with the second UE 115. In some cases, for L2 relay, the first UE 115 and the second UE 115 may communicate messages associated with E2E link setup (e.g., E2E unicast link setup) and messages indicating QoS of the E2E link (e.g., E2E unicast link management for PC5 RLC channels) via the third UE 115. Discovery and relay security key material may be provided to the first UE 115, the second UE 115, and the third UE 115. The UE 115 may perform sidelink communications (e.g., relay communications).

[0066] In some cases, the sidelink communication may include user and / or control data as part of a packet-based network operating according to a layered protocol stack. For example, the control plane and the user plane may include multiple layers as part of a protocol stack. In the user plane (e.g., L2 user plane), the protocol stack may include at least an Internet Protocol (IP) or other non-IP application or service layer, an SDAP layer, a PDCP layer, a sidelink relay adaptation protocol (SRAP) layer, an RLC layer, a MAC layer, and a PHY layer. In some cases, the IP / non-IP, SDAP, and PDCP layers may be associated with an E2E link, and the SRAP, RLC, MAC, and PHY layers may be associated with a relay link. In the control plane (e.g., L2 control plane), the protocol stack may include at least a PC5-S layer, a PDCP layer, a SRAP layer, an RLC layer, a MAC layer, and a PHY layer. In some cases, the PC5-S and PDCP layers may be associated with an E2E link, and the SRAP, RLC, MAC, and PHY layers may be associated with a relay link.

[0067] In some cases, the UE 115 may determine (e.g., detect, receive an indication of) a failure associated with a link of the sidelink communication (e.g., a sidelink RLF). The failure may be associated with the first link, the second link, the third link, or any combination thereof. In some specific implementations, the UE 115 may determine the failure based on satisfying one or more conditions (e.g., existing conditions). For example, the UE 115 may determine an indication (e.g., via an RLC entity) that a retransmission threshold (e.g., a maximum number of retransmissions) associated with a physical location (e.g., a destination) has been met. The UE may determine an indication (e.g., via a MAC entity) that a feedback threshold (e.g., a maximum number of consecutive hybrid automatic repeat requests (HARQ) discontinuous transmissions (DTX)) has been met. In some cases, these conditions may be used for E2E RLF detection. In some examples, the UE 115 may fail to receive a response message (e.g., an RRCReconfigurationSidelink message) for sidelink transmission. UE 115 may perform an integrity check (e.g., an RRC integrity check to verify security, integrity, etc. of data) and determine an integrity failure indication (e.g., from a sidelink PDCP entity) associated with a radio bearer (e.g., sidelink signaling radio bearer (SRB) 2 (SL-SRB2), sidelink SRB3 (SL-SRB3), or both). In some cases, these conditions may be used for relay link (e.g., per-hop) RLF detection.

[0068] Some wireless communication systems 100 may support a recovery process for a communication failure of one or more links of a sidelink relay operation. However, the recovery process may include releasing all links associated with the sidelink communication regardless of where the communication failure is detected, thereby generating overhead and increasing the failure recovery time when reestablishing each link.

[0069] The technology described herein provides an updated link recovery process that maintains one or more links of side link communication, thereby reducing the overhead associated with communication failures and reducing the recovery time associated with communication failures. For example, a first UE may establish a first E2E link between a first UE and a second UE, the E2E link including a second link between the first UE and a third UE configured for relay communication and a third link between the third UE and the second UE. The first UE may determine a link failure on one of these links and perform a recovery process including maintaining the first link (e.g., maintaining one or more parameters associated with the first link). In some specific implementations, the recovery process may include reselecting a third UE for relay communication based on maintaining the first link and reestablishing a second link between the first UE and the third UE via one or more connection messages. In some cases, reestablishing the second link may include restoring the second link for conveying business without releasing the second link (e.g., maintaining the second link), so that before reestablishment, at least some of the same communication parameters (e.g., context, security key, bearer, etc.) may be used for further communication. In some examples, the first UE may reset the communication parameters to a certain value before reselecting the third UE. In some cases, the recovery process may include selecting a fourth UE for relaying communications and releasing the second link. In some examples, the link failure may be associated with the first E2E link, and the first UE may reestablish the first link. Reestablishing the first link may include resetting at least one parameter of the first link.

[0070] Figure 2 An example of a wireless communication system 200 that supports RLF recovery in a sidelink relay between UEs according to one or more aspects of the present disclosure is illustrated. In some examples, the wireless communication system 200 may implement aspects of the wireless communication system 100. For example, the wireless communication system 200 may include UE 115-a, UE 115-b, UE 115-c, and optionally UE 115-d, which may be as described herein. Figure 1Examples of UE 115 described herein. In some cases, UE 115-a may represent an example of a source UE 115, UE 115-b and 115-d may represent examples of a relay UE 115, and UE 115-c may represent an example of a destination UE 115, wherein the source UE 115 and the destination UE 115 perform sidelink communication with the relay UE 115. The source UE 115 may be defined as an initiator of the relay service, and the destination UE 115 may be defined as a destination of the relay service. However, it should be understood that the destination UE 115 may also transmit the service to the source UE 115 via the relay UE 115. UE 115-a, UE 115-b, UE 115-c, and UE 115-d, or any combination thereof, may perform wireless communication.

[0071] The wireless communication system 200 may include a protocol stack. For example, the protocol stack may include a PDCP layer, a SRAP layer, an RLC layer, and a MAC layer. In some cases, the protocol stack may be an L2 relay protocol stack (e.g., relaying occurs at the L2 layer), where the first E2E link 215 may be at the PDCP layer, and the second link 220-a (e.g., the first relay link) and the third link 220-b (e.g., the second relay link) may be at the SRAP layer, the RLC layer, and the MAC layer. In some cases, the UE 115 may process (e.g., utilize, store, retain) parameters associated with each layer (e.g., identification, header, trailer, buffer, counter, other control data) for communications sent as part of the sidelink communication. In some examples, UE 115-b may process parameters associated with second link 220-a and third link 220-b (e.g., per-hop link parameters), UE 115-a may process parameters associated with first link 215 and second link 220-a, and UE 115-c may process parameters associated with first link 220-a and third link 220-b. In some cases, first link 215, second link 220-a, and third link 220-b may include a PC5-S connection, a PC5-RRC connection, or both.

[0072] Some wireless communication systems 200 may support a recovery process for communication failures. The communication failure may be detected by UE 115-a, UE 115-b, UE 115-c, or any combination thereof, and may be associated with the second link 220-a, the third link 220-b, or the first link 215. For example, if the failure is associated with the first link 215, the second link 220-a, or the third link 220-b, the UE 115-a may release the link associated with the failure and other links (e.g., the first link 215, the second link 220-a, and the third link 220-b), regardless of where the failure is detected. Releasing a link may include invalidating (e.g., deleting) a context used to communicate via the link, including invalidating parameters associated with the link. Therefore, in order to continue the sidelink communication with UE 115-c, UE 115-a may discover and select a relay UE (e.g., UE 115-b, UE 115-d), and establish a new link with the same or new relay UE and UE 115-c. However, establishing a new link with the relay UE and UE 115-c may generate avoidable overhead and increase failure recovery time.

[0073] Aspects of the present disclosure may provide improvements to the recovery process, thereby reducing fault recovery time and reducing the overhead associated with fault recovery. For example, UE 115-a may detect a communication failure associated with the second link 220-a. In order to continue the side link communication, UE 115-a may reselect a relay UE. For example, UE 115-a may perform a discovery operation. In some cases, the discovery operation may include receiving one or more broadcast discovery messages (e.g., multiple discovery messages broadcast from candidate relay UEs) and reselecting UE 115-b or optionally selecting UE 115-d (e.g., a new relay UE) based on the discovery message. UE 115-a may communicate one or more connection messages 205-a with the selected relay UE 115 (e.g., UE 115-b or UE 115-d) to set up a relay communication path (e.g., via one or more new relay links). If UE 115-a reselects UE 115-b, UE 115-b may maintain third link 220-b and UE 115-a may maintain first link 215, as described herein with reference to Figure 3 If UE 115-a selects UE 115-d, UE 115-d may set up a fourth link 220-b between UE 115-d and UE 115-c (or maintain fourth link 220-b if it is already connected), and UE 115-a may maintain first link 215, as described herein with reference to Figure 4 As described.

[0074] In both scenarios (UE 115-a selects UE 115-d or if UE 115-a reselects UE 115-b), UE 115-a and UE 115-c may maintain the first link 215. For example, UE 115-a and UE 115-c may maintain one or more parameters associated with the first link 215, thereby reducing the overhead (e.g., latency, additional signaling, power, etc.) associated with communicating parameters to establish another E2E link 215. These parameters may include the context of the first link 215, such as security keys or bearers used to communicate via the first link. In some examples, if UE 115-c detects a failure on the third link 220-b, UE 115-c may perform a similar recovery process (e.g., maintaining the first link 215 and optionally maintaining the second link 220-a). In some other examples, UE 115-c may trigger (e.g., instruct) UE 115-a to perform a recovery process based on detecting a failure on the third link 220-b.

[0075] In some examples, UE 115-b may detect a failure associated with third link 220-b. UE 115-b may attempt to recover communication with UE 115-c. For example, UE 115-b may communicate a connection message 205-b (e.g., a connection setup message, a failure recovery message, or both) with UE 115-c. If UE 115-b successfully communicates with UE 115-c, UE 115-b may reestablish third link 220-b (e.g., reuse at least some of the context associated with third link 220-b, reset one or more parameters of one or more layers associated with third link 220-b, maintain third link 220-b). If the recovery attempt fails (or is skipped), UE 115-b may send a link failure message 210 (e.g., a message indicating a communication failure associated with third link 220-b) to UE 115-a, and UE 115-a may perform a failure recovery process.

[0076] In some examples, UE 115-a may detect a communication failure associated with first link 215. UE 115-a may perform a failure recovery procedure for the E2E link, wherein UE 115-a may reestablish the E2E link (rather than releasing the E2E link), as described herein with reference to Figure 5 According to aspects of the present disclosure, other combinations of any UE 115 involved in sidelink communications detecting and / or indicating a failure and performing recovery procedures (eg, maintaining one or more links, reestablishing one or more links, etc.) are possible.

[0077] In some cases, UE 115-a may establish two or more communication paths (e.g., relay paths) to UE 115-c. For example, UE 115-a may set up a first relay communication path (e.g., first E2E link 215) with UE 115-b by communicating one or more connection messages 205-a with UE 115-b. UE 115-a may discover UE 115-d (e.g., second relay UE 115) and determine to establish a backup per-hop path to UE 115-c. Therefore, UE 115-a may set up a second relay communication path (e.g., second E2E link 215) with UE 115-d by communicating one or more connection messages 205-a with UE 115-d (e.g., UE 115-a may utilize UE 115-d to trigger per-hop connection establishment). In some cases, UE 115-a may negotiate with UE 115-c (e.g., communicate one or more negotiation messages, request and response messages associated with capabilities, authorization, etc.) to set up an auxiliary path to UE 115-d. In some implementations, one of the relay communication paths (e.g., the first path) may be an active communication path (e.g., actively used for communication) while the other relay communication path (e.g., the second path) may be a deactivated path (e.g., in a pending state).

[0078] In some examples, UE 115-a may switch from a first relay communication path to a second relay communication path. For example, UE 115-a may detect a communication failure associated with a second link 220-a (e.g., a link between UE 115-a and UE 115-b). In order to continue the sidelink communication, UE 115-a may determine (e.g., detect) that a second E2E link 215 (e.g., a backup path) including UE 115-d is available. For example, UE 115-a may determine that one or more metrics (e.g., parameters, measurements, etc.) associated with the second E2E link 215 meet a threshold (e.g., greater than a threshold, less than a threshold). In some cases, the threshold may be associated with packet loss, delay, interference, and other channel metrics. The threshold may be preconfigured, configured (e.g., configured by the remote UE 115, the network entity 105, or both), or both.

[0079] Based on determining that the metric satisfies the threshold, UE 115-a may communicate one or more messages with UE 115-c to switch to the second E2E link 215 (e.g., a backup path). For example, UE 115-a may communicate one or more messages 225 (e.g., a negotiation message, an E2E PC5-S message, an RRC message) with UE 115-c (e.g., via UE 115-b, UE 115-d) to negotiate the switching path with UE 115-c. In some specific implementations, UE 115-c may accept the switch to the second E2E link 215, and UE 115-a and UE 115-c may release link 220-a and link 220-b associated with the first E2E link 215 (e.g., a first-hop link and a second-hop link associated with UE 115-b).

[0080] Figure 3 An example of a process flow 300 for supporting RLF recovery in a sidelink relay between UEs according to one or more aspects of the present disclosure is illustrated. In some examples, the process flow 300 may be implemented as described in reference Figure 1 and Figure 2 The process flow 300 may be implemented by, or in accordance with, aspects of the wireless communication systems 100 and 200 described above. For example, the process flow 300 may be implemented by UE 115-e, UE 115-f, and UE 115-g, which may be as described in reference Figure 1 and Figure 2 The corresponding examples of the source UE 115, the relay UE 115, and the destination UE 115 are described. In the following description of the process flow 300, the operations between the UE 115-e, the UE 115-f, and the UE 115-g may be sent in an order different from the example order shown, or the operations performed by the UE 115-e, the UE 115-f, and the UE 115-g may be performed in a different order or at a different time. Some operations may also be omitted from the process flow 300, and other operations may be added to the process flow 300.

[0081] At 305, UE 115-e, UE 115-f, and UE 115-g may perform a relay connection process (e.g., setup). For example, UE 115-e may perform a relay discovery operation and select UE 115-f for relaying communications between UE 115-e and UE 115-g. UE 115-e and UE 115-g may perform a route discovery operation and determine a path (e.g., E2E path, E2E link) including UE 115-e, UE 115-f, and UE 115-g. In some cases, UE 115-f may represent multiple relay UEs for connecting UE 115-e to UE 115-g via an E2E path. In some cases, UE 115-e may select multiple relay UEs to have multiple potential E2E paths between UE 115-e and UE 115-g, with one path being activated and other paths being deactivated (e.g., backup paths). UE 115-e, UE 115-f, and UE 115-g may communicate connection messages to set up a first E2E link. The first E2E link may include a first hop (e.g., a second link) between UE 115-e and UE 115-f and a second hop (e.g., a third link) between UE 115-f and UE 115-g.

[0082] At 310, UE 115-e may determine a communication failure. For example, UE 115-e may determine that the failure is associated with a second link between UE 115-e and UE 115-f. In some cases, UE 115-e may determine the failure based on one or more existing conditions (e.g., a retransmission threshold is met, a feedback threshold is met, etc.), as described herein with reference to Figure 1 A communication failure may be an example of a sidelink RLF.

[0083] In some cases, the UE 115-e may maintain the first link (e.g., E2E link 215) (e.g., as part of a recovery process). For example, the UE 115-e may determine to continue communication with the UE 115-g (e.g., despite the failure associated with the second link). The UE 115-e may maintain one or more parameters associated with the first link (e.g., counters, buffers, control data, identification, etc.). In some cases, the first UE 115-e may maintain these parameters for a duration (e.g., until an amount of time elapsed satisfies a threshold). The UE 115-e may perform a discovery operation of a communication path based on maintaining the first link to continue sidelink communications with the UE 115-g.

[0084] At 315, UE 115-e may send a relay selection message to UE 115-f. For example, in order to continue communication with UE 115-g, UE 115-e may receive (e.g., among multiple discovery messages received from multiple potential UEs 115) a discovery message for discovering a communication path to UE 115-g based on determining a failure associated with the second link. UE 115-e may determine to reselect UE 115-f for relaying communications to UE 115-g. For example, UE 115-e may determine that UE 115-f meets one or more conditions (e.g., location, signal strength, interference, latency, etc.) to be a relay UE between UE 115-e and UE 115-g.

[0085] In some cases, UE 115-e may reestablish the second link based on reselecting UE 115-f for relaying communications of the first link. For example, UE 115-e may utilize at least one parameter associated with the second link before performing a recovery process (e.g., before determining a failure associated with the second link). UE 115-e may store an identifier, buffer, counter, key, etc. associated with UE 115-f, the second link, or both, and utilize these parameters to reduce signaling and control overhead when establishing another second link between UE 115-e and UE 115-f.

[0086] At 320, UE 115-e may communicate one or more re-establishment messages with UE 115-f. In some cases, the re-establishment messages may include one or more connection messages. The connection message may include a PC5 side link message, a PC5 RRC message, a connection setup message, or any combination thereof. As part of the re-establishment process, UE 115-e may communicate a re-establishment message (e.g., using parameters associated with the second link stored prior to performing the discovery process). In some cases, the re-establishment message may include UE 115-e sending a message to UE 115-f indicating a failure recovery. For example, the failure recovery indication may indicate a per-hop RLF recovery to UE 115-f.

[0087] At 325, UE 115-e may optionally re-establish the connection between the RLC layers of UE 115-e and UE 115-f and reset the MAC layer, as described in reference to Figure 2For example, resetting the MAC layer may include resetting (e.g., reverting to original values) one or more MAC parameters of the second link. Additionally or alternatively, UE 115-e may reset one or more other parameters associated with the second link (e.g., parameters associated with other layers of the protocol stack). At 330, UE 115-e may communicate with UE 115-g via UE 115-f (e.g., via the reestablished second link).

[0088] Figure 4 An example of a process flow 400 for supporting RLF recovery in a sidelink relay between UEs according to one or more aspects of the present disclosure is illustrated. In some examples, the process flow 400 may be implemented as described in reference Figure 1 and Figure 2 The process flow 400 may be implemented by or in accordance with various aspects of the wireless communication systems 100 and 200 described above. For example, the process flow 400 may be implemented by UE 115-h, UE 115-i, UE 115-j, and UE 115-k, which may be as described in reference to Figure 1-3 The corresponding examples of the source UE 115, the relay UE 115, and the destination UE 115 are described. In the following description of the process flow 400, the operations between the UE 115-h, the UE 115-i, the UE 115-j, and the UE 115-k may be sent in an order different from the example order shown, or the operations performed by the UE 115-h, the UE 115-i, the UE 115-j, and the UE 115-k may be performed in a different order or at a different time. Some operations may also be omitted from the process flow 400, and other operations may be added to the process flow 400.

[0089] At 405, UE 115-h, UE 115-i, and UE 115-k may perform a relay connection process (e.g., setup). For example, UE 115-h may perform a relay discovery operation and select UE 115-i for relaying communications between UE 115-h and UE 115-k. UE 115-h and UE 115-k may perform a route discovery operation and determine a path (e.g., E2E path, E2E link) including UE 115-h, UE 115-i, and UE 115-k. In some cases, UE 115-i may represent multiple relay UEs for connecting UE 115-h to UE 115-k via an E2E path. In some cases, UE 115-h may select multiple relay UEs to have multiple potential E2E paths between UE 115-h and UE 115-k, where one path is activated and other paths are deactivated (e.g., backup paths). UE 115-h, UE 115-i, and UE 115-k may communicate connection messages to set up a first E2E link. The first E2E link may include a second link (e.g., a first hop) between UE 115-h and UE 115-i and a third link (e.g., a second hop) between UE 115-i and UE 115-k.

[0090] At 410, UE 115-h may determine a communication failure. For example, UE 115-h may determine that the failure is associated with a second link between UE 115-h and UE 115-i. In some cases, UE 115-h may determine the failure based on one or more existing conditions (e.g., a retransmission threshold is met, a feedback threshold is met, etc.), as described herein with reference to Figure 1 A communication failure may be an example of a sidelink RLF.

[0091] At 415, the UE 115-h may release the second link based on determining a failure (e.g., a link failure associated with the second link). For example, the UE 115-h may invalidate (e.g., delete, overwrite, mark as invalid) one or more parameters associated with the second link. In some cases, the UE 115-h may maintain the first link (e.g., E2E link 215) (e.g., as part of a recovery process). For example, the UE 115-h may determine to continue communication with the UE 115-k (e.g., despite the failure associated with the second link). The UE 115-h may maintain one or more parameters associated with the first link (e.g., counters, buffers, keys, control data, identification). In some cases, the first UE 115-h may maintain these parameters for a duration (e.g., until the amount of time that has elapsed satisfies a threshold). The UE 115-h may perform a discovery operation of a communication path based on maintaining the first link to continue sidelink communication with the UE 115-k.

[0092] At 420, UE 115-h may send a relay selection message to UE 115-j. For example, in order to continue communication with UE 115-k, UE 115-h may receive (e.g., among multiple discovery messages received from multiple potential UEs 115) a discovery message for discovering a communication path to UE 115-k based on determining a failure associated with the second link. UE 115-h may select UE 115-j for relaying communications (e.g., of the first link) to UE 115-k. For example, UE 115-h may determine that UE 115-j satisfies one or more conditions (e.g., location, signal strength, interference, latency, etc.) to serve as a relay UE between UE 115-h and UE 115-k.

[0093] At 425, UE 115-h may communicate one or more connection messages with UE 115-j. For example, UE 115-h may establish a fourth link between UE 115-j and UE 115-k based on selecting UE 115-j for relaying communications of the first link. At 430, UE 115-j may optionally communicate one or more connection messages with UE 115-k. In some cases, UE 115-j may have already communicated with UE 115-k (e.g., before UE 115-h communicates the connection message). The connection message may include a PC5 side link message, a PC5 RRC message, a link (e.g., per hop) setup message, or any combination thereof. UE 115-k may release a connection associated with a third link (e.g., between UE 115-i and UE 115-k) based on the fourth link. At 435, UE 115-h may communicate with UE 115-k via UE 115-j (eg, via the newly established second link).

[0094] In some cases, UE 115-i may detect a failure associated with a third link (e.g., a link between UE 115-i and UE 115-k) (e.g., prior to 410). UE 115-i may send a message to UE 115-h (e.g., at 410) indicating that the link failure is associated with the third link. UE 115-h may then follow steps 415 through 435. In some cases, the message may instruct UE 115-h to perform a selection process to determine another UE 115 to select for relaying communications.

[0095] Figure 5 An example of a process flow 500 for supporting RLF recovery in a sidelink relay between UEs according to one or more aspects of the present disclosure is illustrated. In some examples, the process flow 500 may be implemented as described in reference Figure 1 and Figure 2 The process flow 500 may be implemented by or in accordance with various aspects of the wireless communication systems 100 and 200. For example, the process flow 500 may be implemented by UE 115-1, UE 115-m, and UE 115-n, which may be as described in reference Figure 1-4 The corresponding examples of the source UE 115, the relay UE 115, and the destination UE 115 are described. In the following description of the process flow 500, the operations between the UE 115-1, the UE 115-m, and the UE 115-n may be sent in an order different from the example order shown, or the operations performed by the UE 115-1, the UE 115-m, and the UE 115-n may be performed in a different order or at a different time. Some operations may also be omitted from the process flow 500, and other operations may be added to the process flow 500.

[0096] At 505, UE 115-1, UE 115-m, and UE 115-n may perform a relay connection process (e.g., setup). For example, UE 115-1 may perform a relay discovery operation and select UE 115-m for relaying communications between UE 115-1 and UE 115-n. UE 115-1 and UE 115-n may perform a route discovery operation and determine a path (e.g., E2E path, E2E link) including UE 115-1, UE 115-m, and UE 115-n. In some cases, UE 115-m may represent multiple relay UEs for connecting UE 115-1 to UE 115-n via an E2E path. In some cases, UE 115-1 may select multiple relay UEs to have multiple potential E2E paths between UE 115-1 and UE 115-n, where one path is activated and other paths are deactivated (e.g., backup paths). UE 115-1, UE 115-m, and UE 115-n may communicate a connection message to set up a first E2E link. The first E2E link may include a second link (e.g., a first hop) between UE 115-1 and UE 115-m and a third link (e.g., a second hop) between UE 115-m and UE 115-n.

[0097] At 510, UE 115-1 may determine a communication failure. For example, UE 115-1 may determine that the failure is associated with a first link between UE 115-1 and UE 115-n. In some cases, UE 115-1 may determine the failure based on one or more existing conditions (e.g., a retransmission threshold is met, a feedback threshold is met, etc.), as described herein with reference to Figure 1 A communication failure may be an example of a sidelink RLF.

[0098] UE 115-1 may perform a re-establishment process based on determining the failure (e.g., instead of releasing the E2E connection). For example, UE 115-1 may perform a discovery operation of a communication path based on determining the failure to continue sidelink communication with UE 115-n. At 515, UE 115-1 may send a relay selection message to UE 115-m. For example, in order to continue communication with UE 115-n, UE 115-1 may receive (e.g., among multiple discovery messages received from multiple potential UEs 115) a discovery message for discovering a communication path to UE 115-n based on determining the failure associated with the second link. UE 115-1 may determine to reselect UE 115-m for relaying communication to UE 115-n. For example, UE 115-1 may determine that UE 115-m satisfies one or more conditions (eg, location, signal strength, interference, latency, etc.) to serve as a relay UE between UE 115-1 and UE 115-n.

[0099] In some cases, UE 115-1 may re-establish the first link based on reselecting UE 115-m for relaying communications of the first link. For example, UE 115-1 may utilize at least one parameter associated with the first link before performing a recovery process (e.g., before determining a failure associated with the first link). UE 115-1 may store identifiers, buffers, keys, counters, etc. associated with UE 115-m, UE 115-n, the second link, the first link, or any combination thereof, and utilize these parameters to reduce signaling and control overhead when re-establishing the first link between UE 115-1 and UE 115-n.

[0100] At 520, UE 115-1 may communicate one or more re-establishment messages with UE 115-m and UE 115-n (via UE 115-m). For example, UE 115-1 may send a first message to UE 115-n to re-establish the second link, and send a second message to re-establish the first link (e.g., UE 115-m may relay the second message). The first message may include an indication of resetting at least one parameter associated with flow control on the second link. The second message may include an indication of a protocol layer (e.g., a PDCP entity) to re-establish the first link. For example, the first message may include a PC5 RRC message, a connection setup message, or both, and the second message may include an E2E PC5 RRC message, a connection setup message, or both.

[0101] At 525, UE 115-1 may re-establish the RLC connection between UE 115-1 and UE 115-m (eg, reuse at least one RLC parameter) and reset the MAC layer, as described with reference to FIG. Figure 2As described. For example, resetting the MAC layer may include resetting (e.g., reverting to original values) one or more MAC parameters (e.g., sequence number, HARQ process) of the second link. Additionally or alternatively, UE 115-1 may reset one or more other parameters associated with the second link (e.g., parameters associated with other layers of the protocol stack). In some cases, UE 115-n may reestablish a connection between the RLC layer of UE 115-n and UE 115-m, and reset the MAC layer. At 530, UE 115-1 may communicate with UE 115-n via UE 115-m (e.g., via the reestablished second link). In some specific implementations, UE 115-n (e.g., destination UE 115) may perform a similar process (e.g., steps 510 to 530) to reestablish a third link between UE 115-n and UE 115-m (e.g., if UE 115-n determines a failure on the third link) while maintaining the first E2E link.

[0102] Figure 6 A block diagram 600 of a device 605 supporting RLF recovery in a sidelink relay between UEs according to one or more aspects of the present disclosure is shown. The device 605 may be an example of aspects of a UE 115 as described herein. The device 605 may include a receiver 610, a transmitter 615, and a communication manager 620. The device 605 may also include a processor. Each of these components may communicate with each other (e.g., via one or more buses).

[0103] The receiver 610 may provide means for receiving information (such as packets, user data, control information, or any combination thereof) associated with various information channels (e.g., control channels, data channels, information channels related to RLF recovery in sidelink relays between UEs). The information may be delivered to other components of the device 605. The receiver 610 may utilize a single antenna or a collection of multiple antennas.

[0104] The transmitter 615 may provide means for transmitting signals generated by other components of the device 605. For example, the transmitter 615 may transmit information associated with various information channels (e.g., control channels, data channels, information channels related to RLF recovery in a sidelink relay between UEs), such as packets, user data, control information, or any combination thereof. In some examples, the transmitter 615 may be co-located with the receiver 610 in a transceiver module. The transmitter 615 may utilize a single antenna or a collection of multiple antennas.

[0105] The communication manager 620, the receiver 610, the transmitter 615, or various combinations thereof, or various components thereof, may be examples of means for performing various aspects of RLF recovery in a sidelink relay between UEs as described herein. For example, the communication manager 620, the receiver 610, the transmitter 615, or various combinations thereof, or components thereof, may support methods for performing one or more of the functions described herein.

[0106] In some examples, the communication manager 620, the receiver 610, the transmitter 615, or various combinations or components thereof may be implemented in hardware (e.g., in a communication management circuit). The hardware may include a processor, a digital signal processor (DSP), a central processing unit (CPU), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, a microcontroller, discrete gate or transistor logic, discrete hardware components, or any combination thereof that is configured as or otherwise supports components for performing the functions described in the present disclosure. In some examples, the processor and a memory coupled to the processor may be configured to perform one or more of the functions described herein (e.g., by executing instructions stored in the memory by the processor).

[0107] Additionally or alternatively, in some examples, the communication manager 620, the receiver 610, the transmitter 615, or various combinations or components thereof may be implemented in code executed by a processor (e.g., as communication management software or firmware). If implemented in code executed by a processor, the functionality of the communication manager 620, the receiver 610, the transmitter 615, or various combinations or components thereof may be performed by a general purpose processor (e.g., configured as or otherwise supporting components for performing the functions described in the present disclosure), a DSP, a CPU, an ASIC, an FPGA, a microcontroller, or any combination of these or other programmable logic devices.

[0108] In some examples, communication manager 620 may be configured to perform various operations (e.g., receive, obtain, monitor, output, transmit) using or otherwise cooperating with receiver 610, transmitter 615, or both. For example, communication manager 620 may receive information from receiver 610, transmit information to transmitter 615, or be integrated in conjunction with receiver 610, transmitter 615, or both to obtain information, output information, or perform various other operations as described herein.

[0109] According to examples as disclosed herein, the communication manager 620 may support wireless communication at the first UE. For example, the communication manager 620 may be configured to or otherwise support components for establishing a first E2E link between the first UE and the second UE, wherein establishing the first link includes establishing a second link between the first UE and a third UE, the third UE being configured to relay communications between the first UE and the second UE. The communication manager 620 may be configured to or otherwise support components for performing a recovery process based on an indication of a link failure, wherein the recovery process includes maintaining the first link. The communication manager 620 may be configured to or otherwise support components for communicating with the second UE based on maintaining the first link.

[0110] Additionally or alternatively, according to examples as disclosed herein, the communication manager 620 may support wireless communication at the first UE. For example, the communication manager 620 may be configured to or otherwise support components for establishing a first E2E link between the first UE and the second UE, wherein establishing the first link includes establishing a second link between the first UE and a third UE, the third UE being configured to relay communications between the first UE and the second UE. The communication manager 620 may be configured to or otherwise support components for reestablishing the first link based on an indication of a failure associated with the first link, wherein reestablishing the first link includes resetting at least one parameter associated with flow control on the second link. The communication manager 620 may be configured to or otherwise support components for communicating with the second UE based on maintaining the first link.

[0111] By including or configuring a communication manager 620 according to examples as described herein, a device 605 (e.g., a processor controlling a receiver 610, a transmitter 615, a communication manager 620, or a combination thereof or otherwise coupled thereto) may support techniques for reducing the time to recover from a failure (e.g., a link failure), reducing processing, reducing power consumption, and more efficiently utilizing communication resources.

[0112] Figure 7 A block diagram 700 of a device 705 supporting RLF recovery in a sidelink relay between UEs according to one or more aspects of the present disclosure is shown. The device 705 may be an example of aspects of the device 605 or UE 115 as described herein. The device 705 may include a receiver 710, a transmitter 715, and a communication manager 720. The device 705 may also include a processor. Each of these components may communicate with each other (e.g., via one or more buses).

[0113] The receiver 710 may provide means for receiving information (such as packets, user data, control information, or any combination thereof) associated with various information channels (e.g., control channels, data channels, information channels related to RLF recovery in sidelink relays between UEs). The information may be delivered to other components of the device 705. The receiver 710 may utilize a single antenna or a collection of multiple antennas.

[0114] The transmitter 715 may provide means for transmitting signals generated by other components of the device 705. For example, the transmitter 715 may transmit information associated with various information channels (e.g., control channels, data channels, information channels related to RLF recovery in a sidelink relay between UEs), such as packets, user data, control information, or any combination thereof. In some examples, the transmitter 715 may be co-located with the receiver 710 in a transceiver module. The transmitter 715 may utilize a single antenna or a collection of multiple antennas.

[0115] The device 705 or its various components may be examples of components for performing various aspects of RLF recovery in a sidelink relay between UEs as described herein. For example, the communication manager 720 may include an E2E link component 725, a link failure component 730, a communication component 735, a link re-establishment component 740, or any combination thereof. The communication manager 720 may be an example of various aspects of the communication manager 620 as described herein. In some examples, the communication manager 720 or its various components may be configured to perform various operations (e.g., receive, obtain, monitor, output, send) using or otherwise cooperating with the receiver 710, the transmitter 715, or both. For example, the communication manager 720 may receive information from the receiver 710, transmit information to the transmitter 715, or be integrated with the receiver 710, the transmitter 715, or both to obtain information, output information, or perform various other operations as described herein.

[0116] According to examples as disclosed herein, the communication manager 720 may support wireless communication at the first UE. The E2E link component 725 may be configured to or otherwise support components for establishing a first E2E link between the first UE and the second UE, wherein establishing the first link includes establishing a second link between the first UE and a third UE, the third UE being configured to relay communications between the first UE and the second UE. The link failure component 730 may be configured to or otherwise support components for performing a recovery process based on an indication of a link failure, wherein the recovery process includes maintaining the first link. The communication component 735 may be configured to or otherwise support components for communicating with the second UE based on maintaining the first link.

[0117] Additionally or alternatively, according to examples as disclosed herein, the communication manager 720 may support wireless communication at the first UE. The E2E link component 725 may be configured to or otherwise support components for establishing a first E2E link between the first UE and the second UE, wherein establishing the first link includes establishing a second link between the first UE and a third UE, the third UE being configured to relay communications between the first UE and the second UE. The link reestablishment component 740 may be configured to or otherwise support components for reestablishing the first link based on an indication of a failure associated with the first link, wherein reestablishing the first link includes resetting at least one parameter associated with flow control on the second link. The communication component 735 may be configured to or otherwise support components for communicating with the second UE based on maintaining the first link.

[0118] Figure 8 A block diagram 800 of a communication manager 820 that supports RLF recovery in a sidelink relay between UEs according to one or more aspects of the present disclosure is shown. The communication manager 820 can be an example of aspects of the communication manager 620, the communication manager 720, or both as described herein. The communication manager 820 or its various components can be examples of components for performing various aspects of RLF recovery in a sidelink relay between UEs as described herein. For example, the communication manager 820 may include an E2E link component 825, a link failure component 830, a communication component 835, a link re-establishment component 840, a link release component 845, a link establishment component 850, or any combination thereof. Each of these components can communicate with each other directly or indirectly (e.g., via one or more buses).

[0119] According to examples as disclosed herein, the communication manager 820 may support wireless communication at the first UE. The E2E link component 825 may be configured to or otherwise support components for establishing a first E2E link between the first UE and the second UE, wherein establishing the first link includes establishing a second link between the first UE and a third UE, the third UE being configured to relay communications between the first UE and the second UE. The link failure component 830 may be configured to or otherwise support components for performing a recovery process based on an indication of a link failure, wherein the recovery process includes maintaining the first link. The communication component 835 may be configured to or otherwise support components for communicating with the second UE based on maintaining the first link.

[0120] In some examples, to support performing a recovery process, link failure component 830 may be configured or otherwise support components for reselecting a third UE for relaying communications to the second UE based on maintaining the first link and relay discovery operations.

[0121] In some examples, link reestablishment component 840 may be configured as or otherwise support components for reestablishing the second link based on reselecting a third UE for relaying communications of the first link, wherein reestablishing the second link includes utilizing at least one parameter associated with the second link prior to performing a recovery process.

[0122] In some examples, to support reestablishment of the second link, the link reestablishment component 840 may be configured as or otherwise support components for communicating one or more connection messages with a third UE based on reselection of the third UE, the one or more connection messages comprising a PC5 side link message, a PC5 RRC message, a connection setup message, or any combination thereof.

[0123] In some examples, to support reestablishment of the second link, link reestablishment component 840 may be configured as or otherwise support means for sending a message indicating failure recovery to the third UE based on reselecting the third UE.

[0124] In some examples, to support reestablishment of the second link, link reestablishment component 840 may be configured or otherwise support means for resetting one or more media access control parameters to initial values, the at least one parameter including the one or more media access control parameters.

[0125] In some examples, to support performing a recovery process, link failure component 830 may be configured or otherwise support means for selecting a fourth UE for relaying communications of the first link based on maintaining the first link.

[0126] In some examples, link release component 845 can be configured or otherwise support means for releasing the second link based on determining a link failure, where the link failure is associated with the second link.

[0127] In some examples, link establishment component 850 may be configured as or otherwise support components for establishing a third link between the first UE and the fourth UE based on selecting the fourth UE for relaying communications of the first link, wherein communicating with the second UE is also based on establishing the third link.

[0128] In some examples, to support establishment of a third link, link establishment component 850 may be configured as or otherwise support components for communicating one or more connection messages with a fourth UE based on selecting a fourth UE, the one or more connection messages comprising a PC5 side link message, a PC5 RRC message, a link setup message, or any combination thereof.

[0129] In some examples, link failure component 830 may be configured or otherwise support means for receiving a message from a third UE indicating that the link failure is associated with a third link between the second UE and the third UE.

[0130] Additionally or alternatively, according to examples as disclosed herein, the communication manager 820 may support wireless communication at the first UE. In some examples, the E2E link component 825 may be configured to or otherwise support components for establishing a first E2E link between the first UE and the second UE, wherein establishing the first link includes establishing a second link between the first UE and a third UE, the third UE being configured to relay communications between the first UE and the second UE. The link reestablishment component 840 may be configured to or otherwise support components for reestablishing the first link based on an indication of a failure associated with the first link, wherein reestablishing the first link includes resetting at least one parameter associated with flow control on the second link. In some examples, the communication component 835 may be configured to or otherwise support components for communicating with the second UE based on maintaining the first link.

[0131] In some examples, to support reestablishing the first link, link reestablishment component 840 may be configured to or otherwise support a component for sending a first message to reestablish the second link based on selecting a third UE for relaying communications between the first UE and the second UE. In some examples, to support reestablishing the first link, link reestablishment component 840 may be configured to or otherwise support a component for sending a second message to the second UE via the first link.

[0132] In some examples, the first message includes an indication to reset at least one parameter associated with flow control on the second link.

[0133] In some examples, the second message includes an indication to re-establish the protocol layer.

[0134] In some examples, the second message is an E2E PC5 RRC message and the protocol layer is a PDCP entity.

[0135] In some examples, resetting at least one parameter associated with flow control on the second link includes resetting one or more medium access control parameters to initial values.

[0136] Fig. 9A diagram of a system 900 including a device 905 supporting RLF recovery in a sidelink relay between UEs according to one or more aspects of the present disclosure is shown. The device 905 may be an example of a device 605, a device 705, or a UE 115 as described herein, or include components thereof. The device 905 may communicate (e.g., wirelessly) with one or more network entities 105, one or more UEs 115, or any combination thereof. The device 905 may include components for two-way voice and data communications, including components for sending and receiving communications, such as a communication manager 920, an input / output (I / O) controller 910, a transceiver 915, an antenna 925, a memory 930, a code 935, and a processor 940. These components may be electronically communicated or otherwise coupled (e.g., operatively, communicatively, functionally, electronically, electrically) via one or more buses (e.g., a bus 945).

[0137] I / O controller 910 may manage input and output signals for device 905. I / O controller 910 may also manage peripheral devices that are not integrated into device 905. In some cases, I / O controller 910 may represent a physical connection or port to an external peripheral device. In some cases, I / O controller 910 may utilize an operating system such as iOS. ® ANDROID ® , MS-DOS ® 、MS-WINDOWS ® , OS / 2 ® ,UNIX ® 、LINUX ® or another known operating system. Additionally or alternatively, I / O controller 910 may represent or interact with a modem, keyboard, mouse, touch screen, or similar device. In some cases, I / O controller 910 may be implemented as part of a processor (such as processor 940). In some cases, a user may interact with device 905 via I / O controller 910 or via hardware components controlled by I / O controller 910.

[0138] In some cases, the device 905 may include a single antenna 925. However, in some other cases, the device 905 may have more than one antenna 925, which may be capable of concurrently transmitting or receiving multiple wireless transmissions. The transceiver 915 may communicate bidirectionally via one or more antennas 925, wired or wireless links as described herein. For example, the transceiver 915 may represent a wireless transceiver and may communicate bidirectionally with another wireless transceiver. The transceiver 915 may also include a modem for: modulating packets; providing the modulated packets to one or more antennas 925 for transmission; and demodulating packets received from one or more antennas 925. The transceiver 915 or the transceiver 915 and one or more antennas 925 may be examples of transmitters 615, transmitters 715, receivers 610, receivers 710, or any combination thereof or components thereof as described herein.

[0139] The memory 930 may include random access memory (RAM) and read-only memory (ROM). The memory 930 may store computer-readable, computer-executable code 935 including instructions that, when executed by the processor 940, cause the device 905 to perform various functions described herein. The code 935 may be stored in a non-transitory computer-readable medium (such as system memory or another type of memory). In some cases, the code 935 may not be directly executable by the processor 940, but may (for example, when compiled and executed) cause the computer to perform the functions described herein. In some cases, the memory 930 may include, among other things, a basic I / O system (BIOS) that may control basic hardware or software operations, such as interaction with peripheral components or devices.

[0140] The processor 940 may include an intelligent hardware device (e.g., a general-purpose processor, a DSP, a CPU, a microcontroller, an ASIC, an FPGA, a programmable logic device, a discrete gate or transistor logic component, a discrete hardware component, or any combination thereof). In some cases, the processor 940 may be configured to operate a memory array using a memory controller. In some other cases, the memory controller may be integrated into the processor 940. The processor 940 may be configured to execute computer-readable instructions stored in a memory (e.g., a memory 930) to enable the device 905 to perform various functions (e.g., functions or tasks to support RLF recovery in a sidelink relay between UEs). For example, the device 905 or a component of the device 905 may include a processor 940 and a memory 930 coupled to or coupled to the processor 940, and the processor 940 and the memory 930 are configured to perform the various functions described herein.

[0141] According to examples as disclosed herein, the communication manager 920 may support wireless communication at the first UE. For example, the communication manager 920 may be configured to or otherwise support components for establishing a first E2E link between the first UE and the second UE, wherein establishing the first link includes establishing a second link between the first UE and a third UE, the third UE being configured to relay communications between the first UE and the second UE. The communication manager 920 may be configured to or otherwise support components for performing a recovery process based on an indication of a link failure, wherein the recovery process includes maintaining the first link. The communication manager 920 may be configured to or otherwise support components for communicating with the second UE based on maintaining the first link.

[0142] Additionally or alternatively, according to examples as disclosed herein, the communication manager 920 may support wireless communication at the first UE. For example, the communication manager 920 may be configured to or otherwise support components for establishing a first E2E link between the first UE and the second UE, wherein establishing the first link includes establishing a second link between the first UE and a third UE, the third UE being configured to relay communications between the first UE and the second UE. The communication manager 920 may be configured to or otherwise support components for reestablishing the first link based on an indication of a failure associated with the first link, wherein reestablishing the first link includes resetting at least one parameter associated with flow control on the second link. The communication manager 920 may be configured to or otherwise support components for communicating with the second UE based on maintaining the first link.

[0143] By including or configuring a communications manager 920 according to examples as described herein, the device 905 can support techniques for reducing time to recover from failures (eg, link failures), reducing processing, reducing power consumption, and more efficiently utilizing communications resources.

[0144] In some examples, the communication manager 920 may be configured to perform various operations (e.g., receive, monitor, transmit) using or otherwise cooperating with the transceiver 915, one or more antennas 925, or any combination thereof. Although the communication manager 920 is illustrated as a separate component, in some examples, one or more functions described with reference to the communication manager 920 may be supported or performed by the processor 940, the memory 930, the code 935, or any combination thereof. For example, the code 935 may include instructions that are executable by the processor 940 to cause the device 905 to perform various aspects of RLF recovery in a sidelink relay between UEs as described herein, or the processor 940 and the memory 930 may be otherwise configured to perform or support such operations.

[0145] Fig.10A flow chart illustrating a method 1000 for supporting RLF recovery in a sidelink relay between UEs according to one or more aspects of the present disclosure is shown. The operations of the method 1000 may be implemented by a UE or a component thereof as described herein. For example, the operations of the method 1000 may be implemented by a UE or a component thereof as described in reference to Figures 1 to 9 The UE 115 described herein may be executed. In some examples, the UE may execute an instruction set to control the functional elements of the UE to perform the described functions. Additionally or alternatively, the UE may use dedicated hardware to perform various aspects of the described functions.

[0146] At 1005, the method may include establishing a first E2E link between the first UE and the second UE, wherein establishing the first link includes establishing a second link between the first UE and a third UE, the third UE being configured to relay communications between the first UE and the second UE. The operations of 1005 may be performed according to examples as disclosed herein. In some examples, aspects of the operations of 1005 may be performed as described in reference to Figure 8 The E2E link component 825 is used to execute.

[0147] At 1010, the method may include performing a recovery process based on the indication of the link failure, wherein the recovery process includes maintaining the first link. The operations of 1010 may be performed according to examples as disclosed herein. In some examples, aspects of the operations of 1010 may be performed as described in reference to Figure 8 The link failure component 830 is used to perform.

[0148] At 1015, the method may include communicating with the second UE based on maintaining the first link. The operations of 1015 may be performed according to examples disclosed herein. In some examples, aspects of the operations of 1015 may be performed as described in reference Figure 8 The communication component 835 is used to execute.

[0149] Fig.11 A flow chart illustrating a method 1100 for supporting RLF recovery in a sidelink relay between UEs according to one or more aspects of the present disclosure is shown. The operations of the method 1100 may be implemented by a UE or a component thereof as described herein. For example, the operations of the method 1100 may be implemented by a UE or a component thereof as described herein. Figures 1 to 9 The UE 115 described herein may be executed. In some examples, the UE may execute an instruction set to control the functional elements of the UE to perform the described functions. Additionally or alternatively, the UE may use dedicated hardware to perform various aspects of the described functions.

[0150] At 1105, the method may include establishing a first E2E link between the first UE and the second UE, wherein establishing the first link includes establishing a second link between the first UE and a third UE, the third UE being configured to relay communications between the first UE and the second UE. The operations of 1105 may be performed according to examples as disclosed herein. In some examples, aspects of the operations of 1105 may be performed as described in reference to Figure 8 The E2E link component 825 is used to execute.

[0151] At 1110, the method may include performing a recovery process based on the indication of the link failure, wherein the recovery process includes maintaining the first link. The operations of 1110 may be performed according to examples as disclosed herein. In some examples, aspects of the operations of 1110 may be performed as described in reference to Figure 8 The link failure component 830 is used to perform.

[0152] At 1115, the method may include reselecting a third UE for relaying communications to the second UE based on maintaining the first link and the relay discovery operation. The operations of 1115 may be performed according to examples as disclosed herein. In some examples, aspects of the operations of 1115 may be performed as described in reference to Figure 8 The link failure component 830 is used to perform.

[0153] At 1120, the method may include communicating with the second UE based on maintaining the first link. The operations of 1120 may be performed according to examples as disclosed herein. In some examples, aspects of the operations of 1120 may be performed as described in reference Figure 8 The communication component 835 is used to execute.

[0154] Fig.12 A flow chart illustrating a method 1200 for supporting RLF recovery in a sidelink relay between UEs according to one or more aspects of the present disclosure is shown. The operations of the method 1200 may be implemented by a UE or a component thereof as described herein. For example, the operations of the method 1200 may be implemented by a UE or a component thereof as described in reference to Figures 1 to 9 The UE 115 described herein may be executed. In some examples, the UE may execute an instruction set to control the functional elements of the UE to perform the described functions. Additionally or alternatively, the UE may use dedicated hardware to perform various aspects of the described functions.

[0155] At 1205, the method may include establishing a first E2E link between the first UE and the second UE, wherein establishing the first link includes establishing a second link between the first UE and a third UE, the third UE being configured to relay communications between the first UE and the second UE. The operations of 1205 may be performed according to examples as disclosed herein. In some examples, aspects of the operations of 1205 may be performed as described in reference to Figure 8The E2E link component 825 is used to execute.

[0156] At 1210, the method may include performing a recovery process based on the indication of the link failure, wherein the recovery process includes maintaining the first link. The operations of 1210 may be performed according to examples as disclosed herein. In some examples, aspects of the operations of 1210 may be performed as described in reference to Figure 8 The link failure component 830 is used to perform.

[0157] At 1215, the method may include selecting a fourth UE for relaying communications of the first link based on maintaining the first link. The operations of 1215 may be performed according to examples as disclosed herein. In some examples, aspects of the operations of 1215 may be performed as described in reference to Figure 8 The link failure component 830 is used to perform.

[0158] At 1220, the method may include communicating with the second UE based on maintaining the first link. The operations of 1220 may be performed according to examples as disclosed herein. In some examples, aspects of the operations of 1220 may be performed as described in reference to Figure 8 The communication component 835 is used to execute.

[0159] Fig.13 A flow chart illustrating a method 1300 for supporting RLF recovery in a sidelink relay between UEs according to one or more aspects of the present disclosure is shown. The operations of the method 1300 may be implemented by a UE or a component thereof as described herein. For example, the operations of the method 1300 may be implemented by a UE or a component thereof as described in reference to Figures 1 to 9 The UE 115 described herein may be executed. In some examples, the UE may execute an instruction set to control the functional elements of the UE to perform the described functions. Additionally or alternatively, the UE may use dedicated hardware to perform various aspects of the described functions.

[0160] At 1305, the method may include establishing a first E2E link between the first UE and the second UE, wherein establishing the first link includes establishing a second link between the first UE and a third UE, the third UE being configured to relay communications between the first UE and the second UE. The operations of 1305 may be performed according to examples as disclosed herein. In some examples, aspects of the operations of 1305 may be performed as described in reference to Figure 8 The E2E link component 825 is used to execute.

[0161] At 1310, the method may include reestablishing the first link based on an indication of a failure associated with the first link, wherein reestablishing the first link includes resetting at least one parameter associated with flow control on the second link. The operations of 1310 may be performed according to examples as disclosed herein. In some examples, aspects of the operations of 1310 may be performed as described in reference to Figure 8 The link re-establishment component 840 is used to perform the operation.

[0162] At 1315, the method may include communicating with the second UE based on maintaining the first link. The operations of 1315 may be performed according to examples as disclosed herein. In some examples, aspects of the operations of 1315 may be performed as described in reference Figure 8 The communication component 835 is used to execute.

[0163] The following provides an overview of various aspects of the disclosure:

[0164] Aspect 1: A method for performing wireless communications at a first UE, the method comprising: establishing a first E2E link between the first UE and a second UE, wherein establishing the first link includes establishing a second link between the first UE and a third UE, the third UE being configured to relay communications between the first UE and the second UE; performing a recovery process based at least in part on an indication of a link failure, wherein the recovery process includes maintaining the first link; and communicating with the second UE based at least in part on maintaining the first link.

[0165] Aspect 2: The method according to aspect 1, wherein performing the recovery process further includes: reselecting the third UE for relaying communication to the second UE based at least in part on maintaining the first link and relay discovery operation.

[0166] Aspect 3: According to the method of Aspect 2, the method also includes: reestablishing the second link at least in part based on reselecting the third UE for relaying communications of the first link, wherein reestablishing the second link includes utilizing at least one parameter associated with the second link before performing the recovery process.

[0167] Aspect 4: A method according to Aspect 3, wherein reestablishing the second link includes: communicating one or more connection messages with the third UE based at least in part on reselecting the third UE, the one or more connection messages including a PC5 side link message, a PC5 radio resource control message, a connection setup message, or any combination thereof.

[0168] Aspect 5: The method according to any one of aspects 3 to 4, wherein re-establishing the second link comprises: sending a message indicating failure recovery to the third UE based at least in part on reselecting the third UE.

[0169] Aspect 6: The method according to any one of Aspects 3 to 5, wherein re-establishing the second link comprises: resetting one or more medium access control parameters to initial values, the at least one parameter comprising the one or more medium access control parameters.

[0170] Aspect 7: The method according to any one of aspects 1 to 6, the method further comprising: releasing the second link based at least in part on the link failure, wherein the link failure is associated with the second link.

[0171] Aspect 8: The method according to aspect 7, wherein performing the recovery process further comprises: selecting a fourth UE for relaying communications of the first link based at least in part on maintaining the first link.

[0172] Aspect 9: The method according to aspect 8, the method further comprising: receiving a message from the third UE indicating that the link failure is associated with a third link between the second UE and the third UE.

[0173] Aspect 10: According to the method described in any one of Aspects 7 to 9, the method also includes: establishing a third link between the first UE and the fourth UE based at least in part on selecting the fourth UE for relaying communication of the first link, wherein communication with the second UE is also at least in part based on establishing the third link.

[0174] Aspect 11: A method according to Aspect 10, wherein establishing the third link includes: communicating one or more connection messages with the fourth UE based at least in part on selecting the fourth UE, the one or more connection messages including a PC5 side link message, a PC5 radio resource control message, a link setup message, or any combination thereof.

[0175] Aspect 12: A method for performing wireless communications at a first UE, the method comprising: establishing a first E2E link between the first UE and a second UE, wherein establishing the first link includes establishing a second link between the first UE and a third UE, the third UE being configured to relay communications between the first UE and the second UE; reestablishing the first link based at least in part on an indication of a failure associated with the first link, wherein reestablishing the first link includes resetting at least one parameter associated with flow control on the second link; and communicating with the second UE based at least in part on maintaining the first link.

[0176] Aspect 13: A method according to Aspect 12, wherein reestablishing the first link includes: sending a first message to reestablish the second link based at least in part on selecting the third UE for relaying communications between the first UE and the second UE; and sending a second message to the second UE via the first link.

[0177] Aspect 14: The method according to aspect 13, wherein the first message includes an indication to reset at least one parameter associated with flow control on the second link.

[0178] Aspect 15: The method according to any one of Aspects 13 to 14, wherein the second message includes an indication to re-establish a protocol layer.

[0179] Aspect 16: The method according to aspect 15, wherein the second message is an E2E PC5 radio resource control message, and the protocol layer is a PDCP entity.

[0180] Aspect 17: The method according to any one of aspects 12 to 16, wherein resetting the at least one parameter associated with flow control on the second link includes resetting one or more medium access control parameters to initial values.

[0181] Aspect 18: An apparatus for performing wireless communications at a first UE, the apparatus comprising: a processor; a memory coupled to the processor; and instructions stored in the memory and executable by the processor to cause the apparatus to perform a method according to any one of Aspects 1 to 11.

[0182] Aspect 19: An apparatus for wireless communication at a first UE, the apparatus comprising at least one component for performing a method according to any one of aspects 1 to 11.

[0183] Aspect 20: A non-transitory computer-readable medium storing a code for wireless communication at a first UE, the code comprising instructions executable by a processor to perform a method according to any one of aspects 1 to 11.

[0184] Aspect 21: An apparatus for performing wireless communications at a first UE, the apparatus comprising: a processor; a memory coupled to the processor; and instructions stored in the memory and executable by the processor to cause the apparatus to perform a method according to any one of Aspects 12 to 17.

[0185] Aspect 22: An apparatus for wireless communication at a first UE, the apparatus comprising at least one component for performing a method according to any one of aspects 12 to 17.

[0186] Aspect 23: A non-transitory computer-readable medium storing a code for wireless communication at a first UE, the code comprising instructions executable by a processor to perform a method according to any one of aspects 12 to 17.

[0187] It should be noted that the methods described herein describe possible implementations, and that the operations and steps may be rearranged or otherwise modified and other implementations are possible. In addition, aspects from two or more methods may be combined.

[0188] Although aspects of LTE, LTE-A, LTE-A Pro, or NR systems may be described for example purposes, and LTE, LTE-A, LTE-A Pro, or NR terminology may be used in much of the description, the techniques described herein may also be applicable to networks other than LTE, LTE-A, LTE-A Pro, or NR networks. For example, the techniques described may be applicable to various other wireless communication systems, such as Ultra Mobile Broadband (UMB), Institute of Electrical and Electronics Engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDM, and other systems and radio technologies not explicitly mentioned herein.

[0189] The information and signals described herein may be represented using any of a variety of different technologies and methods. For example, data, instructions, commands, information, signals, bits, symbols, and chips mentioned throughout the specification may be represented by voltage, current, electromagnetic waves, magnetic fields or magnetic particles, optical fields or optical particles, or any combination thereof.

[0190] The various illustrative blocks and components described in conjunction with the disclosure herein may be implemented or executed using a general purpose processor, DSP, ASIC, CPU, FPGA or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in an alternative, the processor may be any processor, controller, microcontroller, or state machine. The processor may also be implemented as a combination of computing devices (e.g., a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration).

[0191] The functions described herein can be implemented using hardware, software executed by a processor, firmware, or any combination thereof. When implemented using software executed by a processor, the functions can be stored as one or more instructions or codes of a computer-readable medium, or sent using one or more instructions or codes of a computer-readable medium. Other examples and specific implementations are within the scope of the present disclosure and the appended claims. For example, due to the nature of software, the functions described herein can be implemented using software executed by a processor, hardware, firmware, hard wiring, or a combination of any of these items. Features that implement the functions can also be physically located at different locations, including being distributed so that the various parts of the functions are implemented at different physical locations.

[0192] Computer-readable media include both non-transient computer storage media and communication media, including any media that facilitates the transfer of a computer program from one location to another. Non-transient storage media can be any available media that can be accessed by a general or special computer. By way of example and not limitation, non-transient computer-readable media may include RAM, ROM, electrically erasable programmable ROM (EEPROM), flash memory, compact disc (CD) ROM or other optical disc storage device, disk storage device or other magnetic storage device or can be used to carry or store desired program code components in the form of instructions or data structures and any other non-transient media that can be accessed by a general or special computer or a general or special processor. Moreover, any connection is appropriately referred to as a computer-readable medium. For example, if the software is sent from a website, server or other remote source using coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL) or wireless technologies such as infrared, radio and microwaves, coaxial cable, fiber optic cable, twisted pair, DSL or wireless technologies such as infrared, radio and microwaves are included in the definition of computer-readable media. Disks and optical disks as used herein include CDs, laser optical disks, optical optical disks, digital versatile disks (DVDs), floppy disks, and Blu-ray disks. Disks can reproduce data magnetically, while optical disks can reproduce data optically using lasers. Combinations of the above are also included within the scope of computer-readable media.

[0193] As used herein (including in the claims), "or" used in a list of items (e.g., a list of items followed by a phrase such as "at least one of" or "one or more of") indicates an inclusive list, so that, for example, a list of at least one of A, B, or C means A or B or C or AB or AC or BC or ABC (i.e., A and B and C). In addition, as used herein, the phrase "based on" should not be interpreted as a reference to a closed set of conditions. For example, an example step described as "based on condition A" can be based on both condition A and condition B without departing from the scope of the present disclosure. In other words, as used herein, the phrase "based on" should be interpreted in the same manner as the phrase "based at least in part on".

[0194] The term "determining" encompasses a variety of actions, and thus, "determining" may include calculating, computing, processing, deriving, investigating, looking up (such as via looking up in a table, database or other data structure), ascertaining, and the like. Furthermore, "determining" may include receiving (e.g., receiving information), accessing (e.g., accessing data stored in a memory), etc. Additionally, "determining" may include parsing, obtaining, selecting, choosing, establishing, and other such similar actions.

[0195] In the drawings, similar components or features may have the same reference label. In addition, various components of the same type may be distinguished by following the reference label with a dash and a second label to distinguish between the similar components. If only the first reference label is used in the specification, the description may apply to any of the similar components having the same first reference label, regardless of the second reference label or other subsequent reference labels.

[0196] The descriptions set forth herein in conjunction with the accompanying drawings describe example configurations and do not represent all examples that may be implemented or within the scope of the claims. The term "example" as used herein means "used as an example, instance, or illustration," rather than "preferred" or "advantageous over other examples." The specific implementation includes specific details to provide an understanding of the described techniques. However, these techniques may be practiced without these specific details. In some cases, known structures and devices are shown in block diagram form to avoid obscuring the concepts of the described examples.

[0197] The description herein is provided to enable one of ordinary skill in the art to implement or use the present disclosure. Various modifications to the present disclosure will be apparent to one of ordinary skill in the art, and the general principles defined herein may be applied to other variations without departing from the scope of the present disclosure. Thus, the present disclosure is not limited to the examples and designs described herein, but should be granted the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An apparatus for wireless communication at a first user equipment (UE), the apparatus comprising: processor; a memory coupled to the processor; as well as instructions stored in the memory and executable by the processor to cause the apparatus to: Establishing a first end-to-end link between the first UE and a second UE, wherein establishing the first link includes establishing a second link between the first UE and a third UE, the third UE being configured to relay communications between the first UE and the second UE; performing a recovery procedure based at least in part on the indication of a link failure, wherein the recovery procedure includes maintaining the first link; and Communicating with the second UE is based at least in part on maintaining the first link.

2. The apparatus of claim 1 , wherein the instructions for performing the recovery process are further executable by the processor to cause the apparatus to: The third UE is reselected for relaying communications to the second UE based at least in part on maintaining the first link and relay discovery operations.

3. The apparatus of claim 2, wherein the instructions are further executable by the processor to cause the apparatus to: The second link is reestablished based at least in part on reselecting the third UE for relaying communications of the first link, wherein reestablishing the second link includes utilizing at least one parameter associated with the second link prior to performing the recovery procedure.

4. The apparatus of claim 3, wherein the instructions for reestablishing the second link are executable by the processor to cause the apparatus to: One or more connection messages are communicated with the third UE based at least in part on reselecting the third UE, the one or more connection messages comprising a PC5 sidelink message, a PC5 radio resource control message, a connection setup message, or any combination thereof.

5. The apparatus of claim 3, wherein the instructions for reestablishing the second link are executable by the processor to cause the apparatus to: A message indicating failure recovery is sent to the third UE based at least in part on reselecting the third UE.

6. The apparatus of claim 3, wherein the instructions for reestablishing the second link are executable by the processor to cause the apparatus to: One or more medium access control parameters are reset to initial values, the at least one parameter including the one or more medium access control parameters.

7. The apparatus of claim 1, wherein the instructions are further executable by the processor to cause the apparatus to: The second link is released based at least in part on the link failure, wherein the link failure is associated with the second link.

8. The apparatus of claim 7, wherein the instructions for performing the recovery process are further executable by the processor to cause the apparatus to: A fourth UE is selected for relaying communications of the first link based at least in part on maintaining the first link.

9. The apparatus of claim 8, wherein the instructions are further executable by the processor to cause the apparatus to: A third link is established between the first UE and the fourth UE based at least in part on selecting the fourth UE for relaying communications of the first link, wherein communicating with the second UE is also based at least in part on establishing the third link.

10. The apparatus of claim 9, wherein the instructions for establishing the third link are executable by the processor to cause the apparatus to: One or more connection messages are communicated with the fourth UE based at least in part on selecting the fourth UE, the one or more connection messages comprising a PC5 sidelink message, a PC5 radio resource control message, a link setup message, or any combination thereof.

11. The apparatus of claim 7, wherein the instructions are further executable by the processor to cause the apparatus to: A message is received from the third UE indicating that the link failure is associated with a third link between the second UE and the third UE.

12. An apparatus for wireless communication at a first user equipment (UE), the apparatus comprising: processor; a memory coupled to the processor; as well as instructions stored in the memory and executable by the processor to cause the apparatus to: Establishing a first end-to-end link between the first UE and a second UE, wherein establishing the first link includes establishing a second link between the first UE and a third UE, the third UE being configured to relay communications between the first UE and the second UE; reestablishing the first link based at least in part on an indication of a failure associated with the first link, wherein reestablishing the first link comprises resetting at least one parameter associated with flow control on the second link; as well as Communicating with the second UE is based at least in part on maintaining the first link.

13. The apparatus of claim 12, wherein the instructions for reestablishing the first link are executable by the processor to cause the apparatus to: sending a first message to reestablish the second link based at least in part on selecting the third UE to relay communications between the first UE and the second UE; and A second message is sent to the second UE via the first link.

14. The apparatus of claim 13, wherein the first message includes an indication to reset at least one parameter associated with flow control on the second link.

15. The apparatus of claim 13, wherein the second message includes an indication to re-establish a protocol layer.

16. The apparatus of claim 15, wherein the second message is an end-to-end PC5 Radio Resource Control message, and the protocol layer is a Packet Data Convergence Protocol entity.

17. The apparatus of claim 12, wherein resetting the at least one parameter associated with flow control on the second link comprises resetting one or more medium access control parameters to initial values.

18. A method for wireless communication at a first user equipment (UE), the method comprising: Establishing a first end-to-end link between the first UE and a second UE, wherein establishing the first link includes establishing a second link between the first UE and a third UE, the third UE being configured to relay communications between the first UE and the second UE; performing a recovery procedure based at least in part on the indication of a link failure, wherein the recovery procedure includes maintaining the first link; and Communicating with the second UE is based at least in part on maintaining the first link.

19. The method of claim 18, wherein performing the recovery process further comprises: The third UE is reselected for relaying communications to the second UE based at least in part on maintaining the first link and relay discovery operations.

20. The method according to claim 19, further comprising: The second link is reestablished based at least in part on reselecting the third UE for relaying communications of the first link, wherein reestablishing the second link includes utilizing at least one parameter associated with the second link prior to performing the recovery procedure.

21. The method of claim 20, wherein reestablishing the second link comprises: One or more connection messages are communicated with the third UE based at least in part on reselecting the third UE, the one or more connection messages comprising a PC5 sidelink message, a PC5 radio resource control message, a connection setup message, or any combination thereof.

22. The method of claim 20, wherein reestablishing the second link comprises: A message indicating failure recovery is sent to the third UE based at least in part on reselecting the third UE.

23. The method of claim 20, wherein reestablishing the second link comprises: One or more medium access control parameters are reset to initial values, the at least one parameter including the one or more medium access control parameters.

24. The method according to claim 18, further comprising: The second link is released based at least in part on the link failure, wherein the link failure is associated with the second link.

25. The method of claim 24, wherein performing the recovery process further comprises: selecting a fourth UE for relaying communications of the first link based at least in part on maintaining the first link; establishing a third link between the first UE and the fourth UE based at least in part on selecting the fourth UE for relaying communications of the first link, wherein communicating with the second UE is also based at least in part on establishing the third link; and One or more connection messages are communicated with the fourth UE based at least in part on selecting the fourth UE, the one or more connection messages comprising a PC5 sidelink message, a PC5 radio resource control message, a link setup message, or any combination thereof.

26. The method according to claim 24, further comprising: A message is received from the third UE indicating that the link failure is associated with a third link between the second UE and the third UE.

27. A method for wireless communication at a first user equipment (UE), the method comprising: Establishing a first end-to-end link between the first UE and a second UE, wherein establishing the first link includes establishing a second link between the first UE and a third UE, the third UE being configured to relay communications between the first UE and the second UE; reestablishing the first link based at least in part on an indication of a failure associated with the first link, wherein reestablishing the first link comprises resetting at least one parameter associated with flow control on the second link; as well as Communicating with the second UE is based at least in part on maintaining the first link.

28. The method of claim 27, wherein reestablishing the first link comprises: sending a first message to reestablish the second link based at least in part on selecting the third UE to relay communications between the first UE and the second UE; as well as A second message is sent to the second UE via the first link.

29. The method of claim 28, wherein the first message includes an indication to reset at least one parameter associated with flow control on the second link.

30. The method of claim 28, wherein the second message is an end-to-end PC5 radio resource control message, the second message including an indication to re-establish a protocol layer.

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