Handling of sidelink radio link failure

Abstract

Methods, systems, and apparatus for wireless communications are described. A sending user equipment (UE), a receiving UE, or both of a sidelink communication link may detect a radio link failure (RLF) on the sidelink communication link. For example, the sending UE may perform a radio link monitoring procedure to identify the RLF. Additionally or alternatively, the receiving UE may detect whether the RLF occurs based on the use of a timer or a counter. Thus, the receiving UE may start a timer when no sidelink transmission is received, and may declare an RLF when the timer expires. The receiving UE may start a timer when a data transmission is not received, when a data transmission should have been received but was not received, when sidelink control information (SCI) was not decoded, when the SCI was not received, and so on.

Description

[0001] Cross-references

[0002] This patent application claims the benefit of U.S. Provisional Patent Application No. 62 / 893,675, filed by BAGHEL et al. on August 29, 2019, entitled “HANDLING OF SIDELINK RADIO LINK FAILURE”; and priority to U.S. Patent Application No. 16 / 996,078, filed by BAGHEL et al. on August 18, 2020, entitled “HANDLING OF SIDELINK RADIO LINK FAILURE”, each of which is assigned to the assignee of this application. Technical Field

[0003] The following relates generally to wireless communications and, more particularly, to handling of sidelink radio link failure (RLF). Background Art

[0004] Wireless communication systems are widely deployed to provide various types of communication content, such as voice, video, packet data, messaging, broadcast, etc. These systems can 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, improved LTE (LTE-A) systems, or LTE-A professional systems) and fifth generation (5G) systems (which may be referred to as new radio (NR) systems). These systems may use techniques such as code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), orthogonal frequency division multiple access (OFDMA), or discrete Fourier transform spread orthogonal frequency division multiplexing (DFT-S-OFDM).

[0005] A wireless multiple access communication system may include multiple base stations or network access nodes, each of which simultaneously supports communication for multiple communication devices (which may be further referred to as user equipment (UE)). In some cases, UEs may communicate directly with each other without having to transmit through a base station or relay point. This type of communication may be referred to as sidelink, device-to-device (D2D), vehicle-to-vehicle (V2V) communication, or another term for sidelink communication between two UEs. In sidelink communication, efficient techniques for monitoring and maintaining sidelink connections between UEs are desired. Summary of the invention

[0006] The described techniques relate to improved methods, systems, devices and apparatuses for supporting the handling of sidelink radio link failure (RLF). In general, the described techniques provide for detecting RLF on a sidelink channel (e.g., a sidelink connection) between a sending user equipment (UE) (e.g., a first UE) and a receiving UE (e.g., a second UE). For example, the sending UE may perform a radio link monitoring (RLM) process to monitor the sidelink channel based on an acknowledgement (ACK) feedback from a receiving UE for the sidelink channel to identify the RLF. If the sending UE does not receive several consecutive ACKs, or does not receive an ACK before a timer expires, the sending UE may determine that an RLF has occurred on the sidelink channel and report the RLF. In some cases, the sending UE may report the RLF by sending an indication of the RLF to a scheduling base station (e.g., via radio resource control (RRC) signaling). Additionally or alternatively, the sending UE may send a connection reestablishment request to the scheduling base station to reestablish the sidelink connection with the receiving UE. In some cases, when RLF is declared or determined, the sending UE may stop sending data to the receiving UE.

[0007] Additionally or alternatively, the receiving UE may perform a technique to determine whether RLF occurs on a sidelink channel with the sending UE. For example, the receiving UE may detect whether RLF occurs based on the use of a timer or a counter. Thus, the receiving UE may start a timer (e.g., or a counter) when no sidelink transmission is received from the sending UE, and may declare RLF when the timer expires. The receiving UE may start (e.g., begin) a timer when a data transmission is not received, when a data transmission should be received (e.g., as indicated by the sending UE, based on periodic scheduling, etc.) but is not received, when sidelink control information (SCI) is not decoded, when SCI is not received, and the like. If the SCI is decoded before the timer expires, the receiving UE may reset the timer and begin counting down after the next occurrence of a failed SCI decode. After detecting the RLF, the receiving UE may report the RLF to the scheduling base station (e.g., via RRC signaling) or the sending UE (e.g., via a medium access control (MAC) control element (CE)). In some cases, the receiving UE may release the sidelink connection with the sending UE based on RLF.

[0008] A method of wireless communication at a first UE is described. The method may include: monitoring a sidelink communication link with a second UE as part of an RLM procedure for the sidelink communication link; detecting RLF of the sidelink communication link based on the monitoring; and reporting the RLF based on the detection of the RLF.

[0009] 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 executable by the processor to cause the apparatus to perform the following operations: monitor a sidelink communication link with a second UE as part of an RLM process for the sidelink communication link; detect RLF of the sidelink communication link based on the monitoring; and report the RLF based on the detection of the RLF.

[0010] Another apparatus for wireless communication at a first UE is described. The apparatus may include: means for monitoring a sidelink communication link with a second UE as part of an RLM procedure for the sidelink communication link; means for detecting RLF of the sidelink communication link based on the monitoring; and means for reporting the RLF based on the detection of the RLF.

[0011] A non-transitory computer-readable medium storing code for wireless communication at a first UE is described. The code may include instructions executable by a processor to: monitor a sidelink communication link with a second UE as part of an RLM procedure for the sidelink communication link; detect RLF of the sidelink communication link based on the monitoring; and report the RLF based on the detection of the RLF.

[0012] In some examples of the methods, apparatus, and non-transitory computer-readable media described herein, reporting the RLF may include operations, features, means, or instructions for sending an indication of the RLF to a base station via RRC signaling.

[0013] In some examples of the methods, apparatus, and non-transitory computer-readable media described herein, reporting the RLF may include operations, features, units, or instructions for performing the following operations: sending a request to a base station for sidelink connection reestablishment with a second UE.

[0014] In some examples of the methods, apparatus, and non-transitory computer-readable media described herein, detecting RLF may include operations, features, units, or instructions for performing the following operations: sending one or more sidelink messages to a second UE and via a sidelink communication link in one or more transmission time intervals (TTIs); monitoring the sidelink communication link for feedback messages from the second UE and in response to the one or more sidelink messages in one or more subsequent TTIs after the one or more TTIs; and determining the RLF based on the monitoring, based on one or more unsuccessful receptions of the feedback messages.

[0015] Some examples of the methods, apparatuses, and non-transitory computer-readable media described herein may also include operations, features, means, or instructions for avoiding sending a message to a second UE via a sidelink communication link based on detection of the RLF.

[0016] In some examples of the methods, apparatus, and non-transitory computer-readable media described herein, the first UE may be a transmitting UE for a sidelink communication link and the second UE may be a receiving UE for the sidelink communication link.

[0017] A method of wireless communication at a second UE is described. The method may include: identifying a TTI for a sidelink transmission from a first UE via a sidelink communication link; monitoring the sidelink communication link for one or more sidelink transmissions from the first UE during the TTI; and starting a timer based on unsuccessful reception of the one or more sidelink transmissions in the TTI.

[0018] An apparatus for wireless communication at a second 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 executable by the processor to cause the apparatus to: identify a TTI for a sidelink transmission from a first UE via a sidelink communication link; monitor the sidelink communication link for one or more sidelink transmissions from the first UE during the TTI; and start a timer based on unsuccessful reception of the one or more sidelink transmissions in the TTI.

[0019] Another apparatus for wireless communication at a second UE is described. The apparatus may include: means for identifying a TTI for a sidelink transmission from a first UE via a sidelink communication link; means for monitoring the sidelink communication link for one or more sidelink transmissions from the first UE during the TTI; and means for starting a timer based on unsuccessful reception of the one or more sidelink transmissions in the TTI.

[0020] A non-transitory computer-readable medium storing code for wireless communication at a second UE is described. The code may include instructions executable by a processor to: identify a TTI for a sidelink transmission from a first UE via a sidelink communication link; monitor the sidelink communication link for one or more sidelink transmissions from the first UE during the TTI; and start a timer based on unsuccessful reception of the one or more sidelink transmissions in the TTI.

[0021] Some examples of the methods, apparatus, and non-transitory computer-readable media described herein may also include operations, features, means, or instructions for determining a RLF for the sidelink communication link based on a timer exceeding a threshold value.

[0022] Some examples of the methods, apparatus, and non-transitory computer-readable media described herein may also include operations, features, units, or instructions for performing the following operations: determining a threshold value based on: a preconfigured value, a value determined during establishment of the sidelink communication link, a priority level associated with data sent via the sidelink communication link, an indication from a base station, or a combination thereof.

[0023] In some examples of the methods, apparatus, and non-transitory computer-readable media described herein, the value determined during establishment of the sidelink communication link may be based on a speed of the first UE or the second UE, a congestion level of the sidelink communication link, a priority level associated with data sent via the sidelink communication link, an application for which the sidelink communication link may be used, or a combination thereof.

[0024] Some examples of the methods, apparatus, and non-transitory computer-readable media described herein may also include operations, features, units, or instructions for performing the following operations: determining upper and lower limits for threshold values, wherein the upper and lower limits may be based on: preconfigured values, priority levels associated with data sent via the sidelink communication link, applications that the sidelink communication link may be used for, or a combination thereof.

[0025] Some examples of the methods, apparatus, and non-transitory computer-readable media described herein may also include operations, features, units, or instructions for reconfiguring a threshold value based on a change in a speed of the first UE or the second UE, a congestion level of the sidelink communication link, a change in a priority level associated with data sent via the sidelink communication link, or a combination thereof.

[0026] Some examples of the methods, apparatuses, and non-transitory computer-readable media described herein may also include operations, features, means, or instructions for reporting the RLF based on the determination of the RLF.

[0027] In some examples of the methods, apparatus, and non-transitory computer-readable media described herein, reporting the RLF may include operations, features, means, or instructions for sending an indication of the RLF to a base station via RRC signaling.

[0028] In some examples of the methods, apparatus, and non-transitory computer-readable media described herein, reporting the RLF may also include operations, features, units, or instructions for performing the following operations: sending an indication of the RLF to the first UE via sidelink signaling.

[0029] Some examples of the methods, apparatus, and non-transitory computer-readable media described herein may also include operations, features, means, or instructions for releasing the sidelink communication connection with the first UE based on a determination of RLF.

[0030] Some examples of the methods, apparatus, and non-transitory computer-readable media described herein may also include operations, features, units, or instructions for determining unsuccessful reception of one or more sidelink transmissions based on a failure to decode the SCI or sidelink data during the TTI.

[0031] In some examples of the methods, apparatus, and non-transitory computer-readable media described herein, the timer may include a timer that begins counting down based on unsuccessful reception of one or more sidelink transmissions.

[0032] In some examples of the methods, apparatus, and non-transitory computer-readable media described herein, the first UE may be a transmitting UE for a sidelink communication link and the second UE may be a receiving UE for the sidelink communication link. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 An example of a system for wireless communication that supports handling of sidelink radio link failure (RLF) in accordance with aspects of the present disclosure is shown.

[0034] Figure 2 An example of a wireless communication system supporting processing of sidelink RLF in accordance with aspects of the present disclosure is shown.

[0035] Figure 3A and 3B An example of a slot diagram is shown that supports processing for sidelink RLF in accordance with aspects of the present disclosure.

[0036] Figure 4A and 4B Also shown is an example of a time slot diagram that supports processing for sidelink RLF in accordance with aspects of the present disclosure.

[0037] Figure 5 An example of a receiver RLF detection timer is shown to support processing of sidelink RLF in accordance with aspects of the present disclosure.

[0038] Figure 6An example of a process flow for a process supporting sidelink RLF in accordance with aspects of the present disclosure is shown.

[0039] Figure 7 and 8 A block diagram of a device supporting processing of sidelink RLF in accordance with aspects of the present disclosure is shown.

[0040] Fig. 9 A schematic diagram of a system including devices supporting processing of sidelink RLF in accordance with aspects of the present disclosure is shown.

[0041] Fig.10 and 11 A block diagram of a device supporting processing of sidelink RLF in accordance with aspects of the present disclosure is shown.

[0042] Fig.12 A block diagram of a receiving user equipment (UE) communications manager supporting processing of sidelink RLF according to aspects of the present disclosure is shown.

[0043] Fig.13 A schematic diagram of a system including devices supporting processing of sidelink RLF in accordance with aspects of the present disclosure is shown.

[0044] Figures 14 to 19 A flow chart illustrating a method of processing to support sidelink RLF in accordance with aspects of the present disclosure is shown. DETAILED DESCRIPTION

[0045] In some cases of wireless communication systems, a user equipment (UE) and a base station may communicate via a radio link. The UE or base station may monitor the radio link to check for a radio link failure (RLF). The UE or base station may monitor the RLF by monitoring specific signals in the channel. For example, in the case of a 5G NR downlink, as part of the radio link monitoring (RLM) process, the UE may measure a synchronization signal block (SSB) or a channel state information reference signal (CSI-RS).

[0046] In other cases, one or more UEs may communicate directly with each other on the sidelink communication channel. In some cases, the communication configuration may not include one UE relaying a message to other UEs via a base station. The sidelink communication configuration may be an example of device-to-device (D2D) communication, vehicle-to-vehicle (V2V) communication, or another example of sidelink communication in an Internet of Everything (IoE) communication system.

[0047] In the case of sidelink communications, performing the RLM process by measuring the SSB and CSI-RS of the channel may not be as reliable as in other types of communications (e.g., cellular link to UE communications or base station to UE communications) because multiple UEs may utilize the same SSB. Therefore, measurements on the SSB may not correctly correspond to the intended sidelink channel or UE. In addition, SSB transmissions may be decoupled from data transmissions, resulting in the UE that is sending data may be different from the UE that is sending the SSB. In addition, in some cases, there may also be no CSI-RS in the sidelink communication channel, and therefore, the UE may not rely on the CSI-RS in the sidelink communication to perform the RLM process.

[0048] A UE (e.g., a transmitting UE) transmitting data in a sidelink communication configuration may perform RLM by monitoring and detecting hybrid automatic repeat request (HARQ) feedback (e.g., an acknowledgement (ACK) / negative acknowledgement (NACK) feedback message). For example, a first UE may transmit a data packet to a second UE, and the first UE may then monitor a HARQ response from the second UE, the HARQ response including ACK / NACK feedback indicating a status of reception of the message by the second UE.

[0049] In addition, RLM may be performed in both unicast and multicast sidelink scenarios. In a unicast configuration, RLM may be performed to determine whether a connection between two UEs communicating on a sidelink has failed. RLM may also be performed in a groupcast (e.g., multicast) sidelink scenario, where one UE may send the same data transmission to more than one other UE in a sidelink. In multicast, RLM may be performed to determine whether any connection in a one-to-many connection between a UE sending data and a UE receiving data has failed. A failure in either a unicast configuration or a multicast configuration may be an RLF.

[0050] In a sidelink communication system, a first UE may send a message (e.g., a data packet) to one or more other UEs on a sidelink channel. The UE may monitor ACK / NACK feedback from a receiving UE in a specific transmission time interval (TTI) (e.g., a time slot). In some cases, the first UE may determine that a HARQ feedback failure has occurred in a specific TTI (e.g., a time slot). In order to perform RLM, the first UE may start a counter (e.g., a timer) in a TTI corresponding to an expected transmission of an ACK / NACK from the receiving UE. When the counter counts to a threshold number of failures, or if no successful HARQ feedback is received before the timer counts down to zero, the first UE may declare RLF. The expiration of the counter may correspond to a continuous failure of HARQ feedback from the receiving UE. Failure of HARQ feedback may occur due to a failure in HARQ feedback transmission by the receiving UE (e.g., the receiving UE fails to decode the sidelink control information (SCI) from the transmitting UE and the receiving UE will not send HARQ feedback), a failure in HARQ feedback decoding by the transmitting UE, or if the transmitting UE receives the HARQ feedback, successfully decodes it and determines that the HARQ feedback is a NACK.

[0051] Therefore, the UE may perform RLM based on HARQ feedback detection to determine or declare RLF in a sidelink communication system without SSB or CSI-RS. The UE may declare RLF and may then take actions to restore the connection to resolve the RLF. The UE may then reestablish a connection between the UE and the receiving UE.

[0052] Additionally or alternatively, the receiving UE may also detect whether RLF occurs based on the use of a timer (e.g., or a counter). For example, the receiving UE may start a timer when no sidelink transmission is received, and may declare RLF when the timer expires. The timer may have a value determined based on a preconfigured value, a value negotiated between the communicating UEs (e.g., the transmitting UE and the receiving UE) during sidelink establishment, a value mapped from a data priority, a value indicated by a base station, and the like. Additionally, the negotiation may determine the timer value using UE speed, congestion level, data priority, application type, or a combination thereof. In some cases, the timer may include a range with an upper limit and a lower limit, the upper limit and the lower limit being determined based on a preconfigured value, data priority, application type, or a combination thereof.

[0053] In addition, when a data transmission is not received, when a data transmission should be received (e.g., as indicated by the sending UE, based on a periodic schedule, etc.) but is not received, the receiving UE may start a timer. For example, data transmission not being received may include: no SCI is successfully decoded, the SCI is successfully decoded but the decoding of the data transmission indicated by the SCI fails, etc. If the SCI is decoded before the timer expires, the receiving UE may reset the timer and start counting down after the next occurrence of a failed SCI decoding. In some cases, the timer value may be reconfigured when there is a change in UE speed, a change in congestion level, a change in the priority level of the data, or a combination thereof.

[0054] After detecting the RLF, the sending UE may report the RLF to the scheduling base station via radio resource control (RRC) signaling or by sending a request to the base station for connection reestablishment with the receiving UE. Additionally or alternatively, the receiving UE may also report the RLF to the scheduling base station via RRC signaling, or report the RLF to the sending UE via sidelink signaling (e.g., medium access control (MAC) control element (CE), RRC signaling, etc.). In some cases, the receiving UE may release the sidelink communication connection with the sending UE based on the RLF. Similarly, when the RLF is declared or determined, the sending UE may stop sending data to the receiving UE.

[0055] Aspects of the present disclosure are first described in the context of a wireless communication system. Additionally, aspects of the present disclosure are illustrated by additional wireless communication systems, time slot diagram examples, receiver RLF detection timers, and process flows. Aspects of the present disclosure are further illustrated by and described with reference to apparatus diagrams, system diagrams, and flow diagrams involving the processing of sidelink RLF.

[0056] Figure 1 An example of a wireless communication system 100 that supports processing of sidelink RLF according to aspects of the present disclosure is shown. The wireless communication system 100 includes a base station 105, a UE 115, and a core network 130. In some examples, the wireless communication system 100 can be a long term evolution (LTE) network, an improved LTE (LTE-A) network, an LTE-A professional network, or a new radio (NR) network. In some cases, the wireless communication system 100 can support enhanced broadband communications, ultra-reliable (e.g., mission-critical) communications, low-latency communications, or communications with low-cost and low-complexity devices.

[0057] The base station 105 may communicate wirelessly with the UE 115 via one or more base station antennas. The base station 105 described herein may include or may be referred to by those skilled in the art as a base station transceiver, a radio base station, an access point, a radio transceiver, a node B, an evolved node B (eNB), a next generation node B, or a giga node B (any of which may be referred to as a gNB), a home node B, a home evolved node B, or some other appropriate terminology. The wireless communication system 100 may include different types of base stations 105 (e.g., macro cell base stations or small cell base stations). The UE 115 described herein is capable of communicating with various types of base stations 105 and network devices (including macro eNBs, small cell eNBs, gNBs, relay base stations, etc.).

[0058] Each base station 105 may be associated with a particular geographic coverage area 110 in which it supports communications with various UEs 115. Each base station 105 may provide communication coverage for the respective geographic coverage area 110 via a communication link 125, and the communication link 125 between the base station 105 and the UE 115 may utilize one or more carriers. The communication link 125 shown in the wireless communication system 100 may include an uplink transmission from the UE 115 to the base station 105, or a downlink transmission from the base station 105 to the UE 115. Downlink transmissions may also be referred to as forward link transmissions, and uplink transmissions may also be referred to as reverse link transmissions.

[0059] The geographic coverage area 110 for the base station 105 can be divided into sectors, which constitute a portion of the geographic coverage area 110, and each sector can be associated with a cell. For example, each base station 105 can provide communication coverage for a macro cell, a small cell, a hotspot, or other types of cells, or various combinations thereof. In some examples, the base station 105 can be mobile and, therefore, provide communication coverage for a mobile geographic coverage area 110. In some examples, different geographic coverage areas 110 associated with different technologies can overlap, and the overlapping geographic coverage areas 110 associated with different technologies can be supported by the same base station 105 or different base stations 105. The wireless communication system 100 may include, for example, a heterogeneous LTE / LTE-A / LTE-A professional or NR network, in which different types of base stations 105 provide coverage for each geographic coverage area 110.

[0060] The term "cell" refers to a logical communication entity used for communication with a base station 105 (e.g., on a carrier), and may be associated with an identifier (e.g., a physical cell identifier (PCID), a virtual cell identifier (VCID)) used to distinguish adjacent cells operating via the same or different carriers. In some examples, a carrier may support multiple cells, and different cells may be configured according to different protocol types (e.g., machine type communication (MTC), narrowband Internet of Things (NB-IoT), enhanced mobile broadband (eMBB), or other protocol types), which may provide access for different types of devices. In some cases, the term "cell" may refer to a portion of a geographic coverage area 110 (e.g., a sector) on which the logical entity operates.

[0061] UE 115 can be dispersed throughout the wireless communication system 100, and each UE 115 can be stationary or mobile. UE 115 can also be referred to as a mobile device, a wireless device, a remote device, a handheld device, or a user device, or some other appropriate term, wherein "device" can also be referred to as a unit, a station, a terminal, or a client. UE 115 can be 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 can also refer to a wireless local loop (WLL) station, an Internet of Things (IoT) device, an Internet of Everything (IoE) device, or an MTC device, etc., which can be implemented in various items such as electrical appliances, vehicles, meters, etc.

[0062] Some UEs 115 (e.g., MTC or IoT devices) may be low-cost or low-complexity devices and may provide automated communication between machines (e.g., via machine-to-machine (M2M) communication). M2M communication or MTC may refer to data communication technology that allows devices to communicate with each other or base station 105 without human intervention. In some examples, M2M communication or MTC may include communications from devices that incorporate sensors or meters to measure or capture information and relay the information to a central server or application, which may utilize the information or present the information to a human interacting with the program or application. Some UEs 115 may be designed to collect information or implement automated behavior of machines. Examples of applications for MTC devices include smart metering, inventory monitoring, water level monitoring, equipment monitoring, healthcare monitoring, wildlife monitoring, climate and geological event monitoring, fleet management and tracking, remote security sensing, physical access control, and transaction-based business billing.

[0063] Some UEs 115 may be configured to employ a mode of operation that reduces power consumption, such as half-duplex communication (e.g., a mode that supports one-way communication via transmission or reception rather than simultaneous transmission and reception). In some examples, half-duplex communication may be performed at a reduced peak rate. Other power conservation techniques for UE 115 include entering a power-saving "deep sleep" mode when not engaged in active communications, or operating over limited bandwidth (e.g., in accordance with narrowband communications). In some cases, UE 115 may be designed to support critical functions (e.g., mission-critical functions), and the wireless communication system 100 may be configured to provide ultra-reliable communications for these functions.

[0064] In some cases, UE 115 can also communicate directly with other UE 115 (e.g., using peer-to-peer (P2P) or device-to-device (D2D) protocols). One or more UE 115 in a group of UEs 115 utilizing D2D communication may be within the geographic coverage area 110 of the base station 105. Other UEs 115 in such a group may be outside the geographic coverage area 110 of the base station 105, or otherwise unable to receive transmissions from the base station 105. In some cases, groups of UEs 115 communicating via D2D communication may utilize a one-to-many (1:M) system, wherein each UE 115 transmits to each other UE 115 in the group. In some cases, the base station 105 facilitates the scheduling of resources for D2D communication. In other cases, D2D communication is performed between UEs 115 without involving the base station 105.

[0065] The base stations 105 may communicate with the core network 130 and with each other. For example, the base stations 105 may interface with the core network 130 via a backhaul link 132 (e.g., via S1, N2, N3, or other interface). The base stations 105 may communicate with each other directly (e.g., directly between the base stations 105) or indirectly (e.g., via the core network 130) via a backhaul link 134 (e.g., via X2, Xn, or other interface).

[0066] The core network 130 may provide user authentication, access authorization, tracking, Internet Protocol (IP) connections, and other access, routing or mobility functions. The core network 130 may be an evolved packet core (EPC), which may include at least one mobility management entity (MME), at least one serving gateway (S-GW), and at least one packet data network (PDN) gateway (P-GW). The MME may manage non-access stratum (e.g., control plane) functions such as mobility, authentication, and bearer management for UE 115 served by a base station 105 associated with the EPC. User IP packets may be transmitted through the S-GW, which itself may be connected to the P-GW. The P-GW may provide IP address allocation and other functions. The P-GW may be connected to a network operator IP service. Operator IP services may include access to the Internet, an intranet, an IP multimedia subsystem (IMS), or a packet switched (PS) streaming service.

[0067] At least some of the network devices (e.g., base station 105) may include subcomponents such as access network entities, which may be examples of access node controllers (ANCs). Each access network entity may communicate with UE 115 through multiple other access network transport entities (which may be referred to as radio heads, smart radio heads, or transmit / receive points (TRPs)). In some configurations, the various functions of each access network entity or base station 105 may be distributed across various network devices (e.g., radio heads and access network controllers) or merged into a single network device (e.g., base station 105).

[0068] The wireless communication system 100 can operate using one or more frequency bands, typically in the range of 300 megahertz (MHz) to 300 gigahertz (GHz). Typically, 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 approximately one decimeter to one meter in length. UHF waves may be blocked or redirected by buildings and environmental features. However, for macro cells, the waves can penetrate structures sufficiently to provide services to UEs 115 located indoors. Transmission of UHF waves can be associated with smaller antennas and shorter distances (e.g., less than 100 km) compared to transmission of smaller frequencies and longer waves using the high frequency (HF) or very high frequency (VHF) portion of the spectrum below 300 MHz.

[0069] The wireless communication system 100 may also operate in the Super High Frequency (SHF) region using frequency bands from 3 GHz to 30 GHz (also referred to as centimeter bands). The SHF region includes frequency bands such as the 5 GHz Industrial, Scientific, and Medical (ISM) band, which may be opportunistically used by devices that can tolerate interference from other users.

[0070] The wireless communication system 100 may also operate in the extremely high frequency (EHF) region of the spectrum (e.g., from 30 GHz to 300 GHz), also referred to as the millimeter band. In some examples, the wireless communication system 100 may support millimeter wave (mmW) communications between the UE 115 and the base station 105, and the EHF antennas of the corresponding devices may be even smaller and more closely spaced than the UHF antennas. In some cases, this may facilitate the use of antenna arrays within the UE 115. However, the propagation of EHF transmissions may suffer from even greater atmospheric attenuation and shorter distances than SHF or UHF transmissions. The technology disclosed herein may be employed across transmissions using one or more different frequency regions, and the designated use of frequency bands across these frequency regions may differ according to countries or regulatory agencies.

[0071] In some cases, the wireless communication system 100 can utilize both licensed and unlicensed radio frequency spectrum bands. For example, the wireless communication system 100 can adopt license assisted access (LAA), LTE unlicensed (LTE-U) wireless access technology, or NR technology in an unlicensed band (e.g., a 5GHz ISM band). When operating in an unlicensed radio frequency spectrum band, a wireless device (e.g., a base station 105 and a UE 115) can use a listen-before-talk (LBT) process to ensure that the frequency channel is idle before sending data. In some cases, operations in an unlicensed band can be based on a carrier aggregation configuration (e.g., LAA) in conjunction with a component carrier operating in a licensed band. Operations in an unlicensed spectrum can include downlink transmissions, uplink transmissions, peer-to-peer transmissions, or a combination of these items. Duplexing in an unlicensed spectrum can be based on frequency division duplexing (FDD), time division duplexing (TDD), or a combination of both.

[0072] In some examples, the base station 105 or UE 115 may be equipped with multiple antennas, which may be used to employ techniques such as transmit diversity, receive diversity, multiple-input multiple-output (MIMO) communication, or beamforming. For example, the wireless communication system 100 may use a transmission scheme between a transmitting device (e.g., a base station 105) and a receiving device (e.g., a UE 115), wherein the transmitting device is equipped with multiple antennas and the receiving device is equipped with one or more antennas. MIMO communication may employ multipath signal propagation to improve spectral efficiency by transmitting or receiving multiple signals via different spatial layers, which may be referred to as spatial multiplexing. For example, multiple signals may be transmitted by a transmitting device via different antennas or different combinations of antennas. Similarly, multiple signals may be received by a receiving device via different antennas or different combinations of antennas. Each of the multiple signals may be referred to as a separate spatial stream and may carry bits associated with the same data stream (e.g., the same codeword) or different data streams. Different spatial layers may be associated with different antenna ports for channel measurement and reporting. MIMO technology includes single-user MIMO (SU-MIMO) (where multiple spatial layers are sent to the same receiving device) and multi-user MIMO (MU-MIMO) (where multiple spatial layers are sent to multiple devices).

[0073] Beamforming (which may also be referred to as spatial filtering, directional transmission, or directional reception) is a signal processing technique that can be used at a transmitting device or a receiving device (e.g., a base station 105 or a UE 115) to form or direct an antenna beam (e.g., a transmit beam or a receive beam) along a spatial path between the transmitting device and the receiving device. Beamforming can be achieved by combining signals transmitted via antenna elements of an antenna array so that signals propagating in a particular orientation relative to the antenna array experience constructive interference, while other signals experience destructive interference. Adjustments to signals transmitted via antenna elements may include the transmitting device or the receiving device applying certain amplitude and phase offsets to signals carried via each of the antenna elements associated with the device. Adjustments associated with each of the antenna elements may be defined by a set of beamforming weights associated with a particular orientation (e.g., relative to the antenna array of the transmitting device or the receiving device, or relative to some other orientation).

[0074] In one example, the base station 105 may use multiple antennas or antenna arrays to perform beamforming operations for directional communication with the UE 115. For example, some signals (e.g., synchronization signals, reference signals, beam selection signals, or other control signals) may be sent multiple times by the base station 105 in different directions, and the some signals may include signals sent according to different beamforming weight sets associated with different transmission directions. The transmissions in different beam directions may be used (e.g., by the base station 105 or a receiving device (e.g., UE 115)) to identify the beam direction for subsequent transmission and / or reception by the base station 105.

[0075] Some signals (e.g., data signals associated with a particular receiving device) may be transmitted by base station 105 in a single beam direction (e.g., a direction associated with a receiving device (e.g., UE 115)). In some examples, the beam direction associated with transmissions along a single beam direction may be determined based at least in part on signals transmitted in different beam directions. For example, UE 115 may receive one or more of the signals transmitted by base station 105 in different directions, and UE 115 may report to base station 105 an indication of the signal received by it having the highest signal quality or otherwise acceptable signal quality. Although these techniques are described with reference to signals transmitted by base station 105 in one or more directions, UE 115 may employ similar techniques to transmit signals multiple times in different directions (e.g., for identifying beam directions for subsequent transmissions or receptions by UE 115) or to transmit signals in a single direction (e.g., for transmitting data to a receiving device).

[0076] When receiving various signals (e.g., synchronization signals, reference signals, beam selection signals, or other control signals) from base station 105, a receiving device (e.g., UE 115, which may be an example of a mmW receiving device) may try multiple receiving beams. For example, the receiving device may try multiple receiving directions by receiving via different antenna subarrays, by processing received signals according to different antenna subarrays, by receiving according to different sets of receiving beamforming weights applied to signals received at multiple antenna elements of an antenna array, or by processing received signals according to different sets of receiving beamforming weights applied to signals received at multiple antenna elements of an antenna array (any of the above operations may be referred to as "listening" according to different receiving beams or receiving directions). In some examples, the receiving device may use a single receiving beam to receive along a single beam direction (e.g., when receiving a data signal). A single receive beam can be aligned in a beam direction determined based at least in part on listening according to different receive beam directions (e.g., a beam direction determined to have the highest signal strength, the highest signal-to-noise ratio, or otherwise acceptable signal quality based at least in part on listening according to multiple beam directions).

[0077] In some cases, the antennas of a base station 105 or a UE 115 may be located within one or more antenna arrays that 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 cases, the antennas or antenna arrays associated with a base station 105 may be located at different geographical locations. A base station 105 may have an antenna array having multiple rows and columns of antenna ports that the base station 105 may use to support beamforming for communications with a UE 115. Likewise, a UE 115 may have one or more antenna arrays that may support various MIMO or beamforming operations.

[0078] In some cases, the wireless communication system 100 can be a packet-based network operated according to a layered protocol stack. In the user plane, the communication at the bearer or packet data convergence protocol (PDCP) layer can be based on IP. The radio link control (RLC) layer can perform packet segmentation and reorganization to communicate on the logical channel. The MAC layer can perform priority processing and multiplexing of logical channels to transport channels. The MAC layer can also use HARQ to provide retransmission at the MAC layer to improve link efficiency. In the control plane, the RRC protocol layer can provide the establishment, configuration and maintenance of the RRC connection (which supports the radio bearer for user plane data) between the UE 115 and the base station 105 or the core network 130. At the physical layer, the transport channel can be mapped to the physical channel.

[0079] In some cases, UE 115 and base station 105 can support retransmission of data to increase the possibility that the data is successfully received. HARQ feedback is a technique that increases the possibility that data is correctly received on communication link 125. HARQ can include a combination of error detection (e.g., using cyclic redundancy check (CRC)), forward error correction (FEC) and retransmission (e.g., automatic repeat request (ARQ)). HARQ can improve the throughput at the MAC layer under poor radio conditions (e.g., signal and noise conditions). In some cases, a wireless device can support HARQ feedback for the same time slot, wherein the device can provide HARQ feedback for data received in the previous symbol in the time slot in a specific time slot. In other cases, the device can provide HARQ feedback in subsequent time slots or according to some other time interval.

[0080] The time interval in LTE or NR may be expressed in terms of a basic time unit (which may be referred to as T s =1 / 30,720,000 seconds). The time intervals of the communication resources can be organized according to radio frames each having a duration of 10 milliseconds (ms), where the frame period can be represented as T f =307,200T s . A radio frame may be identified by a system frame number (SFN) ranging from 0 to 1023. Each frame may include 10 subframes numbered from 0 to 9, and each subframe may have a duration of 1 ms. A subframe may be further divided into 2 slots, each slot having a duration of 0.5 ms, and each slot may contain 6 or 7 modulation symbol periods (e.g., depending on the length of a cyclic prefix added in front of each symbol period). Excluding the cyclic prefix, each symbol period may contain 2048 sampling periods. In some cases, a subframe may be the minimum scheduling unit of the wireless communication system 100 and may be referred to as a transmission time interval (TTI). In other cases, the minimum scheduling unit of the wireless communication system 100 may be shorter than a subframe or may be dynamically selected (e.g., in a burst of a shortened TTI (sTTI) or in a component carrier selected to use sTTI).

[0081] In some wireless communication systems, a time slot may be further divided into a plurality of micro-slots comprising one or more symbols. In some instances, a symbol of a micro-slot or a micro-slot may be a minimum scheduling unit. Each symbol may vary in duration according to, for example, a subcarrier spacing or a frequency band of operation. In addition, some wireless communication systems may implement time slot aggregation, wherein a plurality of time slots or micro-slots are aggregated together and used for communication between a UE 115 and a base station 105.

[0082] The term "carrier" refers to a set of radio frequency spectrum resources having a defined physical layer structure for supporting communications on the communication link 125. For example, a carrier of the communication link 125 may include a portion of a radio frequency spectrum band that operates according to a physical layer channel for a given radio access technology. Each physical layer channel may carry user data, control information, or other signaling. A carrier may be associated with a predefined frequency channel (e.g., an Evolved Universal Mobile Telecommunications System Terrestrial Radio Access (E-UTRA) Absolute Radio Frequency Channel Number (EARFCN)) and may be placed according to a channel grid to be discovered by a UE 115. A carrier may be a downlink or an uplink (e.g., in FDD mode), or may be configured to carry downlink and uplink communications (e.g., in TDD mode). In some examples, a signal waveform sent on a carrier may be composed of multiple subcarriers (e.g., using a multi-carrier modulation (MCM) technique such as orthogonal frequency division multiplexing (OFDM) or discrete Fourier transform spread OFDM (DFT-S-OFDM)).

[0083] The organization structure of the carrier may be different for different radio access technologies (e.g., LTE, LTE-A, LTE-A Professional, NR). For example, communications on a carrier may be organized according to TTIs or time slots, each of which may include user data and control information or signaling to support decoding of the user data. A carrier may also include dedicated acquisition signaling (e.g., synchronization signals or system information, etc.) and control signaling to coordinate operations for the carrier. In some examples (e.g., in a carrier aggregation configuration), a carrier may also have acquisition signaling or control signaling to coordinate operations for other carriers.

[0084] Physical channels may be multiplexed on a carrier according to various techniques. For example, a time division multiplexing (TDM) technique, a frequency division multiplexing (FDM) technique, or a hybrid TDM-FDM technique may be used to multiplex a physical control channel and a physical data channel on a downlink carrier. In some examples, the control information sent in the physical control channel may be distributed in a cascaded manner between different control regions (e.g., between a common control region or common search space and one or more UE-specific control regions or UE-specific search spaces).

[0085] A carrier may be associated with a particular bandwidth of radio frequency spectrum, and in some examples, the carrier bandwidth may be referred to as the "system bandwidth" of the carrier or wireless communication system 100. For example, the carrier bandwidth may be one of a plurality of predetermined bandwidths for a carrier for a particular radio access technology (e.g., 1.4, 3, 5, 10, 15, 20, 40, or 80 MHz). In some examples, each served UE 115 may be configured to operate on part or all of the carrier bandwidth. In other examples, some UEs 115 may be configured to operate using a narrowband protocol type associated with a predefined portion or range (e.g., a set of subcarriers or RBs) within a carrier (e.g., an "in-band" deployment of a narrowband protocol type).

[0086] In a system using MCM technology, a resource element may include a symbol period (e.g., the duration of a modulation symbol) and a subcarrier, where the symbol period and the subcarrier spacing are 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). Therefore, the more resource elements received by UE 115 and the higher the order of the modulation scheme, the higher the data rate for UE 115 can be. In a MIMO system, wireless communication resources may refer to a combination of radio frequency spectrum resources, time resources, and space resources (e.g., space layers), and the use of multiple space layers may further increase the data rate for communication with UE 115.

[0087] A device (e.g., base station 105 or UE 115) of wireless communication system 100 may have a hardware configuration that supports communication on a specific carrier bandwidth, or may be configurable to support communication on one of a set of carrier bandwidths. In some examples, wireless communication system 100 may include base station 105 and / or UE 115 that supports simultaneous communication via carriers associated with more than one different carrier bandwidths.

[0088] The wireless communication system 100 may support communication with the UE 115 on multiple cells or carriers, a feature that may be referred to as 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 with both FDD component carriers and TDD component carriers.

[0089] In some cases, the wireless communication system 100 can utilize an enhanced component carrier (eCC). An eCC can be characterized by one or more characteristics including: a wider carrier or frequency channel bandwidth, a shorter symbol duration, a shorter TTI duration, or a modified control channel configuration. In some cases, an eCC can be associated with a carrier aggregation configuration or a dual connectivity configuration (e.g., when multiple serving cells have suboptimal or non-ideal backhaul links). An eCC can also be configured for use in an unlicensed spectrum or a shared spectrum (e.g., where more than one operator is allowed to use the spectrum). An eCC characterized by a wide carrier bandwidth can include one or more segments that can be used by a UE 115 that cannot monitor the entire carrier bandwidth or is otherwise configured to use a limited carrier bandwidth (e.g., to save power).

[0090] In some cases, an eCC may utilize a different symbol duration than other component carriers, which may include using a reduced symbol duration compared to the symbol duration of the other component carriers. A shorter symbol duration may be associated with an increased spacing between adjacent subcarriers. A device (e.g., a UE 115 or a base station 105) utilizing an eCC may transmit a wideband signal (e.g., according to a frequency channel or carrier bandwidth of 20, 40, 60, 80 MHz, etc.) with a reduced symbol duration (e.g., 16.67 microseconds). A TTI in an eCC may include one or more symbol periods. In some cases, the TTI duration (i.e., the number of symbol periods in a TTI) may be variable.

[0091] The wireless communication system 100 may be an NR system that may utilize any combination of licensed, shared, and unlicensed spectrum bands, as well as other spectrum bands. The flexibility of eCC symbol duration and subcarrier spacing may allow eCC to be used across multiple spectrums. In some examples, NR shared spectrum may improve spectrum utilization and spectrum efficiency, particularly through dynamic vertical (e.g., across the frequency domain) and horizontal (e.g., across the time domain) sharing of resources.

[0092] In a sidelink communication configuration, one or more UEs 115 may communicate directly with each other over a communication link. A transmitting UE 115 may perform RLM over a communication link with one or more other receiving UEs 115. Conventionally, RLM over a cellular link between a base station 105 and a UE 115 may typically include monitoring of SSBs transmitted by the UE 115 or the base station 105 or measurements of a radio link using CSI-RS transmitted by the UE 115 or the base station 105. In sidelink communications between one or more UEs 115, SSBs and CSI-RS may not always be available or reliable.

[0093] Therefore, the transmitting UE 115 may perform RLM in the sidelink configuration by monitoring HARQ feedback from other receiving UEs 115 based on an initial data transmission of the transmitting UE 115. Based on the first HARQ feedback failure, the transmitting UE 115 may start a counter or timer to quantify the number of HARQ feedback failures or the amount of time corresponding to the number of HARQ feedback failures. When the counter or timer reaches a threshold value, the transmitting UE 115 may declare RLF in the sidelink channel and may initiate an action to reconnect with one or more other receiving UEs 115. In some cases, after declaring RLF, the transmitting UE 115 may report the RLF to the scheduling base station 105 via RRC signaling or by sending a request for connection reestablishment with one or more receiving UEs 115 to the base station 105. In addition, when RLF is declared, the transmitting UE 115 may stop sending data to one or more receiving UEs 115.

[0094] Additionally or alternatively, one of the receiving UEs 115 may also monitor and detect whether an RLF occurs based on the use of a timer. For example, the receiving UE 115 may start a timer when no sidelink transmission is received, and may declare an RLF when the timer expires. In some cases, the receiving UE 115 may start a timer when a data transmission is not received, when a data transmission should be received (e.g., as indicated by the transmitting UE 115, based on periodic scheduling, etc.) but is not received, when the SCI is not successfully decoded, when the SCI is not received, when the SCI is successfully decoded but the data transmission indicated by the SCI is not decoded, and the like. If the SCI is decoded before the timer expires, the receiving UE 115 may reset the timer and begin counting down after the next occurrence of a failed SCI decode. Subsequently, after detecting the RLF, the receiving UE 115 may report the RLF to the base station 105 (e.g., the scheduling base station 105 or the anchor base station 105 for the receiving UE 115) via RRC signaling, or report the RLF to the sending UE 115 via sidelink signaling (e.g., MAC CE, RRC, etc.). In some cases, the receiving UE 115 may release the sidelink communication with the sending UE 115 based on the RLF.

[0095] Figure 2 An example of a wireless communication system 200 that supports processing of sidelink RLF according to various aspects of the present disclosure is shown. The wireless communication system 200 may be an example of the wireless communication system 100. The wireless communication system 200 may include a base station 105-a and UEs 115-a and 115-b. The base station 105-a may be as described above. Figure 1 UE 115-a and 115-b may be examples of base stations 105 described above. Figure 1 1. An example of a UE 115 is depicted. Base station 105-a may serve one or more UEs 115 within coverage area 110-a. Base station 105-a may communicate with one or more UEs 115 via communication link 215. UE 115-a and UE 115-b may be connected in a sidelink communication configuration and may communicate on sidelink channel 205. Wireless communication system 200 may represent an example of a unicast sidelink configuration, but the RLM techniques described herein may also be applied to multicast or broadcast sidelink configurations.

[0096] UE 115-a may send a first message 210 on the sidelink channel 205. For example, UE 115-a may send message 210 in a first TTI (e.g., in time slot N). Based on the transmission of the first message 210, UE 115-a may expect to receive HARQ feedback, such as an ACK / NACK message, from UE 115-b. UE 115-a may monitor the HARQ feedback in a second TTI (e.g., time slot N+K). Based on monitoring the HARQ feedback in the second TTI, UE 115-a may start a counter or timer that may count the number of consecutive HARQ feedback failures. When the counter counts to a threshold number of HARQ failures or the timer counts down to zero, UE 115-a may declare RLF.

[0097] In some cases, UE 115-a may receive an ACK from UE 115-b on the sidelink channel 205 in the expected TTI, and may correctly decode the ACK. In other cases, there may be a failure of HARQ feedback from UE 115-b. The HARQ feedback failure may be caused by one or more reasons. For example, UE 115-b may send a NACK to UE 115-a, where the NACK indicates a HARQ feedback failure. Additionally or alternatively, UE 115-a may expect and receive HARQ feedback from UE 115-b, where UE 115-b sends an ACK with HARQ feedback, but UE 115-a may not be able to decode the HARQ feedback. Even if UE 115-b sends an ACK, the inability of UE 115-a to decode the HARQ feedback may also be regarded as a HARQ feedback failure. Additionally or alternatively, UE 115-a may correctly decode the HARQ feedback, but the HARQ feedback may indicate a NACK. Therefore, the NACK may also be regarded as a HARQ feedback failure.

[0098] If no HARQ feedback is received in time slot N+K (e.g., or another HARQ feedback failure occurs, as previously described), UE 115-a may start a counter or timer in time slot N+K. If no HARQ feedback is received in time slot N+K or in another later time slot before the counter meets a threshold or the timer counts to zero, UE 115-a may declare RLF. If HARQ feedback is received before the counter or timer expires (e.g., and HARQ feedback containing an ACK is successfully decoded), UE 115-a may reset the counter or timer. In some cases, UE 115-a may start the counter or timer again at the next instance of HARQ feedback that failed in the time slot.

[0099] In the event that UE 115-a declares RLF of sidelink 205 based on a counter or timer reaching a threshold, UE 115-a may perform actions to reestablish a connection with UE 115-b. These actions for reestablishing a connection with UE 115-b may involve communicating with base station 105-a over link 215-a to reestablish contact with UE 115-b over communication link 215-b.

[0100] A counter (or a timer associated with a counter) started by UE 115-a based on monitoring HARQ feedback may have a specified value determined based on one or more parameters. In some cases, the counter may have a common preconfigured value. The preconfigured value may be based on a wireless communication standard (e.g., 3GPP) and may be configured at UE 115-a based on control signaling from base station 105-a or another device (e.g., UE 115-b or another UE 115). In some cases, the counter may be negotiated between UE 115-a and UE 115-b during the establishment of a sidelink connection (e.g., via RRC signaling). The counter value may be negotiated based on one or more UE communication parameters in the UE communication parameters (e.g., the speed of UE 115 (the speed of UE 115-a, the speed of UE 115-b, or the relative speed between UE 115-a and 115-b), congestion level, data priority, application type, or another communication parameter).

[0101] For example, in situations where the congestion level is low, the counter or timer may have a larger value. The congestion level may be measured based on a channel quality measurement, such as reference signal received power (RSRP), reference signal received quality (RSRQ), channel busy ratio (CBR), or another congestion measurement. UE 115-a and UE 115-b may determine a congestion measurement, where the congestion measurement may be negotiated between UE 115-a and 115-b. In other cases, base station 105-a may signal congestion measurements to one or both of UE 115-a and 115-b based on measurements performed by base station 105-a or measurements signaled to base station 105-a. The congestion measurement may then be mapped to a timer value.

[0102] The counter or timer may also be mapped based on data priority. For example, if the data priority is low, the counter may have a larger value. The data priority may be based on the relative priority of the message sent from the sending UE to the receiving UE compared to other data transmissions of the sending UE or other communications within the system. The counter may also have a smaller value if the data transmission is for safety information transmission. Safety message transmission may be an example of a high priority message.

[0103] A counter or timer may also have a value within a specified range rather than having an exact value. The counter value range may have an upper limit and a lower limit. The upper limit and the lower limit may be predefined or preconfigured for UE 115-a and 115-b (e.g., based on a wireless communication standard or control signaling from a base station, or both). The range may also be negotiated between UE 115-a and UE 115-b in a sidelink system. The range of counter values ​​may depend on the data priority or the application type of data transmission. For example, if the data type is a high priority safety message, the counter may still have a value range, but the upper limit of the value range for the timer may be smaller, so that the counter has a smaller value.

[0104] The value of the counter or timer may be indicated by a network node (e.g., base station 105-a). The indication of the value of the counter or timer by the network node may apply to situations where sidelink communications are scheduled by base station 105-a. For example, base station 105-a may select the counter value based on UE speed or congestion level. UEs 115-a and 115-b (e.g., and any additional UEs 115 in coverage area 110-a) may report UE speed or congestion level to base station 105-a.

[0105] A counter or timer may be activated based on UE 115-a monitoring a particular TTI for HARQ feedback from UE 115-b. The counter may be incremented each time UE 115-a detects a HARQ feedback failure. In some cases, the counter may be incremented until a threshold number of HARQ feedback failures occur, at which point UE 115-b may declare RLF. In other cases, the counter may be or correspond to a timer that may count down based on a value of the timer. The value of the timer may be determined based on the same parameters as the value of the counter (e.g., pre-configuration, UE speed, congestion level, application type, data priority, etc.).

[0106] As described above, UE 115-a may be referred to as a sending UE 115-a (e.g., a transmitting UE 115, a first UE 115, etc.) based on sending the first message 210 to UE 115-b on the sidelink channel 205, and correspondingly, UE 115-b may be referred to as a receiving UE 115-b (e.g., a receiving UE 115, a second UE 115, etc.) based on receiving the first message 210 on the sidelink channel 205. In some cases, receiving UE 115-b may monitor and detect RLF for the sidelink channel 205 based on a timer similar to the timer described herein used by transmitting UE 115-a to perform an RLM process to monitor HARQ feedback from receiving UE 115-b.

[0107] For example, a timer used by the receiving UE 115-b to detect RLF may have a specified value determined based on one or more parameters. In some cases, the timer may have a common preconfigured value as described herein. Additionally or alternatively, as described herein, the timer may be negotiated between the UE 115-a and the UE 115-b during establishment of the sidelink connection (e.g., based on one or more UE communication parameters, such as the speed of the UE 115, the congestion level, the data priority, the application type, or another communication parameter). In some cases, the timer may also be mapped based on the data priority as described herein. Additionally or alternatively, the value of the timer may be indicated by a network node (e.g., the base station 105-a), also as described herein. Additionally, the timer used by the receiving UE 115-b to detect RLF may also have a value within a specified range, rather than having an exact value, as described herein.

[0108] The timer used by the receiving UE 115-b to detect RLF may count the elapsed time of consecutive failures of decoding of data transmissions from the transmitting UE 115-a. For example, the receiving UE 115-b may start the timer when no data transmission is received. In some cases, the receiving UE 115-b may successfully decode a first data transmission in time slot n, but then fail to decode a second data transmission in time slot n+1. Therefore, the receiving UE 115-b may count down the timer starting from time slot n+1.

[0109] Additionally or alternatively, the receiving UE 115-b may start a timer from the time when data should be received. For example, the sending UE 115-a may indicate that there will be a data transmission in time slot n (e.g., based on a resource reservation process), but the receiving UE 115-b may fail to decode the data transmission in time slot n. Therefore, the receiving UE 115-b may count down the timer from time slot n. In some cases, the data transmission from the sending UE 115-a may be periodic (e.g., with a period k). Therefore, the receiving UE 115-b may identify when the periodic data transmission should be sent by the sending UE 115-a and received at the receiving UE 115-b. For example, the receiving UE 115-b may successfully decode the periodic data transmission in time slot n, but may not be able to decode the next periodic data transmission that occurs in time slot n+k (e.g., based on period k). Therefore, the receiving UE 115-b may count down the timer from time slot n+k.

[0110] For the described scenario where the receiving UE 115-b is monitoring for RLF, the receiving UE 115-b may start counting down a timer or continue counting down a counter based on a decoding failure of a data transmission. Such a failure to decode a data transmission may include: no SCI from a sending UE 115-a (e.g., a data sender) in the data transmission can be decoded, no SCI from the sending UE 115-a can be decoded, the SCI can be decoded but data decoding of the data transmission fails, or a combination thereof.

[0111] In some cases, the receiving UE 115-b, the sending UE 115-a, or both may reconfigure the value of the timer based on one or more parameter changes. For example, when one or more of the UE communication parameters change since the last negotiation of the timer, a renegotiation of the timer value may be triggered between UE 115-a and UE 115-b. For example, a change in UE speed may trigger a renegotiation of the timer value. In some cases, the UE speed may change from a high-speed category to a medium-speed category, the difference in UE speed may exceed a threshold, or a combination thereof. Additionally or alternatively, a change in the congestion level may trigger a renegotiation of the timer value (e.g., the difference in measured RSRQ exceeds a threshold). In some cases, the timer value renegotiation may also be triggered by a change in the data priority of the data sent on the sidelink channel 205.

[0112] After detecting the RLF, the sending UE 115-a may report the RLF to the base station 105-a (e.g., a scheduling base station) via RRC signaling (e.g., higher layer signaling) or by sending a request to the base station 105-a for reestablishing a connection with the receiving UE 115-b. Additionally or alternatively, the receiving UE 115-b may also report the RLF to the base station 105-a via RRC signaling, or report the RLF to the sending UE 115-a via a MAC CE. In some cases, the receiving UE 115-b may release the sidelink channel 205 (e.g., a sidelink communication link) with the sending UE 115-a based on the RLF. Similarly, when the RLF is declared or determined, the sending UE 115-a may stop sending data to the receiving UE 115-b.

[0113] Figure 3A An example of a time slot diagram 301 for supporting a process for sidelink RLF in accordance with aspects of the present disclosure is shown. A UE 115 operating in a sidelink configuration may receive and send messages based on the time slot diagram 301. First, a sending UE 115 (e.g., as described with respect to Figure 2 The described UE 115-a) may send a data transmission 310 based on the transmission configuration 305-a. Second, a receiving UE 115 (e.g., UE 115-b) may send a HARQ feedback transmission 315 based on the transmission configuration 305-b. The timer 325-a may be initiated by the transmitting UE 115 (e.g., UE 115-a) based on monitoring the HARQ feedback transmission 315 received from the receiving UE 115 (e.g., UE 115-b).

[0114] The first UE 115 (e.g., UE 115-a) may send a data transmission 310 in a particular time slot according to the transmission configuration 305-a. For example, the first UE 115 may send a first data transmission 310-a in a particular time slot or TTI N based on the transmission configuration 305-a. The first UE 115 may send the first data transmission 310-a in a sidelink communication channel (e.g., sidelink channel 205) to the second UE 115. Based on sending the first data transmission 310-a, the first UE 115 may monitor a HARQ feedback transmission 315-a from the second UE 115 in the time slot 320-a.

[0115] In some cases, the HARQ feedback transmission 315-a may correspond to a HARQ feedback failure. A HARQ feedback failure may occur based on the HARQ feedback transmission 315-a being decoded by the first UE, but the HARQ feedback transmission 315-a includes a NACK feedback transmission. In other cases, the HARQ feedback failure may include that the HARQ feedback transmission 315-a is not correctly decoded at the first UE 115. Additionally or alternatively, the HARQ feedback failure may include that the first UE 115 does not receive the HARQ feedback transmission 315-a. In the event of any of these HARQ feedback failures, the first UE 115 may start a timer 325 based on determining that a HARQ feedback failure occurs.

[0116] For example, a HARQ feedback failure may occur in a time slot 320-a (e.g., a time slot corresponding to the time slot in which the second UE 115 is sending the HARQ feedback transmission 315-a). Based on the HARQ feedback failure, the first UE 115 may start a timer 325-a. The timer 325-a may have a time length based on a preconfiguration or based on one or more parameters (such as data priority, speed of the first or second UE, congestion level, or another UE parameter, etc.). The timer 325-a may count down for a configured time length until a threshold time period (counts down to zero or counts to a configured time) or until the HARQ feedback is successfully received. If the timer 325-a counts down to zero (e.g., or counts to a configured time or threshold) before the first UE 115 successfully receives the HARQ feedback, the first UE 115 may declare that an RLF has occurred.

[0117] Alternatively, the HARQ feedback may be received before the timer expires. Figure 3B Another example of a time slot diagram 302 for supporting a process for sidelink RLF in accordance with aspects of the present disclosure is shown. A UE 115 operating in a sidelink configuration may receive and send messages based on the time slot diagram 302. First, a sending UE 115 (e.g., as described with respect to Figure 2The described UE 115-a) may send a data transmission 310 based on the transmission configuration 305-c. Second, a receiving UE 115 (e.g., UE 115-b) may send a HARQ feedback transmission 315 based on the transmission configuration 305-d. The timer 325-b may be initiated by the transmitting UE 115 (e.g., UE 115-a) based on monitoring the HARQ feedback transmission 315 received from the receiving UE 115 (e.g., UE 115-b).

[0118] The first UE 115 (e.g., UE 115-a) may send a data transmission 310 in a particular time slot according to the transmission configuration 305-c. For example, the UE 115 may send a first data transmission 310-b in a particular time slot N based on the transmission configuration 305-c. The first UE 115 may send the first data transmission 310-b in a sidelink communication channel (e.g., sidelink channel 205) to the second UE 115. Based on sending the first data transmission 310-b, the first UE 115 may monitor for a HARQ feedback transmission 315-b from the second UE 115 in a time slot 320-c (e.g., time slot N+K).

[0119] Due to the HARQ feedback failure, the first UE 115 may not receive the expected HARQ feedback in the time slot 320-c. Based on the HARQ feedback failure, the first UE 115 can start a timer 325-b, which can count down to zero until interrupted by successful HARQ feedback. The length of the timer 325-b can be determined based on one or more parameters. As the timer 325-b counts down, the first UE 115 can send another data transmission 310-c, and a HARQ feedback transmission 315-c in response to the data transmission 310-c from the second UE 115 can be expected in the time slot 320-d. In some cases, the first UE 115 may not correctly receive the HARQ feedback transmission 315-c in the time slot 320-d (e.g., or the HARQ feedback transmission 315-c contains a NACK), and the timer 325-b can continue to count down. As the timer 325-b continues to count down, the first UE 115 may send another data transmission 310-d to the second UE 115 on the sidelink communication channel. The second UE 115 may send a HARQ feedback transmission 315-d to the first UE 115 on the sidelink channel in the time slot 320-e, wherein the HARQ feedback transmission 315-d includes feedback for the data transmission 310-d. The first UE 115 may receive the HARQ feedback transmission 315-d in the time slot 320-e, and may successfully decode the HARQ feedback transmission 315-d (e.g., successfully decode the HARQ feedback transmission 315-d to determine that the HARQ feedback transmission 315-d includes an ACK). Therefore, the HARQ feedback transmission 315-d may be a successful HARQ feedback transmission. Based on the successful HARQ feedback transmission, the first UE 115 may reset the timer 325-b and may not declare RLF.

[0120] In the event of a subsequent HARQ feedback failure, the first UE 115 may restart the timer 325. For example, the first UE 115 may send a data transmission 310-e at a later point in time. Based on the data transmission 310-e, the first UE may monitor the time slot 320-f for the expected HARQ feedback transmission 315-e. In some cases, the first UE may receive the HARQ feedback transmission 315-e, successfully decode the HARQ feedback transmission 315-e, and determine that the HARQ feedback transmission 315-e includes an ACK. In other cases, the first UE 115 may not receive the HARQ feedback transmission 315-e, may receive the HARQ feedback transmission 315-e but cannot decode the HARQ feedback transmission 315-e, or may decode the HARQ feedback transmission 315-e and determine that the HARQ feedback transmission 315-e includes a NACK. In any of these situations, the first UE 115 can determine that the HARQ feedback transmission 315-e includes a HARQ feedback failure, and the first UE 115 can therefore start a timer 325-c, which can count to a threshold time length unless the HARQ feedback transmission is a successful transmission.

[0121] Timer 325-c may have the same timer value as timer 325-b, or may have a different value. For example, in the event of a timer reconfiguration, timer 325-c may have a different value. Renegotiation or reconfiguration of timer 325 may occur in the event that one or more UE parameters have changed since the previous negotiation or renegotiation of timer 325. Renegotiation of timer 325 may correspond to an increase or decrease in the timer value. For example, one or both of the first UE 115 and the second UE 115 may change speed. The UE speed or the relative speed between UEs may change from a high speed category to a medium speed category, which may require a change in the timer value. Alternatively, the relative UE speed may exceed a higher or lower threshold boundary, which may also result in a renegotiation of the timer value.

[0122] The congestion level within the communication system may also change, which may affect the renegotiation of the timer. For example, the first or second UE 115 may monitor the RSRQ of the communication channel and may determine that the RSRQ meets (e.g., exceeds) a threshold. Such a determination that the RSRQ meets the threshold may result in the renegotiation of the timer. In another case, the data priority of the data transmission 310 may change. In these cases, the timer 325 may have a value determined based on a data priority of the first data transmission 310. When the data priority changes, the value of the timer 325 may increase (e.g., in the case of a lower priority) or the value of the timer 325 may decrease (e.g., in the case of an increased priority). In other cases, the serving base station 105 may indicate to one or more UEs 115 to change the timer value. The indication may be based on a parameter of a change detected by one of the UEs 115 communicating on the sidelink or signaled to the serving base station 105, or based on a parameter of a change from another UE. Any reason for the timer negotiation may initiate a timer renegotiation at the first UE 115. In some cases, the value of timer 325 may be indicated by base station 105 to UE 115. In other cases, UE 115 may determine to change timer 325 without input from base station 105.

[0123] In other cases, the first UE 115 may monitor HARQ feedback failure based on a counter that counts the number of failures rather than a timer 325 that counts down until successful HARQ feedback occurs.

[0124] Figure 4A An example of a time slot diagram 401 for supporting processing of sidelink RLF in accordance with aspects of the present disclosure is shown. The time slot diagram 401 may include an example of one or more UEs 115 communicating in a sidelink configuration. A UE 115 sending a data transmission to another UE 115 may count the number of consecutive HARQ feedback failures based on a counter 425. A UE 115 operating in a sidelink configuration may receive and send messages based on the time slot diagram 401. First, a sending UE 115 (e.g., regarding a Figure 2 UE 115-a described, or Figure 3A and 3B A first UE 115 (e.g., a first UE 115) may send a data transmission 410 according to the example transmission configuration 405-a. Figure 2 UE 115-b described, or Figure 3A and 3BThe second UE 115 described above may send a HARQ feedback transmission 415 based on the transmission configuration 405-b. The counter 425-a may be initiated by the first, transmitting UE 115 (e.g., UE 115-a) based on monitoring the HARQ feedback transmission 415 received from the second, receiving UE 115 (e.g., UE 115-b).

[0125] The first UE 115 (e.g., UE 115-a) may send a data transmission 410 in a particular time slot according to the transmission configuration 405-a. For example, the first UE 115 may send a first data transmission 410-a in a particular time slot N based on the transmission configuration 405-a. The first UE 115 may send the first data transmission 410-a in a sidelink communication channel (e.g., sidelink channel 205) to the second UE 115. Based on sending the first data transmission 410-a, the first UE 115 may monitor a HARQ feedback transmission 415-a from the second UE 115 in a time slot 420-a (e.g., time slot N+K).

[0126] In some cases, the HARQ feedback transmission 415-a may correspond to a HARQ feedback failure. The HARQ feedback failure may occur based on the HARQ feedback transmission 415-a being a NACK feedback transmission. In other cases, the HARQ feedback failure may include the HARQ feedback transmission 415-a not being correctly decoded at the first UE 115 (e.g., regardless of whether the HARQ feedback transmission 415-a includes an ACK or a NACK). Additionally or alternatively, the HARQ feedback failure may include the first UE 115 not receiving the HARQ feedback transmission 415-a. In any case of a HARQ feedback failure, the first UE 115 may start a counter 425 based on the HARQ feedback failure.

[0127] For example, a HARQ feedback failure may occur in a time slot 420-a (e.g., corresponding to a time slot in which the second UE 115 is sending a HARQ feedback transmission 415-a). Based on the HARQ feedback failure, the first UE 115 may start a counter 425-a. The counter 425-a may have a preconfigured number of failures to be counted (e.g., a preconfigured threshold count number) based on one or more parameters (such as data priority, speed of the first or second UE, congestion level, or another UE parameter). The counter 425-a may be incremented each time a HARQ feedback failure occurs until a HARQ feedback success occurs or until a preconfigured number of failures is reached.

[0128] If the counter 425-a counts to a preconfigured number of failures (e.g., a threshold number of failures) before the first UE 115 successfully receives the HARQ feedback, the first UE 115 may declare that an RLF has occurred. For example, the counter 425-a may be configured for a preconfigured number of failures of five counts. The first UE 115 may monitor the time slot 420-b for the HARQ feedback transmission 415-b based on the data transmission 410-b. The time slot 420-b may be the fifth time slot in which the UE 115 has monitored the HARQ feedback transmission 415 from the second UE 115. Subsequently, the fifth HARQ failure may occur in the time slot 420-b. At this point, the counter 425-a may have reached the threshold number of counts for a particular counter value. Therefore, the first UE 115 may declare an RLF and may continue to perform steps to resolve the RLF and resume sidelink communication with the second UE 115.

[0129] Alternatively, the HARQ feedback may be received before the counter 425 reaches the threshold. Figure 4B Another example of a time slot diagram 402 for supporting processing of sidelink RLF in accordance with aspects of the present disclosure is shown. UEs 115 operating in a sidelink configuration may receive and send messages based on the time slot diagram 402. A first, transmitting UE 115 may send a data transmission 410 based on a transmission configuration 405-c. A second, receiving UE 115 may send a HARQ feedback transmission 415 based on a transmission configuration 405-d. A counter 425-b may be initiated by a first, transmitting UE 115 (e.g., UE 115-a) based on monitoring HARQ feedback transmissions 415 received from a second, receiving UE 115.

[0130] The first UE 115 (e.g., UE 115-a) may send a data transmission 410 in a particular time slot according to the transmission configuration 405-c. For example, the first UE 115 may send a first data transmission 410-c in a particular time slot N based on the transmission configuration 405-c. The first UE 115 may send the first data transmission 410-c in a sidelink communication channel (e.g., sidelink channel 205) to the second UE 115. Based on sending the first data transmission 410-c, the first UE 115 may monitor a HARQ feedback transmission 415-c from the second UE 115 in a time slot 420-c (e.g., time slot N+K).

[0131] Due to the HARQ feedback failure, the first UE 115 may not detect the expected HARQ feedback in the time slot 420-c. Based on the HARQ feedback failure, the first UE 115 may start a counter 425-b. The counter 425-b may be incremented each time a HARQ feedback failure occurs, unless interrupted by an instance of successful HARQ feedback. The first UE 115 may send another data transmission 410-c, and may expect a HARQ feedback transmission 415-d from the second UE 115 in response to the data transmission 410-c in the time slot 420-d. In some cases, the first UE 115 may not detect the HARQ feedback transmission 415-d in the time slot 420-d, and the counter 425-b may be incremented based on the failure. The first UE 115 may send another data transmission 410-d to the second UE 115 on the sidelink communication channel. The second UE 115 may send a HARQ feedback transmission 415-e to the first UE 115 on the sidelink channel in response to the data transmission 410-d. The first UE 115 may receive the HARQ feedback transmission 415-e in the time slot 420-e and may successfully decode the HARQ feedback transmission 415-e, wherein the HARQ feedback transmission 415-e includes an ACK. Therefore, the HARQ feedback transmission 415-e may be a successful HARQ feedback transmission. Based on the successful HARQ feedback transmission, the first UE 115 may reset the counter 425-b and may not declare RLF.

[0132] In the event of a subsequent HARQ feedback failure, the first UE 115 may restart the counter 425. For example, the first UE 115 may send a data transmission 410-f at a later point in time. Based on the data transmission 410-f, the first UE 115 may monitor the time slot 420-f for the expected HARQ feedback transmission 415-f. In some cases, the first UE 115 may receive the HARQ feedback transmission 415-f, successfully decode the HARQ feedback transmission 415-f, and determine that the HARQ feedback transmission 415-f includes an ACK. In this case, the first UE 115 may not start the counter 425. In other cases, the first UE 115 may not receive the HARQ feedback transmission 415-f, may receive the HARQ feedback transmission 415-f but cannot decode the HARQ feedback transmission 415-f, or may be able to decode the HARQ feedback transmission 415-f and determine that the HARQ feedback transmission 415-f includes a NACK. In any of these cases, the first UE 115 may determine that the HARQ feedback transmission 415-f includes a HARQ feedback failure, and the first UE 115 may therefore start a counter 425-c.

[0133] Counter 425-c may have the same timer value as counter 425-b, or may have a different value. Counter 425-c may have a different value in the event that a counter reconfiguration occurs. Renegotiation or reconfiguration of counter 425 may occur in the event that one or more UE parameters have changed since a previous negotiation or renegotiation of counter 425. A renegotiation of a counter may correspond to an increase or decrease in the counter value, as previously described with reference to Figure 3A and 3B Timer renegotiation described in .

[0134] Figure 5 An example of a receiver RLF detection timer 500 that supports processing of a sidelink RLF in accordance with aspects of the present disclosure is shown. In some examples, the receiver RLF detection timer 500 can implement aspects of the wireless communication systems 100 and / or 200. The receiver RLF detection timer 500 can include a transmitting UE 115-c and a receiving UE 115-d communicating with each other on a sidelink communication link (e.g., a sidelink communication channel, a sidelink channel, etc.).

[0135] As described herein, in some cases, the receiving UE 115-d may monitor and detect RLF based on the receiving side RLF detection timer 500. For example, the receiving UE 115-d may identify one or more data transmission opportunities 505 in which a data transmission from the transmitting UE 115-c may be received. In some cases, the one or more data transmission opportunities 505 may also include opportunities for data transmission in which an SCI is transmitted with the data transmission. The receiving UE 115-d may identify the one or more data transmission opportunities 505 based on an indication from the transmitting UE 115-c. In some cases, the receiving UE 115-d may perform blind SCI decoding in each data transmission opportunity 505 to monitor the sidelink transmission from the transmitting UE 115-c.

[0136] Additionally or alternatively, the data transmission opportunities 505 may be configured and occur based on a periodic transmission schedule, wherein the receiving UE 115-d identifies the data transmission opportunities 505 based on the periodic transmission schedule. As shown, the data transmission opportunities 505 may be scheduled according to a period of four (4) TTIs or time slots (e.g., the data transmission opportunities 505 occur once every four (4) TTIs or time slots). As an illustration, for one or more data transmission opportunities 505, each data transmission opportunity 505 may or may not have a data transmission. For example, the transmitting UE 115-c may have declared RLF as described above and has ceased data transmission to the receiving UE 115-d.

[0137] like Figure 5 As shown in the example of , the receiving UE 115-d may perform a successful SCI decoding 510 in time slot n. Subsequently, the next time slot (e.g., TTI) that the receiving UE 115-d expects to decode the SCI in the data transmission opportunity 505 may occur in time slot n+k (e.g., Figure 5 , k=4, as described above with respect to the period of data transmission opportunities 505). However, the receiving UE 115-d may experience an SCI decoding failure 515 in time slot n+k. Therefore, the receiving UE 115-d may, based on the SCI decoding failure 515, start a timer with a timer value 520 (e.g., as described above with respect to Figure 2 The timer described in ( ) starts counting down.

[0138] If no SCI can be decoded before the timer expires (e.g., the timer value 520 reaches zero (0)), the receiving UE 115-d may declare RLF for the sidelink communication link with the transmitting UE 115-c. Alternatively, if the SCI is decoded before the timer expires, the receiving UE 115-d may reset the timer and begin counting down from the next failed SCI decode. Figure 5 As shown in , when the timer value 520 expires, the receiving UE 115-d may reach a number of consecutive decoding failures (e.g., undecoded SCI) and may determine an RLF declaration 525. In some cases, the timer value 520 may include the timer value 520 as described above with reference to Figure 2 , 3A and the duration determined by 3B.

[0139] Figure 6 An example of a process flow 600 for supporting a sidelink RLF process according to various aspects of the present disclosure is shown. In some examples, the process flow 600 can implement aspects of the wireless communication system 100 and / or 200. The process flow 600 can include a base station 105-b (e.g., a scheduling base station 105), a UE 115-e (e.g., a first UE), and a UE 115-f (e.g., a second UE), which can be respectively as described above with reference to Figure 1-5 An example of a corresponding base station 105 and a UE 115 is described. As described herein, UE 115-e and UE 115-f can communicate on a sidelink communication link, wherein, based on the sending UE 115-e sending a data message to the receiving UE 115-f, UE 115-e can be referred to as the sending UE 115-e (e.g., a sending UE), and UE 115-f can be referred to as the receiving UE 115-f (e.g., a receiving UE).

[0140] In the following description of process flow 600, operations between base station 105-b, transmitting UE 115-e, and receiving UE 115-f may be sent in an order different from the order shown, or operations performed by base station 105-b, transmitting UE 115-e, and receiving UE 115-f may be performed in a different order or at a different time. Some operations may also be omitted from process flow 600, or other operations may be added to process flow 600. It is to be understood that although base station 105-b, transmitting UE 115-e, and receiving UE 115-f are shown as performing multiple operations of process flow 600, any wireless device may perform the operations shown.

[0141] At 605, the transmitting UE 115-e may monitor the sidelink communication link with the receiving UE 115-f as part of the RLM procedure for the sidelink communication link.

[0142] At 610, the transmitting UE 115-e may detect RLF of the sidelink communication link based on monitoring. For example, the transmitting UE 115-e may send one or more sidelink messages to the receiving UE 115-f (e.g., a second UE) and via the sidelink communication link in one or more TTIs, and may monitor the sidelink communication link in one or more subsequent TTIs after the one or more TTIs for feedback messages (e.g., HARQ ACK feedback, ACK / NACK feedback, etc.) from the receiving UE 115-f and in response to the one or more sidelink messages. Thus, the UE 115-e may then determine the RLF based on one or more unsuccessful receptions of the feedback messages based on the monitoring. In some cases, the transmitting UE 115-e may avoid sending messages to the receiving UE 115-f via the sidelink communication link based on the detection of the RLF.

[0143] At 615, the transmitting UE 115-e may report the RLF based on the detection of the RLF. For example, the transmitting UE 115-e may send an indication of the RLF to the base station 105-b via RRC signaling. Additionally or alternatively, the transmitting UE 115-e may send a request to the base station 105-b for reestablishment of a sidelink connection with the receiving UE 115-f.

[0144] In addition to or as an alternative to the above steps, at 620, the receiving UE 115-f may identify a TTI for a sidelink transmission from the transmitting UE 115-e via the sidelink communication link.

[0145] At 625, the receiving UE 115-f may monitor the sidelink communication link during the TTI for one or more sidelink transmissions from the transmitting UE 115-e.

[0146] At 630, the receiving UE 115-f may start a timer based on unsuccessful reception of the one or more sidelink transmissions in the TTI. In some cases, the receiving UE 115-f may determine the unsuccessful reception of the one or more sidelink transmissions based on a failure to decode the SCI or sidelink data during the TTI, a failure to receive a sidelink data transmission scheduled by the SCI from the transmitting UE 115-e, or a combination thereof. Additionally, the timer may include a timer that begins counting down based on unsuccessful reception of the one or more sidelink transmissions.

[0147] At 635, the receiving UE 115-f may determine an RLF for the sidelink communication link based on the timer exceeding a threshold value. In some cases, the receiving UE 115-f may determine the threshold value based on a preconfigured value, a value determined during establishment of the sidelink communication link, a priority level associated with data sent via the sidelink communication link, an indication from the base station 105-b, or a combination thereof. For example, the value determined during establishment of the sidelink communication link may be based on the speed of the transmitting UE 115-e or the receiving UE 115-f, a congestion level of the sidelink communication link, a priority level associated with data sent via the sidelink communication link, an application for which the sidelink communication link is used, or a combination thereof.

[0148] In addition, the receiving UE 115-f may determine an upper limit and a lower limit for the threshold value, wherein the upper limit and the lower limit are based on: a preconfigured value, a priority level associated with data sent via the sidelink communication link, an application for which the sidelink communication link is used, or a combination thereof. In some cases, the receiving UE 115-f may reconfigure the threshold value based on: a change in the speed of the transmitting UE 115-e or the receiving UE 115-f, a congestion level of the sidelink communication link, a change in the priority level associated with data sent via the sidelink communication link, or a combination thereof.

[0149] At 640, the receiving UE 115-f may report the RLF based on the determination of the RLF. For example, the receiving UE 115-f may send an indication of the RLF to the base station 105-b via RRC signaling. Additionally or alternatively, the receiving UE 115-f may send an indication of the RLF to the sending UE 115-e via sidelink signaling (e.g., MAC-CE, RRC, etc.). In some cases, the receiving UE 115-f may release a sidelink communication connection (e.g., a sidelink communication link) with the sending UE 115-e based on the determination of the RLF.

[0150] Figure 7 A block diagram 700 of a device 705 that supports processing of sidelink RLF according to aspects of the present disclosure is shown. The device 705 may represent an example of a first UE 115 or a sender UE 115 as described herein. The device 705 may include a receiver 710, a sender UE communication manager 715, and a transmitter 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).

[0151] The receiver 710 may receive information, such as packets, user data, or control information associated with various information channels (e.g., control channels, data channels, and information related to the handling of sidelink RLF, etc.). The information may be communicated to other components of the device 705. The receiver 710 may be a reference Fig. 9 Examples of various aspects of the transceiver 920 are described. The receiver 710 may utilize a single antenna or a group of antennas.

[0152] The sender UE communication manager 715 may monitor the sidelink communication link with the second UE as part of the RLM process for the sidelink communication link. In some cases, the sender UE communication manager 715 may detect the RLF of the sidelink communication link based on the monitoring. In addition, the sender UE communication manager 715 may report the RLF based on the detection of the RLF. The sender UE communication manager 715 may be an example of various aspects of the sender UE communication manager 910 described herein.

[0153] The sender UE communication manager 715 or its subcomponents may be implemented in hardware, code (e.g., software or firmware) executed by a processor, or any combination thereof. If implemented in code executed by a processor, the functions of the sender UE communication manager 715 or its subcomponents may be performed by a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described in the present disclosure.

[0154] The sender UE communication manager 715 or its subcomponents may be physically located at various locations, including being distributed so that portions of the functionality are implemented by one or more physical components at different physical locations. In some examples, according to various aspects of the present disclosure, the sender UE communication manager 715 or its subcomponents may be separate and distinct components. In some examples, according to various aspects of the present disclosure, the sender UE communication manager 715 or its subcomponents may be combined with one or more other hardware components (including but not limited to input / output (I / O) components, transceivers, network servers, another computing device, one or more other components described in the present disclosure, or combinations thereof).

[0155] In some examples, the sender UE communication manager 715 described herein may be implemented as a chipset of a wireless modem, and the receiver 710 and the transmitter 720 may be implemented as a collection of analog components (e.g., amplifiers, filters, phase shifters, antennas, etc.). The wireless modem may obtain and decode a signal from the receiver 710 through a receiving interface, and may output a signal for transmission to the transmitter 720 through a transmitting interface.

[0156] The actions performed by the sender UE communication manager 715 as described herein may be implemented to achieve one or more advantages. One implementation may allow the device 705 to efficiently detect RLF in a sidelink communication link. If the device 705 has not yet detected RLF, the RLF detection may reduce the number of transmissions and retransmissions that may have occurred. In addition, detecting RLF on the sidelink communication link may also allow the device 705 to save power and increase battery life by performing communications more efficiently and restoring connections in the sidelink channel more quickly. Detection of RLF may also result in a more efficient use of resources because the number of retransmissions may be reduced based on declaring RLF earlier and resuming sidelink communications.

[0157] The transmitter 720 can transmit signals generated by other components of the device 705. In some examples, the transmitter 720 can be co-located with the receiver 710 in a transceiver module. For example, the transmitter 720 can be a reference Fig. 9 Examples of various aspects of the transceiver 920 are described. The transmitter 720 may utilize a single antenna or a group of antennas.

[0158] Figure 8 A block diagram 800 of a device 805 that supports processing of a sidelink RLF according to aspects of the present disclosure is shown. The device 805 may be an example of aspects of the device 705, the first UE 115, or the sender UE 115 as described herein. The device 805 may include a receiver 810, a sender UE communication manager 815, and a transmitter 835. The device 805 may also include a processor. Each of these components may communicate with each other (e.g., via one or more buses).

[0159] The receiver 810 may receive information, such as packets, user data, or control information associated with various information channels (e.g., control channels, data channels, and information related to the handling of sidelink RLF, etc.). The information may be communicated to other components of the device 805. The receiver 810 may be a reference Fig. 9 Examples of various aspects of the transceiver 920 are described. The receiver 810 may utilize a single antenna or a group of antennas.

[0160] The sender UE communication manager 815 may be an example of aspects of the sender UE communication manager 715 as described herein. The sender UE communication manager 815 may include an RLM component 820, an RLF detector 825, and an RLF reporter 830. The sender UE communication manager 815 may be an example of aspects of the sender UE communication manager 910 described herein.

[0161] The RLM component 820 may monitor the sidelink communication link with the second UE as part of an RLM process for the sidelink communication link.In some cases, the first UE may be a sending UE for the sidelink communication link, and the second UE may be a receiving UE for the sidelink communication link.

[0162] The RLF detector 825 can detect RLF of the sidelink communication link based on monitoring. In some examples, the RLF detector 825 can send one or more sidelink messages to the second UE and via the sidelink communication link in one or more TTIs, and can monitor the sidelink communication link for feedback messages from the second UE and in response to the one or more sidelink messages in one or more subsequent TTIs after the one or more TTIs. Therefore, the RLF detector 825 can determine the RLF based on one or more unsuccessful receptions of the feedback messages based on monitoring. In addition, in some cases, the RLF detector 825 can avoid sending messages to the second UE via the sidelink communication link based on the detection of RLF.

[0163] The RLF reporter 830 may report the RLF based on the detection of the RLF. In some examples, the RLF reporter 830 may send an indication of the RLF to the base station via RRC signaling. Additionally or alternatively, the RLF reporter 830 may send a request to the base station for reestablishment of the sidelink connection with the second UE.

[0164] The transmitter 835 can transmit signals generated by other components of the device 805. In some examples, the transmitter 835 can be co-located with the receiver 810 in a transceiver module. For example, the transmitter 835 can be a reference Fig. 9 Examples of various aspects of the transceiver 920 are described. The transmitter 835 may utilize a single antenna or a group of antennas.

[0165] The processor of UE 115 can start a timer to efficiently determine when RLF occurs in the sidelink communication channel. Based on configuring UE 115 to detect RLF based on timer expiration, the processor of UE 115 can efficiently determine that RLF has occurred and can take actions to restore the sidelink communication link with one or more other UEs. In some cases, the processor of UE 115 can declare RLF, and the processor can then initiate a command to reestablish communication on the failed link or in some cases on a new link.

[0166] Fig. 9A schematic diagram of a system 900 including a device 905 supporting processing of a sidelink RLF according to aspects of the present disclosure is shown. The device 905 may be an example of or include a component of a device 705, a device 805, a first UE 115, or a sender UE 115 as described herein. The device 905 may include components for two-way voice and data communications, including components for sending and receiving communications, including a sender UE communication manager 910, an I / O controller 915, a transceiver 920, an antenna 925, a memory 930, and a processor 940. These components may communicate electronically via one or more buses (e.g., a bus 945).

[0167] The sender UE communication manager 910 may monitor the sidelink communication link with the second UE as part of a radio link monitoring process for the sidelink communication link. In some cases, the sender UE communication manager 910 may detect RLF of the sidelink communication link based on monitoring. In addition, the sender UE communication manager 910 may report RLF based on detection of RLF.

[0168] I / O controller 915 can manage input and output signals for device 905. I / O controller 915 can also manage peripheral devices that are not integrated into device 905. In some cases, I / O controller 915 can represent a physical connection or port to an external peripheral device. In some cases, I / O controller 915 can utilize an operating system, such as Or another known operating system. In other cases, I / O controller 915 can represent or interact with a modem, keyboard, mouse, touch screen or similar device. In some cases, I / O controller 915 can be implemented as a part of a processor. In some cases, a user can interact with device 905 via I / O controller 915 or via a hardware component controlled by I / O controller 915.

[0169] The transceiver 920 may communicate bidirectionally via one or more antennas, wired or wireless links as described above. For example, the transceiver 920 may represent a wireless transceiver and may communicate bidirectionally with another wireless transceiver. The transceiver 920 may also include a modem to modulate packets and provide the modulated packets to an antenna for transmission, and demodulate packets received from an antenna.

[0170] In some cases, a wireless device may include a single antenna 925. However, in some cases, a device may have more than one antenna 925 that are capable of sending or receiving multiple wireless transmissions simultaneously.

[0171] 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, which includes instructions that, when executed, cause the processor to perform various functions described herein. In some cases, the memory 930 may also contain, among other things, a basic I / O system (BIOS), which may control basic hardware or software operations, such as interaction with peripheral components or devices.

[0172] The processor 940 may include an intelligent hardware device (e.g., a general purpose processor, a DSP, a central processing unit (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 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., memory 930) to cause the device 905 to perform various functions (e.g., functions or tasks to support the processing of the sidelink RLF).

[0173] The code 935 may include instructions for implementing various aspects of the present disclosure, including instructions for supporting wireless communications. The code 935 may be stored in a non-transitory computer-readable medium (e.g., a system memory or other type of memory). In some cases, the code 935 may not be directly executable by the processor 940, but may cause a computer (e.g., when compiled and executed) to perform the functions described herein.

[0174] Fig.10 A block diagram 1000 of a device 1005 that supports processing of a sidelink RLF according to aspects of the present disclosure is shown. The device 1005 may represent an example of aspects of a second UE 115 or a receiving UE 115 as described herein. The device 1005 may include a receiver 1010, a receiving UE communication manager 1015, and a transmitter 1020. The device 1005 may also include a processor. Each of these components may communicate with each other (e.g., via one or more buses).

[0175] The receiver 1010 may receive information, such as packets, user data, or control information associated with various information channels (e.g., control channels, data channels, and information related to the handling of sidelink RLF, etc.). The information may be communicated to other components of the device 1005. The receiver 1010 may be a reference Fig.13Examples of various aspects of the transceiver 1320 are described. The receiver 1010 may utilize a single antenna or a group of antennas.

[0176] The receiving UE communication manager 1015 may identify a TTI for a sidelink transmission from the first UE via the sidelink communication link. In addition, the receiving UE communication manager 1015 may monitor the sidelink communication link for one or more sidelink transmissions from the first UE during the TTI. In some cases, the receiving UE communication manager 1015 may start a timer based on unsuccessful reception of one or more sidelink transmissions in the TTI. The receiving UE communication manager 1015 may be an example of various aspects of the receiving UE communication manager 1310 described herein.

[0177] The receiving UE communication manager 1015 or its subcomponents may be implemented in hardware, code (e.g., software or firmware) executed by a processor, or any combination thereof. If implemented in code executed by a processor, the functions of the receiving UE communication manager 1015 or its subcomponents may be performed by a general purpose processor, DSP, ASIC, FPGA or other programmable logic device designed to perform the functions described in the present disclosure, discrete gate or transistor logic, discrete hardware components, or any combination thereof.

[0178] The receiving UE communication manager 1015 or its subcomponents may be physically located at various locations, including being distributed so that portions of the functionality are implemented by one or more physical components at different physical locations. In some examples, according to various aspects of the present disclosure, the receiving UE communication manager 1015 or its subcomponents may be separate and distinct components. In some examples, according to various aspects of the present disclosure, the receiving UE communication manager 1015 or its subcomponents may be combined with one or more other hardware components (including but not limited to I / O components, transceivers, network servers, another computing device, one or more other components described in the present disclosure, or a combination thereof).

[0179] In some examples, the receiving UE communication manager 1015 described herein may be implemented as a chipset of a wireless modem, and the receiver 1010 and the transmitter 1020 may be implemented as a collection of analog components (e.g., amplifiers, filters, phase shifters, antennas, etc.). The wireless modem may obtain and decode a signal from the receiver 1010 through a receiving interface, and may output a signal for transmission to the transmitter 1020 through a transmitting interface.

[0180] The actions performed by the receiving UE communication manager 1015 as described herein may be implemented to achieve one or more advantages. One implementation may allow the device 1005 to efficiently detect RLF in a sidelink communication link. If the device 1005 has not yet detected the RLF, the RLF detection may reduce the number of transmissions and retransmissions that may have occurred. In addition, detecting RLF on the sidelink communication link may also allow the device 1005 to save power and increase battery life by performing communications more efficiently and resuming connections in the sidelink channel more quickly. Detection of RLF may also result in a more efficient use of resources because the number of retransmissions may be reduced based on declaring the RLF earlier and resuming the sidelink communication.

[0181] The transmitter 1020 can transmit signals generated by other components of the device 1005. In some examples, the transmitter 1020 can be co-located with the receiver 1010 in a transceiver module. For example, the transmitter 1020 can be a reference Fig.13 Examples of various aspects of the transceiver 1320 are described. The transmitter 1020 may utilize a single antenna or a group of antennas.

[0182] Fig.11 A block diagram 1100 of a device 1105 for supporting processing of a sidelink RLF according to aspects of the present disclosure is shown. The device 1105 may be an example of aspects of the device 1005, the second UE 115, or the receiving UE as described herein. The device 1105 may include a receiver 1110, a receiving UE communication manager 1115, and a transmitter 1135. The device 1105 may also include a processor. Each of these components may communicate with each other (e.g., via one or more buses).

[0183] The receiver 1110 may receive information, such as packets, user data, or control information associated with various information channels (e.g., control channels, data channels, and information related to the handling of sidelink RLF, etc.). The information may be communicated to other components of the device 1105. The receiver 1110 may be a reference Fig.13 Examples of various aspects of the transceiver 1320 are described. The receiver 1110 may utilize a single antenna or a group of antennas.

[0184] The receiving UE communication manager 1115 may be an example of aspects of the receiving UE communication manager 1015 as described herein. The receiving UE communication manager 1115 may include a sidelink opportunity identifier 1120, a sidelink monitoring component 1125, and an RLF timer 1130. The receiving UE communication manager 1115 may be an example of aspects of the receiving UE communication manager 1310 described herein.

[0185] The sidelink opportunity identifier 1120 may identify a TTI for a sidelink transmission from the first UE via the sidelink communication link.

[0186] The sidelink monitoring component 1125 may monitor the sidelink communication link during the TTI for one or more sidelink transmissions from the first UE.

[0187] The RLF timer 1130 may start a timer based on unsuccessful reception of one or more sidelink transmissions in a TTI.

[0188] The processor of UE 115 can start a timer to efficiently determine when RLF occurs in the sidelink communication channel. Based on configuring UE 115 to detect RLF based on timer expiration, the processor of UE 115 can efficiently determine that RLF has occurred and can take actions to restore the sidelink communication link with one or more other UEs. In some cases, the processor of UE 115 can declare RLF, and the processor can then initiate a command to reestablish communication on the failed link or in some cases on a new link.

[0189] The transmitter 1135 may transmit signals generated by other components of the device 1105. In some examples, the transmitter 1135 may be co-located with the receiver 1110 in a transceiver module. Fig.13 Examples of various aspects of the transceiver 1320 are described. The transmitter 1135 may utilize a single antenna or a group of antennas.

[0190] Fig.12 A block diagram 1200 of a receiving UE communication manager 1205 supporting processing of a sidelink RLF in accordance with aspects of the present disclosure is shown. The receiving UE communication manager 1205 may be an example of aspects of the receiving UE communication manager 1015, the receiving UE communication manager 1115, or the receiving UE communication manager 1310 described herein. The receiving UE communication manager 1205 may include a sidelink opportunity identifier 1210, a sidelink monitoring component 1215, an RLF timer 1220, an RLF reporting component 1225, and a sidelink release component 1230. Each of these modules may communicate with each other directly or indirectly (e.g., via one or more buses).

[0191] The sidelink opportunity identifier 1210 may identify a TTI for a sidelink transmission from the first UE via the sidelink communication link.In some cases, the first UE may be a transmitting UE for the sidelink communication link and the second UE may be a receiving UE for the sidelink communication link.

[0192] The sidelink monitoring component 1215 can monitor the sidelink communication link for one or more sidelink transmissions from the first UE during the TTI. In some examples, the sidelink monitoring component 1215 can determine unsuccessful reception of one or more sidelink transmissions based on failure to decode the SCI or sidelink data during the TTI, failure to receive a sidelink data transmission scheduled by the SCI from the first UE, or a combination thereof.

[0193] The RLF timer 1220 may start a timer based on an unsuccessful reception of one or more sidelink transmissions in a TTI. In some cases, the timer may include a timer that starts a countdown based on an unsuccessful reception of one or more sidelink transmissions. For example, the RLF timer 1220 may determine an RLF for a sidelink communication link based on the timer exceeding a threshold value. In some cases, the RLF timer 1220 may determine the threshold value based on: a preconfigured value, a value determined during establishment of the sidelink communication link, a priority level associated with data sent via the sidelink communication link, an indication from a base station, or a combination thereof. In some cases, the value determined during establishment of the sidelink communication link may be based on: the speed of the first UE or the second UE, the congestion level of the sidelink communication link, a priority level associated with data sent via the sidelink communication link, an application for which the sidelink communication link is used, or a combination thereof.

[0194] Additionally, the RLF timer 1220 may determine an upper limit and a lower limit for a threshold value, wherein the upper limit and the lower limit are based on a preconfigured value, a priority level associated with data sent via the sidelink communication link, an application for which the sidelink communication link is used, or a combination thereof. In some examples, the RLF timer 1220 may reconfigure the threshold value based on a change in the speed of the first UE or the second UE, a congestion level of the sidelink communication link, a change in the priority level associated with data sent via the sidelink communication link, or a combination thereof.

[0195] The RLF reporting component 1225 can report the RLF based on the determination of the RLF. In some examples, the RLF reporting component 1225 can send an indication of the RLF to the base station via RRC signaling. Additionally or alternatively, the RLF reporting component 1225 can send an indication of the RLF to the first UE via sidelink signaling (e.g., MAC CE, RRC, etc.).

[0196] The sidelink release component 1230 may release the sidelink communication connection with the first UE based on the determination of RLF.

[0197] Fig.13A schematic diagram of a system 1300 including a device 1305 supporting processing of a sidelink RLF according to aspects of the present disclosure is shown. The device 1305 may be an example of or include a component of the device 1005, device 1105, second UE 115, or recipient UE 115 as described herein. The device 1305 may include components for two-way voice and data communications, including components for sending and receiving communications, including a recipient UE communication manager 1310, an I / O controller 1315, a transceiver 1320, an antenna 1325, a memory 1330, and a processor 1340. These components may communicate electronically via one or more buses (e.g., bus 1345).

[0198] The receiving UE communication manager 1310 may identify a TTI for a sidelink transmission from the first UE via the sidelink communication link. Additionally, the receiving UE communication manager 1310 may monitor the sidelink communication link for one or more sidelink transmissions from the first UE during the TTI. In some cases, the receiving UE communication manager 1310 may start a timer based on unsuccessful reception of one or more sidelink transmissions in the TTI.

[0199] I / O controller 1315 can manage input and output signals for device 1305. I / O controller 1315 can also manage peripheral devices that are not integrated into device 1305. In some cases, I / O controller 1315 can represent a physical connection or port to an external peripheral device. In some cases, I / O controller 1315 can utilize an operating system, such as Or another known operating system. In other cases, I / O controller 1315 can represent or interact with a modem, keyboard, mouse, touch screen, or similar device. In some cases, I / O controller 1315 can be implemented as part of a processor. In some cases, a user can interact with device 1305 via I / O controller 1315 or via hardware components controlled by I / O controller 1315.

[0200] The transceiver 1320 may communicate bidirectionally via one or more antennas, wired or wireless links as described above. For example, the transceiver 1320 may represent a wireless transceiver and may communicate bidirectionally with another wireless transceiver. The transceiver 1320 may also include a modem to modulate packets and provide the modulated packets to an antenna for transmission, and demodulate packets received from an antenna.

[0201] In some cases, a wireless device may include a single antenna 1325. However, in some cases, a device may have more than one antenna 1325 that are capable of sending or receiving multiple wireless transmissions simultaneously.

[0202] The memory 1330 may include RAM and ROM. The memory 1330 may store computer-readable, computer-executable code 1335, which includes instructions that, when executed, cause the processor to perform various functions described herein. In some cases, the memory 1330 may also contain, among other things, a BIOS that may control basic hardware or software operations, such as interaction with peripheral components or devices.

[0203] Processor 1340 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, processor 1340 may be configured to operate a memory array using a memory controller. In other cases, the memory controller may be integrated into processor 1340. Processor 1340 may be configured to execute computer-readable instructions stored in a memory (e.g., memory 1330) to cause device 1305 to perform various functions (e.g., functions or tasks to support the processing of sidelink RLF).

[0204] The code 1335 may include instructions for implementing various aspects of the present disclosure, including instructions for supporting wireless communications. The code 1335 may be stored in a non-transitory computer-readable medium (e.g., system memory or other types of memory). In some cases, the code 1335 may not be directly executable by the processor 1340, but may cause a computer (e.g., when compiled and executed) to perform the functions described herein.

[0205] Fig.14 A flow chart illustrating a method 1400 for processing to support sidelink RLF according to aspects of the present disclosure is shown. The operations of the method 1400 may be implemented by a first UE 115 or a sender UE 115 or components thereof as described herein. For example, the operations of the method 1400 may be implemented by a first UE 115 or a sender UE 115 or components thereof as described herein. Figures 7 to 9 The UE may be executed by the sender UE communication manager described in the embodiment of the present invention. In some examples, the UE may execute an instruction set to control the functional elements of the UE to perform the functions described below. Additionally or alternatively, the UE may use dedicated hardware to perform various aspects of the functions described below.

[0206] At 1405, the transmitting UE may monitor a sidelink communication link with a second UE (e.g., a receiving UE) as part of an RLM procedure for the sidelink communication link. The operations of 1405 may be performed according to the methods described herein. In some examples, aspects of the operations of 1405 may be performed as described with reference to Figures 7 to 9 The RLM components described are implemented.

[0207] At 1410, the transmitting UE may detect the RLF of the sidelink communication link based on monitoring. The operations of 1410 may be performed according to the methods described herein. In some examples, aspects of the operations of 1410 may be performed as described with reference to Figures 7 to 9 The RLF detector described is implemented.

[0208] At 1415, the transmitting UE may report the RLF based on the detection of the RLF. The operations of 1415 may be performed according to the methods described herein. In some examples, aspects of the operations of 1415 may be described as in reference to Figures 7 to 9 The RLF reporter described in this document is used to perform the following operations.

[0209] Fig.15 A flow chart illustrating a method 1500 for supporting sidelink RLF processing according to aspects of the present disclosure is shown. The operations of the method 1500 may be implemented by a first UE 115 or a sender UE 115 or components thereof as described herein. For example, the operations of the method 1500 may be implemented by a first UE 115 or a sender UE 115 or components thereof as described herein. Figures 7 to 9 The UE may be executed by the sender UE communication manager described in the embodiment of the present invention. In some examples, the UE may execute an instruction set to control the functional elements of the UE to perform the functions described below. Additionally or alternatively, the UE may use dedicated hardware to perform various aspects of the functions described below.

[0210] At 1505, the transmitting UE may monitor a sidelink communication link with a second UE (e.g., a receiving UE) as part of an RLM procedure for the sidelink communication link. The operations of 1505 may be performed according to the methods described herein. In some examples, aspects of the operations of 1505 may be performed as described with reference to Figures 7 to 9 The RLM components described are implemented.

[0211] At 1510, the transmitting UE may detect the RLF of the sidelink communication link based on monitoring. The operations of 1510 may be performed according to the methods described herein. In some examples, aspects of the operations of 1510 may be performed as described with reference to Figures 7 to 9 The RLF detector described is implemented.

[0212] At 1515, the transmitting UE may report the RLF based on the detection of the RLF. The operations of 1515 may be performed according to the methods described herein. In some examples, aspects of the operations of 1515 may be described with reference to Figures 7 to 9 The RLF reporter described in this document is used to perform the following operations.

[0213] At 1520, the sending UE may send an indication of RLF to the base station via RRC signaling. The operations of 1520 may be performed according to the methods described herein. In some examples, aspects of the operations of 1520 may be described with reference to Figures 7 to 9 The RLF reporter described in this document is used to perform the following operations.

[0214] Fig.16 A flow chart illustrating a method 1600 for processing to support sidelink RLF according to aspects of the present disclosure is shown. The operations of the method 1600 may be implemented by a first UE 115 or a sender UE 115 or components thereof as described herein. For example, the operations of the method 1600 may be implemented by a first UE 115 or a sender UE 115 or components thereof as described herein. Figures 7 to 9 The UE may be executed by the sender UE communication manager described in the embodiment of the present invention. In some examples, the UE may execute an instruction set to control the functional elements of the UE to perform the functions described below. Additionally or alternatively, the UE may use dedicated hardware to perform various aspects of the functions described below.

[0215] At 1605, the transmitting UE may monitor a sidelink communication link with a second UE (e.g., a receiving UE) as part of an RLM procedure for the sidelink communication link. The operations of 1605 may be performed according to the methods described herein. In some examples, aspects of the operations of 1605 may be performed as described with reference to Figures 7 to 9 The RLM components described are implemented.

[0216] At 1610, the transmitting UE may detect the RLF of the sidelink communication link based on monitoring. The operations of 1610 may be performed according to the methods described herein. In some examples, aspects of the operations of 1610 may be performed as described with reference to Figures 7 to 9 The RLF detector described is implemented as follows.

[0217] At 1615, the transmitting UE may report the RLF based on the detection of the RLF. The operations of 1615 may be performed according to the methods described herein. In some examples, aspects of the operations of 1615 may be described with reference to Figures 7 to 9 The RLF reporter described in this document is used to perform the following operations.

[0218] At 1620, the transmitting UE may send a request to the base station for reestablishing a sidelink connection with the second UE. The operations of 1620 may be performed according to the methods described herein. In some examples, aspects of the operations of 1620 may be as described with reference to Figures 7 to 9 The RLF reporter described in this document is used to perform the following operations.

[0219] Fig.17 A flow chart illustrating a method 1700 for processing to support sidelink RLF according to aspects of the present disclosure is shown. The operations of the method 1700 may be implemented by a second UE 115 or a receiving UE 115 or components thereof as described herein. For example, the operations of the method 1700 may be implemented by a second UE 115 or a receiving UE 115 or components thereof as described herein. Figures 10 to 13 The receiving UE communication manager described in the embodiment of the present invention may be executed. In some examples, the UE may execute an instruction set to control the functional elements of the UE to perform the functions described below. Additionally or alternatively, the UE may use dedicated hardware to perform various aspects of the functions described below.

[0220] At 1705, the receiving UE may identify a TTI for a sidelink transmission from a first UE (e.g., a sending UE) via a sidelink communication link. The operations of 1705 may be performed according to the methods described herein. In some examples, aspects of the operations of 1705 may be performed as described with reference to Figures 10 to 13 The sidelink opportunity identifier described is performed.

[0221] At 1710, the receiving UE may monitor the sidelink communication link for one or more sidelink transmissions from the first UE during the TTI. The operations of 1710 may be performed according to the methods described herein. In some examples, aspects of the operations of 1710 may be performed as described with reference to Figures 10 to 13 The sidelink monitoring component described is performed.

[0222] At 1715, the receiving UE may start a timer based on unsuccessful reception of one or more sidelink transmissions in the TTI. The operations of 1715 may be performed according to the methods described herein. In some examples, aspects of the operations of 1715 may be as described with reference to Figures 10 to 13 The RLF timer described in this document is used to perform the following operations.

[0223] Fig.18 A flow chart illustrating a method 1800 for supporting sidelink RLF processing according to aspects of the present disclosure is shown. The operations of the method 1800 may be implemented by a second UE 115 or a receiving UE 115 or components thereof as described herein. For example, the operations of the method 1800 may be implemented by a second UE 115 or a receiving UE 115 or components thereof as described herein. Figures 10 to 13The receiving UE communication manager described in the embodiment of the present invention may be executed. In some examples, the UE may execute an instruction set to control the functional elements of the UE to perform the functions described below. Additionally or alternatively, the UE may use dedicated hardware to perform various aspects of the functions described below.

[0224] At 1805, the receiving UE may identify a TTI for a sidelink transmission from a first UE (e.g., a transmitting UE) via a sidelink communication link. The operations of 1805 may be performed according to the methods described herein. In some examples, aspects of the operations of 1805 may be performed as described with reference to Figures 10 to 13 The sidelink opportunity identifier described is performed.

[0225] At 1810, the receiving UE may monitor the sidelink communication link for one or more sidelink transmissions from the first UE during the TTI. The operations of 1810 may be performed according to the methods described herein. In some examples, aspects of the operations of 1810 may be performed as described with reference to Figures 10 to 13 The sidelink monitoring component described is performed.

[0226] At 1815, the receiving UE may start a timer based on unsuccessful reception of one or more sidelink transmissions in the TTI. The operations of 1815 may be performed according to the methods described herein. In some examples, aspects of the operations of 1815 may be as described with reference to Figures 10 to 13 The RLF timer described in this document is used to perform the following operations.

[0227] At 1820, the receiving UE may determine RLF for the sidelink communication link based on the timer exceeding the threshold value. The operations of 1820 may be performed according to the methods described herein. In some examples, aspects of the operations of 1820 may be as described with reference to Figures 10 to 13 The RLF timer described in this document is used to perform the following operations.

[0228] Fig.19 A flow chart illustrating a method 1900 for supporting sidelink RLF processing according to aspects of the present disclosure is shown. The operations of the method 1900 may be implemented by a second UE 115 or a receiving UE 115 or components thereof as described herein. For example, the operations of the method 1900 may be implemented by a second UE 115 or a receiving UE 115 or components thereof as described herein. Figures 10 to 13 The receiving UE communication manager described in the embodiment of the present invention may be executed. In some examples, the UE may execute an instruction set to control the functional elements of the UE to perform the functions described below. Additionally or alternatively, the UE may use dedicated hardware to perform various aspects of the functions described below.

[0229] At 1905, the receiving UE may identify a TTI for a sidelink transmission from a first UE (e.g., a sending UE) via a sidelink communication link. The operations of 1905 may be performed according to the methods described herein. In some examples, aspects of the operations of 1905 may be performed as described with reference to Figures 10 to 13 The sidelink opportunity identifier described is performed.

[0230] At 1910, the receiving UE may monitor the sidelink communication link for one or more sidelink transmissions from the first UE during the TTI. The operations of 1910 may be performed according to the methods described herein. In some examples, aspects of the operations of 1910 may be performed as described with reference to Figures 10 to 13 The sidelink monitoring component described is performed.

[0231] At 1915, the receiving UE may determine unsuccessful reception of one or more sidelink transmissions based on a failure to decode the sidelink control information or the sidelink data during the TTI, a failure to receive the sidelink data transmission scheduled by the sidelink control information from the first UE, or a combination thereof. The operations of 1915 may be performed according to the methods described herein. In some examples, aspects of the operations of 1915 may be performed as described with reference to Figures 10 to 13 The sidelink monitoring component described is performed.

[0232] At 1920, the receiving UE may start a timer based on unsuccessful reception of one or more sidelink transmissions in the TTI. The operations of 1920 may be performed according to the methods described herein. In some examples, aspects of the operations of 1920 may be as described with reference to Figures 10 to 13 The RLF timer described in this document is used to perform the following operations.

[0233] It should be noted that the methods described herein describe possible implementations, and that operations and steps may be rearranged or otherwise modified, and other implementations are possible. Furthermore, aspects from two or more methods may be combined.

[0234] The techniques described herein can be used in various wireless communication systems, such as code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), orthogonal frequency division multiple access (OFDMA), single carrier frequency division multiple access (SC-FDMA) and other systems. A CDMA system can implement radio technologies such as CDMA2000, Universal Terrestrial Radio Access (UTRA), etc. CDMA2000 covers IS-2000, IS-95 and IS-856 standards. IS-2000 versions can be generally referred to as CDMA2000 1X, 1X, etc. IS-856 (TIA-856) is generally referred to as CDMA2000 1xEV-DO, High Speed ​​Packet Data (HRPD), etc. UTRA includes Wideband CDMA (W-CDMA) and other variants of CDMA. A TDMA system can implement radio technologies such as Global System for Mobile Communications (GSM).

[0235] OFDMA systems can implement radio technologies such as Ultra Mobile Broadband (UMB), Evolved UTRA (E-UTRA), Institute of Electrical and Electronics Engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDM, etc. UTRA and E-UTRA are part of Universal Mobile Telecommunications System (UMTS). LTE, LTE-A, and LTE-A Professional are versions of UMTS that use E-UTRA. UTRA, E-UTRA, UMTS, LTE, LTE-A, LTE-A Professional, NR, and GSM are described in documents from an organization named "3rd Generation Partnership Project" (3GPP). CDMA2000 and UMB are described in documents from an organization named "3rd Generation Partnership Project 2" (3GPP2). The techniques described herein can be used for the systems and radio technologies mentioned herein as well as other systems and radio technologies. Although aspects of LTE, LTE-A, LTE-A Professional, or NR systems may be described for example purposes, and LTE, LTE-A, LTE-A Professional, or NR terminology may be used in much of the description, the techniques described herein may be applicable beyond LTE, LTE-A, LTE-A Professional, or NR applications.

[0236] A macro cell typically covers a relatively large geographic area (e.g., a radius of several kilometers) and may allow unrestricted access by a UE with a service subscription to a network provider. Compared to a macro cell, a small cell may be associated with a lower power base station, and the small cell may operate in the same or different frequency band as the macro cell (e.g., licensed, unlicensed, etc.). According to various examples, a small cell may include a pico cell, a femto cell, and a micro cell. For example, a pico cell may cover a small geographic area and may allow unrestricted access by a UE with a service subscription to a network provider. A femto cell may also cover a small geographic area (e.g., a residence) and may provide restricted access by a UE associated with the femto cell (e.g., a UE in a closed subscriber group (CSG), a UE for a user in a residence, etc.). An eNB for a macro cell may be referred to as a macro eNB. An eNB for a small cell may be referred to as a small cell eNB, a pico eNB, a femto eNB, or a home eNB. An eNB may support one or more (e.g., two, three, four, etc.) cells and may also support communications using one or more component carriers.

[0237] The wireless communication systems described herein may support synchronous or asynchronous operation. For synchronous operation, base stations may have similar frame timing, and transmissions from different base stations may be approximately aligned in time. For asynchronous operation, base stations may have different frame timing, and transmissions from different base stations may not be aligned in time. The techniques described herein may be used for synchronous or asynchronous operation.

[0238] The information and signals described herein may be represented using any of a variety of different techniques and methods. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be mentioned throughout this specification may be represented by voltage, current, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

[0239] The various illustrative blocks and modules described in conjunction with the disclosure herein may be implemented or executed using a general purpose processor, a DSP, an ASIC, an 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 conventional 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, a plurality of microprocessors, a combination of one or more microprocessors and a DSP core, or any other such configuration).

[0240] The functions described herein may be implemented in hardware, software executed by a processor, firmware, or any combination thereof. If implemented in software executed by a processor, the functions may be stored on or sent via a computer-readable medium as one or more instructions or codes. Other examples and implementations are within the scope of this disclosure and the appended claims. For example, due to the nature of software, the functions described herein may be implemented using software executed by a processor, hardware, firmware, hard wiring, or any combination of these. Features that implement the functions may also be physically located at various locations, including being distributed so that parts of the functions are implemented at different physical locations.

[0241] Computer readable medium includes both non-transitory computer storage medium and communication medium, and communication medium includes any medium that promotes the transmission of computer program from one place to another place.Non-transitory storage medium can be any available medium that can be accessed by general-purpose computer or special-purpose computer.By way of example and not limitation, non-transitory computer readable medium can include RAM, ROM, electrically erasable programmable ROM (EEPROM), flash memory, compact disc (CD) ROM or other optical disc storage, disk storage or other magnetic storage device, or can be used for carrying or storing desired program code unit and can be accessed by general-purpose or special-purpose computer or general-purpose or special-purpose processor in the form of instruction or data structure.In addition, any connection is appropriately referred to as computer readable medium.For example, if software is to send from website, server or other remote source using coaxial cable, optical fiber cable, twisted pair, digital subscriber line (DSL) or wireless technology such as infrared, radio and microwave, then coaxial cable, optical fiber cable, twisted pair, DSL or wireless technology such as infrared, radio and microwave are included in the definition of medium. As used herein, disk and disc include CD, laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc, wherein disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above are also included within the scope of computer-readable media.

[0242] As used herein (including in the claims), "or" as used in a list of items (e.g., a list of items ending with 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 exemplary 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."

[0243] In the accompanying drawings, similar components or features may have the same reference number. In addition, various components of the same type may be distinguished by following the reference number with a dash and a second reference number, the second reference number being used to distinguish between similar components. If only the first reference number is used in the specification, the description applies to any one of the similar components having the same first reference number, without regard to the second reference number or other subsequent reference numbers.

[0244] 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 "exemplary" as used herein means "used as an example, instance, or illustration," rather than "preferred" or "advantageous over other examples." For the purpose of providing an understanding of the described techniques, the detailed description includes specific details. However, these techniques may be implemented without these specific details. In some instances, well-known structures and devices are shown in block diagram form to avoid obscuring the concepts of the described examples.

[0245] The description herein is provided to enable those skilled in the art to implement or use the present disclosure. It will be apparent to those skilled in the art that various modifications to the present disclosure will be apparent, and the general principles defined herein may be applied to other variations without departing from the scope of the present disclosure. Therefore, the present disclosure is not limited to the examples and designs described herein, but is to be given the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for wireless communication at a first user equipment (UE), comprising: sending one or more sidelink messages to the second UE via the sidelink communication link in one or more transmission time intervals; monitoring the sidelink communication link with the second UE for one or more feedback messages associated with the one or more sidelink messages in one or more subsequent transmission time intervals after the one or more transmission time intervals as part of a radio link monitoring procedure for the sidelink communication link; modifying a counter based at least in part on receipt of the one or more feedback messages from the second UE, the one or more feedback messages indicating one or more negative determinations; detecting a radio link failure of the sidelink communication link based at least in part on the one or more feedback messages from the second UE indicating the one or more negative determinations and based on the counter satisfying a threshold value, the threshold value being selected from a range of threshold values ​​and determined based at least in part on a value determined during establishment of the sidelink communication link, a priority level associated with data of the one or more sidelink messages sent via the sidelink communication link, or both, wherein the range of threshold values ​​has upper and lower limits determined at least in part based on a preconfigured value, the priority level associated with the data sent via the sidelink communication link, an application associated with the one or more sidelink messages, or any combination thereof; as well as The radio link failure is reported based at least in part on the detection of the radio link failure.

2. The method according to claim 1, wherein: Reporting of a radio link failure includes: An indication of the radio link failure is sent to a network entity via radio resource control (RRC) signaling.

3. The method according to claim 1, wherein: Reporting of a radio link failure includes: A request for reestablishing a sidelink connection with the second UE is sent to a network entity.

4. The method according to claim 1, wherein: Detecting the radio link failure comprises: The radio link failure is detected based at least in part on one or more unsuccessful receptions of the one or more feedback messages.

5. The method according to claim 1, further comprising: Refraining from sending a message to the second UE via the sidelink communication link based at least in part on the detection of the radio link failure.

6. The method according to claim 1, wherein: The first UE comprises a transmitting UE for the sidelink communication link, and the second UE comprises a receiving UE for the sidelink communication link.

7. A method for wireless communication at a second user equipment (UE), comprising: identifying a transmission time interval for sidelink transmissions from the first UE via the sidelink communication link; monitoring the sidelink communications link for one or more sidelink transmissions from the first UE during the transmission time interval; starting a timer based at least in part on unsuccessful reception of the one or more sidelink transmissions in the transmission time interval; and A radio link failure for the sidelink communication link is determined at least in part based on the timer exceeding a threshold value, the threshold value being selected from a threshold value range and being determined at least in part based on a value determined during establishment of the sidelink communication link, a priority level associated with data sent via the sidelink communication link, or both, wherein the threshold value range has upper and lower limits determined at least in part based on a preconfigured value, the priority level associated with the data sent via the sidelink communication link, an application for which the sidelink communication link is used, or any combination thereof.

8. The method according to claim 7, further comprising: The threshold value is determined based at least in part on an indication from a network entity, a preconfigured value, or both.

9. The method according to claim 7, wherein: The value determined during establishment of the sidelink communication link is based at least in part on: a speed of the first UE or the second UE, a congestion level of the sidelink communication link, a priority level associated with data sent via the sidelink communication link, an application for which the sidelink communication link is used, or a combination thereof.

10. The method according to claim 7, further comprising: The threshold value is reconfigured based at least in part on: a change in a speed of the first UE or the second UE, a congestion level of the sidelink communication link, a change in a priority level associated with data sent via the sidelink communication link, or a combination thereof.

11. The method according to claim 7, further comprising: The radio link failure is reported based at least in part on the determination of the radio link failure.

12. The method according to claim 11, wherein: Reporting of a radio link failure includes: An indication of the radio link failure is sent to a network entity via radio resource control (RRC) signaling.

13. The method according to claim 11, wherein: Reporting the radio link failure also includes: An indication of the radio link failure is sent to the first UE via sidelink signaling.

14. The method according to claim 7, further comprising: A sidelink communication connection with the first UE is released based at least in part on the determination of the radio link failure.

15. The method according to claim 7, further comprising: The unsuccessful reception of the one or more sidelink transmissions is determined based at least in part on a failure to decode sidelink control information or sidelink data during the transmission time interval.

16. The method of claim 7, the timer comprising a timer that begins counting down based at least in part on the unsuccessful reception of the one or more sidelink transmissions.

17. The method according to claim 7, wherein: The first UE comprises a transmitting UE for the sidelink communication link, and the second UE comprises a receiving UE for the sidelink communication link.

18. An apparatus for wireless communication at a first user equipment (UE), comprising: means for sending one or more sidelink messages to a second UE via the sidelink communication link in one or more transmission time intervals; means for monitoring the sidelink communication link with the second UE for one or more feedback messages associated with the one or more sidelink messages in one or more subsequent transmission time intervals after the one or more transmission time intervals as part of a radio link monitoring procedure for the sidelink communication link; means for modifying a counter based at least in part on receipt of the one or more feedback messages from the second UE, the one or more feedback messages indicating one or more negative determinations; means for detecting a radio link failure of the sidelink communication link based at least in part on the one or more feedback messages from the second UE indicating the one or more negative determinations and based on the counter satisfying a threshold value, the threshold value being selected from a range of threshold values ​​and determined based at least in part on a value determined during establishment of the sidelink communication link, a priority level associated with data of the one or more sidelink messages sent via the sidelink communication link, or both, wherein the range of threshold values ​​has upper and lower limits determined at least in part based on a preconfigured value, the priority level associated with the data sent via the sidelink communication link, an application associated with the one or more sidelink messages, or any combination thereof; as well as Means for reporting the radio link failure based at least in part on the detection of the radio link failure.

19. The device according to claim 18, wherein: The means for reporting the radio link failure comprises: Means for sending an indication of the radio link failure to a network entity via radio resource control (RRC) signaling.

20. The device according to claim 18, wherein The means for reporting the radio link failure comprises: Means for sending a request to a network entity for sidelink connection re-establishment with the second UE.

21. The device according to claim 18, wherein The means for detecting the radio link failure comprises: Means for detecting the radio link failure based at least in part on one or more unsuccessful receptions of the one or more feedback messages.

22. An apparatus for wireless communication at a second user equipment (UE), comprising: means for identifying a transmission time interval for sidelink transmissions from the first UE via the sidelink communication link; means for monitoring the sidelink communication link for one or more sidelink transmissions from the first UE during the transmission time interval; means for starting a timer based at least in part on unsuccessful reception of the one or more sidelink transmissions in the transmission time interval; as well as A unit for determining a radio link failure for the sidelink communication link based at least in part on the timer exceeding a threshold value, the threshold value being selected from a range of threshold values ​​and determined at least in part based on a value determined during establishment of the sidelink communication link, a priority level associated with data sent via the sidelink communication link, or both, wherein the range of threshold values ​​has upper and lower limits determined at least in part based on a preconfigured value, the priority level associated with the data sent via the sidelink communication link, an application for which the sidelink communication link is used, or any combination thereof.

23. The apparatus according to claim 22, further comprising: Means for determining the threshold value based at least in part on an indication from a network entity, a preconfigured value, or both.

24. The device according to claim 22, wherein: The value determined during establishment of the sidelink communication link is based at least in part on: a speed of the first UE or the second UE, a congestion level of the sidelink communication link, a priority level associated with data sent via the sidelink communication link, an application for which the sidelink communication link is used, or a combination thereof.

25. The apparatus of claim 22, further comprising: A means for reconfiguring the threshold value based at least in part on: a change in speed of the first UE or the second UE, a congestion level of the sidelink communication link, a change in a priority level associated with data sent via the sidelink communication link, or a combination thereof.

26. The apparatus of claim 22, further comprising: Means for reporting the radio link failure based at least in part on the determination of the radio link failure.

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