Sidelink communications on unlicensed carriers

Abstract

In one embodiment, a first user device performs a Listen Before Talk (LBT) procedure on an unlicensed carrier for a sidelink transmission, determines a result of the LBT procedure, transmits a sidelink signal on a channel in the unlicensed carrier to a second user device in response to determining that the result is an LBT success, and in response to determining that the result is an LBT failure, a physical layer entity of the first user device sends an LBT failure indication to a Medium Access Control (MAC) layer entity of the first user device.

Description

[Technical field]

[0001] This document relates generally to sidelink transmissions in wireless communications. [Background technology]

[0002] background Wireless communication is often performed using user terminal devices and base stations. Wireless communication also occurs over carriers or frequency bands. Some carriers are licensed carriers, which are carriers that have been licensed by a government or other trusted entity to a service provider for exclusive use. Other carriers are unlicensed carriers, which are carriers that have not been licensed by such a government agency or other trusted entity. Currently, user terminal devices communicate with each other directly (i.e., without the use of base stations) over licensed carriers. However, a way for user terminal devices to communicate with each other directly over unlicensed carriers may be desirable. Summary of the Invention [Means for solving the problem]

[0003] overview This document relates to methods, systems, apparatus, and devices for wireless communication. In some embodiments, the method for wireless communication includes performing, by a first user device, a Listen Before Talk (LBT) procedure on an unlicensed carrier for a sidelink transmission, determining, by the first user device, a result of the LBT procedure, and in response to determining that the result is an LBT success, transmitting, by the first user device, a sidelink signal on a channel in the unlicensed carrier to a second user device, and in response to determining that the result is an LBT failure, sending, by a physical layer entity of the first user device, an LBT failure indication to a medium access control (MAC) layer entity of the first user device.

[0004] In some other implementations, a device, such as a network device, is disclosed. The device may include one or more processors and one or more memories, where the one or more processors are configured to read computer code from the one or more memories to perform any one of the methods described above.

[0005] In yet some other implementations, a computer program product is disclosed that may include a non-transitory computer-readable program medium having stored thereon computer code that, when executed by one or more processors, causes the one or more processors to perform any one of the methods described above.

[0006] These and other aspects and their implementations are described in more detail in the drawings, specification, and claims. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 illustrates a block diagram of an example wireless communication system.

[0008] [Diagram 2] FIG. 2 shows a block diagram of an example of an arrangement of layer entities for a communication node.

[0009] [Diagram 3] FIG. 3 illustrates a flow chart of an example method for wireless communication including detecting listen-before-talk (LBT) failure.

[0010] [Figure 4] FIG. 4 illustrates a flowchart of an example method for wireless communication that includes detecting radio link failure based on a number of successive hybrid automatic repeat request (HARQ) discontinuous transmissions (DTX).

[0011] [Diagram 5] FIG. 5 illustrates a flow chart of an example method for wireless communication that includes prioritizing unlicensed transmissions over licensed transmissions.

[0012] [Figure 6] FIG. 6 shows a flowchart of an example of a method for wireless communication comprising determining whether to prioritize sidelink or uplink transmissions based on at least one of a first sidelink prioritization threshold for a licensed carrier or a second sidelink prioritization threshold for an unlicensed carrier.

[0013] [Figure 7] FIG. 7 illustrates a flowchart of an example of a method for wireless communication including determining whether to prioritize a sidelink transmission or an uplink transmission based on at least one of a first uplink prioritization threshold for a licensed carrier or a second uplink prioritization threshold for an unlicensed carrier. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Detailed Description Described herein are various embodiments of systems, apparatus, devices, and methods for wireless communication, including sidelink transmissions, including on unlicensed carriers.

[0015] FIG. 1 illustrates a diagram of an exemplary wireless communication system 100 including multiple communication nodes (or simply nodes) configured to wirelessly communicate with each other. In general, the communication nodes include at least one user device 102 and at least one radio access node 104. The exemplary wireless communication system 100 of FIG. 1 is illustrated as including two user devices 102, including a first user device 102(1) and a second user device 102(2), and one radio access node 104. However, various other examples of wireless communication systems 100 including any of various combinations of user devices 102 and radio access nodes 104 include two or more user devices 102 without any radio access node 104, only one user device 102 and only one radio access node 104, only one user device 102 and two or more radio access nodes 104, two or more user devices 102 and one or more radio access nodes 104, or two or more radio access nodes 104 without any user devices 102.

[0016] In general, a user device as described herein, such as user device 102, may include a single electronic device or apparatus or multiple electronic devices or apparatuses (e.g., a network thereof) that can communicate wirelessly over a network. A user device may include or otherwise be referred to as a user terminal, user terminal device, or user equipment (UE). Additionally, a user device may be or include, but is not limited to, a mobile device (such as a mobile phone, a smart phone, a smart watch, a tablet, a laptop computer, a vehicle or other vessel (such as, by way of non-limiting example, a human, motor, or engine-powered vehicle or other vessel, such as an automobile, an airplane, a train, a boat, or a bicycle) or a fixed or stationary device (such as, by way of non-limiting example, an appliance, a desktop computer or other computing device that is not typically moved for long periods of time, such as a computing device used in a commercial or industrial environment). In various embodiments, the user device 102 may include a transceiver circuit 106 coupled to an antenna 108 for wireless communication with the wireless access node 104. The transceiver circuitry 106 may also be coupled to a processor 110, which may be coupled to a memory 112 or other storage device. The memory 112 may store instructions or code that, when read and executed by the processor 110, cause the processor 110 to perform various of the methods described herein.

[0017] Further, in general, a radio access node as described herein, such as the radio access node 104, may include a single electronic device or apparatus, or multiple electronic devices or apparatus (e.g., a network thereof) and may comprise one or more base stations or other wireless network access points that may wirelessly communicate with one or more user devices and / or one or more other radio access nodes 104 over the network. For example, the radio access node 104 may comprise a 4G LTE base station, a 5G NR base station, a 5G central unit base station, a 5G distributed unit base station, a next generation node B (gNB), an enhanced node B (eNB), or other similar or next generation (e.g., 6G) base station, in various embodiments. The radio access node 104 may include a transceiver circuit 114 coupled to an antenna 116, which may include an antenna tower 118 in various manners, for conducting wireless communications with a user device 102 or another radio access node 104. The transceiver circuit 114 may also be coupled to one or more processors 120, which may be coupled to a memory 122 or other storage device. The memory 122 may store instructions or code that, when read and executed by the processor 120, cause the processor 120 to perform one or more of the methods described herein.

[0018] In various embodiments, two communication nodes in the wireless system 100, such as a user device 102 and a radio access node 104, two user devices 102 without a radio access node 104, or two radio access nodes 104 without a user device 102, may be configured to wirelessly communicate with each other in or over a mobile network and / or radio access network in accordance with one or more standards and / or specifications. In general, the standards and / or specifications may define rules or procedures by which the communication nodes may wirelessly communicate, and in various embodiments may include those for communicating in millimeter (mm) wave bands and / or with multiple antenna schemes and beamforming capabilities. Additionally or alternatively, the standards and / or specifications may define radio access and / or cellular technologies, such as, by way of non-limiting examples, Fourth Generation (4G) Long Term Evolution (LTE), Fifth Generation (5G) New Radio (NR), or New Radio Unlicensed (NR-U).

[0019] FIG. 2 illustrates a block diagram of several modules of a communications node (e.g., user device 102 or wireless access node 104), including a physical layer (PHY) entity or module (also referred to herein simply as a PHY layer, PHY module, or PHY entity) 202, a medium access control (MAC) layer entity or module (also referred to herein simply as a MAC layer, MAC module, or MAC entity) 204, a radio link control (RLC) layer entity or module (also referred to herein simply as an RLC layer, RLC entity, or RLC module) 206, a packaged data convergence protocol (PDCP) layer entity or module (also referred to herein simply as a PDCP layer, PDCP entity, or PDCP module) 208, a radio resource control (RRC) layer entity or module (also referred to herein simply as an RRC layer, RRC entity, or RRC module) 210, and a non-access stratum (NAS) layer entity or module (also referred to herein simply as a NAS layer, NAS entity, or NAS module) 212.

[0020] In general, as used herein, unless otherwise specified, the terms "layer," "entity," and "module," used alone or in combination with each other, for one or more components of a communication node, may be electronic devices, such as electronic circuits, including hardware or a combination of hardware and software. In various embodiments, a module or entity may be implemented using a portion, component, or one or more of the components of the communication node of FIG. 1, including the processor 110 / 120, memory 112 / 122, transceiver circuitry 106 / 114, or antennas 108 / 116. For example, the processor 110 / 120 may perform the functions of the module or entity, such as when executing computer code stored in the memory 112 / 116. Furthermore, in various embodiments, the functions performed by the module or entity may be defined by one or more standards or protocols, such as 5G NR.

[0021] 2 may be higher and lower layers relative to one another, where the PHY layer entity 202 is the lowest layer of the layer entities 202-212, the MAC layer entity 204 is higher than the PHY layer entity 202 and lower than the other layer entities 206-212, the RLC layer entity 206 is higher than the PHY layer entity and the MAC layer entities 202 and 204, the PDCP layer entity, the RRC layer entity, and the 2. In the embodiment, the PDCP layer entity 208 is above the PHY, MAC, and RRC layer entities 202-206 and below the RRC and NAS layer entities 210, 212, and the RRC layer entity 210 is above the PHY, MAC, RRC, and PDCP layer entities 202-208 and below the NAS layer entity 212, which is the highest layer entity of the layer entities 202-220 shown in FIG. 2. In various embodiments, the communication nodes of the system 100 may include modules and / or layer entities other than those shown in FIG. 2.

[0022] Further, in various embodiments, two or more of the communication nodes in the wireless system 100 may be configured to communicate according to a vehicle network standard and / or specification. As used herein, vehicle networking refers to a large-scale system for wireless communication and information exchange including vehicles, pedestrians, roadside devices, and the Internet according to any of a variety of communication protocols and data exchange standards. Vehicle network communication can improve vehicle performance in terms of driving safety, traffic efficiency, usability or user convenience features, or entertainment. Further, in any of the various embodiments, vehicle networking communication can be categorized into three types: communication between vehicles (also referred to as vehicle-to-vehicle (V2V)), communication between vehicles and roadside equipment / network infrastructure (referred to as vehicle-to-infrastructure / vehicle-to-network (V2I / V2N)), and communication between vehicles and pedestrians (referred to as vehicle-to-pedestrian (V2P)). These types of communication are collectively referred to as V2X (vehicle-to-everything) communication. The communication nodes involved in V2X can communicate with each other according to any of a variety of V2X standards or specifications.

[0023] In the wireless system 100, the communication nodes are configured to wirelessly communicate signals with each other. In general, communication in the wireless system 100 between two communication nodes can be or include transmission or reception, and generally both occur simultaneously, depending on the perspective of the particular node in the communication. For example, for a given communication between a first node and a second node, where the first node is transmitting a signal to the second node and the second node is receiving a signal from the first node, the first node may be referred to as a source or transmitting node or device, the second node may be referred to as a destination or receiving node or device, and the communication may be considered as a transmission for the first node and a reception for the second node. Of course, since the communication nodes in the wireless system 100 can both transmit and receive signals, a single communication node may be both a transmitting / source node and a receiving / destination node simultaneously, or may switch between a transmitting node and a receiving node.

[0024] Also, a particular signal may be characterized or defined as either an uplink (UL) signal, a downlink (DL) signal, or a sidelink (SL) signal. An uplink signal is a signal transmitted from a user device 102 to a radio access node 104. A downlink signal is a signal transmitted from a radio access node 104 to a user device 102. A sidelink signal is a signal transmitted from one user device 102 to another user device 102 or from one radio access node 104 to another radio access node 104. Also, for sidelink transmission, the first / source user device 102 transmits the sidelink signal directly to the second / destination user device 102 without forwarding the sidelink signal to the radio access node 104.

[0025] In at least some embodiments involving V2X communications, the user devices 102 may perform sidelink transmissions. Such sidelink communications in V2X may be referred to as PC5-based V2X communications or V2X communications. Furthermore, for sidelink communications in V2X, the user devices 102 may communicate sidelink signals with each other using a PC5 interface, where PC5 refers to a reference point at which a user device 102 communicates with another user device 102 over a direct channel.

[0026] As V2X technology advances, including in the automation industry, scenarios for V2X communications are becoming more diverse and require higher performance. Examples of advanced V2X services include vehicle platooning, extended sensors, advanced driving (semi-autonomous and fully autonomous driving), and remote driving. Exemplary performance requirements for these advanced V2X services may include, by way of non-limiting examples, supporting data packets having a size of 50 to 12,000 bytes, a transmission rate of 2 to 50 messages per second, a maximum end-to-end delay of 3 to 500 milliseconds, a reliability of 90% to 99.999%, a data rate of 0.5 to 1,000 megabytes per second (Mbps), or a transmission range of 50 to 1,000 meters.

[0027] In addition, communication nodes using NR radio access operating with shared spectrum channel access may be configured to operate in different modes, where a primary cell (PCell), a primary secondary cell (PSCell), or a secondary cell (SCell) may be in the shared spectrum, and the SCell may or may not be configured with uplink transmission. Furthermore, in both channel access modes, the radio access node 104 and the user device 102 may be configured to apply or perform a listen-before-talk (LBT) procedure before performing a transmission in a cell configured with shared spectrum channel access.

[0028] 3 illustrates an example method 300 for wireless communication including sidelink communication between a first user device 102(1) and a second user device 102(2) on an unlicensed carrier. The embodiment of the method 300 has the first user device 102(1) functioning as a source or transmitting user device that transmits sidelink signals to the second user device 102(2) and the second user device 102(2) functioning as a destination or receiving user device that receives the sidelink signals from the first user device 102(1).

[0029] Also generally, a licensed carrier is a carrier, frequency band, or spectrum that is licensed to a service provider for exclusive use by a government or other trusted entity (e.g., the Federal Communications Commission (FCC) in the United States, or the European Telecommunications Standards Institute (ETSI) in Europe). An unlicensed carrier, also known as shared spectrum, is a carrier, frequency band, or spectrum that is not licensed by a government or other trusted entity.

[0030] In block 302, a first user device 102(1) may perform a listen-before-talk (LBT) procedure on an unlicensed carrier for transmission of a sidelink signal. In general, when a user device 102 wants to transmit a signal (e.g., an uplink signal or a sidelink signal) on a channel of a particular carrier (unlicensed), the user device may perform an LBT procedure on the carrier before transmitting the signal. During the LBT procedure, the user device 102 may listen or sense the channel to determine whether the channel is available (free) or busy. Depending on or as a result of the execution of the LBT procedure, the user device 102 may determine whether the LBT procedure is successful or unsuccessful. Success indicates that the channel is available, and the user device 102 may proceed to transmit the signal. Failure indicates that the channel is busy, and the user device 102 decides not to transmit the signal.

[0031] In various embodiments, in block 302, the first user device 102(1) may perform an LBT procedure according to a sidelink channel access priority. In particular, the amount of time that the first device 102 has to monitor the channel during the LBT procedure may depend on the value of the sidelink channel access priority. Also, the amount of time resources that the channel occupies if the LBT procedure is successful may depend on the value of the sidelink channel access priority.

[0032] In some of these embodiments, the sidelink channel access priority is a sidelink logical sidelink channel access priority. For example, the first user device 102(1) may be configured with multiple logical channels, and each logical channel may have or be mapped to an associated priority value of the sidelink channel access priority. The priority values ​​may be the same or different from each other for different logical channels. Correspondingly, when the first user device 102(1) determines to transmit data (e.g., data of a MAC protocol data unit (PDU)) as part of a sidelink signal, the first user device 102(1) may determine a logical channel corresponding to the data and then determine a priority value corresponding to the logical channel. The first user device 102(1) may then perform an LBT procedure according to the determined priority value.

[0033] Additionally, in at least some embodiments, the data (e.g., in a MAC PDU) may correspond to multiple logical channels, and correspondingly, the first user device 102(1) may determine multiple priority values ​​for the multiple logical channels and then select a value from the multiple priority values ​​that corresponds to the highest priority.

[0034] In other embodiments, the sidelink channel access priority is a sidelink channel access priority of a quality of service (QoS) profile. The QoS profile may identify a set of QoS parameters corresponding to the data to be transmitted, such as a sidelink PC5 QoS identifier (PQI), a sidelink guaranteed flow bit rate (GFBR), a sidelink maximum flow bit rate (MFBR), and / or a sidelink range. In such an embodiment, the first user device 102(1) may identify a QoS profile corresponding to the data to be transmitted in a sidelink transmission. The first user device 102(1) may then identify a priority value corresponding to the QoS profile. The first user device 102(1) may then perform an LBT procedure according to the determined priority value.

[0035] Additionally or alternatively, the first user device 102(1) may receive the sidelink channel access priorities via an RRC message in response to the first user device 102(1) being in an RRC connected state, may receive the sidelink channel access priorities via system information in response to the first user device 102(1) being in an RRC idle state, and / or may be pre-configured with the sidelink channel access priorities in response to the UE being out of coverage.

[0036] Additionally or alternatively, in various embodiments, the first user device 102(1) may use the channel access priority class (CAPC) of the radio bearer (RB) and the MAC control element (CE) for the priority value of the LBT procedure. In some embodiments, the CAPC of the RB and the MAC CE are fixed or configurable. For example, the CAPC may be fixed to the highest priority for the sidelink signaling radio bearer (SRB) and one or more sidelink MAC CEs, may be configured by the network (radio access node 104) for the sidelink data radio bearer (DRB), or may be fixed to the lowest priority for other sidelink MAC CEs. When selecting the CAPC of a given DRB, the radio access node 104 may take into account the PQIs of all QoS flows multiplexed on the given DRB while considering fairness between different traffic types and transmissions. The communication nodes in the system 100 may use the CAPC of the standardized PQI that best matches the QoS characteristics of the non-standardized PQI of the QoS flow corresponding to the non-standardized PQI.

[0037] Additionally or alternatively, in various embodiments, the first user device 102(1) may select a CAPC as a priority for the LBT procedure by selecting a highest priority CAPC for a sidelink DRB in response to a transport block (TB) of the transmitted sidelink signal including multiple sidelink DRBs, by selecting a highest priority CAPC in response to a transport block including at least one sidelink SRB, sidelink broadcast control channel (SBCCH), or sidelink MAC CE with the highest priority CAPC, or by selecting a lowest priority CAPC in response to a transport block including only one or more sidelink MAC CEs with the lowest priority CAPC.

[0038] In block 304, the first user device 102(1) may determine LBT success or LBT failure based on the LBT procedure performed in block 302, i.e., based on whether the LBT procedure results in LBT success or LBT failure. In block 306, the first user device 102(1) may transmit a sidelink signal to the second user device 102(2) in response to the determination of LBT success, or may not transmit a sidelink signal in response to the determination of LBT failure.

[0039] Further, in at least some embodiments, in block 306, the first user device 102(1) can determine whether a sidelink consistency LBT failure exists according to the result of the LBT procedure performed in block 302 and / or the LBT procedure determined in block 304. In various embodiments, the first user device 102(1) can determine a sidelink consistency LBT failure by counting LBT failures over several LBT procedures or LBT procedure iterations. For example, the user device 102 may be configured with a sidelink maximum LBT failure count for sidelink consistency LBT failure detection (SL-lbt-FailureMaxCount), a sidelink failure detection timer for sidelink consistency LBT failure detection (SL-lbt-FailureDetectionTimer), and a sidelink LBT counter for LBT failure (SL-LBT_COUNTER), which may be initially set to zero. If the first user device 102(1) detects an LBT failure of the LBT procedure, the first user device 102(1) can start or restart the sidelink failure detection timer. The first user device 102(1) may also increment the sidelink LBT counter by one. The first user device 102(1) may then compare the current value of the sidelink LBT counter with the sidelink maximum LBT failure count. If the current value is equal to or greater than the sidelink maximum LBT failure count, the first user device 102(1) may detect a sidelink consistency LBT failure. In at least some embodiments, the first user device 102(1) may use a sidelink failure detection timer in conjunction with the count. For example, the first user device 102(1) may count for a duration measured by the sidelink failure detection timer. That is, the first user device 102(1) may determine whether a sidelink consistency LBT failure has occurred based on the sidelink LBT counter counting during the time that the sidelink LBT failure detection timer is running (not expired).Upon expiration of the sidelink LBT failure detection timer or if the sidelink LBT failure detection timer or the sidelink maximum LBT failure count is reset by the MAC layer 204 (or another higher layer), the user device 102 may reset the sidelink LBT counter to 0 or another initial value.

[0040] Also, in at least some embodiments, the PHY layer 202 of the first user device 102(1) may perform the LBT procedure in block 302 and / or determine whether the LBT procedure is successful or unsuccessful in block 304. If the PHY layer 202 determines an LBT failure in block 304, the PHY layer 202 may send a sidelink failure indication to the MAC layer 204 in block 306 indicating the LBT failure detected by the PHY layer 202. The MAC layer 204 may also be configured with a sidelink maximum LBT failure count, a sidelink failure detection timer, and a sidelink LBT counter as described above, and may determine or detect a sidelink consistency LBT failure in response to receiving the sidelink failure indication.

[0041] Further, in at least some embodiments, in response to determining a sidelink consistency LBT failure, the first user device 102(1) can switch the active bandwidth portion from one bandwidth portion to another bandwidth portion. Additionally or alternatively, in response to determining a sidelink consistency LBT failure, the first user device 102(1) can generate a sidelink LBT failure MAC CE that includes a MAC subheader that includes a logical channel identification (LCID) or is otherwise identified by a MAC subheader. Additionally or alternatively, the sidelink LBT failure MAC CE can include N octets, where N is an integer equal to or greater than 1. Further, the N octets include 8*N X fields. In some embodiments, for a given carrier i, the corresponding i-th X field of the N octets can be set to a value of one ("1") in response to a consistent LBT failure being triggered and not cancelled, or otherwise set to a value of zero ("0"), such as in response to a consistent LBT failure not being triggered or cancelled. In other embodiments, for a given destination index i, the corresponding i-th X field may be set to a value of one ("1") in response to a consistency LBT failure being triggered and not cancelled, and may otherwise be set to a value of zero ("0"), such as in response to a consistency LBT failure not being triggered or cancelled. Additionally or alternatively, the sidelink LBT failure MAC CE may include a list of destination indexes for which a sidelink consistency LBT failure is triggered. Each destination index in the list identifies a corresponding destination identity (ID). Additionally or alternatively, the sidelink LBT failure MAC CE includes a list of carrier indexes for which a sidelink consistency LBT failure is triggered.

[0042] Additionally, in at least some embodiments, the first user device 102(1) cancels the triggered or detected sidelink consistency LBT failure. For some of these embodiments, the first user device 102(1) can cancel the triggered or detected sidelink consistency LBT failure in response to the first user device 102(1) transmitting a MAC PDU including an LBT failure MAC CE and the MAC layer 204 does not receive an LBT failure indication from the PHY layer 202.

[0043] In at least some embodiments, in response to the sidelink consistency LBT failure being triggered and not canceled, and further in response to uplink shared channel (UL-SCH) resources being available for a new uplink transmission and these UL-SCH resources being able to accommodate the LBT failure MAC CE and its subheader as a result of the logical channel prioritization, the first user device 102(1) can perform a multiplexing and assembly procedure (e.g., as defined by a wireless communication standard or protocol (e.g., TS38.321) that configures the user device 102 to determine which MAC CEs and / or MAC service data units (SDUs) to include in a MAC PDU of the granted resources) to generate a sidelink LBT failure MAC CE.

[0044] Additionally or alternatively, the first user device 102(1) may trigger a scheduling request for a sidelink LBT failure MAC CE in response to determining a sidelink consistency LBT failure according to the LBT procedure performed in block 302 and / or the result of the LBT procedure determined in block 304. For at least some of these embodiments, the first user device 102(1) may trigger the scheduling request instead of performing the multiplexing and reassembly procedure. Additionally or alternatively, in at least some of these embodiments, the first user device 102(1) may receive a scheduling resource configuration for the sidelink LBT failure MAC CE from the radio access node 104 (network) before triggering the scheduling request for the sidelink LBT failure MAC CE. Additionally or alternatively, for at least some of these embodiments, the first user device 102(1) may transmit a scheduling request to the radio access node 104 in response to determining a sidelink consistency LBT failure and further in response to the unavailability of uplink shared channel (UL-SCH) resources.

[0045] Additionally or alternatively, the first user device 102(1) may, in response to detecting a sidelink consistency LBT failure, transmit a sidelink consistency LBT failure indication information to the second user device 102(2) indicating a sidelink consistency LBT failure. In at least some of these embodiments, if the first user device 102(1) is configured with multiple carriers, when a sidelink consistency LBT failure is triggered for a first sidelink carrier, the first user device 102(1) may transmit the sidelink consistency LBT failure indication information via another carrier. Furthermore, the sidelink consistency LBT failure indication information may include at least one of an indication of a first sidelink carrier for which a sidelink consistency LBT failure has been triggered or an indication that a sidelink consistency LBT failure has been triggered or detected.

[0046] Also, if the first user device 102(1) is configured with only one carrier and a sidelink consistency LBT failure is triggered for only that one carrier, the first user device 102(1) may not transmit the sidelink consistency LBT failure indication information until the first user device 102(1) determines that it has available resources. To illustrate, assume that the first user device 102(1) determines to use time resource t1. Correspondingly, the first user device 102(1) may perform LBT from at least t1-x, where x depends on the CAPC value. If the first user device 102(1) detects an LBT failure in time resource t1, it does not use time resource t1. Then, the first user device 102(1) performs another LBT procedure for the next time resource, e.g., t10. For example, assume that the first user device 102(1) determines an LBT success for the LBT procedure at t10. In response, the first user device 102(1) determines that it has available resources at time resource t10 and then transmits sidelink consistency LBT failure information at time resource t10.

[0047] Additionally or alternatively, the first user device 102(1) may, in response to detecting a sidelink consistency LBT failure, transmit a sidelink consistency LBT failure indication information indicating a sidelink consistency LBT failure to the radio access node 104. The sidelink consistency LBT failure indication information may include at least one of an indication of a first sidelink carrier on which a sidelink consistency LBT failure was triggered, an identification of a destination (e.g., the second user device 102(1) or a connection between the first and second user devices), and a failure type indication indicating that the indicated failure is a sidelink consistency LBT failure.

[0048] Further, in various embodiments, when a first user device 102(1) wants to communicate with a second user device 102(2) via unicast mode, the first and second user devices 102 may first establish a PC5-RRC connection (also referred to as a PC5 link) with each other. Because a user device may communicate with multiple user devices for different types of services, etc., a user device may establish multiple PC5-RRC connections with multiple user devices. A user device may use a destination ID to uniquely identify a PC5-RRC connection to establish with another user device. Once the first and second user devices 102 establish a PC5-RRC connection, they may exchange various information including, as non-limiting examples, UE capability information, RRC configuration messages including measurement configuration information, or bearer configuration information.

[0049] Additionally, the first user device 102(1) may detect a radio link failure (RLF) of a PC5-RRC connection that the first user device established with the second user device 102(2). Upon detecting the RLF, the first user device 102(1) may release the PC5-RRC connection or destination, which may include releasing a DRB for the PC5-RRC connection and / or discarding NR sidelink communication configuration information for the PC5-RRC connection.

[0050] In various embodiments, the first user device 102(1) may determine an RLF for a PC5-RRC connection in response to detecting that a maximum number of consecutive hybrid automatic repeat request (HARQ) discontinuous transmissions (DTXs) ​​has reached a maximum number of consecutive HARQ DTXs (sl-maxNumConsecutiveDTX). In general, the user device may detect a number of HARQ DTXs, which is a number of consecutive time slots configured in a physical sidelink feedback channel (PSFCH) in which it does not receive a HARQ feedback message. The first user device 102(1) may keep track of a current number of consecutive DTXs (numConsecutiveDTX). If the current number reaches or exceeds a maximum number, the first user device 102(1) may detect an RLF. Thus, in various embodiments, the first user device 102(1) may determine whether there is no PSFCH reception in the PSFCH reception opportunity. If so, the first user device 102(1) may increment the current count by one. The first user device 102(1) may then compare whether the current count has reached the maximum number. If so, the first user device 102(1) may detect an RLF (also referred to as a HARQ-based sidelink RLF). Additionally, in at least some embodiments, the MAC layer 204 tracks the current count and determines whether an RLF has occurred by comparing the current count to the maximum number. If the MAC layer 204 detects an RLF, the MAC layer 204 may notify the RRC layer 210.

[0051] In some situations where the first and second user devices 102 communicate on an unlicensed carrier or a shared spectrum, if the second user device 102(2) performs an LBT procedure and the result is an LBT failure, the second user device 102(2) may not be able to send HARQ feedback to the first user device 102(1). In situations where the first and second user devices 102 communicate on a licensed carrier, consecutive HARQ DTX occurs most frequently due to the first and second user devices 102 being far from each other. In situations where the first and second user devices 102 communicate on an unlicensed carrier, consecutive HARQ DTX occurs due to the first and second user devices 102 being far from each other and because it is easier to reach a maximum number of consecutive HARQ DTX for a particular destination. However, if the maximum number of consecutive HARQ DTX is due to consistent LBT failure, the user device may not want to release the PC5-RRC connection for the destination.

[0052] FIG. 4 illustrates a flowchart of another exemplary method 400 for wireless communication. The method 400 relates to determining a maximum number of consecutive HARQ DTXs that the user device 102 may use to detect RLF. Thus, in various embodiments, the first user device 102(1) may be configured with a number of maximum numbers of consecutive HARQ DTXs that the first user device 102(1) selects to detect RLF. In some embodiments, the first user device 102(1) may receive a number of maximum numbers of consecutive HARQ DTXs from the radio access node 104. In other embodiments, the first user device 102(1) may be preconfigured with a number of maximum numbers of consecutive HARQ DTXs. In general, by being preconfigured with certain information, such as a number of maximum numbers of consecutive HARQ DTXs, the user device has internal access to the information and correspondingly does not need to receive the information from another communication node, such as the radio access node 104, to determine or identify the information.

[0053] In block 402, the first user device 102(1) may select one maximum number of consecutive HARQ DTXs from among a plurality of maximum numbers of consecutive HARQ DTXs. In some embodiments, the maximum number of consecutive HARQ DTXs selected by the first user device 102(1) is a first maximum number of consecutive HARQ DTXs used for one or more unlicensed carriers. Further, in at least some embodiments, the plurality of maximum numbers of consecutive HARQ DTXs includes a second maximum number of consecutive HARQ DTXs used for one or more licensed carriers. Thus, the first user device 102(1) may select the first maximum number or the second maximum number based on whether the first user device 102(1) is transmitting or wants to transmit on an unlicensed carrier or is transmitting or wants to transmit on a licensed carrier. That is, if the first user device 102(1) is transmitting or desires to transmit on an unlicensed carrier, the first user device 102(1) may select a first maximum number of consecutive HARQ DTX, and if the first user device 102(1) is transmitting or desires to transmit on a licensed carrier, the first user device 102(1) may select a second maximum number of consecutive HARQ DTX. Further, in at least some embodiments, the first maximum number of consecutive HARQ DTX for an unlicensed carrier is greater than the second maximum number of consecutive HARQ DTX for a licensed carrier.

[0054] Additionally, in at least some embodiments, the first maximum number of consecutive HARQ DTX of the unlicensed carrier includes a plurality of values. In some of these embodiments, each maximum number of the plurality of values ​​corresponds to a respective one of one or more ranges of channel occupancy values. For example, the first value may correspond to a first range of channel occupancy values, the second value may correspond to a second range of channel occupancy values, and so on. Additionally, the channel occupancy is a percentage of received signal strength indicator (RSSI) samples above a predefined threshold (channelOccupanyThreshold). Additionally, the RSSI is or is indicative of a linear average of the total received power observed in the configured orthogonal frequency division multiplexing (OFDM) symbol. Additionally or alternatively, the RSSI may include a linear average of the total received power in a configured measurement bandwidth over N resource blocks corresponding to an LBT bandwidth having a center frequency of a configured absolute radio frequency channel number (ARFCN) by the user device from all sources including co-channel serving and non-serving cells, adjacent channel interference, and thermal noise. For these embodiments, the first user device 102(1) may determine a first channel occupancy value. The first user device 102(1) may then determine, from among one or more ranges of channel occupancy values, a range of channel occupancy values ​​within which the first channel occupancy value falls. The first user device 102(1) may then determine a maximum numerical value that corresponds to the determined range of channel occupancy and select that maximum numerical value for a first maximum number of consecutive HARQ DTXs.

[0055] In embodiments, each maximum value of the plurality of values ​​corresponds to a respective one of one or more ranges of channel busy ratios (CBRs). In general, the CBR may be or may indicate a percentage of a subchannel proportion of sidelink RSSI (s-RSSI) that exceeds a predetermined threshold within a predetermined period (e.g., 100 ms). In these embodiments, the first user device 102(1) may determine a first CBR value. The first user device 102(1) may then determine, from among the one or more ranges of CBR values, a range of CBR values ​​within which the first CBR value falls. The first user device 102(1) may then determine a first maximum value corresponding to the determined range of CBR values ​​and select the first maximum value for a first maximum number of consecutive HARQ DTXs.

[0056] In other embodiments, each maximum numerical value of the multiple values ​​corresponds to a respective one of one or more ranges of RSSI values. In these embodiments, the first user device 102(1) may determine a first RSSI value. The first user device 102(1) may then determine, from among the one or more ranges of RSSI values, a range of RSSI values ​​within which the first RSSI value falls. The first user device 102(1) may then determine a first maximum numerical value that corresponds to the determined range of CBR values ​​and select that value for the first maximum number of consecutive HARQ DTXs.

[0057] In yet other embodiments, each maximum numerical value of the plurality of values ​​corresponds to a respective one of the one or more priority values. In these embodiments, the first user device 102(1) may determine a first priority value. The first user device 102(1) may then determine a priority value from among the one or more priority values ​​that match the first priority value, determine a first maximum numerical value that corresponds to the determined priority value, and select that value for the first maximum number of consecutive HARQ DTXs.

[0058] After selecting the maximum number of consecutive HARQ DTXs in block 404, the first user device 102(1) may determine whether RLF exists for the PC5-RRC connection established with the second user device 102(2) based on the current number of consecutive HARQ DTXs and the selected maximum number of consecutive HARQ DTXs. For example, as described above, the first user device 102(1) may keep track of the current count of consecutive HARQ DTXs, such as by determining whether PSFCH reception is absent in a PSFCH reception opportunity and determining whether the current count has reached the selected maximum number from block 402. If the current count has reached the selected maximum number, the first user device 102(1) may determine that RLF exists. Additionally, if the current count has not reached the selected maximum number, the first user device 102(2) may determine that RLF does not exist. In block 406, if the first user device 102(1) detects an RLF in block 404, the first user device 102(1) may release the PC5-RRC connection, which may include releasing the DRB for the PC5-RRC connection and / or discarding the NR sidelink communication configuration information for the PC5-RRC connection, as described above. Furthermore, if the first user device 102(1) does not detect an RLF in block 404, the first user device 102(2) may maintain or keep the PC5-RRC connection that it established. If the first user device 102(1) decides to maintain the PC5-RRC connection, it may continue to exchange (transmit and / or receive) information with the second user device 102(2) using the PC5-RRC connection.

[0059] Further, in various embodiments, a user device may perform a sidelink RRC reconfiguration procedure if the user device decides to modify a PC5-RRC connection with another user device. As a non-limiting example, a user device may decide to modify a PC5-RRC connection for any of a variety of reasons, such as when deciding to establish, modify, and / or release a sidelink DRB, configure NR sidelink measurement and reporting, or configure sidelink channel state information (CSI) reference signal resources and CSI report latency bounds. If the user device decides to perform a sidelink RRC reconfiguration procedure for a PC5-RRC connection, the user device initiates the reconfiguration procedure with the other user device by transmitting a sidelink RRC reconfiguration (RRCReconfigurationSidelink) message to the other user device with which it has established the PC5-RRC connection. If the other user device successfully performs or completes a sidelink RRC reconfiguration procedure according to the RRC reconfiguration sidelink message, the other user device may respond to the sidelink RRC reconfiguration message by transmitting a sidelink RRC reconfiguration complete (RRCReconfigurationCompleteSidelink) message to the initiating user device. Furthermore, if the other user devices do not successfully perform or complete a sidelink RRC reconfiguration procedure in accordance with the RRC reconfiguration sidelink message, the other user devices may respond to the RRC reconfiguration sidelink message by transmitting a sidelink RRC reconfiguration failure (RRCRreconfigurationFailureSidelink) message to the initiating user device.

[0060] Also, in various embodiments, the first user device 102(1) may determine an LBT failure recovery. In general, congestion on the unlicensed carrier caused by too many user devices wanting to occupy the unlicensed carrier may increase the likelihood that the first user device 102(1) detects an LBT failure of the LBT procedure. Therefore, it may be preferable for the first user device 102(1) to stop using the unlicensed carrier. However, after a certain time has passed, the number of user devices wanting to occupy the unlicensed carrier may be fewer, at which point it may be desirable or at least feasible for the first user device 102(1) to communicate again on the unlicensed carrier. Also, if the first user device 102(1) detects a sidelink consistency LBT failure, the first user device 102(1) may report an LBT failure indication for the sidelink consistency LBT failure to the radio access node 104. In response, the radio access node 104 may stop allocating sidelink resources on the unlicensed carrier for the reporting first user device 102(1). However, the radio access node 104 may not know when the number of user devices occupying the unlicensed carrier decreases (congestion on the unlicensed carrier decreases) so that it is desirable for the first user device 102(1) to communicate on the unlicensed carrier again. Thus, the first user device 102(1) may continue to perform the LBT procedure on the unlicensed carrier after detecting an LBT failure. If it detects an LBT success during a subsequent LBT procedure on the unlicensed carrier, it may report LBT success information to the radio access node 104. The LBT success information may include at least one of an indication of the first sidelink carrier from which the sidelink consistency LBT failure was recovered, an identification of the destination (e.g., the second user device 102(1) or the connection between the first and second user devices), and a recovery type indication indicating that the indicated recovery is a sidelink consistency LBT failure recovery.In response, the radio access node 104 may allocate sidelink resources for the unlicensed carrier to the first user device 102(1). As used herein, the term LBT failure recovery for a carrier refers to a determination that a user device can communicate in a carrier following a previous determination that the user device should not communicate in the carrier, such as due to detection of an LBT failure.

[0061] In various embodiments, the first user device 102(1) may determine an LBT failure recovery for the sidelink carrier (unlicensed) in response to at least one of: expiration of a timer started by the first user device 102(1) in response to detection of an LBT failure of an LBT procedure and / or an LBT failure indication generated for the detected LBT failure, expiration of a timer started by the first user device 102(1) in response to a triggered or detected sidelink consistency LBT failure according to one or more LBT procedures, a successful outcome of the LBT procedure, or a channel occupancy rate lower than a predefined threshold. In various of these embodiments, the first user device 102(1) may receive from the radio access node 104 a timer value indicating when the timer expires and the predefined threshold value for the channel occupancy rate. In other embodiments, the first user device 102(1) may be preconfigured with the timer value and the predefined threshold value for the channel occupancy rate.

[0062] Also, the first user device 102(1) may determine LBT failure recovery in various embodiments of the method 300 of FIG. 3. For example, in various embodiments, if the first user device 102(1) determines an LBT success of the LBT procedure in block 304, the first user device 102(1) may determine LBT failure recovery. As another example, if the first user device 102(1) determines an LBT failure of the LBT procedure in block 304, the first user device 102(1) may start a timer. If the timer expires, the first user device 102(1) may determine LBT failure recovery. Additionally or alternatively, if the first user device 102(1) determines a sidelink consistency LBT failure in block 306, the first user device 102(1) may start a timer. If the timer expires, the first user device 102(1) may determine LBT failure recovery.

[0063] Furthermore, in various embodiments, the first user device 102(1) may prioritize some transmissions over other transmissions. In some circumstances, if the first user device 102(1) prioritizes a first transmission over a second transmission, the first user device 102(1) may drop the second transmission. If the second transmission is a sidelink transmission on an unlicensed carrier, not performing the sidelink transmission may cause the first user device 102(1) to lose resources acquired for the sidelink transmission. This causes the first user device 102(1) to acquire additional resources for the sidelink transmission again. Correspondingly, the package delay budget (PDB) of data for the sidelink transmission may expire, which may lead to failure of sidelink data transmission / reception.

[0064] To minimize such interference, in various embodiments, the first user device 102(1) may determine whether to prioritize transmissions on an unlicensed carrier over transmissions on a licensed carrier and / or whether to prioritize sidelink transmissions over uplink transmissions.

[0065] 5 illustrates an example method 500 for wireless communication including prioritization of transmissions. At block 502, the first user device 102(1) may prioritize a sidelink transmission over a second transmission depending on whether the sidelink transmission is on an unlicensed carrier and the second transmission is on a licensed carrier, or the first user device 102(1) may prioritize a second transmission over a sidelink transmission depending on whether the second transmission is on an unlicensed carrier and the sidelink transmission is on a licensed carrier.

[0066] Further, in various embodiments, the first user device 102(1) may determine to prioritize the transmissions when the sidelink transmission and the second transmission cannot be performed simultaneously. The first user device 102(1) may prioritize the sidelink transmission over the second transmission since the sidelink transmission is a transmission performed on the unlicensed carrier. In other embodiments, if the second transmission is performed on the unlicensed carrier and the sidelink transmission is performed on the licensed carrier, the first user device 102 may prioritize the second transmission over the sidelink transmission since the second transmission is a transmission performed on the unlicensed carrier. Furthermore, as previously mentioned, the second transmission may be another sidelink transmission or an uplink transmission. In various embodiments, the first user device 102(1) may prioritize the sidelink transmission on the unlicensed carrier in response to the uplink transmission not being prioritized by the non-access stratum (NAS) layer entity 212 of the first user device 102(1) or a layer entity higher than the PHY layer entity 202 of the first user device 102(1).

[0067] In block 504, the first user device 102(1) may perform a sidelink transmission on the unlicensed carrier that has priority over the second transmission on the licensed carrier, such as by transmitting a sidelink signal associated with the sidelink transmission to the second user device 102(2). In response, the first user device 102(1) may drop the second transmission on the licensed carrier.

[0068] Further, in various embodiments, the first user device 102(1) can decide to prioritize sidelink transmissions over uplink transmissions or vice versa. In some of these embodiments, the prioritization can be based on a first sidelink prioritization threshold for sidelink transmissions on the licensed carrier and a second sidelink prioritization threshold for sidelink transmissions on the unlicensed carrier. In some embodiments, the first user device 102(1) can receive the first and second sidelink prioritization thresholds from the radio access node 104. In other embodiments, the first user device 102(1) can be preconfigured with the first and second sidelink prioritization thresholds.

[0069] 6 illustrates an example method 600 for wireless communication including prioritization of sidelink and uplink transmissions. In block 602, the first user device 102(1) may determine to prioritize sidelink transmission over uplink transmission, or vice versa, based on at least one of a first sidelink prioritization threshold or a second sidelink prioritization threshold. In at least some of these embodiments, the first user device 102(1) may prioritize sidelink transmission over uplink transmission if the first user device 102(1) cannot simultaneously perform uplink and sidelink transmissions and if the uplink transmission is not prioritized by the MAC layer 204, and further if the first user device 102(1) will perform sidelink transmission on the licensed carrier and if the highest priority value of a logical channel or MAC CE in the MAC PDU for the sidelink transmission is less than the value of the first sidelink prioritization threshold for the licensed carrier. Also, if the first user device 102(1) performs sidelink transmission on an unlicensed carrier and if the highest priority value of a logical channel or MAC CE in the MAC PDU for the sidelink transmission is less than the value of the second sidelink prioritization threshold for the unlicensed carrier, the first user device 102(1) may prioritize the sidelink transmission over an uplink transmission.

[0070] At block 604, the first user device 102(1) may perform the prioritized transmission, such as by transmitting a signal associated with the prioritized transmission. In response, the first user device 102(1) may drop other transmissions that it did not prioritize.

[0071] FIG. 7 illustrates another example method 700 for wireless communication including prioritization of sidelink and uplink transmissions. In block 702, the first user device 102(1) may determine whether to prioritize sidelink transmissions over uplink transmissions, or vice versa, based on at least one of a first uplink prioritization threshold for uplink transmissions on a licensed carrier or a second sidelink prioritization threshold for uplink transmissions on an unlicensed carrier. In some embodiments, the first user device 102(1) may receive the first and second uplink prioritization thresholds from the radio access node 104. In other embodiments, the first user device 102(1) may be preconfigured with the first and second uplink prioritization thresholds. Also, in at least some of these embodiments using first and second uplink prioritization thresholds, if the first user device 102(1) performs a sidelink transmission on a licensed carrier and if the highest priority value of a logical channel in the MAC PDU for uplink transmission is less than the value of the first uplink prioritization threshold of the licensed carrier, the first user device 102(1) may prioritize uplink transmission over sidelink transmission. Also, if the first user device 102(1) performs a sidelink transmission on an unlicensed carrier and if the highest priority value of a logical channel in the MAC PDU for uplink transmission is less than the value of the second uplink prioritization threshold of the unlicensed carrier, the first user device 102(1) may prioritize uplink transmission over sidelink transmission.

[0072] At block 704, the first user device 102(1) may perform the prioritized transmission, such as by transmitting a signal associated with the prioritized transmission. In response, the first user device 102(1) may drop other transmissions that it did not prioritize.

[0073] Furthermore, in various embodiments, some or all of the methods 300, 400, 500, 600 and 700 described with reference to Figures 3-7 may be performed independently of each other or in combination with each other. For example, the LBT procedure and operations related to the detection of LBT failure and sidelink consistency LBT failure described with reference to Figure 3 may be performed by one or more of the operations performed for the same sidelink transmission, e.g., in combination with the maximum number of consecutive HARQ DTX selections and / or RLF detections described with reference to Figure 4 and / or in combination with one or more of the prioritization schemes described with reference to Figures 5-7. As another example, the maximum number of consecutive HARQ DTX selections and / or RLF detections described with reference to Figure 4 may be performed by one or more of the operations performed for the same sidelink transmission, e.g., in combination with one or more of the prioritization schemes described with reference to Figures 5-7. Various combinations may be possible.

[0074] The above description and the accompanying drawings provide certain exemplary embodiments and implementations. However, the described subject matter may be embodied in various different forms, and therefore, it is intended that the subject matter encompassed or claimed be construed as not being limited to any exemplary embodiment described herein. A reasonably broad scope of subject matter as claimed or encompassed is intended. Among other things, for example, the subject matter may be embodied as a method, device, component, system, or non-transitory computer-readable medium for storing computer code. Thus, the embodiments may take the form of, for example, hardware, software, firmware, storage medium, or any combination thereof. For example, the method embodiments described above may be implemented by a component, device, or system including a memory and a processor by executing computer code stored in the memory.

[0075] Throughout this specification and the claims, terms may have subtle meanings that are suggested or implied in the context beyond the meaning explicitly stated. Similarly, the phrase "in one embodiment / implementation" as used herein does not necessarily refer to the same embodiment, and the phrase "in another embodiment / implementation" as used herein does not necessarily refer to a different embodiment. For example, the subject matter described in the claims is intended to include combinations of the example embodiments in whole or in part.

[0076] Generally, terms may be understood at least in part from their use in context. For example, terms such as "and," "or," or "and / or" as used herein may include various meanings that may depend at least in part on the context in which such terms are used. Typically, "or" when used to relate a list such as A, B, or C is intended to mean A, B, and C, which are used here in an inclusive sense, and A, B, or C, which are used here in an exclusive sense. Furthermore, the term "one or more" as used herein may be used to describe any feature, structure, or characteristic in a singular sense, or may be used to describe a combination of features, structures, or characteristics in a plural sense, depending at least in part on the context. Similarly, terms such as "a," "an," or "the" may be understood to convey a singular usage or to convey a plural usage, depending at least in part on the context. Furthermore, the term "based on" may be understood not to be intended to convey a necessarily exclusive set of factors, but may instead allow for the existence of additional factors not necessarily explicitly described, depending at least in part on the context.

[0077] References to features, advantages, or similar language throughout this specification do not imply that all of the features and advantages that may be realized by the solution should or are included in any single implementation aspect thereof. Rather, language referring to features and advantages is understood to mean that the particular feature, advantage, or characteristic described in connection with an embodiment is included in at least one embodiment of the solution. Thus, descriptions of features and advantages throughout this specification, and similar language, may, but do not necessarily, refer to the same embodiment.

[0078] Furthermore, the described features, advantages, and characteristics of the solution may be combined in any suitable manner in one or more embodiments. Those skilled in the art will recognize in light of the description herein that the solution may be practiced without one or more of the specific features or advantages of a particular embodiment. In other instances, additional features and advantages may be recognized in a particular embodiment that may not be present in all embodiments of the solution.

[0079] The subject matter of the present disclosure may also relate to or include, among other aspects, the following:

[0080] A first aspect includes a method for wireless communication, the method including: performing, by a first user device, a listen-before-talk (LBT) procedure on an unlicensed carrier for sidelink transmission; determining, by the first user device, a result of the LBT procedure; and in response to determining that the result is LBT success, transmitting, by the first user device, a sidelink signal on a channel in the unlicensed carrier to a second user device; and in response to determining that the result is LBT failure, sending, by a physical layer entity of the first user device, an LBT failure indication to a medium access control (MAC) layer entity of the first user device.

[0081] A second aspect includes the first aspect, and further includes performing the LBT procedure on the unlicensed carrier by the first user device in accordance with a sidelink channel access priority or a Quality of Service (QoS) profile of the sidelink logical channel.

[0082] A third aspect includes any of the first or second aspects, further comprising: the sidelink signal includes a sidelink transport block, and the method further includes selecting, by the first user device, a channel access priority class (CAPC) for the LBT procedure, wherein the selecting includes one of: selecting a highest priority CAPC for a sidelink data radio bearer in response to a transport block including a plurality of sidelink data radio bearers; selecting a highest priority CAPC in response to the transport block including at least one sidelink signaling radio bearer, a sidelink broadcast control channel (SBCCH), or a sidelink medium access control (MAC) control element (CE) having the highest priority CAPC; or selecting a lowest priority CAPC in response to the transport block including only one or more sidelink medium access control (MAC) control elements (CEs) with the lowest priority CAPC.

[0083] A fourth aspect includes any of the first to third aspects, and further includes determining, by the first user device, a sidelink consistency LBT failure according to an LBT procedure.

[0084] A fifth aspect includes the fourth aspect, further including switching the active sidelink bandwidth portion from one bandwidth portion to another bandwidth portion in response to determining a sidelink consistency LBT failure.

[0085] A sixth aspect includes any of the fourth or fifth aspects and further includes generating, by the first user device, a sidelink LBT failure MAC control element (CE) in response to determining a sidelink consistency LBT failure according to the LBT procedure.

[0086] A seventh aspect includes the sixth aspect, further comprising: the sidelink LBT failure MAC CE being identified by a MAC subheader including a logical channel identity (LCID).

[0087] An eighth aspect includes the sixth aspect, further comprising: the sidelink LBT failure MAC CE comprises: a list of destination indexes for which a sidelink consistency LBT failure has been triggered, each destination index in the list identifying a destination identity; or a list of carrier indexes for which a sidelink consistency LBT failure has been triggered; or N octets comprising 8*N X-fields, N being an integer greater than or equal to 1, wherein the i-th X-field is set to a value of 1 in response to a consistency LBT failure being triggered and not cancelled for carrier index i and the i-th X-field is set to a value of 0 in response to a consistency LBT failure being not triggered or cancelled; or the i-th X-field is set to a value of 1 in response to a consistency LBT failure being triggered and not cancelled for destination index i and the i-th X-field is set to a value of 0 in response to a consistency LBT failure being not triggered or cancelled.

[0088] A ninth aspect includes the sixth aspect, and further includes triggering, by the first user device, a scheduling request for the sidelink LBT failed MAC CE.

[0089] A tenth aspect includes the ninth aspect and further includes receiving, by the first user device, a scheduling request resource configuration for a sidelink LBT failed MAC CE from the radio access node before triggering the scheduling request.

[0090] An eleventh aspect includes any of the first to tenth aspects, and further includes selecting, by the first user device, a first maximum number of consecutive hybrid automatic repeat request (HARQ) discontinuous transmissions (DTX) from among a plurality of maximum numbers of consecutive HARQ DTX.

[0091] A twelfth aspect includes the eleventh aspect, further including receiving, by the first user device, a plurality of maximum numbers of consecutive HARQ DTX from the radio access node.

[0092] A thirteenth aspect includes the eleventh aspect, further comprising: the first user device being pre-configured with a multiple maximum number of consecutive HARQ DTX.

[0093] A fourteenth aspect includes any of the eleventh to thirteenth aspects, further comprising: a first maximum number of consecutive HARQ DTX is used for the one or more unlicensed carriers; and a second maximum number of consecutive HARQ DTX of the plurality of maximum numbers of consecutive HARQ DTX is used for the one or more licensed carriers; and selecting the first maximum number comprises selecting the first maximum number in dependence on the sidelink transmission being on the unlicensed carrier.

[0094] A fifteenth aspect includes the fourteenth aspect, further comprising: the first maximum number of consecutive HARQ DTX includes a plurality of maximum numerical values, each maximum numerical value in the set being associated with a respective one of one or more ranges of channel occupancy values, associated with a respective one of one or more ranges of received signal strength indicator (RSSI) values, or associated with a respective one of the one or more priority values.

[0095] A sixteenth aspect includes the fifteenth aspect, further comprising: each of a plurality of maximum numerical values ​​in the set corresponding to a respective one or more ranges of channel occupancy values, the method further including determining a first channel occupancy value, and selecting a first maximum number of consecutive HARQ DTXs includes selecting the first maximum number in response to the first maximum number corresponding to a range of channel occupancy values ​​within which the first channel occupancy value falls.

[0096] A seventeenth aspect includes the fifteenth aspect, further comprising: each of a plurality of maximum numerical values ​​in the set corresponds to a respective one of one or more ranges of RSSI values, the method further including determining a first RSSI value, and selecting a first maximum number of consecutive HARQ DTX includes selecting the first maximum number in response to the first maximum number corresponding to a range of RSSI values ​​within which the first RSSI value falls.

[0097] An eighteenth aspect includes the fifteenth aspect, and further wherein each of a plurality of maximum numbers of values ​​in the set corresponds to a respective one of the one or more priority values, and the method further includes determining a first priority value, and selecting the first maximum number of consecutive HARQ DTX includes selecting the first maximum number in response to the first maximum number corresponding to a priority value of the one or more priority values ​​that matches the first priority value.

[0098] A 19th aspect includes any of the 1st to 18th aspects, and further includes detecting, by the first user device, a sidelink consistency LBT failure on the unlicensed carrier based on the LBT procedure, and transmitting, by the first user device, sidelink consistency LBT failure indication information to the second user device, indicating the sidelink consistency LBT failure.

[0099] A twentieth aspect includes any of the first to nineteenth aspects, and further includes detecting, by the first user device, a sidelink consistency LBT failure on the unlicensed carrier according to the LBT procedure, and transmitting, by the first user device, sidelink consistency LBT failure indication information to the radio access node, indicating the sidelink consistency LBT failure.

[0100] A twenty-first aspect includes the twentieth aspect, further comprising: the sidelink consistency LBT failure indication information includes at least one of a carrier indication, a destination identity indication, or a failure type indication.

[0101] A twenty-second aspect includes any of the first to twenty-first aspects, further comprising, by the first user device: determining an LBT failure recovery for the unlicensed carrier for sidelink transmission in response to at least one of: an LBT failure indication from the LBT procedure or an expiry of a timer started in response to a sidelink consistency LBT failure triggered in accordance with the LBT procedure, a successful outcome of the LBT procedure, or a channel occupancy being lower than a predefined threshold.

[0102] A 23rd aspect includes the 22nd aspect, and further includes receiving, by the first user device, a timer value indicating when the timer expires and the predetermined threshold from the radio access node in response to the first user device being within coverage of the radio access node.

[0103] A twenty-fourth aspect includes the twenty-second aspect, further comprising preconfiguring by the first user device a timer value indicating when the timer expires and the predetermined threshold.

[0104] A twenty-fifth aspect includes any of the first to twenty-fourth aspects, further comprising: transmitting, by the first user device, information indicating the LBT success to the radio access node in response to determining that the result is LBT success; and wherein the information indicating the LBT success includes at least one of an unlicensed carrier, a destination identity, or a recovery type indication indicating that the recovery is from a sidelink consistency LBT failure.

[0105] A 26th aspect includes any of the 1st to 25th aspects, and further includes: prioritizing, by the first user device, the sidelink transmission over the second transmission in response to the sidelink transmission being on the unlicensed carrier and the second transmission being on the licensed carrier; and prioritizing, by the first user device, the second transmission over the sidelink transmission in response to the second transmission being on the unlicensed carrier and the sidelink transmission being on the licensed carrier.

[0106] A twenty-seventh aspect includes the twenty-sixth aspect, further comprising: the second transmission includes an uplink transmission.

[0107] A twenty-eighth aspect includes the twenty-seventh aspect, further comprising: prioritizing the sidelink transmission on the unlicensed carrier over the uplink transmission on the licensed carrier in response to the uplink transmission not being prioritized by a non-access stratum (NAS) layer entity of the first user device or a layer entity higher than a physical (PHY) layer entity of the first user device.

[0108] A 29th aspect includes any of the 26th to 28th aspects, and further includes determining, by the first user device, a first sidelink prioritization threshold for transmissions on the unlicensed carrier and a second sidelink prioritization threshold for transmissions on the licensed carrier, wherein the prioritizing the sidelink transmission over the second transmission is based on the first sidelink prioritization threshold and the second sidelink prioritization threshold.

[0109] A 30th aspect includes the 29th aspect, further including receiving, by the first user device, the first sidelink prioritization threshold and the second sidelink prioritization threshold from the radio access node.

[0110] A thirty-first aspect includes the twenty-ninth aspect, further comprising: the first user device being pre-configured with a first sidelink prioritization threshold and a second sidelink prioritization threshold.

[0111] A 32nd aspect includes any of the 29th to 31st aspects, and further includes determining, by the first user device, a first uplink prioritization threshold for transmissions on the unlicensed carrier and a second uplink prioritization threshold for transmissions on the licensed carrier, wherein the method further includes prioritizing, by the first user device, uplink transmissions over sidelink transmissions based on the first uplink prioritization threshold and the second uplink prioritization threshold.

[0112] A thirty-third aspect includes the thirty-second aspect, further including receiving, by the first user device, the first uplink prioritization threshold and the second uplink prioritization threshold from the radio access node.

[0113] A thirty-fourth aspect includes the thirty-second aspect, further comprising: the first user device being pre-configured with a first uplink prioritization threshold and a second uplink prioritization threshold.

[0114] A thirty-fifth aspect includes a wireless communications apparatus comprising a processor and a memory, the processor configured to read code from the memory to implement any of the first to thirty-fourth aspects.

[0115] A thirty-sixth aspect includes a computer program product comprising a computer-readable program medium having code stored thereon, the code, when executed by a processor, causing the processor to implement any of the first to thirty-fourth aspects.

[0116] In addition to the features mentioned in each of the independent aspects listed above, some examples may exhibit optional features mentioned in dependent aspects and / or disclosed and illustrated in the above description, either alone or in combination.

Claims

1. 1. A method for wireless communication, the method comprising: performing, by a first user device, a listen-before-talk (LBT) procedure on an unlicensed carrier for sidelink transmission; determining, by the first user device, a result of the LBT procedure; and transmitting, by the first user device, a sidelink signal on a channel in the unlicensed carrier to a second user device in response to determining that the result is LBT success; and In response to determining that the result is an LBT failure, transmitting, by a physical layer entity of the first user device, an LBT failure indication to a medium access control (MAC) layer entity of the first user device. A method comprising:

2. 2. The method of claim 1, wherein performing the LBT procedure on the unlicensed carrier comprises performing, by the first user device, the LBT procedure in accordance with a sidelink channel access priority or a Quality of Service (QoS) profile of a sidelink logical channel.

3. The sidelink signal includes a sidelink transport block, and the method further includes selecting, by the first user device, a channel access priority class (CAPC) for the LBT procedure, the selecting comprising: selecting a highest priority CAPC for a sidelink data radio bearer in response to the transport block including a plurality of sidelink data radio bearers. selecting the highest priority CAPC in response to the transport block including at least one sidelink signaling radio bearer, a sidelink broadcast control channel (SBCCH), or a sidelink medium access control (MAC) control element (CE) having a highest priority CAPC; or selecting the lowest priority CAPC in response to the transport block including only one or more sidelink medium access control (MAC) control elements (CEs) with the lowest priority CAPC. The method of claim 1 , comprising one of:

4. determining, by the first user device, a sidelink consistency LBT failure according to the LBT procedure; The method of claim 1 further comprising:

5. and switching the active sidelink bandwidth portion from one bandwidth portion to another bandwidth portion in response to determining the sidelink consistency LBT failure. The method of claim 4 further comprising:

6. generating, by the first user device, a sidelink LBT failure MAC control element (CE) in response to determining the sidelink consistency LBT failure according to the LBT procedure. The method of claim 4 further comprising:

7. 7. The method of claim 6, wherein the sidelink LBT failure MAC CE is identified by a MAC subheader that includes a Logical Channel Identification (LCID).

8. Triggering a scheduling request for the sidelink LBT failure MAC CE by the first user device. The method of claim 6 further comprising:

9. 10. The method of claim 8, further comprising receiving, by the first user device, a scheduling request resource configuration for the sidelink LBT failure MAC CE from a radio access node before triggering the scheduling request.

10. detecting, by the first user device, a sidelink consistency LBT failure on the unlicensed carrier according to the LBT procedure; transmitting, by the first user device, a sidelink consistency LBT failure indication information indicating the sidelink consistency LBT failure to a radio access node; The method of claim 1 further comprising:

11. by the first user device, expiry of a timer started in response to an LBT failure indication from the LBT procedure or a sidelink consistency LBT failure triggered according to the LBT procedure; the outcome of the LBT procedure is successful; or The channel occupancy rate is lower than a certain threshold. determining an LBT failure recovery for the unlicensed carrier for the sidelink transmission in response to at least one of The method of claim 1 further comprising:

12. receiving, by the first user device, from the radio access node in response to the first user device being within coverage of the radio access node, a timer value indicating when the timer will expire and the predetermined threshold value. The method of claim 11 further comprising:

13. The method of claim 11 , wherein a timer value indicating when the timer expires and the predetermined threshold are preconfigured by the first user device.

14. A wireless communication device comprising a processor and a memory, the processor being configured to read code from the memory to perform a method according to any of claims 1-13.

15. 14. A computer program product comprising a computer readable program medium comprising code stored thereon, the code which, when executed by a processor, causes the processor to perform a method according to any of claims 1 to 13.

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