Adaptation of SL synchronization source based on CCA failure

Abstract

Systems and methods are disclosed for sidelink (SL) synchronization source adaptation based on clear channel assessment (CCA) failure. In some embodiments, a method for selecting and / or maintaining a synchronization source includes obtaining information regarding one or more synchronization sources associated with sidelink operation, including configured and / or available synchronization sources, determining, for a first synchronization source, whether to adapt the selection and / or maintenance of the first synchronization source as a source of synchronization based on a CCA procedure, and adapting the selection and / or maintenance. In some embodiments, a method for operating as a synchronization reference UE includes obtaining information related to the need to transmit SL reference signals (RSs), determining information related to the results of the CCA procedure, and adapting transmission of the SL RSs based on the results of the CCA procedure. Some embodiments enable selection of a reliable synchronization source and / or define an unambiguous synchronization procedure for the sidelink.

Description

[Technical Field]

[0001] Related Applications This application claims the benefit of Provisional Patent Application No. 63 / 446,267, filed February 16, 2023, the entire disclosure of which is incorporated herein by reference.

[0002] V2X, D2D, Sidelink, UE-Network Relay, Proximity Based Services (ProSe), LBT, CCA, Unlicensed Band Operation, Synchronization Reference Resources. [Background technology]

[0003] Unlicensed operation in NR

[0004] Unlicensed spectrum can be shared among multiple networks. Before transmitting on a channel on the unlicensed spectrum, a device / node performs clear channel assessment (CCA) to assess or determine whether the channel is busy. The CCA procedure is also called listen-before-talk (LBT).

[0005] CCA consists of monitoring a channel for a specified time and measuring the received energy and / or, in some technologies (e.g., Wi-Fi), checking for a preamble transmission that indicates the start of another device's transmission. If a device assesses a channel as idle (e.g., based on CCA), it is allowed to transmit a signal on that channel, which may also be referred to as a clear channel, free channel, available channel, unused channel, or not-busy channel. A channel is assessed as idle if the received energy or power during the sensing time duration is below a certain energy detection threshold; otherwise, the channel is considered busy. An example of an energy detection level threshold is −72 dBm, which may further depend on the channel bandwidth, e.g., −72 dBm and −75 dBm for 20 MHz and 10 MHz, respectively. If the channel is assessed as “busy,” the device (UE or BS) is required to defer transmission.

[0006] After sensing that the channel is idle, a device / node is generally allowed to transmit for a certain amount of time, sometimes referred to as the channel occupation time (COT) or maximum channel occupation time (MCOT). The maximum allowable length of the COT depends on the regulation and type of CCA performed (e.g., how long the medium is sensed, e.g., sensing duration), and the COT generally ranges between 1 ms and 10 ms.

[0007] FIG. 1 illustrates LTE LBT and COT, where "s" is the sensing time period. In one example, the sensing period may be 25 μs. In this figure, if the channel is determined to be busy, after some delay time, the device may again attempt to sense on the channel to determine whether the channel is available, and if the channel is available, after some backoff time, the device may begin transmitting signals (during the device's channel occupancy time), but for less than the maximum channel occupancy time (MCOT), which may be, for example, up to 10 ms depending on the region. The backoff time may be deterministic or statistical.

[0008] Sidelink Transmission in NR

[0009] Sidelink (SL) operation allows direct communication between two or more UEs over an SL interface or a PC5 interface.

[0010] D2D operations is a generic term that may include transmission and / or reception of any type of D2D signal (e.g., physical signal, physical channel, etc.) by a D2D communication-enabled UE and / or by a D2D discovery-enabled UE. V2X is a special type of D2D (device to device) operation. Thus, D2D operations are also referred to as D2D transmission, D2D reception, D2D communication, proximity services (ProSe), V2X, etc.

[0011] SL operation is specified for LTE and NR for various applications and use cases, such as proximity services (ProSe) (communication and discovery), vehicular communications (commonly referred to as V2X or V2V), etc. In LTE V2X, only broadcast is supported on the sidelink. NR SL allows broadcast, groupcast, and unicast communications. In groupcast communications, the intended receiver of a message is generally a subset of vehicles near the transmitter, while in unicast communications, there is a single intended receiver. Broadcast, groupcast, and unicast transmissions for V2X operation over SL are supported for in-coverage, out-of-coverage, and partial coverage scenarios. HARQ feedback and HARQ combining at the UE physical layer are supported for unicast and groupcast transmissions over SL.

[0012] Both LTE SL and NR SL can operate with and without network coverage, including support for standalone, network-less operation, and with different degrees of interaction between the UE (User Equipment) and the network.

[0013] SL may be configured on a dedicated carrier (e.g., in a carrier of the ITS band) or on the carrier of the UE's serving cell. In the latter case, SL resources and resources for cellular communication (on the uplink / downlink, also known as the Uu link) are shared in time and / or frequency. Typically, SL resources are time-multiplexed with uplink resources used for cellular communication on the UE's serving cell.

[0014] The embodiments described herein are applicable to any type of D2D operation, including ProSe, V2X, etc.

[0015] Examples of physical channels and reference signals for SL operation NR (previously available in LTE) are:

[0016] PSSCH (Physical Sidelink Shared Channel, SL version of PDSCH): The PSSCH is transmitted by the sidelink transmitter UE and carries sidelink transmission data, system information blocks (SIBs) for radio resource control (RRC) configuration, and part of the sidelink control information (SCI).

[0017] PSFCH (Physical Sidelink Feedback Channel): The PSFCH is transmitted by the sidelink receiver UE for unicast and groupcast, and it carries 1-bit information on 1 RB for HARQ acknowledgment (ACK) and negative ACK (NACK). In addition, channel state information (CSI) is carried in the medium access control (MAC) control element (CE) on the PSSCH instead of the PSFCH.

[0018] PSCCH (Physical Sidelink Common Control Channel, SL version of PDCCH): When traffic to be sent to a receiver UE arrives at a transmitter UE, the transmitter UE should first send a PSCCH, which conveys part of the SCI (Sidelink Control Information, SL version of DCI) to be decoded by any UE for channel sensing purposes, including reserved time-frequency resources for transmission, Demodulation Reference Signal (DMRS) pattern and antenna ports, etc.

[0019] Sidelink Primary Synchronization Signal / Secondary Synchronization Signal (S-PSS / S-SSS): Similar to downlink transmission in NR, sidelink transmission supports primary and secondary synchronization signals (referred to as S-PSS and S-SSS, respectively). Through detecting the S-PSS and S-SSS, the UE can identify the sidelink synchronization identity (SSID) from the UE transmitting the S-PSS / S-SSS. Through detecting the S-PSS / S-SSS, the UE can therefore learn the characteristics of the UE transmitter S-PSS / S-SSS. The process of acquiring timing and frequency synchronization along with the UE's SSID is called initial cell search. Note that the UE transmitting the S-PSS / S-SSS may not necessarily be involved in sidelink transmission, and the node (UE / eNB / gNB) transmitting the S-PSS / S-SSS is called the synchronization source. There are two S-PSS sequences and 336 S-SSS sequences, forming a total of 672 SSIDs in the cell.

[0020] Physical Sidelink Broadcast Channel (PSBCH): The PSBCH is transmitted together with the S-PSS / S-SSS as a synchronization signal / PSBCH block (SSB). The SSB has the same numerology as the PSCCH / PSSCH on that carrier, and the SSB should be transmitted within the configured BWP bandwidth. The PSBCH carries synchronization-related information, such as the Direct Frame Number (DFN), slot- and symbol-level time resource indication for sidelink transmissions, and an in-coverage indicator. The SSB is transmitted periodically every 160 ms.

[0021] DMRS, Phase Tracking Reference Signal (PT-RS), Channel State Information Reference Signal (CSIRS): These physical reference signals supported by NR downlink / uplink transmissions are also employed by sidelink transmissions. Similarly, PT-RS is only applicable to FR2 transmissions.

[0022] Similar to ProSe in LTE, NR sidelink transmission has two modes of resource allocation: Mode 1: Sidelink resources are scheduled by the gNB. Mode 2: The UE autonomously selects sidelink resources from (one or more) (pre-)configured sidelink resource pools based on a channel sensing mechanism.

[0023] For in-coverage UEs, the gNB may be configured to employ Mode 1 or Mode 2. For out-of-coverage UEs, only Mode 2 may be employed.

[0024] As in LTE, scheduling over the sidelink in NR is done differently for Mode 1 and Mode 2.

[0025] As captured in RP-213678 on NR SL evolution in 3GPP Rel-18, the following research goals were defined in 3GPP Rel-18: 1. Study and specify support for sidelink over unlicensed spectrum for both Mode 1 and Mode 2, with Uu operation for Mode 1 restricted to licensed spectrum only [RAN1, RAN2, RAN4] - For sidelink unlicensed operation the channel access mechanism from NR-U shall be reused Assess the applicability of sidelink resource reservations to unlicensed channel access mechanisms and sidelink unlicensed operation within the boundaries of operation from Rel-16 / Rel-17 No special enhancements to the Rel-17 resource allocation mechanism If the existing NR-U channel access framework does not support the required SL-U functionality, the WG will make appropriate recommendations for RAN approval. - Physical Channel Design Framework: Required changes to NR sidelink physical channel structure and procedures for operation on unlicensed spectrum The existing NR sidelink and NR-U channel structure shall be reused as a baseline. - No special enhancements to existing NR SL features - Studies should focus on the FR1 unlicensed bands (n46 and n96 / n102) and should be completed by RAN#98.

[0026] To support sidelink transmissions over unlicensed spectrum (SL-U), new mechanisms for selecting and maintaining a reliable synchronization source are needed because legacy mechanisms are not designed to handle LBT failures at both the transmitting and receiving nodes. Following legacy mechanisms to perform synchronization procedures over unlicensed spectrum may result in the UE selecting a less reliable synchronization source, which ultimately leads to connection failure. Therefore, new synchronization methods are needed to support sidelink operation over unlicensed spectrum. Summary of the Invention

[0027] In some embodiments, a method for selecting and / or maintaining a sidelink (SL) synchronization source based on clear channel assessment (CCA) failures is disclosed. In some embodiments, a method performed by a user equipment (UE) for selecting and / or maintaining a synchronization source includes: acquiring information regarding one or more synchronization sources associated with sidelink operation, the one or more synchronization sources including configured and / or available synchronization sources; determining, for a first synchronization source of the one or more synchronization sources associated with sidelink operation, whether to adapt the selection and / or maintenance of the first synchronization source as a source of synchronization, the determining including determining whether to adapt the selection and / or maintenance of the first synchronization source based on at least one CCA procedure; and adapting the selection and / or maintenance of the first synchronization source as a source of synchronization in response to determining to adapt the selection and / or maintenance of the first synchronization source based on the at least one CCA procedure. In some embodiments, a method performed by a UE to operate as a synchronization reference UE includes obtaining information related to a need to transmit SL reference signals (RSs), determining information related to a result of at least one CCA procedure related to the SRSs, and adapting transmission of the SL RSs based on the result of the at least one CCA procedure. Some embodiments provide one or more benefits, such as enabling selection of a reliable synchronization source when operating in a carrier covered by CCA and / or defining an unambiguous synchronization procedure for the sidelink when operating in a carrier covered by CCA.

[0028] Some embodiments described herein apply to a scenario in which UE1 is configured to operate (e.g., transmit and / or receive) signals between UE1 and at least one other UE, a second UE (UE2), on a second carrier (F2). UE1 and UE2 may be operating in either Sidelink Mode 1 or Sidelink Mode 2. Furthermore, to select a synchronization reference source, UE1 is configured with or follows a list of synchronization sources (e.g., predefined in a specification), where the sources may have the same or different priorities.

[0029] In a first embodiment, a UE1 synchronized to a first synchronization reference source (SRS1) to use a signal transmitted on a first carrier frequency (F1) by SRS1 for sidelink operation determines a result of a CCA procedure performed by SRS1 to transmit the signal on F1, and adapts the synchronization reference source (SRS) based on the determined result of the CCA procedure performed by SRS1 on the signal transmitted on F1.

[0030] The adaptation of the SRS may be determined by UE1 based on one or more rules, which may be predefined, preconfigured (e.g., on a SIM / USIM card), or configured by a node (e.g., by another UE, a network, etc.). Examples of SRS adaptation include continuing to use SRS1, discarding SRS1, changing synchronization to a second synchronization reference source (SRS2) / reselecting SRS2, suspending SRS1 for a period of time, suspending or postponing SRS1 until one or more conditions are met, starting / stopping SRS1, etc. Examples of results of a CCA procedure include the number of CCA failures, the number of successful CCAs, the number of CCA failures over a time period, the number of successful CCAs over a time period, etc. For example, UE1 triggers reselection of a synchronization reference source (e.g., to SRS2) if the number of CCA failures on F1 detected by UE1 exceeds a threshold; otherwise, the UE continues to use SRS1. The signal received from SRS1, whose transmission is subject to the CCA procedure, is used by UE1 to adjust, correct, or obtain timing information to enable SL signals to operate on F1. SRS1 may be a UE, a third UE (UE3), or a first network node (NN1, e.g., a first base station). SRS2 may be a UE, a fourth UE (UE4), or a second network node (NN2, e.g., a second base station).

[0031] In a second embodiment, at least one other UE on a first carrier (F1), a third UE (UE3) configured as a first synchronization reference source (SRS1) for the first UE (UE1), determines a result of a CCA procedure performed by UE3 on F1 and adapts transmission of a SL reference signal (SLRS) on F1 based on the determined result of the CCA procedure performed by UE3 on F1.

[0032] The adaptation of SLRS transmission may be determined by the UE 3 based on one or more rules, which may be predefined, preconfigured (e.g., on a SIM / USIM card), or configured by a node (e.g., by another UE, a network, etc.). Examples of SLRS adaptation include continuing to transmit SLRS, stopping / canceling SLRS transmission, pausing or postponing SLRS transmission for a time period or resuming / restarting SLRS transmission after a time period, pausing or postponing SLRS transmission until or resuming / restarting SLRS transmission after one or more conditions are met, adapting the transmission rate of SLRS (e.g., transmitting SLRS at a rate below a threshold), etc. An example of an SLRS is SLSS. Examples of results of a CCA procedure are the number of CCA failures, the number of successful CCAs, the number of CCA failures over a time period, the number of successful CCAs over a time period, etc. For example, UE3 stops / aborts SLRS transmission if the number of CCA failures on F1 detected by UE3 exceeds a threshold, otherwise UE3 continues transmitting SLRS. UE3 generally transmits periodic SL reference signals (e.g., SLSS).

[0033] The operation between UE1 and UE2 on F2 may or may not be subject to a CCA procedure, i.e., a CCA procedure is applied before transmission of signals. However, the operation between UE1 and SRS1 is subject to CCA. In one example, F1 and F2 are different carrier frequencies. In another example, F1 and F2 are the same carrier frequency.

[0034] The terms synchronization reference source, synchronization source, and synchronization reference are used interchangeably herein.

[0035] Some embodiments provide one or more benefits, such as enabling the selection of a reliable synchronization source when operating in a carrier covered by CCA and / or defining a clear synchronization procedure for the sidelink when operating in a carrier covered by CCA.

[0036] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several aspects of the present disclosure and, together with the description, serve to explain the principles of the disclosure. [Brief explanation of the drawings]

[0037] [Figure 1] 1 is a diagram showing LTE LBT and COT, where "s" is the sensing time period. [Figure 2] FIG. 1 illustrates an example of a cellular communication system, according to some embodiments of the present disclosure. [Figure 3] A diagram showing a scenario in which UE1 engages in SL operation with UE2 and derives timing from a first synchronization reference source (SRS1) subject to CCA. [Figure 4] A diagram showing a scenario in which UE1 changes / reselects its SRS from SRS1 to SRS2 due to a CCA failure on F1 between UE1 and SRS1. [Figure 5] 1 is a schematic block diagram of a radio access node according to some embodiments of the present disclosure. [Figure 6] 6 is a schematic block diagram illustrating a virtualized embodiment of the radio access node of FIG. 5, in accordance with some embodiments of the present disclosure. [Figure 7] 6 is a schematic block diagram of the radio access node of FIG. 5 according to some other embodiments of the present disclosure. [Figure 8] 1 is a schematic block diagram of a user equipment device (UE) in accordance with some embodiments of the present disclosure. [Figure 9] 9 is a schematic block diagram of the UE of FIG. 8 in accordance with some other embodiments of the present disclosure. [Figure 10]FIG. 1 illustrates a communication network connected to a host computer through an intermediate network, according to some embodiments of the present disclosure. [Figure 11] FIG. 2 is a generalized block diagram of a host computer communicating with a UE via a base station over a partial wireless connection, in accordance with some embodiments of the present disclosure. [Figure 12] 1 is a flowchart illustrating a method implemented in a communication system according to one embodiment of the present disclosure. [Figure 13] 1 is a flowchart illustrating a method implemented in a communication system according to one embodiment of the present disclosure. [Figure 14] 1 is a flowchart illustrating a method implemented in a communication system according to one embodiment of the present disclosure. [Figure 15] 1 is a flowchart illustrating a method implemented in a communication system according to one embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0038] The embodiments described below represent information to enable those skilled in the art to practice the embodiments and illustrate the best modes of practicing the embodiments. Upon reading the following description in light of the accompanying drawings, those skilled in the art will understand the concepts of the present disclosure and will recognize applications of these concepts not specifically addressed herein. It is understood that these concepts and applications fall within the scope of the present disclosure.

[0039] Wireless Node: As used herein, a "wireless node" is either a wireless access node or a wireless communication device.

[0040] Radio Access Node: As used herein, a "radio access node" or "radio network node" or "radio access network node" is any node in a Radio Access Network (RAN) of a cellular communications network that operates to transmit and / or receive signals wirelessly. Some examples of a radio access node include, but are not limited to, a base station (e.g., a New Radio (NR) base station (gNB) in a 3rd Generation Partnership Project (3GPP) fifth-generation (5G) NR network or an enhanced or evolved Node B (eNB) in a 3GPP Long Term Evolution (LTE) network), a high-power or macro base station, a low-power base station (e.g., a micro base station, a pico base station, a Home eNB, etc.), a relay node, a network node implementing part of the functionality of a base station, or a network node implementing a gNB distributed unit (gNB-DU), or a network node implementing part of the functionality of some other type of radio access node.

[0041] Core Network Node: As used herein, a "core network node" is any type of node in a core network or any node that implements a core network function. Some examples of core network nodes include, for example, a Mobility Management Entity (MME), a Packet Data Network Gateway (P-GW), a Service Capability Publication Function (SCEF), a Home Subscriber Server (HSS), etc. Some other examples of core network nodes include nodes that implement an Access and Mobility Function (AMF), a User Plane Function (UPF), a Session Management Function (SMF), an Authentication Server Function (AUSF), a Network Slice Selection Function (NSSF), a Network Publication Function (NEF), a Network Function (NF) Repository Function (NRF), a Policy Control Function (PCF), a Unified Data Management (UDM), etc.

[0042] Communications Device: As used herein, a "communications device" is any type of device that has access to an access network. Some examples of communications devices include, but are not limited to, a mobile phone, a smartphone, a sensor device, a meter, a vehicle, a household appliance, a medical appliance, a media player, a camera, or any type of consumer electronic device, such as, but not limited to, a television, a radio, a lighting device, a tablet computer, a laptop computer, or a personal computer (PC). A communications device may be a portable, handheld, computer-equipped, or vehicle-mounted mobile device enabled to communicate voice and / or data via wireless or wired connections.

[0043] Wireless Communication Device: One type of communication device is a wireless communication device, which can be any type of wireless device that has access to (i.e., is served by) a wireless network (e.g., a cellular network). Some examples of wireless communication devices include, but are not limited to, user equipment devices (UEs) in 3GPP networks, machine-type communication (MTC) devices, and Internet of Things (IoT) devices. Such wireless communication devices can be or can be integrated into mobile phones, smartphones, sensor devices, meters, vehicles, household appliances, medical appliances, media players, cameras, or any type of consumer electronics device, such as, but not limited to, televisions, radios, lighting devices, tablet computers, laptop computers, or PCs. Wireless communication devices can be portable, handheld, computer-equipped, or vehicle-mounted mobile devices enabled to communicate voice and / or data over a wireless connection.

[0044] Network Node: As used herein, a "network node" is any node that is part of either the RAN or core network of a cellular communications network / system.

[0045] Transmit / Receive Point (TRP): In some embodiments, a TRP can be either a network node, a radio head, a spatial relationship, or a transmission configuration indicator (TCI) state. In some embodiments, a TRP can be represented by a spatial relationship or a TCI state. In some embodiments, a TRP may use multiple TCI states. In some embodiments, a TRP can be part of a gNB that transmits and receives radio signals to / from a UE according to physical layer properties and parameters specific to that element. In some embodiments, in multiple TRP (multi-TRP) operation, a serving cell can schedule a UE from two TRPs to provide better physical downlink shared channel (PDSCH) coverage, reliability, and / or data rates. There are two different operating modes for multi-TRP: single downlink control information (DCI) and multi-DCI. For both modes, control of uplink and downlink operations is performed by both the physical layer and medium access control (MAC). In single DCI mode, the UE is scheduled by the same DCI for both TRPs, and in multi-DCI mode, the UE is scheduled by independent DCI from each TRP.

[0046] In some embodiments, a set of transmission points (TPs) is a set of geographically collocated transmit antennas (e.g., an antenna array (with one or more antenna elements)) for one cell, part of one cell, or one Positioning Reference Signal (PRS)-dedicated TP. The TPs may include base station (eNB) antennas, remote radio heads (RRHs), remote antennas of base stations, antennas of PRS-dedicated TPs, etc. One cell may be formed by one or more TPs. In the case of a homogeneous deployment, each TP may correspond to one cell.

[0047] In some embodiments, a set of TRPs is a set of geographically collocated antennas (e.g., antenna arrays (with one or more antenna elements)) that support TP and / or receiving point (RP) functionality.

[0048] It should be noted that the description provided herein focuses on 3GPP cellular communication systems, and therefore 3GPP terminology or terminology similar to 3GPP terminology is often used, however, the concepts disclosed herein are not limited to 3GPP systems.

[0049] It should be noted that in the description herein, reference may be made to the term "cell." However, it is important to note that, particularly with regard to 5G NR concepts, beams may be used instead of cells, and therefore the concepts described herein are equally applicable to both cells and beams.

[0050] 2 illustrates an example of a cellular communication system 200 in which embodiments of the present disclosure may be implemented. In the embodiments described herein, the cellular communication system 200 is a 5G system (5GS) including a Next Generation RAN (NG-RAN) and a 5G Core (5GC). In this example, the RAN includes base stations 202-1 and 202-2, which include NR base stations (gNBs) in 5GS and optionally Next Generation eNBs (ng-eNBs) (e.g., LTE RAN nodes connected to 5GC), which control corresponding (macro) cells 204-1 and 204-2. Base stations 202-1 and 202-2 are generally referred to herein collectively as base stations 202 and individually as base stations 202. Similarly, (macro) cells 204-1 and 204-2 are generally referred to herein collectively as (macro) cells 204 and individually as (macro) cells 204. The RAN may also include several low-power nodes 206-1 through 206-4 that control corresponding small cells 208-1 through 208-4. The low-power nodes 206-1 through 206-4 may be small base stations (such as pico base stations or femto base stations) or remote radio heads (RRHs), etc. Notably, although not shown, one or more of the small cells 208-1 through 208-4 may alternatively be provided by the base station 202. The low-power nodes 206-1 through 206-4 are generally collectively referred to herein as low-power nodes 206 and individually referred to as low-power nodes 206. Similarly, the small cells 208-1 through 208-4 are generally collectively referred to herein as small cells 208 and individually referred to as small cells 208. The cellular communication system 200 also includes a core network 210, referred to as 5GC in 5G systems (5GS). The base station 202 (and optionally the low power node 206 ) is connected to a core network 210 .

[0051] Base station 202 and low power node 206 serve wireless communication devices 212-1 through 212-5 in corresponding cells 204 and 208. Wireless communication devices 212-1 through 212-5 are generally referred to herein collectively as wireless communication devices 212 and individually as wireless communication devices 212. In the following description, wireless communication devices 212 are often UEs, although the disclosure is not limited thereto.

[0052] Generalizations and Terminology

[0053] Examples of network nodes are Node B, base station (BS), MSR radio node such as Multi-Standard Radio (MSR) BS, eNodeB, gNodeB, MeNB, SeNB, location measurement unit (LMU), integrated access backhaul (IAB) node, network controller, radio network controller (RNC), base station controller (BSC), relay, donor node controlled relay, base transceiver station (BTS), central unit (e.g., in gNB), distributed unit (e.g., in gNB), baseband unit, centralized baseband, C-RAN, access point (AP), transmission point, transmitting node, transmit receiving point (TRP), RRU, RRH, node in distributed antenna system (DAS), core network node (e.g., MSC, MME, etc.), O&M, OSS, SON, positioning node (e.g., E-SMLC), etc.

[0054] The non-limiting term UE refers to any type of wireless device that communicates with network nodes and / or other UEs in a cellular or mobile communication system. Examples of UEs are target devices, device to device (D2D) UEs, vehicle to vehicle (V2V) UEs, MTC UEs or UEs capable of machine-to-machine (M2M) communications, PDAs, tablets, mobile terminals, smartphones, laptop embedded equipment (LEEs), laptop mounted equipment (LMEs), USB dongles, etc.

[0055] The term radio access technology or RAT may refer to any RAT, for example, UTRA, E-UTRA, Narrowband Internet of Things (NB-IoT), WiFi, Bluetooth, Next Generation RAT, New Radio (NR), 4G, 5G, etc. Any of the equipment denoted by the term node, network node, or radio network node may be capable of supporting a single RAT or multiple RATs.

[0056] The term clear channel assessment (CCA) as used herein may correspond to any type of carrier sense multiple access (CSMA) procedure or mechanism performed by a device on a carrier before deciding to transmit a signal on that carrier. The term carrier may also be referred to interchangeably as a carrier frequency, frequency layer, channel, radio channel, radio frequency channel, etc. CCA may also be referred to interchangeably as a CSMA scheme, a channel assessment scheme, listen-before-talk (LBT), a shared channel access mechanism or mechanism, a shared spectrum channel access mechanism or mechanism, etc. A frequency band of a carrier subject to CCA may also be referred to as an unlicensed band or spectrum, a shared spectrum channel access band, a band for operation with shared spectrum channel access, etc. CCA-based operation is more commonly referred to as contention-based operation. Transmission of signals on a carrier subject to CCA is also referred to as contention-based transmission. Contention-based operation is generally used for transmissions on carriers in unlicensed frequency bands. However, this mechanism may also be applied to operation on carriers belonging to licensed bands, for example, to reduce interference. Transmission of signals on carriers not subject to CCA is also referred to as contention-free transmission. The LBT or CCA procedure may be performed by the UE prior to an UL transmission and / or by a network node (e.g., a base station) prior to a DL transmission or by another SL UE. Thus, CCA may also be referred to as DL CCA (e.g., performed prior to a DL transmission), UL CCA (e.g., performed prior to an UL transmission), etc.

[0057] The term SLRS used in different embodiments may be referred to as any of SL-SSSB, SLSS, S-PSS, S-SSS, PSBCH or any combination, for example, S-SS / PSBCH (S-SS+S-PSS+PSBCH).

[0058] Furthermore, both LBE-based channel access schemes (sometimes called dynamic channel access) and FBE-based channel access schemes (sometimes called semi-static channel access) are covered in the following embodiments.

[0059] The following embodiments are applicable to SL transmissions over unlicensed bands with any cast type, including unicast, groupcast, and broadcast.

[0060] For an SL BWP configured in a UE, the BWP may contain multiple bandwidth segments, e.g., called channels, subbands, BWP segments, etc., and for each segment, different parameters may be configured for that segment: SCS, symbol duration, cyclic prefix (CP) length.

[0061] In this case, the UE may perform an LBT operation for each channel / subband / BWP segment.

[0062] The term "signal operation" may refer to either the transmission of a signal by a device and / or the reception of a signal at a device. The term "signal operation subject to CCA" may refer to a scenario in which a device may apply a CCA procedure to determine whether a channel is idle or busy before transmitting a signal on a carrier; i.e., if the channel is idle, the device transmits a signal; otherwise, the device delays transmission. For simplicity, in some embodiments, the term "carrier subject to CCA" may be used to refer to the operation of a signal on a cell of a carrier when a CCA procedure is applied by a device before transmitting a signal. Each occurrence of a signal, or an occurrence when a UE can operate a signal, is broadly referred to as an occasion, which may be a transmission occasion or a reception occasion. An occasion may also be interchangeably referred to as a signal occasion, a signal operation occasion, a measurement occasion, a signal operation opportunity, a signal duration, an operation occasion, or simply an occasion for operating a signal, etc. Examples of occasions are time resources containing RS (e.g., SLSS, CSI-RS, SSB), SMTC occasions, discovery burst transmission (DBT) windows, etc. An occasion may occur once per RS ​​periodicity (e.g., once per SMTC period), once per DRX cycle, every Q DRX cycles (where Q>1), etc.

[0063] scenario

[0064] The embodiments are described in the context of NR, i.e., two or more SL UEs operate in or are served by the same or different cells, or one or more SL UEs are out of network coverage. However, the embodiments are applicable to LTE or any other technology (e.g., 6G systems) that allows a direct connection between two (or more) devices. The embodiments are also applicable to relay scenarios including UE-network relay or UE-UE relay, where the remote UE and relay UE may be based on an LTE sidelink or an NR sidelink, and the Uu connection between the relay UE and the base station may be an LTE Uu or an NR Uu.

[0065] The scenario includes UE1 configured to operate (e.g., transmit and / or receive) signals with at least another UE (UE2) on a second carrier frequency (F2). In one example, SL operation between UE1 and UE2 on F2 is subject to a CCA procedure, i.e., a CCA procedure is applied prior to transmission of signals. In another example, SL operation between UE1 and UE2 on F2 is not subject to a CCA procedure, i.e., a CCA procedure is not applied prior to transmission of signals. When the SL UE is in-coverage, the UE can operate in either Mode 1 or Mode 2. The key difference between the two modes is that in Mode 1, SL transmissions are scheduled by the network node, while in Mode 2, SL transmissions are scheduled / selected autonomously by the UE.

[0066] A UE involved in sidelink communication is further (pre)configured with a list of synchronization sources (e.g., predefined in a specification), where the sources may have the same or different priorities. An example of a list of synchronization sources including GNSS, UE, or network nodes (e.g., gNB, eNB, BS, etc.) is shown below in order of their priorities: P0 is the one with the highest priority, and P6 is the one with the lowest priority.

[0067] An example in Figure 3 illustrates a possible scenario in some embodiments. Figure 3 illustrates a scenario in which UE1 engages in SL operation with UE2 and acquires timing from a first synchronization reference source (SRS1) subject to CCA, i.e., A) SRS1 is a first network node (NN1), and B) SRS1 is a third UE (UE3). The diagram shows UE1 engaging in SL operation with UE2 over F2. The diagram shows UE1 acquiring time synchronization to a first synchronization reference source (SRS1) operating on F1 subject to CCA, e.g., a carrier belonging to an unlicensed band. In one example shown in Figure 3(A), SRS1 is a first network node (NN1), e.g., a base station, eNB, gNB, access point, etc. In another example shown in Figure 3(B), SRS1 is another UE, e.g., a third UE (UE3). In some embodiments, F1 and F2 are different carrier frequencies operating on the same or different frequency bands. In some embodiments, F1 and F2 are the same carrier frequency, i.e., F1 = F2, in which case the radio link (or signal) between UE1 and UE2 and the radio link (or signal) between UE1 and SRS1 may be orthogonal to each other in the time domain and / or the frequency domain. TIFF2026507570000002.tif48170

[0068] Systems and methods are disclosed for SL synchronization source adaptation based on CCA failure. In some embodiments, a method performed by a UE for selecting and / or maintaining a synchronization source includes obtaining information about configured and / or available synchronization sources, determining whether an SRS needs to be adapted based on at least one CCA procedure, and performing SRS adaptation in response to determining that the SRS needs to be adapted. In some embodiments, a method performed by a UE for operating as a synchronization reference UE includes obtaining information related to a need to transmit an SL RS, determining information related to a result of at least one CCA procedure related to the SRS, and adapting transmission of the SL RS based on the result of the at least one CCA procedure. Some embodiments provide one or more benefits, such as enabling selection of a reliable synchronization source when operating in a carrier that is subject to CCA and / or defining an unambiguous synchronization procedure for the sidelink when operating in a carrier that is subject to CCA.

[0069] Embodiment 1: A method in UE1 for selecting and maintaining a synchronization source. The embodiments described herein may be implemented in any combination. The UE embodiment includes at least the following: Step 1: UE1 obtains information about configured synchronization sources and / or available synchronization sources. Step 2: UE1 determines the need to adapt SRS based on at least a CCA procedure. Step 3: UE1 performs adaptation of SRS that meets the criteria.

[0070] Step 1: UE1 obtains information about SRS

[0071] In this step, UE1 obtains information about configured, supported, or available synchronization reference sources (SRS). In one example, UE1 may obtain information about SRS based on configuration via signaling, such as a message received from a network node, e.g., via RRC, DCI, or MAC-CE. For example, a set of SRSs may be predefined, and UE1 may select one SR, a first SRS (SRS1), from the predefined set of SRSs based on an identifier received from the network node. For example, if UE1 is configured with identifier P1 in the above table, which assumes a gNB / eNB-based synchronization configuration, UE1 selects or uses the gNB / eNB as the synchronization reference source. On the other hand, if UE1 is configured with identifier P3′, UE1 uses GNSS as the synchronization reference source, and so on.

[0072] In another example, a set of SRSs may be predefined, and UE1 selects one SRS from the set of SRSs based on one or more rules, where the set of SRSs may have different priorities, as shown in the table above. In one example, the rules relate to the UE's operating scenario (e.g., in-coverage, out-of-coverage, or partial coverage), etc.

[0073] In another example, UE1 selects an SRS based on the type of carrier on which SL is operated. For example, UE1 may select P0(GNSS) if SL operation is on a carrier covered by CCA, but UE1 may use P0'(gNB / eNB) if SL operation is on a carrier not covered by CCA or on a carrier on which UE1 is also performing WAN operation, such as over a Uu interface. In another example, if SL operation on F2 between UE1 and UE2 is on a carrier covered by CCA, UE1 also selects an SRS (e.g., another UE or a base station) on a carrier covered by CCA.

[0074] In yet another example, UE1 selects an SRS based on the availability of SRS types in a predefined list. For example, UE1 first attempts to use P0 / P0′ as the SRS, but if P0 / P0′ is not available or detectable, UE1 attempts to select P1 / P1′, etc.

[0075] Step 2: UE1 determines information related to the result of the CCA procedure associated with the SRS.

[0076] In this step, UE1 determines information related to the result of the CCA procedure based on one or more rules or parameters related to a CCA failure associated with a signal transmitted by the first SRS (SRS1) on F1. The terms CCA failure, CCA procedure, or information related to the CCA procedure, or rules related to the CCA procedure are used interchangeably. The rules may be predefined, preconfigured (e.g., on a SIM / USIM card), or configured by a node (e.g., by another UE, a network node, etc.).

[0077] Examples of parameters relevant to the CCA procedure include:

[0078] Results of the CCA procedure

[0079] The results of the CCA procedure may be expressed in terms of CCA failures determined by UE1 on the wireless link between UE1 operating on F1 and SRS1. In one example, UE1 autonomously determines or detects a CCA failure by detecting the absence of a signal transmitted by SRS1 on the wireless link or by detecting that the signal quality of a signal transmitted by SRS1 falls below a certain threshold. In another example, UE1 determines or detects a CCA failure by receiving information from another node. For example, UE1 may receive information from a network node (e.g., a serving BS) regarding the number of CCA failures that have occurred for signals that should have been transmitted by SRS1.

[0080] For example, UE1 compares the results of the CCA procedure performed on F1 with a certain threshold over a certain period of time and determines whether the CCA procedure-related criteria are met based on this comparison.

[0081] In one example, the CCA results may be expressed in terms of the number (N) of CCA failures determined by UE1 on a wireless link (e.g., a PC5 link between UE1 and SRS1) during a time period (T0). The number of CCA failures determined during T0 may be contiguous or non-contiguous in time.

[0082] In another example, the CCA result may also be, or alternatively may be expressed in terms of, the number of successful CCAs determined by UE1 over the radio link on F1 during a time period (T0). The number of successful CCAs determined during T0 may be contiguous or non-contiguous in time.

[0083] Also, a CCA failure during an occasion may be expressed as unavailability of a signal (e.g., a reference signal (RS)) at UE1 during that occasion. In one example, N corresponds to the number of RS occasions (e.g., SSB, SMTC, CSI-RS, SLSS, SL-SSB, SL-SMTC occasions) that are not transmitted by SRS1 on F1 during T0 due to UL CCA failure. In another example, N corresponds to the number of RS occasions (e.g., SSB, SMTC, CSI-RS, SLSS, SL-SSB, SL-SMTC occasions) that are unavailable at UE1 in the cell during T0. In one example, N corresponds to the number of DRX cycles each having at least one RS occasion (e.g., SSB, SMTC, CSI-RS, SLSS, SL-SSB, SL-SMTC occasions) that is not transmitted by SRS1 on F1 due to UL CCA failure during T0. In another example, N corresponds to the number of DRX cycles each having at least one RS occasion (e.g., SSB, SMTC, CSI-RS, SLSS, SL-SSB, SL-SMTC occasion) unavailable at UE1 during T0. The term RS occasion unavailable at UE1 may further refer to when the RS occasion (e.g., SSB, SMTC, CSI-RS, SLSS, SL-SSB, SL-SMTC occasion) includes an RS configured by SRS1 on a carrier frequency (e.g., F1) covered by CCA.

[0084] Maximum allowed number of CCA failures on F1 during T0 (N max ). N max may further depend on one or more parameters. max can be predefined or configured by the network node. Examples of parameters are the DRX cycle length, the eDRX cycle length, the periodicity of the reference signal (T RS ) (e.g., SSB periodicity, SMTC periodicity, CSI-RS periodicity, SLSS periodicity, SL-SMTC periodicity, etc.). For example, the DRX cycle length (T DRX )<1.28s, N max = 8, and T DRXIf ≥ 1.28s, N max =4.

[0085] The relationship between N and Nmax. Examples of relationships are ratios, comparisons (e.g., greater than, equal to, or less than). For example, is N>Nmax, or N=Nmax, or N <Nmaxであるのかなど。

[0086] (K) times, UE, N is N max In one example, K is determined over a period of time (T01).

[0087] An example of SRS adaptation when UE1 meets one or more of the criteria associated with the CCA procedure is described in the following section.

[0088] Step 3: UE1 adapts the SRS based on the results of the CCA procedure

[0089] In this step, UE1 adapts one or more procedures related to or involving SRS based on the result of the CCA procedure determined in the previous step. Examples of different types of adaptations performed by UE1 with respect to SRS based on the result of CCA include:

[0090] Continue using SRS1,

[0091] In one example of adaptation, UE1 continues to use SRS1 as the synchronization reference source. For example, if the result of the CCA procedure does not clearly indicate a CCA failure or indicates a limited number of CCA failures, UE1 may continue to use SRS1 as the synchronization reference source for sidelink operation on F1. In a specific example, if it is (N < Nmax) during a certain time period (e.g., T0), UE1 continues to use SRS as the synchronization source. In other cases, UE1 may perform any of the other adaptations described below (such as discarding SRS1, reselecting SRS, interrupting SRS1, etc.). In one example, Nmax = 1, and in another example, Nmax > 1.

[0092] During the time period Tn, discard, interrupt, or postpone SRS1.

[0093] In another example of adaptation, UE1 discards, interrupts, or postpones using SRS1 as the synchronization reference source for a certain time period of time. UE1 may further resume using SRS1 as the synchronization reference source after that time period, or UE1 may discard SRS1. For example, if the result of the CCA procedure indicates a CCA failure or a high number of CCA failures (e.g., the number of CCA failures exceeds a threshold), UE1 may discard, interrupt, or postpone using SRS1 as the synchronization reference source during the time period Tn.

[0094] In a specific example, if (N > Nmax) occurs R1 times during a certain time period (e.g., T0), UE1 discards SRS1 as the synchronization source. In other cases, UE1 may continue to use SRS1 as the synchronization source.

[0095] In another example, UE1 discards SRS1 as the synchronization source when it exceeds the maximum allowable CCA failures (Nmax) by more than K times. In other cases, UE1 may continue to use SRS1 as the synchronization source.

[0096] During the time that UE1 discards, suspends, or defers SRS1, UE1 may fall back to a reference synchronization source (RSS) that may be predefined, preconfigured, or configured by a network node, e.g., a serving BS. An example of such a fallback RSS includes UE1's internal clock using GNSS timing during the time period (Tn) that SRS1 is suspended, deferred, or delayed.

[0097] During the time that UE1 discards, suspends, or suspends SRS1, UE1 may or may not perform SL operations toward UE2. In one example, UE1 may still perform SL operations toward UE2 until a certain period of time that may be predefined or set by another node (e.g., the UE, a network node, etc.).

[0098] Suspending or postponing SRS1, such as until one or more conditions are met.

[0099] After suspending or postponing the use of SRS1 as a synchronization source for a time period, UE1 may resume using SRS1 as a synchronization source when one or more conditions are met, for example, when N1 CCA evaluations are successful. In one particular example, the UE resumes using SRS1 as a synchronization source when the UE detects that at least Z1 consecutive CCAs have been successful. In another particular example, the UE resumes using SRS1 as a synchronization source when the UE detects that at least Z2 CCAs have been successful over a time period. The Z2 CCAs may be consecutive or non-consecutive.

[0100] In another example, UE1 may resume using SRS1 as a synchronization source when UE1 performs reselection to a new cell. The new cell may operate on the same carrier frequency as the carrier frequency of the current / old serving cell, or the new cell may operate on a new carrier frequency. In another example, UE1 may resume using SRS1 as a synchronization source when UE1 performs reselection to a new cell that also operates on a new carrier frequency (i.e., has changed carrier frequency, for example, from F1 to F2). F2 may or may not be subject to CCA.

[0101] During the time that UE1 suspends or suspends SRS1, UE1 may or may not perform SL operations for UE2. In one example, UE1 may still perform SL operations for UE2 until a certain period of time that may be predefined or set by another node (e.g., the UE, a network node, etc.).

[0102] Changing the synchronization reference source to a second synchronization reference source (e.g., SRS2) / reselecting the second synchronization reference source;

[0103] If the results of the CCA procedure indicate a CCA failure or a high number of CCA failures on F1 for time period Tn (e.g., the number of CCA failures exceeds a threshold for a certain time period), the UE may reselect another synchronization source (e.g., SRS2) (i.e., start using a new synchronization reference source).

[0104] In a specific example, if (N>Nmax) occurs K times, UE1 performs SRS reselection (from SRS1 to SRS2). Otherwise, UE1 may continue to use SRS1 as a synchronization source. K≧1. In one example, K=1.

[0105] In another specific example, if (N>Nmax) occurs R1 times during a certain time period (e.g., T0), UE1 performs SRS reselection from SRS1 to SRS2. Otherwise, UE1 may continue to use SRS1 as a synchronization source. R1≧1. In one example, R1=1.

[0106] SRS2 may operate on a third carrier frequency (F3), i.e., UE1 acquires synchronization to SRS2 by receiving a signal (e.g., RS) on F3. UE1 may determine SRS2 and / or F3 based on one or more rules, which may be predefined, configured by another node, or preconfigured in the UE (e.g., stored on UE1's SIM / USIM card). F3 may or may not be subject to CCA. In one example, SRS2 may have a lower or equal priority compared to the priority of SRS1. In one example, UE1 reselects SRS2 as the new SRS if the signal transmitted by SRS2 on F3 is not subject to CCA, e.g., F3 belongs to a licensed frequency band. SRS2 may be a UE, e.g., a fourth UE (UE4), or SRS2 may be a second network node (NN2). 4 illustrates a scenario in which UE1 changes / reselects its SRS from SRS1 to SRS2 due to a CCA failure on F1 between UE1 and SRS1, i.e., A) UE1 changes SRS1 to SRS2, which is a second network node (NN2); and B) UE1 changes SRS1 to SRS2, which is a fourth UE (UE4). Figure 4 illustrates an example in which UE1 changes / reselects its SRS from SRS1 to SRS2 due to an excessive number of CCA failures detected for signals transmitted by SRS1 on F1. In Figure 4(A), UE1 changes SRS1 to SRS2, which is a second network node (NN2). In Figure 4(B), UE1 changes SRS1 to SRS2, which is a fourth UE (UE4). In either case, UE1 acquires synchronization to SRS2 by receiving a signal (e.g., RS) transmitted by SRS2 on F3. In one example, F3 and F2 are different carrier frequencies. In another example, F3 and F2 are the same carrier frequency, i.e., F2=F3.

[0107] Starting / stopping sidelink synchronization signals

[0108] In another example, UE1 adapts transmission of SLSS on a fourth carrier frequency (F4) based on the result of the CCA failure determined by UE1 on F1. The adaptation of transmission of SLSS on F4 by UE1 includes one of starting / initiating transmission of SLSS on F4 and ceasing / stopping transmission of SLSS on F4. F4 is a carrier frequency used or configured for SL operation. In one example, F4 is the same as F1, F2, or F3, or is different from F1, F2, and F3.

[0109] In one example, if the results of the CCA procedure indicate a CCA failure or a high number of CCA failures on F1 for time period Tn (e.g., the number of CCA failures exceeds a threshold for a certain time period), UE1 initiates SLSS transmission on F4. In one example, UE1 also begins acting as a synchronization reference source (SRS) on F4 by initiating transmission of SLSS (e.g., SL-SSB, SLSS, PSBCH, etc.) based on the CCA failures on F1 in addition to existing conditions for starting / stopping SLSS. One example of an existing condition is when a signal measurement (signal strength, e.g., RSRP, etc.) for a signal transmitted by SRS1 on F1 falls below a certain threshold.

[0110] In one particular example, (N>Nmax) is T on F1. evaluate,SLSS_CCA If this occurs K times during the period, UE1 starts transmitting SLSS on F4. Otherwise, UE1 may not transmit SLSS on F4. In the latter case, UE1 will not serve as an SRS for other UEs. In another example, if UE1 is transmitting SLSS and T evaluate,SLSS_CCA UE1 stops / stops transmitting SLSS on F4 if K≧1 on F1 at least once during the period (N≦Nmax). In one example, K=1.

[0111] One or more parameters in the above example of SRS adaptation, such as T0, R1, K, Nmax, Tn, Z1, Z2, etc., may be predefined, preconfigured, or configured by a network node (e.g., by sending a message to UE1, such as via RRC). These parameters may further depend on whether UE1 is configured with normal DRX or extended DRX, a frequency range (e.g., FR1, FR2), the power class of UE1, etc.

[0112] The type of SRS adaptation applied by UE1 based on the result of the CCA procedure may be predefined, preconfigured (e.g., on the SIM / USIM card), or configured by another node (e.g., a network node or another SL UE).

[0113] Specific Example of UE1 Adapting UE1's SRS Based on CCA Failure

[0114] Example 1: SRS selection / reselection by UE1 based on CCA failure

[0115] This first example specifies requirements for selection / reselection of an SL (e.g., V2X) synchronization reference source (SRS) when the carrier on which a signal is transmitted by the SRS (e.g., UE, network node, etc.) is subject to CCA.

[0116] The GNSS synchronization reference source is set as the highest priority, and - When the UE is directly synchronized to the GNSS, - The UE shall not drop SL (e.g., V2X) SLSS and data transmissions for the purpose of selection / reselection to the Synchronization Reference (SyncRef) UE. - when the UE is synchronized to a SyncRef UE that is directly or indirectly synchronized to GNSS; - The UE shall not drop SL (e.g. V2X) data transmissions for the purpose of selection / reselection to a SyncRef UE. The UE shall select a newly detectable intra-frequency SyncRef UE as a SyncRef UE if the SyncRef UE meets the selection / reselection criteria specified in TS38.331 v17.3.0. detect,SyncRef UE_V2X It shall be possible to identify it within T seconds. detect,SyncRef UE_V2X is S-SSB Es / Iot ≥ 0 dB and the UE uses T for selection / reselection purposes to the SyncRef UE. detect,SyncRef UE_V2X If a UE is allowed to drop up to 30% of its SLSS transmissions during SyncRef, the carrier on which the UE transmitted a signal (e.g., RS) will be subject to CCA (10+L SL1 )*X1 seconds. In one example, X1=0.16. In one example, L SL1 SyncRef is a CCA failure in the UE. detect,SyncRef UE_V2X The number of RS occasions (eg, number of S-SSB occasions) of the UE that are not available at the UE during SyncRef. - In other cases, - when the UE is in non-SL-DRX, - The UE shall select a newly detectable intra-frequency SyncRef UE as a SyncRef UE if the UE satisfies the selection / reselection criteria specified in TS38.331 v17.3.0. detect,SyncRef UE_V2X It shall be possible to identify it within T seconds. detect,SyncRef UE_V2X is S-SSB Es / Iot ≥ 0 dB and the UE uses T for selection / reselection purposes to the SyncRef UE. detect,SyncRef UE_V2X If a UE is allowed to drop up to 6% of its SL (e.g., V2X) data and SLSS transmissions during SyncRef, when the carrier on which the UE transmitted a signal (e.g., RS) is subject to CCA, the UE may receive up to 6% of its SL (e.g., V2X) data and SLSS transmissions (50+L SL1 )*X2 seconds. In one example, X2=0.16. - The UE is allowed to drop up to two slots of UE SL (e.g., V2X) data reception per PSBCH monitoring occasion, and the overall drop rate is set to T for selection / reselection purposes for SyncRef UEs. detect,SyncRef UE_V2X During this period, the UE's SL (e.g., V2X) data reception shall not exceed 0.3%. - When the UE is in SL-DRX, - The UE shall select a newly detectable intra-frequency SyncRef UE as a T SyncRef UE if the UE satisfies the selection / reselection criteria specified in TS 38.331 [2]. detect,SyncRef UE_V2X It shall be possible to identify it within T seconds. detect,SyncRef UE_V2X If S-SSB Es / Iot ≥ 0 dB and a SL (e.g., V2X) UE is allowed to drop up to 6% of its SL (e.g., V2X) data and SLSS transmissions for the purpose of selection / reselection to a SyncRef UE, when the carrier on which the SyncRef UE transmitted a signal (e.g., RS) is subject to CCA, then (50+L SL2 )*X3 seconds. In one example, X3=0.16. In another example, X3=max(0.16,SL-DRX length). In one example, L SL2 SyncRef is a CCA failure in the UE. detect,SyncRef UE_V2X SyncRef is the number of RS occasions (e.g., S-SSB occasions) of the UE that are not available at the UE during L SL2 indicates that at least one RS occasion (e.g., an S-SSB occasion) of the SyncRef UE is interrupted due to a CCA failure at the SyncRef UE. detect,SyncRef UE_V2X The number of SL-DRX cycles that are not available at the UE during - The UE is allowed to drop up to two slots of UE SL (e.g., V2X) data reception per PSBCH monitoring occasion, and the UE shall use the T for selection / reselection purposes to the SyncRef UE. detect,SyncRef UE_V2XDuring the UE's SL (e.g., V2X) data reception, it is permitted to drop an aggregated window of at most 24 ms. -UE is T detect,SyncRef UE_V2X of, - SyncRef max((X41*X42+L SL3 )*SL-DRX cycle length, X43s) It is possible to extend This means that the following conditions depend on whether an NR cell is used as the synchronization reference source, or whether an EUTRA cell is used as the synchronization reference source, or whether an SLSS is used as the synchronization reference source, during the evaluation period T evaluate,SLSS When multiple SL-DRX cycles are set, the SL-DRX cycle length is the longest one. In one example, X41=4, X42=50, X43=8, and the SL-DRX cycle length is several seconds. In one example, L SL3 indicates that at least one RS occasion (e.g., an S-SSB occasion) of the SyncRef UE is interrupted due to a CCA failure at the SyncRef UE. detect,SyncRef UE_V2X The number of SL-DRX cycles that are not available at the UE during - SS-RSRP is greater than syncTxThreshOoC. When the serving cell / PCell synchronization reference source is configured as the highest priority, - when the UE is in non-SL-DRX, - The UE shall select a newly detectable intra-frequency SyncRef UE as a SyncRef UE if the UE satisfies the selection / reselection criteria specified in TS38.331 v17.3.0. detect,SyncRef UE_V2X It shall be possible to identify it within T seconds. detect,SyncRef UE_V2XIf SCH Es / Iot ≥ 0 dB and a SL (e.g., V2X) UE is allowed to drop up to 6% of its SL (e.g., V2X) data and SLSS transmissions for the purpose of selection / reselection to a SyncRef UE, when the carrier on which the serving cell transmitted a signal (e.g., RS) is subject to CCA, then (50+L SL1 )*X5ms. In one example, X5=160. - The UE is allowed to drop up to two slots of UE SL (e.g., V2X) data reception per PSBCH monitoring occasion, and the overall drop rate is set to T for selection / reselection purposes for SyncRef UEs. detect,SyncRef UE_V2X During this period, the UE's SL (e.g., V2X) data reception shall not exceed 0.3%. - When the UE is in SL-DRX, - The UE shall select a newly detectable intra-frequency SyncRef UE as a SyncRef UE if the UE satisfies the selection / reselection criteria specified in TS38.331 v17.3.0. detect,SyncRef UE_V2X It shall be possible to identify it within T seconds. detect,SyncRef UE_V2X is the SCH Es / Iot ≥ 0 dB and the UE uses T for selection / reselection purposes to the SyncRef UE. detect,SyncRef UE_V2X If the UE is allowed to drop its SL (e.g., V2X) data and SLSS transmissions in an aggregated window of at most 480 ms, when the carrier on which the serving cell transmitted a signal (e.g., RS) is subject to CCA, then (50+L SL2 )*X6 seconds. In one example, X6=160. - The UE is allowed to drop up to two slots of UE SL (e.g., V2X) data reception per PSBCH monitoring occasion, and the UE shall use the T for selection / reselection purposes to the SyncRef UE. detect,SyncRef UE_V2X During the UE's SL (e.g., V2X) data reception, it is permitted to drop an aggregated window of at most 24 ms. -UE is T detect,SyncRef UE_V2X of, - When the carrier on which the serving cell transmits a signal (e.g., RS) is subject to CCA, max((X71*X72+L SL3 )*SL-DRX cycle length, X73s) It is possible to extend This means that the following conditions depend on whether an NR cell is used as the synchronization reference source, or whether an EUTRA cell is used as the synchronization reference source, or whether an SLSS is used as the synchronization reference source, during the evaluation period T evaluate,SLSS When multiple SL-DRX cycles are set, the SL-DRX cycle length is the longest one. In one example, X71=4, X72=50, X73=8, and the SL-DRX cycle length is several seconds. - SS-RSRP is greater than syncTxThreshOoC.

[0117] UE is T in Table 1 measure,PSBCH-RSRP It shall be possible to perform PSBCH-RSRP measurements for three identified intra-frequency SyncRef UEs in the measurement period. It is assumed that the SyncRef UEs do not drop or delay SLSS transmissions within the measurement period. Otherwise, the measurement period may be extended. TIFF2026507570000003.tif72170

[0118] When the UE is directly synchronized to GNSS, before selecting / reselecting a new synchronization reference source, the UE shall evaluate the GNSS synchronization source reliability for at least 20 seconds before changing synchronization reference from GNSS to another synchronization reference source. The UE shall always be directly synchronized to GNSS during the evaluation of GNSS synchronization source reliability.

[0119] In one example, the UE stops using the current synchronization reference source if any of the following conditions are met: -L SL1 L SL,max1 exceed -L SL2L SL,max2 exceed -L SL3 L SL,max3 exceed -L SL4 L SL,max4 exceed -L SL5 L SL,ma5 exceed

[0120] In another example, the UE further initiates a synchronization reference source reselection procedure when any of the above conditions is met, in which the UE reselects another synchronization reference source.

[0121] In another example, the UE restarts measurements (eg, PSBCH-RSRP measurements) on the SRS of the current SyncRef UE (eg, UE3) if any of the above conditions are met.

[0122] Example 2: Adapting SLRS based on CCA failure when NR cells are used as synchronization reference sources

[0123] This second example specifies requirements for a UE (e.g., UE1) to start and stop SLSS transmission when an NR cell is used as a synchronization reference source (SRS) when the carrier on which a signal is transmitted by the SRS (network node) is subject to CCA.

[0124] When an NR cell is used as a synchronization reference source, the UE evaluate,SLSS It shall be possible to measure the RSRP of the cell used as a synchronization reference source to be evaluated to start / stop SLSS transmission within

[0125] where: -T evaluate,SLSS,CCA is as specified in Table 2 when the UE performs SSB-based measurements without measurement gaps and the measured carrier is subject to CCA. -T evaluate,SLSSis as specified in Table 3 when the UE performs SSB-based measurements with measurement gaps and the measured carrier is subject to CCA. TIFF2026507570000004.tif83170TIFF2026507570000005.tif78170

[0126] The UE shall cease all SLSS transmissions if at least one of the following conditions is met: -L SLSS,1 L SLSS,max,1 exceed -L SLSS,2 L SLSS,max,2 exceed -L SLSS,gaps,1 L SLSS,gaps,max,1 exceed -L SLSS,gaps,2 L SLSS,gaps,max,2 exceed

[0127] Otherwise, the UE evaluate,SLSS Submit your SLSS based on your rating within.

[0128] Example 3: Adaptation of SLRS based on CCA failure when EUTRAN cells are used as synchronization reference sources

[0129] This third example specifies the requirements for starting and stopping SLSS transmissions when a carrier on which a signal is transmitted by a Synchronization Reference Source (SRS) (e.g., a network node) is subject to CCA and when an EUTRAN cell is used as an SRS.

[0130] When a EUTRAN cell is used as a synchronization reference source, the UE evaluate,SLSS,CCA It shall be possible to measure the RSRP of the cell used as a synchronization reference source to be evaluated to start / stop SLSS transmission within

[0131] where: - When DRX is not configured in the UE, T evaluate,SLSS,CCA =(10+LSLSS,3 ) × 0.04 seconds. Here, L SLSS,3 is F1, i.e., the number of RS occasions (e.g., discovery signal occasions) of the E-UTRAN cell with 40 ms periodicity that are unavailable to the UE due to CCA failure on the carrier of the E-UTRAN cell. In another example, when DRX is not configured in the UE, evaluate,SLSS,CCA =(5+L SLSS,4 ) × 0.08 seconds. Here, L SLSS,4 is F1, i.e., the number of RS occasions (e.g., discovery signal occasions) of the E-UTRAN cell with 80 ms periodicity that are unavailable to the UE due to CCA failure on the carrier of the E-UTRAN cell. -T evaluate,SLSS,CCA = , as specified in Table 4 when DRX is configured in the UE and the measured carrier of the E-UTRAN cell is subject to CCA. TIFF2026507570000006.tif72170

[0132] The UE shall cease all SLSS transmissions if at least one of the following conditions is met: -L SLSS,3 L SLSS,max,3 exceed -L SLSS,4 L SLSS,max,4 exceed -L SLSS,5 L SLSS,max,5 exceed -L SLSS,6 L SLSS,max,6 exceed

[0133] Otherwise, the UE evaluate,SLSS Submit your SLSS based on your rating within.

[0134] Example 4: Adapting SLRS based on CCA failure when SyncRef UE is used as synchronization reference source

[0135] This fourth example specifies the requirements for starting and ceasing SLSS transmission when UE1 shall start transmitting SLSS when the carrier on which a signal is transmitted by the SRS (e.g., UE) is subject to CCA.

[0136] The UE can measure the PSBCH-RSRP of the selected SyncRef UE used as the synchronization reference source, and set it as T in Table 5 when the measured carrier is subject to CCA. evaluate,SLSS Within 14 days, the system will be evaluated to activate / deactivate SLSS transmission. TIFF2026507570000007.tif87170

[0137] In one example, a UE (eg, UE1) ceases all SLSS transmissions if at least one of the following conditions is met: -L SLSS,7 L SLSS,max,7 exceed -L SLSS,8 L SLSS,max,8 exceed

[0138] Otherwise, the UE (e.g., UE1) evaluate,SLSS Submit your SLSS based on your rating within.

[0139] In another example, a UE (e.g., UE1) suspends transmission of SLSS during a time period T1. In one example, T1 = N × SL-DRX cycles, where N = 2, 3, 4, etc. The UE may restart SLSS after T, or the UE may stop SLSS after T.

[0140] In another example, the UE restarts measurements (eg, evaluation of SLSS) on the SRS of the current SyncRef UE (eg, UE3) if any of the above conditions are met.

[0141] Embodiment 2: A method in a UE 3 for operating as a synchronization reference UE. The embodiments described herein may be implemented in any combination. The UE embodiment includes at least the following: Step 1: The UE 3 obtains information related to the need to transmit a sidelink reference signal. Step 2: The UE 3 determines information related to the result of a CCA procedure related to an SRS. Step 3: The UE 3 adapts the transmission of an SL RS (e.g., an SLSS) based on whether a related condition is achieved.

[0142] Step 1: UE 3 acquires information related to the need to transmit sidelink reference signals. In this step, UE 3 acquires information on whether UE 3 needs to transmit sidelink reference signals (SLRS), i.e., whether any other sidelink UE (e.g., UE 1) is using UE 3 as a synchronization reference source. In one example, UE 3 determines the need to transmit SLRS if UE 3 is configured to transmit SLRS by another node (e.g., by another UE (e.g., UE 1) or by a network node). In another example, UE 3 determines the need to transmit SLRS based on predefined rules, e.g., UE 3 is required to transmit SLRS periodically. In another example, UE 3 determines the need to transmit SLRS based on preconfigured information in the UE (e.g., stored in UE 1's SIM / USIM card). A sidelink UE acting as an SRS for other sidelink UEs is generally required to transmit sidelink reference signals (SLRS) according to a certain transmission periodicity. An example of an SLRS is the SL Synchronization Signal (SLSS).

[0143] Step 2: UE3 determines information related to the result of the CCA procedure related to the SRS. In this step, UE3 determines information related to the result of the CCA procedure based on one or more rules or parameters related to a CCA failure related to the sidelink reference signal transmitted by UE3 on F1.

[0144] The step of determining information related to the result of the CCA procedure is similar to that described in step 2 in the first embodiment described above.

[0145] Step 3: UE3 adapts transmission of SL reference signals based on the result of the CCA procedure. In this step, UE3 (acting as SRS for other SL UEs) adapts one or more procedures related to or involving the transmission of sidelink reference signals based on the result of the CCA procedure determined in the previous step. Examples of different types of adaptation include:

[0146] Continue transmitting SLRS

[0147] In one example of adaptation, UE 3 continues to transmit SLRS (e.g., SLSS) over F1. For example, if the result of the CCA procedure indicates no CCA failures over F1 or a limited number of CCA failures over F1, UE 3 may continue to transmit SLRS (e.g., SLSS) according to a reference configuration over F1. The reference configuration is one that UE 3 follows for SLRS transmission when UE 3 does not experience a CCA failure over F1, or when the number of CCA failures over F1 is below a certain threshold, or when operating on a carrier not subject to CCA. UE 3 obtains the reference configuration for SLRS transmission based on predefined information, by receiving information from another node (e.g., UE, network node), or based on preconfigured information (e.g., stored on the SIM / USIM card of UE 3, etc.).

[0148] In a specific example, if during a certain time period (e.g., T0’), (N’ < Nmax’), UE3 continues to transmit SLSS to other SL UEs (e.g., UE1) that are using UE3 as a synchronization reference source (e.g., every 160 ms). In other cases, UE3 does not continue to transmit SLRS. For example, UE3 stops / halts the transmission of SLSS on F1. In another example, in the latter case, UE3 may perform any of the adaptations described below (such as stopping / halting SLRS for a certain period of time or interrupting or delaying SLRS).

[0149] Stopping / halting the transmission of SLRS during a time period

[0150] In another example of adaptation, UE3 stops / halts the transmission of SLRS (e.g., SLSS) on F1 during a certain time period. Stopping / halting the transmission of SLRS implies not transmitting SLRS. For example, if the result of the CCA procedure indicates CCA failure or a high number of CCA failures (e.g., the number of CCA failures exceeds a threshold), UE3 may stop / halts the transmission of SLRS (e.g., SLSS) during the time period Tn’. The reasons for stopping / halting the transmission have two parts. First, if UE3 detects that the channel has been extremely busy over the last Nx time periods, attempting to transmit SLRS would be an unnecessary complication and a waste of resources for UE3, where Nx can be expressed in time units such as subframes, DRX cycles, slots, etc. Second, any such transmission may also cause interference to other nearby devices. Therefore, UE3 prefers to abort all SLRS transmissions during the time period.

[0151] In a specific example, if (N’ > Nmax’) occurs K’ times, UE3 stops / halts the transmission of SLRS (e.g., SLSS). In other cases, UE3 may continue to transmit SLRS (e.g., SLSS) according to the reference settings. K’ ≥ 1. In one example, K’ = 1.

[0152] In another specific example, if (N'>Nmax') occurs R1' times during a certain time period (e.g., T0'), UE3 stops / ceases transmitting SLRS (e.g., SLSS) to UE1 using UE3 as a synchronization reference source. Otherwise, the UE may continue to transmit SLRS (e.g., SLSS) according to the reference configuration. R1'≧1. In one example, R1'=1.

[0153] Suspending or postponing the transmission of SLRS for a period of time

[0154] In another example of adaptation, UE 3 suspends or postpones transmission of SLRS (e.g., SLSS) on F1 for a certain period of time. For example, if the result of the CCA procedure indicates a CCA failure or a high number of CCA failures (e.g., the number of CCA failures exceeds a threshold), UE 3 suspends or postpones transmission of SLRS for a time period Tn'. The rationale for suspending or postponing SLRS transmission is to avoid transmission while the channel is occupied by other nodes (e.g., other UEs, network nodes, etc.) and to retry transmission after some time. The time period when transmission is suspended or postponed by UE 3 may further depend on the type of channel access scheme applied.

[0155] In one particular example, if (N'>Nmax') occurs K' times, the UE 3 suspends or postpones transmission of the SLRS (e.g., SLSS). In other cases, the UE 3 may continue to transmit the SLRS (e.g., SLSS) according to the reference configuration. K'≧1. In one example, K'=1.

[0156] In another specific example, if (N'>Nmax') occurs R1' times during a certain time period (e.g., T0'), UE3 suspends or postpones transmission of SLRS (e.g., SLSS) to UE1, which uses UE3 as a synchronization reference source. In other cases, the UE may continue to transmit SLRS (e.g., SLSS) according to the reference configuration. R1'≧1. In one example, R1'=1.

[0157] Indications for SLRS

[0158] If the result of the CCA procedure indicates a CCA failure or a high number of CCA failures (e.g., the number of CCA failures exceeds a threshold), the UE 3 adapts one or more transmission parameters of the SLRS. Examples of transmission parameters of the SLRS include the periodicity of the SLRS transmission, the duration of the occasions at which the SLRS is transmitted (e.g., X1 ms, X2 symbols, X3 slots, etc.), the bandwidth at which the SLRS is transmitted, etc. In one example, the adaptation includes the UE 3 transmitting the SLRS less frequently compared to a reference periodicity (e.g., when not experiencing a CCA failure). In another example, the adaptation includes the UE 3 transmitting the SLRS more frequently compared to the reference periodicity. In another example, the adaptation includes the UE 3 transmitting the SLRS over a bandwidth (BW) smaller than a reference BW. In another example, the adaptation includes the UE 3 transmitting the SLRS over a bandwidth larger than the reference BW. The reference SLRS periodicity and / or the reference BW may be predefined, configured by another node, or preconfigured in the UE 3.

[0159] One or more parameters, T0', R1', K', Nmax', Tn', Z1' in the above example of adaptation may be predefined, preconfigured, or configured by a network node (e.g., by sending a message to the UE 3, such as via RRC). These parameters may further depend on whether the UE 3 is configured with normal DRX or extended DRX, a frequency range (e.g., FR1, FR2), a power class of the UE 3, etc.

[0160] The type of SLRS adaptation applied by UE3 based on the results of the CCA procedure may be predefined, preconfigured (e.g., on the SIM / USIM card), or configured by another node (e.g., a network node or another SL UE).

[0161] A sidelink UE (e.g., UE3) receives the evaluate,SLSS ) for an evaluation period (T). In one example, a UE (e.g., UE 3) synchronized to any other synchronization reference source (such as an NR cell, an E-UTRAN cell, a GNSS, or another sidelink synchronization reference UE) is required to evaluate whether to start / stop the SLRS (e.g., SLSS) for an evaluation period (T). evaluate,SLSS ), the UE (e.g., UE3) initiates SLRS transmission if it detects a certain number of CCA failures (e.g., N) over a time period Tn' even before completing evaluation. In another example, the UE (e.g., UE3) restarts evaluation if it detects a certain number of CCA failures (e.g., N' > Nmax') during an ongoing evaluation period. In yet another example, the SL UE (e.g., UE3) suspends SLRS transmission for a certain time period after restarting evaluation a certain number of times.

[0162] Specific examples of UE3 adapting SLRS based on CCA failure

[0163] Example: SyncRef UE used as a synchronization reference source

[0164] This example specifies requirements for ceasing SLSS transmission when the carrier on which a signal is transmitted by a synchronization reference source (SRS) (e.g., UE3) is subject to CCA, and SyncRef UE (UE3) is used as the SRS for UE1.

[0165] A UE (e.g., UE1) can measure the PSBCH-RSRP of a selected SyncRef UE (e.g., UE3) used as a synchronization reference source, and set it as T in Table 6 when the measured carrier (e.g., F1) is subject to CCA. evaluate,SLSS Within 14 days, the system will be evaluated to activate / deactivate SLSS transmission. TIFF2026507570000008.tif92170

[0166] In one example, a SyncRef UE (eg, UE3) ceases all SLSS transmissions if at least one of the following conditions is met: -L SLSS,9 L SLSS,max,9 exceed -L SLSS,10 L SLSS,max,10 exceed

[0167] Otherwise, the UE (e.g., UE1) evaluate,SLSS Submit your SLSS based on your rating within.

[0168] In another example, a UE (e.g., UE1) suspends transmission of SLSS during a time period T1. In one example, T1 = N × SL-DRX cycles, where N = 2, 3, 4, etc. The UE may restart SLSS after T, or the UE may stop SLSS after T. TIFF2026507570000009.tif153170

[0169] In some embodiments, the UE m,max , M d,max , or M e,max If this is exceeded, the measurement shall be restarted.

[0170] Current RRM specifications (see, for example, TS38.133, Section 12.4) include requirements for the selection and reselection of a synchronization reference source. More specifically, current RRM specifications include requirements for detecting a new synchronization reference source (SyncRefUE) when the UE is synchronized to GNSS, SyncRefUE, or serving cell / PCell. Examples of such requirements are the time to detect a newly detectable SyncRefUE, the measurement period for measuring an identified SyncRefUE, the suspension time, and the dropping rate. These requirements further depend on the activity state of the UE, i.e., whether the UE is in DRX mode or non-DRX mode.

[0171] In a Rel-18 scenario, SL carriers may be subject to CCA, and WAN / Uu carriers are not. Therefore, the selection / reselection of a SyncRefUE on an SL carrier subject to CCA will be affected by a CCA failure on the SL carrier. When a UE operates on a carrier subject to CCA and experiences many CCA failures, it will not be able to meet the existing requirements for the selection / reselection of a SyncRefUE. For example, a UE selecting or reselecting a SyncRefUE as a synchronization reference source on a carrier subject to CCA may result in the UE selecting / reselecting a less reliable or incorrect SyncRefUE under many CCA failures. Therefore, the rationale for specifying the requirements for selecting / reselecting a synchronization reference source (SyncRefUE) when operating on an unlicensed carrier subject to CCA failures may be based on the Rel-16 NR-U requirements.

[0172] Observation 1: An excessive number of CCA failures on an SL carrier that is subject to CCA may result in unreliable or incorrect selection / reselection of a synchronization reference source (SyncRefUE) on that SL carrier.

[0173] Observation 2: Rel-16 NR-U requirements and UE measurement behavior take into account the number of CCA failures on carriers covered by CCA.

[0174] Proposal 1: The requirements for the selection and reselection of a synchronization reference source (SyncRefUE) on an SL carrier subject to CCA shall take into account the impact of CCA failures occurring on the SL carrier during SyncRefUE selection and reselection.

[0175] 5 is a schematic block diagram of a radio access node 500 according to some embodiments of the present disclosure. Optional features are represented by dotted boxes. The radio access node 500 may be, for example, a base station 202 or 206, or a network node that implements all or a portion of the functionality of a base station 202 or gNB described herein. As shown, the radio access node 500 includes a control system 502 that includes one or more processors 504 (e.g., a central processing unit (CPU), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), etc.), a memory 506, and a network interface 508. The one or more processors 504 are also referred to herein as processing circuits. Additionally, the radio access node 500 may include one or more radio units 510, each including one or more transmitters 512 and one or more receivers 514 coupled to one or more antennas 516. The radio units 510 may be referred to as, or be part of, air interface circuitry. In some embodiments, the wireless unit(s) 510 are external to the control system 502 and are connected to the control system 502, for example, via a wired connection (e.g., optical cable). However, in some other embodiments, the wireless unit(s) 510 and potentially the antenna(s) 516 are integrated with the control system 502. The one or more processors 504 operate to provide one or more functions of the wireless access node 500 described herein. In some embodiments, the function(s) are implemented in software, for example, stored in the memory 506 and executed by the one or more processors 504.

[0176] 6 is a schematic block diagram illustrating a virtualized embodiment of a radio access node 500 in accordance with some embodiments of the present disclosure. This description is equally applicable to other types of network nodes. Furthermore, other types of network nodes may have a similar virtualized architecture. Again, optional features are represented by dotted boxes.

[0177] As used herein, a “virtualized” radio access node is an implementation of a radio access node 500 in which at least a portion of the functionality of the radio access node 500 is implemented as virtual component(s) (e.g., via virtual machine(s) executing on physical processing node(s) in network(s)). As shown, in this example, the radio access node 500 may include a control system 502 and / or one or more radio units 510, as described above. The control system 502 may be connected to the radio unit(s) 510 via, for example, an optical cable or the like. The radio access node 500 includes one or more processing nodes 600 coupled to or included as part of the network(s) 602. If present, the control system 502 or the radio unit(s) are connected to the processing node(s) 600 via the network 602. Each processing node 600 includes one or more processors 604 (eg, CPUs, ASICs, FPGAs, etc.), memory 606 , and a network interface 608 .

[0178] In this example, the functions 610 of the radio access node 500 described herein are implemented in one or more processing nodes 600, or distributed in any desired manner across one or more processing nodes 600 and the control system 502 and / or radio unit(s) 510. In some particular embodiments, some or all of the functions 610 of the radio access node 500 described herein are implemented as virtual components executed by one or more virtual machines implemented in virtual environment(s) hosted by the processing node(s) 600. As will be appreciated by those skilled in the art, additional signaling or communication between the processing node(s) 600 and the control system 502 is used to perform at least some of the desired functions 610. Notably, in some embodiments, the control system 502 may not be included, in which case the radio unit(s) 510 communicate directly with the processing node(s) 600 via an appropriate network interface(s).

[0179] In some embodiments, a computer program is provided that includes instructions that, when executed by at least one processor, cause the at least one processor to perform functions of the radio access node 500 or a node (e.g., processing node 600) that implements one or more of the functions 610 of the radio access node 500 in a virtual environment in accordance with any of the embodiments described herein. In some embodiments, a carrier is provided that comprises the above-mentioned computer program product. The carrier is one of an electronic signal, an optical signal, a radio signal, or a computer-readable storage medium (e.g., a non-transitory computer-readable medium such as a memory).

[0180] 7 is a schematic block diagram of a radio access node 500 in accordance with some other embodiments of the present disclosure. The radio access node 500 includes one or more modules 700, each of which is implemented in software. The module(s) 700 provide the functionality of the radio access node 500 described herein. This description is equally applicable to the processing node 600 of FIG. 6, where the module 700 may be implemented in one of the processing nodes 600 or distributed across multiple processing nodes 600 and / or distributed across the processing node(s) 600 and the control system 502.

[0181] 8 is a schematic block diagram of a wireless communication device 800 in accordance with some embodiments of the present disclosure. As shown, the wireless communication device 800 includes one or more processors 802 (e.g., CPUs, ASICs, FPGAs, etc.), a memory 804, and one or more transceivers 806, each including one or more transmitters 808 and one or more receivers 810 coupled to one or more antennas 812. The transceiver(s) 806 include radio front-end circuitry connected to the antenna(s) 812 configured to condition signals communicated between the antenna(s) 812 and the processor(s) 802, as will be appreciated by those skilled in the art. The processor 802 is also referred to herein as a processing circuit. The transceiver 806 is also referred to herein as a radio circuit. In some embodiments, the functionality of the wireless communication device 800 described above may be implemented fully or partially in software, for example, stored in the memory 804 and executed by the processor(s) 802. It should be noted that the wireless communication device 800 may include additional components not shown in FIG. 8 , such as, for example, one or more user interface components (e.g., an input / output interface including a display, buttons, a touchscreen, a microphone, one or more speakers, etc., and / or any other components for enabling input of information to the wireless communication device 800 and / or output of information from the wireless communication device 800), a power supply (e.g., a battery and associated power circuitry), etc.

[0182] In some embodiments, a computer program is provided that includes instructions that, when executed by at least one processor, cause the at least one processor to perform the functions of the wireless communication device 800 in accordance with any of the embodiments described herein. In some embodiments, a carrier is provided that comprises the computer program product described above. The carrier is one of an electronic signal, an optical signal, a radio signal, or a computer-readable storage medium (e.g., a non-transitory computer-readable medium such as a memory).

[0183] 9 is a schematic block diagram of a wireless communication device 800 in accordance with some other embodiments of the present disclosure. The wireless communication device 800 includes one or more modules 900, each of which is implemented in software. The module(s) 900 provide the functionality of the wireless communication device 800 described herein.

[0184] 10 , according to one embodiment, a communication system includes a communication network 1000, such as a 3GPP-type cellular network, comprising an access network 1002, such as a RAN, and a core network 1004. The access network 1002 comprises multiple base stations 1006A, 1006B, 1006C, such as Node Bs, eNBs, gNBs, or other types of wireless access points (APs), each defining a corresponding coverage area 1008A, 1008B, 1008C. Each base station 1006A, 1006B, 1006C can be connected to the core network 1004 via a wired or wireless connection 1010. A first UE 1012 located in the coverage area 1008C is configured to wirelessly connect to or be paged by the corresponding base station 1006C. A second UE 1014 in the coverage area 1008A can wirelessly connect to the corresponding base station 1006A. Although multiple UEs 1012, 1014 are shown in this example, the disclosed embodiments are equally applicable to situations where only one UE is in the coverage area or connects to the corresponding base station 1006A.

[0185] The communications network 1000 is itself connected to a host computer 1016, which may be embodied in hardware and / or software of a standalone server, a cloud-implemented server, a distributed server, or as a processing resource in a server farm. The host computer 1016 may be owned or controlled by a service provider, or may be operated by or on behalf of the service provider. Connections 1018 and 1020 between the communications network 1000 and the host computer 1016 may extend directly from the core network 1004 to the host computer 1016 or may proceed through an optional intermediate network 1022. The intermediate network 1022 may be one of a public network, a private network, or a hosted network, or a combination of two or more of them; the intermediate network 1022 may be a backbone network or the Internet, if present; in particular, the intermediate network 1022 may comprise two or more subnetworks (not shown).

[0186] The communication system of FIG. 10 as a whole enables connectivity between the connected UEs 1012, 1014 and the host computer 1016. The connectivity may be described as an over-the-top (OTT) connection 1024. The host computer 1016 and the connected UEs 1012, 1014 are configured to communicate data and / or signaling via the OTT connection 1024 using the access network 1002, the core network 1004, any intermediate networks 1022, and possible further infrastructure (not shown) as intermediaries. The OTT connection 1024 may be transparent in the sense that the participating communication devices through which the OTT connection 1024 passes are unaware of the routing of the uplink and downlink communications. For example, the base station 1006 may not be, or need not be, informed about the past routing of incoming downlink communications involving data originating from the host computer 1016 that is to be forwarded (e.g., handed over) to the connected UE 1012. Similarly, the base station 1006 does not need to be aware of the future routing of outgoing uplink communications originating from the UE 1012 and destined for the host computer 1016 .

[0187] An exemplary implementation of the UE, base station, and host computer described in the previous paragraph, according to one embodiment, will now be described with reference to FIG. 11 . In the communication system 1100, the host computer 1102 comprises hardware 1104 including a communication interface 1106 configured to set up and maintain wired or wireless connections with interfaces of different communication devices of the communication system 1100. The host computer 1102 further comprises a processing circuit 1108, which may have storage and / or processing capabilities. In particular, the processing circuit 1108 may comprise one or more programmable processors, ASICs, FPGAs, or combinations thereof (not shown) adapted to execute instructions. The host computer 1102 further comprises software 1110 stored on or accessible by the host computer 1102 and executable by the processing circuit 1108. The software 1110 includes a host application 1112. The host application 1112 may be operable to provide services to a remote user, such as a UE 1114 connecting via an OTT connection 1116 that terminates at the UE 1114 and the host computer 1102. In providing services to the remote user, the host application 1112 may provide user data that is transmitted using the OTT connection 1116.

[0188] The communications system 1100 further includes a base station 1118 provided in the communications system, the base station 1118 comprising hardware 1120 that enables the base station 1118 to communicate with the host computer 1102 and the UE 1114. The hardware 1120 may include a communications interface 1122 for setting up and maintaining wired or wireless connections with interfaces of different communications devices of the communications system 1100, as well as a wireless interface 1124 for setting up and maintaining at least a wireless connection 1126 with a UE 1114 located in a coverage area (not shown in FIG. 11 ) served by the base station 1118. The communications interface 1122 may be configured to facilitate a connection 1128 to the host computer 1102. The connection 1128 may be direct, or the connection 1128 may pass through a core network of the communications system (not shown in FIG. 11 ) and / or one or more intermediate networks outside the communications system. In the illustrated embodiment, the hardware 1120 of the base station 1118 further includes processing circuitry 1130, which may comprise one or more programmable processors, ASICs, FPGAs, or combinations thereof (not shown) adapted to execute instructions. The base station 1118 further has software 1132 stored internally or accessible via an external connection.

[0189] The communications system 1100 further includes the previously mentioned UE 1114. The hardware 1134 of the UE 1114 may include a wireless interface 1136 configured to set up and maintain a wireless connection 1126 with a base station serving a coverage area in which the UE 1114 is currently located. The hardware 1134 of the UE 1114 further includes a processing circuit 1138, which may comprise one or more programmable processors, ASICs, FPGAs, or combinations thereof (not shown) adapted to execute instructions. The UE 1114 further includes software 1140 stored on or accessible by the UE 1114 and executable by the processing circuit 1138. The software 1140 includes a client application 1142. The client application 1142, with the support of the host computer 1102, may be operable to provide services to a human or non-human user via the UE 1114. On the host computer 1102, a running host application 1112 may communicate with a running client application 1142 via an OTT connection 1116 that terminates at the UE 1114 and the host computer 1102. In providing services to a user, the client application 1142 may receive request data from the host application 1112 and provide user data in response to the request data. The OTT connection 1116 may transfer both the request data and the user data. The client application 1142 may interact with the user to generate the user data that the client application 1142 provides.

[0190] It should be noted that the host computer 1102, base station 1118, and UE 1114 shown in Figure 11 may be similar to or equivalent to the host computer 1016, one of the base stations 1006A, 1006B, and 1006C, and one of the UEs 1012 and 1014, respectively, of Figure 10. That is, the inner workings of these entities may be as shown in Figure 11, and separately, the surrounding network topology may be that of Figure 10.

[0191] 11, the OTT connection 1116 is depicted abstractly to show communication between the host computer 1102 and the UE 1114 via the base station 1118, without explicit reference to intermediary devices and the exact routing of messages through these devices. The network infrastructure may determine the routing, which may be configured to be hidden from the UE 1114, the service provider operating the host computer 1102, or both. While the OTT connection 1116 is active, the network infrastructure may also make decisions to dynamically change the routing (e.g., based on load balancing considerations or reconfiguration of the network).

[0192] The wireless connection 1126 between the UE 1114 and the base station 1118 follows the teachings of embodiments described throughout this disclosure. One or more of the various embodiments improve the performance of the OTT service provided to the UE 1114 using the OTT connection 1116, of which the wireless connection 1126 forms the final segment. More precisely, the teachings of these embodiments may improve, for example, data rates, latency, power consumption, etc., thereby providing benefits such as, for example, reduced user latency, relaxed limits on file sizes, better responsiveness, extended battery life, etc.

[0193] Measurement procedures may be provided for the purpose of monitoring data rates, latency, and other factors that one or more embodiments improve upon. There may further be optional network functionality for reconfiguring the OTT connection 1116 between the host computer 1102 and the UE 1114 in response to fluctuations in the measurement results. The measurement procedures and / or the network functionality for reconfiguring the OTT connection 1116 may be implemented in the software 1110 and hardware 1104 of the host computer 1102, or in the software 1140 and hardware 1134 of the UE 1114, or both. In some embodiments, sensors (not shown) may be deployed in or associated with communication devices through which the OTT connection 1116 passes, and the sensors may participate in the measurement procedures by providing values ​​of the monitored quantities exemplified above or other physical quantities from which the software 1110, 1140 may calculate or estimate the monitored quantities. The reconfiguration of the OTT connection 1116 may include message formats, retransmission settings, preferred routing, etc., and the reconfiguration need not affect the base station 1118, and the reconfiguration may be unknown or imperceptible to the base station 1118. Such procedures and functions may be known and practiced in the art. In some embodiments, the measurements may involve proprietary UE signaling that facilitates the host computer 1102 measurements of throughput, propagation time, latency, etc. The measurements may be implemented in that the software 1110 and 1140 cause messages, particularly empty or “dummy” messages, to be sent using the OTT connection 1116 while the software 1110 and 1140 monitors propagation time, errors, etc.

[0194] FIG. 12 is a flowchart illustrating a method implemented in a communication system according to one embodiment. The communication system includes a host computer, a base station, and a UE, which may be as described with reference to FIGS. 10 and 11. For simplicity of this disclosure, only a drawing reference to FIG. 12 is included in this section. In step 1200, the host computer provides user data. In sub-step 1202 of step 1200 (which may be optional), the host computer provides the user data by executing a host application. In step 1204, the host computer initiates a transmission carrying the user data to the UE. In step 1206 (which may be optional), the base station transmits the user data carried in the host computer initiated transmission to the UE, according to the teachings of the embodiments described throughout this disclosure. In step 1208 (which may also be optional), the UE executes a client application associated with the host application executed by the host computer.

[0195] FIG. 13 is a flowchart illustrating a method implemented in a communication system according to one embodiment. The communication system includes a host computer, a base station, and a UE, which may be as described with reference to FIGS. 10 and 11. For simplicity of this disclosure, only a drawing reference to FIG. 13 is included in this section. In step 1300 of the method, the host computer provides user data. In an optional sub-step (not shown), the host computer provides the user data by executing a host application. In step 1302, the host computer initiates a transmission carrying the user data to the UE. The transmission may go through a base station in accordance with the teachings of the embodiments described throughout this disclosure. In step 1304 (which may be optional), the UE receives the user data carried in the transmission.

[0196] FIG. 14 is a flowchart illustrating a method implemented in a communications system according to one embodiment. The communications system includes a host computer, a base station, and a UE, which may be as described with reference to FIGS. 10 and 11 . For simplicity of this disclosure, only a drawing reference to FIG. 14 is included in this section. In step 1400 (which may be optional), the UE receives input data provided by the host computer. Additionally or alternatively, in step 1402, the UE provides user data. In sub-step 1404 (which may be optional) of step 1400, the UE provides the user data by executing a client application. In sub-step 1406 (which may be optional) of step 1402, the UE executes a client application that provides the user data in response to the received input data provided by the host computer. In providing the user data, the executed client application may further consider user input received from the user. Regardless of the particular manner in which the user data is provided, the UE initiates transmission of the user data to the host computer in sub-step 1408 (which may be optional). In method step 1410, the host computer receives user data transmitted from the UE according to the teachings of the embodiments described throughout this disclosure.

[0197] Figure 15 is a flowchart illustrating a method implemented in a communication system according to one embodiment. The communication system includes a host computer, a base station, and a UE, which may be as described with reference to Figures 10 and 11. For simplicity of this disclosure, only a drawing reference to Figure 15 is included in this section. In step 1500 (which may be optional), the base station receives user data from the UE in accordance with the teachings of embodiments described throughout this disclosure. In step 1502 (which may be optional), the base station initiates transmission of the received user data to the host computer. In step 1504 (which may be optional), the host computer receives the user data carried in a transmission initiated by the base station.

[0198] Any suitable step, method, feature, function, or benefit disclosed herein may be performed through one or more functional units or modules of one or more virtual devices. Each virtual device may comprise several of these functional units. These functional units may be implemented via processing circuitry, which may include one or more microprocessors or microcontrollers, as well as other digital hardware, which may include digital signal processors (DSPs), dedicated digital logic, and the like. The processing circuitry may be configured to execute program code stored in memory, which may include one or several types of memory, such as read-only memory (ROM), random access memory (RAM), cache memory, flash memory devices, optical storage devices, and the like. The program code stored in memory includes program instructions for implementing one or more communication and / or data communication protocols, as well as instructions for performing one or more of the techniques described herein. In some implementations, the processing circuitry may be used to cause each functional unit to perform a corresponding function according to one or more embodiments of the present disclosure.

[0199] While processes in the figures may indicate a particular order of operations performed by some embodiments of the present disclosure, it should be understood that such order is exemplary (e.g., alternative embodiments may perform operations in a different order, combine some operations, overlap some operations, etc.).

[0200] Embodiment

[0201] Group A Embodiments

[0202] Embodiment 1: A method performed by a user equipment (UE) for selecting and / or maintaining a synchronization source, the method including one or more of: obtaining information about configured and / or available synchronization sources; determining whether a synchronization reference source (SRS) needs to be adapted based on at least a CCA procedure; and performing adaptation of an SRS that meets a criterion.

[0203] Embodiment 2: The method of embodiment 1, wherein obtaining the information includes obtaining information about the SRS based on a message received from a network node (e.g., configuration via signaling, such as via RRC, DCI, or MAC-CE).

[0204] Embodiment 3: The method of embodiment 1 or 2, wherein a set of SRSs may be predefined, and the UE selects one SR, a first SRS (SRS1), from the set of predefined SRSs based on an identifier received from the network node.

[0205] Embodiment 4: The method of any one of embodiments 1 to 3, wherein if the UE is configured with a first identifier that assumes a gNB / eNB-based synchronization configuration, the UE selects or uses a gNB / eNB as a synchronization reference source.

[0206] Embodiment 5: The method according to any one of embodiments 1 to 4, wherein the UE uses the GNSS as a synchronization reference source when the second identifier is configured in the UE.

[0207] Embodiment 6: The method according to any one of embodiments 1 to 5, wherein a set of SRSs is predefined, and the UE selects one SRS from the set of SRSs based on one or more rules.

[0208] Embodiment 7: The method of any one of embodiments 1 to 6, wherein the rule relates to an operation scenario of the UE (e.g., in-coverage, out-of-coverage, or partial coverage).

[0209] Embodiment 8: The method of any one of embodiments 1 to 7, wherein determining whether the SRS needs to be adapted based on at least the CCA procedure includes determining information related to the results of the CCA procedure based on one or more rules or parameters related to a CCA failure associated with a signal transmitted by the first SRS (SRS1).

[0210] Embodiment 9: The method of any one of embodiments 1 to 8, wherein the rules are predefined, preconfigured (e.g., on a SIM / USIM card), and / or configured by a node (e.g., by another UE, a network node).

[0211] Embodiment 10: The method of any one of embodiments 1 to 9, wherein performing the adaptation of SRS that meets the criteria comprises adapting one or more procedures related to or involving SRS based on the determined results of the CCA procedure.

[0212] Embodiment 11: The adaptation performed by the UE with respect to the SRS based on the result of the CCA may include: a. continuing to use SRS1 as a synchronization reference source; b. abandoning, suspending, and / or postponing the use of SRS1 as a synchronization reference source for a period of time; c. after suspending or postponing the use of SRS1 as a synchronization source for a period of time, the UE may resume using SRS1 as a synchronization source when one or more conditions are met (e.g., when N1 CCA evaluations are successful); d. using SRS1 as a synchronization source when the UE performs reselection to a new cell. a. restarting SLSS transmission on F4; b. reselecting another synchronization source (e.g., SRS2) (i.e., starting to use a new synchronization reference source); c. adapting SLSS transmission on a fourth carrier frequency (F4) based on the result of the CCA procedure determined by the UE on F1; and g. if the result of the CCA procedure indicates a CCA failure or a high number of CCA failures on F1 (e.g., the number of CCA failures exceeds a threshold for a certain time period) on F1 for a time period Tn, UE1 starts SLSS transmission on F4.

[0213] Embodiment 12: A method performed by a UE for operating as a synchronization reference user equipment (UE), the method including one or more of: obtaining information related to a need to transmit a sidelink reference signal; determining information related to a result of a CCA procedure related to an SRS; and performing adaptive transmission of an SL RS (e.g., an SLSS) based on whether an associated condition is achieved.

[0214] Embodiment 13: The method of embodiment 12, wherein the obtaining of information includes one or more of: a. obtaining information on whether the UE needs to transmit a sidelink reference signal (SLRS), i.e., whether any other sidelink UE (e.g., UE1) is using UE3 as a synchronization reference source; b. determining the need to transmit SLRS if the UE is configured to transmit SLRS by another node (e.g., by another UE (e.g., UE1) or by a network node); c. determining the need to transmit SLRS if the UE is configured to transmit SLRS by another node (e.g., by another UE (e.g., UE1) or by a network node); d. determining the need to transmit SLRS based on a predefined rule (e.g., UE3 is required to transmit SLRS periodically); and e. determining the need to transmit SLRS based on preconfiguration information in the UE (e.g., stored in a SIM / USIM card of UE1).

[0215] Embodiment 14: The method of embodiment 12 or 13, wherein determining the information related to the result of the CCA procedure includes determining the information related to the result of the CCA procedure based on one or more rules or parameters related to a CCA failure related to a sidelink reference signal transmitted by the UE on F1.

[0216] Embodiment 15: The method of any one of embodiments 12 to 14, wherein performing adaptive transmission of the SL RS comprises adapting one or more procedures related to or involving transmission of sidelink reference signals based on the determined outcome of the CCA procedure.

[0217] Embodiment 16: The adapting of one or more procedures includes: a. continuing to transmit an SLRS (e.g., an SLSS) on F1; b. if the result of the CCA procedure indicates no CCA failure on F1 or a limited number of CCA failures on F1, the UE may continue to transmit an SLRS (e.g., an SLSS) according to a reference configuration on F1; c. stopping / suspending transmission of an SLRS (e.g., an SLSS) on F1 for a certain time period; d. if the result of the CCA procedure indicates a CCA failure or a high number of CCA failures (e.g., the number of CCA failures exceeds a threshold), the UE may stop / suspend transmission of an SLRS (e.g., an SLSS) for a time period Tn'; e. if (N'>Nmax') occurs K' times, the UE stops / suspends transmission of an SLRS (e.g., an SLSS); f. if (N'>Nmax') The method of any one of embodiments 12 to 15, including one or more of: if it occurs R1' times during a certain time period (e.g., T0'), the UE stops / suspends transmission of SLRS (e.g., SLSS) to UE1, which is using the UE as a synchronization reference source; g. suspends or postpones transmission of SLRS (e.g., SLSS) on F1 for a certain time period; h. if the result of the CCA procedure indicates a CCA failure or a high number of CCA failures (e.g., the number of CCA failures exceeds a threshold), the UE suspends or postpones transmission of SLRS for a time period Tn'; and i. if the result of the CCA procedure indicates a CCA failure or a high number of CCA failures (e.g., the number of CCA failures exceeds a threshold), the UE adapts one or more transmission parameters of the SLRS.

[0218] Embodiment 17: The method of any one of embodiments 1 to 16, further comprising providing user data and forwarding the user data to the host computer via transmission to the base station.

[0219] Group B Embodiments

[0220] Embodiment 18: A method performed by a base station, the method including one or more of the features disclosed herein.

[0221] Embodiment 19: The method of embodiment 18, including any of the features from the embodiments of Group A.

[0222] Embodiment 20: The method of embodiment 18 or 19, further comprising obtaining user data and forwarding the user data to a host computer or wireless device.

[0223] Group C Embodiments

[0224] Embodiment 21: A wireless device for selecting and / or maintaining a synchronization source, the wireless device comprising: a processing circuit configured to perform any of the steps recited in any one of the embodiments of Group A; and a power supply circuit configured to supply power to the wireless device.

[0225] Embodiment 22: A base station, the base station comprising: processing circuitry configured to perform any of the steps recited in any one of the embodiments of Group B; and power supply circuitry configured to supply power to the base station.

[0226] Embodiment 23: A user equipment (UE) for selecting and / or maintaining a synchronization source, the UE comprising: an antenna configured to send and receive radio signals; a radio front-end circuit connected to the antenna and a processing circuit and configured to condition signals communicated between the antenna and the processing circuit, the radio front-end circuit being configured to perform any of the steps described in any one of the embodiments of Group A; an input interface connected to the processing circuit and configured to enable information input to the UE to be processed by the processing circuit; an output interface connected to the processing circuit and configured to output information from the UE processed by the processing circuit; and a battery connected to the processing circuit and configured to provide power to the UE.

[0227] Embodiment 24: A communications system including a host computer, the host computer having processing circuitry configured to provide user data and a communications interface configured to forward the user data to a cellular network for transmission to a user equipment (UE), the cellular network having a base station having a wireless interface and processing circuitry, the processing circuitry of the base station configured to perform any of the steps described in any one of the embodiments of Group B.

[0228] Embodiment 25: The communication system of embodiment 24, further comprising a base station.

[0229] Embodiment 26: The communication system of embodiment 24 or 25, further comprising a UE, the UE being configured to communicate with the base station.

[0230] Embodiment 27: A communication system as described in any one of embodiments 24 to 26, wherein the processing circuitry of the host computer is configured to execute a host application and thereby provide user data, and the UE comprises processing circuitry configured to execute a client application associated with the host application.

[0231] Embodiment 28: A method implemented in a communication system including a host computer, a base station, and a user equipment (UE), the method including: providing user data at the host computer; and initiating a transmission at the host computer carrying the user data to the UE via a cellular network including the base station, the base station performing any of the steps described in any one of the embodiments of Group B.

[0232]

[0082] Embodiment 29: The method of embodiment 28, further comprising transmitting user data at the base station.

[0233] Embodiment 30: The method of embodiment 28 or 29, wherein the user data is provided by executing a host application on the host computer, and the method further includes executing, on the UE, a client application associated with the host application.

[0234] Embodiment 31: A user equipment (UE) configured to communicate with a base station, the UE comprising a radio interface and processing circuitry configured to perform the method of any one of embodiments 28 to 30.

[0235] Embodiment 32: A communications system including a host computer, the host computer comprising processing circuitry configured to provide user data and a communications interface configured to forward the user data to a cellular network for transmission to a user equipment (UE), the UE comprising a wireless interface and processing circuitry, and components of the UE configured to perform any of the steps described in any one of the embodiments of Group A.

[0236] Embodiment 33: The communication system of embodiment 32, wherein the cellular network further includes a base station configured to communicate with the UE.

[0237] Embodiment 34: A communication system as described in embodiment 32 or 33, wherein the processing circuitry of the host computer is configured to execute a host application and thereby provide user data, and the processing circuitry of the UE is configured to execute a client application associated with the host application.

[0238] Embodiment 35: A method implemented in a communication system including a host computer, a base station, and a user equipment (UE), the method including: providing user data at the host computer; and initiating a transmission at the host computer to carry the user data to the UE via a cellular network including the base station, wherein the UE performs any of the steps described in any one of the embodiments of Group A.

[0239]

[0082] Embodiment 36: The method of embodiment 35, further comprising: receiving, at the UE, user data from the base station.

[0240] Embodiment 37: A communications system including a host computer, the host computer having a communications interface configured to receive user data originating from a transmission from a user equipment (UE) to a base station, the UE having a wireless interface and processing circuitry, the processing circuitry of the UE configured to perform any of the steps described in any one of the embodiments of Group A.

[0241] Embodiment 38: The communication system of embodiment 37, further comprising a UE.

[0242] Embodiment 39: The communication system of embodiment 37 or 38, further comprising a base station, the base station having a radio interface configured to communicate with the UE and a communication interface configured to forward user data carried by transmissions from the UE to the base station to a host computer.

[0243] Embodiment 40: A communication system as described in any one of embodiments 37 to 39, wherein processing circuitry of the host computer is configured to execute a host application, and processing circuitry of the UE is configured to execute a client application associated with the host application, thereby providing user data.

[0244] Embodiment 41: A communication system as described in any one of embodiments 37 to 40, wherein processing circuitry of the host computer is configured to execute a host application and thereby provide requested data, and processing circuitry of the UE is configured to execute a client application associated with the host application and thereby provide user data in response to the requested data.

[0245] Embodiment 42: A method implemented in a communication system including a host computer, a base station, and a user equipment (UE), the method including receiving, at the host computer, user data transmitted from the UE to the base station, and the UE performing any of the steps described in any one of the embodiments of Group A.

[0246]

[0082] Embodiment 43: The method of embodiment 42, further comprising, in the UE, providing user data to the base station.

[0247] Embodiment 44: The method of embodiment 42 or 43, further comprising: executing, in the UE, a client application, thereby providing user data to be transmitted; and executing, in the host computer, a host application associated with the client application.

[0248] Embodiment 45: The method of any one of embodiments 42 to 44, further comprising: executing a client application in the UE; and receiving input data for the client application in the UE, the input data being provided in a host computer by executing a host application associated with the client application; and the user data to be transmitted being provided by the client application in response to the input data.

[0249] Embodiment 46: A communications system including a host computer, the host computer having a communications interface configured to receive user data originating from a transmission from a user equipment (UE) to a base station, the base station having a wireless interface and processing circuitry, the processing circuitry of the base station configured to perform any of the steps recited in any one of the embodiments of Group B.

[0250] Embodiment 47: The communication system of embodiment 46, further comprising a base station.

[0251] Embodiment 48: The communication system of embodiment 46 or 47, further comprising a UE, the UE being configured to communicate with the base station.

[0252] Embodiment 49: A communication system as described in any one of embodiments 46 to 48, wherein the processing circuitry of the host computer is configured to execute a host application, and the UE is configured to execute a client application associated with the host application, thereby providing user data to be received by the host computer.

[0253] Embodiment 50: A method implemented in a communications system including a host computer, a base station, and a user equipment (UE), the method including receiving, at the host computer, from the base station, user data originating from a transmission received by the base station from the UE, and the UE performing any of the steps described in any one of the embodiments of Group A.

[0254]

[0082] Embodiment 51: The method of embodiment 50, further comprising receiving, at the base station, user data from the UE.

[0255] Embodiment 52: The method of embodiment 50 or 51, further comprising initiating, at the base station, transmission of the received user data to the host computer.

[0256] At least some of the following abbreviations may be used in this disclosure. In the event of inconsistencies between abbreviations, the abbreviation as used above should prevail. If listed multiple times below, the first listing should prevail over the subsequent listing(s). 3GPP 3rd Generation Partnership Project 5G (fifth generation) 5GC 5th generation core 5GS 5th generation system AF application features AMF access and mobility features AN Access Network AP access point ASIC Application Specific Integrated Circuit AUSF authentication server function CCA Clear Channel Assessment CPU Central Processing Unit DCI Downlink Control Information DN Data Network DSP Digital Signal Processor eNB Enhanced or Evolved Node B EPS Evolved Packet System E-UTRA Enhanced Universal Terrestrial Radio Access FPGA Field Programmable Gate Array · gNB New wireless base station gNB-DU New Radio Base Station Distributed Unit GNSS Global Navigation Satellite System HSS Home Subscriber Server IoT (Internet of Things) IP Internet Protocol LTE Long Term Evolution MAC Media Access Control MME Mobility Management Entity MTC Machine Type Communication NEF network publishing function NF network function · NR new radio NRF Network Function Repository Function NSSF network slice selection function OTT (Over-the-Top) PC personal computer PCF policy control function PDSCH Physical Downlink Shared Channel P-GW Packet Data Network Gateway PRS Positioning Reference Signal QoS Quality of Service RAM Random Access Memory RAN Radio Access Network ROM Read-Only Memory RP receiving point RRH Remote Radio Head · RS reference signal RTT Round Trip Time SCEF Service Capability Publishing Function SL side link SLRS Sidelink Reference Signal SLSS Sidelink Synchronization Signal SMF session management function SRS Synchronous Reference Source TCI Transmission Configuration Indicator TP sending point TRP sending / receiving points UDM Integrated Data Management UE User Equipment UPF user plane function

[0257] Those skilled in the art will recognize improvements and modifications to the embodiments of the present disclosure, and all such improvements and modifications are considered within the scope of the concepts disclosed herein.

Claims

1. 1. A method performed by a user equipment (UE) for selecting and / or maintaining a synchronization source, the method comprising: obtaining information regarding one or more synchronization sources associated with sidelink operation, the one or more synchronization sources including configured synchronization sources and / or available synchronization sources; determining, for a first synchronization source of the one or more synchronization sources associated with the sidelink operation, whether to adapt selection and / or maintenance of the first synchronization source as a source of synchronization, wherein determining whether to adapt selection and / or maintenance of the first synchronization source is based on at least one Clear Channel Assessment (CCA) procedure; adapting the selection and / or maintaining of the first synchronization source as the source of synchronization in response to determining to adapt the selection and / or maintaining of the first synchronization source as the source of synchronization based on the at least one CCA procedure; A method comprising:

2. The method of claim 1 , wherein determining whether to adapt the selection and / or maintenance of the first synchronization source as the source of synchronization is based on a number of CCA failures.

3. determining whether to adapt the selection and / or maintenance of the first synchronization source as the source of synchronization based on the number of CCA failures; determining that the number of CCA failures exceeds a maximum value; The method of claim 2 , comprising:

4. 2. The method of claim 1, wherein the UE is currently using the first synchronization source as the source of synchronization, and wherein adapting the selection and / or maintenance of the first synchronization source as the source of synchronization comprises continuing to use the first synchronization source as the source of synchronization based on a number of CCA failures being less than a maximum value.

5. Adapting the selecting and / or maintaining the first synchronization source as the source of synchronization includes: Abandoning, suspending, and / or postponing the selection and / or maintenance of the first synchronization source as the source of synchronization for a period of time based on a number of CCA failures being greater than a maximum value.

5. The method of claim 1 , comprising one or more of:

6. Adapting the selecting and / or maintaining the first synchronization source as the source of synchronization includes: reselecting as the source of synchronization another of the one or more synchronization sources associated with the sidelink operation.

6. The method of claim 1, comprising:

7. Adapting the selecting and / or maintaining the first synchronization source as the source of synchronization includes: after suspending or postponing the selection and / or maintenance of the first synchronization source as the source of synchronization for a period of time, resuming the selection and / or maintenance of the first synchronization source as the source of synchronization when one or more conditions are met; resuming the selection and / or maintenance of the first synchronization source as the source of synchronization when the UE performs reselection to a new cell; adapting transmission of a sidelink synchronization signal (SLSS) on another carrier frequency based on a CCA failure on the first carrier frequency; if the at least one CCA procedure indicates that a number of CCA failures on the first carrier frequency exceeds a maximum value for a time period Tn, initiating an SLSS transmission on another carrier frequency; 7. The method of claim 1, comprising one or more of:

8. 8. The method of claim 1, wherein the obtaining information regarding the one or more synchronization sources associated with the sidelink operation comprises obtaining the information based on a message received from a network node.

9. 9. The method of claim 1, further comprising the UE selecting the first synchronization source from a set of predefined synchronization sources based on an identifier received from a network node.

10. 10. The method of claim 1, further comprising: if the UE is configured with a first identifier that assumes a gNodeB (gNB)-based synchronization configuration or an eNodeB (eNB)-based synchronization configuration, selecting or using a gNB or an eNB as the source of synchronization.

11. The method of claim 1 , further comprising using a Global Navigation Satellite System (GNSS) as the source of synchronization if the UE is configured with a second identifier.

12. 1. A method performed by a user equipment (UE) for operating as a synchronization reference UE, the method comprising: obtaining information related to the need to transmit a Sidelink (SL) Reference Signal (RS); determining information relating to a result of at least one clear channel assessment (CCA) procedure associated with a synchronization reference source (SRS); adapting transmission of the SL RS based on the result of the at least one CCA procedure; A method comprising:

13. The method of claim 12 , wherein determining information related to an outcome of at least one CCA procedure is based on a number of CCA failures.

14. Determining information relating to an outcome of the at least one CCA procedure includes: determining that the number of CCA failures exceeds a maximum value; The method of claim 10, comprising:

15. Adapting one or more procedures may include: Continue transmitting SLRS on the current frequency (F1); If the result of the CCA procedure indicates no CCA failure on F1 or a limited number of CCA failures on F1, the UE continues to transmit SLRS according to a reference configuration on F1. Stopping / canceling transmission of said SLRS on F1 for a period of time; If the result of the CCA procedure indicates a CCA failure or a high number of CCA failures, the UE stops / suspends transmission of SLRS for a time period Tn′. If (N'>Nmax') occurs K' times, the UE stops / aborts transmitting SLRS, where N' is the number of CCA failures, Nmax' is a threshold, and K' is an integer. If (N'>Nmax') occurs R1' times in a certain time period, the UE stops / suspends the transmission of the SLRS; suspending or postponing the transmission of the SLRS on F1 for a period of time; If the result of the CCA procedure indicates a CCA failure or a high number of CCA failures, the UE suspends or postpones transmission of an SLRS for a time period Tn′; and If the result of the CCA procedure indicates a CCA failure or a high number of CCA failures, the UE adapts one or more transmission parameters of an SLRS.

12. The method of any one of claims 9 to 11, comprising one or more of:

16. Obtaining information related to the need to transmit the SLRS includes: Obtaining information on whether the UE needs to transmit an SLRS; and determining the need to transmit the SLRS if the UE is configured by another node to transmit the SLRS; determining the need to transmit the SLRS if the UE is configured by another node to transmit the SLRS; determining the need to transmit the SLRS based on predefined rules; determining the need to transmit the SLRS based on pre-configuration information in the UE; 13. The method of any one of claims 9 to 12, comprising one or more of:

17. A user equipment (UE) (800) comprising a processing circuit (802) and a memory (804), the memory (804) configured to: obtaining information regarding one or more synchronization sources associated with sidelink operation, the one or more synchronization sources including configured synchronization sources and / or available synchronization sources; determining, for a first synchronization source of the one or more synchronization sources associated with the sidelink operation, whether to adapt selection and / or maintenance of the first synchronization source as a source of synchronization, wherein determining whether to adapt selection and / or maintenance of the first synchronization source is based on at least one Clear Channel Assessment (CCA) procedure; adapting the selection and / or maintaining of the first synchronization source as the source of synchronization in response to determining to adapt the selection and / or maintaining of the first synchronization source as the source of synchronization based on the at least one CCA procedure; A user equipment (UE) (800) comprising instructions for causing the UE to:

18. 18. The UE (800) of claim 17, further operable to implement the features of any one of claims 2 to 11.

19. A computer-readable medium comprising instructions that, when executed on at least one processor, cause the at least one processor to perform the method of any one of claims 1 to 11.

20. A user equipment (UE) (800) comprising a processing circuit (802) and a memory (804), the memory (804) configured to: obtaining information related to the need to transmit a Sidelink (SL) Reference Signal (RS); determining information relating to a result of at least one clear channel assessment (CCA) procedure associated with a synchronization reference source (SRS); adapting transmission of the SL RS based on the result of the at least one CCA procedure; A user equipment (UE) (800) comprising instructions for causing the UE to:

21. 21. The UE (800) of claim 20, further operable to implement the features of any one of claims 13 to 16.

22. A computer readable medium comprising instructions that, when executed on at least one processor, cause the at least one processor to perform the method of any one of claims 12 to 16.

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