Adaptation of SL synchronization source based on CCA failure

Abstract

Systems and methods for adaptation of sidelink (SL) synchronization sources based on clear channel assessment (CCA) failures are disclosed. In some embodiments, a method for selecting and / or maintaining synchronization sources includes obtaining information about one or more synchronization sources associated with sidelink operations, the one or more synchronization sources including configured synchronization sources and / or available synchronization sources; for the first synchronization source, determining whether selection and / or maintenance of the first synchronization source as the synchronization source is adapted based on the CCA procedure; and adapting selection and / or maintenance. In some embodiments, a method for operating as a synchronization reference UE includes obtaining information related to a need to transmit an SL reference signal (RS); determining information related to a result of the CCA procedure; and adapting transmission of the SL RS based on a result of the CCA procedure. Some embodiments: enable selection of reliable synchronization sources; and / or defining a clear synchronization procedure for the sidelink.

Description

[0001] Related applications

[0002] This application claims the benefit of provisional patent application serial number 63 / 446,267 filed on February 16, 2023, the entire disclosure of which is hereby incorporated by reference into this document. Technical Field

[0003] V2X, D2D, sidelink, UE-to-network relay, Proximity-based Services (ProSe), LBT, CCA, unlicensed band operation, synchronization reference resources. Background Art

[0004] Unauthorized Operations in NR

[0005] Unlicensed spectrum can be shared between multiple networks. Before transmitting on a channel on the unlicensed spectrum, a device / node performs a Clear Channel Assessment (CCA) to assess or determine whether the channel is busy. The CCA procedure is also known as Listen Before Talk (LBT).

[0006] CCA involves monitoring the channel during some specified time and measuring the received energy and / or checking for a preamble transmission indicating the start of a transmission by another device in some technologies (e.g., Wi-Fi). If the channel is assessed (e.g., based on CCA) to be idle, the device is allowed to transmit a signal on the channel, which may also be referred to as an idle channel, a free channel, an available channel, an unused channel, or a non-busy channel. If the received energy or power during the sensing duration is below a certain energy detection threshold, the channel is assessed to be idle; otherwise, the channel is considered busy. An example of an energy detection level threshold is -72dBm, which may further depend on the channel bandwidth, e.g., -72dBm and -75dBm for 20MHz and 10MHz, respectively. If the channel is assessed to be "busy," the device (UE or BS) is required to suspend transmission.

[0007] After sensing that the channel is idle, a device / node is typically allowed to transmit for a certain amount of time, sometimes referred to as the Channel Occupancy Time (COT) or Maximum Channel Occupancy Time (MCOT). The maximum allowed length of the COT depends on the provisions and type of CCA that has been performed (e.g., how long the medium is sensed, e.g., the sensing duration). The COT is typically in the range of between 1 ms and 10 ms.

[0008] Figure 1LTE LBT and COT are shown, where "s" is the sensing period. In one example, the sensing period can be 25 μs. In this figure, if the channel is determined to be busy, then after a certain delay time, the device may again attempt to sense on the channel to determine whether the channel is available. If the channel is available, the device may begin transmitting signals (during the device's channel occupancy time) after a certain backoff time, but no longer than the maximum channel occupancy time (MCOT), which can be, for example, up to 10 ms, depending on the region. The backoff time can be deterministic or statistical.

[0009] Sidelink transmission in NR

[0010] Sidelink (SL) operation enables direct communication between two or more UEs over the SL or PC5 interface.

[0011] D2D operation is a general term that may include the transmission and / or reception of any type of D2D signal (e.g., physical signal, physical channel, etc.) by a UE with D2D communication capabilities and / or a UE with D2D discovery capabilities. V2X is a special type of device-to-device (D2D) operation. D2D operation is therefore also referred to as D2D transmission, D2D reception, D2D communication, proximity services (ProSe), V2X, etc.

[0012] For LTE and NR, SL operations are specified 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, on the sidelink, only broadcast is supported. NR SL is capable of performing broadcast, multicast and unicast communications. In multicast communications, the intended receivers of the message are typically a subset of vehicles in the vicinity of the transmitter, while in unicast communications, there is a single intended receiver. Broadcast, multicast and unicast transmissions of V2X operations on SL are supported for in-coverage, out-of-coverage and partial coverage scenarios. For unicast and multicast transmissions on SL, HARQ feedback and HARQ combining in the UE's physical layer are supported.

[0013] Both LTE SL and NR SL are capable of operating with and without network coverage, and with varying degrees of interaction between the UE (User Equipment) and the network, including support for standalone, network-free operation.

[0014] SL can be configured on a dedicated carrier (e.g., a carrier in the ITS band) or on a carrier of the UE's serving cell. In the latter case, SL resources are shared in time and / or frequency with resources used for cellular communication (via uplink / downlink, also known as Uu link). Typically, SL resources are time-multiplexed with uplink resources used for cellular communication on the UE's serving cell.

[0015] The embodiments described herein are applicable to any type of D2D operation, including ProSe, V2X, etc.

[0016] Examples of physical channels and reference signals for SL operation NR (previously available in LTE) are:

[0017] PSSCH (Physical Sidelink Shared Channel, SL version of PDSCH): PSSCH is transmitted by the sidelink transmitter UE, and it conveys part of the sidelink transmission data, the system information block (SIB) for radio resource control (RRC) configuration, and the sidelink control information (SCI).

[0018] PSFCH (Physical Sidelink Feedback Channel): The PSFCH is transmitted by the sidelink receiver UE for unicast and multicast. It conveys 1 bit of information on 1 RB for HARQ acknowledgement (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.

[0019] PSCCH (Physical Sidelink Common Control Channel, SL version of PDCCH): When the traffic to be sent to the receiver UE arrives at the transmitter UE, the transmitter UE should first send PSCCH, which conveys part of 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 port, etc.

[0020] Sidelink Primary / 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). By detecting the S-PSS and S-SSS, the UE can identify the sidelink synchronization identifier (SSID) from the UE transmitting the S-PSS / S-SSS. By detecting the S-PSS / S-SSS, the UE can thus learn the characteristics of the UE transmitter of the S-PSS / S-SSS. The series of processes for acquiring timing and frequency synchronization together with the UE's SSID is called initial cell search. Note that the UE transmitting the S-PSS / S-SSS may not necessarily participate 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 in a cell, resulting in a total of 672 SSIDs.

[0021] Physical Sidelink Broadcast Channel (PSBCH): The PSBCH is transmitted as a synchronization signal / PSBCH block (SSB) along with the S-PSS / S-SSS. The SSB has the same parameter set as the PSCCH / PSSCH on this carrier and should be transmitted within the bandwidth of the configured BWP. The PSBCH conveys synchronization-related information such as the Direct Frame Number (DFN), an indication of the slot and symbol-level time resources used for sidelink transmissions, an in-coverage indicator, etc. The SSB is transmitted periodically every 160ms.

[0022] 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 adopted by sidelink transmissions. Similarly, PT-RS is only applicable to FR2 transmissions.

[0023] Similar to ProSe in LTE, NR sidelink transmission has the following two resource allocation modes: Mode 1: Sidelink resources are scheduled by the gNB. Mode 2: Based on the channel sensing mechanism, the UE autonomously selects sidelink resources from (one or more) (pre-)configured sidelink resource pools.

[0024] For in-coverage UEs, the gNB can be configured to use Mode 1 or Mode 2. For out-of-coverage UEs, only Mode 2 can be used.

[0025] Like in LTE, scheduling on the sidelink in NR is done differently for Mode 1 and Mode 2.

[0026] As documented in RP-213678 on NR SL evolution in 3GPP Rel-18, the following study objectives have been defined for 3GPP Rel-18.

[0027] 1. Study and specify support for sidelink on unlicensed spectrum for both Mode 1 and Mode 2, where Uu operation for Mode 1 is restricted to licensed spectrum only [RAN1, RAN2, RAN4]

[0028] - Channel access mechanisms from NR-U should be reused for sidelink unlicensed operation

[0029] ○ Within the boundaries of unlicensed channel access mechanisms and operations, assess the

[0030] Applicability of Rel-16 / Rel-17 sidelink resource reservation to sidelink unlicensed operation

[0031] ■ No specific enhancements to the Rel-17 resource allocation mechanism

[0032] ■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.

[0033] - Physical channel design framework: Changes to the NR sidelink physical channel structure and procedures are required to operate on unlicensed spectrum

[0034] ○ The existing NR sidelink and NR-U channel structure should be reused as a baseline.

[0035] - No specific enhancement of existing NR SL features

[0036] - The study should focus on the FR1 unlicensed bands (n46 and n96 / n102) and will be completed by RAN#98.

[0037] To support sidelink transmissions over unlicensed spectrum (SL-U), a new mechanism for selecting and maintaining a reliable synchronization source is needed, as traditional mechanisms are not designed to handle LBT failures at both the transmitting and receiving nodes. Following traditional mechanisms to perform synchronization procedures over unlicensed spectrum can cause the UE to select a less reliable synchronization source, which ultimately leads to connection failures. Therefore, a new synchronization method is needed to support sidelink operations over unlicensed spectrum. Summary of the Invention

[0038] Disclosed are systems and methods for adapting a sidelink (SL) synchronization source based on a clear channel assessment (CCA) failure. In some embodiments, a method performed by a user equipment (UE) for selecting and / or maintaining a synchronization source includes: obtaining information about one or more synchronization sources associated with a sidelink operation, the one or more synchronization sources including configured synchronization sources and / or available synchronization sources; for a first synchronization source of the one or more synchronization sources associated with the sidelink operation, determining whether to adapt selection and / or maintenance of the first synchronization source as a synchronization source, the determination being based on at least one CCA procedure; and in response to determining to adapt selection and / or maintenance of the first synchronization source as the synchronization source based on the at least one CCA procedure, adapting selection and / or maintenance of the first synchronization source as the synchronization source. 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 reference signal (RS); determining information related to a result of at least one CCA procedure associated with an 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 subject to CCA; and / or defining a clear synchronization procedure for the sidelink when operating in a carrier subject to CCA.

[0039] Some embodiments described herein apply to a scenario where 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 are capable of operating in sidelink Mode 1 or Mode 2. UE1 is further configured with a list of synchronization sources or follows a list of synchronization sources (e.g., predefined in a specification) to select a synchronization reference source, where the sources may have the same or different priorities.

[0040] In a first embodiment, UE1, which is synchronized with a first synchronization reference source (SRS1) to perform sidelink operation using a signal transmitted by SRS1 on a first carrier frequency (F1), determines a result of a CCA procedure performed by SRS1 for transmitting a 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.

[0041] 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, the network, etc.). Examples of SRS adaptation include continuing to use SRS1, discarding SRS1, changing / reselecting synchronization to a second synchronization reference source (SRS2), suspending SRS1 for a certain period of time, suspending or postponing SRS1 until one or more conditions are met, initiating / terminating SLSS, etc. Examples of results of the CCA procedure include the number of CCA failures, the number of successful CCAs, the number of CCA failures over a certain period of time, the number of successful CCAs over a certain period of time, etc. For example, if the number of CCA failures detected by UE1 on F1 exceeds a threshold, UE1 triggers reselection of the synchronization reference source (e.g., reselection to SRS2); otherwise, the UE continues to use SRS1. Signals received from SRS1 (the transmission of which is subject to the CCA procedure) are used by UE1 to adjust, correct, or obtain timing information to enable operation of the SL signal on F1. SRS1 can be a UE (third UE (UE3)) or a first network node (NN1, eg, a first base station). SRS2 can be a UE (fourth UE (UE4)) or a second network node (NN2, eg, a second base station).

[0042] In a second embodiment, a third UE (UE3) configured as a first synchronization reference source (SRS1) for at least one other UE (first UE (UE1)) on a first carrier (F1) 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.

[0043] Adaptation of SLRS transmission may be determined by UE3 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 SLSS transmission, stopping / terminating SLRS transmission, pausing or postponing SLRS transmission for a certain period of time, or resuming / restarting SLRS transmission after a certain period of time, pausing or postponing SLRS transmission until one or more conditions are met, or resuming / restarting SLRS transmission after one or more conditions are met, adapting the SLRS transmission rate (e.g., transmitting SLRS at a rate below a threshold), etc. An example of an SLRS is SLSS. Examples of results of the CCA procedure include the number of CCA failures, the number of successful CCAs, the number of CCA failures over a certain period of time, the number of successful CCAs over a certain period of time, etc. For example, if the number of CCA failures detected by UE3 on F1 exceeds a threshold, UE3 stops / terminates SLRS transmission; otherwise, UE3 continues SLRS transmission. UE3 typically transmits a periodic SL reference signal (e.g., SLSS).

[0044] Operation between UE1 and UE2 on F2 may or may not be subject to CCA procedures, i.e., CCA procedures are applied before the transmission of signals. However, 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.

[0045] The terms "synchronization reference source," "synchronization source," and "synchronization reference" are used interchangeably herein.

[0046] Some embodiments provide one or more benefits, such as enabling selection of a reliable synchronization source when operating in a carrier subject to CCA; and / or defining a clear synchronization procedure for the sidelink when operating in a carrier subject to CCA. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate several aspects of the disclosure and, together with the description, serve to explain the principles of the disclosure.

[0048] Figure 1 LTE LBT and COT are shown, where "s" is the sensing period;

[0049] Figure 2 illustrates an example of a cellular communication system according to some embodiments of the present disclosure;

[0050] Figure 3Illustrated is a scenario in which UE1 and UE2 perform SL operation, obtaining timing from a first synchronization reference source (SRS1) subject to CCA;

[0051] Figure 4 Illustrated is a scenario in which UE1 changes / reselects its SRS from SRS1 to SRS2 due to CCA failure on F1 between UE1 and SRS1;

[0052] Figure 5 is a schematic block diagram of a radio access node according to some embodiments of the present disclosure;

[0053] Figure 6 is a diagram illustrating some embodiments of the present disclosure Figure 5 A schematic block diagram of an embodiment of a virtualization of a radio access node;

[0054] Figure 7 According to some other embodiments of the present disclosure Figure 5 A schematic block diagram of a radio access node;

[0055] Figure 8 is a schematic block diagram of a user equipment device (UE) according to some embodiments of the present disclosure;

[0056] Figure 9 According to some other embodiments of the present disclosure Figure 8 A schematic block diagram of a UE;

[0057] Figure 10 Illustrated is a telecommunications network connected to a host computer via an intermediate network according to some embodiments of the present disclosure;

[0058] Figure 11 is a generalized block diagram of a host computer communicating with a UE via a base station via a partial wireless connection according to some embodiments of the present disclosure;

[0059] Figure 12 is a flow chart illustrating a method implemented in a communication system according to one embodiment of the present disclosure;

[0060] Figure 13 is a flow chart illustrating a method implemented in a communication system according to one embodiment of the present disclosure;

[0061] Figure 14 is a flowchart illustrating a method implemented in a communication system according to one embodiment of the present disclosure; and

[0062] Figure 15 is a flowchart illustrating a method implemented in a communication system according to one embodiment of the present disclosure. DETAILED DESCRIPTION

[0063] The embodiments set forth below represent information that will enable those skilled in the art to implement the embodiments and illustrate the best mode of implementing the embodiments. When 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 discussed herein. It should be understood that these concepts and applications fall within the scope of the present disclosure.

[0064] Radio node: As used herein, a "radio node" is a radio access node or a wireless communication device.

[0065]

[0014] 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 communication network that operates to transmit and / or receive signals wirelessly. Some examples of radio access nodes include, but are not limited to, a base station (e.g., a 3rd Generation Partnership Project (3GPP) fifth generation (5G) New Radio (NR) base station (gNB) in a 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, or the like), a relay node, a network node that implements part of the functionality of a base station or a network node that implements a gNB distributed unit (gNB-DU), or a network node that implements part of the functionality of some other type of radio access node.

[0066] 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 exposure function (SCEF), a home subscriber server (HSS), or the like. Some other examples of core network nodes include: a node that implements 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 exposure function (NEF), a network function (NF) repository function (NRF), a policy control function (PCF), a unified data management (UDM), or the like.

[0067] Communication Device: As used herein, a "communication device" is any type of device that can access an access network. Some examples of communication devices include, but are not limited to, mobile phones, smartphones, sensor devices, meters, vehicles, household appliances, medical devices, media players, cameras, or any type of consumer electronic device, such as, but not limited to, televisions, radios, lighting fixtures, tablet computers, laptop computers, or personal computers (PCs). A communication device can be portable, handheld, a mobile device including a computer, or in a vehicle, capable of transmitting voice and / or data via a wireless or wired connection.

[0068] Wireless communication device: One type of communication device is a wireless communication device, which may be any type of wireless device that can access (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 a wireless communication device may be a mobile phone, a smartphone, a sensor device, a meter, a vehicle, a home 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 fixture, a tablet computer, a laptop computer, or a PC, or such a wireless communication device may be integrated into such devices. A wireless communication device may be a portable, handheld, computer-included, or vehicle-mounted mobile device capable of transmitting voice and / or data via a wireless connection.

[0069] Network node: As used herein, a "network node" is any node that is part of the RAN or core network of a cellular communication network / system.

[0070] Transmission / Reception Point (TRP): In some embodiments, a TRP can be a network node, radio head, spatial relationship, or Transmission Configuration Indicator (TCI) state. In some embodiments, a TRP can be represented by a spatial relationship or TCI state. In some embodiments, a TRP can use multiple TCI states. In some embodiments, a TRP can be part of a gNB, which transmits and receives radio signals to / from a UE based on the physical layer properties and parameters inherent to that component. In some embodiments, in multiple TRP (multi-TRP) operation, a serving cell can schedule UEs from two TRPs, thereby providing improved physical downlink shared channel (PDSCH) coverage, reliability, and / or data rates. For multi-TRP, there are two different operating modes: single downlink control information (DCI) and multi-DCI. In both modes, control of uplink and downlink operations is performed by both the physical layer and the medium access control (MAC). In single-DCI mode, UEs are scheduled with the same DCI for both TRPs, while in multi-DCI mode, UEs are scheduled with independent DCI from each TRP.

[0071] In some embodiments, a transmission point (TP) set is a set of geographically co-located transmit antennas (e.g., an antenna array (having one or more antenna elements)) of a cell, a portion of a cell, or a positioning reference signal (PRS)-only TP. TPs can include base station (eNB) antennas, remote radio heads (RRHs), remote antennas of base stations, antennas of PRS-only TPs, and the like. A cell can be formed by one or more TPs. For homogeneous deployments, each TP can correspond to a cell.

[0072] In some embodiments, a set of TRPs is a set of geographically co-located antennas (e.g., an antenna array (having one or more antenna elements)) that support TP and / or reception point (RP) functionality.

[0073] Note that the description given herein focuses on 3GPP cellular communication systems, and therefore, 3GPP terminology or terms similar to 3GPP terminology are often used. However, the concepts disclosed herein are not limited to 3GPP systems.

[0074] Note that in the description herein, reference may be made to the term "cell"; however, particularly for 5G NR concepts, beams may be used instead of cells, and therefore, it is important to note that the concepts described herein apply equally to both cells and beams.

[0075] Figure 2An example of a cellular communication system 200 in which embodiments of the present disclosure may be implemented is illustrated. In the embodiments described herein, cellular communication system 200 is a 5G system (5GS), comprising 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 in the 5GS comprise NR base stations (gNBs) and, optionally, next-generation eNBs (ng-eNBs) (e.g., LTE RAN nodes connected to the 5GC), controlling 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 a plurality of low-power nodes 206-1 through 206-4, which control corresponding small cells 208-1 through 208-4. Low power nodes 206-1 to 206-4 can be small base stations (such as pico or femto base stations) or RRHs or the like. It is worth noting that, although not shown, one or more of small cells 208-1 to 208-4 may alternatively be provided by base station 202. Low power nodes 206-1 to 206-4 are generally referred to herein as low power nodes 206, and are individually referred to as low power nodes 206. Similarly, small cells 208-1 to 208-4 are generally referred to herein as small cells 208, and are individually referred to as small cells 208. The cellular communication system 200 also includes a core network 210, which is referred to as 5GC in a 5G system (5GS). The base station 202 (and optionally the low power node 206) is connected to the core network 210.

[0076] Base station 202 and low power node 206 provide services to 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 device 212 is often a UE, but the present disclosure is not limited thereto.

[0077] Generalization and terminology

[0078] Examples of network nodes are NodeB, base station (BS), multi-standard radio (MSR) radio node (such as, MSRBS), eNodeB, gNodeB, MeNB, SeNB, location measurement unit (LMU), integrated access backhaul (IAB) node, network controller, radio network controller (RNC), base station controller (BSC), repeater, donor node controlled repeater, 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, transmission node, transmission reception 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.

[0079] The non-limiting term "UE" refers to any type of wireless device that communicates with a network node and / or with another UE in a cellular or mobile communication system. Examples of UEs are target devices, device-to-device (D2D) UEs, vehicle-to-vehicle (V2V) UEs, machine-type UEs, MTC UEs, or UEs capable of performing machine-to-machine (M2M) communication, PDAs, tablet computers, mobile terminals, smartphones, laptop embedded equipment (LEE), laptop mounted equipment (LME), USB dongles, etc.

[0080] 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 device denoted by the term "node", "network node" or "radio network node" may be capable of supporting a single or multiple RATs.

[0081] As used herein, the term "Clear Channel Assessment (CCA)" 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 interchangeably referred to as carrier frequency, frequency layer, channel, radio channel, radio frequency channel, etc. CCA may also be interchangeably referred to as a CSMA scheme, channel assessment scheme, listen-before-talk (LBT), shared channel access mechanism or scheme, shared spectrum channel access mechanism or scheme, etc. The frequency band of a carrier subject to CCA may also be referred to as an unlicensed frequency band or spectrum, a shared spectrum channel access band, a frequency band for operations utilizing shared spectrum channel access, etc. More generally, CCA-based operation is 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 typically used for transmission on carriers in unlicensed frequency bands. However, this mechanism can also be applied to operations on carriers belonging to licensed frequency 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 can be performed by the UE before UL transmission and / or by a network node (e.g., a base station) before DL transmission, or by another SL UE. Therefore, CCA may also be referred to as DL CCA (e.g., performed before DL transmission), UL CCA (e.g., performed before UL transmission), etc.

[0082] The term "SLRS" used in different embodiments may refer to any of the following: SL-SSSB, SLSS, S-PSS, S-SSS, PSBCH, or any combination, e.g., S-SS / PSBCH (S-SS+S-PSS+PSBCH).

[0083] In addition, both the LBE-based channel access scheme (also named dynamic channel access) and the FBE-based channel access scheme (also named semi-static channel access) are covered in the following embodiments.

[0084] The following embodiments are applicable to SL transmission on unlicensed bands using any broadcast type, including unicast, multicast, and broadcast.

[0085] For the SL BWP configured for a UE, the BWP may contain multiple bandwidth segments called, for example, channels, sub-bands, BWP segments, etc. For each segment, it may be configured with the following different parameters: SCS, symbol duration, cyclic prefix (CP) length.

[0086] In this case, the UE may perform LBT operation in each channel / sub-band / BWP segment.

[0087] The term "signal manipulation" may refer to any of the following: the transmission of a signal by a device and / or the reception of a signal at a device. The term "manipulation of a signal subject to CCA" may refer to a scenario in which, before transmitting a signal on a carrier, a device may apply a CCA procedure to determine whether the channel is idle or busy. That is, if the channel is idle, the device transmits the signal; otherwise, it defers transmission. For simplicity, in some embodiments, the term "carrier subject to CCA" may be used to refer to the manipulation of a signal on a cell of a carrier when the CCA procedure is applied by the device before the transmission of the signal. Each occurrence of a signal or occurrence at which a UE can manipulate a signal is broadly referred to as an opportunity, which can be a transmission opportunity or a reception opportunity. Opportunities are also interchangeably referred to as signal opportunities, signal manipulation opportunities, measurement opportunities, signal manipulation opportunities, signal durations, manipulation opportunities, or simply as opportunities for manipulating a signal. Examples of opportunities include time resources containing RSs (e.g., SLSS, CSI-RS, SSB), SMTC opportunities, discovery burst transmission (DBT) windows, etc. The opportunity may occur once per RS periodicity (eg, once per SMTC cycle), once per DRX cycle, once per Qth DRX cycle (where Q>1), and so on.

[0088] Scenario

[0089] The embodiments are described in the context of NR, i.e., two or more SL UEs operate in the same cell or different cells or are served by the same cell or different cells, or one or more SL UEs are located outside the network coverage. However, the embodiments are applicable to LTE or any other technology (e.g., 6th generation systems) that can achieve a direct connection between two (or more) devices. The embodiments are also applicable to relay scenarios, including UE-to-network relay or UE-to-UE relay, where the remote UE and the relay UE can be based on an LTE side link or an NR side link, and the Uu connection between the relay UE and the base station can be an LTE Uu or an NR Uu.

[0090] The scenario includes UE1, which is 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, the SL operation between UE1 and UE2 on F2 is subject to a CCA procedure, i.e., the CCA procedure is applied before the transmission of the signal. In another example, the SL operation between UE1 and UE2 on F2 is not subject to a CCA procedure, i.e., the CCA procedure is not applied before the transmission of the signal. When the operating SL UE is in coverage, the UE is able to operate in mode 1 or mode 2. The main difference between the two modes is that SL transmissions are scheduled by the network node in mode 1, while they are autonomously scheduled / selected by the UE in mode 2.

[0091] UEs participating in sidelink communication are further (pre)configured with a list of synchronization sources (e.g., predefined in the specification), where the sources may have the same or different priorities. An example list of synchronization sources, including GNSS, UE, or network node (e.g., gNB, eNB, BS, etc.), is shown below in order of priority. P0 has the highest priority, while P6 has the lowest priority.

[0092] Figure 3 The examples in illustrate scenarios considered in some of the embodiments. Figure 3 The following illustrates a scenario where UE1 and UE2 perform SL operation and obtain timing from a first synchronization reference source (SRS1) that is subject to CCA: A) SRS1 is a first network node (NN1); B) SRS1 is a third UE (UE3). The figure shows that UE1 performs SL operation with UE2 on F2. The figure shows that UE1 obtains time synchronization with the first synchronization reference source (SRS1) operating on F1 that is subject to CCA (e.g., on a carrier belonging to an unlicensed band). In the example Figure 3 In one example shown in (A), SRS1 is a first network node (NN1), such as a base station, eNB, gNB, access point, etc. Figure 3 In another example shown in (B), SRS1 is another UE, for example, 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 this case, the radio links (or signals) between UE1 and UE2 and between UE1 and SRS1 may be orthogonal to each other in the time domain and / or in the frequency domain.

[0093] GNSS-based Based on gNB / eNB P0: GNSS P0': gNB / eNB P1: UE synchronizes directly with GNSS P1': UE synchronizes directly with gNB / eNB P2: UE is synchronized indirectly with GNSS P2': UE is indirectly synchronized with gNB / eNB P3: gNB / eNB P3': GNSS P4: UE synchronizes directly with gNB / eNB P4': UE synchronizes directly with GNSS P5: UE indirect synchronization with gNB / eNB P5': UE is indirectly synchronized with GNSS P6: The remaining UEs have the lowest priority P6': The remaining UEs have the lowest priority

[0094] List of synchronization sources for the sidelink

[0095] Systems and methods for adaptation of a SL synchronization source based on a CCA failure are disclosed. In some embodiments, a method performed by a UE for selecting and / or maintaining a synchronization source includes: obtaining information about configured synchronization sources and / or available synchronization sources; determining whether an SRS needs to be adapted based on at least one CCA procedure; and in response to determining that the SRS needs to be adapted, performing adaptation of the SRS. In some embodiments, a method performed by a UE for operating as a synchronization reference UE includes: obtaining information related to the need to transmit a SL RS; determining information related to the result of at least one CCA procedure associated with the SRS; and adapting the 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 subject to CCA; and / or defining clear synchronization procedures for the sidelink when operating in a carrier subject to CCA.

[0096] Embodiment 1: Method for selecting and maintaining a synchronization source in UE 1. The embodiments described herein can be implemented in any combination. The UE embodiment includes at least the following: Step 1: UE 1 obtains information about configured synchronization sources and / or available synchronization sources. Step 2: Based on at least a CCA procedure, UE 1 determines the need to adapt an SRS. Step 3: UE 1 performs SRS adaptation that meets the criteria.

[0097] Step 1: UE1 obtains information about SRS

[0098] In this step, UE1 obtains information about configured, supported, or available synchronization reference sources (SRSs). In one example, UE1 may obtain information about SRSs based on a message received from a network node (e.g., configuration via signaling (such as via RRC, DCI, or MAC-CE)). For example, a set of SRSs may be predefined, and UE1 may select an SR, i.e., 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 table above for gNB / eNB-based synchronization configuration, UE1 selects or uses 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, etc.

[0099] In another example, a set of SRSs may be predefined, and UE 1 may select an SRS from the set of SRSs based on one or more rules. The SRSs in the set may have different priorities, as shown in the table above. In one example, the rules are associated with the UE's operating scenario (e.g., in coverage, out of coverage, or partial coverage).

[0100] In another example, UE1 selects SRS based on the type of carrier on which SL is operating. For example, if SL is operating on a carrier subject to CCA, UE1 may select P0 (GNSS), but if SL is operating on a carrier not subject to CCA or on a carrier on which UE1 also performs WAN operations (e.g., on a Uu interface, etc.), UE1 may use P0' (gNB / eNB). In another example, if SL on F2 between UE1 and UE2 is operating on a carrier subject to CCA, UE1 also selects SRS on a carrier also subject to CCA (e.g., another UE or base station).

[0101] In yet another example, UE1 selects SRS based on the availability of SRS types in a predefined list. For example, UE1 first tries to use P0 / P0' as SRS, but if it is not available or detectable, UE1 tries to select P1 / P1' and so on.

[0102] Step 2: UE1 determines information related to the result of the CCA procedure associated with SRS

[0103] In this step, UE1 determines information related to the result of the CCA procedure based on one or more rules or parameters related to the CCA failure associated with the signal transmitted on F1 by the first SRS (SRS1). The terms "CCA failure", "CCA procedure", "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.).

[0104] Examples of parameters relevant to the CCA procedure include:

[0105] Results of the CCA Procedure

[0106] The result of the CCA procedure can be indicated based on a CCA failure determined by UE1 on the radio link between UE1 and SRS1 operating on F1. In one example, UE1 autonomously determines or detects a CCA failure by detecting the absence of a signal transmitted by SRS1 on the radio link or by detecting that the signal quality of a signal transmitted by SRS1 is 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 should have occurred on signals transmitted by SRS1.

[0107] For example, UE1 compares the result of the CCA procedure executed 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.

[0108] In one example, the CCA result may be represented based on the number (N) of CCA failures determined by UE1 on a radio link (e.g., a PC5 link between UE1 and SRS1) during a certain time period (T0). The number of CCA failures determined during T0 may be continuous or non-continuous in time.

[0109] In another example, the CCA result may also or alternatively be represented according to the number of successful CCAs determined by UE1 on the radio link on F1 during a certain time period (T0). The number of successful CCAs determined during T0 may be continuous or non-continuous in time.

[0110] CCA failure during an opportunity can also be expressed as unavailability of a signal (e.g., a reference signal (RS)) at UE1 during the opportunity. In one example, N corresponds to the number of RS opportunities (e.g., SSB, SMTC, CSI-RS, SLSS, SL-SSB, SL-SMTC opportunities) that were not transmitted by SRS1 on F1 during T0 due to UL CCA failure. In another example, N corresponds to the number of RS opportunities (e.g., SSB, SMTC, CSI-RS, SLSS, SL-SSB, SL-SMTC opportunities) that were unavailable at UE1 in the cell during T0. In one example, N corresponds to the number of DRX cycles, each DRX cycle having at least one RS opportunity (e.g., SSB, SMTC, CSI-RS, SLSS, SL-SSB, SL-SMTC opportunity) that was not transmitted by SRS1 on F1 during T0 due to UL CCA failure. In another example, N corresponds to the number of DRX cycles, each DRX cycle having at least one RS opportunity (e.g., SSB, SMTC, CSI-RS, SLSS, SL-SSB, SL-SMTC opportunity) that is unavailable at UE1 during T0. The term "RS opportunity unavailable at UE1" may further refer to a time when the RS opportunity (e.g., SSB, SMTC, CSI-RS, SLSS, SL-SSB, SL-SMTC opportunity) includes an RS configured by SRS1 on a carrier frequency (e.g., F1) that is subject to CCA.

[0111] The maximum allowed number of CCA failures on F1 during T0 (N max ). N max May further depend on one or more parameters. max It can be predefined or configured by the network node. Examples of parameters are DRX cycle length, eDRX cycle length, reference signal periodicity (T RS)(e.g., SSB periodicity, SMTC periodicity, CSI-RS periodicity, SLSS periodicity, SL-SMTC periodicity, etc.). For example, for a DRX cycle length (T DRX ) < 1.28 s, N max = 8, and for T DRX ≥ 1.28 s, N max = 4.

[0112] The relationship between N and Nmax. Examples of relationships are ratios, comparisons (e.g., greater than, equal to, or less than, etc.). For example, whether N > Nmax, N = Nmax, N < Nmax, etc.

[0113] The UE has determined the number of times (K) that N exceeds N max . In one example, K is determined over a certain time period (T01).

[0114] Examples of SRS adaptation when UE1 meets one or more of the criteria associated with the CCA procedure are described in the following sections.

[0115] Step 3: UE1 adapts the SRS based on the result of the CCA procedure

[0116] In this step, based on the result of the CCA procedure determined in the previous step, UE1 adapts one or more procedures related to or involving the SRS. Examples of different types of adaptations performed by UE1 for the SRS based on the result of CCA are as follows:

[0117] Continue to use SRS1,

[0118] In one example of adaptation, UE1 continues to use SRS1 as a synchronization reference source. For example, if the result of the CCA procedure reveals no CCA failures or a limited number of CCA failures, then UE1 may continue to use SRS1 as a synchronization reference source for sidelink operations on F1. In a specific example, if during a certain time period (e.g., T0) (N < Nmax), then UE1 continues to use the SRS as a synchronization source. Otherwise, UE1 may perform any of the other adaptations listed below (such as discarding SRS1, reselecting SRS, pausing SRS1, etc.). In one example, Nmax = 1, and in another example, Nmax > 1.

[0119] During the time period Tn, discard, pause, or postpone SRS1,

[0120] In another example of adaptation, UE1 discards, suspends, or postpones the use of SRS1 as a synchronization reference source during a certain time period. UE1 may further resume the use of SRS1 as a synchronization reference source after the time period, or it may discard SRS1. For example, if the result of the CCA procedure indicates a CCA failure or a large number of CCA failures (e.g., the number of CCA failures is higher than a threshold), it may discard, suspend, or postpone the use of SRS1 as a synchronization reference source during a time period Tn.

[0121] In a specific example, if (N>Nmax) occurs R1 times during a certain time period (eg, T0), UE1 discards SRS1 as a synchronization source. Otherwise, UE1 may continue to use SRS1 as a synchronization source.

[0122] In another example, UE1 discards SRS1 as a synchronization source when the following situation occurs: it has exceeded the maximum allowed CCA failures (Nmax) for more than K times. Otherwise, it may continue to use SRS1 as a synchronization source.

[0123] During the time that UE1 discards, suspends, or defers SRS1, UE1 may fall back to a reference synchronization source (RSS). The RSS may be predefined, preconfigured, or configured by a network node (e.g., a serving BS). Examples of such a fallback RSS include the UE1's internal clock, which uses GNSS timing during the time period (Tn) when SRS1 is suspended, deferred, or delayed.

[0124] During the time when UE1 discards, suspends, or postpones SRS1, UE1 may or may not perform SL operation for UE2. In one example, UE1 may still perform SL operation for UE2 until a certain time period, which may be predefined or configured by another node (e.g., UE, network node, etc.).

[0125] Pause or postpone SRS1 until one or more conditions are met, etc.

[0126] After suspending or deferring the use of SRS1 as a synchronization source for a certain period of time, UE1 may resume using SRS1 as a synchronization source when one or more conditions are met, for example, when N1 CCA evaluations have succeeded. In one specific example, the UE resumes using SRS1 as a synchronization source when it has detected at least Z1 consecutive CCA successes. In another specific example, the UE resumes using SRS1 as a synchronization source when it has detected at least Z2 consecutive CCA successes over a certain period of time. The Z2 CCAs may be consecutive or non-consecutive.

[0127] In another example, when UE1 has performed reselection to a new cell, UE1 may resume using SRS1 as a synchronization source. The new cell may operate on the same carrier frequency as the carrier frequency of the current / old serving cell, or it may operate on a new carrier frequency. In another example, when UE1 has performed reselection to a new cell, which also operates on a new carrier frequency (i.e., changes carrier frequency, e.g., from F1 to F2), UE1 may resume using SRS1 as a synchronization source. F2 may or may not be subject to CCA.

[0128] During the time when UE1 suspends or postpones SRS1, UE1 may or may not perform SL operation for UE2. In one example, UE1 may still perform SL operation for UE2 until a certain time period, which may be predefined or configured by another node (e.g., UE, network node, etc.).

[0129] Changing / reselecting the synchronization reference source to a second synchronization reference source (e.g., SRS2),

[0130] If the result of the CCA procedure indicates a CCA failure or a large number of CCA failures on F1 during time period Tn (e.g., the number of CCA failures over a certain time period is higher than a threshold), the UE may reselect (i.e., start using a new synchronization reference source) another synchronization source (e.g., SRS2).

[0131] In a specific example, if (N>Nmax) occurs K times, UE1 performs SRS reselection (from SRS1 to SRS2). Otherwise, it may continue to use SRS1 as the synchronization source. K≥1. In an example, K=1.

[0132] In another specific example, if (N>Nmax) R1 occurs during a certain time period (eg, T0), UE1 performs SRS reselection from SRS1 to SRS2. Otherwise, UE1 may continue to use SRS1 as the synchronization source. R1≥1. In one example, R1=1.

[0133] SRS2 may operate on a third carrier frequency (F3), i.e., UE1 acquires synchronization with 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 or configured by another node or preconfigured in the UE (e.g., stored on the SIM / USIM card of UE1). F3 may or may not be subject to CCA. In one example, SRS2 may have a lower or equal priority compared to that of SRS1. In one example, if the signal transmitted by SRS2 on F3 is not subject to CCA, for example, F3 belongs to a licensed band, UE1 reselects SRS2 as the new SRS. SRS2 may be a UE, for example, a fourth UE (UE4), or it may be a second network node (NN2). Figure 4 Illustrated are scenarios in which UE1 changes / reselects its SRS from SRS1 to SRS2 due to CCA failure on F1 between UE1 and SRS1: A) UE1 changes SRS1 to SRS2, SRS2 is the second network node (NN2); B) UE1 changes SRS1 to SRS2, SRS2 is the fourth UE (UE4). Figure 4 An example is shown in which UE1 changes / reselects its SRS from SRS1 to SRS2 due to an excessive number of CCA failures detected on the signal transmitted by SRS1 on F1. Figure 4 In (A), UE1 changes SRS1 to SRS2, which is the second network node (NN2). Figure 4 In (B), UE1 changes SRS1 to SRS2, which is the fourth UE (UE4). In both cases, UE1 synchronizes to SRS2 by receiving the 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.

[0134] Start / stop of sidelink synchronization signal

[0135] In another example, based on a CCA failure result determined by UE1 on F1, UE1 adapts transmission of SLSS on a fourth carrier frequency (F4). UE1's adaptation of transmission of SLSS on F4 includes one of the following operations: initiating / starting transmission of SLSS on F4; and terminating / stopping transmission of SLSS on F4. F4 is a carrier frequency used for or configured for SL operation. In one example, F4 is the same as F1, F2, or F3, or different from F1, F2, and F3.

[0136] In one example, if the result of the CCA procedure indicates a CCA failure or a high number of CCA failures on F1 during time period Tn (e.g., the number of CCA failures over a certain time period is above a threshold), UE1 initiates SLSS transmission on F4. In one example, in addition to existing conditions for initiating / terminating SLSS, by initiating transmission of SLSS (e.g., SL-SSB, SLSS, PSBCH, etc.) based on a CCA failure on F1, UE1 also begins using F4 as a synchronization reference source (SRS). An example of an existing condition is when a signal measurement (signal strength, e.g., RSRP, etc.) on a signal transmitted by SRS1 on F1 falls below a certain threshold.

[0137] In a specific example, if (N>Nmax) on F1 at T 评估,SLSS_CCA If this happens K times during the period, UE1 starts transmitting SLSS on F4. Otherwise, it may not transmit any SLSS on F4. In the latter case, UE1 will not be used as SRS for other UEs. In another example, if UE1 is transmitting SLSS and if (N≤Nmax) on F1 at T 评估,SLSS_CCA If the period occurs at least once, UE1 stops / terminates transmitting SLSS on F4. K≥1. In one example, K=1.

[0138] One or more parameters T0, R1, K, Nmax, Tn, Z1, Z2, etc. in the above example of SRS adaptation can be predefined, preconfigured, or configured by a network node (e.g., by transmitting a message to UE1 via RRC). These parameters may further depend on whether UE1 is configured with normal DRX or extended DRX, the frequency range (e.g., FR1, FR2), the power class of UE1, etc.

[0139] The type of adaptation of the SRS applied by UE1 based on the result of the CCA procedure may be predefined, preconfigured (eg, on a SIM / USIM card), or configured by another node (eg, a network node or another SL UE).

[0140] A specific example of UE1 adapting its SRS based on CCA failure

[0141] Example 1: SRS selection / reselection performed by UE1 based on CCA failure

[0142] This first example defines requirements for selection / reselection of a SL (e.g., V2X) synchronization reference source (SRS) when a carrier on which a signal is transmitted by an SRS (e.g., UE, network node, etc.) is subject to CCA.

[0143] When the GNSS synchronization reference source is configured as the highest priority and

[0144] -When the UE is synchronized directly with the GNSS,

[0145] - The UE shall not abandon any SL (e.g. V2X) SLSS and data transmission for the purpose of selection / reselection of a synchronization reference (SyncRef) UE.

[0146] -When the UE is synchronized with the SyncRef UE (SyncRef UE is synchronized directly or indirectly with the GNSS),

[0147] - The UE shall not abandon any SL (e.g. V2X) data transmission for the purpose of selection / reselection of a SyncRef UE. If a newly detectable intra-frequency SyncRef UE meets the selection / reselection criteria defined in TS 38.331 v17.3.0, the UE shall be able to 检测,SyncRef UE_V2X Identify the SyncRef UE within seconds. If S-SSB And the UE is allowed to select / reselect the SyncRef UE in T 检测,SyncRef UE_V2X When the carrier on which the SyncRef UE transmits a signal (eg, RS) is subject to CCA, T 检测,SyncRef UE_V2X It is defined as (10+L SL1 )*X1 seconds. In one example, X1=0.16. In one example, L SL1 Is due to CCA failure in SyncRef UE and T 检测,SyncRef UE_V2X The number of RS opportunities (e.g., the number of S-SSB opportunities) for the UE during which the SyncRef is unavailable to the UE.

[0148] - In other cases

[0149] -When the UE is in non-SL-DRX

[0150] - If a newly detectable co-frequency SyncRef UE meets the selection / reselection criteria defined in TS 38.331 v17.3.0, the UE shall be able to 检测,SyncRef UE_V2X Identify the SyncRef UE within seconds. If S-SSB And the UE is allowed to select / reselect the SyncRef UE in T 检测,SyncRef UE_V2X A maximum of 6% of its SL (e.g., V2X) data and SLSS transmissions are discarded during the period when the carrier on which the SyncRef UE transmits a signal (e.g., RS) is subject to CCA, T 检测,SyncRef UE_V2XDefined as (50+L SL1 )*X2 seconds. In one example, X2=0.16.

[0151] - A UE is allowed to abandon at most 2 slots of its SL (e.g. V2X) data reception per PSBCH monitoring opportunity and the total abandonment ratio should not be increased for the purpose of selection / reselection of SyncRef UEs in T 检测,SyncRef UE_V2X The period exceeds 0.3% of its SL (e.g., V2X) data reception.

[0152] -When the UE is in SL-DRX

[0153] - If a newly detectable co-frequency SyncRef UE meets the selection / reselection criteria defined in TS 38.331 [2], the UE shall be able to 检测,SyncRef UE_V2X Identify the SyncRef UE within seconds. If S-SSB A SL (e.g., V2X) UE is allowed to abandon up to 6% of its SL (e.g., V2X) data and SLSS transmissions for the purpose of selection / reselection of a SyncRef UE when the carrier on which the SyncRef UE transmits a signal (e.g., RS) is subject to CCA. 检测,SyncRef UE_V2X Defined as (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 Is due to CCA failure in SyncRef UE and T 检测,SyncRef UE_V2X The number of RS opportunities (e.g., S-SSB opportunities) during which the UE is unavailable SyncRef. SL2 is the number of SL-DRX cycles during which at least one RS opportunity (e.g., S-SSB opportunity) of the SyncRef UE is not reached within T due to CCA failure at the SyncRef UE. 检测,SyncRef UE_V2X Not available on UE during this period.

[0154] - The UE is allowed to give up to 2 time slots of its SL (e.g. V2X) data reception per PSBCH monitoring opportunity, and the UE is allowed to give up to 2 time slots of its SL (e.g. V2X) data reception per PSBCH monitoring opportunity for the purpose of selection / reselection of SyncRef UE. 检测,SyncRef UE_V2X During which at most a 24 ms aggregation window of SL (e.g., V2X) data reception is abandoned.

[0155] -UE is allowed to T 检测,SyncRef UE_V2X Extended to:

[0156] -max((X41*X42+L SL3 )*SL-DRX cycle length, X43 s), when the carrier on which the SyncRef UE transmits a signal (e.g., RS) is subject to CCA,

[0157] When in the evaluation period T 评估,SLSS The evaluation period depends on whether the NR cell is used as the synchronization reference source, whether the EUTRA cell is used as the synchronization reference source, or whether the SLSS is used as the synchronization reference source when the above conditions are met. If multiple SL-DRX cycles are configured, 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 seconds. In one example, L SL3 is the number of SL-DRX cycles during which at least one RS opportunity (e.g., S-SSB opportunity) of the SyncRef UE is not reached within T due to CCA failure at the SyncRef UE. 检测,SyncRef UE_V2X Not available on UE during this period.

[0158] -SS-RSRP is greater than syncTxThreshOoC.

[0159] When the serving cell / PCell synchronization reference source is configured as the highest priority,

[0160] -When the UE is in non-SL-DRX

[0161] - If a newly detectable co-frequency SyncRef UE meets the selection / reselection criteria defined in TS 38.331 v17.3.0, the UE shall be able to 检测,SyncRef UE_V2X Provided that SCH Es / Iot ≥ 0 dB and the SL (e.g., V2X) UE is allowed to abandon up to 6% of its SL (e.g., V2X data) and SLSS transmissions for the purpose of selection / reselection of the SyncRef UE, when the carrier on which the serving cell transmits a signal (e.g., RS) is subject to CCA, T 检测,SyncRef UE_V2X Defined as (50+L SL1 )*X5 ms. In one example, X5=160.

[0162] - A UE is allowed to abandon at most 2 slots of its SL (e.g. V2X) data reception per PSBCH monitoring opportunity and the total abandonment ratio should not be increased for the purpose of selection / reselection of SyncRef UEs in T 检测,SyncRef UE_V2X The period exceeds 0.3% of its SL (e.g., V2X) data reception.

[0163] -When the UE is in SL-DRX

[0164] - If a newly detectable co-frequency SyncRef UE meets the selection / reselection criteria defined in TS 38.331 v17.3.0, the UE shall be able to 检测,SyncRef UE_V2X If SCH Es / Iot ≥ 0dB, the UE is allowed to select / reselect the SyncRef UE within T 检测,SyncRef UE_V2X The serving cell abandons its SL (e.g., V2X data) and SLSS transmissions during an aggregation window of at most 480 ms when the carrier on which the serving cell transmits signals (e.g., RS) is subject to CCA. 检测,SyncRef UE_V2X Defined as (50+L SL2 )*X6 seconds. In one example, X6=160.

[0165] - The UE is allowed to give up to 2 time slots of its SL (e.g. V2X) data reception per PSBCH monitoring opportunity, and the UE is allowed to give up to 2 time slots of its SL (e.g. V2X) data reception per PSBCH monitoring opportunity for the purpose of selection / reselection of SyncRef UE. 检测,SyncRef UE_V2X During which at most a 24 ms aggregation window of SL (e.g., V2X) data reception is abandoned.

[0166] -UE is allowed to T 检测,SyncRef UE_V2X Extended to:

[0167] -max((X71*X72*+L SL3 )*SL-DRX cycle length, X73 s), when the carrier on which the serving cell transmits a signal (eg, RS) is subject to CCA,

[0168] When in the evaluation period T 评估,SLSS The evaluation period depends on whether the NR cell is used as the synchronization reference source, whether the EUTRA cell is used as the synchronization reference source, or whether the SLSS is used as the synchronization reference source when the above conditions are met. If multiple SL-DRX cycles are configured, 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 seconds.

[0169] -SS-RSRP is greater than syncTxThreshOoC.

[0170] Using the measurement period T in Table 1 测量,PSBCH-RSRP , the UE shall be able to perform PSBCH-RSRP measurements on the three identified co-frequency SyncRef UEs. Assumption: The SyncRef UE does not abandon or delay any SLSS transmission during the measurement period. Otherwise, the measurement period may be extended.

[0171] Table 1: PSBCH-RSRP measurement period for intra-frequency SyncRef UE

[0172]

[0173] When the UE is directly synchronizing with the GNSS, the UE shall evaluate the GNSS synchronization source reliability for a period of at least 20 seconds before selecting / reselecting a new synchronization reference source and before changing the synchronization reference from GNSS to another synchronization reference source. During the evaluation of the GNSS synchronization source reliability, the UE shall always synchronize directly with the GNSS.

[0174] In one example, the UE stops using the current synchronization reference source if any of the following conditions are met:

[0175] -L SL1 More than L SL,max1

[0176] -L SL2 More than L SL,max2

[0177] -L SL3 More than L SL,max3

[0178] -L SL4 More than L SL,max4

[0179] -L SL5 More than L SL,max5

[0180] In another example, if any of the above conditions is met, the UE further initiates a "reselection of synchronization reference source" procedure. In this procedure, the UE reselects another synchronization reference source.

[0181] In another example, if any of the above conditions is met, the UE resumes measurement (eg, PSBCH-RSRP measurement) of the SRS of the current SyncRefUE (eg, UE3).

[0182] Example 2: Adaptation of SLRS based on CCA failure when NR cell is used as synchronization reference source

[0183] This second example defines requirements for a UE (e.g., UE1) to initiate and terminate SLSS transmission when a carrier on which a signal is transmitted by an SRS (network node) is subject to CCA when an NR cell is used as a synchronization reference source (SRS).

[0184] When an NR cell is used as a synchronization reference source, the UE shall be able to measure the RSRP of the cell used as the synchronization reference source to 评估,SLSS Internal evaluation to start / stop SLSS transmission

[0185] in,

[0186] - When the UE performs SSB-based measurement without measurement gaps and the measured carrier is subject to CCA, T 评估,SLSS,CCA As specified in Table 2.

[0187] - When the UE performs SSB-based measurement with measurement gaps and the measured carrier is subject to CCA, T 评估,SLSS As specified in Table 3.

[0188] Table 2: T values measured without measurement gaps when NR cell is used as synchronization reference source (FR1) 评估,SLSS_CCA

[0189]

[0190] Table 3: T values measured with measurement gaps when NR cell is used as synchronization reference source (FR1) 评估,SLSS_CCA

[0191]

[0192] The UE terminates all SLSS transmissions if at least one of the following conditions is met:

[0193] -L SLSS,1 More than L SLSS,max,1

[0194] -L SLSS,2 More than L SLSS,max,2

[0195] -L SLSS,间隙,1 More than L SLSS,间隙,max,1

[0196] -L SLSS,间隙,2 More than L SLSS,间隙,max,2

[0197] Otherwise, based on T 评估,SLSS For evaluation within , the UE transmits SLSS.

[0198] Example 3: Adaptation of SLRS based on CCA failure when EUTRAN cell is used as synchronization reference source

[0199] This third example defines requirements for initiating and terminating SLSS transmission when a carrier on which a signal is transmitted by an SRS (eg, a network node, etc.) is subject to CCA when a EUTRAN cell is used as a Synchronization Reference Source (SRS).

[0200] When a EUTRAN cell is used as a synchronization reference source, the UE shall be able to measure the RSRP of the cell used as the synchronization reference source to 评估,SLSS,CCA Internal evaluation to start / stop SLSS transmission

[0201] in,

[0202] - When the UE is not configured with DRX, T 评估,SLSS,CCA =(10+L SLSS,3 ) x 0.04 seconds. Among them, L SLSS,3 is the number of RS opportunities (eg, discovery signal opportunities) of an E-UTRAN cell configured with 40ms periodicity that are unavailable to the UE due to CCA failure on F1 (ie, the carrier of the E-UTRAN cell).

[0203] In another example, when the UE is not configured with DRX, T 评估,SLSS,CCA =(5+L SLSS,4 ) x 0.08 seconds. Among them, L SLSS,4 is the number of RS opportunities (eg, discovery signal opportunities) of the E-UTRAN cell configured with 80ms periodicity that are unavailable to the UE due to CCA failure on F1 (ie, the carrier of the E-UTRAN cell).

[0204] - When the UE is configured with DRX and the carrier of the measured E-UTRAN cell is subject to CCA, T 评估,SLSS,CCA =As specified in Table 4.

[0205] Table 4: T when EUTRAN cell is used as synchronization reference source 评估,SLSS,CCA

[0206]

[0207] The UE terminates all SLSS transmissions if at least one of the following conditions is met:

[0208] -L SLSS,3 More than L SLSS,max,3

[0209] -L SLSS,4 More than L SLSS,max,4

[0210] -L SLSS,5 More than L SLSS,max,5

[0211] -L SLSS,6 More than L SLSS,max,6

[0212] Otherwise, based on T 评估,SLSS For evaluation within , the UE transmits SLSS.

[0213] Example 4: Adaptation of SLRS based on CCA failure when SyncRef UE is used as synchronization reference source

[0214] This fourth example defines requirements for initiating and terminating SLSS transmission when the carrier on which the SRS (eg, UE, etc.) transmits signals is subject to CCA when UE1 should start transmitting SLSS.

[0215] The UE shall be able to measure the PSBCH-RSRP of the selected SyncRef UE used as synchronization reference source and the T in Table 5 when the measured carrier is subject to CCA 评估,SLSS It is evaluated within to start / terminate SLSS transfer.

[0216] Table 5: T when SyncRef UE is used as synchronization reference source 评估,SLSS,CCA

[0217]

[0218] In one example, the UE (eg, UE1) terminates all SLSS transmissions if at least one of the following conditions is met:

[0219] -L SLSS,7 More than L SLSS,max,7

[0220] -L SLSS,8 More than L SLSS,max,8

[0221] Otherwise, based on T 评估,SLSS For evaluation within, the UE (eg, UE1) transmits a SLSS.

[0222] In another example, during a certain time period T1, the UE (eg, UE1) suspends transmission of SLSS. In one example, T1 = N x SL-DRX cycles, where N = 2, 3, 4, etc. The UE may resume SLSS after T, or it may stop SLSS after T.

[0223] In another example, if any of the above conditions is satisfied, the UE resumes the measurement of the SRS (eg, the evaluation of the SLSS) of the current SyncRefUE (eg, UE3).

[0224] Embodiment 2: Method in UE3 for operating as a synchronization reference UE. The embodiments described herein can be implemented in any combination. The UE embodiment includes at least the following: Step 1: UE3 obtains information related to the need to transmit a sidelink reference signal. Step 2: UE 3 determines information related to the result of the CCA procedure associated with the SRS. Step 3: Based on whether the associated conditions are met, the UE 3 adapts the transmission of the SL RS (eg, SLSS).

[0225] Step 1: UE3 obtains information related to the need to transmit a sidelink reference signal. In this step, UE3 obtains information whether it 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). In one example, if UE3 is configured by another node (e.g., by another UE (e.g., UE1) or by a network node) to transmit SLRS, UE3 determines the need to transmit SLRS. In another example, based on a predefined rule, for example, UE3 needs to transmit SLRS periodically, UE3 determines the need to transmit SLRS. In another example, based on pre-configured information in the UE (e.g., stored on the SIM / USIM card of UE1), UE3 determines the need to transmit SLRS. A sidelink UE that serves as an SRS for other sidelink UEs typically needs to transmit a sidelink reference signal (SLRS) according to a certain transmission periodicity. An example of an SLRS is an SL synchronization signal (SLSS).

[0226] Step 2: UE3 determines information related to the result of the CCA procedure associated with the SRS. In this step, based on one or more rules or parameters related to CCA failure associated with the sidelink reference signal transmitted by UE3 on F1, UE3 determines information related to the result of the CCA procedure.

[0227] The steps of determining information related to the results of the CCA procedure are similar to the steps described in step 2 in the first embodiment discussed above.

[0228] Step 3: Based on the results of the CCA procedure, UE3 adapts the transmission of SL reference signals. In this step, based on the results of the CCA procedure determined in the previous step, UE3 (which is being used as an SRS for other SL UEs) adapts one or more procedures related to or involving the transmission of sidelink reference signals. Examples of different types of adaptation include the following:

[0229] Continue SLRS transmission

[0230] In one example of adaptation, UE3 continues to transmit SLRS (e.g., SLSS) on F1. For example, if the result of the CCA procedure shows that there is no CCA failure on F1 or there is a limited number of CCA failures on F1, then UE3 can continue to transmit SLRS (e.g., SLSS) on F1 according to the reference configuration. The reference configuration is the configuration that UE3 follows for SLRS transmission when it has not experienced any CCA failures on F1 or the number of CCA failures on F1 is below a certain threshold or when operating on a carrier without CCA. 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 UE3, etc.), UE3 obtains the reference configuration for SLRS transmission.

[0231] In a specific example, if during a certain period (e.g., T0’), (N’ < Nmax’), then UE3 continues to transmit SLSS (e.g., every 160 ms) to other SL UEs (e.g., UE1) that are using UE3 as a synchronization reference source. Otherwise, UE3 does not continue the transmission of SLRS. For example, UE3 stops / terminates the transmission of SLSS on F1. In another example, in the latter case, UE3 can perform any of the adaptations listed below (such as stopping / terminating SLRS for a certain period, pausing or postponing SLRS, etc.).

[0232] Stop / terminate the transmission of SLRS during a certain period

[0233] In another example of adaptation, UE3 stops / terminates the transmission of SLRS (e.g., SLSS) on F1 during a certain period. Stopping / terminating the transmission of SLRS means not transmitting SLRS. For example, if the result of the CCA procedure shows CCA failure or a large number of CCA failures (e.g., the number of CCA failures is higher than the threshold), then UE3 can stop / terminate the transmission of SLRS (e.g., SLSS) during the period Tn’. There are two reasons for stopping / terminating the transmission. First, if UE3 has detected that the channel has been very busy in the past Nx periods, where Nx can be expressed in time units (e.g., subframes, DRX cycles, time slots, etc.), then attempting SLRS transmission will cause unnecessary complexity and waste of resources in UE3. Second, any such transmission may also cause interference to other nearby devices. Therefore, UE3 preferably terminates all SLRS transmissions during a certain period.

[0234] In a specific example, if (N'>Nmax') occurs K' times, UE3 stops / terminates transmission of SLRS (eg, SLSS). Otherwise, it may continue to transmit SLRS (eg, SLSS) according to the reference configuration. K'≥1. In an example, K'=1.

[0235] In another specific example, if (N'>Nmax') R1' occurs a number of times during a certain time period (e.g., T0'), UE3 stops / terminates transmitting SLRS (e.g., SLSS) to UE1, which is 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.

[0236] Pause or postpone the transmission of SLRS during a certain period of time

[0237] In another example of adaptation, UE3 suspends or postpones the transmission of SLRS (e.g., SLSS) on F1 during a certain time period. For example, if the result of the CCA procedure indicates a CCA failure or a large number of CCA failures (e.g., the number of CCA failures is higher than a threshold), UE3 suspends or postpones the transmission of SLRS during time period Tn'. The basic principle of suspending or postponing SLRS transmission is to avoid any 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 for which transmission is suspended or postponed by UE3 may further depend on the type of channel access scheme applied.

[0238] In a specific example, if (N'>Nmax') occurs K' times, UE3 suspends or postpones the transmission of SLRS (eg, SLSS). Otherwise, it may continue to transmit SLRS (eg, SLSS) according to the reference configuration. K'≥1. In one example, K'=1.

[0239] In another specific example, if (N'>Nmax') R1' occurs a number of times during a certain time period (e.g., T0'), UE3 suspends or postpones transmitting SLRS (e.g., SLSS) to UE1, which is 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.

[0240] SLRS Adaptation

[0241] If the result of the CCA procedure indicates a CCA failure or a large number of CCA failures (e.g., the number of CCA failures is above a threshold), the UE3 adapts one or more transmission parameters of the SLRS. Examples of SLRS transmission parameters are the periodicity of SLRS transmission, the duration of the opportunity at which the SLRS is transmitted (e.g., X1 ms, X2 symbols, X3 time slots, etc.), the bandwidth at which the SLRS is transmitted, etc. In one example, the adaptation includes the UE3 transmitting the SLRS less frequently than a reference periodicity (e.g., when no CCA failures are experienced). In another example, the adaptation includes the UE3 transmitting the SLRS more frequently than the reference periodicity. In another example, the adaptation includes the UE3 transmitting the SLRS at a BW that is less than a reference bandwidth (BW). In another example, the adaptation includes the UE3 transmitting the SLRS at a bandwidth greater than the reference BW. The reference SLRS periodicity and / or the reference BW can be predefined, configured by another node, or preconfigured in the UE3.

[0242] One or more parameters T0', R1', K', Nmax', Tn', Z1' in the above examples of adaptation can be predefined, preconfigured, or configured by the network node (e.g., by transmitting a message to UE3 via RRC). These parameters may further depend on whether UE3 is configured with normal DRX or extended DRX, the frequency range (e.g., FR1, FR2), the power class of UE3, etc.

[0243] The type of adaptation of the SLRS applied by the UE 3 based on the result of the CCA procedure may be predefined, preconfigured (eg, on a SIM / USIM card), or configured by another node (eg, a network node or another SL UE).

[0244] The sidelink UE (eg, UE3) needs to be 评估,SLSS ) is evaluated whether to start / terminate SLRS (e.g., SLSS). In one example, if a UE (e.g., UE3) synchronized with any other synchronization reference source (such as NR cell, E-UTRAN cell, GNSS, or other side link synchronization reference UE) completes the evaluation period (T 评估,SLSS ) before a certain number of CCA failures (e.g., N) have been detected during the time period Tn', the UE starts transmission of the SLRS. In another example, if the UE (e.g., UE3) has detected a certain number of CCA failures (e.g., N'>Nmax') during the ongoing evaluation period, the UE restarts the evaluation. In yet another example, when the evaluation has been restarted a certain number of times, the SL UE (e.g., UE3) suspends any SLRS transmission for a certain period of time.

[0245] Specific example of UE3 adapting SLRS based on CCA failure

[0246] Example: SyncRef UE is used as a synchronization reference source

[0247] This example defines a requirement to terminate SLSS transmission when a carrier on which signals are transmitted by the SRS (eg, UE3, etc.) is subject to CCA when a SyncRef UE (UE3) is used as a synchronization reference source (SRS) for UE1.

[0248] The UE (e.g., UE1) shall be able to measure the PSBCH-RSRP of the selected SyncRef UE (e.g., UE3) used as the synchronization reference source and the T in Table 6 when the measured carrier (e.g., F1) is subject to CCA. 评估,SLSS It is evaluated within to start / terminate SLSS transfer.

[0249] Table 6: T when SyncRef UE is used as synchronization reference source 评估,SLSS,CCA

[0250]

[0251] In one example, the SyncRef UE (eg, UE3) terminates all SLSS transmissions if at least one of the following conditions is met:

[0252] -L SLSS,9 More than L SLSS,max,9

[0253] -L SLSS,10 More than L SLSS,max,10

[0254] Otherwise, based on T 评估,SLSS For evaluation within, the UE (eg, UE1) transmits a SLSS.

[0255] In another example, during a certain time period T1, the UE (eg, UE1) suspends transmission of SLSS. In one example, T1 = N x SL-DRX cycles, where N = 2, 3, 4, etc. The UE may resume SLSS after T, or it may stop SLSS after T.

[0256] Table: T 检测,NR_Intra_CCA 、T 测量,NR_Intra_CCA and T 评估,NR_Intra_CCA

[0257]

[0258] In some embodiments, in more than M m,max 、M d,max or M e,max, the UE shall restart the measurement.

[0259] Current RRM specifications (see, for example, TS 38.133, section 12.4) include requirements for the selection and reselection of synchronization reference sources. More specifically, they include requirements for detecting a new synchronization reference source (SyncRefUE) when the UE synchronizes with a GNSS, SyncRefUE, or serving cell / PCell. Examples of such requirements are the time to detect a newly detectable SyncRefUE, the measurement period for measurements of identified SyncRefUEs, the interruption time, and the abandonment ratio. These requirements further depend on the activity state of the UE, i.e., whether the UE is in DRX mode or non-DRX mode.

[0260] In Rel-18 scenarios, SL carriers are capable of undergoing CCA, and WAN / Uu carriers are not subject to CCA. Therefore, the selection / reselection of SyncRefUE on the SL carrier subject to CCA will be affected due to CCA failures on the SL carrier. When operating on a carrier subject to CCA and experiencing many CCA failures, the UE will not be able to meet the existing requirements for selection / reselection of SyncRefUE. For example, under a large number of CCA failures, the UE's selection or reselection of 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. Therefore, the principles for defining the requirements for selection / reselection of the synchronization reference source (SyncRefUE) when operating on an unlicensed carrier subject to CCA failures can be based on the Rel-16 NR-U requirements.

[0261] Observation 1: An excessive number of CCA failures on a SL carrier subject to CCA may lead to unreliable or incorrect selection / reselection of the synchronization reference source (SyncRefUE) on that SL carrier.

[0262] Observation 2: Rel-16 NR-U requirements and UE measurement behavior take into account the number of CCA failures on carriers subject to CCA.

[0263] Proposal 1: Requirements for the selection and reselection of a synchronization reference source (SyncRefUE) on a SL carrier subject to CCA should consider the impact of CCA failures occurring on the SL carrier during the selection and reselection of the SyncRefUE.

[0264] Figure 5is a schematic block diagram of a radio access node 500 according to some embodiments of the present disclosure. Optional features are represented by dashed boxes. Radio access node 500 may be, for example, base station 202 or 206, or a network node that implements all or part of the functionality of base station 202 or gNB described herein. As shown in the figure, radio access node 500 includes a control system 502, which 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), and / or the like), a memory 506, and a network interface 508. The one or more processors 504 are also referred to herein as processing circuitry. Furthermore, radio access node 500 may include one or more radio units 510, each of which includes one or more transmitters 512 and one or more receivers 514 coupled to one or more antennas 516. Radio unit 510 may be referred to as, or may be part of, radio interface circuitry. In some embodiments, radio unit(s) 510 are located external to control system 502 and connected to control system 502 via, for example, a wired connection (e.g., a fiber optic cable). However, in some other embodiments, the radio unit(s) 510 and possibly 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 radio access node 500 as described herein. In some embodiments, the function(s) are implemented in software that is stored, for example, in the memory 506 and executed by the one or more processors 504.

[0265] Figure 6 is a schematic block diagram illustrating a virtualized embodiment of a radio access node 500 according to some embodiments of the present disclosure. This discussion is equally applicable to other types of network nodes. In addition, other types of network nodes may have similar virtualized architectures. Again, optional features are represented by dashed boxes.

[0266] 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 one or more virtual components (e.g., via one or more virtual machines executing on one or more physical processing nodes in one or more networks). As shown in the figure, 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, which are 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 (e.g., CPUs, ASICs, FPGAs, and / or the like), memory 606, and a network interface 608.

[0267] In this example, the functionality 610 of the radio access node 500 described herein is implemented in any desired manner on one or more processing nodes 600, or distributed across one or more processing nodes 600 and the control system 502 and / or the radio unit(s) 510. In some specific embodiments, some or all of the functionality 610 of the radio access node 500 described herein is implemented as a virtual component executed by one or more virtual machines implemented in a virtual environment(s) hosted by the processing node(s) 600. As will be appreciated by one of ordinary skill 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 functionality 610. Notably, in some embodiments, the control system 502 may not be included, in which case the radio unit(s) 510 communicates directly with the processing node(s) 600 via an appropriate network interface(s).

[0268] In some embodiments, a computer program is provided, comprising instructions that, when executed by at least one processor, cause the at least one processor to perform the functionality of a radio access node 500 according to any of the embodiments described herein, 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 some embodiments, a carrier comprising the aforementioned computer program product is provided. 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).

[0269] Figure 7 is a schematic block diagram of a radio access node 500 according to 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 discussion applies equally to Figure 6 6. The processing nodes 600 of FIG. 5 are shown in FIG. 5, wherein the module 700 may be implemented on one of the processing nodes 600 or may be distributed across multiple processing nodes 600 and / or may be distributed across (one or more) processing nodes 600 and the control system 502.

[0270] Figure 8 is a schematic block diagram of a wireless communication device 800 according to some embodiments of the present disclosure. As shown in the figure, the wireless communication device 800 includes one or more processors 802 (e.g., CPU, ASIC, FPGA and / or the like), memory 804 and one or more transceivers 806, each transceiver 806 including one or more transmitters 808 and one or more receivers 810 coupled to one or more antennas 812. The (one or more) transceivers 806 include a radio front-end circuit system connected to the (one or more) antennas 812, and the radio front-end circuit system is configured to condition signals transmitted between the (one or more) antennas 812 and the (one or more) processors 802, as will be understood by one of ordinary skill in the art. The processor 802 is also referred to herein as the processing circuit system. The transceiver 806 is also referred to herein as the radio circuit system. In some embodiments, the functionality of the wireless communication device 800 described above may be implemented in whole or in part in software, which is stored, for example, in the memory 804 and executed by the (one or more) processors 802. Note that the wireless communication device 800 may include Figure 8Additional components not shown in the figure, such as, for example, one or more user interface components (e.g., input / output interfaces, including displays, buttons, touch screens, microphones, (one or more) speakers and / or the like and / or any other components for allowing information to be input into the wireless communication device 800 and / or allowing information to be output from the wireless communication device 800), a power source (e.g., a battery and associated power circuitry), etc.

[0271] In some embodiments, a computer program is provided, comprising instructions that, when executed by at least one processor, cause the at least one processor to perform the functionality of the wireless communication device 800 according to any of the embodiments described herein. In some embodiments, a carrier comprising the aforementioned computer program product is provided. 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).

[0272] Figure 9 8 is a schematic block diagram of a wireless communication device 800 according to 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.

[0273] Reference Figure 10 According to an embodiment, a communication system includes a telecommunications network 1000, such as a 3GPP-type cellular network, comprising an access network 1002 (e.g., a RAN) and a core network 1004. Access network 1002 includes a plurality of 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 is connectable to core network 1004 via a wired or wireless connection 1010. A first UE 1012 located in coverage area 1008C is configured to wirelessly connect to or be paged by the corresponding base station 1006C. A second UE 1014 in coverage area 1008A is also wirelessly connectable to the corresponding base station 1006A. Although multiple UEs 1012 , 1014 are illustrated in this example, the disclosed embodiments are equally applicable to scenarios where a single UE is located in the coverage area or where a single UE is connecting to the corresponding base station 1006 .

[0274] Telecommunications network 1000 itself is connected to a host computer 1016, which may be embodied in the hardware and / or software of a standalone server, a cloud-enabled server, a distributed server, or as processing resources in a server farm. Host computer 1016 may be owned or controlled by a service provider, or may be operated by or on behalf of a service provider. Connections 1018 and 1020 between telecommunications network 1000 and host computer 1016 may extend directly from core network 1004 to host computer 1016, or may extend via an optional intermediary network 1022. Intermediary network 1022 may be one of a public, private, or managed network, or a combination of more than one of these networks; if any intermediary network 1022 is present, it may be a backbone network or the Internet; in particular, intermediary network 1022 may include two or more subnetworks (not shown).

[0275] Figure 10 The communication system as a whole enables connectivity between connected UEs 1012, 1014 and a host computer 1016. This connectivity can be described as an over-the-top (OTT) connection 1024. The host computer 1016 and the connected UEs 1012, 1014 are configured to transmit data and / or signaling via the OTT connection 1024, using the access network 1002, the core network 1004, any intermediate networks 1022, and possibly additional infrastructure (not shown) as intermediaries. The OTT connection 1024 can be transparent in the sense that the participating communication devices through which the OTT connection 1024 passes are unaware of the routing of uplink and downlink communications. For example, the base station 1006 may not be informed or need not be informed of the past routing of incoming downlink communications having data originating from the host computer 1016 to be forwarded (e.g., handed over) to the connected UE 1012. Similarly, base station 1006 need not be aware of the future routing of outgoing uplink communications originating from UE 1012 toward host computer 1016 .

[0276] Now refer to Figure 11Describe the exemplary implementation of the UE, base station and host computer discussed in the previous paragraphs according to the embodiment. In the communication system 1100, the host computer 1102 includes hardware 1104, and the hardware 1104 includes a communication interface 1106, which is configured to establish and maintain a wired or wireless connection with the interface of different communication devices of the communication system 1100. The host computer 1102 also includes a processing circuit system 1108, which may have storage and / or processing capabilities. In particular, the processing circuit system 1108 may include one or more programmable processors, ASICs, FPGAs, or a combination of these (not shown) suitable for executing instructions. The host computer 1102 also includes software 1110, which is stored in the host computer 1102 or can be accessed by the host computer 1102 and can be executed by the processing circuit system 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 connected via an OTT connection 1116 terminating between the UE 1114 and the host computer 1102. In providing services to the remote user, the host application 1112 may provide user data transmitted using the OTT connection 1116.

[0277] The communication system 1100 also includes a base station 1118, which is provided in the telecommunications system and includes hardware 1120 that enables the base station 1118 to communicate with the host computer 1102 and with the UE 1114. The hardware 1120 may include: a communication interface 1122 for establishing and maintaining wired or wireless connections for interfacing with different communication devices of the communication system 1100; and a radio interface 1124 for establishing and maintaining connections with at least the wireless devices located in the coverage area ( Figure 11 The communication interface 1122 may be configured to facilitate a connection 1128 to the host computer 1102. The connection 1128 may be a direct connection, or it may pass through the core network ( Figure 11 The base station 1118 may also include a processor 1130, which may include one or more programmable processors, ASICs, FPGAs, or a combination thereof (not shown) adapted to execute instructions. The base station 1118 may also include software 1132, which may be stored internally or accessible via an external connection.

[0278] The communication system 1100 also includes the previously mentioned UE 1114. The hardware 1134 of the UE 1114 may include a radio interface 1136 configured to establish and maintain a wireless connection 1126 with a base station serving the coverage area in which the UE 1114 is currently located. The hardware 1134 of the UE 1114 also includes a processing circuit system 1138, which may include one or more programmable processors, ASICs, FPGAs, or a combination thereof (not shown) adapted to execute instructions. The UE 1114 also includes software 1140, which is stored in or accessible to the UE 1114 and executable by the processing circuit system 1138. The software 1140 includes a client application 1142. The client application 1142 may be operable to provide services to a human or non-human user via the UE 1114 under the support of the host computer 1102. In the host computer 1102, a host application 1112 executing therein can communicate with a client application 1142 executing therein via an OTT connection 1116 terminated between the UE 1114 and the host computer 1102. When providing a service to a user, the client application 1142 can receive request data from the host application 1112 and provide user data in response to the request data. The OTT connection 1116 can transmit both the request data and the user data. The client application 1142 can interact with the user to generate the user data it provides.

[0279] Notice, Figure 11 The host computer 1102, base station 1118 and UE 1114 shown in FIG can be respectively Figure 10 The host computer 1016, one of the base stations 1006A, 1006B, 1006C and one of the UEs 1012, 1014 are similar or identical. That is, the internal workings of these entities may be similar to Figure 11 As shown in , and independently, the surrounding network topology can be Figure 10 network topology.

[0280] exist Figure 11 In FIG, OTT connection 1116 has been abstractly drawn to illustrate communication between host computer 1102 and UE 1114 via base station 1118, without explicitly mentioning any intermediary devices and the precise routing of messages through these devices. The network infrastructure can determine the routing, which can be configured to be hidden from UE 1114, from the service provider operating host computer 1102, or from both. While OTT connection 1116 is active, the network infrastructure can further make decisions that dynamically change the routing (e.g., based on load balancing considerations or reconfiguration of the network).

[0281] The wireless connection 1126 between the UE 1114 and the base station 1118 is consistent with the teachings of the embodiments described throughout this disclosure. One or more of the various embodiments improve the performance of OTT services provided to the UE 1114 using the OTT connection 1116, in which the wireless connection 1126 forms the last segment. More specifically, the teachings of these embodiments can improve, for example, data rates, latency, power consumption, etc., thereby providing benefits such as reduced user latency, relaxed file size constraints, better responsiveness, and extended battery life.

[0282] For the purpose of monitoring the data rate, latency, and other factors improved by one or more embodiments, measurement procedures may be provided. Optional network functionality may also be present for reconfiguring the OTT connection 1116 between the host computer 1102 and the UE 1114 in response to changes in measurement results. The measurement procedures and / or 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 in both. In some embodiments, a sensor (not shown) may be deployed in or associated with the communication device through which the OTT connection 1116 passes; the sensor may participate in the measurement procedure by supplying the values of the monitored quantities exemplified above or by supplying the values of other physical quantities, based on which the software 1110, 1140 may calculate or estimate the monitored quantities. Reconfiguration of the OTT connection 1116 may include message formats, retransmission settings, preferred routes, etc.; the reconfiguration need not affect the base station 1118 and it may be unknown or imperceptible to the base station 1118. Such procedures and functionality may be known and implemented in the art. In certain embodiments, the measurements may involve proprietary UE signaling that facilitates the host computer 1102 to measure throughput, propagation time, latency, and the like. The measurements may be implemented because the software 1110 and 1140 causes messages (particularly, empty messages or "dummy" messages) to be transmitted using the OTT connection 1116 while it monitors propagation time, errors, etc.

[0283] Figure 12 The communication system includes a host computer, a base station and a UE, and the host computer, the base station and the UE may be referenced. Figure 10 and 11 For the sake of simplicity of this disclosure, only the host computer, base station and UE are described. Figure 12References to the accompanying figures will be included in this section. In step 1200, the host computer provides user data. In sub-step 1202 of step 1200 (sub-step 1202 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 (step 1206 may be optional), in accordance with the teachings of the embodiments described throughout this disclosure, the base station transmits the user data carried in the host computer-initiated transmission to the UE. In step 1208 (step 1208 may also be optional), the UE executes a client application associated with the host application executed by the host computer.

[0284] Figure 13 The communication system includes a host computer, a base station and a UE, and the host computer, the base station and the UE may be referenced. Figure 10 and 11 For the sake of simplicity of this disclosure, only the host computer, base station and UE are described. Figure 13 References to the accompanying figures will be included in this section. In step 1300 of the method, a 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. According to the teachings of the embodiments described throughout this disclosure, the transmission may pass through a base station. In step 1304 (which may be optional), the UE receives the user data carried in the transmission.

[0285] Figure 14 The communication system includes a host computer, a base station and a UE, and the host computer, the base station and the UE may be referenced. Figure 10 and 11 For the sake of simplicity of this disclosure, only the host computer, base station and UE are described. Figure 14References to the accompanying drawings will be included in this section. In step 1400 (step 1400 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 of step 1400 (sub-step 1404 may be optional), the UE provides the user data by executing a client application. In sub-step 1406 of step 1402 (sub-step 1406 may be optional), the UE executes the client application, which provides the user data in response to the input data received from the host computer. When providing the user data, the executed client application may further consider user input received from the user. Regardless of the specific manner in which the user data is provided, the UE initiates the transmission of the user data to the host computer in sub-step 1408 (sub-step 1408 may be optional). In step 1410 of the method, the host computer receives the user data transmitted from the UE in accordance with the teachings of the embodiments described throughout this disclosure.

[0286] Figure 15 The communication system includes a host computer, a base station and a UE, and the host computer, the base station and the UE may be referenced. Figure 10 and 11 For the sake of simplicity of this disclosure, only the host computer, base station and UE are described. Figure 15 References to the accompanying figures will be included in this section. In step 1500 (which may be optional), in accordance with the teachings of the embodiments described throughout this disclosure, the base station receives user data from the UE. In step 1502 (which may be optional), the base station initiates a 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 the transmission initiated by the base station.

[0287] Any suitable steps, methods, features, functions or benefits disclosed herein may be performed by one or more functional units or modules of one or more virtual devices. Each virtual device may include multiple functional units in these functional units. These functional units may be implemented via processing circuit systems and other digital hardware, and the processing circuit systems may include one or more microprocessors or microcontrollers, and the other digital hardware may include digital signal processors (DSPs), dedicated digital logic and the like. The processing circuit system may be configured to execute program code stored in a memory, and the memory may include one or more types of memory, such as read-only memory (ROM), random access memory (RAM), cache memory, flash memory device, optical storage device, etc. The program code stored in the memory includes program instructions for executing one or more telecommunications and / or data communication protocols and instructions for executing one or more of the technologies described herein. In some implementations, the processing circuit system may be used to cause the corresponding functional units to perform the corresponding functions according to one or more embodiments of the present disclosure.

[0288] Although the processes in the accompanying figures may illustrate a particular order of operations performed by certain 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 certain operations, overlap certain operations, etc.).

[0289] Example

[0290] Group A Examples

[0291] Embodiment 1: A method for selecting and / or maintaining a synchronization source, performed by a user equipment UE, the method comprising one or more of the following: obtaining information about configured synchronization sources and / or available synchronization sources; determining whether adaptation of a synchronization reference source SRS is required based on at least a CCA procedure; and performing adaptation of the SRS that meets the criteria.

[0292] Embodiment 2: The method as described in the previous embodiment, wherein obtaining the information comprises obtaining the information about the SRS based on a message received from a network node (eg, configuration via signaling (such as via RRC, DCI, or MAC-CE)).

[0293] Embodiment 3: The method as in any of the preceding embodiments, wherein a set of SRSs may be predefined, and the UE selects one SR, ie, the first SRS (SRS1), from the set of predefined SRSs based on an identifier received from the network node.

[0294] Embodiment 4: A method as described in any of the preceding embodiments, wherein if the UE is configured with a first identifier that adopts a gNB / eNB-based synchronization configuration, the UE selects or uses the gNB / eNB as a synchronization reference source.

[0295] Embodiment 5: The method as in any of the preceding embodiments, wherein if the UE is configured with the second identifier, the UE uses GNSS as a synchronization reference source.

[0296] Embodiment 6: The method as in any of the preceding embodiments, wherein a set of SRSs is predefined, and the UE selects one SRS from the set of SRSs based on one or more rules.

[0297] Embodiment 7: The method as in any of the preceding embodiments, wherein the rule is associated with an operation scenario of the UE (eg, in coverage, out of coverage, or partial coverage).

[0298] Embodiment 8: A method as described in any of the preceding embodiments, wherein determining whether SRS adaptation is required based on at least a 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 a first SRS (SRS1).

[0299] Embodiment 9: The method as in any of the preceding embodiments, wherein the rules are: predefined, preconfigured (eg, on a SIM / USIM card) and / or configured by a node (eg, by another UE, a network node).

[0300] Embodiment 10: The method as in any of the preceding embodiments, wherein performing adaptation of the SRS that meets the criteria comprises adapting one or more procedures related to or involving the SRS based on the determined results of the CCA procedure.

[0301] Embodiment 11: A method as described in any of the preceding embodiments, wherein the adaptation performed by the UE on the SRS based on the result of the CCA includes one or more of the following: 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 during a certain period of time; c. after suspending or postponing the use of SRS1 as a synchronization source during a certain period of time, when one or more conditions are met (for example, when N1 CCA evaluations have succeeded), the UE may resume using SRS1 as a synchronization source; d. when U E. When reselection of a new cell is performed, restart using SRS1 as the synchronization source; e. Reselect (i.e., start using a new synchronization reference source) another synchronization source (e.g., SRS2); f. Adapt the transmission of SLSS on the fourth carrier frequency (F4) based on the result of the CCA failure determined by the UE on F1; and g. If the result of the CCA procedure indicates a CCA failure or a large number of CCA failures on F1 during the time period Tn (e.g., the number of CCA failures over a certain time period is higher than a threshold), UE1 starts the transmission of SLSS on F4.

[0302] Embodiment 12: A method performed by a user equipment UE for operating as a synchronization reference UE, the method comprising one or more of the following: obtaining information related to the need for transmitting a sidelink reference signal; determining information related to a result of a CCA procedure associated with an SRS; and performing adaptive transmission of an SL RS (e.g., SLSS) based on whether an associated condition is met.

[0303] Embodiment 13: A method as described in any of the previous embodiments, wherein obtaining information includes one or more of the following: a. obtaining information on whether it 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 by another node (e.g., by another UE (e.g., UE1) or by a network node) to transmit SLRS; c. determining the need to transmit SLRS if the UE is configured by another node (e.g., by another UE (e.g., UE1) or by a network node) to transmit SLRS; d. determining the need to transmit SLRS based on a predefined rule (e.g., UE3 needs to transmit SLRS periodically); and e. determining the need to transmit SLRS based on pre-configuration information in the UE (e.g., stored on the SIM / USIM card of UE1).

[0304] Embodiment 14: A method as described in any of the preceding embodiments, wherein determining information related to the result of the CCA procedure includes determining 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 sidelink reference signal transmitted by the UE on F1.

[0305] Embodiment 15: The method of any of the preceding embodiments, wherein performing adapted transmission of the SL RS comprises adapting one or more procedures related to or involving transmission of a sidelink reference signal based on a result of a determined CCA procedure.

[0306] Embodiment 16: A method as described in any of the preceding embodiments, wherein adapting one or more procedures includes one or more of the following: a. continuing to transmit SLRS (e.g., SLSS) on F1; b. if the result of the CCA procedure shows that there is no CCA failure on F1 or there are a limited number of CCA failures on F1, the UE may continue to transmit SLRS (e.g., SLSS) on F1 according to the reference configuration; c. stopping / terminating the transmission of SLRS (e.g., SLSS) on F1 during a certain time period; d. if the result of the CCA procedure shows a CCA failure or a large number of CCA failures (e.g., the number of CCA failures is higher than a threshold), the UE may stop / terminating the transmission of SLRS (e.g., SLSS) during the time period Tn'; e. if (N'>Nmax') K' occurs times, the UE stops / terminates the transmission of SLRS (e.g., SLSS); f. if (N'>Nmax') R1' times occur during a certain time period (e.g., T0'), the UE stops / terminates the transmission of SLRS (e.g., SLSS) to UE1 that is using the UE as a synchronization reference source; g. during a certain time period, suspend or postpone the transmission of SLRS (e.g., SLSS) on F1; h. if the result of the CCA procedure indicates CCA failure or a large number of CCA failures (e.g., the number of CCA failures is higher than a threshold), the UE suspends or postpones the transmission of SLRS during the time period Tn'; and i. if the result of the CCA procedure indicates CCA failure or a large number of CCA failures (e.g., the number of CCA failures is higher than a threshold), the UE adapts one or more transmission parameters of SLRS.

[0307] Embodiment 17: The method as in any of the preceding embodiments, further comprising: providing user data; and forwarding the user data to a host computer via a transmission to a base station.

[0308] Group B Examples

[0309] Embodiment 18: A method performed by a base station, the method comprising one or more of the features disclosed herein.

[0310] Embodiment 19: The method of the preceding embodiment, including any of the features from Group A embodiments.

[0311] Embodiment 20: The method as in any of the preceding embodiments, further comprising: obtaining user data; and forwarding the user data to a host computer or a wireless device.

[0312] Group C Examples

[0313] Embodiment 21: A wireless device for selecting and / or maintaining a synchronization source, the wireless device comprising: a processing circuit system configured to perform any of the steps described in any of the embodiments in Group A; and a power circuit system configured to supply power to the wireless device.

[0314] Embodiment 22: A base station comprising: a processing circuit system configured to perform any of the steps described in any of the embodiments in Group B; and a power circuit system configured to supply power to the base station.

[0315] Embodiment 23: A user equipment UE for selecting and / or maintaining a synchronization source, the UE comprising: an antenna configured to send and receive wireless signals; a radio front-end circuit system connected to the antenna and to a processing circuit system, and configured to adjust the signal transmitted between the antenna and the processing circuit system; the processing circuit system is configured to perform any of the steps described in any of the embodiments in Group A; an input interface connected to the processing circuit system, and configured to allow information to be input into the UE for processing by the processing circuit system; an output interface connected to the processing circuit system, and configured to output information that has been processed by the processing circuit system from the UE; and a battery connected to the processing circuit system, and configured to supply power to the UE.

[0316] Embodiment 24: A communication system comprising a host computer, the host computer comprising: a processing circuit system configured to provide user data; and a communication interface configured to forward the user data to a cellular network for transmission to a user equipment UE; wherein the cellular network comprises a base station having a radio interface and a processing circuit system, the processing circuit system of the base station being configured to perform any of the steps described in any of the embodiments in Group B.

[0317] Embodiment 25: The communication system as described in the previous embodiment further includes the base station.

[0318] Embodiment 26: The communication system as described in the previous two embodiments further includes the UE, wherein the UE is configured to communicate with the base station.

[0319] Embodiment 27: A communication system as described in the previous three embodiments, wherein: the processing circuit system of the host computer is configured to execute a host application, thereby providing the user data; and the UE includes a processing circuit system, which is configured to execute a client application associated with the host application.

[0320] Embodiment 28: A method implemented in a communication system comprising a host computer, a base station and a user equipment UE, the method comprising: providing user data in the host computer; and initiating, in the host computer, a transmission carrying the user data to the UE via a cellular network, the cellular network comprising the base station, wherein the base station performs any of the steps described in any of the embodiments in Group B.

[0321] Embodiment 29: The method described in the previous embodiment further includes: transmitting the user data at the base station.

[0322] Embodiment 30: The method according to the two preceding embodiments, wherein the user data is provided on the host computer by executing a host application, and the method further comprises executing a client application associated with the host application on the UE.

[0323] Embodiment 31: A user equipment (UE) is configured to communicate with a base station. The UE comprises a radio interface and a processing circuit system. The processing circuit system is configured to execute the method as described in the above three embodiments.

[0324] Embodiment 32: A communication system comprising a host computer, the host computer comprising: a processing circuit system configured to provide user data; and a communication interface configured to forward the user data to a cellular network for transmission to a user equipment UE; wherein the UE comprises a radio interface and a processing circuit system, and components of the UE are configured to perform any of the steps described in any of the embodiments in Group A.

[0325] Embodiment 33: The communication system as described in the previous embodiment, wherein the cellular network further includes a base station configured to communicate with the UE.

[0326] Embodiment 34: The communication system as described in the previous two embodiments, wherein: the processing circuit system of the host computer is configured to execute a host application, thereby providing the user data; and the processing circuit system of the UE is configured to execute a client application associated with the host application.

[0327] Embodiment 35: A method implemented in a communication system comprising a host computer, a base station and a user equipment UE, the method comprising: providing user data in the host computer; and initiating, in the host computer, a transmission carrying the user data to the UE via a cellular network, the cellular network comprising the base station, wherein the UE performs any of the steps described in any of the embodiments in Group A.

[0328] Embodiment 36: The method as described in the previous embodiment further includes: at the UE, receiving the user data from the base station.

[0329] Embodiment 37: A communication system comprising a host computer, the host computer comprising: a communication interface configured to receive user data originating from a transmission from a user equipment UE to a base station; wherein the UE comprises a radio interface and a processing circuit system, the processing circuit system of the UE being configured to perform any of the steps described in any of the embodiments in Group A.

[0330] Embodiment 38: The communication system as described in the previous embodiment further includes the UE.

[0331] Embodiment 39: The communication system as described in the previous two embodiments further includes the base station, wherein the base station includes a radio interface and a communication interface, the radio interface is configured to communicate with the UE, and the communication interface is configured to forward the user data carried by the transmission from the UE to the base station to the host computer.

[0332] Embodiment 40: The communication system as described in the previous three embodiments, wherein: the processing circuit system of the host computer is configured to execute a host application; and the processing circuit system of the UE is configured to execute a client application associated with the host application, thereby providing the user data.

[0333] Embodiment 41: A communication system as described in the previous four embodiments, wherein: the processing circuit system of the host computer is configured to execute a host application, thereby providing request data; and the processing circuit system of the UE is configured to execute a client application associated with the host application, thereby providing the user data in response to the request data.

[0334] Embodiment 42: A method implemented in a communication system including a host computer, a base station and a user equipment UE, the method comprising: receiving, at the host computer, user data transmitted from the UE to the base station, wherein the UE performs any of the steps described in any of the embodiments in Group A.

[0335] Example 43: The method as described in the previous embodiment further includes: at the UE, providing the user data to the base station.

[0336] Embodiment 44: The method as described in the previous two embodiments further includes: executing a client application on the UE to provide the user data to be transmitted; and executing a host application associated with the client application on the host computer.

[0337] Embodiment 45: The method as described in the previous three embodiments further includes: executing a client application at the UE; and receiving input data of the client application at the UE, and providing the input data at the host computer by executing a host application associated with the client application; wherein the user data to be transmitted is provided by the client application in response to the input data.

[0338] Embodiment 46: A communication system comprising a host computer, the host computer comprising a communication interface, the communication interface being configured to receive user data originating from a transmission from a user equipment UE to a base station, wherein the base station comprises a radio interface and a processing circuit system, the processing circuit system of the base station being configured to perform any of the steps described in any of the embodiments in Group B.

[0339] Example 47: The communication system as described in the previous embodiment further includes the base station.

[0340] Embodiment 48: The communication system as described in the previous two embodiments further includes the UE, wherein the UE is configured to communicate with the base station.

[0341] Embodiment 49: A communication system as described in the previous three embodiments, wherein: the processing circuit system 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 the user data to be received by the host computer.

[0342] Embodiment 50: A method implemented in a communication system comprising a host computer, a base station and a user equipment UE, the method comprising: at the host computer, receiving from the base station user data originating from a transmission that the base station has received from the UE, wherein the UE performs any of the steps described in any of the embodiments in Group A.

[0343] Embodiment 51: The method as described in the previous embodiment further includes: receiving the user data from the UE at the base station.

[0344] Embodiment 52: The method as described in the previous two embodiments further includes: initiating, at the base station, transmission of the received user data to the host computer.

[0345] At least some of the following abbreviations may be used in this disclosure. If there is an inconsistency between abbreviations, the way it is used above should take precedence. If listed multiple times below, the first listing should take precedence over any subsequent (one or more) listings.

[0346] 3GPP Third Generation Partnership Project

[0347] 5G fifth generation

[0348] 5GC fifth generation core

[0349] 5GS fifth generation system

[0350] AF application function

[0351] AMF access and mobility functions

[0352] AN Access Network

[0353] AP access point

[0354] ASIC (Application Specific Integrated Circuit)

[0355] AUSF authentication server functionality

[0356] CCA Clear Channel Assessment

[0357] CPU Central Processing Unit

[0358] DCI Downlink Control Information

[0359] DN Data Network

[0360] DSP digital signal processor

[0361] eNB Enhanced or Evolved Node B

[0362] EPS Evolved Packet System

[0363] E-UTRA Evolved Universal Terrestrial Radio Access FPGA Field Programmable Gate Array

[0364] gNB new air interface base station

[0365] gNB-DU New Radio Base Station Distributed Unit GNSS Global Navigation Satellite System

[0366] HSS Home Subscriber Server

[0367] IoT

[0368] IP Internet Protocol

[0369] LTE Long Term Evolution

[0370] MAC Media Access Control

[0371] MME Mobility Management Entity

[0372] MTC Machine Type Communication

[0373] NEF network exposure function

[0374] NF Network Function

[0375] NR New Radio

[0376] NRF Network Function Repository functionality

[0377] NSSF network slice selection function

[0378] OTT Over-the-Top

[0379] PC personal computer

[0380] PCF policy control function

[0381] PDSCH Physical Downlink Shared Channel P-GW Packet Data Network Gateway

[0382] PRS Positioning Reference Signal

[0383] QoS Quality of Service

[0384] RAM Random Access Memory

[0385] RAN Radio Access Network

[0386] ROM Read Only Memory

[0387] RP receiving point

[0388] RRH Remote Radio Head

[0389] RS reference signal

[0390] RTT round trip time

[0391] SCEF service capability exposure function

[0392] SL side link

[0393] SLRS side link reference signal

[0394] SLSS side link synchronization signal

[0395] SMF session management capabilities

[0396] SRS Synchronous Reference Source

[0397] TCI Transmission Configuration Indicator

[0398] TP teleportation point

[0399] TRP Transmit / Receive Point

[0400] UDM unified data management

[0401] UE User Equipment

[0402] UPF User Plane Function

[0403] Those skilled in the art will appreciate improvements and modifications to the embodiments of the present disclosure, and all such improvements and modifications are considered to be within the scope of the concepts disclosed herein.

Claims

1. A method for selecting and / or maintaining a synchronization source, performed by a user equipment (UE), the method comprising: obtaining information regarding one or more synchronization sources associated with sidelink operations, 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 synchronization source, the determination being based on at least one clear channel assessment (CCA) procedure; and In response to determining to adapt selection and / or maintenance of the first synchronization source as the synchronization source based on the at least one CCA procedure, selection and / or maintenance of the first synchronization source as the synchronization source is adapted. 2 . The method of claim 1 , wherein determining whether to adapt selection and / or maintenance of the first synchronization source as the synchronization source is based on a number of CCA failures.

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

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

5. The method according to any one of claims 1 to 4, wherein adapting the selection and / or maintenance of the first synchronization source as the synchronization source comprises one or more of the following: Based on the number of CCA failures being greater than a maximum value, selection and / or maintenance of the first synchronization source as the synchronization source is discarded, suspended, and / or postponed during a certain time period.

6. The method according to any one of claims 1 to 5, wherein adapting the selection and / or maintenance of the first synchronization source as the synchronization source comprises: Another synchronization source among the one or more synchronization sources associated with the sidelink operation is reselected as the synchronization source.

7. The method according to any one of claims 1 to 6, wherein adapting the selection and / or maintenance of the first synchronization source as the synchronization source comprises one or more of the following: After pausing or deferring selection and / or maintenance of the first synchronization source as the synchronization source for a certain period of time, resuming selection and / or maintenance of the first synchronization source as the synchronization source when one or more conditions are satisfied; When the UE has performed reselection of a new cell, resuming selection and / or maintenance of the first synchronization source as the synchronization source; Adapting transmission of a sidelink synchronization signal SLSS on another carrier frequency based on a CCA failure on the first carrier frequency; and If the at least one CCA procedure indicates that the number of CCA failures on the first carrier frequency during the time period Tn exceeds a maximum, SLSS transmission on another carrier frequency is initiated.

8. The method of any one of claims 1 to 7, wherein obtaining information about the one or more synchronization sources associated with the sidelink operation comprises: The information is obtained based on messages received from network nodes.

9. The method according to any one of claims 1 to 8, further comprising: Based on an identifier received from a network node, the UE selects the first synchronization source from a set of predefined synchronization sources.

10. The method according to any one of claims 1 to 9, further comprising: If the UE is configured with a first identifier that adopts a gNB-based synchronization configuration or an eNB-based synchronization configuration, gNodeB, gNB or eNodeB, eNB is selected or used as the synchronization source.

11. The method according to any one of claims 1 to 10, further comprising: If the UE is configured with a second identifier, a Global Navigation Satellite System (GNSS) is used as the synchronization source.

12. 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 related to a result of at least one clear channel assessment (CCA) procedure associated with a synchronization reference source (SRS); and Based on a result of the at least one CCA procedure, transmission of the SL RS is adapted.

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

14. The method of claim 10, wherein determining information related to the results of at least one CCA procedure comprises: It is determined that the number of CCA failures exceeds a maximum value.

15. The method of any one of claims 9 to 11, wherein adapting one or more procedures comprises one or more of the following: Continue to transmit SLRS on the current frequency (F1); If the result of the CCA procedure shows that there is no CCA failure on F1 or there is a limited number of CCA failures on F1, the UE continues to transmit SLRS on F1 according to the reference configuration; During a certain time period, stop / terminate the transmission of the SLRS on F1; If the result of the CCA procedure shows CCA failure or a large number of CCA failures, the UE stops / terminates transmission of SLRS during a time period Tn′; If (N'>Nmax') occurs K' times, the UE stops / terminates transmission of SLRS, where N' is the number of CCA failures, Nmax' is a threshold, and K' is an integer; If (N'>Nmax') R1' occurs during a certain time period, the UE stops / terminates the transmission of SLRS; suspending or postponing the transmission of the SLRS on F1 during a certain time period; If the result of the CCA procedure indicates a CCA failure or a large number of CCA failures, the UE suspends or defers transmission of SLRS during a time period Tn′; and If the result of the CCA procedure indicates a CCA failure or a large number of CCA failures, the UE adapts one or more transmission parameters of the SLRS.

16. The method of any one of claims 9 to 12, wherein obtaining information related to the need to transmit the SLRS comprises one or more of the following: Obtain information on whether the UE needs to transmit SLRS; If the UE is configured by another node to transmit the SLRS, determining a need to transmit the SLRS; If the UE is configured by another node to transmit the SLRS, determining a need to transmit the SLRS; Based on predefined rules, determining the need to transmit the SLRS; and Based on pre-configured information in the UE, a need to transmit the SLRS is determined.

17. A user equipment (UE) (800) comprising processing circuitry (802) and memory (804), the memory (804) comprising instructions, the instructions causing the UE (800) to: obtaining information regarding one or more synchronization sources associated with sidelink operations, the one or more synchronization sources including configured synchronization sources and / or available synchronization sources; For a first synchronization source of the one or more synchronization sources associated with the sidelink operation, determining whether to adapt selection and / or maintenance of the first synchronization source as a synchronization source, the determination being based on at least one clear channel assessment (CCA) procedure; and In response to determining to adapt selection and / or maintenance of the first synchronization source as the synchronization source based on the at least one CCA procedure, selection and / or maintenance of the first synchronization source as the synchronization source is adapted.

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

19. A computer-readable medium comprising instructions, which, 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 processing circuitry (802) and memory (804), the memory (804) comprising instructions, the instructions causing the UE (800) to: Obtaining information related to the need to transmit a sidelink SL reference signal RS; determining information related to a result of at least one clear channel assessment (CCA) procedure associated with a synchronization reference source (SRS); and Based on a result of the at least one CCA procedure, transmission of the SL RS is adapted.

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

22. A computer-readable medium comprising instructions which, 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.

Images