WO2024096787A1 - Methods, apparatus and computer-readable media for performing sidelink positioning using one or more reference user equipments - Google Patents

Abstract

Embodiments described herein relate to methods and apparatuses for performing sidelink positioning using one or more reference user equipments, UEs. A method in a method performed by a target user equipment, UE, comprises selecting one or more reference UEs from one or more candidate UEs based on, for each candidate UE, an identification of a SL synchronization source utilized by the candidate UE utilized by the candidate UE.

Description

METHODS, APPARATUS AND COMPUTER-READABLE MEDIA FOR PERFORMING

SIDELINK POSITIONING USING ONE OR MORE REFERENCE USER EQUIPMENTS

TECHNICAL FIELD

Embodiments described herein relate to methods and apparatuses for performing sideline positioning using one or more reference UEs.

BACKGROUND

Positioning in Uu

[0] Positioning has been a topic in Long Term Evolution (LTE) standardization since the 3^rd Generation Partnership Project (3GPP) Release 9. The primary objective is to fulfill regulatory requirements for emergency call positioning. Positioning in New Radio (NR) is proposed to be supported by the architecture shown in Figure 1. A Location Management Function (LMF) is the location node in NR. There are also interactions between the location node and the gNodeB via the NRPPa protocol. The interaction between the gNodeB and the device is supported via the Radio Resource Control (RRC) protocol.

[1] The gNB and ng-eNB may not always both be present. When both the gNB and ng-eNB are present, the NG-C interface is only present for one of them.

[2] In the legacy LTE standards, the following techniques are supported:

Enhanced Cell identification (ID): Which may comprise cell ID information to associate the device to the serving area of a serving cell, and then additional information to determine a finer granularity position.

Assisted Global Navigation Satellite System (GNSS): GNSS information retrieved by the device, supported by assistance information provided to the device from Enhanced Serving Mobile Location Center (E-SMLC).

OTDOA (Observed Time Difference of Arrival): The device estimates the time difference of reference signals from different base stations and sends to the E-SMLC for multilateration.

UTDOA (Uplink Time Difference of Arrival (TDOA)): The device is requested to transmit a specific waveform that is detected by multiple location measurement units (e.g. an eNB) at known positions. These measurements are forwarded to E-SMLC for multilateration.

Sensor methods such as Biometric pressure sensor which provides vertical position of the device and Inertial Motion Unit (IMU) which provides displacement.

[3] NR supports the below Radio Access Technology (RAT) Dependent positioning methods: [4] Downlink TDOA (DL-TDOA): The DL TDOA positioning method makes use of the Downlink (DL) Reference Signal Time Difference (RSTD) (and optionally DL Positioning Reference Signal (PRS) Reference Signal Received Power (RSRP)) of downlink signals received from multiple (Transmission Points) TPs, at the UE. The UE measures the DL RSTD (and optionally DL PRS RSRP) of the received signals using assistance data received from the positioning server, and the resulting measurements are used along with other configuration information to locate the UE in relation to the neighbouring TPs.

[5] Multi-Round Trip Time (RTT): The Multi-RTT positioning method makes use of the UE Rx-Tx measurements and DL PRS RSRP of downlink signals received from multiple Transmission Reception Points (TRPs), measured by the UE and the measured gNB Rx-Tx measurements and Uplink (UL) Sounding Reference Signal (SRS) Reference Signal Received Power (RSRP) at multiple TRPs of uplink signals transmitted from UE.

[6] UL-TDOA: The UL TDOA positioning method makes use of the UL TDOA (and optionally UL SRS-RSRP) at multiple Reception Points (RPs) of uplink signals transmitted from UE. The RPs measure the UL TDOA (and optionally UL SRS-RSRP) of the received signals using assistance data received from the positioning server, and the resulting measurements are used along with other configuration information to estimate the location of the UE.

[7] DL-AoD: The Downlink (DL) Angle of Departure (AoD) positioning method makes use of the measured DL PRS RSRP of downlink signals received from multiple TPs, at the UE. The UE measures the DL PRS RSRP of the received signals using assistance data received from the positioning server, and the resulting measurements are used along with other configuration information to locate the UE in relation to the neighbouring TPs.

[8] Uplink (UL)-Angle of Arrival (AoA): The UL AoA positioning method makes use of the measured azimuth and zenith of arrival at multiple RPs of uplink signals transmitted from the UE. The RPs measure A-AoA and Z-AoA of the received signals using assistance data received from the positioning server, and the resulting measurements are used along with other configuration information to estimate the location of the UE.

[9] New Radio (NR) -ECID: NR Enhanced Cell ID (NR E-CID) positioning refers to techniques which use additional UE measurements and/or NR radio resource and other measurements to improve the UE location estimate.

[10] The positioning modes can be categorized in below three areas:

UE- Assisted: The UE performs measurements with or without assistance from the network and sends these measurements to the Enhanced Serving Mobile Location Center (E-SMLC) where the position calculation may take place.

UE-Based: The UE performs measurements and calculates its own position with assistance from the network. Standalone: The UE performs measurements and calculates its own position without network assistance.

Sidelink transmissions in NR

[11] Sidelink transmissions over NR are specified for Rel. 16. These are enhancements of the ProSe (Proximity-based Services) specified for LTE. Four new enhancements are particularly introduced to NR sidelink transmissions as follows:

Support for unicast and groupcast transmissions are added in NR sidelink. For unicast and groupcast, the physical sidelink feedback channel (PSFCH) is introduced for a receiver UE to reply the decoding status to a transmitter UE.

Grant-free transmissions, which are adopted in NR uplink transmissions, are also provided in NR sidelink transmissions, to improve the latency performance.

To alleviate resource collisions among different sidelink transmissions launched by different UEs, it enhances channel sensing and resource selection procedures, which also lead to a new design of Physical Sidelink Control Channel (PSCCH).

To achieve a high connection density, congestion control and thus the Quality of Service (QoS) management is supported in NR sidelink transmissions.

[12] To enable the above enhancements, new physical channels and reference signals are introduced in NR (available in LTE before.):

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

PSFCH (Physical Sidelink, SL version of PUCCH): The PSFCH is transmitted by a sidelink receiver UE for unicast and groupcast, which conveys 1 bit information over 1 RB for the HARQ acknowledgement (ACK) and the negative ACK (NACK). In addition, channel state information (CSI) is carried in the medium access control (MAC) control element (CE) over the PSSCH instead of the PSFCH.

PSCCH (Physical Sidelink Common Control Channel, SL version of PDCCH): When the traffic to be sent to a receiver UE arrives at a transmitter UE, a transmitter UE should first send the PSCCH, which conveys a part of SCI (Sidelink Control information, SL version of DO) to be decoded by any UE for the channel sensing purpose, including the reserved time -frequency resources for transmissions, demodulation reference signal (DMRS) pattern and antenna port, etc.

Sidelink Primary/Secondary Synchronization Signal (S-PSS/S-SSS): Similar to downlink transmissions in NR, in sidelink transmissions, primary and secondary synchronization signals (called S-PSS and S-SSS, respectively) are supported. Through detecting the S-PSS and S-SSS, a UE is able to identify the sidelink synchronization identity (SSID) from the UE sending the S-PSS/S-SSS. Through detecting the S-PSS/S-SSS, a UE is therefore able to know the characteristics of the UE transmitting the S-PSS/S-SSS. A series of process of acquiring timing and frequency synchronization together with SSIDs of UEs is called initial cell search. Note that the UE sending the S-PSS/S-SSS may not be necessarily involved in sidelink transmissions, and a node (UE/eNB/gNB) sending the S-PSS/S-SSS is called a synchronization source. There are two S-PSS sequences and 336 S-SSS sequences forming a total of 672 SSIDs in a cell (for example, as there are 2 different sequence code for SL Primary Synch signal and 336 seq codes for SL Secondary Synch signal: in total (by multiplying these 2) we can get unique 672 codes). Physical Sidelink Broadcast Channel (PSBCH): The PSBCH is transmitted along with the S- PSS/S-SSS as a synchronization signal/PSBCH block (SSB). The SSB has the same numerology as PSCCH/PSSCH on that carrier, and an SSB should be transmitted within the bandwidth of the configured BWP. The PSBCH conveys information related to synchronization, such as the direct frame number (DFN), indication of the slot and symbol level time resources for sidelink transmissions, in-coverage indicator, etc. The SSB is transmitted periodically at every 160 ms.

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, the PT-RS is only applicable for FR2 transmission.

[13] Another new feature is the two-stage sidelink control information (SCI). This SCI is a version of the DO for SL. Unlike the DO, only part (first stage) of the SCI is sent on the PSCCH. This part is used for channel sensing purposes (including the reserved time-frequency resources for transmissions, demodulation reference signal (DMRS) pattern and antenna port, etc.) and can be read by all UEs while the remaining (second stage) scheduling and control information such as a 8 -bits source identity (ID) and a 16-bits destination ID, NDI, RV and HARQ process ID is sent on the PSSCH to be decoded by the receiver UE.

[14] Similar as for Proximity based services (PRoSE) in LTE, NR sidelink transmissions have the following two modes of resource allocations:

Mode 1: Sidelink resources are scheduled by a gNB.

Mode 2: The UE autonomously selects sidelink resources from a (pre-)configured sidelink resource pool(s) based on the channel sensing mechanism.

[15] For the in-coverage UE, a gNB can be configured to adopt Mode 1 or Mode 2. For the out-of- coverage UE, only Mode 2 can be adopted. [16] As in LTE, scheduling over the sidelink in NR is done in different ways for Mode 1 and Mode 2.

[17] Mode 1 supports the following two kinds of grants:

Dynamic grant: When the traffic to be sent over sidelink arrives at a transmitter UE, this UE should launch the four-message exchange procedure to request sidelink resources from a gNB (SR on UL, grant, BSR on UL, grant for data on SL sent to UE). During the resource request procedure, a gNB may allocate a sidelink radio network temporary identifier (SL-RNTI) to the transmitter UE. If this sidelink resource request is granted by a gNB, then a gNB indicates the resource allocation for the PSCCH and the PSSCH in the downlink control information (DO) conveyed by PDCCH with Cyclic Redundancy Check (CRC) scrambled with the SL-RNTI. When a transmitter UE receives such a DO, a transmitter UE can obtain the grant only if the scrambled CRC of DO can be successfully solved by the assigned SL-RNTI. A transmitter UE then indicates the time-frequency resources and the transmission scheme of the allocated PSSCH in the PSCCH, and launches the PSCCH and the PSSCH on the allocated resources for sidelink transmissions. When a grant is obtained from a gNB, a transmitter UE can only transmit a single TB. As a result, this kind of grant is suitable for traffic with a loose latency requirement. Configured grant: For the traffic with a strict latency requirement, performing the four-message exchange procedure to request sidelink resources may induce unacceptable latency. In this case, prior to the traffic arrival, a transmitter UE may perform the four-message exchange procedure and request a set of resources. If a grant can be obtained from a gNB, then the requested resources are reserved in a periodic manner. Upon traffic arriving at a transmitter UE, this UE can launch the PSCCH and the PSSCH on the upcoming resource occasion. In fact, this kind of grant is also known as grant-free transmissions.

[18] In both dynamic grant and configured grant, a sidelink receiver UE cannot receive the Downlink Control Information (DO) (since it is addressed to the transmitter UE), and therefore a receiver UE should perform blind decoding to identify the presence of PSCCH and find the resources for the PSSCH through the SCI.

[19] When a transmitter UE launches the PSCCH, CRC is also inserted in the SCI without any scrambling.

Mode 2 Resource allocation

[20] In the Mode 2 resource allocation, when traffic arrives at a transmitter UE, this transmitter UE should autonomously select resources for the PSCCH and the PSSCH. To further minimize the latency of the feedback HARQ ACK7NACK transmissions and subsequently retransmissions, a transmitter UE may also reserve resources for PSCCH/PSSCH for retransmissions. To further enhance the probability of successful TB decoding in one shot, and thus suppress the probability to perform retransmissions, a transmitter UE may repeat the TB transmission along with the initial TB transmission. This mechanism is also known as blind retransmission. As a result, when traffic arrives at a transmitter UE, then this transmitter UE may select resources for the following transmissions:

1) The PSSCH associated with the PSCCH for initial transmission and blind retransmissions.

2) The PSSCH associated with the PSCCH for retransmissions.

[21] Since each transmitter UE in sidelink transmissions may be required to autonomously select resources for the above transmissions, the question of how to prevent different transmitter UEs from selecting the same resources turns out to be a critical issue in Mode 2. A particular resource selection procedure is therefore imposed to Mode 2 based on channel sensing. The channel sensing algorithm involves measuring RSRP on different subchannels and requires knowledge of the different UEs power levels of DMRS on the PSSCH or the DMRS on the PSCCH depending on the configuration. This information is known only after receiver SCI launched by (all) other UEs. The sensing and selection algorithm is rather complex.

[22] As described in clause 6.3.2.2 in TR 37.985 V17.1.1, Mode 2 is for UE autonomous resource selection. Its basic structure is of a UE sensing, within a (pre-)configured resource pool, which resources are not in use by other UEs with higher -priority traffic, and choosing an appropriate amount of such resources for its own transmissions. Having selected such resources, the UE can transmit and re-transmit in them a certain number of times, or until a cause of resource reselection is triggered.

[23] The mode 2 sensing procedure can select and then reserve resources for a variety of purposes reflecting that NR Vehicle-to-everything (V2X) introduces sidelink HARQ in support of unicast and groupcast in the physical layer. It may reserve resources to be used for a number of blind (retransmissions or HARQ-feedback-based (re-)transmissions of a transport block, in which case the resources are indicated in the SCI(s) scheduling the transport block. Alternatively, it may select resources to be used for the initial transmission of a later transport block, in which case the resources are indicated in an SCI scheduling a current transport block, in a manner similar to the LTE-V2X scheme (clause 5.2.2.2). Finally, an initial transmission of a transport block can be performed after sensing and resource selection, but without a reservation.

[24] The first-stage SCIs transmitted by UEs on PSCCH indicate the time -frequency resources in which the UE will transmit a PSSCH. These SCI transmissions are used by sensing UEs to maintain a record of which resources have been reserved by other UEs in the recent past. When a resource selection is triggered (e.g. by traffic arrival or a re-selection trigger), the UE considers a sensing window which starts a (pre-)configured time in the past and finishes shortly before the trigger time. The window can be either 1100 ms or 100 ms wide, with the intention that the 100 ms option is particularly useful for aperiodic traffic, and 1100 ms particularly for periodic traffic. A sensing UE also measures the SL- RSRP in the slots of the sensing window, which implies the level of interference which would be caused and experienced if the sensing UE were to transmit in them. In NR-V2X, SL-RSRP is a (pre- )configurable measurement of either PSSCH-RSRP or PSCCH-RSRP.

[25] The sensing UE then selects resources for its (re-)transmission(s) from within a resource selection window. The window starts shortly after the trigger for (re-)selection of resources, and should not be longer than the remaining latency budget of the packet due to be transmitted. Reserved resources in the selection window with SL-RSRP above a threshold are excluded from being candidates by the sensing UE, with the threshold set according to the priorities of the traffic of the sensing and transmitting UEs. Thus, a higher priority transmission from a sensing UE can occupy resources which are reserved by a transmitting UE with sufficiently low SL-RSRP and sufficiently lower-priority traffic.

[26] If the set of resources in the selection window which have not been excluded is less than a certain proportion of the available resources within the window, the SL-RSRP exclusion threshold is relaxed in 3 dB steps. The proportion is set by (pre-)configuration to 20%, 35%, or 50% for each traffic priority. The UE selects an appropriate amount of resources randomly from this non-excluded set. The resources selected are not in general periodic. Up to three resources can be indicated in each SCI transmission, which can each be independently located in time and frequency. When the indicated resources are for semi-persistent transmission of another transport block, the range of supported periodicities is expanded compared to LTE-V2X, in order to cover the broader set of envisioned use cases in NR-V2X.

[27] Shortly before transmitting in a reserved resource, a sensing UE re-evaluates the set of resources from which it can select, to check whether its intended transmission is still suitable, taking account of late-arriving SCIs due, typically, to an aperiodic higher-priority service starting to transmit after the end of the original sensing window. If the reserved resources would not be part of the set for selection at this time (T3), then new resources are selected from the updated resource selection window. The cutoff time T3 is long enough before transmission to allow the UE to perform the calculations relating to resource re-selection.

[28] Figure 2 illustrates a summary of the sensing and resource (re-)selection procedures in TR 37.985 V 17.1.1.

[29] The timeline of the sensing and resource (re-)selection windows with respect to the time of trigger n, are shown in Figure 6.3.2.2-2(a) in TR 37.985 V 17.1.1 (Figure 3 herein), and the effect of the possibility of re-evaluation before first use of the reservation in Figure 6.3.2.2-2(b) in TR 37.985 V 17.1.1 (Figure 4 herein).

[30] There are a number of triggers for resource re-selection, several of which are similar to LTE- V2X in Clause 5.2.2.2 in TR 37.985 V 17.1.1. In addition, there is the possibility to configure a resource pool with a pre-emption function designed to help accommodate aperiodic sidelink traffic, so that a UE reselects all the resources it has already reserved in a particular slot if another nearby UE with higher priority indicates it will transmit in any of them, implying a high-priority aperiodic traffic arrival at the other UE, and the SL-RSRP is above the exclusion threshold. The application of pre-emption can apply between all priorities of data traffic, or only when the priority of the pre-empting traffic is higher than a threshold and higher than that of the pre-empted traffic. A UE does not need to consider the possibility of pre-emption later than time T3 before the particular slot containing the reserved resources.

Inter-UE coordination for Mode 2 Resource allocation in 3GPP Rel-17

[31] The 3GPP Rel-17 NR sidelink enhancement WID RP-201385 has defined objectives to specify solutions which can enhance NR sidelink for the V2X, public safety and commercial use cases.

Study the feasibility and benefit of the enhancement(s) in mode 2 for enhanced reliability and reduced latency in consideration of both Packet Reception Ratio (PRR) and Packet Interreception (PIR) defined in TR37.885 (by RAN#91), and specify the identified solution if deemed feasible and beneficial [RAN 1 , RAN2] . o Inter-UE coordination with the following until RAN#90.

■ A set of resources is determined at UE-A. This set is sent to UE-B in mode 2, and UE-B takes this into account in the resource selection for its own transmission. o Note: The study scope after RAN#90 is to be decided in RAN#90. o Note: The solution should be able to operate in-coverage, partial coverage, and out-of- coverage and to address consecutive packet loss in all coverage scenarios. o Note: RAN2 work will start after [RAN#89].

[32] For the above study objective, an inter-UE coordination mechanism will be studied for enhancements in SL resource allocation Mode 2. With the mechanism, a UE (e.g., UE-A) will be able to signal “A set of resources determined at the UE-A” to another UE (e.g., UE-B). Another UE can consider the received signaling into its own resource selection procedure. The detailed signaling alternatives are pending to be addressed. The possible signaling alternatives are expected to include at least PC5-RRC signaling, LI signaling, and MAC CE.

[33] As described in clause 16.9.8 of TS 38.300 V 17.2.0, the SL UE can support inter-UE coordination (IUC) in Mode 2, whereby a UE-A sends information about resources to UE-B, which UE-B then uses for resource (re)selection. The following schemes of inter-UE coordination are supported:

IUC scheme 1 , where the IUC information sent from a UE-A to a UE-B is the preferred or nonpreferred resources for UE-B's transmission, and

IUC scheme 2, where the IUC information sent from a UE-A to a UE-B is the presence of expected/potential resource conflict on the resources indicated by UE-B's SCI. [34] In scheme 1 , the transmission of IUC information from UE-A can be triggered by an explicit request from UE-B, or by a condition at UE-A. UE-A determines the set of resources reserved by other UEs or slots where UE-A, when it is the intended receiver of UE-B, does not expect to perform SL reception from UE-B due to half-duplex operation. UE-A uses these resources as the set of nonpreferred resources, or excludes these resources to determine a set of preferred resources and sends the preferred/non-preferred resources to UE-B. UE-B's resources for resource (re)selection can be based on both UE-B's sensing results (if available) and the IUC information received from UE-A, or it can be based only on IUC information received from UE-A. For scheme 1 , MAC CE and second-stage SCI or MAC CE only can be used to send IUC information. It will be appreciated that transmission of the explicit request and reporting for IUC information in a unicast manner is supported.

[35] In scheme 2, UE-A determines the expected/potential resource conflict within the resources indicated by UE-B's SCI as either resources reserved by other UEs and identified by UE-A as fully/partially overlapping with the resources indicated by UE-B's SCI, or as slots where UE-A is the intended receiver of UE-B and does not expect to perform SL reception on those slots due to half-duplex operation. UE-B uses the conflicting resources to determine the resources to be reselected and exclude the conflicting resources from the reselected resources. For scheme 2, PSFCH is used to send IUC information.

SL Synchronization references and priorities

[36] As described in clause 6.2.2.1 of TS 37.985 v 17.1.1, there are four basic sources, or references, from which a V2X UE can derive its own synchronization: GNSS, a gNB/eNB, another UE transmitting SLSS (here termed a SyncRef UE), or its own internal clock. In general, GNSS or eNB/gNB are regarded as the highest-quality sources. SyncRef UEs are distinguished between those which are directly synchronized to GNSS or a gNB/eNB, those which are one further step away, and those which are greater than or equal to two further steps away from GNSS or gNB/eNB. As a last resort, a UE unable to find any other synchronization reference will use its own internal clock to transmit S-SSB. The V2X synchronization procedure defines a hierarchy or set of priorities among such synchronization references and requires all UEs to continuously search the hierarchy to get to the highest-quality one they can find. The general preference order is as follows:

Level 1. Either GNSS or eNB/gNB, according to (pre-)configuration.

Level 2. A SyncRef UE directly synchronized to a Level 1 source.

Level 3. A SyncRef UE synchronized to a Level 2 source, i.e. indirectly synchronized to a Level 1 source.

Level 4. Whichever of GNSS or eNB/gNB was not (pre-)configured as the Level 1 source.

Level 5. A SyncRef UE directly synchronized to a Level 4 source. Level 6. A SyncRef UE synchronized to a Level 5 source, i.e. indirectly synchronized to a Level 4 source.

Level 7. Any other SyncRef UE.

Level 8. UE's internal clock.

[37] The NR V2X scheme is intended to allow the merging of otherwise-separate hierarchies derived from GNSS and gNB/eNB, so that a UE is able to move between nearby such hierarchies without loss of sidelink service. However, since it is possible that a gNB/eNB does not itself have synchronization to GNSS, use of Levels 4-6 can be disabled when GNSS is used as Level 1, so that there is no deviation from the hierarchy being derived from GNSS.

[38] As described in clause 6.2.2.2.1 of TS 37.985 v 17.1.1, the Sidelink synchronization signal identity (SLSSID) itself conveys information about the synchronization source of the transmitting UE. In general, the further a UE is away from a high-quality source of GNSS or gNB/eNB, the lower quality will be its own synchronization and thus the quality of an SLSS it transmits. There are a series of association rules among SLSS IDs, designed to allow the identification, and propagation through the system of, high-quality synchronization sources. The operation of this procedure is essentially the same as LTE-V2X, described in Clause 5.1.2.2.1, with the main difference being that there are 672 Sidelink Synchronization Signal (SLSS) IDs in NR-V2X, divided into 0, 1, ... , 335 for in-coverage indication and 336, ... , 671 for out-of-coverage indication. The special SLSS IDs of 0, 336, and 337 in NR-V2X are used equivalently to 0, 168, and 169 respectively in LTE-V2X.

SL based positioning in 3GPP Rel-18

[39] In 3GPP Rel-18, SL positioning is being studied. The following study objective has been defined in RP-213561 regarding SL positioning protocol architecture and signaling procedures:

Study of positioning architecture and signalling procedures (e.g. configuration, measurement reporting, etc) to enable sidelink positioning covering both UE based and network based positioning.

[40] The studies need to be performed for the UE (i.e., the target UE which needs to be positioned) in various scenarios with different network coverage, including full coverage, partial coverage and out of coverage, as shown in Figure 5.

[41] In Figure 5, the assisting UE (may be also referred to as a reference UE) provides SL measurement assistance to the target UE.

[42] For a target UE out of coverage, there may be different options for the target UE to get positioned. In one option, the target UE may choose to connect to the network via a SL User Equipment to Network (U2N) relay UE. In this case, the network can be involved in the positioning procedure for the target UE. In another option, the target UE may apply UE based positioning by involving an assisting UE. If there is not any assisting UE found in the proximity, the target UE can reach an assisting UE in further range via a User equipment to User Equipment (U2U) relay UE. [43] The same positioning methods including DL-TDOA, UL-TDOA, and Multi-RTT etc are expected to be also applicable for SL based positioning. For these methods, multiple assisting/reference UEs would be required, as shown in Figure 6.

[44] For SL based positioning, certain method such as TDOA may require tight synchronization among multiple assisting/reference UEs so that the transmissions of positioning reference signals from these reference UEs can arrive at the target UE in synchronized fashion. This can improve both positioning accuracy and avoid interference among reference UEs.

In regards to SL positioning, the following terms are defined as:

SL Reference UE: A UE, supporting positioning of target UE, e.g., by transmitting and/or receiving reference signals for positioning, providing positioning -related information, etc., using sidelink. An SL Reference UE is understood as “Anchor UE” in RANI TR 38.859. “Reference UE” mentioned in Key Issues (KIs) and Solutions of the SA2 TR 23. 700 86 v 030 refers to “SL Reference UE”.

Target UE: A UE whose distance, direction and/or position is measured with the support from one or multiple SL Reference UEs using Sidelink in the Ranging based service and Sidelink positioning.

Anchor UE: A UE supporting positioning of target UE, e.g., by transmitting and/or receiving reference signals for positioning, providing positioning -related information, etc., over the SL interface.

SUMMARY

[45] There currently exist certain challenge(s). For SL based positioning methods (e.g., TDOA, multi- RTT, etc.), coordination between a reference UE and a target UE, and/or coordination between the reference UEs themselves, ensures increased positioning accuracy. That is, some of the SL positioning methods (e.g., TDOA) require tight/accurate synchronization between reference UEs (also referred to as assisting UEs throughout this disclosure), and/or tight/accurate synchronization between reference UEs and a target UE. However, the existing SL synchronization mechanism is performed per UE link without requiring the UEs involved to synchronize with neighboring UEs. In other words, different transmitting reference/target UEs may have different synchronization sources, and therefore may not be tightly/accurately synchronized. This is insufficient for achieving accurate SL positioning.

[46] Certain aspects of the disclosure and their embodiments may provide solutions to these or other challenges.

[47] Aspects of the disclosure enhance existing SL IUC and synchronization mechanisms for SL positioning to achieve tight/accurate synchronization between reference UEs in order to improve SL positioning accuracy. They also enhance IUC mechanisms to coordinate reference UEs and/or the target UE for more accurate SL positioning.

[48] Aspects of the disclosure are disclosed in figure 7. Figure 7 illustrates an example procedure to achieve tight synchronization between UEs for SL.

[49] In particular, Figure 7 illustrates the following features:

[50] - One of the UEs, 700, (e.g., Master UE (group leader; first vehicle in the platoon), Initiator UE, Anchor UE, reference UE (defined in TR 38.859)) identifies the synchronization (“sync” or “synch”) requirements which are derived based upon positioning Quality of Service requirements.

The synchronization requirements are provided to ((steps 701a to 701c) the participating UEs, 710, 720 and 730, and their synchronization capabilities are obtained (steps 702a to 702c).

The UEs may be dropped if they cannot fulfil the synchronization requirements and new UEs may be added.

A common synchronization source is identified (step 703), which can be for example GNSS or a synchRefUE. An indication of the common synchronization source is provided to (steps 704a to 704c) the participating UEs. o If available synchronization sources are deemed to provide insufficient accuracy relative to the requirements, additional synchronization procedures may be initiated, e.g., involving additional signal or message exchanges. In this case, some of UEs (e.g. one or more UEs) involved in the procedure may apply a different synchronization source from the synchronization source of other UEs.

The timing is derived based upon the identified common synchronization source.

[51] According to some embodiments there is provided a method performed by a target user equipment, UE, for performing sidelink, SL, positioning using one or more reference UEs. The method comprises selecting one or more reference UEs from one or more candidate UEs based on, for each candidate UE, an identification of a SL synchronization source utilized by the candidate UE utilized by the candidate UE.

[52] According to some embodiments there is provided a method performed by a candidate user equipment, UE, for enabling performance of sidelink, SL, positioning of a target UE using one or more reference UEs, the method comprises transmitting to the target UE one or more of: a type of the SL synchronization source utilized by the candidate UE; a priority of the SL synchronization source utilized by the candidate UE; and an identification of the SL synchronization source utilized by the candidate UE.

[53] According to some embodiments there is provided a method performed by a candidate user equipment, UE, for enabling performance of sidelink, SL, positioning of a target UE using one or more reference UEs. The method comprises receiving from the target UE an identification of a SL synchronization source utilized by the target UE; and determining whether a SL synchronization source utilized by the candidate UE is the same as the SL synchronization source utilized by the target UE. The method further comprises responsive to the SL synchronization source utilized by the candidate UE being the same as the SL synchronization source utilized by the target UE, indicating to the target UE that the candidate UE may be used as a reference UE.

[54] According to some embodiments there is provided a method in a network node for enabling performance of sidelink, SL, positioning of a potential target UE using a plurality of reference UEs. The method comprises configuring the potential target UE with one or more of: one or more supported SL positioning methods; and for each supported SL positioning method: an indication of whether accurate synchronization is required between the one or more reference UEs and/or between the reference UEs and the potential target UE; and an indication of a minimum number of reference UEs for positioning the potential target UE with a required accuracy.

[55] According to some embodiments there is provided a target user equipment, UE, for performing sidelink, SL, positioning using one or more reference UEs. The target UE comprises processing circuitry and memory, the memory containing instructions executable by the processing circuitry whereby the target UE is operable to: select one or more reference UEs from one or more candidate UEs based on, for each candidate UE, an identification of a SL synchronization source utilized by the candidate UE utilized by the candidate UE.

[56] According to some embodiments there is provided a candidate user equipment, UE, for enabling performance of sidelink, SL, positioning of a target UE using one or more reference UEs. The candidate UE comprises processing circuitry and memory, the memory containing instructions executable by the processing circuitry whereby the candidate UE is operable to: transmit to the target UE one or more of: a type of the SL synchronization source utilized by the candidate UE; a priority of the SL synchronization source utilized by the candidate UE; and an identification of the SL synchronization source utilized by the candidate UE.

[57] According to some embodiments there is provided a candidate user equipment, UE, for enabling performance of sidelink, SL, positioning of a target UE using one or more reference UEs. The candidate UE comprises processing circuitry and memory, the memory containing instructions executable by the processing circuitry whereby the candidate UE is operable to: receive from the target UE an identification of a SL synchronization source utilized by the target UE, determine whether a SL synchronization source utilized by the candidate UE is the same as the SL synchronization source utilized by the target UE, and responsive to the SL synchronization source utilized by the candidate UE being the same as the SL synchronization source utilized by the target UE, indicate to the target UE that the candidate UE may be used as a reference UE. [58] According to some embodiments there is provided a network node for enabling performance of sidelink, SL, positioning of a potential target UE using a plurality of reference UEs. The network node comprises processing circuitry and memory, the memory containing instructions executable by the processing circuitry whereby the network node is operable to: configure the potential target UE with one or more supported SL positioning methods; and for each supported SL positioning method configuring the potential target UE with: an indication of whether accurate synchronization is required between the one or more reference UEs and/or between the reference UEs and the potential target UE; and an indication of a minimum number of reference UEs for positioning the potential target UE with a required accuracy.

[59] According to some embodiments there is provided a target user equipment, UE, for performing sidelink, SL, positioning using one or more reference UEs. The target UE is operable to select one or more reference UEs from one or more candidate UEs based on, for each candidate UE, an identification of a SL synchronization source utilized by the candidate UE utilized by the candidate UE.

[60] According to some embodiments there is provided a candidate user equipment, UE, for enabling performance of sidelink, SL, positioning of a target UE using one or more reference UEs. The candidate UE is operable to: transmit to the target UE one or more of: a type of the SL synchronization source utilized by the candidate UE; a priority of the SL synchronization source utilized by the candidate UE; and an identification of the SL synchronization source utilized by the candidate UE.

[61] According to some embodiments there is provided a candidate user equipment, UE, for enabling performance of sidelink, SL, positioning of a target UE using one or more reference UEs. The candidate UE is operable to: receive from the target UE an identification of a SL synchronization source utilized by the target UE, determine whether a SL synchronization source utilized by the candidate UE is the same as the SL synchronization source utilized by the target UE, and responsive to the SL synchronization source utilized by the candidate UE being the same as the SL synchronization source utilized by the target UE, indicate to the target UE that the candidate UE may be used as a reference UE.

[62] According to some embodiments there is provided a network node for enabling performance of sidelink, SL, positioning of a potential target UE using a plurality of reference UEs. The network node is operable to: configure the potential target UE with one or more supported SL positioning methods; and for each supported SL positioning method configuring the potential target UE with:

[63] an indication of whether accurate synchronization is required between the one or more reference UEs and/or between the reference UEs and the potential target UE; and an indication of a minimum number of reference UEs for positioning the potential target UE with a required accuracy. [64] According to some embodiments there is provided a computer program comprising instructions which, when executed on at least one processor, cause the at least one processor to carry out any of the methods described above.

[65] According to some embodiments there is provided a carrier containing the computer program as described above, wherein the carrier comprises one of an electronic signal, optical signal, radio signal or computer readable storage medium.

[66] According to some embodiments there is provided a computer-readable medium comprising instructions that, when executed on at least one processor, cause the at least one processor to perform any of the methods described above.

[67] According to some embodiments there is provided a computer program product comprising non transitory computer readable media having stored thereon a computer program as described above.

[68]

[69] Certain embodiments may provide one or more of the following technical advantage(s).

[70] With the proposed mechanisms, a target UE may only select references UE which are able to provide accurate synchronization sources. In this way, positioning accuracy may be improved.

[71] With the proposed mechanisms, a target UE may reselect new reference UEs to replace the current reference UEs when the new reference UEs give more accurate synchronization sources than the current ones. In this way, positioning accuracy may be improved.

[72] SL positioning requirement(s), or Quality of Service (QoS) requirement(s) of services requiring positioning, are well guaranteed.

[73] Brief Description of the Drawings

[74] For a better understanding of the embodiments of the present disclosure, and to show how it may be put into effect, reference will now be made, by way of example only, to the accompanying drawings, in which:

[75] Fig. 1 is a schematic diagram illustrating NG-RAN Rel-15 LCS protocols;

[76] Fig. 2 is a flow chart illustrating a sensing and resource (re-)selection procedure;

[77] Fig. 3 is a timeline of a sensing and resource (re-)selection procedure;

[78] Fig. 4 is a timeline of a sensing and resource (re-)selection procedure;

[79] Fig. 5: is a schematic diagram illustrating SE positioning for UEs in different coverage scenarios;

[80] Fig. 6 is a schematic diagram illustrating SL positioning and ranging;

[81] Fig.7 is a signaling diagram illustrating an example procedure to achieve tight synchronization between UEs for SL based positioning;

[82] Fig. 8 is a flow chart illustrating a method in accordance with some embodiments;

[83] Fig. 9 is a flow chart illustrating a method in accordance with some embodiments; [84] Fig. 10 is a flow chart illustrating a method in accordance with some embodiments;

[85] Fig. 11 is a flow chart illustrating a method in accordance with some embodiments;

[86] Fig. 12 shows an example of a communication system in accordance with some embodiments;

[87] Fig. 13 shows a UE in accordance with some embodiments;

[88] Fig. 15 is a block diagram of a host;

[89] Fig. 16 is a block diagram illustrating a virtualization environment in which functions implemented by some embodiments may be virtualized; and

[90] Fig. 17 shows a communication diagram of a host communicating via a network node with a UE over a partially wireless connection in accordance with some embodiments.

DETAILED DESCRIPTION

[91] Some of the embodiments contemplated herein will now be described more fully with reference to the accompanying drawings. Embodiments are provided by way of example to convey the scope of the subject matter to those skilled in the art.

[92] Figure 8 depicts a method in accordance with particular embodiments. The method of Figure 8 may be performed by a target UE or wireless device (e.g. the UE 1212 or UE 1300 as described later with reference to Figures 12 and 13 respectively) and is for performing sidelink (SL) positioning using one or more reference UEs. The method begins at step 802 with the target UE selecting one or more reference UEs from one or more candidate UEs based on, for each candidate UE, an identification of a SL synchronization source utilized by the candidate UE.

[93] In some embodiments, step 802 may comprise receiving, for each candidate UE, the identification of the SL synchronization source utilized by the candidate UE. The UE may then select the one or more reference UEs as candidate UEs that utilize the same SL synchronization source.

[94] On the other hand, responsive to an insufficient number of candidate UEs utilizing the same SL synchronization source, step 802 may further comprise selecting the one or more reference UEs as candidate UEs that utilize similar synchronization sources.

[95] Two SL synchronization sources may be considered similar when one or more conditions are met. For example, one of these conditions may be that the two SL synchronization sources are associated with priority levels within a first predetermined range. Another example of one of these conditions is a difference between signalling radio quality of the SL synchronization sources being within a second predetermined range. A further example of one of these conditions is timing differences of the two SL synchronization sources being within a third predetermined range.

[96] In some embodiments, a minimum number of reference UEs may be required for positioning the target UE with a required accuracy. As such, step 802 may comprise selecting a first set of candidate UEs as the one or more reference UEs responsive to the first set of candidate UEs: utilizing the same SL synchronization source; and comprising a number of candidate UEs greater than or equal to the minimum number of reference UEs.

[97] For example, in some embodiments, the target UE may be configured with one or more supported SL positioning methods. For each supported SL positioning method, the target UE may be configured with an indication of whether accurate synchronization is required between the one or more reference UEs and/or between the reference UEs and the target UE. For each supported SL positioning method, the target UE may be configured with an indication of a minimum number of reference UEs for positioning the target UE with a required accuracy.

[98] In some embodiments, step 802 may comprise selecting the one or more reference UEs as candidate UEs that provide a radio channel quality above a first threshold. Additionally or alternatively, step 802 may comprise selecting one or more reference UEs based on a quality of a SL synchronization source utilized by candidate UEs.

[99] In some embodiments, step 802 may comprise selecting one or more reference UEs based on a priority of a SL synchronization source utilized by candidate UEs. For example, the method of Figure 8 may further comprise receiving, for each candidate UE, an indication of a priority of the SL synchronization source utilized by the candidate UE.

[100] In some embodiments, step 802 may comprise selecting the one or more reference UEs as candidate UEs that utilize a preferred type of the SL synchronization source. For example, the method of Figure 8 may further comprise receiving, for each candidate UE, an indication of a type of the SL synchronization source utilized by the candidate UE.

[101] In some embodiments, the method of Figure 8 may further comprise transmitting, to the one or more candidate UEs, one or more of: an identification of a SL synchronization source utilized by the target UE; an indication of a priority of the SL synchronization source utilized by the target UE; and a type of the SL synchronization source utilized by the target UE.

[102] In some embodiments, the method of Figure 8 may further comprise receiving, from each candidate UE, an indication of whether the candidate UE may operate as a reference UE for the target UE.

[103] In some embodiments, the method of Figure 8 may further comprise the target UE triggering selection and/or reselection of the one or more reference UEs responsive to the target UE needing to be positioned via SL based positioning. Additionally or alternatively, the method of Figure 8 may further comprise initiating reselection of the one or more reference UEs responsive to an additional candidate UE being discovered that meets one or more conditions. One example condition may be that the additional candidate UE utilizes a high-quality SL synchronization source. Another example condition may be that the additional candidate UE utilizes a high priority SL synchronization source. [104] Figure 9 depicts a method in accordance with particular embodiments. The method of Figure 9 may be performed by a candidate UE or wireless device (e.g. the UE 1212 or UE 1300 as described later with reference to Figures 12 and 13 respectively) and is for enabling performance of sidelink (SL) positioning of a target UE using one or more reference UEs. The method begins at step 902 with the candidate UE transmitting to the target UE one or more of: a type of the SL synchronization source utilized by the candidate UE; a priority of the SL synchronization source utilized by the candidate UE; and an identification of the SL synchronization source utilized by the candidate UE.

[105] Figure 10 depicts a method in accordance with particular embodiments. The method of Figure 10 may be performed by a candidate UE or wireless device (e.g. the UE 1212 or UE 1300 as described later with reference to Figures 12 and 13 respectively) and is for enabling performance of sidelink (SL) positioning of a target UE using one or more reference UEs.

[106] The method begins at step 1002 with the candidate UE receiving from the target UE an identification of a SL synchronization source utilized by the target UE. At step 1004, the candidate UE determines whether a SL synchronization source utilized by the candidate UE is the same as the SL synchronization source utilized by the target UE. At step 1006, responsive to the SL synchronization source utilized by the candidate UE being the same as the SL synchronization source utilized by the target UE, the candidate UE indicates to the target UE that the candidate UE may be used as a reference UE.

[107] Figure 11 depicts a method in accordance with particular embodiments. The method of Figure 11 may be performed by a network node (e.g. the network node 1210 or network node 1400 as described later with reference to Figures 12 and 14 respectively). The method may be performed by a network node for enabling performance of SL positioning of a potential target UE using a plurality of reference UEs. The method begins at step 1102 with configuring the potential target UE with one or more of: one or more supported SL positioning methods; and for each supported SL positioning method: an indication of whether accurate synchronization is required between the one or more reference UEs and/or between the reference UEs and the potential target UE; and an indication of a minimum number of reference UEs for positioning the potential target UE with a required accuracy.

In other words, a UE (e.g. a potential target UE or a reference UE) may be configured by the network or preconfigured with at least one of the following:

One or multiple supported SL positioning methods, e.g., RTT, TDOA, multi-RTT etc; For each SL positioning method, whether tight/accurate sync is required between reference UEs and/or between the reference UEs and the target UE;

For each SL positioning method, the (minimum) number of reference UEs which are required for positioning the target UE with a required positioning accuracy is also configured/preconfigured.

[108] The embodiments below are described in the context of NR (i.e., target UE and reference/assisting UE are deployed in a same or different NR cell). The link between a target UE and an assisting UE may be based on LTE sidelink, NR sidelink, or any other short-range communication technology (e.g., Wifi ). The Uu connection between the target UE or the reference UE and base station may be LTE Uu or NR Uu.

[109] The embodiments cover aspects on how to achieve tight synchronization between reference UEs. A target UE aims to select or reselect reference UEs which are associated with the same or similar synchronization sources.

[HO] In some embodiments, for SL based positioning, a UE (i.e., potential target UE) is configured by the network or preconfigured with at least one of the following: one or multiple supported SL positioning methods (e.g., RTT, TDOA, multi-RTT etc.); for each SL positioning method, whether tight/accurate synchronization is required between reference UEs and/or between the reference UEs and the target UE; and for each SL positioning method, the (minimum) number of reference UEs which are required for positioning the target UE with a required positioning accuracy is also configured/preconfigured.

[111] In other words, in some embodiments, the target UE may be configured with one or more supported SL positioning methods. For each supported SL positioning method, the target UE may be configured with: an indication of whether accurate synchronization is required between the one or more reference UEs and/or between the reference UEs and the target UE; and/or an indication of a minimum number of reference UEs for positioning the target UE with a required accuracy.

[112] According to the above (pre)configuration, the UE triggers selection and reselection of one or multiple assisting/referring UEs when the UE is to be positioned via SL based positioning. In other words, the method of Figure 8 may further comprise the target UE triggering selection and/or reselection of the one or more reference UEs responsive to the target UE needing to be positioned via SL based positioning.

[113] In some embodiments, the UE (i.e., the target UE) selects (in a step corresponding to step 802 of figure 8) one or more reference UEs according to at least one of the following conditions:

1) Whether the sidelink between the reference UE and the UE gives sufficiently strong radio channel quality (e.g., a high-quality radio channel may be a radio channel with a radio channel quality above a given threshold). In other words, step 802 may comprise selecting the one or more reference UEs as candidate UEs that provide a radio channel quality above a first threshold, and/or selecting one or more reference UEs based on a quality of a SL synchronization source utilized by candidate UEs.

2) Whether the reference UE is associated with the same synchronization source as other references UEs which are already selected by the UE (e.g., a same synchronization source may be where the selected synchronization sources are associated with the same SLSS ID). In other words, step 802 may comprise receiving, for each candidate UE, an identification of a SL synchronization source utilized by the candidate UE. The UE may then select the one or more reference UEs as candidate UEs that utilize the same SL synchronization source.

3) For a given synchronization source, whether there are sufficient reference UEs which can assist the UE to perform positioning to meet the required positioning accuracy. In other words, a minimum number of reference UEs may be required for positioning the target UE with a required accuracy. As such, 802 may comprise selecting a first set of candidate UEs as the one or more reference UEs responsive to the first set of candidate UEs: utilizing the same SL synchronization source; and comprising a number of candidate UEs greater than or equal to the minimum number of reference UEs.

4) Whether the selected reference UEs are associated with high-quality synchronization sources (high quality (e.g., in terms of synchronization signal radio quality) synchronization sources are helpful to improve positioning accuracy and reduce timing errors between reference UEs and/or between reference UEs and the target UE). In other words, step 802 may comprise selecting one or more reference UEs based on a quality of a SL synchronization source utilized by candidate UEs. The quality of different types of synchronization source may be as discussed in the background section herein.

5) Whether the selected reference UEs are associated with high-priority synchronization sources (high priority synchronization sources are helpful to improve positioning accuracy and reduce timing errors between reference UEs and/or between reference UEs and the target UE). In other words, step 802 may comprise selecting one or more reference UEs based on a priority of a SL synchronization source utilized by candidate UEs. For example, the method 8 may further comprise receiving, for each candidate UE, indication of a priority of the SL synchronization source utilized by the candidate UE. The priority of different synchronization sources may be according to the level hierarchy discussed in the background section herein.

[114] In this way, all selected reference UEs for SL positioning would have the same synchronization sources. [115] In some embodiments, a UE which may operate as a reference/assisting UE for other UEs, may send signaling to UEs in its proximity, wherein the signaling indicates information on its synchronization source and comprises at least one of:

1) The type of the SL synchronization source (e.g., GNSS, gNB/eNB, UE etc).

2) The priority of the SL synchronization source. For example, a given SL synchronization source may have a priority level between a lowest priority and a highest priority, wherein a lower value corresponds to a higher priority synchronization source to be used by the reference and target UEs (or in other embodiments, a lower priority synchronization source). For NR SL, the SL synchronization source may have a priority level between the value 1 and the value 9. On the other hand, for LTE SL, the SL synchronization source may have a priority level between the value 1 and the value 5. The priority of different synchronization sources may be according to the level hierarchy discussed in the background section herein.

3) the ID of the SL synchronization source (e.g., SLSS ID).

[116] Upon reception of the signaling, the other UE which is to be positioned can consider the above information during the procedure of selection and reselection of referencing UEs. In other words, step 802 may comprise any one of the following: selecting the one or more reference UEs as candidate UEs that utilize a preferred type of the SL synchronization source (for example, the method of Figure 8 may further comprise receiving, for each candidate UE, an indication of a type of the SL synchronization source utilized by the candidate UE); selecting one or more reference UEs based on a priority of a SL synchronization source utilized by candidate UEs; and selecting one or more reference UEs based on an ID of a SL synchronization source utilized by candidate UEs.

[117] In some embodiments, a target UE which is to be positioned may also send similar signaling to the plurality of candidate UEs (e.g. neighbor UEs) indicating information on its synchronization source and comprising similar content to that listed above. Upon reception of the signaling, a candidate UE may check if it has the same synchronization source as the target UE. Each candidate UE may then decide whether it can operate as a reference UE for the target UE.

[118] In other words, the method of figure 8 may further comprise transmitting, to the one or more candidate UEs, one or more of: an identification of a SL synchronization source utilized by the target UE; an indication of a priority of the SL synchronization source utilized by the target UE; and a type of the SL synchronization source utilized by the target UE. The candidate UE may then perform the method as described with reference to Figure 10. [119] In some embodiments, a target UE may decide to reselect one or multiple reference UEs for SL positioning purposes whenever additional reference UE candidates are found that meet at least one of the following conditions: the additional reference UE candidates are associated with higher quality synchronization sources; and the additional reference UE candidates are associated with higher priority synchronization sources.

[120] In other words, the method of Figure 8 may further comprise further comprise initiating reselection of the one or more reference UEs responsive to an additional candidate UE being discovered that meets one or more conditions. One example condition may be that the additional candidate UE utilizes a high-quality SL synchronization source. A high-quality SL synchronization source may be a SL synchronization source which transmits synchronization signals in a channel with a high radio channel quality (e.g., above a quality threshold). A high quality SL synchronization source may comprise a source that would fall into one or more of the higher quality levels defined in the background section herein. Another example condition may be that the additional candidate UE utilizes a high priority SL synchronization source.

[121] In some embodiments, a target UE may select or reselect reference UEs with similar synchronization sources if there are no sufficient reference UEs available for any synchronization source. Two SL synchronization sources are similar in term of at least one of the following: associated with similar priority (e.g., the priority levels are in the similar range); provide similar SL synchronization signaling radio quality; and the timing differences are in a limited range (e.g., the timing differences are lower than a threshold).

[122] In other words, responsive to an insufficient number of candidate UEs utilizing the same SL synchronization source, step 802 may further comprise selecting the one or more reference UEs as candidate UEs that utilize similar synchronization sources. Two SL synchronization sources may be considered similar when one or more conditions are met. For example, one of these conditions may be that the two SL synchronization sources are associated with priority levels within a first predetermined range. Another example of one of these conditions is a difference between signalling radio quality of the SL synchronization sources being within a second predetermined range. A further example of one of these conditions is timing differences of the two SL synchronization sources being within a third predetermined range.

[123] In some embodiments, for any one of the above embodiments, a signaling between any two UEs (i.e., reference UE, target UE) may be at least one of the following: a discovery message; PC5-S signaling; PC5-RRC signaling; a MAC CE; a Control PDU of a protocol layer (e.g., SDAP, PDCP, RLC or an adaptation layer in case of SL relay); and LI signaling on physical channels (e.g., PSSCH, PSCCH, PSFCH etc).

[124] In some embodiments, the method of Figure 8 may further comprise receiving, from each candidate UE, an indication of whether the candidate UE may operate as a reference UE for the target UE.

[125] Figure 12 shows an example of a communication system 1200 in accordance with some embodiments.

[126] In the example, the communication system 1200 includes a telecommunication network 1202 that includes an access network 1204, such as a radio access network (RAN), and a core network 1206, which includes one or more core network nodes 1208. The access network 1204 includes one or more access network nodes, such as network nodes 1210a and 1210b (one or more of which may be generally referred to as network nodes 1210), or any other similar 3^rd Generation Partnership Project (3GPP) access node or non-3GPP access point. The network nodes 1210 facilitate direct or indirect connection of user equipment (UE), such as by connecting UEs 1212a, 1212b, 1212c, and 1212d (one or more of which may be generally referred to as UEs 1212) to the core network 1206 over one or more wireless connections.

[127] Example wireless communications over a wireless connection include transmitting and/or receiving wireless signals using electromagnetic waves, radio waves, infrared waves, and/or other types of signals suitable for conveying information without the use of wires, cables, or other material conductors. Moreover, in different embodiments, the communication system 1200 may include any number of wired or wireless networks, network nodes, UEs, and/or any other components or systems that may facilitate or participate in the communication of data and/or signals whether via wired or wireless connections. The communication system 1200 may include and/or interface with any type of communication, telecommunication, data, cellular, radio network, and/or other similar type of system.

[128] The UEs 1212 may be any of a wide variety of communication devices, including wireless devices arranged, configured, and/or operable to communicate wirelessly with the network nodes 1210 and other communication devices. Similarly, the network nodes 1210 are arranged, capable, configured, and/or operable to communicate directly or indirectly with the UEs 1212 and/or with other network nodes or equipment in the telecommunication network 1202 to enable and/or provide network access, such as wireless network access, and/or to perform other functions, such as administration in the telecommunication network 1202.

[129] In the depicted example, the core network 1206 connects the network nodes 1210 to one or more hosts, such as host 1216. These connections may be direct or indirect via one or more intermediary networks or devices. In other examples, network nodes may be directly coupled to hosts. The core network 1206 includes one more core network nodes (e.g., core network node 1208) that are structured with hardware and software components. Features of these components may be substantially similar to those described with respect to the UEs, network nodes, and/or hosts, such that the descriptions thereof are generally applicable to the corresponding components of the core network node 1208. Example core network nodes include functions of one or more of a Mobile Switching Center (MSC), Mobility Management Entity (MME), Home Subscriber Server (HSS), Access and Mobility Management Function (AMF), Session Management Function (SMF), Authentication Server Function (AUSF), Subscription Identifier De-concealing function (SIDE), Unified Data Management (UDM), Security Edge Protection Proxy (SEPP), Network Exposure Function (NEF), and/or a User Plane Function (UPF).

[130] The host 1216 may be under the ownership or control of a service provider other than an operator or provider of the access network 1204 and/or the telecommunication network 1202, and may be operated by the service provider or on behalf of the service provider. The host 1216 may host a variety of applications to provide one or more services. Examples of such applications include the provision of live and/or pre-recorded audio/video content, data collection services, for example, retrieving and compiling data on various ambient conditions detected by a plurality of UEs, analytics functionality, social media, functions for controlling or otherwise interacting with remote devices, functions for an alarm and surveillance center, or any other such function performed by a server.

[131] As a whole, the communication system 1200 of Figure 12 enables connectivity between the UEs, network nodes, and hosts. In that sense, the communication system may be configured to operate according to predefined rules or procedures, such as specific standards that include, but are not limited to: Global System for Mobile Communications (GSM); Universal Mobile Telecommunications System (UMTS); Long Term Evolution (LTE), and/or other suitable 2G, 3G, 4G, 5G standards, or any applicable future generation standard (e.g., 6G); wireless local area network (WLAN) standards, such as the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standards (WiFi); and/or any other appropriate wireless communication standard, such as the Worldwide Interoperability for Microwave Access (WiMax), Bluetooth, Z-Wave, Near Field Communication (NFC) ZigBee, LiFi, and/or any low-power wide-area network (LPWAN) standards such as LoRa and Sigfox.

[132] In some examples, the telecommunication network 1202 is a cellular network that implements 3GPP standardized features. Accordingly, the telecommunications network 1202 may support network slicing to provide different logical networks to different devices that are connected to the telecommunication network 1202. For example, the telecommunications network 1202 may provide Ultra Reliable Low Latency Communication (URLLC) services to some UEs, while providing Enhanced Mobile Broadband (eMBB) services to other UEs, and/or Massive Machine Type Communication (mMTC)/Massive loT services to yet further UEs.

[133] In some examples, the UEs 1212 are configured to transmit and/or receive information without direct human interaction. For instance, a UE may be designed to transmit information to the access network 1204 on a predetermined schedule, when triggered by an internal or external event, or in response to requests from the access network 1204. Additionally, a UE may be configured for operating in single- or multi-RAT or multi-standard mode. For example, a UE may operate with any one or combination of Wi-Fi, NR (New Radio) and LTE, i.e. being configured for multi-radio dual connectivity (MR-DC), such as E-UTRAN (Evolved-UMTS Terrestrial Radio Access Network) New Radio - Dual Connectivity (EN-DC).

[134] In the example illustrated in Figure 12, the hub 1214 communicates with the access network 1204 to facilitate indirect communication between one or more UEs (e.g., UE 1212c and/or 1212d) and network nodes (e.g., network node 1210b). In some examples, the hub 1214 may be a controller, router, a content source and analytics node, or any of the other communication devices described herein regarding UEs. For example, the hub 1214 may be a broadband router enabling access to the core network 1206 for the UEs. As another example, the hub 1214 may be a controller that sends commands or instructions to one or more actuators in the UEs. Commands or instructions may be received from the UEs, network nodes 1210, or by executable code, script, process, or other instructions in the hub 1214. As another example, the hub 1214 may be a data collector that acts as temporary storage for UE data and, in some embodiments, may perform analysis or other processing of the data. As another example, the hub 1214 may be a content source. For example, for a UE that is a VR headset, display, loudspeaker or other media delivery device, the hub 1214 may retrieve VR assets, video, audio, or other media or data related to sensory information via a network node, which the hub 1214 then provides to the UE either directly, after performing local processing, and/or after adding additional local content. In still another example, the hub 1214 acts as a proxy server or orchestrator for the UEs, in particular in if one or more of the UEs are low energy loT devices.

[135] The hub 1214 may have a constant/persistent or intermittent connection to the network node 1210b. The hub 1214 may also allow for a different communication scheme and/or schedule between the hub 1214 and UEs (e.g., UE 1212c and/or 1212d), and between the hub 1214 and the core network 1206. In other examples, the hub 1214 is connected to the core network 1206 and/or one or more UEs via a wired connection. Moreover, the hub 1214 may be configured to connect to an M2M service provider over the access network 1204 and/or to another UE over a direct connection. In some scenarios, UEs may establish a wireless connection with the network nodes 1210 while still connected via the hub 1214 via a wired or wireless connection. In some embodiments, the hub 1214 may be a dedicated hub - that is, a hub whose primary function is to route communications to/from the UEs from/to the network node 1210b. In other embodiments, the hub 1214 may be a non-dedicated hub - that is, a device which is capable of operating to route communications between the UEs and network node 1210b, but which is additionally capable of operating as a communication start and/or end point for certain data channels.

[136] Figure 13 shows a UE 1300 in accordance with some embodiments. As used herein, a UE refers to a device capable, configured, arranged and/or operable to communicate wirelessly with network nodes and/or other UEs. Examples of a UE include, but are not limited to, a smart phone, mobile phone, cell phone, voice over IP (VoIP) phone, wireless local loop phone, desktop computer, personal digital assistant (PDA), wireless camera, gaming console or device, music storage device, playback appliance, wearable terminal device, wireless endpoint, mobile station, tablet, laptop, laptop-embedded equipment (LEE), laptop-mounted equipment (LME), smart device, wireless customer-premise equipment (CPE), vehicle-mounted or vehicle embedded/integrated wireless device, etc. Other examples include any UE identified by the 3rd Generation Partnership Project (3GPP), including a narrow band internet of things (NB-IoT) UE, a machine type communication (MTC) UE, and/or an enhanced MTC (eMTC) UE.

[137] A UE may support device-to-device (D2D) communication, for example by implementing a 3GPP standard for sidelink communication, Dedicated Short-Range Communication (DSRC), vehicle- to-vehicle (V2V), vehicle-to-infrastructure (V2I), or vehicle-to-everything (V2X). In other examples, a UE may not necessarily have a user in the sense of a human user who owns and/or operates the relevant device. Instead, a UE may represent a device that is intended for sale to, or operation by, a human user but which may not, or which may not initially, be associated with a specific human user (e.g., a smart sprinkler controller). Alternatively, a UE may represent a device that is not intended for sale to, or operation by, an end user but which may be associated with or operated for the benefit of a user (e.g., a smart power meter).

[138] The UE 1300 includes processing circuitry 1302 that is operatively coupled via a bus 1304 to an input/output interface 1306, a power source 1308, a memory 1310, a communication interface 1312, and/or any other component, or any combination thereof. Certain UEs may utilize all or a subset of the components shown in Figure 13. The level of integration between the components may vary from one UE to another UE. Further, certain UEs may contain multiple instances of a component, such as multiple processors, memories, transceivers, transmitters, receivers, etc.

[139] The processing circuitry 1302 is configured to process instructions and data and may be configured to implement any sequential state machine operative to execute instructions stored as machine -readable computer programs in the memory 1310. The processing circuitry 1302 may be implemented as one or more hardware-implemented state machines (e.g., in discrete logic, field- programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), etc.); programmable logic together with appropriate firmware; one or more stored computer programs, general-purpose processors, such as a microprocessor or digital signal processor (DSP), together with appropriate software; or any combination of the above. For example, the processing circuitry 1302 may include multiple central processing units (CPUs). The processing circuitry 1302 may be operable to provide, either alone or in conjunction with other UE 1300 components, such as the memory 1310, UE 1300 functionality. For example, the processing circuitry 1302 may be configured to cause the UE 1302 to perform the methods as described with reference to Figure 8, Figure 9, and/or Figure 10.

[140] In the example, the input/output interface 1306 may be configured to provide an interface or interfaces to an input device, output device, or one or more input and/or output devices. Examples of an output device include a speaker, a sound card, a video card, a display, a monitor, a printer, an actuator, an emitter, a smartcard, another output device, or any combination thereof. An input device may allow a user to capture information into the UE 1300. Examples of an input device include a touch-sensitive or presence-sensitive display, a camera (e.g., a digital camera, a digital video camera, a web camera, etc.), a microphone, a sensor, a mouse, a trackball, a directional pad, a trackpad, a scroll wheel, a smartcard, and the like. The presence-sensitive display may include a capacitive or resistive touch sensor to sense input from a user. A sensor may be, for instance, an accelerometer, a gyroscope, a tilt sensor, a force sensor, a magnetometer, an optical sensor, a proximity sensor, a biometric sensor, etc., or any combination thereof. An output device may use the same type of interface port as an input device. For example, a Universal Serial Bus (USB) port may be used to provide an input device and an output device.

[141] In some embodiments, the power source 1308 is structured as a battery or battery pack. Other types of power sources, such as an external power source (e.g., an electricity outlet), photovoltaic device, or power cell, may be used. The power source 1308 may further include power circuitry for delivering power from the power source 1308 itself, and/or an external power source, to the various parts of the UE 1300 via input circuitry or an interface such as an electrical power cable. Delivering power may be, for example, for charging of the power source 1308. Power circuitry may perform any formatting, converting, or other modification to the power from the power source 1308 to make the power suitable for the respective components of the UE 1300 to which power is supplied.

[142] The memory 1310 may be or be configured to include memory such as random access memory (RAM), read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), magnetic disks, optical disks, hard disks, removable cartridges, flash drives, and so forth. In one example, the memory 1310 includes one or more application programs 1314, such as an operating system, web browser application, a widget, gadget engine, or other application, and corresponding data 1316. The memory 1310 may store, for use by the UE 1300, any of a variety of various operating systems or combinations of operating systems.

[143] The memory 1310 may be configured to include a number of physical drive units, such as redundant array of independent disks (RAID), flash memory, USB flash drive, external hard disk drive, thumb drive, pen drive, key drive, high-density digital versatile disc (HD-DVD) optical disc drive, internal hard disk drive, Blu-Ray optical disc drive, holographic digital data storage (HDDS) optical disc drive, external mini-dual in-line memory module (DIMM), synchronous dynamic random access memory (SDRAM), external micro-DIMM SDRAM, smartcard memory such as tamper resistant module in the form of a universal integrated circuit card (UICC) including one or more subscriber identity modules (SIMs), such as a USIM and/or ISIM, other memory, or any combination thereof. The UICC may for example be an embedded UICC (eUICC), integrated UICC (iUICC) or a removable 1 UICC commonly known as ‘SIM card.’ The memory 1310 may allow the UE 1300 to access instructions, application programs and the like, stored on transitory or non-transitory memory media, to off-load data, or to upload data. An article of manufacture, such as one utilizing a communication system may be tangibly embodied as or in the memory 1310, which may be or comprise a device- readable storage medium.

[144] The processing circuitry 1302 may be configured to communicate with an access network or other network using the communication interface 1312. The communication interface 1312 may comprise one or more communication subsystems and may include or be communicatively coupled to an antenna 1322. The communication interface 1312 may include one or more transceivers used to communicate, such as by communicating with one or more remote transceivers of another device capable of wireless communication (e.g., another UE or a network node in an access network). Each transceiver may include a transmitter 1318 and/or a receiver 1320 appropriate to provide network communications (e.g., optical, electrical, frequency allocations, and so forth). Moreover, the transmitter 1318 and receiver 1320 may be coupled to one or more antennas (e.g., antenna 1322) and may share circuit components, software or firmware, or alternatively be implemented separately.

[145] In some embodiments, communication functions of the communication interface 1312 may include cellular communication, Wi-Fi communication, LPWAN communication, data communication, voice communication, multimedia communication, short-range communications such as Bluetooth, near-field communication, location-based communication such as the use of the global positioning system (GPS) to determine a location, another like communication function, or any combination thereof. Communications may be implemented in according to one or more communication protocols and/or standards, such as IEEE 802.11, Code Division Multiplexing Access (CDMA), Wideband Code Division Multiple Access (WCDMA), GSM, LTE, New Radio (NR), UMTS, WiMax, Ethernet, transmission control protocol/internet protocol (TCP/IP), synchronous optical networking (SONET), Asynchronous Transfer Mode (ATM), QUIC, Hypertext Transfer Protocol (HTTP), and so forth.

[146] Regardless of the type of sensor, a UE may provide an output of data captured by its sensors, through its communication interface 1312, via a wireless connection to a network node. Data captured by sensors of a UE can be communicated through a wireless connection to a network node via another UE. The output may be periodic (e.g., once every 15 minutes if it reports the sensed temperature), random (e.g., to even out the load from reporting from several sensors), in response to a triggering event (e.g., when moisture is detected an alert is sent), in response to a request (e.g., a user initiated request), or a continuous stream (e.g., a live video feed of a patient).

[147] As another example, a UE comprises an actuator, a motor, or a switch, related to a communication interface configured to receive wireless input from a network node via a wireless connection. In response to the received wireless input the states of the actuator, the motor, or the switch may change. For example, the UE may comprise a motor that adjusts the control surfaces or rotors of a drone in flight according to the received input or controls a robotic arm performing a medical procedure according to the received input.

[148] A UE, when in the form of an Internet of Things (loT) device, may be a device for use in one or more application domains, these domains comprising, but not limited to, city wearable technology, extended industrial application and healthcare. Non-limiting examples of such an loT device are devices which are or which are embedded in: a connected refrigerator or freezer, a TV, a connected lighting device, an electricity meter, a robot vacuum cleaner, a voice controlled smart speaker, a home security camera, a motion detector, a thermostat, a smoke detector, a door/window sensor, a flood/moisture sensor, an electrical door lock, a connected doorbell, an air conditioning system like a heat pump, an autonomous vehicle, a surveillance system, a weather monitoring device, a vehicle parking monitoring device, an electric vehicle charging station, a smart watch, a fitness tracker, a head-mounted display for Augmented Reality (AR) or Virtual Reality (VR), a wearable for tactile augmentation or sensory enhancement, a water sprinkler, an animal- or item-tracking device, a sensor for monitoring a plant or animal, an industrial robot, an Unmanned Aerial Vehicle (UAV), and any kind of medical device, like a heart rate monitor or a remote controlled surgical robot. A UE in the form of an loT device comprises circuitry and/or software in dependence on the intended application of the loT device in addition to other components as described in relation to the UE 1300 shown in Figure 13.

[149] As yet another specific example, in an loT scenario, a UE may represent a machine or other device that performs monitoring and/or measurements, and transmits the results of such monitoring and/or measurements to another UE and/or a network node. The UE may in this case be an M2M device, which may in a 3GPP context be referred to as an MTC device. As one particular example, the UE may implement the 3GPP NB-IoT standard. In other scenarios, a UE may represent a vehicle, such as a car, a bus, a truck, a ship and an airplane, or other equipment that is capable of monitoring and/or reporting on its operational status or other functions associated with its operation.

[150] In practice, any number of UEs may be used together with respect to a single use case. For example, a first UE might be or be integrated in a drone and provide the drone’s speed information (obtained through a speed sensor) to a second UE that is a remote controller operating the drone. When the user makes changes from the remote controller, the first UE may adjust the throttle on the drone (e.g. by controlling an actuator) to increase or decrease the drone’s speed. The first and/or the second UE can also include more than one of the functionalities described above. For example, a UE might comprise the sensor and the actuator, and handle communication of data for both the speed sensor and the actuators.

[151] Figure 14 shows a network node 1400 in accordance with some embodiments. As used herein, network node refers to equipment capable, configured, arranged and/or operable to communicate directly or indirectly with a UE and/or with other network nodes or equipment, in a telecommunication network. Examples of network nodes include, but are not limited to, access points (APs) (e.g., radio access points), base stations (BSs) (e.g., radio base stations, Node Bs, evolved Node Bs (eNBs) and NR NodeBs (gNBs)).

[152] Base stations may be categorized based on the amount of coverage they provide (or, stated differently, their transmit power level) and so, depending on the provided amount of coverage, may be referred to as femto base stations, pico base stations, micro base stations, or macro base stations. A base station may be a relay node or a relay donor node controlling a relay. A network node may also include one or more (or all) parts of a distributed radio base station such as centralized digital units and/or remote radio units (RRUs), sometimes referred to as Remote Radio Heads (RRHs). Such remote radio units may or may not be integrated with an antenna as an antenna integrated radio. Parts of a distributed radio base station may also be referred to as nodes in a distributed antenna system (DAS).

[153] Other examples of network nodes include multiple transmission point (multi-TRP) 5G access nodes, multi-standard radio (MSR) equipment such as MSR BSs, network controllers such as radio network controllers (RNCs) or base station controllers (BSCs), base transceiver stations (BTSs), transmission points, transmission nodes, multi-cell/multicast coordination entities (MCEs), Operation and Maintenance (O&M) nodes, Operations Support System (OSS) nodes, Self-Organizing Network (SON) nodes, positioning nodes (e.g., Evolved Serving Mobile Location Centers (E-SMLCs)), and/or Minimization of Drive Tests (MDTs).

[154] The network node 1400 includes processing circuitry 1402, a memory 1404, a communication interface 1406, and a power source 1408, and/or any other component, or any combination thereof. The network node 1400 may be composed of multiple physically separate components (e.g., a NodeB component and a RNC component, or a BTS component and a BSC component, etc.), which may each have their own respective components. In certain scenarios in which the network node 1400 comprises multiple separate components (e.g., BTS and BSC components), one or more of the separate components may be shared among several network nodes. For example, a single RNC may control multiple NodeBs. In such a scenario, each unique NodeB and RNC pair, may in some instances be considered a single separate network node. In some embodiments, the network node 1400 may be configured to support multiple radio access technologies (RATs). In such embodiments, some components may be duplicated (e.g., separate memory 1404 for different RATs) and some components may be reused (e.g., a same antenna 1410 may be shared by different RATs). The network node 1400 may also include multiple sets of the various illustrated components for different wireless technologies integrated into network node 1400, for example GSM, WCDMA, LTE, NR, WiFi, Zigbee, Z-wave, LoRaWAN, Radio Frequency Identification (RFID) or Bluetooth wireless technologies. These wireless technologies may be integrated into the same or different chip or set of chips and other components within network node 1400.

[155] The processing circuitry 1402 may comprise a combination of one or more of a microprocessor, controller, microcontroller, central processing unit, digital signal processor, application-specific integrated circuit, field programmable gate array, or any other suitable computing device, resource, or combination of hardware, software and/or encoded logic operable to provide, either alone or in conjunction with other network node 1400 components, such as the memory 1404, network node 1400 functionality. For example, the processing circuitry 1402 may be configured to cause the network node to perform the methods as described with reference to Figure 11.

[156] In some embodiments, the processing circuitry 1402 includes a system on a chip (SOC). In some embodiments, the processing circuitry 1402 includes one or more of radio frequency (RF) transceiver circuitry 1412 and baseband processing circuitry 1414. In some embodiments, the radio frequency (RF) transceiver circuitry 1412 and the baseband processing circuitry 1414 may be on separate chips (or sets of chips), boards, or units, such as radio units and digital units. In alternative embodiments, part or all of RF transceiver circuitry 1412 and baseband processing circuitry 1414 may be on the same chip or set of chips, boards, or units.

[157] The memory 1404 may comprise any form of volatile or non-volatile computer-readable memory including, without limitation, persistent storage, solid-state memory, remotely mounted memory, magnetic media, optical media, random access memory (RAM), read-only memory (ROM), mass storage media (for example, a hard disk), removable storage media (for example, a flash drive, a Compact Disk (CD) or a Digital Video Disk (DVD)), and/or any other volatile or non-volatile, non- transitory device-readable and/or computer-executable memory devices that store information, data, and/or instructions that may be used by the processing circuitry 1402. The memory 1404 may store any suitable instructions, data, or information, including a computer program, software, an application including one or more of logic, rules, code, tables, and/or other instructions capable of being executed by the processing circuitry 1402 and utilized by the network node 1400. The memory 1404 may be used to store any calculations made by the processing circuitry 1402 and/or any data received via the communication interface 1406. In some embodiments, the processing circuitry 1402 and memory 1404 is integrated.

[158] The communication interface 1406 is used in wired or wireless communication of signaling and/or data between a network node, access network, and/or UE. As illustrated, the communication interface 1406 comprises port(s)/terminal(s) 1416 to send and receive data, for example to and from a network over a wired connection. The communication interface 1406 also includes radio front-end circuitry 1418 that may be coupled to, or in certain embodiments a part of, the antenna 1410. Radio front-end circuitry 1418 comprises filters 1420 and amplifiers 1422. The radio front-end circuitry 1418 may be connected to an antenna 1410 and processing circuitry 1402. The radio front-end circuitry may be configured to condition signals communicated between antenna 1410 and processing circuitry 1402. The radio front-end circuitry 1418 may receive digital data that is to be sent out to other network nodes or UEs via a wireless connection. The radio front-end circuitry 1418 may convert the digital data into a radio signal having the appropriate channel and bandwidth parameters using a combination of filters 1420 and/or amplifiers 1422. The radio signal may then be transmitted via the antenna 1410. Similarly, when receiving data, the antenna 1410 may collect radio signals which are then converted into digital data by the radio front-end circuitry 1418. The digital data may be passed to the processing circuitry 1402. In other embodiments, the communication interface may comprise different components and/or different combinations of components.

[159] In certain alternative embodiments, the network node 1400 does not include separate radio frontend circuitry 1418, instead, the processing circuitry 1402 includes radio front-end circuitry and is connected to the antenna 1410. Similarly, in some embodiments, all or some of the RF transceiver circuitry 1412 is part of the communication interface 1406. In still other embodiments, the communication interface 1406 includes one or more ports or terminals 1416, the radio front-end circuitry 1418, and the RF transceiver circuitry 1412, as part of a radio unit (not shown), and the communication interface 1406 communicates with the baseband processing circuitry 1414, which is part of a digital unit (not shown).

[160] The antenna 1410 may include one or more antennas, or antenna arrays, configured to send and/or receive wireless signals. The antenna 1410 may be coupled to the radio front-end circuitry 1418 and may be any type of antenna capable of transmitting and receiving data and/or signals wirelessly. In certain embodiments, the antenna 1410 is separate from the network node 1400 and connectable to the network node 1400 through an interface or port.

[161] The antenna 1410, communication interface 1406, and/or the processing circuitry 1402 may be configured to perform any receiving operations and/or certain obtaining operations described herein as being performed by the network node. Any information, data and/or signals may be received from a UE, another network node and/or any other network equipment. Similarly, the antenna 1410, the communication interface 1406, and/or the processing circuitry 1402 may be configured to perform any transmitting operations described herein as being performed by the network node. Any information, data and/or signals may be transmitted to a UE, another network node and/or any other network equipment.

[162] The power source 1408 provides power to the various components of network node 1400 in a form suitable for the respective components (e.g., at a voltage and current level needed for each respective component). The power source 1408 may further comprise, or be coupled to, power management circuitry to supply the components of the network node 1400 with power for performing the functionality described herein. For example, the network node 1400 may be connectable to an external power source (e.g., the power grid, an electricity outlet) via an input circuitry or interface such as an electrical cable, whereby the external power source supplies power to power circuitry of the power source 1408. As a further example, the power source 1408 may comprise a source of power in the form of a battery or battery pack which is connected to, or integrated in, power circuitry. The battery may provide backup power should the external power source fail. [163] Embodiments of the network node 1400 may include additional components beyond those shown in Figure 14 for providing certain aspects of the network node’s functionality, including any of the functionality described herein and/or any functionality necessary to support the subject matter described herein. For example, the network node 1400 may include user interface equipment to allow input of information into the network node 1400 and to allow output of information from the network node 1400. This may allow a user to perform diagnostic, maintenance, repair, and other administrative functions for the network node 1400.

[164] Figure 15 is a block diagram of a host 1500, which may be an embodiment of the host 1216 of Figure 12, in accordance with various aspects described herein. As used herein, the host 1500 may be or comprise various combinations hardware and/or software, including a standalone server, a blade server, a cloud-implemented server, a distributed server, a virtual machine, container, or processing resources in a server farm. The host 1500 may provide one or more services to one or more UEs.

[165] The host 1500 includes processing circuitry 1502 that is operatively coupled via a bus 1504 to an input/output interface 1506, a network interface 1508, a power source 1510, and a memory 1512. Other components may be included in other embodiments. Features of these components may be substantially similar to those described with respect to the devices of previous figures, such as Figure 13, such that the descriptions thereof are generally applicable to the corresponding components of host 1500.

[166] The memory 1512 may include one or more computer programs including one or more host application programs 1514 and data 1516, which may include user data, e.g., data generated by a UE for the host 1500 or data generated by the host 1500 for a UE. Embodiments of the host 1500 may utilize only a subset or all of the components shown. The host application programs 1514 may be implemented in a container-based architecture and may provide support for video codecs (e.g., Versatile Video Coding (VVC), High Efficiency Video Coding (HE VC), Advanced Video Coding (A VC), MPEG, VP9) and audio codecs (e.g., FLAC, Advanced Audio Coding (AAC), MPEG, G.711), including transcoding for multiple different classes, types, or implementations of UEs (e.g., handsets, desktop computers, wearable display systems, heads-up display systems). The host application programs 1514 may also provide for user authentication and licensing checks and may periodically report health, routes, and content availability to a central node, such as a device in or on the edge of a core network. Accordingly, the host 1500 may select and/or indicate a different host for over-the-top services for a UE. The host application programs 1514 may support various protocols, such as the HTTP Live Streaming (HLS) protocol, Real-Time Messaging Protocol (RTMP), Real-Time Streaming Protocol (RTSP), Dynamic Adaptive Streaming over HTTP (MPEG-DASH), etc.

[167] Figure 16 is a block diagram illustrating a virtualization environment 1600 in which functions implemented by some embodiments may be virtualized. In the present context, virtualizing means creating virtual versions of apparatuses or devices which may include virtualizing hardware platforms, storage devices and networking resources. As used herein, virtualization can be applied to any device described herein, or components thereof, and relates to an implementation in which at least a portion of the functionality is implemented as one or more virtual components. Some or all of the functions described herein may be implemented as virtual components executed by one or more virtual machines (VMs) implemented in one or more virtual environments 1600 hosted by one or more of hardware nodes, such as a hardware computing device that operates as a network node, UE, core network node, or host. Further, in embodiments in which the virtual node does not require radio connectivity (e.g., a core network node or host), then the node may be entirely virtualized.

[168] Applications 1602 (which may alternatively be called software instances, virtual appliances, network functions, virtual nodes, virtual network functions, etc.) are run in the virtualization environment Q400 to implement some of the features, functions, and/or benefits of some of the embodiments disclosed herein.

[169] Hardware 1604 includes processing circuitry, memory that stores software and/or instructions executable by hardware processing circuitry, and/or other hardware devices as described herein, such as a network interface, input/output interface, and so forth. Software may be executed by the processing circuitry to instantiate one or more virtualization layers 1606 (also referred to as hypervisors or virtual machine monitors (VMMs)), provide VMs 1608a and 1608b (one or more of which may be generally referred to as VMs 1608), and/or perform any of the functions, features and/or benefits described in relation with some embodiments described herein. The virtualization layer 1606 may present a virtual operating platform that appears like networking hardware to the VMs 1608.

[170] The VMs 1608 comprise virtual processing, virtual memory, virtual networking or interface and virtual storage, and may be run by a corresponding virtualization layer 1606. Different embodiments of the instance of a virtual appliance 1602 may be implemented on one or more of VMs 1608, and the implementations may be made in different ways. Virtualization of the hardware is in some contexts referred to as network function virtualization (NFV). NFV may be used to consolidate many network equipment types onto industry standard high volume server hardware, physical switches, and physical storage, which can be located in data centers, and customer premise equipment.

[171] In the context of NFV, a VM 1608 may be a software implementation of a physical machine that runs programs as if they were executing on a physical, non-virtualized machine. Each of the VMs 1608, and that part of hardware 1604 that executes that VM, be it hardware dedicated to that VM and/or hardware shared by that VM with others of the VMs, forms separate virtual network elements. Still in the context of NFV, a virtual network function is responsible for handling specific network functions that run in one or more VMs 1608 on top of the hardware 1604 and corresponds to the application 1602.

[172] Hardware 1604 may be implemented in a standalone network node with generic or specific components. Hardware 1604 may implement some functions via virtualization. Alternatively, hardware 1604 may be part of a larger cluster of hardware (e.g. such as in a data center or CPE) where many hardware nodes work together and are managed via management and orchestration 1610, which, among others, oversees lifecycle management of applications 1602. In some embodiments, hardware 1604 is coupled to one or more radio units that each include one or more transmitters and one or more receivers that may be coupled to one or more antennas. Radio units may communicate directly with other hardware nodes via one or more appropriate network interfaces and may be used in combination with the virtual components to provide a virtual node with radio capabilities, such as a radio access node or a base station. In some embodiments, some signaling can be provided with the use of a control system 1612 which may alternatively be used for communication between hardware nodes and radio units.

[173] Figure 17 shows a communication diagram of a host 1702 communicating via a network node 1704 with a UE 1706 over a partially wireless connection in accordance with some embodiments. Example implementations, in accordance with various embodiments, of the UE (such as a UE 1212a of Figure 12 and/or UE 1300 of Figure 13), network node (such as network node 1210a of Figure 12), and host (such as host 1216 of Figure 12 and/or host 1500 of Figure 15) discussed in the preceding paragraphs will now be described with reference to Figure 17.

[174] Eike host 1500, embodiments of host 1702 include hardware, such as a communication interface, processing circuitry, and memory. The host 1702 also includes software, which is stored in or accessible by the host 1702 and executable by the processing circuitry. The software includes a host application that may be operable to provide a service to a remote user, such as the UE 1706 connecting via an over- the-top (OTT) connection 1750 extending between the UE 1706 and host 1702. In providing the service to the remote user, a host application may provide user data which is transmitted using the OTT connection 1750.

[175] The network node 1704 includes hardware enabling it to communicate with the host 1702 and UE 1706. The connection 1760 may be direct or pass through a core network (like core network 1206 of Figure 12) and/or one or more other intermediate networks, such as one or more public, private, or hosted networks. For example, an intermediate network may be a backbone network or the Internet.

[176] The UE 1706 includes hardware and software, which is stored in or accessible by UE 1706 and executable by the UE’s processing circuitry. The software includes a client application, such as a web browser or operator-specific “app” that may be operable to provide a service to a human or non-human user via UE 1706 with the support of the host 1702. In the host 1702, an executing host application may communicate with the executing client application via the OTT connection 1750 terminating at the UE 1706 and host 1702. In providing the service to the user, the UE’s client application may receive request data from the host's host application and provide user data in response to the request data. The OTT connection 1750 may transfer both the request data and the user data. The UE’s client application may interact with the user to generate the user data that it provides to the host application through the OTT connection 1750.

[177] The OTT connection 1750 may extend via a connection 1760 between the host 1702 and the network node 1704 and via a wireless connection 1770 between the network node 1704 and the UE 1706 to provide the connection between the host 1702 and the UE 1706. The connection 1760 and wireless connection 1770, over which the OTT connection 1750 may be provided, have been drawn abstractly to illustrate the communication between the host 1702 and the UE 1706 via the network node 1704, without explicit reference to any intermediary devices and the precise routing of messages via these devices.

[178] As an example of transmitting data via the OTT connection 1750, in step 1708, the host 1702 provides user data, which may be performed by executing a host application. In some embodiments, the user data is associated with a particular human user interacting with the UE 1706. In other embodiments, the user data is associated with a UE 1706 that shares data with the host 1702 without explicit human interaction. In step 1710, the host 1702 initiates a transmission carrying the user data towards the UE 1706. The host 1702 may initiate the transmission responsive to a request transmitted by the UE 1706. The request may be caused by human interaction with the UE 1706 or by operation of the client application executing on the UE 1706. The transmission may pass via the network node 1704, in accordance with the teachings of the embodiments described throughout this disclosure. Accordingly, in step 1712, the network node 1704 transmits to the UE 1706 the user data that was carried in the transmission that the host 1702 initiated, in accordance with the teachings of the embodiments described throughout this disclosure. In step 1714, the UE 1706 receives the user data carried in the transmission, which may be performed by a client application executed on the UE 1706 associated with the host application executed by the host 1702.

[179] In some examples, the UE 1706 executes a client application which provides user data to the host 1702. The user data may be provided in reaction or response to the data received from the host 1702. Accordingly, in step 1716, the UE 1706 may provide user data, which may be performed by executing the client application. In providing the user data, the client application may further consider user input received from the user via an input/output interface of the UE 1706. Regardless of the specific manner in which the user data was provided, the UE 1706 initiates, in step 1718, transmission of the user data towards the host 1702 via the network node 1704. In step 1720, in accordance with the teachings of the embodiments described throughout this disclosure, the network node 1704 receives user data from the UE 1706 and initiates transmission of the received user data towards the host 1702. In step 1722, the host 1702 receives the user data carried in the transmission initiated by the UE 1706.

[180] One or more of the various embodiments improve the performance of OTT services provided to the UE 1706 using the OTT connection 1750, in which the wireless connection 1770 forms the last segment. More precisely, the teachings of these embodiments may improve the accuracy with which UEs may be synchronized and thereby provide benefits such as improved accuracy of SL based positioning estimations.

[181] In an example scenario, factory status information may be collected and analyzed by the host 1702. As another example, the host 1702 may process audio and video data which may have been retrieved from a UE for use in creating maps. As another example, the host 1702 may collect and analyze real-time data to assist in controlling vehicle congestion (e.g., controlling traffic lights). As another example, the host 1702 may store surveillance video uploaded by a UE. As another example, the host 1702 may store or control access to media content such as video, audio, VR or AR which it can broadcast, multicast or unicast to UEs. As other examples, the host 1702 may be used for energy pricing, remote control of non-time critical electrical load to balance power generation needs, location services, presentation services (such as compiling diagrams etc. from data collected from remote devices), or any other function of collecting, retrieving, storing, analyzing and/or transmitting data.

[182] In some examples, a measurement procedure may be provided for the purpose of monitoring data rate, latency and other factors on which the one or more embodiments improve. There may further be an optional network functionality for reconfiguring the OTT connection 1750 between the host 1702 and UE 1706, in response to variations in the measurement results. The measurement procedure and/or the network functionality for reconfiguring the OTT connection may be implemented in software and hardware of the host 1702 and/or UE 1706. In some embodiments, sensors (not shown) may be deployed in or in association with other devices through which the OTT connection 1750 passes; the sensors may participate in the measurement procedure by supplying values of the monitored quantities exemplified above, or supplying values of other physical quantities from which software may compute or estimate the monitored quantities. The reconfiguring of the OTT connection 1750 may include message format, retransmission settings, preferred routing etc.; the reconfiguring need not directly alter the operation of the network node 1704. Such procedures and functionalities may be known and practiced in the art. In certain embodiments, measurements may involve proprietary UE signaling that facilitates measurements of throughput, propagation times, latency and the like, by the host 1702. The measurements may be implemented in that software causes messages to be transmitted, in particular empty or ‘dummy’ messages, using the OTT connection 1750 while monitoring propagation times, errors, etc.

[183] Although the computing devices described herein (e.g., UEs, network nodes, hosts) may include the illustrated combination of hardware components, other embodiments may comprise computing devices with different combinations of components. It is to be understood that these computing devices may comprise any suitable combination of hardware and/or software needed to perform the tasks, features, functions and methods disclosed herein. Determining, calculating, obtaining or similar operations described herein may be performed by processing circuitry, which may process information by, for example, converting the obtained information into other information, comparing the obtained information or converted information to information stored in the network node, and/or performing one or more operations based on the obtained information or converted information, and as a result of said processing making a determination. Moreover, while components are depicted as single boxes located within a larger box, or nested within multiple boxes, in practice, computing devices may comprise

31 multiple different physical components that make up a single illustrated component, and functionality may be partitioned between separate components. For example, a communication interface may be configured to include any of the components described herein, and/or the functionality of the components may be partitioned between the processing circuitry and the communication interface. In another example, non-computationally intensive functions of any of such components may be implemented in software or firmware and computationally intensive functions may be implemented in hardware.

[184] In certain embodiments, some or all of the functionality described herein may be provided by processing circuitry executing instructions stored on in memory, which in certain embodiments may be a computer program product in the form of a non-transitory computer-readable storage medium. In alternative embodiments, some or all of the functionality may be provided by the processing circuitry without executing instructions stored on a separate or discrete device -readable storage medium, such as in a hard-wired manner. In any of those particular embodiments, whether executing instructions stored on a non-transitory computer-readable storage medium or not, the processing circuitry can be configured to perform the described functionality. The benefits provided by such functionality are not limited to the processing circuitry alone or to other components of the computing device, but are enjoyed by the computing device as a whole, and/or by end users and a wireless network generally.

EMBODIMENTS

Group A Embodiments

1. A method performed by a target user equipment, UE, for performing sidelink, SL, positioning using one or more reference UEs, the method comprising: selecting one or more reference UEs from one or more candidate UEs based on, for each candidate UE, an identification of a SL synchronization source utilized by the candidate UE utilized by the candidate UE.

2. The method of embodiment 1 wherein the step of selecting comprises: receiving, for each candidate UE, the identification of the SL synchronization source utilized by the candidate UE.

3. The method of embodiment 2 wherein the step of selecting further comprises: selecting the one or more reference UEs as candidate UEs that utilize the same SL synchronization source.

4. The method of embodiment 2 or 3 wherein the step of selecting further comprises: responsive to an insufficient number of candidate UEs utilizing the same SL synchronization source, selecting the one or more reference UEs as candidate UEs that utilize similar synchronization sources.

5. The method of embodiment 4 wherein two SL synchronization sources are similar when one of the following conditions is met: the two SL synchronization sources are associated with priority levels within a first predetermined range; a difference between signalling radio quality of the SL synchronization sources is within a second predetermined range; and timing differences of the two SL synchronization sources are within a third predetermined range.

6. The method of any previous embodiment wherein the step of selecting comprises: selecting the one or more reference UEs as candidate UEs that provide a radio channel quality above a first threshold.

7. The method of any previous embodiment wherein a minimum number of reference UEs is required for positioning the target UE with a required accuracy, and wherein the step of selecting comprises selecting a first set of candidate UEs as the one or more reference UEs responsive to the first set of candidate UEs: utilizing the same SL synchronization source; and comprising a number of candidate UEs greater than or equal to the minimum number of reference UEs. The method of any previous embodiment wherein the step of selecting comprises: selecting one or more reference UEs based on a quality of a SL synchronization source utilized by candidate UEs. The method of any previous embodiment wherein the step of selecting comprises: selecting one or more reference UEs based on a priority of a SL synchronization source utilized by candidate UEs. The method of any previous embodiment further comprising receiving, for each candidate UE, an indication of a priority of the SL synchronization source utilized by the candidate UE. The method of any previous embodiment further comprising receiving, for each candidate UE, an indication of a type of the SL synchronization source utilized by the candidate UE. The method of embodiment 1 further comprising one or more of: transmitting, to the one or more candidate UEs, an identification of a SL synchronization source utilized by the target UE; and receiving, from each candidate UE, an indication of whether the candidate UE may operate as a reference UE for the target UE. The method of embodiment 12 further comprising: transmitting, to the one or more candidate UEs, one or more of: an indication of a priority of the SL synchronization source utilized by the target UE, and a type of the SL synchronization source utilized by the target UE. The method of any previous embodiment further comprising initiating reselection of the one or more reference UEs responsive to an additional candidate UE being discovered that meets one or more of the following conditions: the additional candidate UE utilizes a high-quality SL synchronization source; and the additional candidate UE utilizes a high priority SL synchronization source. The method of any previous embodiments wherein the target UE is configured with one or more of: one or more supported SL positioning methods; and for each supported SL positioning method: an indication of whether accurate synchronization is required between the one or more reference UEs and/or between the reference UEs and the target UE; and an indication of a minimum number of reference UEs for positioning the target UE with a required accuracy. The method of any previous embodiment wherein the target UE triggers selection and/or reselection of the one or more reference UEs responsive to the target UE needing to be positioned via SL based positioning. A method performed by a candidate user equipment, UE, for enabling performance of sidelink, SL, positioning of a target UE using one or more reference UEs, the method comprising: transmitting to the target UE one or more of: a type of the SL synchronization source utilized by the candidate UE; a priority of the SL synchronization source utilized by the candidate UE; and an identification of the SL synchronization source utilized by the candidate UE. A method performed by a candidate user equipment, UE, for enabling performance of sidelink, SL, positioning of a target UE using one or more reference UEs, the method comprising: receiving from the target UE an identification of a SL synchronization source utilized by the target UE, determining whether a SL synchronization source utilized by the candidate UE is the same as the SL synchronization source utilized by the target UE, and responsive to the SL synchronization source utilized by the candidate UE being the same as the SL synchronization source utilized by the target UE, indicating to the target UE that the candidate UE may be used as a reference UE. The method of any of the previous embodiments, further comprising: providing user data; and forwarding the user data to a host via the transmission to the network node.

Group B Embodiments

20. A method in a network node for enabling performance of SL positioning of a potential target UE using a plurality of reference UEs, the method comprising: configuring the potential target UE with one or more of: one or more supported SL positioning methods; and for each supported SL positioning method: an indication of whether accurate synchronization is required between the one or more reference UEs and/or between the reference UEs and the potential target UE; and an indication of a minimum number of reference UEs for positioning the potential target UE with a required accuracy.

Group C Embodiments

21. A user equipment, UE, for performing sidelink, SL, positioning using one or more reference UEs, comprising: processing circuitry configured to cause the user equipment to perform any of the steps of any of the Group A embodiments; and power supply circuitry configured to supply power to the processing circuitry.

22. A network node for enabling performance of SL positioning of a potential target UE using a plurality of reference UEs, the network node comprising: processing circuitry configured to cause the network node to perform any of the steps of any of the Group B embodiments; power supply circuitry configured to supply power to the processing circuitry.

23. A user equipment, UE, for enabling performance of sidelink, SL, positioning of a target UE using one or more reference UEs: processing circuitry configured to cause the user equipment to perform any of the steps of any of the Group A embodiments; and power supply circuitry configured to supply power to the processing circuitry.

24. A user equipment (UE) for performing sidelink, SL, positioning using one or more reference UEs, the UE comprising: an antenna configured to send and receive wireless signals; radio front-end circuitry connected to the antenna and to processing circuitry, and configured to condition signals communicated between the antenna and the processing circuitry; the processing circuitry being configured to perform any of the steps of any of the Group A embodiments; an input interface connected to the processing circuitry and configured to allow input of information into the UE to be processed by the processing circuitry; an output interface connected to the processing circuitry and configured to output information from the UE that has been processed by the processing circuitry; and a battery connected to the processing circuitry and configured to supply power to the UE.

25. A user equipment (UE) for enabling performance of sidelink, SL, positioning of a target UE using one or more reference UE: an antenna configured to send and receive wireless signals; radio front-end circuitry connected to the antenna and to processing circuitry, and configured to condition signals communicated between the antenna and the processing circuitry; the processing circuitry being configured to perform any of the steps of any of the Group A embodiments; an input interface connected to the processing circuitry and configured to allow input of information into the UE to be processed by the processing circuitry; an output interface connected to the processing circuitry and configured to output information from the UE that has been processed by the processing circuitry; and a battery connected to the processing circuitry and configured to supply power to the UE.

26. A host configured to operate in a communication system to provide an over-the-top (OTT) service, the host comprising: processing circuitry configured to provide user data; and a network interface configured to initiate transmission of the user data to a cellular network for transmission to a user equipment (UE), wherein the UE comprises a communication interface and processing circuitry, the communication interface and processing circuitry of the UE being configured to perform any of the steps of any of the Group A embodiments to receive the user data from the host. 27. The host of the previous embodiment, wherein the cellular network further includes a network node configured to communicate with the UE to transmit the user data to the UE from the host.

28. The host of the previous 2 embodiments, wherein: the processing circuitry of the host is configured to execute a host application, thereby providing the user data; and the host application is configured to interact with a client application executing on the UE, the client application being associated with the host application.

29. A method implemented by a host operating in a communication system that further includes a network node and a user equipment (UE), the method comprising: providing user data for the UE; and initiating a transmission carrying the user data to the UE via a cellular network comprising the network node, wherein the UE performs any of the operations of any of the Group A embodiments to receive the user data from the host.

30. The method of the previous embodiment, further comprising: at the host, executing a host application associated with a client application executing on the UE to receive the user data from the UE.

31. The method of the previous embodiment, further comprising: at the host, transmitting input data to the client application executing on the UE, the input data being provided by executing the host application, wherein the user data is provided by the client application in response to the input data from the host application.

32. A host configured to operate in a communication system to provide an over-the-top (OTT) service, the host comprising: processing circuitry configured to provide user data; and a network interface configured to initiate transmission of the user data to a cellular network for transmission to a user equipment (UE), wherein the UE comprises a communication interface and processing circuitry, the communication interface and processing circuitry of the UE being configured to perform any of the steps of any of the Group A embodiments to transmit the user data to the host.

33. The host of the previous embodiment, wherein the cellular network further includes a network node configured to communicate with the UE to transmit the user data from the UE to the host.

34. The host of the previous 2 embodiments, wherein: the processing circuitry of the host is configured to execute a host application, thereby providing the user data; and the host application is configured to interact with a client application executing on the UE, the client application being associated with the host application.

35. A method implemented by a host configured to operate in a communication system that further includes a network node and a user equipment (UE), the method comprising: at the host, receiving user data transmitted to the host via the network node by the UE, wherein the UE performs any of the steps of any of the Group A embodiments to transmit the user data to the host.

36. The method of the previous embodiment, further comprising: at the host, executing a host application associated with a client application executing on the UE to receive the user data from the UE.

37. The method of the previous embodiment, further comprising: at the host, transmitting input data to the client application executing on the UE, the input data being provided by executing the host application, wherein the user data is provided by the client application in response to the input data from the host application.

38. A host configured to operate in a communication system to provide an over-the-top (OTT) service, the host comprising: processing circuitry configured to provide user data; and a network interface configured to initiate transmission of the user data to a network node in a cellular network for transmission to a user equipment (UE), the network node having a communication interface and processing circuitry, the processing circuitry of the network node configured to perform any of the operations of any of the Group B embodiments to transmit the user data from the host to the UE.

39. The host of the previous embodiment, wherein: the processing circuitry of the host is configured to execute a host application that provides the user data; and the UE comprises processing circuitry configured to execute a client application associated with the host application to receive the transmission of user data from the host.

40. A method implemented in a host configured to operate in a communication system that further includes a network node and a user equipment (UE), the method comprising: providing user data for the UE; and initiating a transmission carrying the user data to the UE via a cellular network comprising the network node, wherein the network node performs any of the operations of any of the Group B embodiments to transmit the user data from the host to the UE.

41. The method of the previous embodiment, further comprising, at the network node, transmitting the user data provided by the host for the UE.

42. The method of any of the previous 2 embodiments, wherein the user data is provided at the host by executing a host application that interacts with a client application executing on the UE, the client application being associated with the host application.

43. A communication system configured to provide an over-the-top service, the communication system comprising: a host comprising: processing circuitry configured to provide user data for a user equipment (UE), the user data being associated with the over-the-top service; and a network interface configured to initiate transmission of the user data toward a cellular network node for transmission to the UE, the network node having a communication interface and processing circuitry, the processing circuitry of the network node configured to perform any of the operations of any of the Group B embodiments to transmit the user data from the host to the UE.

44. The communication system of the previous embodiment, further comprising: the network node; and/or the user equipment.

45. A host configured to operate in a communication system to provide an over-the-top (OTT) service, the host comprising: processing circuitry configured to initiate receipt of user data; and a network interface configured to receive the user data from a network node in a cellular network, the network node having a communication interface and processing circuitry, the processing circuitry of the network node configured to perform any of the operations of any of the Group B embodiments to receive the user data from a user equipment (UE) for the host.

46. The host of the previous embodiment, wherein: the processing circuitry of the host is configured to execute a host application, thereby providing the user data; and the host application is configured to interact with a client application executing on the UE, the client application being associated with the host application.

47. The host of the any of the previous 2 embodiments, wherein the initiating receipt of the user data comprises requesting the user data.

48. A method implemented by a host configured to operate in a communication system that further includes a network node and a user equipment (UE), the method comprising: at the host, initiating receipt of user data from the UE, the user data originating from a transmission which the network node has received from the UE, wherein the network node performs any of the steps of any of the Group B embodiments to receive the user data from the UE for the host.

49. The method of the previous embodiment, further comprising at the network node, transmitting the received user data to the host. ABBREVIATIONS

At least some of the following abbreviations may be used in this disclosure. If there is an inconsistency between abbreviations, preference should be given to how it is used above. If listed multiple times below, the first listing should be preferred over any subsequent listing(s).

SI System Information

NAS Non-Access Stratum

LMF Location Management Function

AMF Access Management Function lx RTT CDMA2000 lx Radio Transmission Technology

3GPP 3rd Generation Partnership Project

5G 5th Generation

6G 6th Generation

ABS Almost Blank Subframe

ARQ Automatic Repeat Request

AWGN Additive White Gaussian Noise

BCCH Broadcast Control Channel

BCH Broadcast Channel

CA Carrier Aggregation

CC Carrier Component

CCCH SDU Common Control Channel SDU

CDMA Code Division Multiplexing Access

CGI Cell Global Identifier

OR Channel Impulse Response

CP Cyclic Prefix

CPICH Common Pilot Channel

CPICH Ec/No CPICH Received energy per chip divided by the power density in the band

CQI Channel Quality information

C-RNTI Cell RNTI

CSI Channel State Information

DCCH Dedicated Control Channel

DL Downlink

DM Demodulation

DMRS Demodulation Reference Signal

DRX Discontinuous Reception DTX Discontinuous Transmission

DTCH Dedicated Traffic Channel

DUT Device Under Test

E-CID Enhanced Cell-ID (positioning method) eMBMS evolved Multimedia Broadcast Multicast Services

E-SMLC Evolved-Serving Mobile Location Centre

ECGI Evolved CGI eNB E-UTRAN NodeB ePDCCH Enhanced Physical Downlink Control Channel

E-SMLC Evolved Serving Mobile Location Center

E-UTRA Evolved UTRA

E-UTRAN Evolved UTRAN

FDD Frequency Division Duplex

FFS For Further Study gNB Base station in NR

GNSS Global Navigation Satellite System

HARQ Hybrid Automatic Repeat Request

HO Handover

HSPA High Speed Packet Access

HRPD High Rate Packet Data

LOS Line of Sight

LPP LTE Positioning Protocol

LTE Long-Term Evolution

MAC Medium Access Control

MAC Message Authentication Code

MBSFN Multimedia Broadcast multicast service Single Frequency Network

MBSFN ABS MBSFN Almost Blank Subframe

MDT Minimization of Drive Tests

MIB Master Information Block

MME Mobility Management Entity

MSC Mobile Switching Center

NPDCCH Narrowband Physical Downlink Control Channel

NR New Radio

OCNG OFDMA Channel Noise Generator

OFDM Orthogonal Frequency Division Multiplexing

OFDMA Orthogonal Frequency Division Multiple Access OSS Operations Support System

OTDOA Observed Time Difference of Arrival

O&M Operation and Maintenance

PBCH Physical Broadcast Channel

P-CCPCH Primary Common Control Physical Channel

PCell Primary Cell

PCFICH Physical Control Format Indicator Channel

PDCCH Physical Downlink Control Channel

PDCP Packet Data Convergence Protocol

PDP Profile Delay Profile

PDSCH Physical Downlink Shared Channel

PGW Packet Gateway

PHICH Physical Hybrid- ARQ Indicator Channel

PLMN Public Land Mobile Network

PMI Precoder Matrix Indicator

PRACH Physical Random Access Channel

PRS Positioning Reference Signal

PSS Primary Synchronization Signal

PUCCH Physical Uplink Control Channel

PUSCH Physical Uplink Shared Channel

RACH Random Access Channel

QAM Quadrature Amplitude Modulation

RAN Radio Access Network

RAT Radio Access Technology

RLC Radio Link Control

RLM Radio Link Management

RNC Radio Network Controller

RNTI Radio Network Temporary Identifier

RRC Radio Resource Control

RRM Radio Resource Management

RS Reference Signal

RSCP Received Signal Code Power

RSRP Reference Symbol Received Power OR Reference Signal Received Power

RSRQ Reference Signal Received Quality OR Reference Symbol Received Quality

RSSI Received Signal Strength Indicator

RSTD Reference Signal Time Difference SCH Synchronization Channel

SCell Secondary Cell

SDAP Service Data Adaptation Protocol

SDU Service Data Unit

SFN System Frame Number

SGW Serving Gateway

SI System Information

SIB System Information Block

SNR Signal to Noise Ratio

SON Self Optimized Network

SS Synchronization Signal

SSS Secondary Synchronization Signal

TDD Time Division Duplex

TDOA Time Difference of Arrival

TOA Time of Arrival

TSS Tertiary Synchronization Signal

TTI Transmission Time Interval

UE User Equipment

UL Uplink

USIM Universal Subscriber Identity Module

UTDOA Uplink Time Difference of Arrival WCDMA Wide CDMA

WLAN Wide Local Area Network

Claims

1. A method performed by a target user equipment, UE, for performing sidelink, SL, positioning using one or more reference UEs, characterized in that the method comprises: selecting (802) one or more reference UEs from one or more candidate UEs based on, for each candidate UE, an identification of a SL synchronization source utilized by the candidate UE utilized by the candidate UE.

2. The method of claim 1 wherein the method further comprise: receiving, for each candidate UE, the identification of the SL synchronization source utilized by the candidate UE.

3. The method of claim 2 wherein the selecting further comprises: selecting the one or more reference UEs as candidate UEs that utilize the same SL synchronization source.

4. The method of claim 2 or 3 wherein the selecting further comprises: responsive to an insufficient number of candidate UEs utilizing the same SL synchronization source, selecting the one or more reference UEs as candidate UEs that utilize similar synchronization sources.

5. The method of claim 4 wherein two SL synchronization sources are similar when one of the following conditions is met: the two SL synchronization sources are associated with priority levels within a first predetermined range; a difference between signalling radio quality of the SL synchronization sources is within a second predetermined range; and timing differences of the two SL synchronization sources are within a third predetermined range.

6. The method of any one of claims 1 to 5, wherein the selecting comprises: selecting the one or more reference UEs as candidate UEs that provide a radio channel quality above a first threshold.

7. The method of any one of claims 1 to 6, wherein a minimum number of reference UEs is required for positioning the target UE with a required accuracy, and wherein the step of selecting comprises selecting a first set of candidate UEs as the one or more reference UEs responsive to the first set of candidate UEs: utilizing the same SL synchronization source; and comprising a number of candidate UEs greater than or equal to the minimum number of reference UEs. The method of any one of claims 1 to 7, wherein the selecting comprises: selecting one or more reference UEs based on a quality of a SL synchronization source utilized by candidate UEs. The method of any one of claims 1 to 8, wherein the selecting comprises: selecting one or more reference UEs based on a priority of a SL synchronization source utilized by candidate UEs. The method of any one of claims 1 to 9, further comprising receiving, for each candidate UE, an indication of a priority of the SL synchronization source utilized by the candidate UE. The method of any one of claims 1 to 9, further comprising receiving, for each candidate UE, an indication of a type of the SL synchronization source utilized by the candidate UE. The method of claim 1 further comprising one or more of: transmitting, to the one or more candidate UEs, an identification of a SL synchronization source utilized by the target UE; and receiving, from each candidate UE, an indication of whether the candidate UE may operate as a reference UE for the target UE. The method of claim 12 further comprising: transmitting, to the one or more candidate UEs, one or more of: an indication of a priority of the SL synchronization source utilized by the target UE, and a type of the SL synchronization source utilized by the target UE. The method of any one of claims 1 to 13, further comprising initiating reselection of the one or more reference UEs responsive to an additional candidate UE being discovered that meets one or more of the following conditions: the additional candidate UE utilizes a high-quality SL synchronization source; and the additional candidate UE utilizes a high priority SL synchronization source. The method of any one of claims 1 to 14, wherein the target UE is configured with one or more of: one or more supported SL positioning methods; and for each supported SL positioning method: an indication of whether accurate synchronization is required between the one or more reference UEs and/or between the reference UEs and the target UE; and an indication of a minimum number of reference UEs for positioning the target UE with a required accuracy. The method of any one of claims 1 to 15, wherein the target UE triggers selection and/or reselection of the one or more reference UEs responsive to the target UE needing to be positioned via SL based positioning. A method performed by a candidate user equipment, UE, for enabling performance of sidelink, SL, positioning of a target UE using one or more reference UEs, characterized in that method comprises: transmitting (902) to the target UE one or more of: a type of the SL synchronization source utilized by the candidate UE; a priority of the SL synchronization source utilized by the candidate UE; and an identification of the SL synchronization source utilized by the candidate UE. A method performed by a candidate user equipment, UE, for enabling performance of sidelink, SL, positioning of a target UE using one or more reference UEs, characterized in that method comprises: receiving (1002) from the target UE an identification of a SL synchronization source utilized by the target UE, determining (1004) whether a SL synchronization source utilized by the candidate UE is the same as the SL synchronization source utilized by the target UE, and responsive to the SL synchronization source utilized by the candidate UE being the same as the SL synchronization source utilized by the target UE, indicating (1006) to the target UE that the candidate UE may be used as a reference UE. A method in a network node for enabling performance of sidelink, SL, positioning of a potential target UE using a plurality of reference UEs, characterized in that the method comprises: configuring (1102) the potential target UE with one or more of: one or more supported SL positioning methods; and for each supported SL positioning method: an indication of whether accurate synchronization is required between the one or more reference UEs and/or between the reference Ues and the potential target UE; and an indication of a minimum number of reference Ues for positioning the potential target UE with a required accuracy. A target user equipment, UE, (1300) for performing sidelink, SL, positioning using one or more reference Ues, the target UE comprising processing circuitry (1302) and memory (1310), characterized in that the memory containing instructions executable by the processing circuitry whereby the target UE is operable to: select (802) one or more reference UEs from one or more candidate Ues based on, for each candidate UE, an identification of a SL synchronization source utilized by the candidate UE utilized by the candidate UE. The target UE as claimed in claim 20 wherein the memory further contains instructions executable by the processing circuitry whereby the target UE is operable to perform the method as claimed in any one of claims 2 to 16. A candidate user equipment, UE, (1300) for enabling performance of sidelink, SL, positioning of a target UE using one or more reference UEs, the candidate UE comprising processing circuitry (1302) and memory (1310), characterized in that the memory containing instructions executable by the processing circuitry whereby the candidate UE is operable to: transmit to the target UE one or more of: a type of the SL synchronization source utilized by the candidate UE; a priority of the SL synchronization source utilized by the candidate UE; and an identification of the SL synchronization source utilized by the candidate UE. A candidate user equipment, UE, (1300) for enabling performance of sidelink, SL, positioning of a target UE using one or more reference UEs, the candidate UE comprising processing circuitry (1302) and memory (1310), characterized in that the memory containing instructions executable by the processing circuitry whereby the candidate UE is operable to: receive from the target UE an identification of a SL synchronization source utilized by the target UE, determine whether a SL synchronization source utilized by the candidate UE is the same as the SL synchronization source utilized by the target UE, and responsive to the SL synchronization source utilized by the candidate UE being the same as the SL synchronization source utilized by the target UE, indicate to the target UE that the candidate UE may be used as a reference UE. A network node (1400) for enabling performance of sidelink, SL, positioning of a potential target UE using a plurality of reference UEs, the network node comprising processing circuitry (1402) and memory (1410), characterized in that the memory containing instructions executable by the processing circuitry whereby the network node is operable to: configure the potential target UE with one or more supported SL positioning methods; and for each supported SL positioning method configuring the potential target UE with: an indication of whether accurate synchronization is required between the one or more reference UEs and/or between the reference UEs and the potential target UE; and an indication of a minimum number of reference UEs for positioning the potential target UE with a required accuracy. A target user equipment, UE, for performing sidelink, SL, positioning using one or more reference UEs, characterized in that the target UE is operable to: select (802) one or more reference UEs from one or more candidate UEs based on, for each candidate UE, an identification of a SL synchronization source utilized by the candidate UE utilized by the candidate UE. The target UE as claimed in claim 25 wherein the target UE is further operable to perform the method as claimed in any one of claims 2 to 16. A candidate user equipment, UE, for enabling performance of sidelink, SL, positioning of a target UE using one or more reference UEs, characterized in that the candidate UE is operable to: transmit (902) to the target UE one or more of: a type of the SL synchronization source utilized by the candidate UE; a priority of the SL synchronization source utilized by the candidate UE; and an identification of the SL synchronization source utilized by the candidate UE.

28. A candidate user equipment, UE, for enabling performance of sidelink, SL, positioning of a target UE using one or more reference UEs, characterized in that the candidate UE is operable to: receive (1002) from the target UE an identification of a SL synchronization source utilized by the target UE, determine (1004) whether a SL synchronization source utilized by the candidate UE is the same as the SL synchronization source utilized by the target UE, and responsive to the SL synchronization source utilized by the candidate UE being the same as the SL synchronization source utilized by the target UE, indicate (1006) to the target UE that the candidate UE may be used as a reference UE.

29. A network node for enabling performance of sidelink, SL, positioning of a potential target UE using a plurality of reference UEs, characterized in that the network node is operable to: configure (1102) the potential target UE with one or more supported SL positioning methods; and for each supported SL positioning method configuring the potential target UE with: an indication of whether accurate synchronization is required between the one or more reference UEs and/or between the reference UEs and the potential target UE; and an indication of a minimum number of reference UEs for positioning the potential target UE with a required accuracy.

30. A computer program, comprising instructions which, when executed on at least one processor, cause the at least one processor to carry out a method according to any of claims 1 to 16.

31. A carrier containing the computer program according to claim 30, wherein the carrier comprises one of an electronic signal, optical signal, radio signal or computer readable storage medium.

32. A computer-readable medium comprising instructions that, when executed on at least one processor, cause the at least one processor to perform the method according to any of claims 1 to 16.

33. A computer program product comprising non transitory computer readable media having stored thereon a computer program according to claim 30.