Time compensation via sidelink relays in communication systems

Abstract

An apparatus includes a memory and processing circuitry. The processing circuitry is configured to cause the apparatus to: request synchronization reference source information from a user equipment; and determining whether to perform offset compensation based on the synchronization reference source information, and in response to determining to perform offset compensation, obtaining a first propagation delay associated with the apparatus, determining a reference time based on the first propagation delay, and forwarding the reference time to the user equipment.

Description

Technical Field

[0001] One or more example embodiments relate to a wireless communication network. Background Art

[0002] The fifth generation (5G) wireless communication network is the next generation of mobile communication networks. Standards for 5G communication networks are currently being developed by the Third Generation Partnership Project (3GPP). These standards are known as 3GPP New Radio (NR) standards. Summary of the invention

[0003] The scope of protection sought for the various example embodiments is set out by the independent claims. Example embodiments and / or features described in this specification that do not belong to the scope of the independent claims, if any, are to be construed as examples useful for understanding the various embodiments.

[0004] At least one example embodiment provides an apparatus, the apparatus comprising a memory and a processing circuit. The processing circuit is configured to cause the apparatus to: request synchronization reference source information from a user device; determine whether to perform offset compensation based on the synchronization reference source information, and in response to determining to perform offset compensation, obtain a first propagation delay associated with the apparatus, determine a reference time based on the first propagation delay, and forward the reference time to the user device.

[0005] According to at least one example embodiment, the processing circuit is further configured to cause the apparatus to: obtain a second propagation delay between the user equipment and the apparatus; and obtain a third propagation delay between the user equipment and the synchronization reference source based on the synchronization reference source information.

[0006] According to at least one example embodiment, the synchronization reference source information identifies a type of the synchronization source and a priority of the synchronization source.

[0007] According to at least one example embodiment, the processing circuit is further configured to cause the apparatus to determine not to perform offset compensation in response to the synchronization source being a Global Navigation Satellite System (GNSS).

[0008] According to at least one example embodiment, the processing circuit is also configured to cause the device to: obtain the second propagation delay by: sending a request to a user equipment to send a physical sidelink control channel (PSSCH) transmission with a reference signal, the reference signal including a transmission time and a reception time of a next PSSCH reception from the device, sending a first PSSCH transmission to the user equipment, and recording the first time of sending the first PSSCH transmission to the user equipment; receiving an Rx-Tx value from the user equipment corresponding to the difference between a second transmission time of sending the second PSSCH transmission to the device and a second reception time of receiving the first PSSCH transmission from the device, and determining the second propagation delay based on the Rx-Tx value, the first transmission time and the first reception time.

[0009] According to at least one example embodiment, the processing circuit is further configured to cause the apparatus to set the offset compensation value equal to the first propagation delay; and determine the reference time based on the offset compensation value.

[0010] According to at least one example embodiment, the processing circuit is further configured to cause the apparatus to set the offset compensation value equal to the first propagation delay; and determine the reference time based on the offset compensation value.

[0011] According to at least one example embodiment, the processing circuit is further configured to cause the apparatus to: determine whether the second propagation delay is greater than a first threshold, and whether the third propagation delay is greater than a second threshold; and in response to the first propagation delay being greater than the second threshold and the third propagation delay being greater than the second threshold, set the offset compensation value equal to the offset compensation value plus a difference between the first propagation delay and the second propagation delay.

[0012] According to at least one example embodiment, the processing circuit is further configured to cause the apparatus to: in response to the second propagation delay being greater than the first threshold and the third propagation delay being not greater than the second threshold, set the offset compensation value equal to the offset compensation value plus the second propagation delay.

[0013] According to at least one example embodiment, the processing circuit is further configured to cause the apparatus to: determine whether the first propagation delay is greater than a third threshold; and in response to the first propagation delay being greater than the third threshold, set the offset compensation value equal to the offset compensation value minus the first propagation delay.

[0014] At least one example embodiment provides an apparatus comprising a memory and a processing circuit, the processing circuit being configured to cause the apparatus to: receive a request for time information from a first user device, take a first propagation delay associated with a second user device, determine a reference time based on the first propagation delay, and forward the reference time to the first user device.

[0015] According to at least one example embodiment, the processing circuit is further configured to: obtain a second propagation delay between the first user equipment and the second user equipment; and obtain a third propagation delay between the first user equipment and the synchronization reference source.

[0016] According to at least one example embodiment, the processing circuit is further configured to cause the apparatus to: set the offset compensation value equal to the first propagation delay; and determine the reference time based on the offset compensation value.

[0017] According to at least one example embodiment, the processing circuit is further configured to cause the device to determine whether the second propagation delay is greater than a first threshold and whether the third propagation delay is greater than a second threshold; and in response to the first propagation delay being greater than the first threshold and the second propagation delay being greater than the second threshold, set the offset compensation value equal to the offset compensation value plus the difference between the first propagation delay and the second propagation delay.

[0018] According to at least one example embodiment, the processing circuit is further configured to cause the apparatus to set the offset compensation value equal to the offset compensation value plus the second propagation delay in response to the second propagation delay being greater than the first threshold and the third propagation delay being not greater than the second threshold.

[0019] According to at least one example embodiment, the processing circuit is further configured to cause the apparatus to determine whether the first propagation delay is greater than a third threshold; and in response to the first propagation delay being greater than the third threshold, set the offset compensation value equal to the offset compensation value minus the first propagation delay.

[0020] According to at least one example embodiment, the processing circuit is further configured to cause the apparatus to: determine a first threshold based on an amount of change in the DFN boundary; determine a second threshold based on an estimated round trip time of arrival between the first user equipment and the second user equipment; and determine a third threshold based on the amount of change in the DFN boundary.

[0021] At least one example embodiment provides a method for synchronizing reference time in a sidelink relay. The method includes: requesting synchronization reference source information from a first user device; determining whether to perform offset compensation based on the synchronization reference source information; and in response to determining to perform offset compensation, obtaining a first propagation delay of a second user device; determining a reference time based on the first propagation delay, and forwarding the reference time to the first user device.

[0022] At least one example embodiment provides a method for synchronizing a reference time in a sidelink relay. The method includes: receiving a request for time information from a first user device, obtaining a first propagation delay associated with a second user device; determining a reference time based on the first propagation delay; and forwarding the reference time to the first user device.

[0023] At least one example embodiment provides an apparatus comprising: a component for requesting synchronization reference source information from a user device; a component for determining whether to perform offset compensation based on the synchronization reference source information, and in response to determining to perform offset compensation, a component for acquiring a first propagation delay associated with the apparatus, a component for determining a reference time based on the first propagation delay, and a component for forwarding the reference time to the user device.

[0024] At least one example embodiment provides an apparatus comprising: a component for receiving a request for time information from a first user device, a component for obtaining a first propagation delay associated with a second user device, a component for determining a reference time based on the first propagation delay, and a component for forwarding the reference time to the first user device.

[0025] At least one example embodiment provides a non-transitory computer-readable storage medium storing computer-readable instructions, which, when executed, cause one or more processors to cause an apparatus to: request synchronization reference source information from a user device; determine whether to perform offset compensation based on the synchronization reference source information, and in response to determining to perform offset compensation, obtain a first propagation delay associated with the apparatus, determine a reference time based on the first propagation delay, and forward the reference time to the user device.

[0026] At least one example embodiment provides a non-transitory computer-readable storage medium storing computer-readable instructions that, when executed, cause one or more processors to cause an apparatus to: receive a request for time information from a first user device, obtain a first propagation delay associated with a second user device, determine a reference time based on the first propagation delay, and forward the reference time to the first user device. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Example embodiments will be more fully understood from the detailed description and accompanying drawings given below, in which like elements are denoted by like reference numerals, which are given by way of illustration only, and thus do not limit the present disclosure.

[0028] Figure 1 A simplified diagram of a portion of a 3rd Generation Partnership Project (3GPP) New Radio (NR) access deployment is shown for explaining an example embodiment.

[0029] Figure 2 is a block diagram illustrating an example embodiment of a gNB according to an example embodiment.

[0030] Figure 3 is a block diagram illustrating an example embodiment of a UE according to an example embodiment.

[0031] Figure 4 is an example timing diagram showing the Distinguishing Characteristic Network (DFN) number offset by the Uu interface propagation delay.

[0032] Figure 5 is a timing diagram according to an example embodiment.

[0033] Figure 6 is a flow chart illustrating a method according to an example embodiment.

[0034] Figure 7 is a flow chart illustrating an example method for estimating a propagation delay between a remote UE and a relay UE using Rx-Tx based RTT estimation according to an example embodiment.

[0035] Figure 8 is a flow chart illustrating an example method for performing offset compensation according to an example embodiment.

[0036] Fig.9A is a timing diagram according to an example embodiment.

[0037] Fig. 9B is a timing diagram according to an example embodiment.

[0038] Fig. 9C is a timing diagram according to an example embodiment.

[0039] Fig.10 Shows Figures 6 to 8 The signaling flow of the method shown.

[0040] Fig.11 is a flow chart illustrating an example method for performing offset compensation according to an example embodiment.

[0041] FIG. 12A to FIG. 12B A signaling flow of a method according to an example embodiment is shown. DETAILED DESCRIPTION

[0042] Various example embodiments will now be described more fully with reference to the accompanying drawings, in which some example embodiments are shown.

[0043] Detailed illustrative embodiments are disclosed herein. However, the specific structural and functional details disclosed herein are only for the purpose of describing the exemplary embodiments. However, the exemplary embodiments can be embodied in many alternative forms and should not be construed as being limited to the embodiments set forth herein.

[0044] It should be understood that the exemplary embodiments are not intended to be limited to the specific forms disclosed. On the contrary, the exemplary embodiments will cover all modifications, equivalents and alternatives that fall within the scope of the present disclosure. Throughout the description of the drawings, the same reference numerals represent the same elements.

[0045] Although one or more example embodiments may be described from the perspective of a radio access network (RAN) or a radio network element (e.g., a gNB), a user equipment (UE), etc., it should be understood that one or more example embodiments discussed herein may be performed by one or more processors (or processing circuits) at an applicable device. For example, according to one or more example embodiments, at least one memory may include or store computer program code, and at least one memory and the computer program code may be configured to, together with at least one processor, cause a radio network element (or user equipment) to perform the operations discussed herein.

[0046] As discussed herein, the terms "one or more" and "at least one" can be used interchangeably.

[0047] As discussed herein, a gNB may also be referred to as a base station, access point, enhanced NodeB (NodeB) (eNodeB), or more generally, a radio access network element, a radio network element, or a network node. A UE may also be referred to herein as a mobile station and may include a mobile phone, a cellular phone, a smart phone, a handset, a personal digital assistant (PDA), a tablet computer, a laptop computer, a phablet, etc.

[0048] It should be understood that various example embodiments may be used in combination.

[0049] The 3rd Generation Partnership Project (3GPP) Release (Rel)-16 introduced accurate time synchronization with support for Time Sensitive Networking (TSN) for industrial communication purposes. 3GPP Rel-17 expanded the purpose of accurate time synchronization to cover use cases beyond the Industrial Internet of Things (IIoT) for wide-area deployments applicable to electricity meters, payment terminals, vehicles, etc. With the help of accurate time synchronization, the UE can obtain an accurate time of day (ToD) relative to a global time domain (e.g., Universal Coordinated Time (UTC)). This can be used directly as a function of how the device behaves (e.g., a robot coordinates its actions, or executes at a specific time instance), or alternatively, to timestamp events (packets, actions, transactions, etc.) to determine the global order of events.

[0050] Accurate 5G system (5GS) time synchronization can be achieved using a framework with two aspects: first, specific events can be identified at the air interface, these events are time-stamped at the gNB, and then the UE can identify these events and receive timestamps relative to these events from the gNB to obtain ToD; second, accurate 5GS time synchronization can further include a mechanism for propagation delay compensation (PDC).

[0051] With regard to the mechanism used for PDC, the air interface event that the gNB timestamps is the end boundary of the reference system frame number (SFN). The timestamp is carried in the ReferenceTimeInfo-r16 Information Element (IE) (RTI) which may be sent in SIB9 (e.g., for broadcast), or the RTI may be sent as part of a DLInformationTransfer via dedicated Radio Resource Control (RRC) signaling. In the case of RRC-carried RTI, the reference SFN to which the timestamp refers is given explicitly (and may go back and forth in time), but in the case of System Information Block (SIB) 9-carried RTI, the reference SFN is given implicitly by the SFN in which the ongoing System Information Window (SI Window) ends.

[0052] Sidelink (SL) communications can extend coverage by allowing UEs outside the coverage of the gNB to be served. For example, with 3GPP Rel-16, the first version of NR SL supports vehicle-to-everything (V2X) related services, while Rel-17 provides further coverage extensions for sidelink-based communications, such as UE-to-network (U2N) coverage extension and UE-to-UE coverage extension in 3GPP Rel-18. To support UE-to-network relay, SIB forwarding can be enabled to allow remote UEs to obtain system information from the network.

[0053] The challenge of using the underlying 5G radio frame timing at the gNB and UE as a common reference for delivering the Time of Day (ToD) is that the radio frame boundaries (and hence the SFN boundaries) at the gNB and UE are not perfectly aligned in time with respect to each other. The downlink frame boundaries at the UE are shifted by the propagation delay (PD), i.e., by the time it takes for the radio frame to propagate through the air from the gNB to the UE, relative to the corresponding frame boundaries at the gNB. When the UE synchronizes its clock timing by associating the time information carried by SIB9 / RRC messages with its own refSFN boundary, the UE understands that the ToD will be delayed by the PD compared to the gNB’s ToD. This may not be a problem if the PD is relatively small compared to the maximum allowed timing error (e.g., every 10m of distance may add 33.3ns of time error between the UE and gNB clocks due to the PD). However, considering that the maximum synchronization error on the 5G RAN can be less than 275ns for each Uu interface in a control-to-control scenario in Release 17, and may be even smaller in future releases, and that the distance of the UE from the gNB may be such that the PD alone will introduce a larger error, the inventors have found that there is a need to compensate for this offset. Therefore, a UE according to an example embodiment may compensate for the PD on the time information received in a SIB9 or unicast RRC message, for example by adding its current PD estimate to the time information.

[0054] The PD estimate is derived using measurements of link delay, typically estimated from Rx-Tx round trip time (RTT) measurements, assuming symmetric delays in UL / DL. This can be derived from the positioning framework (multi-RTT measurements) or from the UE Timing Advance (TA), which is a measure of how much the UE's UL transmission should be advanced relative to the DL reception time. Once achieved, the DL / PD is approximately RTT / 2.

[0055] In the TA procedure, the UE may receive a TA command from the gNB during the random access procedure or after any UL transmission via a medium access control (MAC) message. In multi-RTT, the UE may be configured to measure the DL reference signal (RS) when the gNB measures the arrival timing of the UE UL RS transmission. The RTT procedure for positioning can be simplified to apply to time-synchronized PD estimation since only single-cell Rx-Tx measurements are required.

[0056] The transmission time at the PC5 interface depends on whether the UE is a synchronization reference (SyncRef) UE (e.g., the PC5 synchronization master that will subsequently broadcast the S-SSB) and the time synchronization source (which may be in category gNB / eNB, GNSS and / or other categories).

[0057] Depending on the synchronization source detected, the UE will initiate transmissions at slightly different PC5 timings. 3GPP TS 38.331, 6.3.4 specifies UE performance requirements and includes Uu and PC5 transmission timing requirements. For PC5 transmissions, the timing requirements depend on the synchronization source type. The entire contents of 3GPP TS 38.331, 6.3.4 are incorporated herein by reference.

[0058] In Release 16, the UE selects its SyncRef based on different priorities of the sources as outlined in Table 1 (where P0 to P6 correspond to highest to lowest priority, respectively), depending on whether it is GNSS based synchronization (GNSS as the highest priority) or gNB / eNB based synchronization (gNB / eNB has the highest priority). Table 1

[0059] Figure 1 A simplified diagram of a portion of a 3rd Generation Partnership Project (3GPP) New Radio (NR) access deployment is shown for explaining an example embodiment.

[0060] Figure 1 The portion of a 3GPP NR access deployment shown illustrates an example of a sidelink connection according to an example embodiment. Figure 1The sidelink connection shown includes a UE-to-network relay UE 110, a remote UE 120, a SyncRef UE 130, and a gNB 100. The relay UE 110 may be configured to relay reference time information (RTI) to the remote UE 120. The relay UE 110 and the remote UE 120 may not select the same SyncRef UE 130. In some example embodiments, the relay UE 110 may also act as the SyncRef UE 130.

[0061] Figure 2 is a block diagram illustrating an example embodiment of a gNB according to an example embodiment.

[0062] Reference Figure 2 , gNB 100 may also be referred to as a base station, access point, enhanced NodeB (e Node B) or more generally, a radio access network element, a radio network element or a network node. gNB 100 may include memory 101, processing circuitry (such as at least one processor 102) and / or a wireless communication interface 103. Memory 101 may include various application specific program codes including computer executable instructions that may cause gNB 100 to perform one or more of the methods of the example embodiments. The wireless communication interface may include a PC5 air interface.

[0063] In at least one example embodiment, the processing circuitry may include at least one processor (and / or processor core, distributed processor, networked processor, etc.), such as at least one processor 102, which may be configured to control one or more elements of the gNB 100 and thereby cause the gNB 100 to perform various operations. The processing circuitry (e.g., at least one processor 102, etc.) is configured to perform processing by retrieving program code (e.g., computer-readable instructions) and data from the memory 101, thereby performing dedicated control and functions throughout the gNB 100. Once the dedicated program instructions are loaded into, for example, at least one processor 102, etc., the at least one processor 102 executes the dedicated program instructions, thereby transforming the at least one processor 102 into a dedicated processor.

[0064] In at least one example embodiment, memory 101 may be a non-transitory computer-readable storage medium and may include random access memory (RAM), read-only memory (ROM), and / or a permanent mass storage device such as a disk drive or solid-state drive. Stored in memory 101 are program codes (i.e., computer-readable instructions) related to operating gNB 100.

[0065] Figure 3 is a block diagram illustrating an example embodiment of a UE according to an example embodiment.

[0066] refer to Figure 3 , the relay UE may include a memory 111, a processing circuit (such as at least one processor 112), a wireless communication interface 113 and / or a global navigation satellite system (GNNS) receiver 114. The relay UE 110 may be, but is not limited to, any one of a mobile device, a smart phone, a tablet computer, a laptop computer, a desktop computer, etc.

[0067] Descriptions of the memory 111, the processor 112, and the wireless communication interface 113 may be substantially similar to the memory 101, the processor 102, and the communication interface 103, respectively, and thus omitted. The GNNS receiver may be an interface for communicating with and / or receiving signals from the GNNS.

[0068] The description of the configurations of the Remote UE 120 and the SyncRefUE 130 may be substantially similar to that of the Relay UE 110 and thus is omitted.

[0069] Return to reference Figure 1 When a remote UE 120 uses a SyncRef source that is a direct or indirect gNB / eNB, its PC5 reception time may be offset relative to the SFN boundary time sent at the gNB 100 by the Uu interface propagation delay (experienced at the remote UE 120 in the case of direct synchronization to the gNB / eNB, or at the SyncRefUE 130 in the case of direct or indirect synchronization to the gNB / eNB). This offset is reflected as an additional ToD error when the remote UE 120 reads the timestamp carried in the RTI. The Uu propagation delay may be hundreds of ns, and the resulting ToD error may be unacceptable for some time synchronization use cases that use less than 1μs accuracy.

[0070] Figure 4 is an example timing diagram illustrating the problem of the DFN number being offset by the Uu interface propagation delay.

[0071] Reference Figure 4 , when the SyncRefUE 130 (to which the Remote UE 120 PC5 air interface is synchronized) or the Remote UE 120 itself is using the eNB / gNB as the SyncRef source for its PC5 air interface, an offset occurs between the DFN boundary perceived at the Remote UE 120 and the timestamped SFN boundary indicated in the RTI. In this case, the PC5 transmission time is offset by at least the propagation delay from the eNB / gNB to the SyncRef UE 130 (indirect synchronization case) or the Remote UE 120 (direct synchronization case).

[0072] In addition, the relay UE 110 (relay RTI) may not be the same device as the SyncRef UE 130 (and the SyncRef UE 130 used by the remote UE 120 may not be the same as the SyncRef UE 130 used by the relay UE 110). In this case, the relay UE 110 may not be aware of the timing source of the SyncRef UE 130 used by the remote UE 120. Therefore, the RTI forwarded by the relay UE 110 to the remote UE 120 may provide an inaccurate ToD at the remote UE 120 due to the SFN and DFN misalignment. This may affect IIoT-like use cases that may use high timing accuracy.

[0073] Some example embodiments relate to methods and apparatus for improving the accuracy of RTI information relayed via a sidelink at a remote UE 120. The RTI information may be requested by the remote UE.

[0074] For example, the remote UE 120 may move out of the coverage of the gNB. In this case, for the purpose of having a global time domain understanding, the remote UE 120 may request a time synchronization service for at least one of the following reasons: support for TSN, TSC and / or PTP clock synchronization and / or local synchronization of the 5G clock. The remote UE 120 may request a time service as described in U.S. Provisional Application No. 63 / 270,528, the entire contents of which are incorporated herein by reference.

[0075] As another non-limiting example, a remote UE 120 connected to the gNB 100 via a side link via the relay UE 110 may request a time synchronization service in response to a request from an application running on the remote UE 120.

[0076] Figure 5 is a timing diagram illustrating offsets that may be compensated for according to example embodiments.

[0077] like Figure 5 As shown, there may be a first propagation delay Uu PD between the relay UE 110 and the gNB 100. A second offset between the DFN boundary perceived at the remote UE 120 and the timestamped SFN boundary indicated in the RTI may be caused by a propagation delay Relay2Remote PD between the remote UE and the relay UE. A third offset Relay2SyncRef may be caused by a propagation delay between the remote UE and the remote UE's SyncRef source. Example embodiments may compensate for these offsets by calculating the Remote2SyncRef PD offset, as described later.

[0078] Figure 6 is a flow chart illustrating a method according to an example embodiment.

[0079] refer to Figure 6 At S600, in response to a request from the remote UE 120, the relay UE 110 may request SyncRef source information from the remote UE 120. The remote UE 120 may respond by sending its SyncRef source type to the relay UE 110. For example, the remote UE 120 may send SyncRef source information including 4 bits. The first bit of the SyncRef source information may indicate GNSS or gNB / eNB based synchronization. The 3-bit SyncRef source information may indicate the priority of the SyncRef source, as shown in Table 1.

[0080] At S610, the relay UE 110 determines whether it may be beneficial (or necessary) to perform offset compensation based on the SyncRef source information provided by the remote UE 120. For example, the relay UE 110 may determine whether the SyncRef UE 130 is performing synchronization based on a GNSS source or a gNB / eNB source based on the first bit of the SyncRef source information.

[0081] If the SyncRefUE 130 performs synchronization based on a GNSS source, the Relay UE 110 determines that offset compensation will not be beneficial (or necessary) ("No" at S610), and proceeds to S680.

[0082] At S680, the method ends.

[0083] Returning to S610 , if the SyncRef UE 130 does not perform synchronization based on a GNSS source, the Relay UE 110 determines that offset compensation may be beneficial (“YES” at S610 ) and proceeds to S620 .

[0084] At S620, the relay UE 110 obtains the propagation delay Relay2Remote PD between the remote UE 120 and the relay UE 110. The Relay2Remote PD may be estimated according to any known method for estimating propagation delay, such as by using Rx-Tx based RTT estimation, using a zone, a signal level and / or a mode 1 physical sidelink control channel (PSSCH).

[0085] The area can be used to estimate the Relay2Remote PD by the remote UE 120, and the relay UE 110 calculates and exchanges their respective area IDs based on their respective geographic coordinates and the configured area length. The relay UE 110 can then estimate the distance based on the difference between the area and the area length. The estimated difference can then be converted to Relay2RemotePD. For example, the Relay2Remote PD can be estimated based on the time it takes for a signal to propagate at the speed of light c between the relay UE 110 in one area and the remote UE 120 in another area. For example, if the area length is z and it is found that the relay UE 110 is in area n and the remote UE 120 is in area m, the Relay 2RemotePD can be estimated by Equation 1. Equation 1

[0086] In another example embodiment, the signal level may be used to estimate the Relay2Remote PD by the relay UE 110 estimating the Relay2Remote PD based on the signal level received from other UE transmissions. For example, the relay UE 110 may measure the side link resource occupancy level (SL RSRP) and map the SL RSRP to a corresponding Relay2Remote PD value.

[0087] Figure 7 is a flow chart illustrating an example method for estimating a propagation delay between a remote UE 120 and a relay UE 110 using Rx-Tx based RTT estimation according to an example embodiment.

[0088] refer to Figure 7 At S620-00, the relay UE 110 sends a request to the remote UE 120 to record the reception time T of the first PSSCH transmission received from the relay UE 110. Rx1 , and records the transmission time T of the second PSSCH transmission sent to the relay UE 110 Tx1 .

[0089] At S620 - 10 , the relay UE 110 sends a request to the remote UE 120 to send a second PSSCH transmission with a reference signal (RS), such as a demodulation reference signal (DMRS), to the relay UE 110 .

[0090] At S620 - 20 , the relay UE 110 sends a first PSSCH transmission with an RS (eg, DMRS) to the remote UE 120 .

[0091] At S620-30, the relay UE 110 records the transmission time T of the first PSSCH transmission to the remote UE 120. Tx0 .

[0092] At S620-40, the remote UE 120 records the reception time T of the first PSSCH transmission received from the relay UE 110. Rx1 .

[0093] At S620 - 50 , the remote UE 120 transmits a second PSSCH to the relay UE 110 .

[0094] At S620-60, the relay UE 110 records the reception time (T Rx0 ).

[0095] At S620-70, the remote UE 120 records the transmission time (T Tx1 ).

[0096] At S620-80, the remote UE 120 calculates the Rx1 The reception time of the first PSSCH and the second PSSCH transmission time to the relay UE 110 are Tx1 The Rx-Tx offset between the transmission times of the relay UE 110 is calculated and the calculated T Rx1 -T Tx1 Offset value.

[0097] At S620-90, the relay UE 110 calculates the T received from the remote UE 120 based on the calculated T Rx1 -T Tx1 The value and the transmission time T recorded at the relay UE 110 Tx0 and receiving time T Rx0 For example, the relay UE 110 may calculate the Relay2Remote PD according to Equation 2. Equation 2 ((T Rx0 -T Tx0 )+(T Rx1 -T Tx1 )) / 2.

[0098] return Figure 6At S630, relay UE 110 obtains a propagation delay between remote UE 120 and a SyncRef source of remote UE 120. For example, relay UE 110 may request remote UE 120 to measure an offset between remote UE 120 and a SyncRef source associated with the remote UE 120. According to some example embodiments, the SyncRef source may be SyncRef UE 130.

[0099] The remote UE 120 may measure the offset between the remote UE 120 and its associated SyncRef source at the next DFN boundary. The remote UE 120 may measure the offset inferred from the symbol timing. For example, the remote UE 120 may measure the offset using a relative time of arrival (RToA) method.

[0100] The remote UE 120 may perform RToA by measuring the arrival time of a first reference signal (e.g., DMRS, CSI-RS, etc.) from a first source and the arrival time of a second reference signal from a second source. For example, the remote UE 120 may request the SyncRef UE 130 to send a first reference signal, and the remote UE 120 may request the relay UE 110 to send a second reference signal. If the arrival time of the first reference signal and the arrival time of the second reference signal occur at different DFNs (e.g., the arrival times are so far apart that they will refer to two different DFNs), the remote UE 120 converts the ToA to the nearest DFN frame boundary for each of them. The remote UE 120 then reads the DFN number of the frame boundary from the sidelink control information. If the DFN number refers to a different DFN, the remote UE 120 adds a known DFN length (e.g., 1 ms) so that both timestamps refer to the same SFN. The remote UE 120 then calculates the offset of the two arrival times based on the timestamps as the Relay2SyncRef offset. The remote UE 120 then reports the Relay2SyncRef offset to the relay UE 110 .

[0101] return Figure 6 At S640, the relay UE 110 obtains its Uu interface propagation delay (Uu PD). The relay UE 110 may obtain the Uu PD by any known method. For example, the relay UE 110 may obtain the Uu PD via a conventional timing advance (TA), an enhanced TA, and / or a round trip time (RTT). The relay UE 110 may determine the SFN boundary compensated by the PD based on the Uu PD.

[0102] At S650, the relay UE 110 sets a local variable equal to Uu PD. For example, the relay UE may set a local variable SFN2DFN equal to Uu PD.

[0103] At S660 , the relay UE 110 performs offset compensation to determine compensated ReferenceTime Info.

[0104] Figure 8 is a flow chart illustrating an example method for performing offset compensation according to an example embodiment.

[0105] If the offset component (e.g., Relay2Remote PD, Relay2SyncRef PD, and / or Uu PD) is too small compared to the estimation / measurement accuracy adopted when obtaining the offset component, then using the obtained offset component to determine the compensated offset may risk introducing a larger error than using uncompensated time information. The relay UE 110 may therefore determine whether to perform the first offset compensation, the second offset compensation, and / or the third offset compensation by comparing the Uu PD, the Relay2Remote PD, and / or the Relay2SyncRef PD with the first threshold T1, the second threshold T2, and / or the third threshold T3, respectively. The first to third thresholds T1T3 may be determined by the gNB 100. The determination of the first to third thresholds T1-T3 will be discussed in more detail later.

[0106] Reference Figure 8 , at S660-00, the relay UE 110 determines whether to perform the first offset compensation by comparing the Relay2Remote PD and the Relay2SyncRef PD with the second threshold T2 and the third threshold T3, respectively. Specifically, the relay UE 110 determines whether the Relay2Remote PD is greater than the second threshold T2, and the relay UE 110 determines whether the Relay2SyncRef PD is greater than the third threshold T3. If the Relay2Remote PD is greater than the second threshold T2, and the Relay2SyncRef PD is greater than the third threshold T3 ("Yes" at S660-00), the relay UE 110 performs the first offset compensation at S660-10. The first offset compensation will be described in more detail later.

[0107] If the Relay2Remote PD is not greater than the second threshold T2, or the Relay2SyncRef PD is not greater than the third threshold T3 ("No" at S660-00), the relay UE 110 determines whether to perform second offset compensation at S660-20.

[0108] At S660-20, the relay UE 110 determines whether to perform the second offset compensation by comparing the Relay2Remote PD with the second threshold T2. If the Relay2Remote PD is not greater than the second threshold T2 ("No" at S660-20), the relay UE 110 determines whether to perform the third offset compensation at S660. S660-40 will be described in more detail later.

[0109] If Relay2Remote PD is greater than the second threshold T2 (Yes at S660-20), relay UE 110 performs second offset compensation at S660-30. In other words, if Relay2Remote PD is greater than the second threshold T2 and Relay2SyncRef PD is not greater than the third threshold T3, relay UE 110 may perform second offset compensation.

[0110] At S660-30, the relay UE 110 performs a second offset compensation by updating the SFN2DFN to the SFN2DFN plus the Relay2Remote PD. Then, the process proceeds to S660-40.

[0111] Returning to S660-10, if Relay2Remote PD is greater than the second threshold T2, and Relay2SyncRef PD is greater than the third threshold T3 ("Yes" at S660-00), the relay UE 110 performs the first offset compensation by updating SFN2DFN equal to the difference between elay2RemotePD and Relay2SyncRef PD added to SFN2DFN. Then, the process proceeds to S660-40.

[0112] At S660-40, the relay UE 110 determines whether to perform third offset compensation based on the Uu PD and the first threshold. The relay UE 110 may determine whether the Uu PD is greater than the first threshold.

[0113] If the Uu PD of the relay UE 110 is not greater than the first threshold T1 ("No" at S660-40), the relay UE 110 receives a ReferenceTimeInfo timestamp from the gNB 100 at S660-60, which will be described in more detail later.

[0114] If the Uu propagation delay of the relay UE 110 is greater than the first threshold T1 (Yes at S660-40), the relay UE 110 performs a third compensation offset at S660-50 by updating SFN2DFN equal to the difference between SFN2DFN and Uu PD. The process then proceeds to S660-60.

[0115] At S660-60, the relay UE 110 receives a first ReferenceTimeInfo timestamp from the gNB 100. The first ReferenceTimeInfo timestamp may be received from the gNB 100 via, for example, SIB9 and / or RRC. For example, in the case where the first ReferenceTimeInfo timestamp is received via SIB9, the gNB 100 may provide the ReferenceTimeInfo timestamp in a broadcast signal. In the case where the first ReferenceTimeInfo timestamp is received via RRC, the gNB 100 may provide the first ReferenceTimeInfo timestamp via the ReferenceTimeInfoPreference field in the UEAssistanceInformation IE in response to a request from the relay UE 110, as described in 3GPP TS 38.331. Alternatively, the relay UE 110 may forward a request from the remote UE 120 to receive the ReferenceTimeInfo as described in U.S. Provisional Application No. 63 / 270,528.

[0116] At S660-70, the relay UE 110 decodes the ReferenceTimeInfo timestamp. Any known method may be used to decode the ReferenceTimeInfo timestamp into a ReferenceTimeInfo value. For example, the ReferenceTimeInfo may include ReferenceTime-r16 information (e.g., UTC time information), where days, seconds, milliseconds, and nanoseconds are encoded as integers and delivered via SIB9 or RRC, as described above.

[0117] At S660 - 80 , the relay UE 110 updates the ReferenceTimeInfo value by adding the offset compensation value SFN2DFN to the ReferenceTimeInfo value.

[0118] At S660-90, the ReferenceTimeInfo value is encoded as a second ReferenceTimeInfo timestamp using any known method. For example, the relay UE 110 may encode the ReferenceTimeInfo value as ReferenceTimeInfoo-r16 information.

[0119] return Figure 6 At S670 , the relay UE 110 forwards the second ReferenceTimeInfo timestamp to the remote UE 120 .

[0120] In some example embodiments, as Figures 6 to 8 As an alternative to the method shown in , S660-60 to S660-90 may be omitted, and the relay UE 110 may not incorporate the SFN2DFN offset into the ReferenceTimeInfo timestamp. In this case, at S670, the relay UE 110 forwards the SFN2DFN offset to the remote UE 120. This has the following benefits: decoding and encoding of the ReferenceTimeInfo timestamp is not performed at the relay UE 110, and the SFN2DFN offset may be forwarded "as is".

[0121] In some example embodiments, relay UE 110 may send a SFN2DFN offset to gNB 100 instead of sending the SFN2DFN offset or the ReferenceTimeInfo timestamp to remote UE 120. In this case, before sending the ReferenceTimeInfo timestamp to remote UE 120, gNB 100 may perform PD pre-compensation on the ReferenceTimeInfo timestamp using the SFN2DFN offset.

[0122] In some example embodiments, at S600, if the SyncRef source of the remote UE 120 is a SyncRef UE, the relay UE 110 may request and obtain the sidelink synchronization signal identifier (SLSSID) and the in-coverage status of the SyncRef UE 130. Here, the SLSSID provides an identifier of the SyncRef UE 130 and together with the in-coverage indicator, the relay UE 110 may uniquely identify the SyncRef UE 130 in its vicinity. In this case, at S630, the relay UE may obtain the propagation delay between the remote UE 120 and the SyncRef UE 130 by monitoring the SL-SSB transmitted by the SyncRef UE 130. If the relay UE 110 may also monitor the SyncRef UE 130, the relay UE 110 may determine the Relay2SyncRef offset without requesting further information or processing from the remote UE 120.

[0123] 9A to 9C is an example timing diagram according to an example embodiment.

[0124] refer to Figure 9A-9C , Figure 9A-9C The timing diagram shown represents a case where the Relay UE 110 also acts as the SyncRef UE 130 for the Remote UE 120 .

[0125] refer to Fig.9A , Fig.9A The timing diagram shown in shows the timing results when the relay UE 110 includes a GNSS receiver and is configured to use GNSS as its synchronization source. Fig.9A As shown in the timing diagram of , relay UE 110 will most likely not perform offset compensation.

[0126] refer to Fig. 9B , Fig. 9B The timing diagram shown in shows the timing results for a relay UE 110 that includes a GNSS receiver but is configured to use gNB 100 as its synchronization source. Fig. 9B As shown in the timing diagram of , relay UE 110 will most likely perform offset compensation.

[0127] refer to Fig. 9C , Fig. 9C The timing diagram shown in FIG. 1 shows the timing results when the relay UE 110 does not include a GNSS receiver. In this case, Fig. 9C As shown in the timing diagram of , relay UE 110 will most likely perform offset compensation.

[0128] Fig.10 Shows Figures 6 to 8 The signaling flow of the method shown.

[0129] Fig.10 The description of the steps shown in can be basically similar to that of reference Figures 6 to 8 Therefore, repeated description is omitted.

[0130] As described above, the first to third thresholds T1-T3 may be determined by the gNB 100. The first threshold T1 may correspond to an estimate of the minimum size of the Uu PD for the offset PD to be meaningful. The second threshold T2 may correspond to an estimate of the PD between the relay UE 110 and the remote UE 120. The third threshold T3 may correspond to the timing difference between the relay UE 110 and the remote UE 120 experienced by the SyncRef UE 130.

[0131] In some example embodiments, the gNB 100 may determine at least one of the first threshold T1 to the third threshold T3 by monitoring the amount of change in the DFN boundary, for example by collecting statistics. If the amount of change is large compared to the PD value of the Uu interface (e.g., the PD between the gNB 100 and the relay UE 110), then offsetting the PD may not be beneficial and the gNB 100 sets the first threshold T1 to be similar or the same as the Uu PD value (e.g., at least in the order of magnitude thereof). If not, the gNB 100 may set the first threshold T1 to be lower. This will be subject to empirical adjustment.

[0132] The gNB 100 may determine the second threshold T2 and / or the third threshold T3 for the respective associated PDs in a manner similar to the first threshold. For example, the gNB 100 may determine whether the amount of change in the DFN boundary is large compared to the PD between the relay UE 110 and the remote UE 120 (e.g., Relay2Remote PD), and the gNB 100 may set the second threshold T2 to be similar or the same as the Relay2Remote PD value (e.g., at least in the order of it). If not, the gNB 100 may set the second threshold T2 to be lower. Similarly, the gNB 100 may determine whether the amount of change in the DFN boundary is large compared to the PD between the SyncRef UE 130 and the relay UE 110 (e.g., Relay2Sync PD).

[0133] In some example embodiments, the gNB 100 may determine at least one of the first to third thresholds T1-T3 by configuration. By assuming some performance on each PC5 hop (e.g., from the SyncRef UE 130 to the remote UE 120), each will introduce an error. In the worst case, the error is given by the transmission error (Te) of the UE applying the Tx time to PC5. For example, the gNB 100 may configure the first to third thresholds T1-T3 taking into account the maximum allowed transmit timing error of the remote UE 120. For example, the threshold may be higher than the transmission error Te specified in section 7 of 3GPP TS 38.133 for the Uu interface, and the transmission error Te specified in section 12.2 of 3GPP TS 38.133 for the sidelink interface.

[0134] In some example embodiments, instead of relay UE 110 performing PD offset compensation, gNB 100 may perform PD offset compensation.

[0135] Fig.11 is a flow chart illustrating an example method for performing offset compensation according to an example embodiment.

[0136] Fig.11 Some operations shown in can be basically similar to those described in Figure 6 Therefore, the description of such operations is omitted.

[0137] Reference Fig.11 , at S1100, the gNB 100 receives a request for RTI information (e.g., ReferenceTimeInfo) from the remote UE 120.

[0138] At S1110, the gNB requests and receives synchronization reference source information from the remote UE 120 and the relay UE 110. The synchronization reference source information is described above with respect to S600. Therefore, repeated description will be omitted.

[0139] At S1120, the gNB configures PC5 PD estimation for the relay UE 110 and the remote UE. The gNB 100 configures the Rx-Tx process on the relay UE 110 and the remote UE 120, and receives the RxTx1 value from the relay UE 110, and receives the RxTx2 value from the remote UE 120. The Rx-TX process may be a known method. For example, in some example embodiments, the gNB 100 may configure the relay UE 110 and the remote UE 120 to perform Rx-Tx measurements between the next (in time) PC5 transmission starting from a specified DFN boundary, which includes a reference signal (e.g., DM-RS). The gNB 100 may then configure the PC5 allocation on each of the relay UE 110 and the remote UE 120 to be as close to the DFN boundary as possible.

[0140] In some example embodiments, a channel state information reference signal (CSI-RS) may be used that all has a unique ID. Transmissions on PC5 are all on the physical sidelink shared channel (PSSCH) and do not reach the gNB 100. The gNB 100 may configure the CSI-RS via RRC signaling as specified in 3GPP TS 38.331.

[0141] At S1130, the gNB 100 calculates the Relay2Remote PD based on RxTx1 and RxTx2. For example, the gNB 100 calculates the Relay2Remote PD according to Equation 3. Equation 3 Relay2Remote=(RxTx1+RxTx2) / 2

[0142] At S1140, the gNB 100 configures the remote UE 120 to measure the propagation delay Relay2SyncRef offset between the remote UE 120 and the SyncRef UE 130. The remote UE 120 may obtain the propagation delay as described with reference to S630. Therefore, repeated descriptions are omitted. The gNB 100 receives the calculated Relay2SyncRef offset from the remote UE 120.

[0143] At S1150, the gNB 100 obtains the Uu propagation delay of the relay UE 110. The gNB 100 may request the relay UE 110 to obtain and provide the Uu propagation delay of the relay UE 110. In this case, the relay UE obtains its Uu propagation delay as described with reference to S640.

[0144] In some example embodiments, gNB 100 may determine the Uu PD of relay UE 110. For example, gNB 100 may determine the Uu PD of relay UE 110 by TA. The TA value may be configured to offset UL transmissions. gNB 100 may determine that the Uu PD is equal to TA / 2. For another example, gNB 100 may determine the Uu PD of relay UE 110 from Rx-Tx round trip time (RTT) measurements, assuming symmetric delays in UL / DL. This may be obtained through the positioning framework (multi-RTT measurement). gNB 100 may then determine that the Uu PD is equal to RTT / 2.

[0145] At S1160, the gNB 100 sets a local variable equal to the Uu propagation delay of the relay UE 110. For example, the relay UE may set a local variable SFN2DFN equal to Uu PD.

[0146] At S1170, the gNB 100 may define the first threshold to the third threshold T1 to T3. The above description of defining the first threshold to the third threshold T1 to T3 is provided for the gNB 100. Therefore, the repeated description is omitted.

[0147] At S1180, the gNB 100 may perform offset compensation. The gNB 100 may perform offset compensation in accordance with the method described in S660 and Figure 8 The execution of the offset compensation performed by the relay UE 110 described above is substantially the same, and therefore repeated description is omitted.

[0148] At S1190, the gNB 100 may forward the ReferenceTimeInfo to the remote UE 120.

[0149] FIG. 12A to FIG. 12B Shows Fig.11 The signaling flow of the method shown.

[0150] FIG. 12A to FIG. 12B The operations shown may be substantially similar to those described with respect to Fig.11 Therefore, the description of such operations is omitted.

[0151] Although the terms first, second, etc. can be used to describe various elements in this article, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element. For example, without departing from the scope of the present disclosure, the first element can be referred to as the second element, and similarly, the second element can be referred to as the first element. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0152] When an element is referred to as being "connected" or "coupled" to another element, it may be directly connected or coupled to the other element, or there may be intervening elements. Conversely, when an element is referred to as being "directly connected" or "directly coupled" to another element, there are no intervening elements. Other words used to describe the relationship between elements should be interpreted in a similar manner (e.g., "between" versus "directly between," "adjacent," "directly adjacent," etc.).

[0153] The terms used herein are only used for the purpose of describing specific embodiments and are not intended to be restrictive. As used herein, the singular forms "a", "an", and "the" are also intended to include plural forms unless the context clearly indicates otherwise. It will be further understood that the terms "comprise", "comprises", "includes", and / or "comprising" when used herein specify the presence of the features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0154] It should also be noted that in some alternative implementations, the functions / actions noted may occur in the order noted in the drawings. For example, two figures shown in succession may actually be executed substantially simultaneously, or may sometimes be executed in the reverse order, depending on the functions / actions involved.

[0155] Specific details are provided in the following description to provide a thorough understanding of the example embodiments. However, one of ordinary skill in the art will appreciate that the example embodiments may be practiced without these specific details. For example, the system may be shown in a block diagram so as not to obscure the example embodiments with unnecessary detail. In other cases, well-known processes, structures, and techniques may be shown without unnecessary detail in order to avoid obscuring the example embodiments.

[0156] As discussed herein, the illustrative embodiments will be described with reference to symbolic representations of acts and operations (e.g., in the form of flowcharts, flow diagrams, data flow diagrams, structure diagrams, block diagrams, etc.), which may be implemented as routines, programs, objects, components, data structures, etc. that perform specific tasks or implement specific abstract data types, and may be implemented using existing hardware at, for example, existing user equipment, base stations, eNBs, RRHs, gNBs, femto base stations, network controllers, computers, etc. Such existing hardware may be processing or control circuitry such as, but not limited to, one or more processors, one or more central processing units (CPUs), one or more controllers, one or more arithmetic logic units (ALUs), one or more digital signal processors (DSPs), one or more microcomputers, one or more field programmable gate arrays (FPGAs), one or more systems on chips (SoCs), one or more programmable logic units (PLUs), one or more microprocessors, one or more application specific integrated circuits (ASICs), or any other device or apparatus capable of responding to and executing instructions in a defined manner.

[0157] Although a flowchart may describe operations as a sequential process, many of the operations may be performed in parallel, concurrently, or simultaneously. In addition, the order of the operations may be rearranged. A process may terminate when its operations are completed, but may also have additional steps not included in the diagram. A process may correspond to a method, function, procedure, subroutine, subprogram, etc.

[0158] As disclosed herein, the term "storage medium", "computer-readable storage medium" or "non-transitory computer-readable storage medium" may refer to one or more devices for storing data, including read-only memory (ROM), random access memory (RAM), magnetic RAM, core memory, magnetic disk storage media, optical storage media, flash memory devices and / or other tangible machine-readable media for storing information. The term "computer-readable medium" may include, but is not limited to, portable or fixed storage devices, optical storage devices, and various other media capable of storing, containing or carrying instructions and / or data.

[0159] In addition, the example embodiments can be implemented by hardware, software, firmware, middleware, microcode, hardware description language or any combination thereof. When implemented in software, firmware, middleware or microcode, the program code or code segment for performing the necessary tasks can be stored in a machine or computer-readable medium such as a computer-readable storage medium. When implemented in software, one or more processors will perform the necessary tasks. For example, as described above, according to one or more example embodiments, at least one memory may include or store computer program code, and at least one memory and computer program code may be configured to enable a network element or network device to perform necessary tasks together with at least one processor. In addition, the processor, memory and example algorithm encoded as a computer program code are used as a device for providing or causing the execution of the operation discussed herein.

[0160] The code segment of a computer program code may represent any combination of a process, function, subprogram, program, routine, subroutine, module, software package, class or instruction, data structure or program statement. A code segment may be coupled to another code segment or hardware circuit by passing and / or receiving information, data, independent variables, parameters or memory contents. Information, independent variables, parameters, data, etc. may be passed, forwarded or transmitted via any suitable technology including memory sharing, message passing, token passing, network transmission, etc.

[0161] As used herein, the terms "including" and / or "having" are defined as including (i.e., open language). As used herein, the term "coupled" is defined as connected, but not necessarily directly, and not necessarily mechanically. Terms derived from the word "indicate" (e.g., "indicate" and "specify") are intended to cover all various techniques that can be used to communicate or reference the indicated object / information. Some but not all examples of techniques that can be used to communicate or reference the object / information being indicated include: communication of the indicated object / information, communication of an identifier of the indicated object / information, communication of information used to generate the indicated object / information, communication of some portion or part of the indicated object / information, communication of some derivation of the indicated object / information, and communication of some symbol representing the indicated object / information.

[0162] According to example embodiments, user equipment, base stations, eNBs, RRHs, gNBs, femto base stations, network controllers, computers, etc. may be (or include) hardware, firmware, hardware executing software, or any combination thereof. Such hardware may include processing or control circuitry such as, but not limited to, one or more processors, one or more CPUs, one or more controllers, one or more ALUs, one or more DSPs, one or more microcomputers, one or more FPGAs, one or more SoCs, one or more PLUs, one or more microprocessors, one or more ASICs, or any other device or apparatus capable of responding to and executing instructions in a defined manner.

[0163] The benefits, other advantages, and solutions to problems are described above with respect to specific embodiments of the invention. However, the benefits, advantages, solutions to problems, and any elements that may lead to or result in such benefits, advantages, or solutions, or that result in such benefits, advantages, or solutions, should not be construed as key, required, or essential features or elements of any or all of the claims.

Claims

1. A device comprising: Memory; as well as processing circuitry configured to cause the apparatus to: requesting synchronization reference source information from a user device; determining whether to perform offset compensation based on the synchronization reference source information, and In response to determining to perform the offset compensation, obtaining a first propagation delay associated with the device, determining a reference time based on the first propagation delay, and The reference time is forwarded to the user equipment.

2. The apparatus of claim 1 , wherein the processing circuit is further configured to cause the apparatus to: acquiring a second propagation delay between the user equipment and the apparatus; and Based on the synchronization reference source information, a third propagation delay between the user equipment and a synchronization reference source is acquired. 3 . The apparatus according to claim 1 , wherein the synchronization reference source information identifies a type of synchronization source and a priority of the synchronization source. 4 . 4 . The apparatus of claim 2 , wherein the processing circuit is further configured to cause the apparatus to determine not to perform the offset compensation in response to the synchronization reference source being a global navigation satellite system (GNSS).

5. The apparatus according to any one of claims 2 and 4, wherein the processing circuit is further configured to cause the apparatus to: The second propagation delay is obtained by: sending a request to the user equipment to send a physical sidelink control channel (PSSCH) transmission with a reference signal including a transmission time and a reception time of a next PSSCH reception from the apparatus, sending a first PSSCH transmission to the user equipment, Recording a first time of sending the first PSSCH transmission to the user equipment; receiving a second PSSCH transmission from the user equipment, Recording a first reception time of receiving the second PSSCH transmission from the user equipment; receiving, from the user equipment, an Rx-Tx value corresponding to a difference between the second transmission time at which the second PSSCH transmission is sent to the apparatus and a second reception time at which the first PSSCH transmission is received from the apparatus, and The second propagation delay is determined based on the Rx-Tx value, the first transmission time, and the first reception time.

6. The apparatus according to any one of claims 2 and 4 to 5, wherein the processing circuit is further configured to cause the apparatus to: setting an offset compensation value equal to the first propagation delay; and The reference time is determined based on the offset compensation value.

7. The apparatus of claim 6, wherein the processing circuit is further configured to cause the apparatus to: determining whether the second propagation delay is greater than a first threshold, and whether the third propagation delay is greater than a second threshold; and In response to the first propagation delay being greater than the second threshold and the third propagation delay being greater than the second threshold, setting the offset compensation value equal to the offset compensation value plus a difference between the first propagation delay and the second propagation delay.

8. The apparatus of claim 7, wherein the processing circuit is further configured to cause the apparatus to: In response to the second propagation delay being greater than the first threshold and the third propagation delay being not greater than the second threshold, setting the offset compensation value equal to the offset compensation value plus the second propagation delay.

9. The apparatus according to any one of claims 7 to 8, wherein the processing circuit is further configured to cause the apparatus to: determining whether the first propagation delay is greater than a third threshold; and In response to the first propagation delay being greater than the third threshold, the offset compensation value is set equal to the offset compensation value minus the first propagation delay.

10. An apparatus comprising: Memory; as well as processing circuitry configured to cause the apparatus to: receiving a request for time information from a first user device, obtaining a first propagation delay associated with a second user equipment, determining a reference time based on the first propagation delay, and The reference time is forwarded to the first user equipment.

11. The apparatus of claim 10, wherein the processing circuit is further configured to: acquiring a second propagation delay between the first user equipment and the second user equipment; and A third propagation delay between the first user equipment and a synchronization reference source is obtained.

12. The apparatus of claim 11, wherein the processing circuit is further configured to cause the apparatus to: setting an offset compensation value equal to the first propagation delay; and The reference time is determined based on the offset compensation value.

13. The apparatus of claim 12, wherein the processing circuit is further configured to cause the apparatus to: determining whether the second propagation delay is greater than a first threshold and whether the third propagation delay is greater than a second threshold; and In response to the first propagation delay being greater than the first threshold and the second propagation delay being greater than the second threshold, setting the offset compensation value equal to the offset compensation value plus a difference between the first propagation delay and the second propagation delay.

14. The apparatus of claim 13, wherein the processing circuit is further configured to cause the apparatus to: In response to the second propagation delay being greater than the first threshold and the third propagation delay being not greater than the second threshold, setting the offset compensation value equal to the offset compensation value plus the second propagation delay.

15. The apparatus according to any one of claims 13 to 14, wherein the processing circuit is further configured to cause the apparatus to: determining whether the first propagation delay is greater than a third threshold; and In response to the first propagation delay being greater than the third threshold, the offset compensation value is set equal to the offset compensation value minus the first propagation delay.

16. The apparatus of claim 15, wherein the processing circuit is further configured to cause the apparatus to: Determining the first threshold based on the change amount of the DFN boundary; determining the second threshold based on an estimated round trip time of arrival between the first user equipment and the second user equipment; and The third threshold is determined based on the amount of change in the DFN boundary.

17. A method for synchronizing a reference time in a sidelink relay, the method comprising: requesting synchronization reference source information from the first user equipment; Determining whether to perform offset compensation based on the synchronization reference source information; as well as In response to determining to perform the offset compensation, Acquire a first propagation delay of a second user equipment; determining a reference time based on the first propagation delay, and The reference time is forwarded to the first user equipment.

18. The method according to claim 17, further comprising: Acquire a second propagation delay between the first user equipment and the second user equipment; as well as Based on the synchronization reference source information, a third propagation delay between the first user equipment and the synchronization reference source is acquired.

19. The method according to any one of claims 17 to 18, wherein the synchronization reference source information identifies the type of synchronization source and the priority of the synchronization source, and the method further comprises: In response to the synchronization source being a global navigation satellite system (GNSS), it is determined not to perform the offset compensation.

20. The method of claim 18, wherein obtaining the second propagation delay comprises: sending a request to the first user equipment to send a physical sidelink control channel (PSSCH) transmission with a reference signal, the reference signal including a transmission time and a reception time of a next PSSCH reception from the second user equipment; Sending a first PSSCH transmission to the first user equipment; Recording a first time of sending the first PSSCH transmission to the first user equipment; receiving a second PSSCH transmission from the first user equipment; Recording a first reception time of receiving the second PSSCH transmission from the first user equipment; receiving, from the first user equipment, an Rx-Tx value corresponding to a difference between the second transmission time of sending the second PSSCH to the second user equipment and a second reception time of receiving the first PSSCH transmission from the second user equipment; as well as The second propagation delay is determined based on the Rx-Tx value, the first transmission time, and the first reception time.

21. The method according to any one of claims 17 to 20, wherein determining the reference time comprises: setting an offset compensation value equal to the first propagation delay; as well as The reference time is determined based on the offset compensation value.

22. The method of claim 21, wherein determining the reference time further comprises: determining whether the second propagation delay is greater than a first threshold, and whether the third propagation delay is greater than a second threshold; In response to the second propagation delay being greater than the first threshold and the third propagation delay being greater than the second threshold, setting the offset compensation value equal to the offset compensation value plus a difference between the second propagation delay and the third propagation delay; as well as In response to the second propagation delay being greater than the first threshold and the third propagation delay being not greater than the second threshold, setting the offset compensation value equal to the offset compensation value plus the second propagation delay.

23. The method according to any one of claims 21 to 22, wherein determining the reference time further comprises: determining whether the first propagation delay is greater than a third threshold; as well as In response to the first propagation delay being greater than the third threshold, the offset compensation value is set equal to the offset compensation value minus the first propagation delay.

24. A method for synchronizing a reference time in a sidelink relay, the method comprising: receiving a request for time information from a first user device, and obtaining a first propagation delay associated with a second user device; determining a reference time based on the first propagation delay; as well as The reference time is forwarded to the first user equipment.

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