WO2022028716A1

WO2022028716A1 - Ue based time synchronization in 5gs with gm clock on the ue side

Info

Publication number: WO2022028716A1
Application number: PCT/EP2020/072270
Authority: WO
Inventors: Rüdiger Halfmann; Rakash SIVASIVA GANESAN; Vladimir Vukadinovic; Pilar ANDRÉS MALDONADO; Klaus Hugl; Devaki Chandramouli; Troels Emil Kolding; David KOZIOL; Peter Rost; Christian Markwart; Kari Juhani NIEMELÄ; Thomas Haaning Jacobsen
Original assignee: Nokia Technologies Oy
Priority date: 2020-08-07
Filing date: 2020-08-07
Publication date: 2022-02-10

Abstract

A method of operating a first user equipment (UE) of a communications network includes receiving, at the first UE, a synchronization message from a second UE of the communications network, the synchronization message including a timestamp of a grand master (GM) clock; determining, by the first UE, whether to compensate residence time information of the synchronization message based on a propagation delay of the first UE and a propagation delay of the second UE; updating the residence time information based on the determination; and transmitting the synchronization message with the updated residence time information to a network element of the communications network.

Description

UE BASED TIME SYNCHRONIZATION IN 5GS WITH GM CLOCK ON THE UE SIDE

TECHNICAL FIELD

[0001] One or more example embodiments relate generally to wireless communications and, more specifically, to Third Generation Partnership Project (3GPP) New Radio (NR), Institute of Electrical and Electronics Engineers (IEEE) time sensitive network (TSN), and (3GPP) time sensitive communications (TSC) technology, and synchronization protocols including, for example, IEEE precision time protocol (PTP) and IEEE generic PTP (gPTP).

BACKGROUND

[0002] One goal of time sensitive networking (TSN) is to provide deterministic services over Institute of Electrical and Electronics Engineers (IEEE) standard 802.3 Ethernet wired networks. This means guaranteed packet transport with low and bounded latency, low packet delay variation, and low packet loss. TSN features can be enabled for specific data streams in a network that also handles best effort type of traffic, for example, converged industrial networks, where data streams from different applications with varying timing requirements are carried together with information technology flows on the same network infrastructure.

[0003] In Third Generation Partnership Project (3GPP) technical specification (TS) 23.501 “System Architecture for the 5G System” (rel. 16), 3GPP technologies are applied in addition to wired time sensitive networking. Further, a 5G system is integrated with the external TSN network as a logical TSN bridge. The logical TSN bridge includes TSN translator (TT) functionality for interoperation between the TSN and the 5G system (5GS) both for a user plane and a control plane. 5GS-specific procedures in the 5G core and radio access network (RAN) may be hidden from the TSN network. To achieve such transparency to the TSN network and for the 5G system to appear as any other TSN Bridge, the 5G system provides TSN ingress and egress ports via the TSN translator functionality at the user equipment (UE) side called device side TT (DS-TT) and via the TSN translator functionality on the 5G Core side called network side TT (NW-TT).

[0004] TSN provides industrial networks with deterministic delay to handle time sensitive traffic. Time synchronization is important for achieving very low deterministic end-to-end delay and to synchronously perform tasks like cooperative transport of goods.

[0005] In 3GPP currently several mechanisms are discussed (e.g., in 3GPP technical report (TR) 23.734 Chapter 6.11) to synchronize devices and network elements connected to a 5G system acting as a logical TSN bridge, which may also be referred to as a 5G system (5GS) bridge. However, one issue is that the clock of the TSN network connected either to DS-TT or to NW-TT of the 5GS bridge needs to be synchronized with the clock of the TSN network on NW-TT or DS-TT, respectively of the 5GS bridge.

SUMMARY

[0006] According to at least some example embodiments, a method of operating a first user equipment (UE) of a communications network includes receiving, at the first UE, a synchronization message from a second UE of the communications network, the synchronization message including a timestamp of a grand master (GM) clock; determining, by the first UE, whether to compensate residence time information of the synchronization message based on a propagation delay of the first UE and a propagation delay of the second UE; updating the residence time information based on the determination; and transmitting the synchronization message with the updated residence time information to a network element of the communications network.

[0007] The determining may include determining, by the first UE, whether to compensate residence time information of the synchronization message based on a difference between the propagation delay of the first UE and the propagation delay of the second UE, and a propagation delay compensation threshold.

[0008] The updating may include compensating the residence time information in response to determining that the difference between the propagation delay of the first UE and the propagation delay of the second UE is greater that the propagation delay compensation threshold.

[0009] The method may further include capturing, by the first UE, an egress timestamp based on a 5G system GM clock at a time when the synchronization message is received, wherein, the received synchronization message includes an ingress timestamp based on the 5G system GM clock.

[0010] The compensating of the residence time information may include compensating at least one timestamp from among the egress timestamp and the ingress timestamp based on a difference between the propagation delay of the first UE and the propagation delay of the second UE, and determining the compensated residence time information based on the compensated at least one timestamp.

[0011] The received synchronization message may include an indication of the propagation delay of the first UE.

[0012] The method may further include receiving, at the first UE, via direct signaling from a next generation Node B (gNB) of the communications network, an indication of the propagation delay of the first UE.

[0013] The direct signaling may be radio resource control (RRC) signaling.

[0014] The method may further include receiving, at the first UE, via Non-Access Stratum (NAS) signaling from an access and mobility management function (AMF) element or a session management function (SME) element of the communications network, an indication of the propagation delay of the first UE.

[0015] The GM clock may be a time-sensitive networking (TSN) generalized precision time protocol (gPTP) GM clock.

[0016] The GM clock may be a precision time protocol (PTP) GM clock.

[0017] According to at least some example embodiments, a method of operating a network element of a communications network includes sending, from the network element to a first UE of the communications network, a request for a first propagation delay, the first propagation delay being a propagation delay of the first UE; and receiving, at the network element, the first propagation delay.

[0018] The network element may be a next generation node B (gNB) of the communications network, and the method further may further include transmitting the first propagation delay from the gNB to a second UE through radio resource control (RRC) signaling.

[0019] The network element may be a core network (CN) element of the communications network.

[0020] The CN element may be an access and mobility management function (AMF) or session management function (SME) of the communications network, and the method may further include transmitting the first propagation delay from the CN element to a second UE through network access stratum (NAS) signaling.

[0021] The CN element may be an access and mobility management function (AMF) or session management function (SMF) of the communications network, and the method may further include using network access stratum (NAS) signaling to transmit the first propagation delay from the CN element to a second UE via a gNB of the communications network.

[0022] According to at least some example embodiments, a method of operating a first UE of a communications network includes determining, at the first UE, a propagation delay of the first UE; and transmitting the propagation delay to a network element of the communications network.

[0023] The network element may be a core network (CN) element of the communications network, the transmitting may include transmitting the propagation delay to the CN element through radio resource control (RRC) signaling, and the CN element may be an access and mobility management function (AMF) or session management function (SMF) of the communications network, or the network element may be a next generation node B (gNB) of the communications network, and the transmitting may include transmitting the propagation delay to the gNB through radio resource control (RRC) signaling.

[0024] The method may further include receiving, at the first UE, a propagation delay request, wherein the transmitting includes transmitting the propagation delay to the network element in response to the received propagation delay request.

[0025] The method may further include iteratively determining new propagation delays of the first UE; and for each determined new propagation delay, determining a difference between the new propagation delay and a propagation delay of the first UE most recently sent from the first UE to the network element, and sending the new propagation delay to the network element in response to determining that the determined difference exceeds a trigger threshold value.

[0026] According to at least some example embodiments, a first user equipment (UE) of a communications network includes receiving means for receiving, at the first UE, a synchronization message from a second UE of the communications network, the synchronization message including a timestamp of a grand master (GM) clock; determining means for determining, by the first UE, whether to compensate residence time information of the synchronization message based on a propagation delay of the first UE and a propagation delay of the second UE; updating means for updating the residence time information based on the determination; and transmitting means for transmitting the synchronization message with the updated residence time information to a network element of the communications network.

[0027] According to at least some example embodiments, a network element of a communications network includes sending means for sending, from the network element to a first UE of the communications network, a request for a first propagation delay, the first propagation delay being a propagation delay of the first UE; and receiving means for receiving, at the network element, the first propagation delay.

[0028] According to at least some example embodiments, a first user equipment (UE) of a communications network includes determining means for determining a propagation delay of the first UE; and transmitting means for transmitting the propagation delay to a network element of the communications network.

[0029] According to at least some example embodiments, a first user equipment (UE) of a communications network includes memory storing computer-executable instructions; and a processor configured to execute the computer-executable instructions such that the first UE is configured to perform operations including receiving, at the first UE, a synchronization message from a second UE of the communications network, the synchronization message including a timestamp of a grand master (GM) clock, determining, by the first UE, whether to compensate residence time information of the synchronization message based on a propagation delay of the first UE and a propagation delay of the second UE, updating the residence time information based on the determination; and transmitting the synchronization message with the updated residence time information to a network element of the communications network.

[0030] According to at least some example embodiments, a network element of a communications network includes memory storing computer-executable instructions; and a processor configured to execute the computer-executable instructions such that the network element is configured to perform operations including sending, to a first user equipment (UE) of the communications network, a request for a first propagation delay, the first propagation delay being a propagation delay of the first UE, and receiving, at the network element, the first propagation delay.

[0031] According to at least some example embodiments, a first user equipment (UE) of a communications network includes memory storing computer-executable instructions; and a processor configured to execute the computer-executable instructions such that the first UE is configured to perform operations including determining a propagation delay of the first UE; and transmitting the propagation delay to a network element of the communications network.

[0032] According to at least some example embodiments, a method of operating a network element of a communications network includes receiving, at the network element, a synchronization message from a user equipment (UE), the synchronization message including a timestamp of a grand master (GM) clock and an ingress time of the synchronization message; determining an egress time of the synchronization message based on a time at which the network element received the synchronization message; receiving, at the network element, a propagation delay of the UE; determining a residency time based on the ingress time, the egress time and the propagation delay of the UE, the determining including compensating at least one the ingress time and the egress time based on the propagation delay of the UE; updating a residence time of the synchronization message with the determined residence time; and transmitting the synchronization time having the determined residence time to another network element of the communications network.

[0033] According to at least some example embodiments, a network element of a communications network includes receiving means for receiving a synchronization message from a user equipment (UE), the synchronization message including a timestamp of a grand master (GM) clock, and receiving an ingress time of the synchronization message, and receiving a propagation delay of the UE; determining means for determining an egress time of the synchronization message based on a time at which the network element received the synchronization message, and determining a residency time based on the ingress time, the egress time and the propagation delay of the UE, the determining of the residency time including compensating at least one the ingress time and the egress time based on the propagation delay of the UE; updating means for updating a residence time of the synchronization message with the determined residence time; and transmitting means for transmitting the synchronization time having the determined residence time to another network element of the communications network.

[0034] According to at least some example embodiments, a network element of a communications network includes memory storing computer-executable instructions; and a processor configured to execute the computer-executable instructions such that the first network element is configured to perform operations including receiving, at the network element, a synchronization message from a user equipment (UE), the synchronization message including a timestamp of a grand master (GM) clock and an ingress time of the synchronization message; determining an egress time of the synchronization message based on a time at which the network element received the synchronization message; receiving, at the network element, a propagation delay of the UE; determining a residency time based on the ingress time, the egress time and the propagation delay of the UE, the determining including compensating at least one the ingress time and the egress time based on the propagation delay of the UE; updating a residence time of the synchronization message with the determined residence time; and transmitting the synchronization time having the determined residence time to another network element of the communications network.

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Example embodiments will become more fully understood from the detailed description given herein below and the accompanying drawings, wherein like elements are represented by like reference numerals, which are given by way of illustration only and thus are not limiting of this disclosure.

[0036] FIG. 1 is a diagram illustrating an example operation for performing user equipment (UE)-UE synchronization in a first communications network that includes a time-sensitive network (TSN)- integrated 5G system (5GS) and a UE-side TSN grand master (GM) clock.

[0037] FIG. 2A illustrates an example embodiment of a network element.

[0038] FIG. 2B illustrates another example embodiment of a network element.

[0039] FIG. 3 is a diagram illustrating an example of selectively applying propagation delay compensation in an operation for performing UE-UE synchronization in a second communications network that includes a UE-side ( (g)PTP) GM clock, according to at least some example embodiments.

[0040] FIG. 4 is a flowchart illustrating a method of operating a UE to facilitate a UE-UE synchronization operation by using UE-based selective application of propagation delay compensation, according to at least some example embodiments.

[0041] FIG. 5 illustrates a timing accuracy error chart, according to at least some example embodiments.

[0042] FIG. 6 is a flowchart illustrating a method of operating a network to facilitate a UE-UE synchronization operation by using UE-based selective application of propagation delay compensation, according to at least some example embodiments.

[0043] It should be noted that these figures are intended to illustrate the general characteristics of methods, structure and/or materials utilized in certain example embodiments and to supplement the written description provided below. These drawings are not, however, to scale and may not precisely reflect the precise structural or performance characteristics of any given embodiment, and should not be interpreted as defining or limiting the range of values or properties encompassed by example embodiments. The use of similar or identical reference numbers in the various drawings is intended to indicate the presence of a similar or identical element or feature.

DETAILED DESCRIPTION

[0044] Various example embodiments will now be described more fully with reference to the accompanying drawings in which some example embodiments are shown.

[0045] Detailed illustrative embodiments are disclosed herein. However, specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments. The example embodiments may, however, be embodied in many alternate forms and should not be construed as limited to only the embodiments set forth herein.

[0046] It should be understood that there is no intent to limit example embodiments to the particular forms disclosed. On the contrary, example embodiments are to cover all modifications, equivalents, and alternatives falling within the scope of this disclosure. Like numbers refer to like elements throughout the description of the figures.

1. TSN time synchronization

[0047] As is discussed above, when a 5G system (5GS) is serving as a logical TSN bridge (e.g., a 5GS bridge), one issue is that the clock of the TSN network connected either to a device side TSN translator (DS-TT) or to a network side TSN translator (NW-TT) of the 5GS bridge needs to be synchronized with the clock of the TSN network on NW-TT or DS-TT, respectively of the 5GS bridge.

[0048] In Third Generation Partnership Project (3GPP) Release (Rel.) 16, the solution specified by SA2 (3GPP technical specification (TS) 23.501) for TSN time synchronization support by a 5GS bridge in downlink (DL) direction in accordance with Algorithm 1 :

Algorithm 1

Al. Elements of the 5GS (e.g., user equipment (UE), a user plane function (UPF), and one or more next generation Node Bs (gNBs)) are all synchronized to the 5GS clock. This 5GS clock synchronization can be achieved, for example, by providing a common clock source to gNB and UPF (e.g. GNSS) or by distributing the 5GS clock from one node to other nodes using, for example, the precision time protocol (PTP) in the transport network between UPF and gNB. The synchronization between the UE and other network nodes in the 5GS may be achieved by sending 5GS reference time information from gNB to the UEs using either unicast or broadcast radio resource control (RRC) signaling (e.g., a DLInformationTransfer or system information block 9 (SIB9) message, respectively).

A2. Once the nodes within the 5GS bridge are synchronized to the 5GS clock, the (g)PTP message from the TSN node on the network side can be transported to the TSN node on the UE side by adding the residence time within the 5GS bridge to the (g)PTP message time correction field. The residence time is measured by time stamping at the ingress, namely at NW-TT, and at the egress namely, DS-TT. Details of the time synchronization mechanism are discussed, for example, in section 5.27.1 of 3GPP TS 23.501.

[0049] In the present disclosure, the term “(g)PTP” is used to refer, collectively, to the Institute of Electrical and Electronics Engineers (IEEE) 802. IAS generalized precision time protocol (gPTP) and the IEEE 1588 precision time protocol (PTP).

2. Propagation delay compensation

[0050] The above-referenced time stamping at the ingress and at the egress port of the 5GS bridge in order to calculate the residence time generally works only if the 5GS clocks at the points of ingress and at the egress are synchronized. In the synchronization solution in Rel. 16 discussed above with respect to Algorithm 1, clock synchronization at the points of ingress and egress with respect to the 5GS bridge is achieved as indicated in step Al of Algorithm 1. Investigations in RAN (Rl- 1900935) show that a 5GS synchronization of less than 500 nanoseconds (ns) is achievable for cell area up to 1 sqkm. For larger areas (i.e., when the distance between the gNB and UE is more than 200 meters (m), according to 3GPPTR 38.825), propagation delay compensation needs to be applied to the reference time information sent from the gNB to the UE to achieve a synchronization accuracy of no greater than Ips, which may be parameter specified by some specifications and/or TSN-integrated 5GS implementations. The studies have also shown that propagation delay compensation can be beneficial at UE-to-gNB distances of around 100m, but not required. Below UE-to-gNB distances of 100m, the accuracy might deteriorate when using propagation delay compensation.

[0051] Timing Advance (TA) is used for compensation of propagation delay in UL to ensure that the bursts transmitted by different terminals arrive at the correct UL time frame at the base station without overlapping and therefore, UE individual TA offset (TAi) corresponds to 2 times the propagation delay of the corresponding node i (PDi). TA is therefore also a likely candidate for compensating the propagation delay for the purpose of accurate time synchronization.

[0052] Among the synchronization errors that limit the synchronization accuracy to ~0.5 micro-seconds, the TA adjustment granularity, TA adjustment accuracy, UE timing error, gNB UL receive timing estimation error and gNB time alignment error are the key contributors. These errors appear due to the fact that the propagation delay between the UE and gNB needs to be estimated. Furthermore, the processing time at the gNB and the UE generally need to be estimated in order to correctly know the time at which the frame is received or transmitted. 3. Example architecture of a TSN-integrated 5GS with UE-side TSN GM clock and an example structure of a network element thereof

[0053] 3GPP release- 17 addresses a scenario in which the 5GS supports the situation where the working clock (e.g., the grand master (GM)) of a TSN/time- sensitive communications (TSC) device resides behind a UE (at a DS-TT), and one or more other UEs are synchronized to the GM clock. The baseline solution for this is described in 3GPP TR 23.700-20. FIG. 1 illustrates an example operation for performing UE-UE synchronization in a first communications network 100 that includes a TSN-integrated 5GS and a UE-side TSN GM clock. FIG. 1 is discussed in greater detail below.

[0054] As is illustrated in FIG. 1, the first communications network 100 includes next generation radio access network (NG-RAN) and Third Generation Partnership Project (3GPP) 5G New Radio (NR) radio access technology and is part of a 5GS. For example, referring to FIG. 1, the first communications network 100 includes a first UE 125_R connected to a first DS-TT 120_R, a second UE 125_O connected to a second DS-TT 120_O, a gNB 110, and a user plane function (UPF) 135 connected to a NW-TT 130. The first UE 125_R may also be referred to in the present disclosure as the reference UE 125_R or UE_ref. The second UE 125_O may also be referred to in the present disclosure as the other UE 125_O or UE_other. The first communications network 100 may further include a 5GS clock 15 (e.g., a 5GS master or grand master (GM) clock). Further, clocks of 5G elements within the first communications network 100 (i.e., local references 15L to the GM 5GS clock 15 at the first and second UEs 125_R and 125_O, the gNB 110 and/or the UPF 135) may be synchronized to the 5GS GM clock.

[0055] According to at least some example embodiments, the first DS-TT 120_R and second DS-TT 120_O are embodied by the first UE 125_R and second UE 125_O, respectively (e.g., as software /firmware executed by processors of the first UE 125_R and second UE 125_O and/or circuitry included in the first DS-TT 120_R and second DS-TT 120_O). Thus, according to at least some example embodiments, operations described as being performed by (or with respect to) the first DS-TT 120_R and/or second DS-TT 120_O may be performed by (or with respect to) the first UE 125_R and/or the second UE 125_O, respectively.

[0056] According to at least some example embodiments, at least some 5G network elements of the first communications network 100 may be included in a 5GS bridge 160 of the first communications network 100. The 5GS bridge 160 may be connected to TSN nodes including, for example, a first TSN grand master (GM) clock 20, a second TSN GM clock 30, first TSN end stations 150, second TSN end stations 152, and third TSN end stations 140. According to at least some example embodiments, the first TSN GM clock 20 may be a GM clock of a first TSN domain (i.e., TSN Domain 1), the first TSN end stations 150 and third TSN end stations 140 may be end stations of the first TSN domain, the second TSN GM clock 30 may be a TSN GM clock of a second TSN domain (i.e., TSN Domain 2), and the second TSN end stations 152 may be TSN domain end stations of the second TSN domain. As is illustrated in FIG. 1, TSN nodes may include local references 20L and/or 30L to the TSN GMs 20 and 30, respectively, which may be synchronized to the TSN GMs 20 and 30.

[0057] In the example illustrated in FIG. 1, the 5GS bridge 160 includes the first UE 125_R, the first DS-TT 120_R, the second UE 125_O, the second DS-TT 120_G, the gNB 110, the UPF 135 and the NW-TT 130. The 5GS bridge 160 may also be referred in the present disclosure as the TSN bridge 160 or the logical TSN bridge 160. Further, in the example illustrated in FIG. 1, the 5GS bridge 160 is connected to the first TSN GM clock 20 and the second TSN GM clock 30 via the first DS_TT

120_R, connected to the first TSN end stations 150 and second TSN end stations 152 via the NW_TT 130, and connected to the third TSN end stations 140 via the second DS-TT 120_O. In the present disclosure, a grand master (GM) clock may also be referred to, simply, as GM.

[0058] Further, though not illustrated, the first communications network 100 may further include 5G core (5GC) network elements. For example, the gNB 110 may be connected to an access and mobility management function (AMF) element. Additionally, though not illustrated, the first communications network 100 may further include long-term evolution (LTE) network elements that are connected to one or more of the gNB 110, the first UE 125_R and the second UE 125_O. Examples of such LTE elements include, but are not limited to, LTE radio access technology (RAT) network elements (e.g., evolved universal mobile telecommunications system (UMTS) terrestrial radio access network (E-UTRAN) network elements) such as evolved node Bs (eNBs), and LTE core network elements (e.g., evolved packet core (EPC) network elements) such as mobility management entities (MMEs) . An example structure which may be used to embody one or more radio network elements (e.g., gNBs, UEs, UPFs etc.) of the first communications network 100 will now be discussed below with respect to FIGS. 2A and 2B.

[0059] FIG. 2A illustrates an example embodiment of a network element. In the example illustrated in FIG. 2A, the network element is a gNB (i.e., gNB 102).

[0060] As shown, the gNB 102 includes: a memory 740; a processor 720 connected to the memory 740; various interfaces 760 connected to the processor 720; and one or more antennas or antenna panels 765 connected to the various interfaces 760. The various interfaces 760 and the antenna 765 may constitute a transceiver for transmitting/ receiving data to/from a UE, a gNB, and/or other radio network element via a plurality of wireless beams. According to at least some example embodiments, in addition to including interfaces for supporting wireless communications, interfaces 760 may also include interfaces for supporting wired communications. According to example embodiments, the memory 740, processor

720, and interfaces 760, collectively, are an example of a central unit (CU) of the gNB 102, and the one or more antennas or antenna panels 765 are an example of a distributed unit (DU) or DUs of the gNB 102.

[0061] As will be appreciated, depending on the implementation of the gNB 102, the gNB 102 may include many more components than those shown in FIG. 2 A. However, it is not necessary that all of these generally conventional components be shown in order to disclose the illustrative example embodiment.

[0062] The memory 740 may be a computer readable storage medium that generally includes a random access memory (RAM), read only memory (ROM), and/or a permanent mass storage device, such as a disk drive. The memory 740 also stores an operating system and any other routines / modules / applications for providing the functionalities of the gNB (e.g., functionalities of a gNB, methods according to example embodiments, etc.) to be executed by the processor 720. These software components may also be loaded from a separate computer readable storage medium into the memory 740 using a drive mechanism (not shown). Such separate computer readable storage medium may include a disc, tape, DVD/CD-ROM drive, memory card, or other like computer readable storage medium (not shown). In some example embodiments, software components may be loaded into the memory 740 via one of the various interfaces 760, rather than via a computer readable storage medium.

[0063] The processor 720 may be configured to carry out instructions of a computer program by performing the arithmetical, logical, and input/ output operations of the system. Instructions may be provided to the processor 720 by the memory 740.

[0064] The various interfaces 760 may include components that interface the processor 720 with the one or more antennas 765, or other input/output components. As will be understood, the various interfaces 760 and programs stored in the memory 740 to set forth the special purpose functionalities of the gNB 102 will vary depending on the implementation of the gNB 102.

[0065] The interfaces 760 may also include one or more user input devices (e.g., a keyboard, a keypad, a mouse, or the like) and user output devices (e.g., a display, a speaker, or the like).

[0066] Further, though the network element of FIG. 2A is illustrated as a gNB, other network elements (e.g., UEs, other radio access and backhaul network elements, network elements embodying one or more of a UPF, AMF, TSN GM clock, TSN end station, DS-TT, NW-TT or the like) may also have the structure of the network element illustrated in FIG. 2A. In this regard, for example, the memory 740 may store an operating system and any other routines/ modules/ applications for providing the functionalities of the UEs, UPF, AMF, TSN GM clock, TSN end station, DS-TT, NW-TT, etc. (e.g., functionalities of these elements, methods according to the example embodiments, etc.) to be executed by the processor 720. For example, any or all of the first UE 125_R, the second UE 125_O, the gNB 110, the UPF 135, the first and second DS-TTs 120_R and 120_O, the NW-TT 130, the first and second TSN GMs 20 and 30, the first TSN end stations 150, the second TSN end stations 152, and/or the third TSN end stations 140 may be embodied by the network element illustrated in FIG. 2 A, in which case the memory 740 stores computer-executable instructions that, when executed by the processor 720, cause the processor 720 to perform the operations described in the present disclosure as being performed by the first UE 125_R, the second UE 125_O, the gNB 110, the UPF 135, the first DS-TT 120_R, the second DS-TT 120_O, the NW-TT 130, the first and second TSN GMs 20 and 30, the first TSN end stations 150, the second TSN end stations 152, and/or the third TSN end stations 140.

[0067] FIG. 2B illustrates another example embodiment of a network element.

Referring to FIG. 2B, network element 104 includes a determining/updating means 210, a transmitting/ sending means 220 and a receiving means 230. According to at least some example embodiments, the determining/ up dating means 210 is embodied by the processor 720 and memory 740 of FIG. 2 A. According to at least some example embodiments, the transmitting/ sending means 220 is embodied by the communications interfaces 760 and the one or more antennas 765 of FIG. 2A. According to at least some example embodiments, the receiving means 230 is embodied by the communications interfaces 760 and the one or more antennas 765 of FIG. 2A. Accordingly, the processor 720 and memory 740 are an example of a “determining means,” the processor 720 and memory 740 are an example of an “updating means,” the communications interfaces 760 and the one or more antennas 765 are an example of a “transmitting means” and the communications interfaces 760 and the one or more antennas 765 are an example of a “sending means.” [0068] Returning to FIG. 1 , FIG. 1 illustrates an example of a solution described in 3GPP TR 23.700-20 for performing UE-UE synchronization in a TSN-integrated 5GS with a UE-side GM (i.e., a TSN GM that is behind a UE). For example, when the TSN GM (e.g., the first TSN GM 20) provides a message including a TSN GM timestamp to the DS-TT connected to the reference UE (e.g., the first DS-TT 120_R connected to the first UE 125_R), the message is timestamped with an ingress timestamp (i.e., with respect to the 5GS clock). The message and the ingress timestamp are delivered to the gNB (e.g., gNB 110) and to the UPF (e.g., UPF 135) where the NW-TT (e.g., NW-TT 130) updates its local reference of the TSN GM based on the TSN GM timestamp included in the message. The UPF (e.g., UPF 135) is also capable of conducting local switching of the message, timestamping of the message with an ingress timestamp, and delivering the message to another UE connected to a TSN device being synchronized to the TSN GM (e.g., the second UE 125_O). The DS-TT connected to the other UE (e.g., the second DS-TT 120_O connected to the second UE 125_O) adds an egress timestamp to the message as well and can therefore calculate the residence time between the two DS-TT (e.g., the first DS_TT 125_R and the second DS_TT 125_O).

4. Problems with performing UE-UE synchronization in a TSN-integrated 5GS with a UE-side TSN GM clock

[0069] As is shown below by Algorithm 2, for UL synchronization, where the GM is on the DS-TT side of the 5G system, in 3GPP TR 23.700-20, a solution has been proposed (e.g., solution #1 in Section 6.1) which is the reverse of the DL synchronization procedure specified in 3 GPP TS 23.501 (see Section 5.27) and described above with reference to Algorithm 1.

Algorithm 2

Bl. All 5G system nodes synchronize to the 5GS clock (same as in the DL case explained above with reference to Algorithm 1).

B2. The (g)PTP message including a TSN GM timestamp is transported from the UE side TSN node (e.g., the first DS-TT 120_R attached to the first UE 125_R) to the network side TSN node (e.g., NW_TT 130) and the TSN nodes attached to the other UEs (e.g., the second DS-TT 120_O attached to the second UE 125_O). So here the ingress stamping (i.e., with respect to the 5GS clock) is performed at the DS-TT of the UE providing TSN GM clock (e.g., the first DS-TT 120_R attached to the first UE 125_R) by sending (g)PTP messages, and the egress stamping (i.e., with respect to the 5GS clock) is performed at the NW-TT or at the DS-TT (sink UEs, i.e. the UEs which receive and ‘consume’ the synchronization information carried in (g)PTP messages).

[0070] When the TSN GM (e.g., first TSN GM 20) resides on the reference UE side (e.g., the first UE 125_R or UE_ref), and this is to be synchronized to another UE (e.g., the second UE 125_O or UE_other), the relative synchronization error introduced by propagation delay compensation (e.g. TA inaccuracies discussed above in section 2) between the two UEs may become nearly twice as large when using propagation delay compensation. On the other hand, the UEs may be located far away from each other and the PD can be quite different. Hence, if not using propagation delay compensation, the relative error depends on the difference (APDi) between a propagation delay from gNB (e.g., gNB 110) to UE_ref and a propagation delay from gNB (e.g., gNB 110 or another gNB) to UE_other, and thus, the relative error can be significant.

[0071] Accordingly, propagation delay compensation may improve the synchronization accuracy, when APDi is large, but may have a small and/or negative impact on synchronization accuracy when APDi is small. If this relationship between synchronization accuracy APDi is not accounted for when determining if propagation delay compensation should be used or not, some specified 3GPP 5GS parameters (e.g., a synchronization accuracy not exceeding Ips) might not be met, or the accuracy may be undesirably poor. Accordingly, it would be advantageous to develop a manner of avoiding poor synchronization accuracy resulting from the misapplication of propagation delay compensation.

5. UE-based selective application of propagation delay compensation in a UE-UE synchronization operation

[0072] As is discussed in greater detail below with reference to FIGS. 3-5, by employing a selective application of propagation delay compensation, UE-UE synchronization accuracy may be improved or, alternatively, optimized for situations where a (g)PTP GM (e.g., the first TSM GM 20 and/or second TSM GM 30 in FIG. 1) resides on the UE side.

[0073] FIG. 3 is a diagram illustrating an example of selectively applying propagation delay compensation in an operation for performing UE-UE synchronization in a second communications network 200 that includes a UE-side generalized precision time protocol ((g)PTP) GM clock, according to at least one example embodiment. Like the first communications network 100, the second communications network 200 includes the first UE 125_R connected to the first DS- TT 120_R, the second UE 125_O connected to the second DS-TT 120_O, the gNB 110, the user plane function (UPF) 135 connected to the NW-TT 130, the 5GS bridge 160, the first TSN GM 20, first TSN end stations 150, and third TSN end stations 140. Further, like the first communications network 100, the second communications network 200 may further include the 5GS clock 15 (e.g., a 5GS GM clock), and clocks of 5G elements within the second communications network 200 (i.e., local references 15L to the GM 5GS clock 15 at the first and second UEs 125_R and 125_O, the gNB 110, and/or the UPF 135) may be synchronized to the 5GS GM clock 15. According to at least some example embodiments, the UPF 135 and the NW-TT 130 may be implemented by the same network element (e.g., the same network node, computer, server, etc.). According to at least some example embodiments, the NW-TT 130 may be implemented as part of the UPF 135.

[0074] In the example illustrated in FIG. 3, the 5GS bridge 160 includes the first UE 125_R connected to the first DS-TT 120_R, the second UE 125_O connected to the second DS-TT 120_O, the gNB 110, and the UPF 135 connected to the NW-TT 130. Further, though not illustrated, the second communications network 200 may include 5GC elements (e.g., an AMF and/or session management function (SMF)) and / or LTE elements, in the same manner discussed above with respect to the first communications network 100 of FIG. 1.

[0075] In the example illustrated in FIG. 3, UE_ref and UE_other (i.e., the first UE 125_R and the second US 125_O) are attached to the same serving gNB, gNB 110 in the second communications network 200. However, according to at least some example embodiments, UE_ref and UE_other may be respectively attached to separate serving gNBs: reference gNB gNB_ref and other gNB gNB_other (not illustrated). Further, gNB_ref and gNB_other may each be connected to the UPF 135.

[0076] For the purpose of simplicity, the second communications network 200 is illustrated as using TSN in the example illustrated in FIG. 3. Thus, in FIG. 3, the second communications network 200 is illustrated as including a 5GS integrated with elements of a TSN network architecture. For example, the UE-side (g)PTP GM clock of the second communications network 200 is implemented by the first TSN GM 20. However, it should be understood that the second communications network 200 is not limited to using TSN.

[0077] For example, in a first alternative example of the second communications network 200, the second communications network 200 does not use TSN, and the UE-side (g)PTP GM clock of the second communications network 200 is an IEEE 802. IAS gPTP GM clock. As another example, in a second alternative example of the second communications network 200, the second communications network 200 does not use TSN, and the UE-side (g)PTP GM clock of the second communications network 200 is an IEEE 1588 PTP GM clock. According to at least some example embodiments, when the second communications network 200 is implemented without using TSN , the second communications network 200 does not include the logical TSN bridge 160.

[0078] Methods of using UE-based selective application of propagation delay compensation to facilitate a UE-UE synchronization operation will now be discussed in greater detail below with reference to FIGS. 4 and 5.

[0079] FIG. 4 is a flowchart illustrating a method of operating a UE to facilitate a UE-UE synchronization operation by using UE-based selective application of propagation delay compensation. FIG. 4 will be explained from the perspective of the other UE UE_other (i.e., the second UE 125_O of the second communications network 200 of FIG. 3). However, according to at least some example embodiments, some or all of the operations discussed as being performed by UE_other may be performed by the DS-TT connected to UE_other (e.g., the second DS-TT 120_O).

[0080] Referring to FIG. 4, in step S410, UE_other receives a (g)PTP message including an ingress time stamp (TSi) and a propagation delay PD_ref of the reference UE UE_ref (i.e., the first UE 125_R of the second communications network 200 of FIG. 3). According to at least some example embodiments, the (g)PTP message may be a SYNC message. According to at least some example embodiments, the ingress time stamp TSi indicates a time (with respect to the 5GS GM 15L or a local reference thereto 15L) at which the (g)PTP message entered the 5GS bridge 160. According to at least some example embodiments, the (g)PTP message may include a timestamp of a (g)PTP GM clock (e.g., the first TSN GM 20) for performing a synchronization operation with a (g)PTP slave (e.g., a TSN node’s local reference 20L to the TSN GM 20).

[0081] According to at least some example embodiments, as an alternative to UE_other receiving PD_ref in the (g)PTP message, UE_other receives PD_ref from the gNB 110 through the direct signaling from the gNB 110 (e.g., radio resource control (RRC) signaling). For example, the gNB 110 may send a request for PD_ref to UE_ref, UE_ref may receive the request from the gNB 110 and respond to the request by sending PD_ref to the gNB 110 through direct signaling (e.g., radio resource control (RRC) signaling) such that the gNB 110 receives PD_ref through the direct signaling (e.g., radio resource control (RRC) signaling )from UE_ref, and the gNB 110 may send PD_ref to UE_other through direct signaling (e.g., radio resource control (RRC) signaling) such that UE_other receives PD_ref from the gNB 110 through the direct signaling from the gNB 110.

[0082] As yet another alternative to UE_other receiving PD_ref in the (g)PTP message, UE_other may receive PD_ref via Non-Access Stratum (NAS) signaling from a core network (CN) element (e.g., an AMF or SMF) of the 5G core of the 5GS in the second communications network 200. For example, the core network element may send a request for PD_ref to UE_ref, UE_ref may receive the request from the CN element and respond to the request by sending PD_ref to the CN element through NAS signaling such that the CN element receives PD_ref from UE_ref through NAS signaling, and the CN element may send PD_ref to UE_other through NAS signaling such that UE_other receives PD_ref from the CN element through NAS signaling. Further, according to at least some example embodiments, the CN element may use NAS signaling to send PD_ref to the gNB 110, which may then send PD_ref to UE_other (or multiple UE_others).

[0083] With respect to the above-referenced alternatives to UE_other receiving PD_ref in the (g)PTP message include UE_ref sending PD_ref to a network element (e.g., the gNB 110 or the CN element of the second communications network 200) in response to receiving a request from the gNB 10 or the CN element. As an alternative to UE_ref sending PD_ref to a network element (e.g., the gNB 110 or the CN element of the second communications network 200) in response to receiving a request from the gNB 10 or the CN element in the manner discussed above, UE_ref may determine PD_ref periodically, UE_ref may compare its currently determined PD_ref to a PD value the gNB most recently transmitted to the network element (i.e., the gNB 110 or the CN element of the second communications network 200), and, when UE_ref determines that a difference between its currently determined PD_ref value and its most recently transmitted PD_ref value exceeds a desired threshold value, UE_ref is triggered to send its currently determined PD_ref value to the network element (i.e., the gNB 110 or the CN element of the second communications network 200). According to at least some example embodiments, the aforementioned desired threshold value may be referred to as a trigger threshold. A value of the trigger threshold may be determined in accordance with the preferences of a designer or operator of the second communications network 200, for example, based on an empirical analysis on the effects of different values for the trigger threshold on a frequency with which UE_ref sends updated PD_ref values and/or an amount of network traffic created by the PD_ref values sent by UE_ref. According to at least some example embodiments, multiple methods of generating and transmitting PD_ref, from among the alternatives discussed above, may be used together.

[0084] In step S420, UE_other captures an egress time stamp (TSe) corresponding to the arrival time of the (g)PTP message by, for example, referencing a current time indicated by UE_other’s local reference 15L to the 5GS GM 15.

[0085] In step S425, UE_other performs a comparison operation based on its own propagation delay PD_other, UE_ref’s propagation delay PD_ref received in step S410, and a propagation delay compensation threshold PD_threshold. For example, in step S425, UE_other may determine whether the difference between PD_other and PD_ref is less than the propagation delay compensation threshold PD_threshold in accordance with the following expression:

PD_other - PD_ref < PD_threshold.

[0086] According to at least some example embodiments, propagation delay compensation is applied when the delta between PD_other (i.e., the propagation delay of the other UE UE_other) and PD_ref (i.e., the propagation delay of the reference UE UE_ref) (APDi) is larger than PD_threshold. Thus, PD_threshold may be determined (e.g., offline, before the steps of FIG. 4 begin, by a designer or operator of the second communications network 200 or one or more elements thereof) based on timesynchronization error models generated from an empirical analysis of factors including, for example, the error sources that occur as soon as propagation delay compensation is being done. For example, FIG. 5 illustrates a timing accuracy error chart. The timing accuracy error chart plots synchronization errors as a function of APDi both without propagation delay compensation (510) and with propagation delay compensation (520). In the example illustrated in FIG. 5, it can be seen that a suitable PD_threshold would be around 220 ns. However, according to at least some example embodiments, it may be desirable to further tune a PD_threshold determined from a timing accuracy error chart based on the particular implementation of the synchronization protocol-utilizing 5GS being used and, for example, an empirical analysis of aspects of the particular implementation that may affect synchronization accuracy generally or the applicability of a particular timing accuracy error chart.

[0087] According to at least some example embodiments, PD_threshold, is assumed to be semi-static value that does not change dynamically. According to at least some example embodiments, the PD_threshold may be conveyed to UE_other by implementing new signaling information fields to deliver PD_threshold in one of the following ways:

(a) PD_threshold is signaled to UE_other from the 5G core, e.g. using the Non-Access Stratum (NAS) protocol;

(b) PD_threshold is signaled to UE_other from gNB_other, e.g. using the radio resource control (RRC) protocol (either broadcast or unicast signaling) .

[0088] Based on the results of the comparison operation performed in step S425, UE_other selectively chooses between applying propagation delay compensation to a residence time of the (g)PTP message (S440) and not applying propagation delay compensation to the residence time of the (g)PTP message (S430).

[0089] For example, according to at least some example embodiments, if UE_other determines in step S425 that the difference between PD_other and PD_ref is not less than PD_threshold (N), then UE_other proceeds to step S440.

[0090] In step S440, UE_other applies propagation delay compensation to the resident time of the (g)PTP message. For example, UE_other may apply the propagation delay compensation by updating the residence time of the (g)PTP message based on the ingress time stamp TSi, the egress time stamp TSe, UE_refs propagation delay PD_ref and UE_other’s propagation delay PD_other. For example, UE_other may apply the propagation delay compensation by updating the residence time of the (g)PTP message in accordance with the following expression:

(TSe+PD_other) - (TSi+PD_ref) .

[0091] After step S440, UE_other proceeds to step S450. In step S450, UE_other transmits the (g)PTP message with the updated residence time. For example, UE_other may transmit the (g)PTP message to a (g)PTP slave (e.g., the second DS-TT 120_O connected to UE_other) so the (g)PTP slave can use the updated residence time and the timestamp of the (g)PTP GM clock (e.g., the first TSN GM 20) included in the (g)PTP message to synchronize the (g)PTP slave, for example, by updating a local reference to the (g)PTP GM clock (e.g., local reference 20L to the first TSN GM 20).

[0092] Returning to step S425, according to at least some example embodiments, if UE_other determines in step S425 that the difference between PD_other and PD_ref is less than PD_threshold (N), then UE_other proceeds to step S430.

[0093] In step S440, UE_other updates the residence time of the (g)PTP message without applying propagation delay compensation to the residence time of the (g)PTP message. For example, UE_other may update the residence time of the (g)PTP message to the difference between the egress timestamp TSe and the ingress timestamp TSi in accordance with the following expression:

TSe-TSi.

[0094] After step S440, UE_other proceeds to step S450, and transmits the (g)PTP message with the updated residence time in the manner previously discussed above with respect to step S450.

[0095] According to at least some example embodiments, steps S420-S450 of FIG.

4 are an example implementation of step 6 of FIG. 6, which will now be discussed below.

[0096] FIG. 6 is a flowchart illustrating a method of operating a network to facilitate a UE-UE synchronization operation by using UE-based selective application of propagation delay compensation. FIG. 6 will be explained with reference to the second communications network 200 of FIG. 3. FIG. 6 illustrates communications of the reference UE UE_ref, the other UE UE_other and network elements of the second communications network 200 which are collectively referred to as NW. NW may include, for example, the gNB 110, the UPF 135/NW-TT 130, and/or 5GC elements such as the AMF and/or SMF (not illustrated). The UPF 135/NW-TT 130 and the AMF and/or SMF may be also be referred to as core network (CN) elements of the second communications network 200.

[0097] Referring to FIG. 6, in step 1, a (g)PTP node (e.g., TSN GM 20) connected to UE_ref sends a (g)PTP sync message, which includes a timestamp of the (g)PTP GM clock (e.g., TSN GM 20), to UE_ref (e.g., the first UE 125_R). After step 1, the method proceeds to step 2.

[0098] In step 2, UE_ref updates the (g)PTP sync message by including a link delay, rateRatio and ingress timestamp (TSi) based on the 5GS GM clock, uncompensated. Additionally, in step 2, UE_ref (or, alternatively, the first DS-TT 120_R connected to UE_ref) includes, in the (g)PTP sync message, PD_ref. PD_ref indicates UE_refs current propagation delay estimation. Alternatively, in step 2, the gNB 110 directly signals PD_ref to UE_other (e.g., the second UE 125_O) using, for example, radio resource control (RRC) signaling. As another alternative, in step 2, an AMF or SMF of the 5G core of the 5GS in the second communications network 200 sends PD_ref to UE_other via Non-Access Stratum (NAS) signaling. As yet another alternative, the gNB 110 may attach PD_ref as a separate field in the (g)PTP sync message (e.g., in step 4b). After step 2, the method proceeds to step 3.

[0099] In step 3, UE_ref sends the (g)PTP sync message to UPF 135 /NW-TT 130. After step 3, the method proceeds to step 4.

[O1OO] Step 4 includes sub-steps 4a and 4b. In step 4, the UPF 135/NW-TT 130 processes the (g)PTP sync message depending on its destination. For example, for a (g)PTP message which is to be sent to a (g)PTP device or (g)PTP network segment which is behind an N6 interface, the method proceeds to sub-step 4a. In sub-step 4a, the UPF 135/NW-TT 130 captures an egress timestamps (TSe), and calculates the residence time as a difference between TSe and the ingress timestamp (TSi) compensated with PD_ref, for example in accordance with the following expression:

TSe - (TSi+PD_ref) .

[0101] The UPF 135/NW-TT 130 then updates the residence time of the (g)PTP sync message with the aforementioned calculated residence time, and sends the (g)PTP sync message to a (g)PTP slave.

[0102] Alternatively, for a (g)PTP message which is to be sent to a (g)PTP device or (g)PTP network segment which is behind which is behind UE_other, the method proceeds to sub-step 4b. In sub-step 4b, the UPF 135/NW-TT 130 sends the (g)PTP sync message to UE_other. According to at least some example embodiments, sub- step 4b corresponds to step S410 of FIG. 4. After step 4b, the method proceeds to step 6.

[0103] As is discussed above, step S420-S450 discussed above with reference to FIG. 4 are an example of step 6 of FIG. 6.

[0104] Alternative methods of obtaining PD_ref at NW will now be discussed below.

6. Alternative methods of obtaining PD ref at NW

[0105] The reference propagation delay of UE_ref, PD_ref, can be acquired by NW from UE_ref using one of the following alternative ways (alternative to the preferred option where UE_ref attaches PD_ref to the (g)PTP message): a) A reference gNB, gNB_ref, (i.e., a gNB serving UE_ref such a gNB 110) estimates PD_ref. b) The reference gNB gNB_ref acquires PD_ref from UE_ref, e.g. via separate medium access control (MAC) or RRC signaling. c) The AMF or SME receives PD_ref from UE_ref using separate NAS signaling.

[0106] According to at least some example embodiments, the NW (gNB_ref, gNB_other, UPF) checks each recipient of the (g)PTP messages from UE_ref and takes appropriate actions. The recipient may be another UE (UE_other) as UE_other may be in a different gNB (gNB_other) compared to UE_ref. The network would have to execute the following steps to make the solution applicable for UE synchronizing to UE in other cells:

1. Either UE_ref or gNB_ref signals PD_ref to the 5GC (e.g. to AMF or SMF).

2. AMF/ SMF determines the gNBs which need to receive PD_ref based on, for example: a. Determination of which gNBs serve UE_other, e.g. based on (g)PTP sessions being established with those UEs; b. gNBs indicating the need to receive PD_ref to the AMF/SMF based on the fact that the gNB is providing 5GS reference timing to the UE using unicast RRC signaling; and / or c. UE_other indicating to the AMF/SMF that UE_other needs to receive synchronization information using NAS signaling.

3. AMF/SMF provides PD_ref to gNBs that require it as determined in step 3 (gNB_other) and to the UPF.

[0107] Further, a recipient may be connected via a 5GS bridge port (e.g. the NW- TT) where propagation delay compensation for PD_ref should always be applied based on known propagation delay considerations. For the case where the recipient is on the NW side, it is desirable for the PD_ref to be provided to the UPF 135/NW- TT 130 using one of the following ways: a) Signaling PD_ref from gNB_other to AMF/SMF and from SMF to UPF 135; b) Signaling PD_ref from a UE to AMF/SMF and from SMF to UPF 135; and c) Including PR_ref in a (g)PTP message.

[0108] Although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and similarly, a second element could be termed a first element, without departing from the scope of this disclosure. As used herein, the term "and / or," includes any and all combinations of one or more of the associated listed items.

[0109] When an element is referred to as being "connected," or "coupled," to another element, it can be directly connected or coupled to the other element or intervening elements may be present. By contrast, when an element is referred to as being "directly connected," or "directly coupled," to another element, there are no intervening elements present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., "between," versus "directly between," "adjacent," versus "directly adjacent," etc.).

[0110] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used herein, the singular forms "a," "an," and "the," are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises," "comprising," "includes," and/or "including," when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. [0111] It should also be noted that in some alternative implementations, the functions/ acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may in fact be executed substantially concurrently or may sometimes be executed in the reverse order, depending upon the functionality / acts involved.

[0112] Specific details are provided above to provide a thorough understanding of example embodiments. However, it will be understood by one of ordinary skill in the art that example embodiments may be practiced without these specific details. For example, systems may be shown in block diagrams so as not to obscure the example embodiments in unnecessary detail. In other instances, well-known processes, structures and techniques may be shown without unnecessary detail in order to avoid obscuring example embodiments.

[0113] As discussed herein, illustrative embodiments will be described with reference to acts and symbolic representations of operations (e.g., in the form of flow charts, flow diagrams, data flow diagrams, structure diagrams, block diagrams, etc.) that may be implemented as program modules or functional processes include routines, programs, objects, components, data structures, etc., that perform particular tasks or implement particular abstract data types and may be implemented using existing hardware at, for example, existing UE, base stations, eNBs, RRHs, gNBs, femto base stations, network controllers, computers, Central Units (CUs), ng-eNBs, other radio access or backhaul network elements, or the like. 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 System-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 devices capable of responding to and executing instructions in a defined manner.

[0114] Although a flow chart may describe the 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 re-arranged. A process may be terminated when its operations are completed, but may also have additional steps not included in the figure. A process may correspond to a method, function, procedure, subroutine, subprogram, etc. When a process corresponds to a function, its termination may correspond to a return of the function to the calling function or the main function.

[0115] As disclosed herein, the term "storage medium," "computer readable storage medium" or "non-transitory computer readable storage medium” may represent one or more devices for storing data, including read only memory (ROM), random access memory (RAM), magnetic RAM, core memory, magnetic disk storage mediums, optical storage mediums, flash memory devices and/or other tangible machine-readable mediums 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 mediums capable of storing, containing or carrying instruction (s) and/or data.

[0116] Furthermore, example embodiments may be implemented by hardware, software, firmware, middleware, microcode, hardware description languages, or any combination thereof. When implemented in software, firmware, middleware or microcode, the program code or code segments to perform the necessary tasks may be stored in a machine or computer readable medium such as a computer readable storage medium. When implemented in software, a processor or processors will perform the necessary tasks. For example, as mentioned above, according to one or more example embodiments, at least one memory may include or store computer program code, and the at least one memory and the computer program code may be configured to, with at least one processor, cause a network element or network device to perform the necessary tasks. Additionally, the processor, memory and example algorithms, encoded as computer program code, serve as means for providing or causing performance of operations discussed herein.

[0117] A code segment of computer program code may represent a procedure, function, subprogram, program, routine, subroutine, module, software package, class, or any combination of instructions, data structures or program statements. A code segment may be coupled to another code segment or a hardware circuit by passing and/or receiving information, data, arguments, parameters or memory contents. Information, arguments, parameters, data, etc. may be passed, forwarded, or transmitted via any suitable technique including memory sharing, message passing, token passing, network transmission, etc.

[0118] The terms “including” and/or “having,” as used herein, are defined as comprising (i.e., open language). The term “coupled,” as used herein, is defined as connected, although not necessarily directly, and not necessarily mechanically. Terminology derived from the word “indicating” (e.g., “indicates” and “indication”) is intended to encompass all the various techniques available for communicating or referencing the object/ information being indicated. Some, but not all, examples of techniques available for communicating or referencing the object /information being indicated include the conveyance of the object/ information being indicated, the conveyance of an identifier of the object /information being indicated, the conveyance of information used to generate the object/ information being indicated, the conveyance of some part or portion of the object/ information being indicated, the conveyance of some derivation of the object/information being indicated, and the conveyance of some symbol representing the object/information being indicated.

[0119] According to example embodiments, UEs, base stations, eNBs, RRHs, gNBs, femto base stations, network controllers, computers, Central Units (CUs), ng- eNBs, other radio access or backhaul network elements, or the like, 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 devices capable of responding to and executing instructions in a defined manner.

[0120] Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments of the invention. However, the benefits, advantages, solutions to problems, and any element(s) that may cause or result in such benefits, advantages, or solutions, or cause such benefits, advantages, or solutions to become more pronounced are not to be construed as a critical, required, or essential feature or element of any or all the claims.

Claims

What is claimed is:

1. A method of operating a first user equipment (UE) of a communications network, the method comprising: receiving, at the first UE, a synchronization message from a second UE of the communications network, the synchronization message including a timestamp of a grand master (GM) clock; determining, by the first UE, whether to compensate residence time information of the synchronization message based on a propagation delay of the first UE and a propagation delay of the second UE; updating the residence time information based on the determination; and transmitting the synchronization message with the updated residence time information to a network element of the communications network.

2. The method of claim 1, wherein the determining includes determining, by the first UE, whether to compensate residence time information of the synchronization message based on, a difference between the propagation delay of the first UE and the propagation delay of the second UE, and a propagation delay compensation threshold.

3. The method of claim 2, wherein the updating comprises: compensating the residence time information in response to determining that the difference between the propagation delay of the first UE and the propagation delay of the second UE is greater that the propagation delay compensation threshold.

4. The method of claim 3, further comprising:

36 capturing, by the first UE, an egress timestamp based on a 5G system GM clock at a time when the synchronization message is received, wherein, the received synchronization message includes an ingress timestamp based on the 5G system GM clock.

5. The method of claim 4, wherein the compensating of the residence time information includes, compensating at least one timestamp from among the egress timestamp and the ingress timestamp based on a difference between the propagation delay of the first UE and the propagation delay of the second UE, and determining the compensated residence time information based on the compensated at least one timestamp.

6. The method of claim 1, wherein the received synchronization message includes an indication of the propagation delay of the first UE.

7. The method of claim 1, further comprising: receiving, at the first UE, via direct signaling from a next generation Node Bs (gNBs) of the communications network, an indication of the propagation delay of the first UE.

8. The method of claim 7, wherein the direct signaling is radio resource control (RRC) signaling.

9. The method of claim 1, further comprising: receiving, at the first UE, via Non-Access Stratum (NAS) signaling from an access and mobility management function (AMF) element or a session management

37 function (SMF) element of the communications network, an indication of the propagation delay of the first UE.

10. The method of claim 1, wherein the GM clock is a time-sensitive networking (TSN) generalized precision time protocol (gPTP) GM clock.

11. The method of claim 1 , wherein the GM clock is a precision time protocol (PTP) GM clock.

12. A method of operating a network element of a communications network, the method comprising: sending, from the network element to a first user equipment (UE) of the communications network, a request for a first propagation delay, the first propagation delay being a propagation delay of the first UE; and receiving, at the network element, the first propagation delay.

13. The method of claim 12, wherein the network element is a next generation node B (gNB) of the communications network, and wherein the method further comprises transmitting the first propagation delay from the gNB to a second UE through radio resource control (RRC) signaling.

14. The method of claim 12, wherein the network element is a core network (CN) element of the communications network.

15. The method of claim 14, wherein the CN element is an access and mobility management function (AMF) or session management function (SMF) of the communications network, and wherein the method further comprises: transmitting the first propagation delay from the CN element to a second UE through network access stratum (NAS) signaling.

16. The method of claim 14, wherein the CN element is an access and mobility management function (AMF) or session management function (SMF) of the communications network, and wherein the method further comprises: using network access stratum (NAS) signaling to transmit the first propagation delay from the CN element to a second UE via a gNB of the communications network.

17. A method of operating a first user equipment (UE) of a communications network, the method comprising: determining, at the first UE, a propagation delay of the first UE; and transmitting the propagation delay to a network element of the communications network.

18. The method of claim 17, wherein, the network element is a core network (CN) element of the communications network, the transmitting includes transmitting the propagation delay to the CN element through radio resource control (RRC) signaling, and the CN element is an access and mobility management function (AMF) or session management function (SMF) of the communications network, or the network element is a next generation node B (gNB) of the communications network, and the transmitting includes transmitting the propagation delay to the gNB through radio resource control (RRC) signaling.

19. The method of claim 17, further comprising: receiving, at the first UE, a propagation delay request, wherein the transmitting includes transmitting the propagation delay to the network element in response to the received propagation delay request.

20. The method of claim 17, further comprising: iteratively determining new propagation delays of the first UE; and for each determined new propagation delay, determining a difference between the new propagation delay and a propagation delay of the first UE most recently sent from the first UE to the network element, and sending the new propagation delay to the network element in response to determining that the determined difference exceeds a trigger threshold value.