WO2022208398A1 - Systems and methods for performing time synchronization in a wireless communication network - Google Patents

Abstract

Systems and methods for performing time synchronization in a wireless communication network are provided. In some embodiments, a method for performing time synchronization between an access node and a wireless communication device in a wireless communication network includes the following steps carried out at the access node: receiving a Physical Random Access Channel (PRACH) preamble for enhancing timing detection or an Uplink (UL) Reference Signal (RS) from the wireless communication device; deriving timing-related information based on the preamble for enhancing timing detection or the UL RS; and sending the timing-related information or clock time for the wireless communication device determined based on the timing-related information to the wireless communication device. In this way, the detection error of uplink signals can be reduced to ensure clock synchronization in a 5G system, which is required to satisfy the performance of a Time Sensitive Network (TSN).

Description

SYSTEMS AND METHODS FOR PERFORMING TIME SYNCHRONIZATION IN A WIRELESS COMMUNICATION NETWORK Related Applications [0001] This application claims the benefit of provisional patent application serial number PCT/CN2021/084174, filed March 30, 2021, the disclosure of which is hereby incorporated herein by reference in its entirety. Technical Field [0002] This disclosure generally relates to performing time synchronization between an access node and a wireless communication device in a wireless communication network. Background [0003] For supporting Time Sensitive Network (TSN) time synchronization, 5GS is integrated with the external network as a TSN bridge (or time-aware system). There are two synchronization systems under consideration: 5GS synchronization and TSN domain synchronization. The 5GS synchronization is specified in 3GPP specifications for NG RAN synchronization while the TSN domain synchronization follows IEEE 802.1AS and provides synchronization service to TSN network. [0004] The 5G system (5GS) time synchronization needs to satisfy stringent accuracy requirement in order to support inter-working with TSN. A demanding use case in the context of TSN-5GS interworking is when TSN Grandmaster clocks are located at end stations connected to UE/DS-TTs. This new Rel-17 use case involves two Uu interfaces in the 5GS path (i.e., 5GS ingress to 5GS egress) over which a TSN Grandmaster clock is relayed. One variant of the use case is illustrated in Figure 1 where two UEs can be connected to different gNBs, thereby introducing the potential for increasing uncertainty compared to the case where each UE is connected to the same gNB. [0005] The 5GS synchronicity budget is the portion of the end-to-end synchronicity budget applicable between the ingress and egress of the 5G system, as shown in Figure 1. The per Uu interface synchronization error represents a portion of the end- to-end synchronicity budget and consists of the uncertainty introduced when (a) sending the 5G reference time from gNB antenna to the UE antenna by including ReferenceTimeInfo in either a DLInformationTransfer RRC message or SIB9 and then (b) adjusting the 5G reference time to reflect the downlink propagation delay. [0006] The range of uncertainty for a single Uu interface shown in Table 1 below was agreed at 3GPP TSG-RAN WG2 #113-e. Table 1 – Range of Uncertainty for a Single Uu interface

[0007] The Rel-17 RAN work item “Enhanced Industrial Internet of Things (IoT) and ultra-reliable and low latency communication (URLLC) support for NR” has the following objective, where propagation delay compensation is used to achieve time synchronization between the UE and its associated gNB: 5. Enhancements for support of time synchronization: a. RAN impacts of SA2 work on uplink time synchronization for TSN, if any. [RAN2] b. Propagation delay compensation enhancements (including mobility issues, if any). [RAN2, RAN1, RAN3, RAN4] [0008] RAN1 has agreed in RAN1#102e that The following options for propagation delay compensation are further studied in RAN1 • Option 1: TA-based propagation delay • Option 1a: Propagation delay estimation based on legacy Timing advance (potentially with enhanced TA indication granularity). • Option 1b: Propagation delay estimation based on timing advanced enhanced for time synchronization (as 1a but with updated RAN4 requirements to TA adjustment error and Te) • Option 1c: Propagation delay estimation based on a new dedicated signaling with finer delay compensation granularity (Separated signaling from TA so that TA procedure is not affected) • Option 2: RTT based delay compensation: • Propagation delay estimation based on an RAN managed Rx-Tx procedure intended for time synchronization (FFS to expand or separate procedure/signaling to positioning). TA based propagation delay compensation [0009] Timing Advance command is utilized in cellular communication for uplink transmission synchronization. It is further classified as two types: 1. In the beginning, at connection setup, an absolute timing advance command is communicated to a UE in the MAC PDU Random Access Response (RAR) or in the Absolute Timing Advance Command MAC Control Element (CE) of the MSGB. 2. After connection setup, a relative timing correction can be sent to a UE using Timing Advance Command MAC CE (e.g., UEs can move or due to multi-path because of changing environment). [0010] The downlink Propagation Delay (PD) can be estimated for a given UE by (a) first summing the TA value indicated by the RAR (random access response) and all subsequent TA values sent using the MAC CE and (b) taking some portion of the total TA value resulting from summation of all the TA values (e.g., 50% could be used assuming the downlink and uplink propagation delays are essentially the same). The PD can be utilized to understand time synchronization dynamics, e.g., accurately tracking the value of a clock at UE side relative to the value of that clock in other network nodes. RTT based propagation delay compensation [0011] For the RTT (round-trip time) based method, the UE Rx-Tx Time Difference and/or gNB Rx-Tx Time Difference are measured at UE side and gNB side, respectively, and then used to derive the propagation delay. [0012] For instance, two types of Timing Advance (T_ADV) can be defined: - Type1: TADV = (gNB Rx – Tx time difference) + (UE E-UTRA Rx – Tx time difference); - Type2: TADV = gNB Rx – Tx time difference. [0013] With either Type 1 or Type 2, the propagation delay can be estimated as ½* TADV. [0014] For Type 2 TADV, the Rx – Tx time difference corresponds to a received uplink radio frame containing PRACH from the respective UE. UL time synchronization in NR [0015] In RRC_CONNECTED, the gNB is responsible for maintaining the timing advance to keep the L1 synchronized. Serving cells having UL to which the same timing advance applies and using the same timing reference cell are grouped in a TAG. Each TAG contains at least one serving cell with configured uplink, and the mapping of each serving cell to a TAG is configured by RRC. [0016] For the primary TAG the UE uses the PCell as timing reference, except with shared spectrum channel access where an SCell can also be used in certain cases (see clause 7.1 of TS 38.133). In a secondary TAG, the UE may use any of the activated SCells of this TAG as a timing reference cell but should not change it unless necessary. [0017] Timing advance updates are signaled by the gNB to the UE via MAC CE commands. Such commands restart a TAG-specific timer which indicates whether the L1 can be synchronized or not: when the timer is running, the L1 is considered synchronized, otherwise, the L1 is considered non-synchronized (in which case uplink transmission can only take place on PRACH). [0018] The TA timer is configured in TAG-Config IE in the IE MAC-CellGroupConfig which is used to configure MAC parameters for a cell group, including DRX.

Timing estimation error at gNB [0019] PRACH timing detection error tolerance (see 38.104 V17.1.0) in NR is described as follows.

Summary [0020] Systems and methods for performing time synchronization in a wireless communication network are provided. In some embodiments, a method for performing time synchronization between an access node and a wireless communication device in a wireless communication network includes the following steps carried out at the access node: receiving a Physical Random Access Channel (PRACH) preamble for enhancing timing detection or an Uplink (UL) Reference Signal (RS) from the wireless communication device; deriving timing-related information based on the preamble for enhancing timing detection or the UL RS; and sending the timing-related information or clock time for the wireless communication device determined based on the timing- related information to the wireless communication device. In this way, the detection error of uplink signals can be reduced to ensure clock synchronization in a 5G system, which is required to satisfy the performance of a Time Sensitive Network (TSN). [0021] In TSN network, a more accurate time offset estimation is required for clock synchronization. [0022] In NR up to NR Rel-16, the Timing Advance (TA) estimated based on PRACH may have a detection time error larger than the requirement of maximum time error for time sensitive network, which makes the uplink timing at gNB side not as synchronized as required by the TSN. This issue mainly happens in low band when a Small Subcarrier Spacing (SCS) is applied as the number of PRBs used by one PRACH preamble transmission is fixed to be 12 PRBs. Thus, the PRACH bandwidth is smaller when a smaller SCS is used. This leads to larger detection error since the detection error is approximately inverse of the uplink signal bandwidth. [0023] Thus, an enhanced PRACH or other enhanced uplink reference signals are needed for clock synchronization. And adapt to the enhanced uplink reference signal, the estimated time synchronization information (referred to as Time Synchronization Command (TSC), e.g., carrying a more accurate TA), needs to be transmitted in a downlink so as to provide better TSN time synchronization. [0024] The present disclosure discloses embodiments on improving the time estimation accuracy to ensure the uplink synchronization in a TSN by constructing a TSC for conveying one of the following timing-related information: absolute timing advance information; timing advance adjustment information; propagation delay information. [0025] In some embodiments, the access node comprises an eNB or gNB, and the wireless communication device is selected from a group consisting of: User Equipment, UE, Tablet, mobile terminals, smart phone, laptop embedded equipped, laptop mounted equipment, and Internet of Things, IoT, device. [0026] In some embodiments, transmission of the preamble for enhancing timing detection occupies more physical resources as compared to one with a purpose of establishing or repairing a data link between the access node and the wireless communication device. [0027] In some embodiments, the UL RS is one selected from a group consisting of: wideband or enhanced Sounding Reference Signal (SRS), Demodulation Reference Signal (DMRS), and Phase Tracking Reference Signal (PTRS). [0028] In some embodiments, the wireless communication device is in a RRC CONNECTED State and prior to step a), comprising: sending a Downlink (DL) signal to trigger transmission of the PRACH preamble for enhancing timing detection or the UL RS by the wireless communication device. [0029] In some embodiments, the timing-related information is carried by an MAC Control Element (CE) for TSC with an enhanced granularity sent from the access node to the wireless communication device. [0030] In some embodiments, the timing-related information is absolute TA. In some embodiments, the timing-related information is TA adjustment. In some embodiments, the timing-related information is Propagation Delay (PD). In some embodiments, the enhanced granularity is finer than a legacy granularity. In some embodiments, the MAC CE for TSC has the same format as a legacy timing advance MAC CE. Brief Description of the Drawings [0031] The accompanying drawing figures incorporated in and forming a part of this specification illustrate several aspects of the disclosure, and together with the description serve to explain the principles of the disclosure. [0032] Figure 1 shows a use case where two UEs can be connected to different gNBs, thereby introducing the potential for increasing uncertainty compared to the case where each UE is connected to the same gNB. [0033] Figure 2 illustrates an example of a wireless communication network. Wireless communication devices can communicate with an access node. [0034] Figure 3 is a flowchart illustrating a method for performing time synchronization implemented in a communication system, in accordance with one embodiment. [0035] Figure 4 is a flowchart illustrating a method for performing time synchronization implemented in a communication system, in accordance with another embodiment. [0036] Figure 5 illustrates a processor-based implementation of a network node which may be used for implementing the above-described embodiments. [0037] Figure 6 illustrates a processor-based implementation of a wireless communication device which may be used for implementing the above-described embodiments. [0038] Figures 7A and 7B illustrate a TSC command, in accordance with some embodiments. Detailed Description [0039] The embodiments set forth below represent information to enable those skilled in the art to practice the embodiments and illustrate the best mode of practicing the embodiments. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure. [0040] As used herein, relational terms, such as “first” and “second,” “top” and “bottom,” and the like, may be used solely to distinguish one entity or element from another entity or element without necessarily requiring or implying any physical or logical relationship or order between such entities or elements. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the concepts described herein. 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. [0041] In some embodiments described herein, the term “coupled,” “connected,” and the like, may be used herein to indicate a connection, although not necessarily directly, and may include wired and/or wireless connections. [0042] The term “wireless communication device” herein can be any type of device capable of communicating with a network node or another communication device over radio signals. The wireless communication device might be a radio communication device, target device, a user equipment (UE), a device to device (D2D) wireless device, machine type wireless device or wireless device capable of machine to machine communication (M2M), low-cost and/or low-complexity wireless device, a sensor equipped with wireless device, Tablet, mobile terminals, smart phone, laptop embedded equipped (LEE), laptop mounted equipment (LME), USB dongles, Customer Premises Equipment (CPE), an Internet of Things (IoT) device, or a Narrowband IoT (NB-IOT) device, etc. The communication device might be a vehicle capable of supporting V2X communications. [0043] In the discussion below, it is assumed that the wireless communication device, e.g., UE is a node for determining the clock time for itself, with signaling provided by an access node, e.g., eNB or gNB to assist the communication device. Hence the access node may send time information (e.g., absolute timing advance, timing advance adjustment, propagation delay information) to the communication device. [0044] It is understood that the same methodology can be modified/adapted such that the access node is a node for determining the clock time for the wire communication device. In this case, the gNB may estimate the propagation delay for the UE and take this into account before sending the reference time to UE, e.g., via a UE-specific signaling (dedicated RRC signaling, or MAC CE in the MAC PDU, or L1 physical layer signaling). It is understood that the procedures described below can be easily adapted. [0045] In the discussion below, it is assumed that the accurate reference time delivery and its associated propagation delay compensation estimation and compensation is for the purpose of providing accurate time stamping clock in the TSN time synchronization procedure. More precisely, it is used for the TSN time synchronization procedure which requires very accurate synchronization on the Uu interface, for example, with an accuracy of 100 ns or even lower. However, embodiments below can be independently utilized to provide, e.g., timing source (alternative for GPS clock) for UE, delivering of the local clock to the UE, and etc. [0046] Any other applications that require accurate clock synchronization between two nodes in a network can use the embodiments of the present disclosure as well, i.e., “TSN” term mentioned in the embodiments can be replaced by other similar network or use case as well. [0047] Figure 2 illustrates an example of a wireless communication network. Wireless communication devices (e.g., user equipments (UEs)) 101 and 103 can communicate with an access node 105 (e.g., eNodeB or gNB). The wireless communication devices 101 and 103 communicates with the access node 105 over the Uu physical interface. [0048] Figure 3 is a flowchart illustrating a method for time synchronization implemented in a communication system, in accordance with one embodiment. The communication system includes a network node and a wireless communication device and may be one described with reference to Figure 2. [0049] At step 310, the access node 105 receives a Physical Random Access Channel (PRACH) preamble for enhancing timing detection or an Uplink (UL) Reference Signal (RS) from the wireless communication device 101. [0050] In the present embodiment, optionally, transmission of the preamble for the enhancing timing detection occupies more or separate physical resources, e.g., bandwidth, as compared to normal level or one without the purpose of enhancing timing detection, e.g., for the purposes of random access and normal timing detection. [0051] Optionally, the UL RS is one selected from a group consisting of wideband or enhanced Sounding Reference Signal (SRS), Demodulation Reference Signal (DMRS) and Phase Tracking Reference Signal (PTRS). [0052] Optionally, the physical resources for the transmission of the preamble for enhancing timing detection are shared by all wireless devices in a cell associated with the access node, i.e., UEs 101 and 103 in Figure 2. [0053] At step 320, the access node 105 derives timing-related information based on the preamble for enhancing timing detection or the UL RS. Optionally, the timing- related information is at least one of absolute Timing Advance (TA), TA adjustment, and Propagation Delay (PD). [0054] At step 330, the access node 105 sends the timing-related information or clock time for the wireless communication device determined based on the timing- related information to the wireless communication device 101. [0055] In the present embodiment, the timing-related information may be carried by an MAC Control Element (CE) for Time Synchronization Command (TSC) with an enhanced granularity sent from the access node 105 to the wireless communication device 101. Preferably, the MAC CE for TSC is signaled with a granularity smaller or finer than a legacy granularity for normal transmission timing adjustment for Physical Uplink Control Channel (PUCCH)/Physical Uplink Shared Channel (PUSCH) /Sounding Reference Signal (SRS). [0056] In an illustrative example, the wireless communication device 101 is in a RRC CONNECTED State. Prior to step 310, the access node 105 sends a Downlink (DL) signal to the wireless communication device 101 to trigger transmission of the PRACH preamble for enhancing timing detection or the UL RS. [0057] Optionally, the MAC CE for TSC has the same format as a legacy timing advance MAC CE. [0058] Figure 4 is a flowchart illustrating a method for time synchronization implemented in a communication system, in accordance with another embodiment. The communication system includes a network node and a wireless communication device and may be one described with reference to Figure 2. [0059] At step 410, the wireless communication device receives from the access node 105 a Downlink (DL) signal to trigger transmission of the PRACH preamble for enhancing timing detection or the UL RS. [0060] In the present embodiment, step 410 is optional. That is, the transmission of the PRACH preamble for enhancing timing detection or the UL RS can be either triggered by a signal from network side, e.g., the DL signal from the access node or triggered spontaneously at the wireless communication device according to configuration previously signalled from the access node. [0061] At step 420, the wireless communication device 101 transmits a Physical Random Access Channel (PRACH) preamble for enhancing timing detection or a UL RS. In the present embodiment, transmission of the preamble for the enhancing timing detection occupies more or separate physical resources, e.g., bandwidth, as compared to normal level, e.g., for the purposes of random access and normal timing detection. Optionally, wherein the UL RS is one selected from a group consisting of wideband or enhanced Sounding Reference Signal (SRS), Demodulation Reference Signal (DMRS) and Phase Tracking Reference Signal (PTRS). [0062] At step 430, the wireless communication device 101 receives from the access node 105 timing-related information derived based on the preamble for enhancing timing detection or the UL RS or clock time for the wireless communication device determined based on the timing-related information. Optionally, the timing-related information is at least one of absolute TA, TA adjustment, and PD. [0063] In the present embodiment, the timing-related information is carried by an MAC Control Element (CE) for Time Synchronization Command (TSC) with a granularity sent from the access node 105 to the wireless communication device 101. Preferably, the MAC CE for TSC is signaled with a granularity smaller or finer than a legacy granularity for normal transmission timing adjustment for Physical Uplink Control Channel (PUCCH)/Physical Uplink Shared Channel (PUSCH) /Sounding Reference Signal (SRS). Optionally, the MAC CE for TSC has the same format as a legacy timing advance MAC CE. [0064] At step 440, the wireless communication device 101 adjusts UL transmission timing based on the timing-related information or the clock time. Absolute timing advance [0065] Optionally, the timing-related information is absolute TA, and at step 440, the wireless communication device 101 adjusts the UL transmission timing according to the absolute timing advance carried by the MAC CE for TSC received from the access node at step 430. [0066] As an example, in the case of the timing-related information being the absolute TA, the wireless communication device 101 adjusts the UL transmission timing according to legacy timing advance requirement at step 440. A value for the legacy timing advance requirement can be determined as follows:

where ^^^^^^ is the value for the legacy timing advance requirement, N_TA is the

absolute timing advance, g0 is a legacy granularity, and g1 is an enhanced granularity being finer than the legacy granularity, K is an integer as a power of 2 value. [0067] As another example, in the case of the timing-related information being the absolute TA, the wireless communication device 101 adjusts the UL transmission timing according to the absolute timing advance and estimates a PD between the access node 105 and the wireless communication device 101 at step 440. The estimating can be performed as follows:

where Tc is a basic timing unit as predefined, Δf_max = 480 ∙ 10³ Hz, Nf=4096, NTA is the absolute timing advance, T_A is an integer value carried in the MAC CE for TSC, g₁ is an enhanced granularity being finer than a legacy granularity, K is an integer as a power of 2 value. TA adjustment [0068] Optionally, the timing-related information is TA adjustment, and step 440 is performed by the wireless communication device 101 in the following manner: [0069] The wireless communication device 101 adjusts the UL transmission timing according to the TA adjustment carried by the MAC CE for TSC received from the access node at step 430. Then, the wireless communication device 101 estimates a PD between the access node and the wireless communication device as follows:

where T_c is a basic timing unit as predefined, Δf_max = 480 ∙ 10³ Hz, N_f=4096, N_TA is the current absolute timing advance, TA,delta is the TA adjustment, and g2 is an enhanced granularity being finer than a legacy granularity, K is an integer as a power of 2 value. As an example, T₀ is set as is the maximum possible

value, function f( ) is one of the following functions: ceil( ), round( ), and floor(). As another example, T₀ is a function of uplink SCS. As another example, T0 is taken for FR1 or FR2. [0070] Regarding N_TA in equation (6), it can be determined in one of the following ways: (1) obtaining the current absolute timing advance from a legacy timing advance command MAC CE received from the access node network; (2) computing the current absolute timing advance from a granular TSC MAC CE command received previously from the access node; and (3) obtaining the current absolute timing advance from the MAC CE for TSC received from the access node. Propagation delay [0071] Optionally, the timing-related information is propagation delay, and step 440 is performed by estimating a PD between the access node 105 and the wireless communication device 101 as follows:

where TPD is a propagation delay as estimated by the access node 105 and carried in the MAC CE for TSC received from the access node 105, T_c is a basic timing unit as predefined, Δf_max = 480 ∙ 10³ Hz, Nf=4096, and g3 is an enhanced granularity being finer than a legacy granularity, K is an integer as a power of 2 value. [0072] In the present embodiment, the enhanced granularity can be determined based on one or more of the following: (1) UL SCS of SPCell and/or DL SCS of SPCell; (2) SCS of a TAG if only one SCS is configured per TAG; (3) The largest SCS of a set of SCS values for cells in a TAG when multiple SCS are configured for the cells in the TAG; and (4) granularity configured in RRC signalling, and/or a MAC PDU and/or Layer 1 DCI. [0073] Optionally, the enhanced granularity may be a function of the number of PRBs occupied by UL signal. [0074] Figure 5 illustrates a processor-based implementation of a network node which may be used for implementing the above-described embodiments. For example, the structures as illustrated in Figure 5 may be used for implementing the concepts in any of the above-mentioned access nodes. [0075] As illustrated, the node 500 may include one or more radio interfaces 510. The radio interface(s) 510 may for example be based on the NR technology or the LTE technology. The radio interface(s) 510 may be used for controlling wireless communication devices, such as any of the above-mentioned UEs. In addition, the node 500 may include one or more network interfaces 520. The network interface(s) 520 may for example be used for communication with one or more other nodes of the wireless communication network. [0076] Further, the node 500 may include one or more processors 530 coupled to the interfaces 510, 520 and a memory 540 coupled to the processor(s) 530. By way of example, the interfaces 510, 520, the processor(s) 530, and the memory 540 could be coupled by one or more internal bus systems of the node 500. The memory 540 may include a Read-Only-Memory (ROM), e.g., a flash ROM, a Random Access Memory (RAM), e.g., a Dynamic RAM (DRAM) or Static RAM (SRAM), a mass storage, e.g., a hard disk or solid-state disk, or the like. As illustrated, the memory 540 may include software 550 and/or firmware 560. The memory 540 may include suitably configured program code to be executed by the processor(s) 530 so as to implement the above- described functionalities for time synchronization, such as explained in connection with Figure 3. [0077] It is to be understood that the structure as illustrated in Figure 5 is merely schematic and that the node 500 may actually include further components which, for the sake of clarity, have not been illustrated, e.g., further interfaces, such as a dedicated management interface, or further processors. Also, it is to be understood that the memory 540 may include further program code for implementing known functionalities of an eNB or gNB. [0078] According to some embodiments, also a computer program may be provided for implementing functionalities of the node 500, e.g., in the form of a physical medium storing the program code and/or other data to be stored in the memory 540 or by making the program code available for download or by streaming. [0079] Figure 6 illustrates a processor-based implementation of a wireless communication device which may be used for implementing the above-described embodiments. [0080] As illustrated, the wireless communication device 600 includes one or more radio interfaces 610. The radio interface(s) 610 may for example be based on the NR technology or the LTE technology. [0081] Further, the wireless communication device 600 may include one or more processors 620 coupled to the radio interface(s) 610 and a memory 630 coupled to the processor(s) 620. [0082] By way of example, the radio interface(s) 610, the processor(s) 620, and the memory 630 could be coupled by one or more internal bus systems of the wireless communication device 600. The memory 630 may include a Read-Only-Memory (ROM), e.g., a flash ROM, a Random Access Memory (RAM), e.g., a Dynamic RAM (DRAM) or Static RAM (SRAM), a mass storage, e.g., a hard disk or solid-state disk, or the like. As illustrated, the memory 630 may include software 640 and/or firmware 650. The memory 630 may include suitably configured program code to be executed by the processor(s) 620 so as to implement the above-described functionalities for time synchronization, such as explained in connection with Figure 4. [0083] It is to be understood that the structure as illustrated in Figure 6 is merely schematic and that the wireless communication device 600 may actually include further components which, for the sake of clarity, have not been illustrated, e.g., further interfaces, such as a dedicated management interface, or further processors. Also, it is to be understood that the memory 630 may include further program code for implementing known functionalities of a UE. [0084] According to some embodiments, also a computer program may be provided for implementing functionalities of the wireless communication device 600, e.g., in the form of a physical medium storing the program code and/or other data to be stored in the memory 630 or by making the program code available for download or by streaming. PRACH based procedure with a MAC CE for time synchronization [0085] In these embodiments, the procedure uses enhanced PRACH on the uplink, but the response by gNB is a MAC CE defined for carrying timing information, i.e., gNB does not send a RAR. In the discussion below, a new MAC CE for timing information, which is referred to as Time Synchronization Command (TSC) MAC CE or MAC CE for STC, is introduce. The enhanced PRACH herein refers to a PRACH that is designated for UL timing synchronization purpose and is different from the normal PRACH which is used to establish or repair the data link between gNB and UE. [0086] The procedure includes one or more of the following steps: • Step (a): The gNB sends a downlink command to trigger the UE to transmit an enhanced PRACH; • Step (b): The enhanced PRACH is transmitted by UE to the gNB; • Step (c): The gNB performs uplink timing detection based on the transmitted enhanced PRACH, and derives the timing information; • Step (d): The gNB sends the timing information to the UE with a TSC MAC CE. TSC MAC CE carries absolute timing advance information [0087] While the TSC MAC CE is of new format, the timing value carried can be absolute timing advance ^_^^, similar to the TA carried by RAR. Value ^ and ^ is the integer value carried in TSC MAC CE.

[0088] The absolute timing advance value is ^ The propagation delay

between the gNB and the UE can be estimated as:

where Tc is a basic timing unit as predefined, Δf_max = 480 ∙ 10³ Hz, Nf=4096, NTA is the absolute timing advance, T_A is an integer value carried in the MAC CE for TSC, g₁ is an enhanced granularity, K is an integer as a power of 2 value. Exemplary values of K include: K = {8*64, 4*64, 2*64, 64, 32, 16}. [0089] Optionally, if the TSC MAC CE is received, then the UE can adjust its uplink transmission timing according to the legacy timing advance requirement. Suppose the ^_^^ is the value in the TSC MAC CE, the enhanced granularity is g1 while the legacy granularity is g0, the value for legacy uplink transmission timing adjustment is computed as

[0090] With this approach, the legacy timing advance command MAC CE is not required to be sent from the network to the UE and thus it reduces signalling overhead and UE power consumption by not adjusting the UL transmission for each PD related MAC CE which has a more stringent requirement than the Rel-15/Rel-16 uplink transmission timing alignment requirement. [0091] Optionally, if the TSC MAC CE is received, then the UE adjusts its uplink transmission timing according to the N_TA in the TSC MAC CE. TSC MAC CE carries timing advance adjustment information [0092] The TSC MAC CE carries incremental TA information, TA,delta, i.e., TA adjustment rather than absolute TA. The value carried by TSC MAC CE, TA,delta, is applied on top of the current TA value NTA used by UE to adjust timing of UL transmission. Then the propagation delay between the gNB and the UE can be estimated as:

where T_c is a basic timing unit as predefined, Δf_max = 480 ∙ 10³ Hz, N_f=4096, N_TA is the current absolute timing advance, TA,delta is the TA adjustment, and g2 is an enhanced granularity, K is an integer as a power of 2 value. As an example, T₀ is set as

is the maximum possible value, function f( ) is one of the following functions: ceil( ), round( ), and floor(). As another example, T0 is a function of uplink SCS. As another example, T0 is taken for FR1 or FR2. [0093] The enhanced TA adjustment granularity g₂ can be where integer

K is preferably a power of 2 value. Exemplary values of K include: K= {8*64, 4*64, 2*64, 64, 32, 16}. [0094] Optionally, the current TA value N_TA used by UE to adjust timing of UL transmission can be: • transmitted by the network to the UE using the legacy (Rel-15 and Rel-16) timing advance command MAC CE; or • computed, using the equation (14), from the granular TSC MAC CE command sent previously from the network to the UE; or • transmitted by the network to the UE using the TSC MAC CE and the UE adjusts its uplink transmission timing according to the N_TA in the TSC MAC CE. [0095] Optionally, the value carried by TSC MAC CE, TA,delta, is additionally utilized to adjust the timing of the UL transmission, and the UL transmission is adjusted according to the legacy requirement. In other words, the UE consider the value in the TSC MAC CE as if it is transmitted in the legacy timing advanced command MAC CE. TSC MAC CE carries PDinformation [0096] The TSC MAC CE carries the PD value T_PD as estimated by gNB. The carried value is associated with a PD granularity g3. The propagation delay between the gNB and the UE can be calculated as:

[0097] The granularity g₃ can be

where integer K is preferably a power of 2 value. Exemplary values of K include: K = {8*64, 4*64, 2*64, 64, 32, 16}. Other uplink reference signal (other than PRACH) based procedure for time synchronization [0098] In these embodiments, the procedure uses uplink reference signal (i.e., not PRACH) on the uplink for the gNB to estimate uplink timing. In one example, the uplink reference signal (RS) is an enhanced SRS. Other examples of uplink reference signal include demodulation reference signal (DMRS), Phase Tracking RS (PTRS). The discussion below assumes SRS, though DMRS and PTRS can be used with similar procedure. [0099] In response to the enhanced SRS from the UE, the gNB sends a new MAC CE carrying timing information. [0100] Similar to the PRACH-based procedure as described above, the new MAC CE of these embodiments is time synchronization command (TSC). The TSC may carry one or more of the information below: a) TSC MAC CE carries absolute timing advance information, and PD is estimated using equation (11). b) TSC MAC CE carries timing advance adjustment information, and PD is estimated using equation (15). c) TSC MAC CE carries propagation delay information, and PD is estimated using equation (16). TSC MAC CE construction [0101] In these embodiments, one of the issues to be addressed is how to determine the granularity of the TSC. [0102] Optionally, the granularity associated with the timing synchronization command (TSC) can be determined based on one or more of the following: • The numerology of the cell, e.g., uplink SCS of the SPCell (i.e., Pcell in MCG and PScell in SCG), and/or downlink SCS of the SPCell; • The SCS of a TAG if only one SCS is configured per TAG; • The largest SCS of the set of SCS values for cells in a TAG when multiple SCS are configured for the cells in the TAG; • The granularity can be configured in RRC signalling, and/or a MAC PDU and/or Layer 1 DCI. [0103] Alternatively, the granularity associated with the TSC MAC CE is a function of the number of PRBs occupied by the uplink signal (e.g., PRACH, SRS, DMRS, PTRS). [0104] Another issue is the format of the TSC command which is addressed as follows. Optionally, the number of bits in the TSC command to signal timing information is predefined in the specification. If necessary, reserved bits ‘R’ is added to make the TSC octet aligned. The value of the Reserved bit is typically set to "0" but ignored by the UE. [0105] As an example, a 15 bits TSC can be defined as illustrated in Figure 7A. In another example, the timing advance command can be with 12 bits, the same as the TAC defined in the Absolute Timing Advance Command MAC CE. This is illustrated in Figure 7B. [0106] Optionally, a new MAC CE is defined for the TSC MAC CE with a reserved LCID or eLCID value. [0107] Optionally, the TSC MAC CE has the same format as the legacy timing advance MAC CE, such as the absolute timing advance command MAC CE and the timing advance command MAC CE. This is achieved by using the same MAC subheader with the same (e)LCID. The MAC CE is used to convey the value of the timing information, where the timing information may be absolute timing advance, timing advance adjustment, or propagation delay estimation. The exact value of the associated granularity (i.e., g1, g2, g3 present in equations (11), (15) and (16)) depends on a RRC configuration. In this approach, the legacy timing advance command MAC CE is re-used, in other words, the UE has to adjust the uplink transmission timing according to the values sent in the MAC CE. With reference to two follow-up examples for some embodiments, the UE can: 1) by using equation (14), obtain a coarse granularity timing advance command corresponding to the Rel-15 and Rel-16 uplink transmission timing alignment requirement; or 2) adjust its uplink transmission according to the timing advance value in the MAC CE, and thus UL transmission synchronization accuracy is improved as a by- product. [0108] It will be obvious to a person skilled in the art that, as the technology advances, the inventive concept can be implemented in various ways. The above- described embodiments are given for describing rather than limiting the disclosure, and it is to be understood that modifications and variations may be resorted to without departing from the scope of the disclosure as those skilled in the art readily understand. Such modifications and variations are considered to be within the scope of the disclosure and the appended claims. The protection scope of the disclosure is defined by the accompanying claims. [0109] At least some of the following abbreviations may be used in this disclosure. If there is an inconsistency between abbreviations, preference should be given to how it is used above. If listed multiple times below, the first listing should be preferred over any subsequent listing(s). • 3GPP Third Generation Partnership Project • 5G Fifth Generation • 5GC Fifth Generation Core • 5GS Fifth Generation System • AF Application Function • AN Access Network • AP Access Point • CE Control Element • CPU Central Processing Unit • DCI Downlink Control Information • DL Downlink • DMRS Demodulated Reference Signal • DN Data Network • DSP Digital Signal Processor • eLCID Extended Logical Channel ID • eNB Enhanced or Evolved Node B • E-UTRA Evolved Universal Terrestrial Radio Access • FPGA Field Programmable Gate Array • FR Frequency Range • gNB New Radio Base Station • IoT Internet of Things • IP Internet Protocol • LCID Logical Channel ID • LTE Long Term Evolution • MAC Medium Access Control • MME Mobility Management Entity • NF Network Function • NR New Radio • PC Personal Computer • PCF Policy Control Function • PD Propagation Delay • PDU Protocol Data Unit • P-GW Packet Data Network Gateway • PRACH Physical Random Access Channel • PRB Physical Resource Block • PTRS Phase Tracking Reference Signal • RAM Random Access Memory • RAN Radio Access Network • ROM Read Only Memory • RRC Radio Resource Control • RRH Remote Radio Head • RTT Round Trip Time • SCS Small Subcarrier Spacing • SMF Session Management Function • SRS Sounding Reference Signal • TA Timing Advance • TAG Timing Advance Group • TSC Time Synchronization Command • TSN Time Sensitive Network • UDM Unified Data Management • UE User Equipment • UL Uplink • URLLC Ultra-Reliable and Low Latency Communication [0110] Those skilled in the art will recognize improvements and modifications to the embodiments of the present disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein.

Claims

Claims 1. A method for performing time synchronization between an access node (105, 500) and a wireless communication device (101, 103, 600) in a wireless communication network, comprising: a) receiving (310) a Physical Random Access Channel, PRACH, preamble for enhancing timing detection or an Uplink, UL, Reference Signal, RS, from the wireless communication device (101, 103, 600); b) deriving (320) timing-related information based on the PRACH preamble for enhancing timing detection or the UL RS; and c) sending (330) the timing-related information or a clock time for the wireless communication device (101, 103, 600) determined based on the timing-related information to the wireless communication device (101, 103, 600).

2. The method according to claim 1, wherein the access node (105, 500) comprises an eNB or gNB, and the wireless communication device (101, 103, 600) is selected from the group consisting of: User Equipment, UE, Tablet, mobile terminals, smart phone, laptop embedded equipped, laptop mounted equipment, and Internet of Things, IoT, device.

3. The method according to claim 2, wherein transmission of the PRACH preamble for enhancing timing detection occupies more physical resources as compared to one with a purpose of establishing or repairing a data link between the access node (105, 500) and the wireless communication device (101, 103, 600).

4. The method according to claim 2, wherein the UL RS is one selected from the group consisting of: wideband or enhanced Sounding Reference Signal, SRS, Demodulation Reference Signal, DMRS, and Phase Tracking Reference Signal, PTRS.

5. The method according to claim 3 or 4, the wireless communication device (101, 103, 600) is in a Radio Resource Control, RRC, CONNECTED State and prior to step a), comprising: sending a Downlink, DL, signal to trigger transmission of the PRACH preamble for enhancing timing detection or the UL RS by the wireless communication device (101, 103, 600).

6. The method according to any one of claims 1 to 5, wherein the timing-related information is carried by a Medium Access Control, MAC, Control Element, CE, for a Time Synchronization Command, TSC, with an enhanced granularity sent from the access node (105, 500) to the wireless communication device (101, 103, 600).

7. The method according to claim 6, wherein the timing-related information is an absolute Timing Advance, TA.

8. The method according to claim 6, wherein the timing-related information is a Timing Advance, TA, adjustment.

9. The method according to claim 6, wherein the timing-related information is a Propagation Delay, PD.

10. The method according to claim 6, wherein the enhanced granularity is finer than a legacy granularity.

11. The method according to any one of claims 7-10, wherein the MAC CE for the TSC has the same format as a legacy timing advance MAC CE.

12. An access node (105, 500), comprising: at least one processor (530); and a memory (540) containing program code (550) executable by the at least one processor (530); whereby execution of the program code (550) by the at least one processor (530) causes the access node (105, 500) to perform the method according to any one of claims 1-11.

13. A computer program product being embodied in a computer readable storage medium and comprising program code (550) to be executed by at least one processor (530) of an access node (105, 500), whereby execution of the program code causes the access node (105, 500) to perform the method according to any one of claims 1-11.

14. A method for performing time synchronization between an access node (105, 500) and a wireless communication device (101, 103, 600) in a wireless communication network, comprising: a) transmitting (420) a Physical Random Access Channel, PRACH, preamble for enhancing timing detection or an Uplink, UL, Reference Signal, RS, to the access node (105, 500); and b) receiving (430) from the access node (105, 500) timing-related information derived based on the PRACH preamble for enhancing timing detection or the UL RS or a clock time for the wireless communication device (101, 103, 600) determined based on the timing-related information.

15. The method according to claim 14, wherein the access node (105, 500) comprises an eNB or gNB, and the wireless communication device (101, 103, 600) is selected from the group consisting of: User Equipment, UE, Tablet, mobile terminals, smart phone, laptop embedded equipped, laptop mounted equipment, and Internet of Things, IoT, device.

16. The method according to claim 15, wherein transmission of the PRACH preamble for enhancing timing detection occupies more physical resources as compared to one with a purpose of establishing or repairing a data link between the access node (105, 500) and the wireless communication device (101, 103, 600).

17. The method according to claim 15, wherein the UL RS is one selected from the group consisting of wideband or enhanced Sounding Reference Signal, SRS, Demodulation Reference Signal, DMRS, and Phase Tracking Reference Signal, PTRS.

18. The method according to any one of claims 14 to 17, wherein the timing-related information is carried by a Medium Access Control, MAC, Control Element, CE, for Time Synchronization Command, TSC, with an enhanced granularity sent from the access node (105, 500) to the wireless communication device (101, 103, 600).

19. The method according to claim 18, further comprising: c) adjusting (440) UL transmission timing based on the timing-related information or the clock time.

20. The method according to any one of claims 14 to 19, the wireless communication device (101, 103, 600) is in a Radio Resource Control, RRC, CONNECTED State and prior to step -a), comprising: receiving (410) a Downlink, DL, signal to trigger transmission of the PRACH preamble for enhancing timing detection or the UL RS from the access node (105, 500).

21. The method according to claim 19, wherein the timing-related information is an absolute Timing Advance, TA, and step –c) comprising: adjusting UL transmission timing according to the absolute timing advance.

22. The method according to claim 19, wherein the timing-related information is an absolute Timing Advance, TA, and step –c) comprises: adjusting UL transmission timing according to a legacy timing advance requirement, a value for the legacy timing advance requirement being determined as follows:

where

is the value for the legacy timing advance requirement, N_TA is the absolute timing advance, g0 is a legacy granularity, and g1 is the enhanced granularity being finer than the legacy granularity, K is an integer K as a power of 2 value.

23. The method according to claim 21, wherein the timing-related information is an absolute Timing Advance, TA, and step –c) comprises: estimating a propagation delay, PD, between the access node (105, 500) and the wireless communication device (101, 103, 600) as follows:

where Tc is a basic timing unit as predefined, Δf_max = 480 ∙ 10³ Hz, N_f=4096, N_TA is the absolute timing advance, TA is an integer value carried in the MAC CE for TSC, g1 is the enhanced granularity being finer than a legacy granularity, K is an integer as a power of 2 value.

24. The method according to claim 19, wherein the timing-related information is a Timing Advance, TA, adjustment, and step –c) comprises: adjusting UL transmission timing according to the TA adjustment; and estimating a Propagation Delay, PD, between the access node (105, 500) and the wireless communication device (101, 103, 600) as follows:

where T_c is a basic timing unit as predefined, Hz, N_f=4096, N_TA

is a current absolute timing advance, TA,delta is the TA adjustment, T0 is set as

is the maximum possible value, function f( ) is one of the following functions: ceil( ), round( ), and floor(), and g2 is the enhanced granularity being finer than a legacy granularity, K is an integer as a power of 2 value.

25. The method according to claim 19, wherein the timing-related information is a Timing Advance, TA, adjustment, and step –c) comprises: adjusting UL transmission timing according to the TA adjustment; and estimating a Propagation Delay, PD, between the access node (105, 500) and the wireless communication device (101, 103, 600) as follows:

where Tc is a basic timing unit as predefined, Δf_max = 480 ∙ 10³ Hz, Nf=4096, NTA is a current absolute timing advance, T_A,delta is the TA adjustment, T₀ is a function of uplink Small Subcarrier Spacing, SCS, and g2 is the enhanced granularity being finer than a legacy granularity, K is an integer as a power of 2 value.

26. The method according to claim 19, wherein the timing-related information is a Timing Advance, TA, adjustment, and step –c) comprises: adjusting UL transmission timing according to the TA adjustment; and estimating a Propagation Delay, PD, between the access node (105, 500) and the wireless communication device (101, 103, 600) as follows:

where Tc is a basic timing unit as predefined, Δf_max = 480 ∙ 10³ Hz, Nf=4096, NTA is a current absolute timing advance, T_A,delta is the TA adjustment, T₀ is taken for FR1 or FR2, and g2 is the enhanced granularity being finer than a legacy granularity, K is an integer as a power of 2 value.

27. The method according to any one of claims 24 to 26, wherein step –c) comprises one of the following steps: (1) obtaining the current absolute timing advance from a legacy timing advance command MAC CE received from the access node (105, 500) network; (2) computing the current absolute timing advance from a granular TSC MAC CE command received previously from the access node (105, 500); and (3) obtaining the current absolute timing advance from the MAC CE for TSC received from the access node (105, 500).

28. The method according to claim 19, wherein the timing-related information is propagation delay, and step –c) comprises: estimating a Propagation Delay, PD, between the access node (105, 500) and the wireless communication device (101, 103, 600) as follows:

where TPD is a propagation delay as estimated by the access node (105, 500) and carried in the MAC CE for TSC received from the access node (105, 500), Tc is a basic timing unit as predefined, Hz, N_f=4096, and g₃ is the enhanced

granularity being finer than a legacy granularity, K is an integer as a power of 2 value.

29. The method according to any one of claims 18-28, wherein the MAC CE for TSC has the same format as a legacy timing advance MAC CE.

30. The method according to any one of claims 18-29, wherein the enhanced granularity is determined based on one or more of the following: (1) UL SCS of SPCell and/or DL SCS of SPCell; (2) SCS of a Timing Advance Group, TAG, if only one SCS is configured per TAG; (3) The largest SCS of a set of SCS values for cells in the TAG when multiple SCSs are configured for the cells in the TAG; and (4) granularity configured in RRC signalling, and/or a MAC Protocol Data Unit, PDU and/or Layer 1 Downlink Control Information, DCI.

31. The method according to any one of claims 18-29, wherein the enhanced granularity is a function of a number of Physical Resource Blocks, PRBs, occupied by a UL signal.

32. A wireless communication device (101, 103, 600), comprising: at least one processor (620); and a memory (630) containing program code (640) executable by the at least one processor (620), whereby execution of the program code (640) by the at least one processor (620) causes the access node (105, 500) to perform the method according to any one of claims 14-31.

33. A computer program product being embodied in a computer readable storage medium and comprising program code (640) to be executed by at least one processor (620) of an access node (105, 500), whereby execution of the program code causes the access node (105, 500) to perform the method according to any one of claims 14-31.