WO2022089754A1

WO2022089754A1 - Apparatus, methods, and computer programs

Info

Publication number: WO2022089754A1
Application number: PCT/EP2020/080496
Authority: WO
Inventors: Devaki Chandramouli
Original assignee: Nokia Technologies Oy
Priority date: 2020-10-30
Filing date: 2020-10-30
Publication date: 2022-05-05

Abstract

There is provided an apparatus for an access point to a communication network, the apparatus being arranged to: determine to obtain a timing signal provided by a backhaul access point configured to provide a wireless backhaul to the communication network; receive the timing signal via the wireless backhaul; and signal the timing signal received to a terminal.

Description

APPARATUS, METHODS, AND COMPUTER PROGRAMS

Field

[0001]The present disclosure relates to apparatus, methods, and computer programs, and in particular but not exclusively to apparatus, methods and computer programs for network apparatuses.

Background

[0002]A communication system can be seen as a facility that enables communication sessions between two or more entities such as user terminals, access nodes and/or other nodes by providing carriers between the various entities involved in the communications path. A communication system can be provided for example by means of a communication network and one or more compatible communication devices. The communication sessions may comprise, for example, communication of data for carrying communications such as voice, electronic mail (email), text message, multimedia and/or content data and so on. Content may be multicast or uni-cast to communication devices.

[0003]A user can access the communication system by means of an appropriate communication device or terminal. A communication device of a user is often referred to as user equipment (UE) or user device. The communication device may access a carrier provided by an access node, and transmit and/or receive communications on the carrier.

[0004]The communication system and associated devices typically operate in accordance with a required standard or specification which sets out what the various entities associated with the system are permitted to do and how that should be achieved. Communication protocols and/or parameters which shall be used for the connection are also typically defined. One example of a communications system is UTRAN (3G radio). Another example of an architecture that is known is the long-term evolution (LTE) or the Universal Mobile Telecommunications System (UMTS) radioaccess technology. Another example communication system is so called 5G radio or new radio (NR) access technology.

Summary [0005]According to a first aspect, there is provided an apparatus for an access point to a communication network, the apparatus comprising: means for determining to obtain a timing signal provided by a backhaul access point configured to provide a wireless backhaul to the communication network; means for receiving the timing signal via the wireless backhaul; and means for signalling the timing signal received to a terminal.

[0006] The apparatus may comprise means for signaling the backhaul access point to request the timing signal before receiving the timing signal.

[0007]The apparatus may comprise means for signaling to the terminal an indication that a residence time of the timing signal in the communication network depends on at least two transmissions of the timing signal being made over a radio air interface. [0008] The means for determining to obtain the timing signal may comprise means for determining that a clock associated with the apparatus and the communication network has failed and/or that the apparatus is not associated with such a clock.

[0009] The timing signal may be received via a resource control signaling or a System Information Block.

[0010]The timing signal may comprise timing information for the communication network.

[0011]The wireless backhaul may be a backhaul New Radio llu.

[0012] According to a second aspect, there is provided an apparatus for an access point to a communication network, the apparatus comprising: means for providing a wireless backhaul to the communication network; means for receiving, from a first access point, a request for a timing signal; and means for signalling the timing signal to the first access point.

[0013]The timing signal may comprise timing information for the communication network.

[0014] The wireless backhaul may be a backhaul New Radio llu.

[0015] The timing signal may be signaled to the first access point via a resource control signaling or a System Information Block.

[0016] According to a third aspect, there is provided an apparatus for a terminal, the apparatus comprising: means for receiving at least one timing signal from an access point configured to provide access to a communication network, the at least one timing signal comprising timing information for at least the communication network; and means for determining a residence time of the at least one timing signal in the communication network in dependence on at least two transmissions of the timing signal being made over a radio air interface.

[0017] The apparatus may comprise means for receiving from the access point an indication to determine the residence time in dependence on the at least two transmissions of the timing signal being made over radio air interface.

[0018] At least part of the timing information may be comprised within the at least one timing signal is associated with a master entity in the time sensitive network.

[0019] The apparatus may comprise means for providing the residence time to an entity in a time sensitive network.

[0020] According to a fourth aspect, there is provided an apparatus for an access point to a communication network, the apparatus comprising: at least one processor; and at least one memory comprising code that, when executed by the at least one processor, causes the apparatus to: determine to obtain a timing signal provided by a backhaul access point configured to provide a wireless backhaul to the communication network; receive the timing signal via the wireless backhaul; and signal the timing signal received to a terminal.

[0021]The apparatus may be caused to signal the backhaul access point to request the timing signal before receiving the timing signal.

[0022] The apparatus may be caused to signal to the terminal an indication that a residence time of the timing signal in the communication network depends on at least two transmissions of the timing signal being made over a radio air interface.

[0023]The determining to obtain the timing signal may comprise determining that a clock associated with the apparatus and the communication network has failed and/or that the apparatus is not associated with such a clock.

[0024] The timing signal may be received via a resource control signaling or a System Information Block.

[0025]The timing signal may comprise timing information for the communication network.

[0026] The wireless backhaul may be a backhaul New Radio llu.

[0027]According to a fifth aspect, there is provided an apparatus for an access point to a communication network, the apparatus comprising: at least one processor; and at least one memory comprising code that, when executed by the at least one processor, causes the apparatus to: provide a wireless backhaul to the communication network; receive, from a first access point, a request for a timing signal; and signal the timing signal to the first access point.

[0028]The timing signal may comprise timing information for the communication network.

[0029] The wireless backhaul may be a backhaul New Radio llu.

[0030] The timing signal may be signaled to the first access point via a resource control signaling or a System Information Block.

[0031]According to a sixth aspect, there is provided an apparatus for a terminal, the apparatus comprising: at least one processor; and at least one memory comprising code that, when executed by the at least one processor, causes the apparatus to: receive at least one timing signal from an access point configured to provide access to a communication network, the at least one timing signal comprising timing information for at least the communication network; and determine a residence time of the at least one timing signal in the communication network in dependence on at least two transmissions of the timing signal being made over a radio air interface.

[0032] The apparatus may be caused to receive from the access point an indication to determine the residence time in dependence on the at least two transmissions of the timing signal being made over radio air interface.

[0033]At least part of the timing information may be comprised within the at least one timing signal is associated with a master entity in the time sensitive network.

[0034] The apparatus may be caused to provide the residence time to an entity in a time sensitive network.

[0035]According to a seventh aspect, there is provided a method for an apparatus for an access point to a communication network, the method comprising: determining to obtain a timing signal provided by a backhaul access point configured to provide a wireless backhaul to the communication network; receiving the timing signal via the wireless backhaul; and signalling the timing signal received to a terminal.

[0036]The method may comprise signaling the backhaul access point to request the timing signal before receiving the timing signal.

[0037] The method may comprise signaling to the terminal an indication that a residence time of the timing signal in the communication network depends on at least two transmissions of the timing signal being made over a radio air interface. [0038]The determining to obtain the timing signal may comprise determining that a clock associated with the apparatus and the communication network has failed and/or that the apparatus is not associated with such a clock.

[0039] The timing signal may be received via a resource control signaling or a System Information Block.

[0040]The timing signal may comprise timing information for the communication network.

[0041]The wireless backhaul may be a backhaul New Radio llu.

[0042]According to an eighth aspect, there is provided a method for an apparatus for an access point to a communication network, the method comprising: providing a wireless backhaul to the communication network; receiving, from a first access point, a request for a timing signal; and signalling the timing signal to the first access point. [0043]The timing signal may comprise timing information for the communication network.

[0044] The wireless backhaul may be a backhaul New Radio llu.

[0045] The timing signal may be signaled to the first access point via a resource control signaling or a System Information Block.

[0046]According to a ninth aspect, there is provided a method for an apparatus for a terminal, the method comprising: receiving at least one timing signal from an access point configured to provide access to a communication network, the at least one timing signal comprising timing information for at least the communication network; and determining a residence time of the at least one timing signal in the communication network in dependence on at least two transmissions of the timing signal being made over a radio air interface.

[0047] The method may comprise receiving from the access point an indication to determine the residence time in dependence on the at least two transmissions of the timing signal being made over radio air interface.

[0048]At least part of the timing information may be comprised within the at least one timing signal is associated with a master entity in the time sensitive network.

[0049] The method may comprise providing the residence time to an entity in a time sensitive network.

[0050]According to a tenth aspect, there is provided an apparatus for an access point to a communication network, the apparatus comprising: determining circuitry for determining to obtain a timing signal provided by a backhaul access point configured to provide a wireless backhaul to the communication network; receiving circuitry for receiving the timing signal via the wireless backhaul; and signaling circuitry for signaling the timing signal received to a terminal.

[0051]The apparatus may comprise signaling circuitry for signaling the backhaul access point to request the timing signal before receiving the timing signal.

[0052] The apparatus may comprise signaling circuitry for signaling to the terminal an indication that a residence time of the timing signal in the communication network depends on at least two transmissions of the timing signal being made over a radio air interface.

[0053]The determining circuitry for determining to obtain the timing signal may comprise determining circuitry for determining that a clock associated with the apparatus and the communication network has failed and/or that the apparatus is not associated with such a clock.

[0054] The timing signal may be received via a resource control signaling or a System Information Block.

[0055]The timing signal may comprise timing information for the communication network.

[0056] The wireless backhaul may be a backhaul New Radio llu.

[0057]According to an eleventh aspect, there is provided an apparatus for an access point to a communication network, the apparatus comprising: providing circuitry for providing a wireless backhaul to the communication network; receiving circuitry for receiving, from a first access point, a request for a timing signal; and siganll ing circuitry for signalling the timing signal to the first access point.

[0058]The timing signal may comprise timing information for the communication network.

[0059] The wireless backhaul may be a backhaul New Radio llu.

[0060] The timing signal may be signaled to the first access point via a resource control signaling or a System Information Block.

[0061]According to a twelfth aspect, there is provided an apparatus for a terminal, the apparatus comprising: receiving circuitry for receiving at least one timing signal from an access point configured to provide access to a communication network, the at least one timing signal comprising timing information for at least the communication network; and determining circuitry for determining a residence time of the at least one timing signal in the communication network in dependence on at least two transmissions of the timing signal being made over a radio air interface.

[0062] The apparatus may comprise receiving circuitry for receiving from the access point an indication to determine the residence time in dependence on the at least two transmissions of the timing signal being made over radio air interface.

[0063]At least part of the timing information may be comprised within the at least one timing signal is associated with a master entity in the time sensitive network.

[0064] The apparatus may comprise providing circuitry for providing the residence time to an entity in a time sensitive network.

[0065]According to a thirteenth aspect, there is provided non-transitory computer readable medium comprising program instructions for causing an apparatus for an access point to a communication network to perform at least the following: determine to obtain a timing signal provided by a backhaul access point configured to provide a wireless backhaul to the communication network; receive the timing signal via the wireless backhaul; and signal the timing signal received to a terminal.

[0066] The apparatus may be caused to signal the backhaul access point to request the timing signal before receiving the timing signal.

[0067] The apparatus may be caused to signal to the terminal an indication that a residence time of the timing signal in the communication network depends on at least two transmissions of the timing signal being made over a radio air interface.

[0068]The determining to obtain the timing signal may comprise determining that a clock associated with the apparatus and the communication network has failed and/or that the apparatus is not associated with such a clock.

[0069] The timing signal may be received via a resource control signaling or a System Information Block.

[0070]The timing signal may comprise timing information for the communication network.

[0071]The wireless backhaul may be a backhaul New Radio llu.

[0072]According to a fourteenth aspect, there is provided non-transitory computer readable medium comprising program instructions for causing an apparatus for an access point to a communication network to perform at least the following: provide a wireless backhaul to the communication network; receive, from a first access point, a request for a timing signal; and signal the timing signal to the first access point. [0073]The timing signal may comprise timing information for the communication network.

[0074] The wireless backhaul may be a backhaul New Radio llu.

[0075] The timing signal may be signaled to the first access point via a resource control signaling or a System Information Block.

[0076]According to a fifteenth aspect, there is provided non-transitory computer readable medium comprising program instructions for causing an apparatus for a terminal to perform at least the following receive at least one timing signal from an access point configured to provide access to a communication network, the at least one timing signal comprising timing information for at least the communication network; and determine a residence time of the at least one timing signal in the communication network in dependence on at least two transmissions of the timing signal being made over a radio air interface.

[0077] The apparatus may be caused to receive from the access point an indication to determine the residence time in dependence on the at least two transmissions of the timing signal being made over radio air interface.

[0078]At least part of the timing information may be comprised within the at least one timing signal is associated with a master entity in the time sensitive network.

[0079] The apparatus may be caused to provide the residence time to an entity in a time sensitive network.

[0080]According to a sixteenth aspect, there is provided a computer program comprising program instructions for causing a computer to perform any method as described above.

[0081]According to a seventeenth aspect, there is provided a computer program product stored on a medium may cause an apparatus to perform any method as described herein.

[0082]According to an eighteenth aspect, there is provided an electronic device that may comprise apparatus as described herein.

[0083] According to a nineteenth aspect, there is provided a chipset that may comprise an apparatus as described herein.

[0084]Various other aspects are also described in the following detailed description and in the attached claims.

Brief description of Figures [0085] Embodiments will now be described, by way of example only, with reference to the accompanying Figures in which:

[0086] Figure 1 shows a schematic representation of a 5G system;

[0087] Figure 2 shows a schematic representation of a network apparatus;

[0088] Figure 3 shows a schematic representation of a user equipment;

[0089] Figure 4 shows a schematic representation of a non-volatile memory medium storing instructions which when executed by a processor allow a processor to perform one or more of the steps of the methods of some embodiments;

[0090] Figure 5 shows a schematic representation of a system architecture;

[0091] Figure 6 shows an example signaling between at least some of the elements shown in Figure 5;

[0092] Figures 7 to 9 show schematic representation of a system architecture;

[0093] Figure 10 shows example signaling;

[0094] Figure 11 shows a schematic representation of a system architecture;

[0095] Figure 12 shows an example signaling between at least some of the elements shown in Figure 11 ;

[0096] Figures 13 to 15 are flowcharts illustrating potential operations that may be performed by apparatuses described herein.

Detailed description

[0097] In the following certain embodiments are explained with reference to mobile communication devices capable of communication via a wireless cellular system and mobile communication systems serving such mobile communication devices. Before explaining in detail the exemplifying embodiments, certain general principles of a 5G wireless communication system are briefly explained with reference to Figure 1.

[0098] Figure 1 shows a schematic representation of a 5G system (5GS) 100. The 5GS may comprise a user equipment (UE) 102 (which may also be referred to as a communication device or a terminal), a 5G access network (AN) (which may be a 5G Radio Access Network (RAN) or any other type of 5G AN such as a Non-3GPP Interworking Function (N3IWF) /a Trusted Non3GPP Gateway Function (TNGF) for Untrusted / Trusted Non-3GPP access or Wireline Access Gateway Function (W-AGF) for Wireline access) 104, a 5G core (5GC) 106, one or more application functions (AF) 108 and one or more data networks (DN) 110. [0099]The 5G RAN may comprise one or more gNodeB (gNB) distributed unit functions connected to one or more gNodeB (gNB) unit functions. The RAN may comprise one or more access nodes.

[0100] The 5GC 106 may comprise one or more access management functions (AMF) 112, one or more session management functions (SMF) 114, one or more authentication server functions (ALISF) 116, one or more unified data management (UDM) functions 118, one or more user plane functions (UPF) 120, one or more unified data repository (UDR) functions 122, one or more network repository functions (NRF) 128, and/or one or more network exposure functions (NEF) 124. Although NRF 128 is not depicted with its interfaces, it is understood that this is for clarity reasons and that NRF 128 may have a plurality of interfaces with other network functions.

[0101]The 5GC 106 also comprises a network data analytics function (NWDAF) 126. The NWDAF is responsible for providing network analytics information upon request from one or more network functions or apparatus within the network. Network functions can also subscribe to the NWDAF 126 to receive information therefrom. Accordingly, the NWDAF 126 is also configured to receive and store network information from one or more network functions or apparatus within the network. The data collection by the NWDAF 126 may be performed based on at least one subscription to the events provided by the at least one network function.

[0102] The 5GC (5G Core network) has been defined as a Service Based Architecture (SBA). Service-Based Architectures provide a modular framework from which common applications can be deployed using components of varying sources and suppliers. Control plane functionality and common data repositories of a 5G network may thus be delivered by way of a set of interconnected Network Functions (NFs), each with authorization to access each other’s services, with Network Function (NF) service producers exposing services to NF service consumers. NFs may act as service consumers and/or service providers. NF service providers register their NF profile in a Network Repository Function (NRF). An NRF maintains an updated repository of 5G elements available in the operator's network, along with the services provided by each of the elements in the 5G core that are expected to be instantiated, scaled and/or terminated without or minimal manual intervention. In other words, the NRF maintains a record of available NF instances and their supported services. The NRF allows other NF instances to subscribe and be notified of registrations from NF instances of a given type. The NRF may support service discovery, by receipt of Discovery Requests from NF instances and details which NF instances support specific services. Therefore NF Service consumers or Service Communication Proxies (SCP) (which obtain NF services on behalf of another network entity) may discover NF service producers by performing for example, an NF Discovery procedure towards the NRF.

[0103] One of the systems popularized in 5G is the Integrated Access and Backhaul (IAB) network. IAB is a wireless backhaul system. IAB can provide flexible and scalable multi-hop backhauling, using the same or different frequency bands (e.g mmWave, below 6GHz) for access and backhaul. The backhaul may be efficiently forwarded across the wirelessly interconnected radio nodes, with the backhaul links terminated by an IAB mobile termination (IAB-MT) function.

[0104]To assist with this, the IAB network utilizes existing concepts in 5G NR. In particular, the access point/gNB in 5G may be considered to be a logical node, that may be split into one central unit (CU) and one or more distributed units (DU). The central unit hosts the higher layer protocols to the UE and terminates the control plane and user plane interfaces to the 5GC. The central unit may control the distributed unit nodes, where the distributed unit node hosts the lower layers for the interface to the UE (such as the NR Uu interface). The entity that provides the wireless backhaul links is known as a donor node. In other words, an IAB donor may be considered to be a logical node that provides the NR-based wireless backhaul and comprises a central unit and donor distributed unit(s). The donor-distributed unit(s) may be wire-connected to the central unit. As these are all functional/logical entities, they may all be comprised within a single physical gNB.

[0105] Recently, the industrial internet of things (HoT) has been deployed on large scales. I loT is the use of smart sensors and actuators to enhance manufacturing and industrial processes by leveraging the power of smart machines and real-time analytics to take advantage of the data that 'dumb machines' have produced in industrial settings for years. The use of such smart machines can place an ever- increasing demand on communication networks to which they are connected. To address this, 5G systems have been provisioned to help mitigate the effects of this.

[0106] 5G RAN includes several functionalities to achieve low latency for selected data flows, particularly in its provision of Ultra reliable low-latency communications (URLLC). One of these functionalities relates to time synchronization. Time synchronization is embedded into the 5G cellular radio systems as a part of their operation. The radio network components themselves may also be time synchronized, for instance, through the precision time protocol telecom profile.

[0107]5G Ultra reliable low-latency communication (URLLC) capabilities may provide a good match to time sensitive networking (TSN) features. TSN is a set of open standards specified by IEEE 802.1 that were primarily developed for IEEE Std 802.3 Ethernet applications. Part of these standards are included to enable time synchronization across such a network. The TSN tool for time synchronization is the generalized Precision Time Protocol (gPTP), which is a profile of the Precision Time Protocol standard (IEEE 1588). The gPTP provides reliable time synchronization, which can be used by other TSN tools, such as Scheduled Traffic (802.1 Qbv).

[0108]When the 5G System (5GS) and the TSN system are combined, the 5G system (5GS) may appear from the rest of the network to be a set of TSN bridges, with one virtual TSN bridge per User Plane Function (UPF). The 5GS may include TSN translator functionality for translating between the 5GS and the TSN domain, both for the user plane and the control plane. Such TSN translator (TT) functionality may hide the 5GS internal procedures from the TSN network.

[0109] Time synchronization is a key component in all cellular networks. Providing time synchronization in a 5G-TSN combined industrial deployment brings in new aspects. In most cases, end devices need time references, while bridges using a TSN feature that is based on time, such as Scheduled Traffic (802.1 Qbv) may also need time references.

[0110] As gPTP is the default time synchronization solution for TSN-based industrial automation, an interworking 5GS with such a network may also comprise functionality to interwork with the gPTP of the connected TSN network. This functionality may be provided through the TSN translator functionality. The 5GS may thus act as a virtual gPTP time-aware system and support the forwarding of gPTP time synchronization information between end stations and bridges through the 5G user plane TSN translator functionality.

[0111]The following considers issues when access points, such as gNBs, are unable to support time synchronization when there is no access to the access point’s own clock, or the access point’s clock has failed.

[0112] This has particular relevance to scenarios with mixed RAN deployments. For example, 1 -2 base stations operating at lower frequencies e.g. 3.7 GHz covering the hole environment but capacity limited due to bandwidth provide communication to ‘mobile’ equipment, such as automated guided vehicles (AGVs). As another example, multiple base stations operating at mmWave to serve capacity issues, which are aimed to provide communication to single production lines, local UPF, ultra-high availability requirements (multi connectivity might be a precondition)

[0113] The issue of providing a time synchronization when either an access point has no clock or its clock has failed has not previously been considered in such scenarios. It would also be useful to provide a time synchronization mechanism that can be applied/adapted to a plurality of different scenarios, or that otherwise may yield advantages. For example, it would be useful to provide a mechanism that is as cost effective as a wired time synchronization mechanism and may thus be applied when there is a higher density of access points in areas with only sparse fiber availability. It would also be useful to provide a mechanism that may also provide indoor coverage, and that avoids relying on the access point itself, while also being able to operate in a multi-radio access network deployment. It would also be useful to provide a time synchronization mechanism that may also be used for external (e.g. IEEE 802.1 AS or IEEE 1588) clocks with IAB (Integrated access & backhaul) deployment.

[0114] One current mechanism for providing external clock time synchronization is described in reference to Figures 5 and 6.

[0115] Figure 5 illustrates the entities and at least some of their interfaces that may be involved in the current mechanism.

[0116] Figure 5 shows a gPTP slave 501 in a TSN network that exchanges gPTP signaling with a first timestamping entity 502 in a user equipment TSN translator functionality 503. This first timestamping entity 502 is for synchronizing TSN timestamping with 5GS time. The user equipment TSN translator functionality 503 interfaces with a 5G UE 504, which communicates with a 5G access point 505 (e.g. over a llu interface). The llu interface may be considered to be the New Radio air interface. The 5G access point 505 interfaces with a user plane function 506 for that UE 504 (e.g. over an N3 interface), which in turn communicates with a network TSN translator functionality 507 comprising a second timestamping entity 508. The second timestamping entity 508 interfaces with a gPTP master 509 on the TSN.

[0117] Signalling between at least some of the entities depicted in Figure 5 is described with reference to Figure 6.

[0118] Figure 6 shows signaling between a gPTP slave entity 601 , TSN/5GS TSN translator functionality of a UE 602 (“the UE TSN translator functionality”), TSN/5GS TSN translator functionality of the network 603 (“the network TSN translator functionality), and a gPTP master entity 604.

[0119] At 6001 , the gPTP master entity 604 transmits a synchronization signal to the network TSN translator functionality 603.

[0120] At 6002, the network TSN translator functionality 603 timestamps the synchronization signal with a first time T 1 .

[0121] At 6003, the network TSN translator functionality 603 sends the synchronization signal (with the T1 timestamp) to the UE TSN translator functionality 602.

[0122]At 6004, the gPTP master entity 604 transmits a follow-up synchronization signal to the network TSN translator functionality 603.

[0123] At 6005, the network TSN translator functionality 603 timestamps the follow-up synchronization signal with the first time T 1 .

[0124] At 6006, the network TSN translator functionality 603 updates the follow-up information for that synchronization signal with a path delay and cumulative rate ratio. The cumulative rate ratio may be said to be a frequency shift that represents the cumulative ratio of the frequency of the 5GS clock to the frequency of the clock of the TSN domain.

[0125]At 6007, the UE TSN translator functionality 602 transmits the synchronization signal to the gPTP slave entity 601 .

[0126] At 6008, the UE TSN translator functionality 602 timestamps the synchronization signal with a second time, T2.

[0127] At 6009, the network TSN translator functionality 603 sends the follow-up synchronization signal to the UE TSN translator functionality 602.

[0128] At 6010, the UE TSN translator functionality 602 calculates a residence time of the synchronization signals in the 5G network (i.e. in the network between the UE TSN translator functionality 602 and the network TSN translator functionality 603).

[0129]At 6011 , the UE TSN translator functionality 602 updates the follow-up information with the calculated residence time, and removes the first time, T1 , from the synchronization signals.

[0130] At 6012, the UE TSN translator functionality 602 sends the follow-up synchronization signal to the gPTP slave entity 601 .

[0131]The following proposes to provide a time synchronization mechanism by leveraging Integrated Access and Backhaul (IAB) deployment to use external clocks behind donor nodes for time synchronization support. In other words, external clocks behind entities in the access network may be used to provide a time synchronization mechanism. This time synchronization support may be used for both a 5G reference in addition to an external clock domain. This synchronization support may be used when the over the air link between the UE and the network and the backhaul links between network elements use different spectrum/bands.

[0132]Thus, when a gNB’s own clock fails, the gNB may use a neighbor gNB clock that is available via its backhaul. This mechanism may also be particularly useful when when wired connectivity/X2 support is a challenge as IAB relies upon NR llu support for back-haul link and donor gNB to provide the connectivity to the clock. In such arrangements, any calculation of the residence time within the 5GS may take IAB deployment into consideration. This may be, as later illustrated, twice the NR delay between the UE and the gNB (e.g. twice the NR Uu delay).

[0133] Figures 7 to 9 illustrate some of the example IAB deployments in which the presently described techniques may be used.

[0134] Figure 7 shows a 5G core network entity 701 that interfaces with an IAB donor gNB 702. The IAB donor gNB interfaces with an IAB node 703 (e.g. using a NR Uu link). The IAB node 703 interfaces with a UE 704 (e.g. using a NR Uu link). The UE 704 may be standalone with the 5G core network entity 701 . The IAB node 703 may be standalone with the 5G core network entity 701 . In general, a node may be said to be standalone if it is supported by 5G infrastructure. In contrast, a node may be said to be non-standalone if it supported (at least in part) by non-5G infrastructure, such as 4G infrastructure.

[0135] Figure 8 shows a 5G core network entity 801 that interfaces with an IAB donor gNB 802. The IAB donor gNB interfaces with an IAB node 803 (e.g. using a NR Uu link). The IAB node 803 interfaces with a UE 804 (e.g. using a NR Uu link). Also shown is an enhanced packet core 805 (i.e. a network compatible with the 5G radio access network system). The enhanced packet core 805 may interface with eNB 806 (e.g. over an S1 interface), which in turn interfaces with the IAB donor gNB 802 (e.g. over an X2 interface) and with the UE 804 (e.g. over an LTE Uu interface). The UE 804 may be non-standalone with the enhanced packet core 805. The IAB node 803 may be standalone with the 5G core network entity 801 .

[0136] Figure 9 shows an enhanced packet core 901 that interfaces with an IAB donor gNB 902. The IAB donor gNB interfaces with an IAB node 903 (e.g. using a NR Uu link). The IAB node 903 interfaces with a UE 904 (e.g. using a NR Uu link). The enhanced packet core 901 may interface with eNB 905 (e.g. over an S1 interface), which in turn interfaces with the IAB donor gNB 902 (e.g. over an X2 interface), with the IAB node 903, and with the UE 804 (e.g. over an LTE llu interface). The UE 804 may be non-standalone with the enhanced packet core 805. The IAB node 803 may be non-standalone with the 5G core network entity 801 .

[0137] As a default, a gNB may rely on its own clock for providing 5G time reference the UE. This time reference may be signaled to the UE using, for example, radio resource control signaling/a System information Block (e.g. SIB9).

[0138] However, when the gNB cannot rely upon its own clock due to failure or it simply does not have its own clock, the gNB may rely upon 5G timing information provided by the donor gNB over NR Uu for providing updated 5G timing information towards the UE using NR Uu.

[0139]When the gNB does not have its own clock and always relies on timing information provided by the donor gNB, the gNB may request for 5G timing reference information to be provided via the NR Uu. The gNb may also register for any updates relating to the 5G clock drift.

[0140] In case of failure situations, the gNB may be configured to both detect the failure and to notify the donor gNB (over NR Uu) regarding the need for the donor gNB to provide 5G reference timing that can be forwarded to the UE.

[0141]The gNB may also be configured to update all the UE(s) with the updated 5G timing information. This may be signaled to the UE using, for example, radio resource control signaling/a System information Block (e.g. SIB9).

[0142]A single donor gNB may provide timing information to multiple gNBs/IAB- node(s) in the area. In other words, a single donor gNB may be relied on to insert a time stamp into signaling and to forward (g)PTP messages to multiple access nodes without internal timing information. The (g)PTP messages may be signaled using, for example, the NR Uu interface.

[0143] In case of IAB deployment, if gPTP timing information is received from the donor gNB and there is no discrepancy between the gNB’s and the received timing information, the receiving lAB-node may simply forward the gPTP message. Otherwise, if the external clock is behind the lAB-node, the lAB-node may insert a time stamp into the gPTP message before and forward the gPtP message.

[0144] Correction time determination, sync and follow up messages may be adapted for IAB deployment. [0145]The following will describe some specific examples of the presently described techniques, before a more general overview is provided.

[0146] Figure 10 is a signaling diagram between a donor gNB 1001 and an IAB node gNB 1002. This Figure illustrates the functional impact for a gNB to leverage IAB deployment for timing reference information.

[0147] At 10001 , the IAB node gNB 1002 makes a decision to use timing information from a donor gNB. This decision may be made, for example, in response to detection and/or determination of a failure of a 5G clock in the IAB node gNB 1002. This decision may be made, for example, in response to detection and/or determination that the IAB node gNB 1002 does not have a 5G clock.

[0148] At 10002, the IAB node gNB 1002 signals the donor gNB 1001 to request 5G timing information from the donor gNB 1001 .

[0149] At 10003, the donor gNB 1001 responds to the signaling of 10002 with signaling for 5G timing. This signaling may be, for example, using radio resource control signaling and/or using System Information Block, such as SIB9. This information may be signaled, for example, using the NR llu interface.

[0150]At 10004, the IAB node gNB 1002 relays the received 5G timing to a UE.

[0151] Figures 11 and 12 illustrate the architectural and functional impacts to supporting the presently described time synchronization mechanism.

[0152] Figure 11 shows a gPTP slave 1101 in a TSN network that exchanges gPtP signaling with a first timestamping entity 1102 in a user equipment TSN translator functionality 1103. This first timestamping entity 1102 is for synchronizing TSN timestamping with 5GS time. The user equipment TSN translator functionality 1103 interfaces with a 5G UE 1104, which communicates with a 5G access point/gNB 1105 (e.g. over a Uu interface). The 5G access point 1105 interfaces with another 5G access point/gNB 1106 using a Uu interface, which in turn interfaces with a user plane function 1107 for that UE 1104 (e.g. over an N3 interface). The user plane function 1107 interfaces with a network TSN translator functionality 1108, which comprises a second timestamping entity 1109. The second timestamping entity 1109 interfaces with a gPTP master 1110 on the TSN.

[0153] Figure 12 illustrates potential signaling between at least some of the entities identified in Figure 11 . [0154] Figure 12 shows signaling between a gPTP slave entity 1201 , a UE TSN translator functionality 1202, a network TSN translator functionality 1203 and a gPTP master entity 1204.

[0155]At 12001 , the gPTP master entity 1204 transmits a synchronization signal to the network TSN translator functionality 1203.

[0156] At 12002, the network TSN translator functionality 1203 timestamps the synchronization signal with a first time T 1 .

[0157] At 12003, the network TSN translator functionality 1203 sends the synchronization signal (with the T1 timestamp) to the UE TSN translator functionality 1202.

[0158] At 12004, the gPTP master entity 1204 transmits a follow-up synchronization signal to the network TSN translator functionality 1203.

[0159] At 12005, the network TSN translator functionality 1203 timestamps the followup synchronization signal with the first time T1 .

[0160]At 12006, the network TSN translator functionality 1203 updates the follow-up information for that synchronization signal with a path delay and cumulative rate ratio. [0161]At 12007, the UE TSN translator functionality 1202 transmits the synchronization signal to the gPTP slave entity 1201 .

[0162] At 12008, the UE TSN translator functionality 1202 timestamps the synchronization signal with a second time, T2.

[0163] At 12009, the network TSN translator functionality 1203 sends the follow-up synchronization signal to the UE TSN translator functionality 1202.

[0164] At 12010, the UE TSN translator functionality 1202 calculates a residence time of the synchronization signals in the 5G network (i.e. in the network between the UE TSN translator functionality 1202 and the network TSN translator functionality 1203). This calculation of residence time may account for twice NR Uu delay over the Uu link, as shown in Figure 11 , and discussed further below.

[0165]

[0166] At 12011 , the UE TSN translator functionality 1202 updates the follow-up information with the calculated residence time, and removes the first time, T1 , from the synchronization signals.

[0167] At 12012, the UE TSN translator functionality 1202 sends the follow-up synchronization signal to the gPTP slave entity 1201 .

[0168] We now consider options for how to calculate the residence time. [0169] Previously, as per Figure 6, residence time calculation without IAB calculated both a bridge delay attributed to a time for the timing signal to traverse between 5GS bridges, and delay for the timing signal to extend between the UE and the TSN translator on the device-side. These were, respectively calculated as follows. a. 5GS Bridge delay = PDB (Packet delay budget) based on a quality of service identifier (e.g. 5QI) assigned for the QoS Flow. This would comprise both a delay resulting from NR llu and the delay resulting from N3. b. UE-DS-TSN translator Residence Time = DS-TT residence time + UE residence time, where DS is device (e.g. UE) side and DS-TT = Device (UE) side TSN Translator.

[0170] There are several options for calculating residence times based on the currently presented system.

[0171] As a first example: a. 5GS Bridge delay = PDB based on 5QI assigned for the QoS Flow This may comprise both a delay resulting from NR Uu and a delay resulting from N3. b. UE-DS-TT Residence Time = DS-TT residence time + UE residence time + NR Uu delay.

[0172] As a second example: a. 5GS Bridge delay = PDB based on 5QI assigned for the QoS Flow. This may comprise a delay resulting from two transmissions over NR Uu and a delay resulting from N3. b. UE-DS-TT Residence Time = DS-TT residence time + UE residence time + NR Uu delay.

[0173] Figures 13 to 15 are flowcharts illustrating potential operations that may be performed by apparatuses performing at least some of the presently described mechanisms.

[0174] Figure 13 illustrates operations that may be performed by apparatus for an access point to a communication network. The apparatus of Figure 13 may interact with the apparatuses of Figures 14 and 15.

[0175]At 1301 , the apparatus may determine to obtain a timing signal provided by a backhaul access point configured to provide a wireless backhaul to the communication network. [0176]The determining to obtain the timing signal may comprise determining that a clock associated with the apparatus and the communication network has failed and/or that the apparatus is not associated with such a clock.

[0177] At 1302, the apparatus may receive the timing signal via the wireless backhaul.

[0178] At 1303, the apparatus may signal the timing signal received (e.g. the signal of 1302) to a terminal.

[0179]The apparatus may signal the backhaul access point to request the timing signal before receiving the timing signal.

[0180] The apparatus may signal to the terminal an indication that a residence time of the timing signal in the communication network depends on at least two transmissions of the timing signal being made over a radio air interface.

[0181]The timing signal may be received via a resource control signaling or a System Information Block.

[0182]The timing signal may comprise timing information for the communication network.

[0183] The wireless backhaul may be a backhaul New Radio llu

[0184] Figure 14 is a flow chart illustrating operations that may be performed by an apparatus for an access point to a communication network. The apparatus of claim 14 may interact with the apparatus of claim 13.

[0185]At 1401 , the apparatus provides a wireless backhaul to the communication network.

[0186] At 1402, the apparatus receives, from a first access point (e.g. the apparatus of Figure 13), a request for a timing signal.

[0187]At 1403, the apparatus signals the timing signal to the first access point.

[0188]The timing signal may comprise timing information for the communication network.

[0189] The wireless backhaul may be a backhaul New Radio llu.

[0190] The timing signal may be signaled to the first access point via a resource control signaling or a System Information Block.

[0191] Figure 15 is a flow chart illustrating potential operations that may be performed by a terminal (e.g. a UE). The apparatus of Figure 15 may interact with the apparatus of Figure 13. [0192] At 1501 , the apparatus receives at least one timing signal from an access point configured to provide access to a communication network, the at least one timing signal comprising timing information for at least the communication network.

[0193] At 1502, the apparatus determines a residence time of the at least one timing signal in the communication network in dependence on at least two transmissions of the timing signal being made over a radio air interface.

[0194]The apparatus may receive from the access point an indication to determine the residence time in dependence on the at least two transmissions of the timing signal being made over radio air interface.

[0195] At least part of the timing information comprised within the at least one timing signal may be associated with a master entity in the time sensitive network.

[0196]The apparatus may provide the residence time to an entity in a time sensitive network.

[0197]The presently described timing system has numerous advantages.

[0198] For example, IAB deployment is a cost-effective solution compared to the ‘wired’ case, and IAB has been widely considered by many operators in view of the wide range of spectrum in which NR is deployed. Thus it may be cost effective to leverage IAB mechanisms for Time Sync support.

[0199] Further, the presently described mechanism provides a backup solution for provisioning of additional clock redundancy, and is compatible with standalone I self- sufficient solutions (e.g. local operation of mmWave) or proprietary installations (additive sensing). Moreover, there is a single additional link for distribution of reference signal, which minimizes reconfiguration of the network, and there is no dependency on the performance of any non-3GPP equipment.

[0200] Figure 2 shows an example of a control apparatus for a communication system, for example to be coupled to and/or for controlling a station of an access system, such as a RAN node, e.g. a base station, gNB, a central unit of a cloud architecture or a node of a core network such as an MME or S-GW, a scheduling entity such as a spectrum management entity, or a server or host, for example an apparatus hosting an NRF, NWDAF, AMF, SMF, UDM/UDR etc. The control apparatus may be integrated with or external to a node or module of a core network or RAN. In some embodiments, base stations comprise a separate control apparatus unit or module. In other embodiments, the control apparatus can be another network element such as a radio network controller or a spectrum controller. The control apparatus 200 can be arranged to provide control on communications in the service area of the system. The apparatus 200 comprises at least one memory 201 , at least one data processing unit 202, 203 and an input/output interface 204. Via the interface the control apparatus can be coupled to a receiver and a transmitter of the apparatus. The receiver and/or the transmitter may be implemented as a radio front end or a remote radio head. For example, the control apparatus 200 or processor 201 can be configured to execute an appropriate software code to provide the control functions.

[0201]A possible wireless communication device will now be described in more detail with reference to Figure 3 showing a schematic, partially sectioned view of a communication device 300. Such a communication device is often referred to as user equipment (UE) or terminal. An appropriate mobile communication device may be provided by any device capable of sending and receiving radio signals. Non-limiting examples comprise a mobile station (MS) or mobile device such as a mobile phone or what is known as a ’smart phone’, a computer provided with a wireless interface card or other wireless interface facility (e.g., USB dongle), personal data assistant (PDA) or a tablet provided with wireless communication capabilities, or any combinations of these or the like. A mobile communication device may provide, for example, communication of data for carrying communications such as voice, electronic mail (email), text message, multimedia and so on. Users may thus be offered and provided numerous services via their communication devices. Non-limiting examples of these services comprise two-way or multi-way calls, data communication or multimedia services or simply an access to a data communications network system, such as the Internet. Users may also be provided broadcast or multicast data. Non-limiting examples of the content comprise downloads, television and radio programs, videos, advertisements, various alerts and other information.

[0202]A wireless communication device may be for example a mobile device, that is, a device not fixed to a particular location, or it may be a stationary device. The wireless device may need human interaction for communication or may not need human interaction for communication. In the present teachings the terms UE or “user” are used to refer to any type of wireless communication device.

[0203] The wireless device 300 may receive signals over an air or radio interface 307 via appropriate apparatus for receiving and may transmit signals via appropriate apparatus for transmitting radio signals. In Figure 3 transceiver apparatus is designated schematically by block 306. The transceiver apparatus 306 may be provided for example by means of a radio part and associated antenna arrangement. The antenna arrangement may be arranged internally or externally to the wireless device.

[0204]A wireless device is typically provided with at least one data processing entity 301 , at least one memory 302 and other possible components 303 for use in software and hardware aided execution of tasks it is designed to perform, including control of access to and communications with access systems and other communication devices. The data processing, storage and other relevant control apparatus can be provided on an appropriate circuit board and/or in chipsets. This feature is denoted by reference 704. The user may control the operation of the wireless device by means of a suitable user interface such as keypad 305, voice commands, touch sensitive screen or pad, combinations thereof or the like. A display 308, a speaker and a microphone can be also provided. Furthermore, a wireless communication device may comprise appropriate connectors (either wired or wireless) to other devices and/or for connecting external accessories, for example hands-free equipment, thereto.

[0205] Figure 4 shows a schematic representation of non-volatile memory media 400a (e.g. computer disc (CD) or digital versatile disc (DVD)) and 400b (e.g. universal serial bus (USB) memory stick) storing instructions and/or parameters 402 which when executed by a processor allow the processor to perform one or more of the steps of the methods of Figure 10.

[0206] The embodiments may thus vary within the scope of the attached claims. In general, some embodiments may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. For example, some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device, although embodiments are not limited thereto. While various embodiments may be illustrated and described as block diagrams, flow charts, or using some other pictorial representation, it is well understood that these blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

[0207]The embodiments may be implemented by computer software stored in a memory and executable by at least one data processor of the involved entities or by hardware, or by a combination of software and hardware. Further in this regard it should be noted that any procedures, e.g., as in Figure 10, may represent program steps, or interconnected logic circuits, blocks and functions, or a combination of program steps and logic circuits, blocks and functions. The software may be stored on such physical media as memory chips, or memory blocks implemented within the processor, magnetic media such as hard disk or floppy disks, and optical media such as for example DVD and the data variants thereof, CD.

[0208] The memory may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor-based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The data processors may be of any type suitable to the local technical environment, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASIC), gate level circuits and processors based on multi-core processor architecture, as non-limiting examples.

[0209] Alternatively or additionally some embodiments may be implemented using circuitry. The circuitry may be configured to perform one or more of the functions and/or method steps previously described. That circuitry may be provided in the base station and/or in the communications device.

[0210] As used in this application, the term “circuitry” may refer to one or more or all of the following:

(a) hardware-only circuit implementations (such as implementations in only analogue and/or digital circuitry);

(b) combinations of hardware circuits and software, such as:

(i) a combination of analogue and/or digital hardware circuit(s) with software/firmware and

(ii) any portions of hardware processor(s) with software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as the communications device or base station to perform the various functions previously described; and

(c) hardware circuit(s) and or processor(s), such as a microprocessor(s) or a portion of a microprocessor(s), that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation. [0211]This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and/or firmware. The term circuitry also covers, for example integrated device.

[0212]The foregoing description has provided by way of exemplary and non-limiting examples a full and informative description of some embodiments. However, various modifications and adaptations may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings and the appended claims. However, all such and similar modifications of the teachings will still fall within the scope as defined in the appended claims.

Claims

1 ) An apparatus for an access point to a communication network, the apparatus comprising: means for determining to obtain a timing signal provided by a backhaul access point configured to provide a wireless backhaul to the communication network; means for receiving the timing signal via the wireless backhaul; and means for signalling the timing signal received to a terminal.

2) An apparatus as claimed in claim 1 , comprising means for signaling the backhaul access point to request the timing signal before receiving the timing signal.

3) An apparatus as claimed in any preceding claim, comprising means for signaling to the terminal an indication that a residence time of the timing signal in the communication network depends on at least two transmissions of the timing signal being made over a radio air interface.

4) An apparatus as claimed in any preceding claim, wherein the means for determining to obtain the timing signal comprises means for determining that a clock associated with the apparatus and the communication network has failed and/or that the apparatus is not associated with such a clock.

5) An apparatus as claimed in any preceding claim, wherein the timing signal is received via a resource control signaling or a System Information Block.

6) An apparatus for an access point to a communication network, the apparatus comprising: means for providing a wireless backhaul to the communication network; means for receiving, from a first access point, a request for a timing signal; and means for signalling the timing signal to the first access point.

7) An apparatus as claimed in claim 6, wherein the timing signal is signaled to the first access point via a resource control signaling or a System Information Block.

26 ) An apparatus as claimed in any preceding claim, wherein the timing signal comprises timing information for the communication network. ) An apparatus as claimed in any preceding claim, wherein the wireless backhaul is a backhaul New Radio llu. 0)An apparatus for a terminal, the apparatus comprising: means for receiving at least one timing signal from an access point configured to provide access to a communication network, the at least one timing signal comprising timing information for at least the communication network; and means for determining a residence time of the at least one timing signal in the communication network in dependence on at least two transmissions of the timing signal being made over a radio air interface. 1 )An apparatus as claimed in claim 10, comprising means for receiving from the access point an indication to determine the residence time in dependence on the at least two transmissions of the timing signal being made over radio air interface. 2)An apparatus as claimed in any of claims 10 to 11 , wherein at least part of the timing information comprised within the at least one timing signal is associated with a master entity in the time sensitive network. 3)An apparatus as claimed in any of claims 10 to 12, comprising means for providing the residence time to an entity in a time sensitive network. 4)A method for an apparatus for an access point to a communication network, the method comprising: determining to obtain a timing signal provided by a backhaul access point configured to provide a wireless backhaul to the communication network; receiving the timing signal via the wireless backhaul; and signalling the timing signal received to a terminal. )A method as claimed in claim 14, comprising signaling the backhaul access point to request the timing signal before receiving the timing signal. )A method as claimed in any of claims 14 and 15, comprising signaling to the terminal an indication that a residence time of the timing signal in the communication network depends on at least two transmissions of the timing signal being made over a radio air interface. )A method as claimed in any of claims 14 to 16, wherein the determining to obtain the timing signal comprises determining that a clock associated with the apparatus and the communication network has failed and/or that the apparatus is not associated with such a clock. )A method as claimed in any of claims 14 to 17, wherein the timing signal is received via a resource control signaling or a System Information Block. )A method for an apparatus for an access point to a communication network, the method comprising: providing a wireless backhaul to the communication network; receiving, from a first access point, a request for a timing signal; and signalling the timing signal to the first access point. )A method as claimed in claim 19, wherein the timing signal is signaled to the first access point via a resource control signaling or a System Information Block. )A method as claimed in any of claims 14 to 20, wherein the timing signal comprises timing information for the communication network. )A method as claimed in any of claims 14 to 21 , wherein the wireless backhaul is a backhaul New Radio llu. )A method for an apparatus for a terminal, the method comprising: receiving at least one timing signal from an access point configured to provide access to a communication network, the at least one timing signal comprising timing information for at least the communication network; and determining a residence time of the at least one timing signal in the communication network in dependence on at least two transmissions of the timing signal being made over a radio air interface. )A method as claimed in claim 23, comprising receiving from the access point an indication to determine the residence time in dependence on the at least two transmissions of the timing signal being made over radio air interface. )A method as claimed in any of claims 23 to 24, wherein at least part of the timing information comprised within the at least one timing signal is associated with a master entity in the time sensitive network. )A method as claimed in any of claims 23 to 25, comprising providing the residence time to an entity in a time sensitive network. ) A computer program product that, when run on at least one processor of an apparatus for an access point to a communication network, causes the apparatus to perform: determining to obtain a timing signal provided by a backhaul access point configured to provide a wireless backhaul to the communication network; receiving the timing signal via the wireless backhaul; and signalling the timing signal received to a terminal. ) A computer program product that, when run on at least one processor of an apparatus for an access point to a communication network, causes the apparatus to perform: providing a wireless backhaul to the communication network; receiving, from a first access point, a request for a timing signal; and signalling the timing signal to the first access point. ) A computer program product that, when run on at least one processor of an apparatus for a terminal, causes the apparatus to perform:

29 receiving at least one timing signal from an access point configured to provide access to a communication network, the at least one timing signal comprising timing information for at least the communication network; and determining a residence time of the at least one timing signal in the communication network in dependence on at least two transmissions of the timing signal being made over a radio air interface.

30