WO2020151806A1

WO2020151806A1 - Time synchronization mechanisms for wireless end points

Info

Publication number: WO2020151806A1
Application number: PCT/EP2019/051410
Authority: WO
Inventors: Rakash SivaSiva GANESAN; Peter Rost; Kari Juhani NIEMELÄ; Vladimir Vukadinovic; Troels Emil Kolding
Original assignee: Nokia Technologies Oy
Priority date: 2019-01-22
Filing date: 2019-01-22
Publication date: 2020-07-30

Abstract

There is provided an apparatus, said apparatus comprising means for, at user equipment associated with a first network, receiving an indication of a reference clock time from the first network, performing a synchronisation procedure with a clock of a second network, determining a relation between the reference clock time and the clock of the second network and providing an indication of the relation to the first network.

Description

Time synchronization mechanisms for wireless end points

Field

The present application relates to a method, apparatus, system and computer program and in particular but not exclusively to Time synchronization and signaling mechanisms for synchronizing wireless end stations in an integrated 5GS-time sensitive networking (TSN) network.

Background

A communication system can be seen as a facility that enables communication sessions between two or more entities such as user terminals, base stations 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 (also referred to as station or user equipment) and/or application servers. The communication sessions may comprise, for example, communication of data for carrying communications such as voice, video, electronic mail (email), text message, multimedia, content data, time-sensitive network (TSN) flows and/or data in an industrial application such as critical system messages between an actuator and a controller, critical sensor data (such as measurements, video feed etc.) towards a control system and so on. Non-limiting examples of services provided comprise two-way or multi-way calls, data communication or multimedia services and access to a data network system, such as the Internet.

In a wireless communication system at least a part of a communication session, for example, between at least two stations or between at least one station and at least one application server (e.g. for video), occurs over a wireless link. Examples of wireless systems comprise public land mobile networks (PLMN) operating based on 3GPP radio standards such as E- UTRA, New Radio, satellite based communication systems and different wireless local networks, for example wireless local area networks (WLAN). The wireless systems can typically be divided into cells, and are therefore often referred to as cellular systems.

A user can access the communication system by means of an appropriate communication device or terminal. A communication device of a user may be referred to as user equipment (UE) or user device. A communication device is provided with an appropriate signal receiving and transmitting apparatus for enabling communications, for example enabling access to a communication network or communications directly with other users. The communication device may access one or more carriers provided by the network, for example a base station of a cell, and transmit and/or receive communications on the one or more carriers.

The communication system and associated devices typically operate in accordance with a given 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). Other examples of communication systems are the long-term evolution (LTE) of the Universal Mobile Telecommunications System (UMTS) based on the E-UTRAN radio-access technology, and so-called 5G system (5GS) including the 5G or next generation core (NGC) and the 5G Access network based on the New Radio (NR) radio-access technology. 5GS including NR are being standardized by the 3rd Generation Partnership Project (3GPP).

Summary

In a first aspect there is provided an apparatus, said apparatus comprising means for, at a user equipment associated with a first network, receiving an indication of a reference clock time from the first network, performing a synchronisation procedure with a clock of a second network, determining a relation between the reference clock time and the clock of the second network and providing an indication of the relation to the first network.

The first network may be a radio access network. The second network may be a time sensitive network.

The apparatus may comprise means for providing the indication of the relation to the first network via a base station of the radio access network.

The apparatus may comprise means for receiving the indication of the reference clock time from a base station of the radio access network.

The apparatus may comprise means for receiving the indication of the reference clock time from a core network entity associated with the radio access network. The apparatus may provide means for providing an indication of the relation to a translator associated with the second network.

In a second aspect there is provided an apparatus, said apparatus comprising means for, at a first network, receiving, from a user equipment associated with the first network, an indication of a relation between a reference clock time provided to a plurality of user equipments associated with the first network and a clock of a second network and providing the indication of the relation to the plurality of user equipments.

The apparatus may comprise means for receiving from the user equipment associated with the first network or providing to the plurality of user equipments the indication of the relation via a base station of the radio access network.

The apparatus may comprise means for, at the first network, receiving the indication of the relation from the user equipment associated with the first network at a translator function associated with the second network.

In a third aspect, there is provided a method comprising, at a user equipment associated with a first network, receiving an indication of a reference clock time from the first network, performing a synchronisation procedure with a clock of a second network, determining a relation between the reference clock time and the clock of the second network and providing an indication of the relation to the first network.

The method may comprise providing the indication of the relation to the first network via a base station of the radio access network.

The method may comprise receiving the indication of the reference clock time from a base station of the radio access network.

The method may comprise receiving the indication of the reference clock time from a core network entity associated with the radio access network. The method may comprise providing an indication of the relation to a translator function associated with the second network.

In a fourth aspect there is provided a method comprising, at a first network, receiving, from a user equipment associated with the first network, an indication of a relation between a reference clock time provided to a plurality of user equipments associated with the first network and a clock of a second network and providing the indication of the relation to the plurality of user equipments.

The method may comprise receiving from the user equipment associated with the first network or providing to the plurality of user equipments the indication of the relation via a base station of the radio access network.

The method may comprise, at the first network, receiving the indication of the relation from the user equipment associated with the first network at a translator function associated with the second network.

In a fifth aspect, there is provided an apparatus comprising: at least one processor and at least one memory including a computer program code, the at least one memory and computer program code configured to, with the at least one processor, cause the apparatus at a user equipment associated with a first network at least to

receive an indication of a reference clock time from the first network, perform a synchronisation procedure with a clock of a second network, determine a relation between the reference clock time and the clock of the second network and provide an indication of the relation to the first network.

The apparatus may be configured to provide the indication of the relation to the first network via a base station of the radio access network. The apparatus may be configured to receive the indication of the reference clock time from a base station of the radio access network.

The apparatus may be configured to receive the indication of the reference clock time from a core network entity associated with the radio access network.

The apparatus may be configured to provide an indication of the relation to a translatorfunction associated with the second network.

In a sixth aspect there is provided an apparatus comprising: at least one processor and at least one memory including a computer program code, the at least one memory and computer program code configured to, with the at least one processor, cause the apparatus at least to receive, from a user equipment associated with the first network, an indication of a relation between a reference clock time provided to a plurality of user equipments associated with the first network and a clock of a second network and provide the indication of the relation to the plurality of user equipments.

The apparatus may be configured to receive from the user equipment associated with the first network, or provide to the plurality of user equipments, the indication of the relation via a base station of the radio access network.

The apparatus may be configured to, at the first network, receive the indication of the relation from the user equipment associated with the first network at a translator function associated with the second network.

In a seventh aspect there is provided a computer readable medium comprising program instructions for causing an apparatus to perform at least the following: receiving an indication of a reference clock time from the first network, performing a synchronisation procedure with a clock of a second network, determining a relation between the reference clock time and the clock of the second network and providing an indication of the relation to the first network.

The first network may be a radio access network. The second network may be a time sensitive network. The apparatus may be caused to perform providing the indication of the relation to the first network via a base station of the radio access network.

The apparatus may be caused to perform receiving the indication of the reference clock time from a base station of the radio access network.

The apparatus may be caused to perform receiving the indication of the reference clock time from a core network entity associated with the radio access network.

The apparatus may be caused to perform providing an indication of the relation to a translator function associated with the second network.

In an eighth aspect, there is provided a computer readable medium comprising program instructions for causing an apparatus to perform at least the following: receiving, from a user equipment associated with the first network, an indication of a relation between a reference clock time provided to a plurality of user equipments associated with the first network and a clock of a second network and providing the indication of the relation to the plurality of user equipments.

The apparatus may be caused to perform receiving from the user equipment associated with the first network or providing to the plurality of user equipments the indication of the relation via a base station of the radio access network.

The apparatus may be caused to perform, at the first network, receiving the indication of the relation from the user equipment associated with the first network at a translator function associated with the second network.

In a ninth aspect there is provided a non-transitory computer readable medium comprising program instructions for causing an apparatus to perform at least the method according to the first or second aspect.

In the above, many different embodiments have been described. It should be appreciated that further embodiments may be provided by the combination of any two or more of the embodiments described above. Description of Figures

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

Figure 1 shows a schematic diagram of an example communication system comprising a base station and a plurality of communication devices;

Figure 2 shows a schematic diagram of an example mobile communication device;

Figure 3 shows a schematic diagram of an example control apparatus;

Figure 4 shows a signalling diagram for a precision time protocol between two adjacent network elements;

Figure 5 shows a schematic diagram of an example integration of a 3GPP network with a wired industrial TSN network;

Figure 6 shows a flowchart according to an example embodiment;

Figure 7 shows a flowchart according to an example embodiment;

Figure 8 shows a schematic diagram of an integration of a 3GPP network with a wired industrial TSN network according to an example embodiment;

Figure 9 shows a signalling flow between elements of an integrated 3GPP/TSN network according to an example embodiment;

Figure 10 shows a signalling flow between elements of an integrated 3GPP/TSN network according to an example embodiment;

Figure 1 1 shows a signalling flow between elements of an integrated 3GPP/TSN network according to an example embodiment;

Figure 12 shows a signalling flow between elements of an integrated 3GPP/TSN network according to an example embodiment. Detailed description

Before explaining in detail the examples, certain general principles of a wireless communication system and mobile communication devices are briefly explained with reference to Figures 1 to 3 to assist in understanding the technology underlying the described examples.

In a wireless communication system 100, such as that shown in figure 1 , mobile communication devices or user equipment (UE) 102, 104, 105 are provided wireless access via at least one base station (e.g. next generation NB, gNB) or similar wireless transmitting and/or receiving node or point. Base stations may be controlled or assisted by at least one appropriate controller apparatus, so as to enable operation thereof and management of mobile communication devices in communication with the base stations. The controller apparatus may be located in a radio access network (e.g. wireless communication system 100) or in a core network (CN) (not shown) and may be implemented as one central apparatus or its functionality may be distributed over several apparatuses. The controller apparatus may be part of the base station and/or provided by a separate entity such as a Radio Network Controller. In Figure 1 control apparatus 108 and 109 are shown to control the respective macro level base stations 106 and 107. The control apparatus of a base station can be interconnected with other control entities. The control apparatus is typically provided with memory capacity and at least one data processor. The control apparatus and functions may be distributed between a plurality of control units. In some systems, the control apparatus may additionally or alternatively be provided in a radio network controller.

In Figure 1 base stations 106 and 107 are shown as connected to a wider communications network 1 13 via gateway 1 12. A further gateway function may be provided to connect to another network.

The smaller base stations 1 16, 1 18 and 120 may also be connected to the network 1 13, for example by a separate gateway function and/or via the controllers of the macro level stations. The base stations 1 16, 1 18 and 120 may be pico or femto level base stations or the like. In the example, stations 1 16 and 1 18 are connected via a gateway 1 1 1 whilst station 120 connects via the controller apparatus 108. In some embodiments, the smaller stations may not be provided. Smaller base stations 1 16, 1 18 and 120 may be part of a second network, for example WLAN and may be WLAN APs. The communication devices 102, 104, 105 may access the communication system based on various access techniques, such as code division multiple access (CDMA), or wideband CDMA (WCDMA). Other non-limiting examples comprise time division multiple access (TDMA), frequency division multiple access (FDMA) and various schemes thereof such as the interleaved frequency division multiple access (I FDMA), single carrier frequency division multiple access (SC-FDMA) and orthogonal frequency division multiple access (OFDMA), space division multiple access (SDMA) and so on.

An example of wireless communication systems are architectures standardized by the 3rd Generation Partnership Project (3GPP). A latest 3GPP based development is often referred to as the long term evolution (LTE) of the Universal Mobile Telecommunications System (UMTS) radio-access technology. The various development stages of the 3GPP specifications are referred to as releases. More recent developments of the LTE are often referred to as LTE Advanced (LTE-A). The LTE (LTE-A) employs a radio mobile architecture known as the Evolved Universal Terrestrial Radio Access Network (E-UTRAN) and a core network known as the Evolved Packet Core (EPC). Base stations of such systems are known as evolved or enhanced Node Bs (eNBs) and provide E-UTRAN features such as user plane Packet Data Convergence/Radio Link Control/Medium Access Control/Physical layer protocol (PDCP/RLC/MAC/PHY) and control plane Radio Resource Control (RRC) protocol terminations towards the communication devices. Other examples of radio access system comprise those provided by base stations of systems that are based on technologies such as wireless local area network (WLAN) and/or WiMax (Worldwide Interoperability for Microwave Access). A base station can provide coverage for an entire cell or similar radio service area. Core network elements include Mobility Management Entity (MME), Serving Gateway (S-GW) and Packet Gateway (P-GW).

An example of a suitable communications system is the 5G or NR concept. Network architecture in NR may be similar to that of LTE-advanced. Base stations of NR systems may be known as next generation Node Bs (gNBs). Changes to the network architecture may depend on the need to support various radio technologies and finer QoS support, and some on-demand requirements for e.g. QoS levels to support QoE of user point of view. Also network aware services and applications, and service and application aware networks may bring changes to the architecture. Those are related to Information Centric Network (ICN) and User-Centric Content Delivery Network (UC-CDN) approaches. NR may use multiple input - multiple output (MIMO) antennas, many more base stations or nodes than the LTE (a so- called small cell concept), including macro sites operating in co-operation with smaller stations and perhaps also employing a variety of radio technologies for better coverage and enhanced data rates.

Future networks may utilise network functions virtualization (NFV) which is a network architecture concept that proposes virtualizing network node functions into“building blocks” or entities that may be operationally connected or linked together to provide services. A virtualized network function (VNF) may comprise one or more virtual machines running computer program codes using standard or general type servers instead of customized hardware. Cloud computing or data storage may also be utilized. In radio communications this may mean node operations to be carried out, at least partly, in a server, host or node operationally coupled to a remote radio head. It is also possible that node operations will be distributed among a plurality of servers, nodes or hosts. It should also be understood that the distribution of labour between core network operations and base station operations may differ from that of the LTE or even be non-existent.

An example 5G core network (CN) comprises functional entities. The CN is connected to a UE via the radio access network (RAN). An UPF (User Plane Function) whose role is called PSA (PDU Session Anchor) may be responsible for forwarding frames back and forth between the DN (data network) and the tunnels established over the 5G towards the UE(s) exchanging traffic with the DN.

The UPF is controlled by an SMF (Session Management Function) that receives policies from a PCF (Policy Control Function). The CN may also include an AMF (Access & Mobility Function).

A possible mobile communication device will now be described in more detail with reference to Figure 2 showing a schematic, partially sectioned view of a communication device 200. 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.

In an industrial application a communication device may be a modem integrated into an industrial actuator (e.g. a robot arm) and/or a modem acting as an Ethernet-hub that will act as a connection point for one or several connected Ethernet devices (which connection may be wired or unwired).

A mobile device is typically provided with at least one data processing entity 201 , at least one memory 202 and other possible components 203 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 204. The user may control the operation of the mobile device by means of a suitable user interface such as key pad 205, voice commands, touch sensitive screen or pad, combinations thereof or the like. A display 208, a speaker and a microphone can be also provided. Furthermore, a mobile 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.

The mobile device 200 may receive signals over an air or radio interface 207 via appropriate apparatus for receiving and may transmit signals via appropriate apparatus for transmitting radio signals. In Figure 2 transceiver apparatus is designated schematically by block 206. The transceiver apparatus 206 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 mobile device.

Figure 3 shows an example embodiment 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, eNB or gNB, a relay node or a core network node such as an MME or S-GW or P-GW, or a core network function such as AMF/SMF, or a server or host. The method may be implanted in a single control apparatus or across more than one control apparatus. 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. In some embodiments, each base station may have such a control apparatus as well as a control apparatus being provided in a radio network controller. The control apparatus 300 can be arranged to provide control on communications in the service area of the system. The control apparatus 300 comprises at least one memory 301 , at least one data processing unit 302, 303 and an input/output interface 304. Via the interface the control apparatus can be coupled to a receiver and a transmitter of the base station. The receiver and/or the transmitter may be implemented as a radio front end or a remote radio head.

The following may be applicable in the tactile industrial network, also known as Industrial loT (lloT) or Industry 4.0 networks. Here, 3GPP technologies are applied, in addition to wired time sensitive networking (TSN) networks, in industrial environments. This combination may provide flexibility (in terms of mobility) and/or scalability (in terms of number of sensors or actuators). Synchronization of all the communication entities may be a key requirement for TSN.

Time sensitive networking (TSN) provides industrial networks with deterministic delay to handle time sensitive traffic. Currently, wired links are assumed for connecting sensors and controllers of an industrial network. Moving from wired to wireless sensors and actuators may provide mobility, scalability, low cost maintenance and so on. To connect the wireless devices (e.g. sensors and actuators) to a TSN network, wireless transmission mechanisms such as the ones defined in 3GPP may be used.

A key enabler of deterministic communication in a network is synchronizing the network elements to a master clock. In a wired TSN network, the time synchronization is achieved using generalized precision time protocol (gPTP) as defined in IEEE 802.1AS - Rev.

TSN is currently standardized as the mechanism for communication within industrial networks. In parallel to TSN standardization in IEEE, a 3GPP Rel-16 study on communication for Automation in Vertical Domains to identify respective requirements for wireless communication has been started. These two standards are developed independently to provide E2E connections.

In TSN, a set of IEEE 802.1 protocols is applied to achieve deterministic data transmission with guaranteed low latency with time-aware devices (which need to be configured properly). Figure 4 shows a signaling diagram for a synchronization procedure for a wired industrial network which is based on the precision time protocol (PTP). First, a master broadcasts a Sync message to all devices in its domain, which may be followed up by a “Follow Up” message. The master includes a timestamp when the Sync message was sent (80 in the example) while the devices timestamp the reception of the message (102 in the example). Afterwards, the devices unicast a“Delay_Req” message, which is again timestamped at the device (86 in the example) and the reception at the master is timestamped (90 in the example). Finally, the master responds to each unicast “Delay_Req” with a unicast “Delay_Resp” including the timestamp of the reception of the“Delay_Req” messges. Assuming symmetric delay between master and devices, the device can determine the clock offset to the master’s clock.

In a 3GPP 5GS, this method is not applicable because the delay in downlink and uplink may be asymmetric. First, the corresponding IEEE 1588 messages may experience different waiting times until they are scheduled and transmitted (including waiting for the next OFDM frame); in TDD systems, this may be emphasized due to waiting for a corresponding UL or DL transmission slot. Therefore, the IEEE 1588 procedure is not applicable more broadly.

A 3GPP network may be transparently integrated with a TSN network. In one example, a 3GPP network is modeled as a TSN bridge (3GPP bridge). The TSN network may interact with this bridge in a manner as defined in IEEE 802.1 Q specifications. The 3GPP network thus provides wireless connectivity service to the TSN network in a transparent way.

Figure 5 illustrates an example mechanism for transparent integration of wired TSN network and a 3GPP network. In this example, two entities, namely TSN Translator and Translator Client are defined which provide a control and user plane interface towards the TSN network. Using the TSN Translator and the TSN Translator Client, the 3GPP network is modelled as a TSN bridge towards the TSN network so that the 3GPP network is transparent to the TSN protocols. This encapsulated 3GPP network presented as a TSN bridge is named a 3GPP bridge. Although only one end station attached to each TSN bridge is shown in the example of Figure 5, multiple TSN End stations may be connected to a TSN bridge. There has been no discussion of how synchronization shall be performed for such a mechanism.

A Centralized User Configuration (CUC) element is shown in Figure 5. In the example mechanism shown in Figure 5, the CUC provides application requirements to the system and configures the devices (e.g. the CUC specifies what messages are needed between a robot and its controller, and once the schedules are decided, will configure the robot and controller to respect the time-lines).

A Centralized Network Configuration (CNC) element is shown in Figure 5. In the example mechanism shown in Figure 5, the CNC receives information about what applications should be supported, e.g. via the CUCs, and information about the performance and connections of the network (e.g. the CNC is aware of network topology as well as the performance of each of the bridges and links). In this example mechanism, the CNC computes the end to end schedule and configures the bridges in the network.

In the example mechanism of Figure 5, the 3GPP network (which may be a 5GS) together with the translators form a virtual TSN bridge. That is, the 3GPP network: UE, RAN, CN together with the TSN translator and TSN translator client behave as if it were a bridge. This virtual bridge appears as a true TSN bridge (i.e., it has all interfaces needed to plug it into a TSN network), but internally it is not. The presence of the wireless network may thus be transparent to the TSN network. A further TSN bridge is shown in Figure 5 which may be“true” bridge, i.e., a physical TSN bridge (e.g. wired) that implements IEEE 802.1 Q functionalities.

For a 3GPP network acting as a bridge, it is sufficient to synchronize the clocks of the end points namely, the UE and the UPF to the TSN clock. For example, the IEEE 802.1AS-Rev protocol, which is part of the TSN protocol suite, may be used to sync the UPF clock to the TSN clock (e.g., by using the“true” TSN bridge as a TSN clock source). This synchronization mechanism relies on gPTP and assumes deterministic propagation delay between the UPF and TSN bridge. However, it may not be possible to synchronize UE and UPF with the needed accuracy using IEEE 802.1AS-Rev because the delay incurred by the gPTP packets transferred between UE and UPF is time-varying and the delay jitter may limit the synchronization precision.

For scenarios where it is sufficient to have only UEs synchronized with each other (but not to the TSN clock), the RAN may be utilized as the centralized entity that distributes the common clock to the UEs. Even in this case, delay jitter of the radio transmission between the RAN and the UEs may limit the achieved synchronization precision of gPTP.

In the example shown in Figure 5, the TSN Translator maintains a LocalClock, which may be a ClockSlave towards the TSN network on the right side. Similarly, the TSN Translator Client LocalClock (shown by dotted lines) is a ClockSlave to the TSN Translator and ClockMaster towards TSN End Station A. A mechanism to synchronize the TSN Translator Client LocalClock to the base station (RAN) has been proposed in international application no. PCT/IB2018/055565. Here, sub-sampling based gPTP procedure has been introduced to synchronize the TSN Translator Client with the RAN to nanosecond precision. For this procedure, all the UEs need the capability to support gPTP procedure to estimate the delay offset and the propagation delay. Furthermore, this procedure assumes that the propagation delay is symmetric in uplink and downlink which may be realized to some extent with TDD but not for FDD. A TSN radio bearer has been proposed to overcome the delay jitter introduced by the protocol stack in the UE / RAN. In order to synchronize the LocalClocks of the TSN T ranslator and the TSN T ranslator Client, in addition to the UE and RAN, the CN needs to be synchronized as well.

The following relates to providing mechanisms for synchronization of communication devices, of which some are connected to a TSN network through a wireless network.

A method to synchronize time-aware TSN end stations through a 3GPP 5GS to a TSN grandmaster (GM) clock is proposed. Each TSN end station is time synchronized from a 5G UE. Either the standardized synchronization protocol IEEE 1588/PTP (or IEEE 802.1AS- Rev/gPTP, which is based on IEEE 1588/PTP) or the 5G-native RRS/SIB-based synchronization method may be applied to deliver timing information from RAN to the 5G UEs. The method may enable the RAN to adjust the timing information delivered to the 5G UEs with the help of a single, or multiple, dedicated 5G UE connected directly to the PTP domain of the TSN GM, so that the 5G UEs are synchronized to the TSN clock with high accuracy.

Figure 6 shows a flowchart of a method performed at a user equipment associated with a first network according to an embodiment.

In a first step, S1 , the method comprises receiving an indication of a reference clock time from the first network.

In a second step, S2, the method comprises performing a synchronisation procedure with a clock of a second network.

In a third step, S3, the method comprises a relation between the reference clock time and the clock of the second network. In a fourth step, S4, the method comprises providing an indication of the relation to the first network.

Figure 7 shows a flowchart of a method which may be performed at a first network according to an example embodiment.

In a first step, T 1 , the method comprises receiving, from a user equipment associated with the first network, an indication of a relation between a reference clock time provided to a plurality of user equipments associated with the first network and a clock of a second network.

In a second step, T2, the method comprises providing an indication of the relation to the plurality of user equipments.

The first network may be a radio access network (RAN). The second network may be a TSN network.

The clock of the second network may be a grandmaster clock or master clock. The master and grandmaster clocks have different features and functions, and, based on the context, the clock functions can accordingly interchange.

The relation between the reference clock time and the clock of the second network may be an offset. The offset may include time unit conversion,

That is, a plurality of UEs are synchronised to a reference clock time in the first step of the method shown in Figure 6. The reference time may be based on broadcast information from the RAN.

The determined relation is provided to the plurality of UEs by the first network. The plurality of UEs may be synchronized to the grandmaster clock of the time sensitive network based on the determined relation, for example by applying the offset to the reference clock time.

The first network may comprise a TSN translator as described above. The TSN translator is a time-aware device which has been synchronised to the GM. The TSN translator may be located in a base station of the radio access network or in a core network entity (e.g. UPF) of the core network associated with the RAN. The method may comprise receiving the indication of the reference clock time from a core network entity associated with the radio access network, e.g., UPF. The indication of the reference clock time may comprise a timestamped IEEE 1588 event message. In one example embodiment, a TSN Translator located at UPF sends a timestamped IEEE 1588 event messages to a group of UEs. The PDUs carrying an event message for all of these UEs must be scheduled in the same 3GPP transmission time interval (TTI) or during the same system frame number (SFN). Each UE syncs its LocalClock by associating the timestamp in the IEEE 1588 event message with a point in the 3GPP frame structure, i.e. boundary of TTI or SFN in which the message is received. The resulting difference between the TSN Translator LocalClock and User Terminal LocalClock may be difficult to measure due to unpredictable (and difficult to measure) effects such as N3/F1 latencies, TTI boundaries (it is unclear how long an event message would wait until it can be scheduled for a TTI), or TDD patterns. A reference time measurement point (reference plane in IEEE 1588) could be defined in 3GPP RAN2. The IEEE 1588 event message may be sent via multicast (MBMS) to make sure that all user terminals in a group receive the packet in the same TTI.

The method may comprise receiving the indication of the reference clock time from a base station associated with the radio access network. Instead of a timestamped IEEE 1588 message, the indication of the reference clock time be provided over Uu interface from gNB to UE using in RRC/SIB-based signalling. Hence, in another example embodiment, the gNB distributes its local clock to user terminals using RRC/SIB-based signaling. Each user terminal synchronizes its LocalClock by associating timelnfo in the SIB/RRC message with the predefined point in the gNB frame structure that is used as a reference for the timelnfo, i.e. boundary of SFN in which the SIB/RRC message is transmitted.

One of the plurality of UEs, e.g. a dedicated UE, is used to determine the relation between the TSN grandmaster clock (GM clock) and the reference time to which all the UEs (including the dedicated UE) are synchronized. The dedicated UE is connected to a wired TSN network. The connection may be wired or unwired. The dedicated UE used for synchronising the network may be connected to the base station through RF cabling, CPRI, or any other suitable connection to provide an integrated solution.

For example, one UE out of the plurality of UEs may be connected to the same PTP domain as the GM and performs the IEEE 1588 synchronization procedure over a wireline Ethernet network. This UE has exact knowledge of the difference (offset) of the GM clock and the reference time obtained by the plurality of UEs. The translator function may be located at a core network entity associated with the RAN, e.g. UPF or a base station of the RAN, e.g., gNB, or may be a separate entity. The indication of the relation may be provided to the translator function via the translator client-translator interface or a base station of the RAN. The indication of the relation may be sent via a gNB, UPF or any other entity in 3GPP network.

If there are multiple UEs connected to the TSN wired network, then the best clock may be chosen based on clock quality. If there are multiple UEs able to calculate the relation within a single TSN time domain, where the relation comprises an offset, then the offsets may be weighted averaged based on e.g. UE category/quality of clock.

If multiple TSN domains are supported, then the first network may maintain a domain specific relation between the reference clock time and the GM clock. The relation is specific to the TSN time domain. There may be multiple TSN time domain supported by a 3GPP TSN bridge. In this case, there will be at least one UE per time domain which will be able to calculate the relation.

The time difference information (or relation, e.g., offset) is provided to the plurality of UEs. The time difference information may be provided through the TSN translator or through the RAN (for example via a gNB). How the time difference information is provided to the UEs may depend on where the translator is located.

The plurality of UEs update their clocks based on the time difference information. In an example embodiment, the TSN Translator is able to adjust the LocalClock in each user terminal to match the GM clock.

Through this process, the UEs are synchronized to the TSN GM clock. With this method, the propagation delays in the RAN-UPF links (i.e. F1 fronthaul and N3 backhaul) do not need to be deterministic for synchronization of the UEs to the GM.

UEs may be synchronized in multiple groups, e.g., if not all user terminals would fit in the same TTI.

Due to the small area coverage in an industrial network, the different distance of UEs to the base station may have only marginal impact. For example, for a distance of 100m (which would be large for a cell within a factory hall) the propagation time difference is at maximum 0.3ps. If different base stations in RAN are synchronized, then all UEs within a RAN can be synchronized.

In addition to the synchronization of the UEs to the GM clock, the RAN may also synchronize to the GM clock. This may not be necessary to synchronize the UEs to the UPF. However, if the RAN matches its schedule and transmission timing to the frame timing of the TSN streams the E2E delay may be minimized.

When the gNB distributes its local clock signal to user terminals using RRC/SIB-based signaling, the same offset used to synchronize UEs to the GM may be used to synchronize gNB to GM since UEs and gNB are already synchronized via SIB/RRC.

When the TSN Translator sends timestamped IEEE 1588 event messages to a group of user terminals the following options are possible to synchronise the RAN: connect the RAN to the wired TSN network; connect the RAN to one of the UEs using a RF cable; use gPTP based mechanism to synchronize the RAN and the UEs or UE determines time relation between TSN GM and edge of SFNx and informs the gNB, possibly with or without compensating radio propagation delay.

Figure 8 shows a network architecture in which this method may be implemented. TSN end station A and TSN end station C are connected via the TSN bridge to TSN end station B. A dedicated UE 801 has a wired connection with the TSN translator 802 and so can perform a synchronisation procedure with the TSN GM clock located at the TSN translator 802. The UEs associated with the 3GPP network (801 ; 803; 804) may receive an indication of the reference clock time. The UEs 803; 804 connected to the TSN end stations A and C receive an indication of the relation between the reference clock time and the TSN GM clock from the first network.

Figure 9 shows an example embodiment. In this example, two UEs are connected to gNB1 . UE1 is additionally connected to a wired TSN network. UE1 take part in the gPTP protocol executed periodically in the wired TSN network and hence, is aware of the GM clock of the TSN network. This GM clock is provided to all the UEs in the network as follows. First the TSN translator or UPF (the two may be collocated on the same physical device) sends a 1588 message sync to the UEs indicating current time. This message is scheduled at the gNB1 to all the UEs in the same TTI. The UEs use a reference point, for example the start of the PSS/SSS sequence, and record this as the time indicated by the TSN translator (i.e. the reference clock time). Note that, the propagation delay is ignored in the first instant by the UEs. UE1 , which is aware of the TSN GM clock, now calculates the offset between the local reference clock time and the TSN GM clock. This offset is conveyed to the TSN translator. The TSN translator-translator client session established between the Translator at the UPF side and the translator client at the UE side may be used for this purpose. The TSN translator provides the UEs with an indication of the offset observed by UE1. The UEs update their clock and are synchronized to the TSN GM clock.

The 1588 message from the translator and the clock update message from the UEs may take place in a periodic manner. Alternatively, or in addition, when the UE or the translator observes a change in the clock from the wired TSN network, these messages shall be triggered from both sides

In the example embodiment shown in figure 9, the 1588 message is transparent to the gNB1 .

Figure 10 shows an alternative example implementation. In this example, RRC/SIB signaling is used to deliver the reference clock time to UEs. Compared to the solution in Figure 9, no 1588 Sync messages are sent from the UPF to UEs. The UEs obtain the reference clock time (in this case, gNB clock) via SIB/RRC messages. The translator, which, in this example implementation, distributes the clock offset with respect to the TSN GM clock, is located in the gNB.

In Figures 1 1 and 12, the gNB1 is connected to the wired TSN network and hence, has access to the TSN GM clock. This enables gNB1 to optimize its schedule and transmission to match the transmission timings of the individual streams at the egress ports at the UEs. In Figures 1 1 and 12, only one gNB is depicted. However, there may be more than one gNB and either one or all the gNBs may be connected to the wired-TSN network. If there are multiple UEs of a single TSN domain spread across a number gNBs, then the clock offset measured by a UE served by one gNB shall be conveyed to other gNBs serving different UEs of the same TSN domain. For this purpose, the gNB may maintain a list of TSN domain specific offset.

Figure 1 1 shows a message sequence diagram for synchronization of the UEs when the TSN Translator sends timestamped IEEE 1588 event messages to a group of user terminals and the TSN Translator is at UPF for the case when gNB is connected to the wired TSN network.

Figure 12 shows a message sequencing diagram for synchronisation of the UEs when the gNB distributes its local clock to user terminals using RRC/SIB-based signaling and the TSN translator is at the at gNB for the case when gNB is connected to the wired TSN network. In this case, the reference clock (gNB clock) is already synchronized to the GM, so offset may be optionally provided for timing correction.

In an example embodiment, the GM broadcasts a Sync message to all devices (clocks) within its domain. In the case of a 3GPP network, these messages may be sent using a multicast- broadcast bearer to all devices, which subscribed to a time-sensitive communication service. This bearer may be dedicated to synchronization messages. This also ensures that all devices receive the Sync message at the same time (except for different propagation times, which are ignored here) and all messages received on this bearer are timestamped. Note that the GM may be 3GPP specific boundary clock or a GM outside the 3GPP domain.

Each individual device in the domain would timestamp the reception time of the Sync message, including the dedicated UE, which is also connected to the GM using a wireline connection. Using dedicated NAS signalling, the dedicated UE informs the 3GPP 5GS of the actual reception time of the Sync message (given the fact that the dedicated UE has been synchronized with the GM using its wireline connection). Hence, the 3GPP 5GS needs to configure at least one dedicated UE to provide this information. The exchange of this information may also take place directly between Translator functions at network and device side. The 3GPP 5GS provides the exact reception time of the Sync message to all devices in its domain. This may take place using a multicast message. The message exchange can be performed using dedicated NAS signalling or between Translator functions.

Each device responds to the GM with a Delay_Req message, which is again timestamped at the device. However, the UE (e.g., Translator function) intercepts this message and using the exact timing information provided before, a Delay_Resp message is prepared and provided to the device. The device would then be able to sync based on the provided Delay_Resp message.

The advantage of this example embodiment is that the GM may be outside the 3GPP 5GS; each device may perform the standardized IEEE 1588 synchronization procedure. The method may be applicable to integrated devices as well.

The method may be implemented in a user equipment as described with reference to Figure 2 or a control apparatus as described with reference to figure 3.

An apparatus may comprise means for, at a user equipment associated with a first network, receiving an indication of a reference clock time, performing a synchronisation procedure with a clock of a second network, determining a relation between the reference clock time and the clock of the second network and providing an indication of the relation to the first network.

Alternatively, or in addition, an apparatus may comprise means for, at a first network, receiving, from a user equipment associated with the first network, an indication of a relation between a reference clock time provided to a plurality of user equipments associated with the first network and a clock of a second network and providing the indication of the relation to the plurality of user equipments.

It should be understood that the apparatuses may comprise or be coupled to other units or modules etc., such as radio parts or radio heads, used in or for transmission and/or reception. Although the apparatuses have been described as one entity, different modules and memory may be implemented in one or more physical or logical entities.

It is noted that whilst embodiments have been described in relation to LTE and 5G NR, similar principles can be applied in relation to other networks and communication systems where clock synchronization is required. Therefore, although certain embodiments were described above by way of example with reference to certain example architectures for wireless networks, technologies and standards, embodiments may be applied to any other suitable forms of communication systems than those illustrated and described herein.

It is also noted herein that while the above describes example embodiments, there are several variations and modifications which may be made to the disclosed solution without departing from the scope of the present invention.

In general, the various example embodiments may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. Some aspects of the invention 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 the invention is not limited thereto. While various aspects of the invention 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. Example embodiments of this invention may be implemented by computer software executable by a data processor of the mobile device, such as in the processor entity, or by hardware, or by a combination of software and hardware. Computer software or program, also called program product, including software routines, applets and/or macros, may be stored in any apparatus-readable data storage medium and they comprise program instructions to perform particular tasks. A computer program product may comprise one or more computer- executable components which, when the program is run, are configured to carry out embodiments. The one or more computer-executable components may be at least one software code or portions of it.

Further in this regard it should be noted that any blocks of the logic flow as in the Figures 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. The physical media is a non-transitory media.

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 comprise one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASIC), FPGA, gate level circuits and processors based on multi core processor architecture, as non-limiting examples.

Example embodiments of the inventions may be practiced in various components such as integrated circuit modules. The design of integrated circuits is by and large a highly automated process. Complex and powerful software tools are available for converting a logic level design into a semiconductor circuit design ready to be etched and formed on a semiconductor substrate.

The foregoing description has provided by way of non-limiting examples a full and informative description of the exemplary embodiment of this invention. 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 of this invention will still fall within the scope of this invention as defined in the appended claims. Indeed, there is a further embodiment comprising a combination of one or more embodiments with any of the other embodiments previously discussed.

Claims

1. An apparatus, said apparatus comprising means for, at a user equipment associated with a first network:

receiving an indication of a reference clock time from the first network; performing a synchronisation procedure with a clock of a second network;

determining a relation between the reference clock time and the clock of the second network; and

providing an indication of the relation to the first network.

2. An apparatus according to claim 1 , wherein the first network is a radio access network and the second network is a time sensitive network.

3. An apparatus according to claim 2, comprising means for:

providing the indication of the relation to the first network via a base station of the radio access network.

4. An apparatus according to claim 2, comprising means for:

receiving the indication of the reference clock time from a base station of the radio access network.

5. An apparatus according to claim 2 or claim 3, comprising means for:

receiving the indication of the reference clock time from a core network entity associated with the radio access network.

6. An apparatus according to any of claims 1 to 5, comprising means for:

providing an indication of the relation to a translator associated with the second network.

7. An apparatus, said apparatus comprising means for, at a first network:

receiving, from a user equipment associated with the first network, an indication of a relation between a reference clock time provided to a plurality of user equipments associated with the first network and a clock of a second network; and providing the indication of the relation to the plurality of user equipments.

8. An apparatus according to claim 7, wherein the first network is a radio access network and the second network is a time sensitive network.

9. An apparatus according to claim 8, comprising means for: receiving from the user equipment associated with the first network or providing to the plurality of user equipments the indication of the relation via a base station of the radio access network.

10. An apparatus according to any of claims 7 to 9, comprising means for, at the first network:

receiving the indication of the relation from the user equipment associated with the first network at a translator function associated with the second network.

1 1. A method comprising, at a user equipment associated with a first network:

receiving an indication of a reference clock time from the first network;

performing a synchronisation procedure with a clock of a second network;

providing an indication of the relation to the first network.

12. A method comprising, at a first network:

receiving, from a user equipment associated with the first network, an indication of a relation between a reference clock time provided to a plurality of user equipments associated with the first network and a clock of a second network; and

providing the indication of the relation to the plurality of user equipments.

13. An apparatus comprising: at least one processor and at least one memory including a computer program code, the at least one memory and computer program code configured to, with the at least one processor, cause the apparatus at least to, at a user equipment associated with a first network:

receive an indication of a reference clock time from the first network;

perform a synchronisation procedure with a clock of a second network;

determine a relation between the reference clock time and the clock of the second network; and

provide an indication of the relation to the first network.

14. An apparatus comprising: at least one processor and at least one memory including a computer program code, the at least one memory and computer program code configured to, with the at least one processor, cause the apparatus at least to, at a first network:

receive, from a user equipment associated with the first network, an indication of a relation between a reference clock time provided to a plurality of user equipments associated with the first network and a clock of a second network; and

provide the indication of the relation to the plurality of user equipments.

15. A computer readable medium comprising program instructions for causing an apparatus to perform at least the following at a user equipment associated with a first network:

receiving an indication of a reference clock time from the first network;

performing a synchronisation procedure with a clock of a second network;

providing an indication of the relation to the first network.

16. A computer readable medium comprising program instructions for causing an apparatus to perform at least the following at a first network:

providing the indication of the relation to the plurality of user equipments.