FIELD OF THE INVENTION

The exemplary and non-limiting embodiments of the invention relate gen erally to wireless communication systems. The exemplary and non limiting embodi ments of the invention relate especially to apparatuses and methods in wireless com munication networks.

BACKGROUND

In wireless telecommunication synchronous systems such as Global System for Mobile Communications, GSM, long term evolution advanced, LTE Advanced, LTE- A or new radio, NR, 5G may provide to user terminals information about network time over radio interface, which may be for instance Coordinated Universal Time, UTC. Net work time may be used for internal clock synchronisation of the user terminals, for example. In general, time references in the user terminals have a poor stability and the internal clocks need to be periodically synchronized with Network time. This applies also to radio access nodes serving the user terminals. The internal clock of a radio ac cess node needs to be synchronized with Precision Reference Clock, PRC, of the net work. PRC may be obtained from Global Navigation Satellite System, GNSS, time or from atomic clock, for example.

If PRC synchronization is lost, a mobile network may continue operation for the given period based on internal clocks of the network elements. For example, if the network time is based on GNSS time, a malfunction or outage of satellite-based system may occur. Examples of such scenarios may be solar flares or jamming attacks. Also, in case of atomic clocks there may be system failures. If a cumulative time or frequency error caused by some malfunction grows too large, further operation of the network may be in danger. This also applies to operation over a radio interface, where a user terminal may continue operation without synchronization by the given, relatively short period of time.

SUMMARY

The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is not intended to identify key elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to a more detailed description that is presented later.

According to an aspect of the present invention, there is provided an appa ratus in a communication network, comprising: means for storing information on a ref erence propagation delay between the apparatus and one or more radio access nodes; means for controlling reception of a reference signal from one or more radio access nodes, the reference signal comprising information on the transmission time instant of the signal; means for determining the reception time instant of the reference signal; means for determining the propagation delay of the reference signal based on the time difference of the reception time instant and the transmission time instant; and means for determining correctness of time references of the apparatus and the one or more radio access nodes based on the determined and stored propagation delays.

According to an aspect of the present invention, there is provided an appa ratus in a communication network, comprising: means for controlling transmission of a reference signal to a user terminal, the reference signal comprising information on the transmission time instant of the signal; means for controlling reception of an indi cation from the user equipment, the indication comprising information on the correc tion for the time reference of the apparatus; means for correcting the time reference of the apparatus based on the indication.

According to an aspect of the present invention, there is provided a method, comprising: storing information on a reference propagation delay between an appa ratus and one or more radio access nodes; controlling reception of a reference signal from one or more radio access nodes, the reference signal comprising information on the transmission time instant of the signal; determining the reception time instant of the reference signal; determining the propagation delay of the reference signal based on the time difference of the reception time instant and the transmission time instant; and determining correctness of time references of the apparatus and the one or more radio access nodes based on the determined and stored propagation delays.

According to an aspect of the present invention, there is provided a method in a communication network, comprising: controlling transmission of a reference sig nal to a user terminal, the reference signal comprising information on the transmission time instant of the signal; controlling reception of an indication from the user equip ment, the indication comprising information on the correction for the time reference of the apparatus; and correcting the time reference of the apparatus based on the indi cation. According to an aspect of the present invention, there is provided a com puter program comprising instructions for causing an apparatus to perform at least the following: storing information on a reference propagation delay between the appa ratus and one or more radio access nodes; controlling reception of a reference signal from one or more radio access nodes, the reference signal comprising information on the transmission time instant of the signal; determining the reception time instant of the reference signal; determining the propagation delay of the reference signal based on the time difference of the reception time instant and the transmission time instant; and determining correctness of time references of the apparatus and the one or more radio access nodes based on the determined and stored propagation delays.

According to an aspect of the present invention, there is provided a com puter program comprising instructions for causing an apparatus to perform at least the following: controlling transmission of a reference signal to a user terminal, the refer ence signal comprising information on the transmission time instant of the signal; con trolling reception of an indication from the user equipment, the indication comprising information on the correction for the time reference of the apparatus; and correcting the time reference of the apparatus based on the indication.

One or more examples of implementations are set forth in more detail in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims. The embodiments and or ex amples and features, if any, described in this specification that do not fall under the scope of the independent claims are to be interpreted as examples useful for under standing various embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be described in greater detail by means of preferred embodiments with reference to the attached drawings, in which

Figures 1 and 2 illustrate examples of simplified system architecture of a communication system;

Figures 3 and 4 are flowcharts illustrating some embodiments;

Figures 5A, 5B, 6A, 6B, 7A and 7B illustrate examples of some embodiments;

Figure 8 is a flowchart illustrating an example of user equipment calibra tion;

Figure 9 illustrates a numerical example;

Figure 10 is a flowchart illustrating an example of operation of a calibrated user equipment;

Figures 11, 12, 13 and 14 are flowcharts illustrating some examples of some embodiments;

Figures 15 and 16 illustrate examples of apparatuses of some embodiments.

DETAILED DESCRIPTION

The following embodiments are only examples. Although the specification may refer to "an", "one", or "some" embodiment(s) in several locations, this does not necessarily mean that each such reference is to the same embodiment(s), or that the feature only applies to a single embodiment. Single features of different embodiments may also be combined to provide other embodiments. Furthermore, words "compris ing" and "including" should be understood as not limiting the described embodiments to consist of only those features that have been mentioned and such embodiments may also contain features, structures, units, modules etc. that have not been specifically mentioned.

Some embodiments of the present invention are applicable to user equip ment, user terminal, a base station, eNodeB, gNodeB, a distributed realisation of a base station, a network element of a communication system, a corresponding component, and/or to any communication system or any combination of different communication systems that support required functionality.

The protocols used, the specifications of communication systems, servers and user equipment, especially in wireless communication, develop rapidly. Such de velopment may require extra changes to an embodiment. Therefore, all words and ex pressions should be interpreted broadly, and they are intended to illustrate, not to re strict, embodiments.

In the following, different exemplifying embodiments will be described us ing, as an example of an access architecture to which the embodiments may be applied, a radio access architecture based on long term evolution advanced (LTE Advanced, LTE-A) or new radio (NR, 5G), without restricting the embodiments to such an archi tecture, however. The embodiments may also be applied to other kinds of communica tions networks having suitable means by adjusting parameters and procedures appro priately. Some examples of other options for suitable systems are the universal mobile telecommunications system (UMTS) radio access network (UTRAN or E-UTRAN), long term evolution (LTE, the same as E-UTRA), wireless local area network (WLAN or WiFi), worldwide interoperability for microwave access (WiMAX), Bluetooth®, per sonal communications services (PCS), ZigBee®, wideband code division multiple ac cess (WCDMA), systems using ultra-wideband (UWB) technology, sensor networks, mobile ad-hoc networks (MANETs) and Internet Protocol multimedia subsystems (IMS) or any combination thereof.

Fig. 1 depicts examples of simplified system architectures showing some el ements and functional entities, all or some being logical units, whose implementation may differ from what is shown. The connections shown in Fig. 1 are logical connections; the actual physical connections may be different. It is apparent to a person skilled in the art that the system typically comprises also other functions and structures than those shown in Fig. 1.

The embodiments are not, however, restricted to the system given as an ex ample but a person skilled in the art may apply the solution to other communication systems provided with necessary properties.

The example of Fig. 1 shows a part of an exemplifying radio access network.

Fig. 1 shows devices 100 and 102. The devices 100 and 102 may, for exam ple, be user devices or user terminals. The devices 100 and 102 are configured to be in a wireless connection on one or more communication channels with a node 104. The node 104 is further connected to a core network 106. In one example, the node 104 may be an access node such as (e/g)NodeB providing or serving devices in a cell. In one example, the node 104 may be a non-3GPP access node. The physical link from a device to a (e/g)NodeB is called uplink or reverse link and the physical link from the (e/g)NodeB to the device is called downlink or forward link. It should be appreciated that (e/g)NodeBs or their functionalities may be implemented by using any node, host, server or access point etc. entity suitable for such a usage.

A communications system typically comprises more than one (e/g)NodeB in which case the (e/g)NodeBs may also be configured to communicate with one an other over links, wired or wireless, designed for the purpose. These links may be used for signalling purposes. The (e/g)NodeB is a computing device configured to control the radio resources of communication system it is coupled to. The NodeB may also be referred to as a base station, an access point or any other type of interfacing device including a relay station capable of operating in a wireless environment. The (e/g)NodeB includes or is coupled to transceivers. From the transceivers of the (e/g)NodeB, a connection is provided to an antenna unit that establishes bi-directional radio links to devices. The antenna unit may comprise a plurality of antennas or an tenna elements. The (e/g)NodeB is further connected to the core network 106 (CN or next generation core NGC). Depending on the system, the counterpart on the CN side can be a serving gateway (S-GW, routing and forwarding user data packets), packet data network gateway (P-GW), for providing connectivity of devices (UEs) to external packet data networks, or mobile management entity (MME), etc.

The device (also called user device, a subscriber unit, user equipment (UE), user terminal, terminal device, etc.) illustrates one type of an apparatus to which re sources on the air interface are allocated and assigned, and thus any feature described herein with a device may be implemented with a corresponding apparatus, such as a relay node. An example of such a relay node is a layer 3 relay (self-backhauling relay) towards the base station.

The device typically refers to a device ( e.g. a portable or non-portable com puting device) that includes wireless mobile communication devices operating with or without an universal subscriber identification module (US1M), including, but not lim ited to, the following types of devices: a mobile station (mobile phone), smartphone, personal digital assistant (PDA), handset, device using a wireless modem (alarm or measurement device, etc.), laptop and/or touch screen computer, tablet, game console, notebook, and multimedia device. It should be appreciated that a device may also be a nearly exclusive uplink device, of which an example is a camera or video camera load ing images or video clips to a network. A device may also be a device having capability to operate in Internet of Things (loT) network which is a scenario in which objects are provided with the ability to transfer data over a network without requiring human-to- human or human-to-computer interaction, e.g. to be used in smart power grids and connected vehicles. The device may also utilise cloud. In some applications, a device may comprise a user portable device with radio parts (such as a watch, earphones or eyeglasses) and the computation is carried out in the cloud. The device (or in some embodiments a layer 3 relay node) is configured to perform one or more of user equip ment functionalities.

Various techniques described herein may also be applied to a cyber-physi cal system (CPS) (a system of collaborating computational elements controlling physi cal entities). CPS may enable the implementation and exploitation of massive amounts of interconnected information and communications technology, 1CT, devices (sensors, actuators, processors microcontrollers, etc.) embedded in physical objects at different locations. Mobile cyber physical systems, in which the physical system in question has inherent mobility, are a subcategory of cyber-physical systems. Examples of mobile physical systems include mobile robotics and electronics transported by humans or animals. Additionally, although the apparatuses have been depicted as single enti ties, different units, processors and/or memory units (not all shown in Fig. 1) may be implemented.

5G enables using 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 employing a variety of radio technologies depending on service needs, use cases and/or spectrum available. 5G mobile communications supports a wide range of use cases and related applications including video streaming, augmented reality, different ways of data sharing and vari ous forms of machine type applications (such as (massive) machine-type communica tions (mMTC), including vehicular safety, different sensors and real-time control. 5G is expected to have multiple radio interfaces, namely below 6GHz, cmWave and mmWave, and also being integrable with existing legacy radio access technologies, such as the LTE. Integration with the LTE may be implemented, at least in the early phase, as a system, where macro coverage is provided by the LTE and 5G radio inter face access comes from small cells by aggregation to the LTE. In other words, 5G is planned to support both inter-RAT operability (such as LTE-5G) and inter-Rl operabil ity (inter-radio interface operability, such as below 6GHz - cmWave, below 6GHz - cmWave - mmWave). One of the concepts considered to be used in 5G networks is net work slicing in which multiple independent and dedicated virtual sub-networks (net work instances) may be created within the same infrastructure to run services that have different requirements on latency, reliability, throughput and mobility.

The current architecture in LTE networks is fully distributed in the radio and fully centralized in the core network. The low latency applications and services in 5G require to bring the content close to the radio which leads to local break out and multi-access edge computing (MEC). 5G enables analytics and knowledge generation to occur at the source of the data. This approach requires leveraging resources that may not be continuously connected to a network such as laptops, smartphones, tablets and sensors. MEC provides a distributed computing environment for application and service hosting. It also has the ability to store and process content in close proximity to cellular subscribers for faster response time. Edge computing covers a wide range of technologies such as wireless sensor networks, mobile data acquisition, mobile signa ture analysis, cooperative distributed peer-to-peer ad hoc networking and processing also classifiable as local cloud/fog computing and grid/mesh computing, dew compu ting, mobile edge computing, cloudlet, distributed data storage and retrieval, auto nomic self-healing networks, remote cloud services, augmented and virtual reality, data caching, Internet of Things (massive connectivity and/or latency critical), critical communications (autonomous vehicles, traffic safety, real-time analytics, time-critical control, healthcare applications).

The communication system is also able to communicate with other net works, such as a public switched telephone network or the Internet 112, or utilize ser vices provided by them. The communication network may also be able to support the usage of cloud services, for example at least part of core network operations may be carried out as a cloud service (this is depicted in Fig. 1 by "cloud" 114). The communi cation system may also comprise a central control entity, or a like, providing facilities for networks of different operators to cooperate for example in spectrum sharing.

The technology of Edge cloud may be brought into a radio access network (RAN) by utilizing network function virtualization (NVF) and software defined net working (SDN). Using the technology of edge cloud may mean access node operations to be carried out, at least partly, in a server, host or node operationally coupled to a remote radio head or base station comprising radio parts. It is also possible that node operations will be distributed among a plurality of servers, nodes or hosts. Application of cloudRAN architecture enables RAN real time functions being carried out at the RAN side (in a distributed unit, DU 104) and non-real time functions being carried out in a centralized manner (in a centralized unit, CU 108).

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. Some other technology advancements probably to be used are Big Data and all-IP, which may change the way networks are being constructed and man aged. 5G (or new radio, NR) networks are being designed to support multiple hierar chies, where MEC servers can be placed between the core and the base station or nodeB (gNB). It should be appreciated that MEC can be applied in 4G networks as well.

5G may also utilize satellite communication to enhance or complement the coverage of 5G service, for example by providing backhauling. Possible use cases are providing service continuity for machine-to-machine (M2M) or Internet of Things (IoT) devices or for passengers on board of vehicles, or ensuring service availability for critical communications, and future railway/maritime/aeronautical communications. Satellite communication may utilise geostationary earth orbit (GEO) satellite systems, but also low earth orbit (LEO) satellite systems, in particular mega-constellations (sys tems in which hundreds of (nano)satellites are deployed). At least one satellite 110 in the mega-constellation may cover several satellite-enabled network entities that cre ate on-ground cells. The on-ground cells may be created through an on-ground relay node 104 or by a gNB located on-ground or in a satellite.

It is obvious for a person skilled in the art that the depicted system is only an example of a part of a radio access system and in practice, the system may comprise a plurality of (e/g)NodeBs, the device may have an access to a plurality of radio cells and the system may comprise also other apparatuses, such as physical layer relay nodes or other network elements, etc. At least one of the (e/g)NodeBs may be a Home(e/g)nodeB. Additionally, in a geographical area of a radio communication sys tem a plurality of different kinds of radio cells as well as a plurality of radio cells may be provided. Radio cells may be macro cells (or umbrella cells) which are large cells, usually having a diameter of up to tens of kilometers, or smaller cells such as micro-, femto- or picocells. The (e/g)NodeBs of Fig. 1 may provide any kind of these cells. A cellular radio system may be implemented as a multilayer network including several kinds of cells. Typically, in multilayer networks, one access node provides one kind of a cell or cells, and thus a plurality of (e/g)NodeBs may be needed to provide such a network structure.

For fulfilling the need for improving the deployment and performance of communication systems, the concept of "plug-and-play" (e/g)NodeBs has been intro duced. Typically, a network which is able to use "plug-and-play" (e/g)Node Bs, in cludes, in addition to Home (e/g)NodeBs (H(e/g)nodeBs), a home node B gateway, or HNB-GW (not shown in Fig. 1). An HNB Gateway (HNB-GW), which is typically installed within an operator’s network may aggregate traffic from a large number of HNBs back to a core network.

Fig.2 illustrates an example of a communication system based on 5G net work components. A user terminal or user equipment 200 communicating via a 5G net work 202 with a data network 204. The user equipment 200 is connected to a base station or gNB 206 which provides the user equipment a connection to data network 204 via one or more User Plane Functions 208. The user equipment 200 is further con nected to Core Access and Mobility Management Function, AMF 210, which is a control plane core connector for (radio) access network and can be seen from this perspective as the 5G version of Mobility Management Entity, MME, in LTE. The 5G network further comprises Session Management Function, SMF 212, which is responsible for subscriber sessions, such as session establishment, modify and release and a Policy Control Func tion 214 which is configured to govern network behavior by providing policy rules to control plane functions. The network further comprises operations and maintenance unit (O&M) 220 of the operator of the network.

In order to operate, wireless communications synchronous systems need common time reference. Otherwise communication over the radio interface may fail as network elements transmit/receive in erroneous times. This requirement for stabile and accurate time source requires provision of Precision Reference Clock, PRC, such as GNSS time or atomic clocks. This may be costly for network operators, and also creates the risk of single point of failure, which may be related to availability of PRC service. Thus, there is a need for monitoring accuracy of provided Network Time over radio interface even in standalone mode operations for radio access nodes such as eNBs, when PRC was lost. A possibility to correct erroneous timing would be valuable.

Fig.3 is a flowchart illustrating an embodiment. The flowchart illustrates an example of the operation of the apparatus or network element acting as a user equip ment or a part of a user equipment.

In step 300, the apparatus is configured to store information on a reference propagation delay between the apparatus and one or more radio access nodes.

In step 302, the apparatus is configured to control reception of a reference signal from one or more radio access nodes, the reference signal comprising infor mation on the transmission time instant of the signal.

In step 304, the apparatus is configured to determine the reception time in stant of the reference signal.

In step 306, the apparatus is configured to determine the propagation delay of the reference signal based on the time difference of the reception time instant and the transmission time instant.

In step 308, the apparatus is configured to determine correctness of time references of the apparatus and the one or more radio access nodes based on the de termined and stored propagation delays.

In an embodiment, if the determined and stored propagation delays related to more than one radio access nodes are unequal, the apparatus may be configured to determine that the time reference of the apparatus is incorrect.

In an embodiment, if the determined and stored propagation delay related to a first radio access node is unequal and the determined and stored propagation delay related to a second radio access nodes is equal with a given margin, the apparatus may be configured to determine that the time reference of the first radio access node is in correct.

In an embodiment, determine correction for the incorrect time reference.

In an embodiment, the apparatus may be configured to control transmis sion of an indication to the first radio access node, the indication comprising infor mation on the correction for the incorrect time reference. In an embodiment, the apparatus may be configured to correct the time ref erence of the apparatus based on the determined correction.

Fig.4 is a flowchart illustrating an embodiment. The flowchart illustrates an example of the operation of the apparatus or network element acting as a radio access node or a part of a radio access node.

In step 400, the apparatus is configured to control transmission of a refer ence signal to a user equipment, the reference signal comprising information on the transmission time instant of the signal.

In step 402, the apparatus is configured to control reception of an indication from the user equipment, the indication comprising information on the correction for the time reference of the apparatus.

In step 404, the apparatus is configured to correct the time reference of the apparatus based on the indication.

In an embodiment, a user equipment may be utilised to monitor the timing of radio access nodes and timing of the user equipment itself. The method described above thus assures that time alignment within the network monitored by user equip ment is stable, even if radio access nodes operated in a standalone mode, without PRC for unlimited time.

Figs 5A and 5B illustrate an example. The figure shows a user equipment 500. The user equipment 500, which may be denoted as Reference User Terminal, Ref UT, or Reference User Equipment, Ref UE, may be an Internet of Things, IoT, device or wideband UE. It may be in the coverage area of a number of cells from different radio access nodes, for example eNBs. In the example of Fig. 5A, the Ref UE 500 is shown to be in the coverage area of two access nodes 502, 504, for simplicity. In an embodiment, the Ref UE may be stationery, for example mounted on a mast or any other suitable facility. In an embodiment, the location of the Ref UE may enable line of sight visibility to radio access nodes within the coverage of Ref UE.

It may be possible to measure a line of sight distance between Ref UE and eNBs within the coverage and then convert this distance to time equivalent as micro- waves utilises on the radio interface travel at speed of light.

In an embodiment, radio access nodes may be configured to transmit or broadcast a Reference Signal, which comprises information about the physical signal transmission time To. The time To uses as a time reference the internal clock of the access node. Let us assume here that eNBl 502 transmitted the reference signal. The transmission time may be denoted as To(el). The reference signal may be any selected frame, subframe or symbol. Reference signal transmitted by a radio access node may be received by the Ref UE at time Ti. Time Ti uses as a reference the internal clock of the Ref UE. The reception time may be denoted as Ti(ue).

Thus, a Time Of Arrival, TOA, time difference Ti - To may correspond to sig nal propagation delay but two different reference time sources are used - access node and Ref UE. As synchronous transmission is used, time relation between many meas urements may be compared. Using above notation, the time difference of reference sig nal transmitted by eNBl 502 may be denoted as T _pr0p (eNBl, T _ei , T _ue ).

As mentioned above, the Ref UE may be configured to store information on a reference propagation delay between the apparatus and one or more radio access nodes. The reference propagation delay 506 between user equipment 500 and access node eNBl 502 may be denoted as T _ref (eNBl) and reference propagation delay 510 between user equipment 500 and access node eNB2 504 may be denoted as T _ref (eNB2).

The determined TOA propagation delay between Ref UE and an access node may be compared with reference propagation delay for the same access node. Any de viation in TOA measurement may indicate that time reference source at the access node or Ref UE side drifted in time. By analysing TOA measurements to other access nodes, the Ref UE may determine whether reference clock drift is present at the access node or Ref UE side.

In an embodiment, Ref UE may propose a time compensation to access node or Ref UE accordingly. The Ref UE may determine the source of time drift and may pro vide time correction to eNB or to Ref UE internal reference clock. This way a bottom- up time synchronization may be provided, which differ with respect to legacy top- down approach for time synchronization.

In the example of Fig 5A and 5B, the reference propagation delay 506 be tween user equipment 500 and access node eNBl 502 T _ref (eNBl) and reference prop agation delay 510 between user equipment 500 and access node eNB2 504 T _ref (eNB2) have been determined at some earlier point of time.

For example, the distance between the user equipment Ref UE and access node eNBl 502 and access node eNB2 504 may be measured, for example utilising a laser range finder with the accuracy of millimetres. The propagation time is propor tional to the distance. For example, for access node eNBl, following applies:

Tref where T _ref (eNBl) is reference signal propagation delay to eNBl based on distance measurement, c is the speed of light and D _ref (eNBl) is measured reference distance between Ref UE and eNBl.

The access node eNBl 502 transmits a reference signal 508 to the user equipment 500 at a time To and the user equipment receives the signal at a time Ti. Respectively, the access node eNB2 504 transmits a reference signal 512 to the user equipment 500 at a time T3 and the user equipment receives the signal at a time T4.

Using the above method, it is possible to determine corresponding TOA rings, with radius 514, 516, proportional to TOA propagation delay. The equation to determine reference signal propagation delay, using eNBl as an example, is as follows:

TpropfeNBl, Tel, Tue) = Ti(T _ue ) - To(Tei), (Eq.2) where T _pr0p (eNBl, T _ei , T _ue ) is the reference signal propagation delay, which is a function of distance between Ref UE and eNBl, and reference clocks of eNBl and Ref UE, Ti(T _ue ) is time of physical reference signal reception by Ref UE, which depends on Ref UE clock and To(T _ei ) is time of physical reference signal transmission by eNBl, which depends on eNBl clock.

In the example of Fig.5A, the reference clocks of Ref UE, eNBl and eNB2 are in correct time. Thus, following conditions of equations 3 and 4 are met (using again eNBl as an example):

If the above equations match, then there is no error in the reference clocks. It may be that the both the access point eNB and Ref UE are synchronized with precise reference clock PRC, which may be defined as a function T _ue (T _ei (T)), what is a typical situation for mobile network operations. Typically, the access point provides synchro nisation for the user equipment. Thus, in a normal situation the reference time in user equipment is a function of the reference time of the user equipment, which in turn is a function of the reference time of the access point.

Based on equations 3 and 4, it may be possible to determine whether refer ence times T _ue or T _ei are correct as relative TOA propagation delay needs to be sub stantially equal reference delay determined by accurate distance measurement equip ment. If equations 3 and 4 are fulfilled, the time references of access point and Ref UE are in order. If the equations do not match, there is an error in either the reference time of access point of the Ref UE.

Further, if one of the equations does not match, by analysing equations Eq. 3 and Eq.4 for more than one access point, it may be possible to determine whether instability of reference time source is related to an access point of for whether there is a common point of failure - Ref UE. If there is an error regarding one access point but other access point equations match, the respective access point may have erroneous timing in its reference clock. If more than one access point equations indicate error, the faulty timing is in the Ref UE.

In an embodiment, a given error tolerance may be applied when determin ing the correctness of equations 3 and 4.

Fig. 5A and 5B illustrate a situation where propagation delays of reference signal transmissions of both eNBl and eNB2 are substantially equal to the respective reference signal propagation delays. Figs. 6A and 6B in turn illustrate an example, where the access point eNBl 502 lost synchronization with PRC for a period of time. It means that eNBl needs to rely on own internal clock to maintain clock synchroniza tion. In this case, time relation may be denoted as T _Ue (T _ei (T _ei )). In the example of Figs 6A and 6B this lack of PRC has led to instability of the clock of the eNBl.

Fig. 6A and 6B illustrate an example where TOA propagation delay distance between Ref UE and eNBl is not substantially equal to the reference delay to eNBl, and conditions defined by equations 3 and 4 are not met. Propagation delay Ti(T _ue ) - To (T _ei ) is greater than reference delay T _ref (eNBl):

Tl(Tue) - To(Tel) > Tref (eNBl).

As neither eNBl and Ref UE position is not changed, the reason for TOA er ror may be reference time source drift at either eNBl or Ref UE. This is the option as speed of microwave is constant. At this moment, based on one TOA measurement to one eNB, it may not be possible to determine whether problem lies in Ref UE reference time source, T _ue , or in eNBl reference time source, T _ei .

Ref UE may unambiguously indicate the source of time drift by analysing further pairs of eNBs - Ref UE and associated TOA measurements. In the example of Figs. 6A and 6B, TOA measurement to eNB2 fulfils conditions in equations 3 and 4:

T ₄ (T _ue ) - T ₃ (T _e2 ) = Tref (eNB2).

This indicates that Ref UE reference time source T _ue , and eNB2 reference time source T _e2 have the common reference clock with the given tolerance. As for TOA measurement with eNBl the same Ref UE clock T _ue is used, it can be determined that the problem is associated with eNBl internal clock T _ei , as it affects time determined by To (Tel).

In the example of Figs 6A and 6B, the error causes too long propagation de lay. Similar scenario may be when particular TOA propagation delay is shorter than corresponding reference delay, i.e. where Propagation delay Ti(T _ue ) - To(T _ei ) is shorter than reference delay T _ref (eNBl). Figs. 7 A and 7B illustrate another example. In this example, neither the ref erence signal transmitted by eNBl nor the reference signal transmitted by eNB2 satisfy the equation 3: T _ref (eNBl), Tref (eNB2).

This kind of situation may occur when, due to any reason, the Ref UE 500 has lost synchronization, for example. The wrong reference time at Ref UE may cause incorrect TOA measurements as T _ue affects time determined by Ti(T _ue ) and T4(T _ue ). As T _ue is common for TOA measurements, any TOA propagation measurement may be in correct.

It may be noted currently user equipment needs to periodically synchronize with a radio access node, which procedure requires a Random Access procedure and consumes radio resources.

Similar scenario as in Figs. 7A and 7B may also be when any TOA propaga tion delay is shorter than any related reference delay.

It may be noted that a typical time drift is a continuous and gradual process, which with respect to Ref UE sampling period may be enough for time drift modelling. A parameter for allowed time drift, e.g. T _driftiMax for eNBl may be determined in order to specify whether any correction action from Ref UE is needed.

An intersection area for TOA measurements with different current T _drifti in dications may be used for further assessment of reference time stability and may also trigger optimum corrective action.

In an embodiment, the Ref UE 500 may be calibrated prior usage. In LTE, a basic time unit T _s = 0,0325 microsecond is used, as it is sampling time of an OFDM sym bol. This T _s = 0,0325 microsecond creates a granularity (accuracy) of 4,875 m in dis tance, which is poor accuracy with respect to values of T _ref , which may be determined with an accuracy of nanoseconds.

Fig. 8 illustrates an example of an activity diagram for a Ref UE calibration process for three eNBs. However, a similar process applies for any number of eNBs.

At the step 800, "PRC: Precise Reference Clock", a time from a precise refer ence clock T is provided to eNBl, which may be common for eNBs. It may be assumed that this requirement may be fulfilled during calibration.

At the step 802 "eNBl: Synchronize internal clock", the eNBl internal clock may be synchronized with PRC. Thus, the eNBl internal clock T _ei is a function of T, i.e. T _ei (T). If PRC is available for eNBs, the substantially same time is used within entire mobile network: T _el (T) = T _e2 (T). (Eq. 5)

Without synchronisation with PRC, time T _ei needs to rely on stability of its own crystal oscillator (or other means), in which case T _ei time value may be expressed as T _ei (T _ei ) and relation equation 5 may not be true.

At the step 804, "eNBl: Send TOA Reference Symbol", the eNBl broadcasts or transmits a reference symbol, which comprise information about the physical refer ence symbol transmission time. In an embodiment, it may be the transmission time from the eNBl antenna system. In this case, To(T _ei ) may be provided in a form of HH:MM:SS:MS:US:NS and due to latching process, To depends on quality of T _ei . As To (T _ei ) represents the physical transmission time, an eNBl processing and eNBl spe cific transmission delay may need to be compensated.

At the next step 806, "Ref UE: Synchronize internal clock with eNBl", the Ref UE may perform a random access procedure in order to receive network time. This way, the Ref UE may synchronize its own internal clock T _ue with the connected eNBl, which means initially a function T _Ue (T _ei ). Any inaccuracies in T _ei may affect T _ue . This step is for calibration. Also, Ref UE time drift may be expected, so after some period synchronisation may be lost:

Tue (T _Ue ) ⁼ Tue (Tel). (Eq. 6)

If PRC is available for Ref UE, Ref UE time may be a function of time T as specified in equation 7, which may be considered as typical case. T _ue time drift may be regularly compensated when Ref UE synchronize with the network.

Tue (Tue) = Tue (Tel) = T _Ue (Tel (T)) . (Eq. 7)

At the step 808, "Ref UE: Receive TOA Reference Symbol from eNBl", the Ref UE may receive the reference symbol and latch time of its reception Ti with respect to own time reference source T _ue , which means it is a function Ti(T _ue ). Ref UE may take into consideration Ref UE processing and transmission delay.

At the step 810, "Ref UE: Measure TOA Propagation Delay to eNBl", the Ref UE measures TOA signal propagation delay to eNBl using To and Ti values. Signal prop agation delay T _pr0pi (eNBl, T _ei , T _ue ) is determined by equation 2 but is measured with granularity of basic time unit T _s .

In step 812, "Ref UE: Reference Delay (Distance) to eNBl", reference delays for eNBs may be determined as specified by equation 1.

The step 814, "Ref UE: Calibration Ref UE TOA Propagation Delay (Distance) for eNBl" describes a process of fine tuning TOA accuracy improvement. A TOA related correction factor eNBlcorr is determined. This correction factor may be added to TOA propagation delay measurements for the given eNB. This may be explained on the fol lowing numerical example with exemplary data also illustrated in Fig. 9. The non-lim iting numerical values are merely an illustrative example.

Ref UE is in this example fully synchronized with the network time, i.e. T _Ue (T _Ue ) = T _ue (T _ei ); this assures that any initial time drift is compensated.

Transmission time of reference signal To(T _ei ) is HH:MM:SS:MS:US:NS = 00:00:00:00:00:00.

In this example, RefUE is at a distance D _refi (eNBl) = 10000 m from the eNB antenna system 900, which corresponds to 33,356 microseconds for microwave signal propagation and to T _refi (eNBl) = 102,64 Ts; 00:00:00:00:33:36.

Ref UE may latch information about Ti(T _ue ) with T _s resolution 902, which means Ti(T _ue ) = 103 T _s. There may be an error related to Ti(T _ue ) granularity, which may be equal -0,36 T _s , which may be denoted as eNBlcorr.

In the next step eNBlcorr = -0,36 T _s may be added to T _Ue (T _Ue ) for reference to eNBl, which in this case may be denoted as T _Uei (T _Ue ):

Tuel (Tue)= Tue (T _ue ) - eNBlcorr. (Eq. 8)

Based on equation 8, any following TOA measurement regarding eNBl may be compensated by eNBlcorr. In the result, T _s boundary is aligned with real propaga tion delay determined by T _refi (eNBl). A slight difference in the accuracy of time refer ence in Ti(T _ue ) maybe then signaled by change of indicated T _s , which maybe 103 T _s (if on the left side of Fig. 9) or 104 T _s (if on the right of Fig. 9);

Further, additional accuracy of TOA measurement may be achieved by the usage of quadrature time references T _Uei I(T _Ue ) 904 and T _Uei Q(T _Ue ) 906, shifted by 0,5 T _s ; as it may be seen, for T _Uei I(T _Ue ) reference symbol may be latched at Ti(T _ue ) = 104 T _s , whereas for T _Uei Q(T _Ue ) at Ti(T _ue ) = 103 T _s ;

In the result, Ti(T _ue ) event may be allocated with accuracy of ¼ T _s , which may be four times better with respect to regular TOA measurement, for example.

By adding eNBlcorr to time reference at Ref UE side, it may be possible to detect any changes in TOA measurements, which means higher TOA precision. In an embodiment, correction eNBlcorr is static. Other corrections factors may be deter mined for any other eNBs.

Moving back to Fig. 8, at the step 816, "Ref UE: Measure reference clock drift for eNBl", Ref UE measures stability of T _drifti (T _ei , T _uei ). By usage of T _Uei I(T _Ue ) and T _uei Q(T _ue ) (or more shifted reference clocks for TOA measurements), TOA accuracy may be enhanced. In this case, it may be detected a time shift of 8,125 ns, which may be sufficient for mobile network time monitoring and verification. This may be also denoted as T _driftiMax value, which may be used as a trigger if measured TOA delay ex ceeds this limit with respect to T _refi (eNBl).

In an embodiment, higher TOA precision may be also possible by usage of more T _s shifts as a time reference at Ref UE, which is not technically complicated as Ti latching process needs to be multiplied for shifted reference times such as:

TuelI(Tue)= Tuel (Tue), (Eq. 9A)

TuelQ(Tue)= Tuel (T _ue )+- T _s . (Eq. 9B)

In an embodiment, once Ref UE is calibrated, any changes in TOA propaga tion delay may be caused by instabilities related to Ref UE T _ue for Ti(T _ue ), or to eNBl Tei for To (Tel).

In an embodiment, instabilities at eNBl T _ei (T _ei ) may have impact on TOA measurement related to eNBl.

In an embodiment, instabilities at Ref UE T _Ue (T _Ue ) may have impact on any TOA measurement performed by Ref UE with respect to any other eNB, as time floor T _Ue (T _Ue ) may be common and any added corrections are static, such as equation 8.

In normal mobile network operations where PRC is available, time refer ence at eNBs are within tolerances, which also means that Ref UE (or any UE) con nected to the network may have accurate and precise time. The timing of UEs may be periodically resynchronised to cover any instabilities at UE reference time source. However, if PRC is not available to some eNB, the resynchronisation mechanism may give wrong results.

Finally, in step 818, Ref UE TOA measurements may be calibrated with any eNBs in the coverage. Parameter T _driftiMax for eNBl may determine accuracy and may be used as a trigger, if exceeded, for T _ue or T _ei time corrections. As explained, higher precision may be achieved if quadrature or similar technique is used, see equations 9A and 9B.

Fig. 10 illustrates an example of an activity diagram for a calibrated Ref UE 500. In this example, eNBl may have lost synchronisation with PRC. However, PRC may be still available for eNB2 and eNBX. ENBl operation is based on its own internal clock. In an embodiment, Ref UE may detect any reference time drift once TOA measurement utilising a reference signal transmitted by eNBl exceeds the given threshold level, such as T _driftiMax - It may be that although an access node has lost synchronisation, the inter nal clock of the node may still keep time accurately enough, at least for a period of time. In the example of Fig. 10, time drift of ENB1 may still be within limits although it lost synchronization with PRC. Ref UE may determine that TOA measurements from eNBs are correct, which means conditions in equation 3 and 4 are true for eNBs. No further action is needed from Ref UE. This state may correspond to scenario shown in Figs. 5A and 5B.

With respect to Fig. 10, after the given period of time, the internal clock of eNBl may drift beyond TOA defined TdriftiMax threshold. In such a case, Ref UE may de tect this state as illustrated in Fig. 11 by NOK state from step 1100 for eNBl. This may correspond to scenario shown in Figs. 6A and 6B.

In order to determine the source of problem, Ref UE may measure TOA propagation delays to other eNBs in the vicinity, which may be eNB2 and eNBX. These additional TOA measurements are in this example correct, as indicated by OK state from steps 1102 and 1104. This confirms to Ref UE that the problem is related to T _ei drift of eNBl. The reference time at Ref UE, T _ue , is correct because T _ue is common for eNBs (eNBlcorr is a static shift).

In an embodiment, eNBl T _ei time drift may be assessed to be substantially equal to TdriftiMax, or in general Tdrifti, if better accuracy is needed. A change may be positive or negative, which may be denoted as ⁺ / —Tdrifti.

In an embodiment, when Ref UE has determined that the eNBl internal clock Tei needs to be adjusted, it may perform actions as illustrated on Fig. 12.

In Fig. 12, at the step 1200, "Ref UE: Required Time Correction to eNBl", Ref UE determines that time correction for eNBl may be needed by +/-T _d rif _ti , which may be exact value, if precise reference time floor is available as explained earlier, or

T driftiMax-

Ref UE requests an RRC Connection to eNBl.

Then, at the step 1202, "Ref UE: Send eNB Time Correction", Ref UE may report to eNBl that eNBl internal clock needs to be adjusted by +/-T _d rif _ti , which means that Tei time should be changed to T _ei +/-T _d rif _ti .

At the step 1204, "eNBl: Resynchronize internal clock", eNBl is configured to adjust the internal clock of eNBl to T _ei +/-T _d nf _ti . This also affects any UE connected to this eNB. Thus, any other UE will receive corrected time per legacy synchronization mechanism, even if the given eNB operate without connection with PRC.

At the step 1206, "Ref UE: Resynchronize internal clock", Ref UE, which is in RRC Connected state, also adjust its internal clock T _ue (T _ei +/-T _d rif _ti ), which means both eNBl and Ref UE will have common reference clock for TOA measurements.

In step 1208, eNBl sends a reference signal at time instant To. Ref UE re ceives signal at step 1210 as time instant Ti _, as described earlier. These transmissions occur during updated internal clocks of eNBl and Ref UE. For Ref UE, it means that TOA measurement to eNBl is correct again.

Ref UE is configured to continuously measure also other TOA measure ments to verify whether other measurements are still correct, which confirms that problem was solved by T _ei time adjustment. If other TOA measurements are ok, prob lem is solved, and no further actions are needed. Synchronization is restored.

If PRC is not available for larger number of eNBs or not present at all, Ref UE may determine time drift in more than one eNB, as illustrated on Fig. 13, where two NOK states 1300, 1302 may be received. This scenario also applies for instability of Ref UE internal clock, T _ue . This condition may be signalled by more than one TOA measure ment errors, which is different condition if one eNB is affected.

In this case, Ref UE may determine which TOA measurements are incorrect and assess errors by TdriftiMax or Tdrifti values respectively for eNBs. Then, Ref UE may determine time correction for T _ue , which may be as illustrated by equation 10: min(Tdrifti,Tdrift2), (Eq. 10) where Tdrifti, Tdrift2 are values for different eNBs.

Proposed solution ensures that changes are implemented in smaller incre ments, which improves management of such changes. It may be noted, that a change in T _ue also affects other TOA measurements. Fig. 14 illustrates an example how a change to reference time at Ref UE, (equation 10), may be implemented. Ref UE may stay in RRC Idle state, or if it is already in RRC Connected state, changes may be applied to received time value, so current time value may have no impact on these changes.

After implementation of changes in Ref UE internal clock reference time, Ref UE may be configured to repeat TOA measurements until TOA measurements are sim ilar to these from calibration.

In an embodiment, in more complicated scenarios, corrections may be pro posed both to any eNB and to Ref UE until results are correct again.

Thus, as illustrated in the above example, Ref UE may be able to distinguish whether reference time source needs to be corrected at eNB or Ref UE, which is useful if mobile network needs to operate without access to PRC due to any reason. This may be the case when the network utilises satellite-based synchronization and when the performance of the satellite-based synchronization is affected by natural phenomena such as solar flare or is jammed, or such system is not available. As illustrated, the proposed solution does not require sophisticated and costly equipment with respect to PRC in the form of atomic clock, for example. Ref UE may be loT/LTE-M or Wideband UE and still its performance may be sufficient for maintaining operation.

Fig. 15 illustrates an embodiment. The figure illustrates a simplified exam ple of an apparatus or network entity applying embodiments of the invention. In some embodiments, the apparatus may be a user equipment such as Ref UE 500 or a part of RefUE.

It should be understood that the apparatus is depicted herein as an example illustrating some embodiments. It is apparent to a person skilled in the art that the ap paratus may also comprise other functions and/or structures and not all described functions and structures are required. Although the apparatus has been depicted as one entity, different modules and memory may be implemented in one or more physi cal or logical entities.

The apparatus 500 of the example includes a control circuitry 1500 config ured to control at least part of the operation of the apparatus.

The apparatus may comprise a memory 1502 for storing data. Furthermore, the memory may store software 1504 executable by the control circuitry 1500. The memory may be integrated in the control circuitry.

The apparatus further comprises one or more interface circuitries 1506 configured to connect the apparatus to other devices and network elements or entities of the radio access network, such as access nodes or eNBs.

In an embodiment, the software 1504 may comprise a computer program comprising program code means adapted to cause the control circuitry 1500 of the ap paratus to realise at least some of the embodiments described above.

Fig. 16 illustrates an embodiment. The figure illustrates a simplified exam ple of an apparatus or network entity applying embodiments of the invention. In some embodiments, the apparatus may be a network element or network entity acting as a radio access node or eNB 502, or a part of a radio access node or eNB.

It should be understood that the apparatus is depicted herein as an example illustrating some embodiments. It is apparent to a person skilled in the art that the ap paratus may also comprise other functions and/or structures and not all described functions and structures are required. Although the apparatus has been depicted as one entity, different modules and memory may be implemented in one or more physi cal or logical entities. The apparatus 502 of the example includes a control circuitry 1600 config ured to control at least part of the operation of the apparatus.

The apparatus may comprise a memory 1602 for storing data. Furthermore, the memory may store software 1604 executable by the control circuitry 1600. The memory may be integrated in the control circuitry.

The apparatus further comprises one or more interface circuitries 1606, 1608, configured to connect the apparatus to other devices and network elements or entities of the radio access network, such as core network and user terminals. The in terfaces may provide wired or wireless connections.

In an embodiment, the software 1604 may comprise a computer program comprising program code means adapted to cause the control circuitry 1600 of the ap paratus to realise at least some of the embodiments described above.

The steps and related functions described in the above and attached figures are in no absolute chronological order, and some of the steps may be performed sim ultaneously or in an order differing from the given one. Other functions can also be executed between the steps or within the steps. Some of the steps can also be left out or replaced with a corresponding step.

The apparatuses or controllers able to perform the above-described steps may be implemented as an electronic digital computer, processing system or a circuitry which may comprise a working memory (random access memory, RAM), a central pro cessing unit (CPU), and a system clock. The CPU may comprise a set of registers, an arithmetic logic unit, and a controller. The processing system, controller or the cir cuitry is controlled by a sequence of program instructions transferred to the CPU from the RAM. The controller may contain a number of microinstructions for basic opera tions. The implementation of microinstructions may vary depending on the CPU design. The program instructions may be coded by a programming language, which may be a high-level programming language, such as C, Java, etc., or a low-level programming lan guage, such as a machine language, or an assembler. The electronic digital computer may also have an operating system, which may provide system services to a computer program written with the program instructions.

As used in this application, the term 'circuitry' refers to all of the following: (a) hardware-only circuit implementations, such as implementations in only analog and/or digital circuitry, and (b) combinations of circuits and software (and/or firm ware), such as (as applicable): (i) a combination of processor(s) or (ii) portions of pro- cessor(s)/software including digital signal processor(s), software, and memory(ies) that work together to cause an apparatus to perform various functions, and (c) circuits, such as a microprocessor(s) or a portion of a microprocessor(s), that require software or firmware for operation, even if the software or firmware is not physically present.

This definition of 'circuitry' applies to all uses of this term in this applica tion. As a further example, as used in this application, the term 'circuitry' would also cover an implementation of merely a processor (or multiple processors) or a portion of a processor and its (or their) accompanying software and/or firmware. The term 'circuitry' would also cover, for example and if applicable to the particular element, a baseband integrated circuit or applications processor integrated circuit for a mobile phone or a similar integrated circuit in a server, a cellular network device, or another network device.

An embodiment provides a computer program embodied on a distribution medium, comprising program instructions which, when loaded into an electronic ap paratus, are configured to control the apparatus to execute the embodiments described above.

The computer program may be in source code form, object code form, or in some intermediate form, and it may be stored in some sort of carrier, which may be any entity or device capable of carrying the program. Such carriers include a record medium, computer memory, read-only memory, and a software distribution package, for example. Depending on the processing power needed, the computer program may be executed in a single electronic digital computer or it may be distributed amongst a number of computers.

The apparatus may also be implemented as one or more integrated circuits, such as application-specific integrated circuits ASIC. Other hardware embodiments are also feasible, such as a circuit built of separate logic components. A hybrid of these dif ferent implementations is also feasible. When selecting the method of implementation, a person skilled in the art will consider the requirements set for the size and power consumption of the apparatus, the necessary processing capacity, production costs, and production volumes, for example.

In an embodiment, an apparatus comprises at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the appa ratus at least to perform: store information on a reference propagation delay between the apparatus and one or more radio access nodes; control reception of a reference signal from one or more radio access nodes, the reference signal comprising infor mation on the transmission time instant of the signal; determine the reception time instant of the reference signal; determine the propagation delay of the reference signal based on the time difference of the reception time instant and the transmission time instant; determine correctness of time references of the apparatus and the one or more radio access nodes based on the determined and stored propagation delays.

In an embodiment, an apparatus comprises at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the appa ratus at least to perform: control transmission of a reference signal to user equipment, the reference signal comprising information on the transmission time instant of the signal; control reception of an indication from the user equipment, the indication com prising information on the correction for the time reference of the apparatus; and cor rect the time reference of the apparatus based on the indication.

In an embodiment, a non-transitory computer readable medium comprises program instructions for causing an apparatus to perform at least the following: stor ing information on a reference propagation delay between the apparatus and one or more radio access nodes; controlling reception of a reference signal from one or more radio access nodes, the reference signal comprising information on the transmission time instant of the signal; determining the reception time instant of the reference sig nal; determining the propagation delay of the reference signal based on the time dif ference of the reception time instant and the transmission time instant; and determin ing correctness of time references of the apparatus and the one or more radio access nodes based on the determined and stored propagation delays.

In an embodiment, a non-transitory computer readable medium comprises program instructions for causing an apparatus to perform at least the following: con trolling transmission of a reference signal to a user terminal, the reference signal com prising information on the transmission time instant of the signal; controlling recep tion of an indication from the user equipment, the indication comprising information on the correction for the time reference of the apparatus; and correcting the time ref erence of the apparatus based on the indication.

It will be obvious to a person skilled in the art that, as the technology ad vances, the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.