Field of the Invention

The invention relates to a method and apparatus of synchronisation of network elements in communication systems. It is particularly but not exclusively applicable communication systems which use long term evolution (LTE) of 3GPP, including LTE advanced; and has also particular but not exclusive application to the TDD mode of 3GPP. It is also particularly applicable to network elements which are Access Points (APs) such as base stations (node Bs).

Background of the Invention

A communication system is a facility which facilitates the communication between two or more entities such as communication devices, network entities and other nodes. A communication system may be provided by one more interconnected networks. A communication device can be understood as a device provided with appropriate communication and control capabilities for enabling use thereof for communication with others parties. The communication may comprise, for example, communication of voice, electronic mail (email), text messages, data, multimedia and so on. A communication device typically enables a user of the device to receive and transmit communication via a communication system and can thus be used for accessing various service applications. In cellular systems a network entity in the form of a base station provides a node for communication with mobile devices in one or more cells. A base station is often referred to as a 'Node B'. There are many different techniques for processing signals for transmission between the base station and the user equipment. Typically the operation of a base station apparatus and other apparatus of an access system required for the communication is controlled by a particular control entity. The control entity is typically interconnected with other control entities of the particular communication network.

It is known to use local area base stations (eNBs) in wireless communication networks, which reduce costs. These node Bs are often referred to as Access points(APs). Typically such access points do not have global synchronisation (e.g. via a GPS clock). Those OTAC commands facilitate synchronisation. The term "Access Point" is hereinafter used to include any distributed network elements which are part of a communications network and typically communicate with User Equipment (UE) and such like as well as other Access Points including eNodeBs and base stations.

In local area systems such as real office environments, a subscriber of a User Equipment (UE) such as a mobile phone may connect to an Access Point AP that is further away geographically that the nearest Access Point due to various limitations such as subscriptions limitations or closed subsystem group issues. For example, the Access Point to which the UE can connect due to subscription access issues may not be the closest AP. In such a scenario the AP closest to the UE and that to which the UE directly communicates, may not be able to see each other i.e. establish a viable direct communication link between them. Therefore in such cases the two Access Points cannot become synchronised. In the past convergence of synchronisation in networks has been studied. However the problem with such solutions is that they use very complex methodology. It is an object of the invention to provide a simple solution using inventive techniques described hereinafter.

Summary of Invention

The invention comprises, in a communication system, a method of synchronising a first network element with a second network element, where said first and second network elements are not in communication with one another, comprising the steps of: establishing a third network element; determining to what extent one or both of said first and second network elements are synchronised; deciding to synchronise as a result, either said first network element with said second network element or said second network element with said first network element appropriately; sending a synchronisation message via said third network element to the appropriate first or second network element to enable said synchronisation to take place; and synchronising the network element which receives said forwarded synchronisation message.

In an embodiment it may use synchronisation information sent from either said second network and/or said first network element.

Also said determining may include noting that no synchronisation information is received from one or both of first and second network elements. A preferred embodiment includes preferably the initial step of synchronising the third network element either with said first network element or said second network element.

The synchronisation information may include a synchronisation parameter.The synchronisation parameter may indicate any of the following: the synchronisation state, whether the network element is synchronised or free running; whether it is globally synchronised, to what extent and to how many other network elements it is synchronised with; and the quality of the signal between network elements.

In an embodiment where it is determined that both first and second network elements are both synchronised or both unsynchronised, a random choice is made.

The synchronisation message may include time shift information.

The invention also comprises a network element adapted to synchronise a second network element with a third network element: said third network element not being in direct communication with said second network element having: means to determine to what extent one or both of said second and third network elements are synchronised;

means to decide to synchronise as a result, either said third network element with said second network element or said second network element with said third network element appropriately; and means to send a synchronisation message to the appropriate second or third network element to enable said synchronisation to take place. In a preferred embodiment the determining means includes means receive to use synchronisation information sent from either said second network and/or said first network element. The determining means may also includes means to note that no synchronisation information is received from one or more of first and second network elements.

Preferably the network element includes means to synchronising itself to said second or third network element.

The synchronisation information may include a synchronisation parameter. The synchronisation parameter may indicate any of the following: the synchronisation state, whether the network element is synchronised or free running; whether it is globally synchronised, to what extent and to how many other network elements it is synchronised with; and the quality of the signal between network elements.

In an embodiment the deciding means includes means to make a random choice.

The synchronisation message includes time shift information.

The invention further comprises a method of synchronising network elements in a communication system including the steps of: transmitting synchronisation information from a first network element to a second network element informing that the first network element is in a particular synchronisation state; and determining that the second network element should adopt the said synchronisation state; and, adopting said synchronisation state in said second network element. In a preferred embodiment the synchronisation state is installed in said second network element for a pre-set time, T _valid after where the synchronisation of said second element reverts to its original or an alternative state.

A preferred embodiment includes further transmitting/forwarding said synchronisation information from said second network element to a third network element informing that it is in said first synchronisation state.

Preferably the synchronisation information is forwarded within a pre-set time.

A preferred embodiment includes further installing said first synchronisation state in said third network element.

In an embodiment the received synchronisation information is ignored if it is received before a pre-set time after previous synchronisation information message has been received.

The invention also includes a network element having means to receive a synchronisation message from a second network element that the second network element is in a particular synchronisation state; means to determine that it should adopt the said synchronisation state; and, means to adopt said synchronisation state. In a preferred embodiment the network element includes means to install said synchronisation state in said second network element for a pre-set time after which it reverts to its original or an alternative state.

In a preferred embodiment the network element includes means to further transmit or forward said synchronisation information from to a third network element informing that it is in said first synchronisation state.

In a preferred embodiment the network element sends the synchronisation information is forwarded/transmitted to said third network element within a pre-set time.

In a further preferred embodiment the network element is adapted to ignore received synchronisation information if it is received before a pre-set time after the last synchronisation message has been received.

Summary of Figures

For a better understanding of the present invention and how the same may be carried into effect, reference will now be made by way of example only to the accompanying drawings in which:

Figure 1 shows a schematic presentation of a communication system wherein the invention may be embodied;

Figure 2 shows a sectioned view of communication User Equipment. Figures 3a to 3d illustrate how one embodiment of the invention may be implemented.

Figure 4 outlines a flow diagram according to one embodiment of the invention.

Figure 5 shows a schematic representation of a communications system illustrating a further embodiment of the invention.

Figure 6 shows a flow diagram illustrating a further refined embodiment according to the invention.

Before explaining in detail a few exemplifying embodiments, a brief explanation of wireless access is given with reference to Figure 1 showing a communication system providing wireless communications to a plurality of communication devices 1. A communication device 1, for example a mobile user device or equipment, can be used for accessing various services and/or applications provided via the wireless communication system. A communication device can typically access wirelessly a communication system via at least one wireless transmitter and/or receiver node 10 of an access system. Non-limiting examples of access nodes are a base station of a cellular system, for example a 3G WCDMA Node B, a enhanced Node B (eNB) of 3GPP LTE (long term evolution), a base station of a wireless local area network (WLAN) and a satellite station of a satellite based communication system. The communication devices 1 may also communicate directly with each other. The communications may be arranged in various manners based on an appropriate radio access technology or technologies. The access is provided via radio channels also known as access channels. Each communication device 1 may have one or more radio channels open at the same time. Each communication device may be connected to more than one base station 10 or similar entity. Also, a plurality of communicate devices may communicate with a base station or similar, and/or attempt to access the communication system via the same base station. A plurality of communication devices may also share a channel. For example, to start communications or to connect to a new access system, a plurality of communications devices may attempt to make the initial contact via a single channel, for example via a random access channel (RACH). The attempts to access may be made substantially at the same time.

The base station 10 of the access system can be connected to other parts of the communication system via appropriate connections, for one or more appropriate gateway nodes. These are not shown for clarity. A base station is typically controlled by at least one appropriate controller apparatus (this is true for GSM and WCDMA. However in LTE and WiMAX there is no controller anymore, but control functionality is distributed to appropriate network elements such as general access nodes, base stations, nodeB's, eNBs, AP's) generally denoted by 11 in Figure 1. The controller apparatus 11 can be provided for managing of the operation of the base station and/or communications via the base station. The controller apparatus is typically provided with memory capacity and at least one data processor. Various functional entities may be provided in the controller by means of the data processing capability thereof. The functional entities provided in the base station controller may provide functions relating to radio resource control, access control, packet data context control, relay control and so forth. Network elements, such as base stations 10 are managed by using network management operations support system (OSS). OSS 's role is to supporting processes such as maintaining network inventory, provisioning services, configuring network components, and managing faults. OSS architecture is based on four layers: Business Management Level (BML), Service Management Level (SML), Network Management Level (NML), Element Management Level (EML). Network elements can be managed from network management system (NMS) or element management system (EMS). Base stations 10 are connected to NMS over open Itf-N (so called northbound interface) or to EMS over proprietary Itf-S interface (southbound interface).

A communication device 1 can be used for various tasks such as making and receiving phone calls, for receiving and sending data from and to a data network and for experiencing, for example, multimedia or other content. For example, a communication device may access applications provided via a telephone network and/or a data network, such as applications that are provided based on the Internet Protocol (IP) or any other appropriate protocol. An appropriate mobile communication device may be provided by any device capable of at least sending and/or receiving wireless signals from the access system. Non-limiting examples include a mobile station (MS) such as a mobile phone or a smart phone, a portable computer provided with a wireless interface card or other wireless interface facility, personal data assistant (PDA) provided with wireless communication capabilities, or any combinations of these or the like. As shown in Figure 2, a communication device 1 is typically provided with appropriate data processing apparatus, such as at least one data processor 5. At least one memory device 6 is also typically provided. The data processing and storage entities can be provided on an appropriate circuit board and/or in chipsets. Different functions and operations may be provided by different chips. Alternatively, at least partially integrated chips may be used. Antenna means 4, a display 2, and/or a keypad 3 may also be provided.

Detailed Description of Exemplary Embodiments

As mentioned, base stations are often in communication with each other by means of a network controller. Often there may be more than one network or sub-networks present within a geographical area, each having their own base stations which may be located in the same vicinity as base stations of a different network. Normally base stations of different networks do not communicate with each other directly, although they are often connected via RNC and various gateway nodes. Furthermore autonomous networks are networks where there is no overall control by a Radio Network Controller as such. These systems just comprise of a network of base stations (or access points) with which User Equipment communicates. It is often desirable to synchronise base stations to each other even if they are in separate networks. Often direct communication between base stations (Access Points), whether within the same network/sub-network or not, is not possible because of geographical, functional, subscriber issues.

Example 1 Figure 3 a shows a schematic representation of a communication system showing one embodiment of a method according to the invention. It shows in step 1 two APs (API and APx) which are already synchronised with each other. APx may be regarded as a single AP or a network of (i.e. a plurality of) APs and not just a single AP. A further AP designated AP2 is isolated from both APx and API and runs its own ( i.e. has its own synchronisation). The term "isolation" means it does not have any direct communication with either APx or API, via for example OTAC transmissions. An isolation barrier 11 is shown; there may not be a physical barrier present; the isolation may be due to system differences and subscriber issues, as explained. The isolation barrier could also be constituted by a simple radio propagation loss, that is, the radio signals from one AP are attenuated in such a way that it is not possible for the other AT to correctly decode information from the first AP.

Figure 3b shows at step 2 a new AP, designated AP3 is powered on. AP3 can communicate directly with both API and AP2. As part of OTAC signalling, API informs AP3 that it is synchronised to other AP' s i.e. APx. AP2 which is free running, i.e. not synchronised with other AP's, informs AP3 that it is not synchronised to the other AP's.

AP3 determines that synchronisation with API takes precedence over synchronisation to AP2 (as API is already synchronised) and will complete its synchronisation to API at step 3 in figure 3c. This figure also shows that AP3 becomes synchronised to API and will report this fact in its OTAC signal to AP2.

At step 4 in figure 3d AP2 then determines that AP3 has no intention to synchronise to itself so AP2 will synchronise to AP3 instead. In this way all APs become synchronised together. The above process is also illustrated in the flow chart of figure 4.

In the example given the synchronisation messages are preferably incorporated into standard OTAC signalling. In other words the signals to indicate synchronisation are part of standardized OTAC signalling for APs to exchange whether they are already synchronised to other APs. However the invention is not limited to this and synchronisation information may be transmitted in separate messages.

There are a number of alternative embodiments which are covered by the scope of the invention. In a simple embodiment according to the invention, AP3 may not become synchronised with any particular or even any other AP but may just act effectively as a relay between API, APx and AP3.

However in a preferred practical embodiment AP3 becomes synchronised to the other APs in the network as explained in the example above. Moreover in preferred embodiments it is AP3 which is the first network element to change its synchronisation.

In yet further preferred embodiments, it is AP3 i.e. the intermediate Access Point which decides which synchronisation state it and/or other access points should take. Synchronisation messages as mentioned may or may not be part of the standardised OTAC signalling. The synchronisation information in any case that is passed between network elements (e.g. Access Points) may include a variety of synchronisation parameters. These parameters in preferred embodiments are used to decide which network elements (APs) should be synchronised with which other network elements. In other words it may be determined that all APs should synchronise with a particular AP.

Example 2

According to one preferred embodiment, a standardized rule may be that APs are synchronised preferably with other APs which are already synchronised. For example synchronisation of a particular AP to one already synchronised takes precedence over its synchronisation to unsynchronised APs.

In order to implement certain such embodiments of the invention synchronisation messages passed between network elements (APs), whether part of standard OTAC signalling may include one or more synchronisation parameters. These parameters may for example indicate any of the following: whether the network element is synchronised or free running; whether it is globally synchronised, to what extent and to how many other network elements it is synchronised with; or whether it is globally synchronised. Of course the synchronisation parameters are not limited to these. Such parameters are used in preferred embodiments when deciding to which AP or group of APs the remaining APs should be synchronised with.

One embodiment includes having a rule whereby existing "free running" AP (e.g. AP that has been online for a long time but is not synchronized to other APs) is to re-update its synchronisation to neighbours that are synchronised to other APS.

Example 3

There may be situations where even having all the synchronisation parameters to hand, it is not obvious with which AP a particular AP should synchronise. For example, where with reference to figure 3, neither API or AP2 are synchronised to any other APs, or where they are both synchronised to further APs.

According to one embodiment of the invention, a random choice may be made (by AP3 for example) as to which AP to initially become synchronised with. In the example of figure 3, if neither API or AP2 are synchronised, AP3 may randomly choose to synchronise with AP2. In this case the process in similar to that described in figure 3 and in step 3 the two synchronised APs (i.e. AP3 and the AP to which AP3 becomes synchronised with) update their status, that is to say they register that they are now synchronised, and the remaining unsynchronised AP then follows suit and becomes synchronised with the other APs.

Example 4

In one preferred alternative embodiment where neither API or AP2 are synchronised to anyone (for example where the OTAC signal is zero), or where they are both synchronised with other APs, when AP3 sets up its synchronisation;, AP3 may take a qualified choice as to which AP to synchronise with. The qualified choice could for example based upon strongest signal, indicating least interference to the other AP.

In an alternative embodiment of the invention the decision as to which AP to synchronize to is based on the extent to which the APs in question are synchronised already. For example, this may be the case if API and AP2 are both synchronised initially with other APs, but these two groups have different synchronisation. Synchronisation information (e.g. in the OTAC signals) from both API and AP2 indicate therefore that they are synchronised but these synchronisations are different. In one embodiment API and AP2 may determine and inform AP3 how many APs they are each synchronised with. AP3 decides to synchronise its signal with that AP (AP 1 or AP2) which is synchronised with the most APs. The remaining one of API of AP2 then determines that AP3 will not synchronise with it so decides to synchronize with AP3 itself. This is efficient as it reduces the amount of steps and signals which need to be sent.

There are further embodiments which come under the scope of the invention. In an alternative embodiment there may be three options of the synchronisation status of an AP; not synchronised with any other visible AP; synchronised with another AP, (via OTAC signalling for example); or, synchronised with another AP that reports it is synchronised via a GPS clock or synced to GPS clock myself.

According to further embodiments of the invention, where the AP3 has an option which AP's to initially synchronise with; it may choose particular preferences from the above. As described above the invention may be set up such that at intervals each AP has some responsibility to re-evaluate its network synchronization. This may be done by taking synchronisation measurements at certain times and perhaps putting its traffic to idle when needed i.e. during this time. _In one particular embodiment, the methods may prefer to initiate synchronisation with APs which are synchronised with or via a GPS clock. The procedure in such embodiments may be similar to the procedure described above with reference to figures 3a to 3d.

In the embodiment illustrated in figure 5, once the AP3 starts its synchronisation procedure, (e.g. when it is turning on its power) it builds a list of APs it has direct communication with and their synchronisation states. This may be done either by direct communication or through sensing of the network environment.

AP3 will see API and AP2 and enable OTA communication with both APs. In the example APx is synchronised to a GPS clock. AP3 determines that API is indirectly connected to GPS clock while AP2 is free running AP when it comes to GPS connection (i.e. AP2 is not synchronised relative to GPS clock)

The enabling access point (AP3) may establish OTA communication with both AP2 and API. AP3 continues with signalling with all GPS synced APs under usual procedures.

AP3 then signals to all free running APs (or those APs synchronised but not globally) that it has found GPS clock and that free running APs need to update their network synchronisation (e.g. this can be considered as "push mode")

Free running APs like for example an APy which may be connected and synchronised to AP2 need also to update its synchronisation. In fact any chain (group) of any free running APs need to update their synchronisation. AP3 will indicate to AP2 that it should adapt to the global synchronisation (the GPS clock) and correspondingly, before AP2 adjusts the timing, it communicate the change of timing to its own connected APs, that is APy in the example illustrated by figure 5.

It would be understood by the skilled person that there would be various alternative embodiments which would fall under the scope of the invention. APs which may in alternative embodiment be synchronised but not to a GPS clock may preferably be synchronised to the GPS clock. In such a particular embodiment, global synchronisation takes precedence over any other synchronisation. In other preferred embodiments free running APs are synchronised to already synchronised APs.

Example 8

Depending on the format of the OTAC messages, in a further preferred embodiment, an OTAC message (from AP3 to AP2) contains information of the intended time shift relative to AP2 that it will use when adjusting and synchronizing to API. In this way AP2 will be able to re-adjust its timing to synchronise to e.g. the global clock rapidly. Correspondingly the API should have means to communicate to connected UEs that the global timing will change at a certain time instant (to allow for cell -level change of global timing). This may be done by RRC signalling or other cell-level broadcast signalling means.

There will now be described further enhanced embodiments of the invention. The above embodiments assume that network elements are relatively stable. However there is a problem of nodes (APs) abruptly disappearing from a network. The embodiments below describe further enhancements of the invention which overcomes these difficulties.

In such further embodiments of the invention, a network synchronization procedure may include forcing Synchronized APs to 'advertise' to other connected APs that they have a particular synchronisation (such as global synchronization) .

Further, APs that obtain their synchronization from other APs (derived synchronization) may also advertise their synchronisation status e.g. "connected to global clock" to their further connected APs.

To be able to recover from disappearing APs, in a further embodiment of the invention a "validity timer" may be included which indicates the time duration for which the synchronization is valid.

In a further preferred embodiment, there may be a policy in each AP, which ensures that the synchronisation information (e.g. globally synced) is forwarded to connected APs. The combination of these parameters (and proper settings) will ensure that each APs understanding of its synchronization is be updated to best effect.

A more detailed example of this embodiment will now be described. In order to describe the method, a set of parameters are defined. The synchronization state (AP_Sync) of a AP can take various values such as "synchronised"; "global synchronized", "free-running" and such like. A further parameter may be set up which is validity time (T_ _va iid)- This is defined as the time duration that a communicated synchronisation information sent from another AP, is valid (for implementation of a change in synchronisation state) in a particular AP. As validity of transferred synchronisation information should be valid throughout the network, this has to be set as a minimum compared to hardware stability (e.g. accuracy of clock and time drift). Hence, in a preferred embodiment it should be requirement in the specification that an AP that has been synchronized to another base station (or GPS clock) that becomes unsynchronised or which loses communication with the AP from which it received synchronisation information, it should maintain its synchronization (within defined accuracy) for T _y&M . A further parameter is Forward Time (T_ _fo rward) is the time within which the AP should at maximum have forwarded the synchronisation information (e.g. "Global synchronized" message) to other connected APs. Again, this is preferably specified beforehand to ensure network stability and is preferably set according to the anticipated number of inter-connected APs that rely on the same global source of clock reference. The parameter Grace Timer (T_ _grace ) is defined as the time period by which an AP should ignore additional received synchronisation information (e.g. global synchronised) messages from other APs. This is to prevent circular messages creating loops in the network.

Example 9

An AP directly connected to a global clock should always, in one embodiment of the invention, be in a "global synchronized" state, and all non-connected APs should by default be in the free-running state or have a different "non-globalised synchronisation state". If an AP gets a synchronization message (e.g. "globally synchronised") from another AP, it changes it state to that synchronisation (e.g. "global synchronized"), and transmits the same message to other connected APs (either through direct inter- AP communication or broadcast communication) within the T_ _fonvard time period. It is preferable that the AP communicates completely within the T _forWard time duration. When the time T_ _va π _d has expired, the synchronization state should be reverted back to its previous synchronisation state or changed to "free-running" or unless new pertinent synchronisation information (e.g. "global synchronization" message) is received. When an AP has received synchronisation information (e.g. a "global synchronization" message), it preferably enters a grace period (time duration: T^ _race ) where it will ignore further synchronisation messages/information (e.g. any new "global synchronization" messages) . This is to ensure that loops in the network will not create false understanding of the network synchronization.

For proper operation of this synchronization mechanism, the parameters should have the following properties:

I jvalid ^ -l- _^ grace ^" l _forward

Further, the parameter T_ _va ij _d should be set such that T_ _va ii _d ⁺ N*T_ _fonvard is larger than the parameter T _hardware , which denotes the time over which an APs time synchronization can be maintained without updates, and N is the "propagation depth" of the overall network (that is, the number of hops that at maximum is accepted from GPS-synchronized AP to the outermost non- GP S -synchronized AP in the network). T_ _hardwar e denotes the "stability" of a node's understanding of time. As some nodes may be built using relatively cheap oscillators, the node will only be accurate for a limited period of time. Propagation depth is denoting the number of links that are in the "chain" of interconnected Nodes/APs. If we use the example of Figure 5, the depth will be 5, as we have APx-AP 1-AP3-AP2- APy connected to each other. Each of these nodes denote a link for the propagation of the global timing message. If we remove the wall and have much better conditions, we may have the situation where all APs (API, AP2, AP3, and APy can hear APx, and here we would have a depth of 2, as there are at most 2 nodes in a single chain of interconnected Nodes exchanging timing information. In this example, APx will simply provide timing information to all at the same time.) Example values for these parameters could be : T_ _va ii _d = 120 seconds ; T _Jgrace = 60 seconds ; T _forward ⁼ 5 seconds

To ensure that new "global synchronization" messages are not sent out by the truly global synchronized APs too often, these APs may preferably transmit the messages at time instants that are defined from T _va iid and T_gr _ace (one example could be to use (T_ _va ii _d +T_ _graCe )/2 as a default value. This will ensure that APs will get updates after the grace period, and before the AP is switched to the "free-running" state. Further, the truly global synchronized AP should always be in the grace period (as this is global synchronized to GPS, it should ignore messages from other APs).

Figure 5 shows describes an embodiment of how one example of how an embodiment may be implemented. Inter-connected APs (APx, API, AP3, AP2, and APy) are synchronized to each other, and adapted to a global (GPS) clock which is carried by APx In general, APx may refer to a network of APs or just a single AP. AP2 and APy are isolated from the network constructed of APx and AP2, and will only be able to synchronize to the global timing through AP3. The procedure of propagation of the global synchronization message throughout the network in is shown in figure 6. In Step 1 at time t=0, the global connected APx sends a message that it is globally synchronized. This message is received by API. APx_Sync =Global. APl_Sync=Global. Step 2, before t=T _forward has elapsed, API forwards the "Global synchronized" message to AP3. (In a preferred embodiment forwarding of synchronisation messages/information is to all connected APs, the message may be sent to APx, but this is ignored, as APx is connected to GPS). AP3_Sync now becomes "Global". In Step 3, before t=2*T_ _fonvard has elapsed, AP3 will have forwarded the "Global synchronized" message to API and AP2. As grace period for API has not elapsed, this information is ignored by API. AP2_Sync now becomes "Global". In Step 4, before t=3*T_ _forward has elapsed, AP2 will have forwarded the "Global synchronized" message to AP3 and APy. The same rules as above applies. APy_Sync becomes "Global". At time t=(T_ _va i _id +T_ _grace )/2, APx will retransmit its "Global synchronized" message to API, and as grace timer has expired, this message will be accepted, and APl_sync=Global. In Step5, AP3 has now switched off the power for it, such that is it not able to be part of the network. At time t=2*T_forward + T_valid, AP2 will notice that no "Global synchronized" message has been received, and change synchronized state. running. In Step 6, at time t=3*T _jbrward ^÷ T_ _va i _id , APy will notice that no "Global synchronized" message has been received, and change synchronized state. APy_sync=free-running.

In this way we have a network which is capable of autonomously updating its own understanding of its individual synchronicity states. The above described functions can be provided by means of appropriate software and data processing apparatus. Functions may be incorporated into any appropriate network element or management system and may be provided by means of one or more data processors. The data processor may be provided by means of, for example, at least one chip. Appropriate data processing may be provided in a processing unit provided in association with a communication device, for example a mobile station. The data processing may be distributed across several data processing modules. The above described functions may be provided by separate processors or by an integrated processor. An appropriately adapted computer program code product or products may be used for implementing the embodiments, when loaded on an appropriate data processing apparatus. The program code product for providing the operation may be stored on and provided by means of an appropriate carrier medium. An appropriate computer program can be embodied on a computer readable record medium. A possibility is to download the program code product to a communication device via a data network.

It is also noted that although certain embodiments were described above by way of example with reference to certain exemplifying 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 exemplifying embodiments of the invention, there are several variations and modifications which may be made to the disclosed solution without departing from the scope of the present invention.