GB2494660A

GB2494660A - Method and apparatus for managing synchronisation between a first network and a second network

Info

Publication number: GB2494660A
Application number: GB1115900.1A
Authority: GB
Inventors: Pascal Lagrange; Tristan Halna Du Fretay; Pierre Visa
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 2011-09-14
Filing date: 2011-09-14
Publication date: 2013-03-20
Anticipated expiration: 2031-09-14
Also published as: GB2494660B; GB201115900D0

Abstract

A method of managing synchronisation between a first network 110 and a second network 120 , wherein the first network 110 includes a parent coÂordinator node 111 and the second network 120 comprises a plurality of network nodes and a designated co-ordinator node 121, the method comprising a network node of said plurality of network nodes performing the steps of: determining S601 the capability of reception of a predefined signal transmitted from the parent co-ordinator node of the first network 110; and providing an indication of the determined reception capability to the designated co-ordinator node 121 of the second network to enable the designated coordinator node to select a network node from among the plurality of network nodes and the designated co-ordinator node 121 as a time synchronisation reference node based on the respective reception capability of each of the plurality of network nodes and a reception capability of the designated co-ordinator node 121. Accordingly, communication between the first network and the second network may be maintained even when the designated co-ordinator node of the network has a poor quality radio link with the parent co-ordinator of the first network. The risk of synchronisation loss between the two networks is therefore reduced.

Description

METHOD AND APPARATUS FOR MANAGING SYNCHRONISATION

BETWEEN A FIRST NETWORK AND A SECOND NETWORK

The present invention concerns a method and a device for managing synchronisation between a first network and a second network. The invention further relates to a method and a device for synchronising a first network and a second network.

With the proliferation of high definition signal applications there is an increasing need for high rate transmission of large quantities of data in communication systems such as wireless communication networks. Extremely high frequency range wireless communication systems such as wireless communication systems operating in around the 800Hz range allow particularly high transmission rates for the transmission of high-definition video, audio and other data signals.

60GHz radio communication networks are particularly well suited to the transmission of data at very high bit rates over limited distances. Such a communication network may be used for example in a home cinema network for the exchange, within a limited range of the order of about ten meters, of audio and video data at very high bit rates of over one gigabit per second.

Such wireless systems, although advantageous from the viewpoint of their installation and although they permit particularly high application bit rates at the high frequencies, are nevertheless highly sensitive to phenomena of interference and shadowing which can lead to a loss of data on a transmission path between a transmission device and a receiving device. These phenomena can for instance be due to the presence of an unexpected obstacle on the transmission path for example a human being who passes between the sender and the receiver at the time of transmission.

Several standardization working groups are currently addressing the issue of very high throughput wireless networking in the 60 GHz unlicensed band. Two standards, the ECMA-387 and the WirelessHD 1.0 specifications, have already been published while the Wireless Gigabit Alliance (WiGig) has recently initiated an effort for standardizing 60 GHz technology. WirelessHD is intended for uncompressed HD video transmission, targeting the wireless video area network (WVAN), while ECMA-387 focuses on Bulk data transfer and HD streaming, hence addressing the high-rate wireless personal area network (WPAN). WiGig aims at providing a technology supporting instantaneous file transfers, wireless display and docking, and streaming high definition media on a variety of devices.

Additionally two amendments to current IEEE specifications, namely the IEEE 802.15.3c and the IEEE 802.llad, are also targeting the 60 GHz band. IEEE 802.15.3c provides a millimeter Wave approach to the existing IEEE 802.15.3 WPAN standard, so as to provide portable point-to-point file transfer and streaming. IEEE 802.11 Very High Throughput (VHT) Study Group has recently initiated the IEEE 802.llad standardization effort, introducing modifications to the IEEE 802.11 WLAN standard specification to allow it to operate in the 60 GHz band, in order to address WLAN applications such as rapid upload/download, wireless display, and distribution of HOW.

Wireless HD or WiGig approaches are mainly "static" point to point communication schemes. Their centric approach, as IEEE 802.15.3c or IEEE 802.llad, make them very sensitive to network transient perturbations.

Moreover, their lack of synchronization flexibility prevents them from addressing efficiently multi stream and hybrid wired/wireless systems. Such wireless standards may allow foreign devices (i.e. devices that do not implement said standards) to operate over the same wireless channel as the devices actually implementing these standards. In this respect, IEEEBO2.15.3 uses a time division multiple access (IDMA) scheme for operating both native and foreign devices over the same wireless channel within the 60GHz unlicensed band.

Non-802.15.3 devices may be granted synchronous time slots within the 802 15.3c superframe, referred to as pseudo-static channel time allocations, or P-CTA, to operate a network of their own, also referred as a dependent piconet.

A dependent piconet may be of two kinds: a child or a neighbour. The main 802.15.3 piconet is then referred to as the parent piconet. A child piconet requires that all of the devices it accommodates are compliant with the IEEE8D2.15.3-2003 and IEEE8O2.15.3c-2009 standards. A neighbour piconet only requires that one of its devices, referred as the neighbour coordinator, or neighbour PNC, device implements some features of the IEEE8O2.15.3-2003 and IEEE802.15.3c-2009 standards so as to set-up, maintain and terminate the neighbour piconet.

In order to keep a dependent piconet synchronized to the parent piconet, the dependent piconet coordinator, or dependent PNC, listens to the beacon information sent by the parent piconet coordinator. Such beacon information, sent at the very beginning of each piconet superframe by the parent PNC, describes the whole channel access scheme to be applied during the current superframe time interval. In particular, it embeds information on the timing (start time, duration) of the pseudo-static channel time allocation, or P-CTA, granted to the dependent PNC to operate its dependent piconet. This beacon frame, sent by the parent PNC, is also used by the dependent PNC as a timing reference so as to perform clock drift correction on order to avoid the transmissions performed by the devices belonging to the dependent piconet, including itself, to interfere with the transmissions of the devices belonging to the parent piconet. Indeed, the devices belonging to the dependent piconet are most likely to use the dependent PNC frame transmission as a timing reference for compensating their own clock jitter and to avoid interfering with each other.

In order to be allowed to operate a dependent piconet over the same wireless channel as the parent piconet, a dependent PNC shall notify the parent PNC of its ability to receive the parent piconet beacon frame by regularly sending a dedicated frame to the parent PNC, during a dedicated contention access period.

In the case where the dependent piconet coordinator fails to receive the parent beacon frame for a maximum predefined period of time (i.e. 8 superframes), the parent piconet ceases operating the dependent piconet it was in charge of, even though the overall quality of the communication links within the dependent piconet was satisfactory. This is due to the fact that the dependent PNC, in the case where it no longer receives the parent beacon frame, may be incapable of detecting a change in the channel access scheme to be applied during the superframe time interval and may thus interfere with parent piconet devices by performing a transmission within a time interval that is no longer allotted to it.

Moreover, a lack of reception of the parent beacon over too long a period of time would lead, as mentioned earlier, to interferences with the parent piconet transmissions due to the clock jitter, and resulting clock drift, at the dependent PNC level, even if the parent PNC made no changes to the channel access scheme for the superframe piconet.

With regard to the clock drift issue at the level of the dependent coordinator using significant interframe spacing between the time slots located right before and after the pseudo-static channel time allocation dedicated to dependent piconet operation may be considered, to mitigate the effects of the dependent piconet coordinator device's clock drift. However, increasing interframe spacing leads to a loss of channel bandwidth.

To overcome the issue of a dependent piconet being shut down, or causing interference, due to the parent and dependent coordinator devices being hidden from each other, the devices belonging to a dependent child piconet may perform a PNC handover as soon as the dependent child PNC no longer receives the parent beacon information through the parent beacon frame.

However, a PNC handover process requires that the devices taking part in the handover process are IEEE8O2.15.3-2003 standard compatible, which excludes applying such a scheme to neighbour piconets. Such handover processes also require a significant amount of transactions (handshake protocol) between the network devices, which makes completing such a process within an mMaxLostBeacons period (i.e. 8 superframes) very unlikely. Finally, relying on the PNC handover process would imply that all the devices belonging to the child piconet implement the hardware and software resources required for having the PNC capability.

W02009130650 describes how to use some devices belonging to different networks, operated over different channels, as proxy devices for maintaining communication facilities between the different networks. These proxy devices allow data exchange to be performed between devices belonging to different networks, but do not provide any solution for mitigating the effects of clock jitter and resulting clock drift between any two different networks.

US20051 36835 describes a radio relay device capable of relaying a packet received from a first electronic device to a second electronic device, while preventing collision of communication data when the communication data is relayed in a plurality of radio networks. Such a radio relay device performs a timing correction, based on source device synchronization timing, in order to perform timing correction and prevent transmission timings of the relayed packets from gradually shifting. However, the relay device disclosed in this document operates in a stand-alone way, addressing the synchronization between a source and a destination device; it does not support the synchronization of a whole network. Moreover, when a shadowing phenomenon occurs in between the source device and the relay device, the relay device is no longer able to perform clock drift correction and maintain synchronous data relaying.

The present invention has been devised to address one or more of the foregoing concerns.

According to a first aspect of the invention there is provided a method for managing synchronisation between a first network and a second network, wherein the first network includes a parent co-ordinator node and the second network comprises a plurality of network nodes and a designated co-ordinator node, the method comprising a network node of said plurality of network nodes performing the steps of: determining the capability of reception of a predefined signal transmitted from the parent co-ordinator node of the first network; and providing an indication of the determined reception capability to the designated co-ordinator node of the second network to enable the designated coordinator node to select a network node from among the plurality of network nodes and the designated co-ordinator node as a time synchronisation reference node based on the respective reception capability of each of the plurality of network nodes and a reception capability of the designated co-ordinator node.

According'y, communication between the first network and the second network may be maintained even when the designated co-ordinator node of the network has a poor quality radio link with the parent co-ordinator of the first network. The risk of synchronisation loss between the two networks is thereby reduced and the interference between devices of the two networks is minimised.

Consequently communication robustness and quality of service are not compromised by poor radio link conditions between the parent co-ordinator node of the first network and the designated co-ordinator node of the second network.

In an embodiment the method further comprises determining a first time drift between the local clock of the parent co-ordinator node and the local clock of said network node to enable a time correction value between the local clock of the designated co-ordinator node and the parent co-ordinator to be provided in the case where said network node is selected as the time synchronisation reference node. Accordingly time drift compensation may be performed between the two networks to avoid interference between devices of the two networks. Capability of the network node as a time synchronisation reference device from a time drift point of view may thus be assessed.

In an embodiment the time correction value is determined based on the first time drift and an estimated second time drift between the local clock of the network node and the local clock of the designated co-ordinator node.

In an embodiment the first time drift is determined based on the time of reception of at least two consecutive predefined signals received from the parent co-ordinator node of the first network, and a duration of a transmission cycle of said parent co-ordiriator node.

In an embodiment the second time drift is determined based on the reception of at least two consecutive predefined signals received from the designated co-ordinator and a duration of a transmission cycle of said designated co-ordinator node.

The method may include the step of providing the indication of the determined reception capability to at least one of the other network nodes of the second network.

The method may include the step of providing the first time drift and/or the second time drift to at least one of the other network nodes of the second network. The first time drift and/or the second time drift may be provided to all the other network nodes of the second network. This enables network devices of the second network to apply accurate clock drift compensation based on a clock drift estimation performed by the most capable network device of the second network. Each network device of the second network may thus perform the same time compensation and interference between transmissions from network devices of the second network may thereby be minimised.

In an embodiment of the invention the capability of reception of a predefined signal is determined by measuring at least one of the signal to noise ratio and the received signal strength indication of the predefined signal.

In an embodiment of the invention the capability of reception of a predefined signal is determined by consideration of the antenna pattern used to receive the predefined signal.

In an embodiment of the invention the capability of reception of a predefined signal is determined by determining the number of predefined signals received during a predefined number of transmission cycles.

Each network may operate in accordance with a mesh communication mode.

The method may include receiving a notification from the designated co-ordinator node indicating the selected time synchronisation reference node.

The network node selected as the time synchronisation reference node may receive a notification from the designated co-ordinator node designating the network node receiving the notification as a time synchronisation reference node.

The network node selected as the time synchronisation reference node may provide to the designated co-ordinator node the time correction value for application to the local clock of the designated co-ordinator node.

The network node selected as the time synchronisation reference node may operate as a proxy device between the designated co-ordinator node and the parent co-ordinator node.

According to a second aspect of the invention there is provided network device for managing synchronisation between a first network and a second network, wherein the first network includes a parent co-ordinator node and the second network comprises a plurality of network nodes including the network device and a designated co-ordinator node, the network device comprising: receiving means for receiving a predefined signal from the parent co-ordinator node of the first network wherein the receiving means are operable to determine the capability of reception of the predefined signal; and indication means for providing an indication of the determined reception capability to the designated co-ordinator node of the second network to enable the designated coordinator node to select a network node from among the plurality of network nodes and the designated co-ordinator node as a time synchronisation reference node based on the respective reception capability of each of the plurality of network nodes and a reception capability of the designated co-ordinator node.

The device may include processing means operable to determine a first time drift between the local clock of the parent co-ordinator node and the local clock of said network node to enable a time correction value between the local clock of the designated co-ordinator node and the parent co-ordinator to be provided in the case where said network node is selected as the time synchronisation reference node.

The processing means may be configured to determine the time correction value based on the first time drift and an estimated second time drift between the local clock of the network node and the local clock of the designated co-ordinator node.

The processing means may be configured to determine the first time drift based on the time of reception of at least two consecutive predefined signals received from the parent co-ordinator node of the first network, and a duration of a transmission cycle of said parent co-ordinator node.

The processing means may be configured to determine the second time drift based on the reception of at least two consecutive predefined signals received from the designated co-ordinator and a duration of a transmission cycle of said designated co-ordinator node.

The indication means may be configured to provide the indication of the determined reception capability to at least one of the other network nodes of the second network.

The indication means may be configured to provide the first time drift and/or the second time drift to at least one of the other network nodes of the second network.

The reception means may be configured to determine the capability of reception of a predefined signal by measuring at least one of the signal to noise ratio and the received signal strength indication of the predefined signal.

The reception means may be configured to determine the capability of reception of a predefined signal by consideration of the antenna pattern used to receive the predefined signal.

The reception means may be configured to determine the capability of reception of a predefined signal by determining the number of predefined signals received during a predefined number of transmission cycles.

In a particular embodiment the network device is operable in accordance with a mesh communication mode.

The reception means may be configured to receive a notification from the designated co-ordinator node indicating the selected time synchronisation reference node.

The reception means may be configured to receive a notification from the designated co-ordinator node designating the network node receiving the notification as a time synchronisation reference node.

The processing means may be configured to provide to the designated co-ordinator node the time correction value for application to the local clock of the designated co-ordinator node.

In an embodiment the device is operable as a proxy device between the designated co-ordinator node and the parent co-ordinator node. This avoids the need for providing several nodes capable of performing the role of a co-ordinator node.

According to a third aspect of the invention there is provided a method of managing synchronisation between a first network and a second network, wherein the first network includes a parent co-ordinator node and the second network comprises a plurality of network nodes and a designated co-ordinator node, the method comprising the designated co-ordinator node performing the steps of: receiving, from each of the plurality of network nodes an indication of a capability of the respective network node to receive a predefined signal from the parent co-ordinator node of the first network; and selecting a network node from among the plurality of network nodes and the designated co-ordinator node as a time synchronisation reference node based on the respective reception capability of each of the plurality of network nodes and a reception capability of the designated co-ordinator node.

This enables the co-ordinator device of a dependent network to determine which device is the most capable device for correcting the clock drift of the dependent network. The dependent co-ordinator node may still remain the reference for defining the channel access scheme for the dependent network.

Accordingly, a dependent wireless communication network may be operated regardless of the actual communication link quality between the parent coordinator device of a parent wireless communication network and the dependent coordinator device of the dependent wireless communication network.

The method may further include determining if the reception capability of the designated co-ordinator node of the second network is sufficient to receive timing information directly from the parent co-ordinator node of the first network, and wherein if it is determined that the reception capability of the designated co-ordinator node of the second network is sufficient, selecting the designated co-ordinator device of the second network as the time synchronisation reference node, otherwise, selecting another network node of the plurality of network nodes of the second network as the time synchronisation reference node.

In an embodiment the method further includes applying, to the local clock of the designated co-ordinator node, a time correction value determined based on a first time drift between the local clock of the selected time synchronisation node and clock of the parent co-ordinator node.

In an embodiment the time correction value is determined based on the first time drift and an estimated second time drift between the local clock of the selected time synchronisation reference node and the local clock of the designated co-ordinator node.

In an embodiment the method includes transmitting a notification to each network node of the second network indicating the selected time synchronisation reference node.

In an embodiment the received indication of a capability of the respective network node to receive a predefined signal comprises a value indicatIve of at least one of the signal to noise ratio and the received signal strength indication of the received predefined signal.

In an embodiment the indication of a capability of the respective network node to receive a predefined signal comprises a value indicative of the antenna pattern used to receive the predefined signal.

In an embodiment the indication of a capability of the respective network node to receive a predefined signal comprises a value indicative the number of predefined signals received during a predefined number of transmission cycles.

In an embodiment the designated co-ordinator node operates in accordance with a mesh communication mode.

A fourth aspect of the invention provides a network device for managing synchronisation between a first network and a second network, wherein the first network includes a parent co-ordinator node and the second network comprises a plurality of network nodes and the network device operable as a designated co-ordinator node, the network device comprising: reception means for receiving, from each of the plurality of network nodes an indication of a capability of the respective network node to receive a predefined signal from the parent co-ordinator node of the first network; and selection means for selecting a network node from among the plurality of network nodes and the designated co-ordinator node as a time synchronisation reference node based on the respective reception capability of each of the plurality of network nodes and a reception capability of the designated co-ordinator node.

In an embodiment the device further includes processing means for determining if the reception capability of the designated co-ordinator node of the second network is sufficient to receive timing information directly from the parent co-ordinator node of the first network, and wherein if it is determined that the reception capability of the designated co-ordinator node of the second network is sufficient, the selection device selects the designated co-ordinator device of the second network as the time synchronisation reference node, otherwise, the selection device selects another network node of the plurality of network nodes of the second network as the time synchronisation reference node.

In an embodiment the device further includes clock regulation means for applying, to the local clock of the designated co-ordinator node, a time correction value determined based on a first time drift between the local clock of the selected time synchronisation node and clock of the parent co-ordinator node.

In an embodiment the processing means is operable to determine a third time drift between the designated co-ordinator node and the parent co-ordinator node based on the reception of at least two consecutive predefined signals received from the parent co-ordinator node, and a duration of a transmission cycle of said parent co-ordinator node.

In an embodiment the device includes notification means for providing a notification to each network node of the second network indicating the selected time synchronisation reference node.

In an embodiment the received indication of a capability of the respective network node to receive a predefined signal comprises a value indicative of the antenna pattern used to receive the predefined signal.

In an embodiment the received indication of a capability of the respective network node to receive a predefined signal comprises a value indicative the number of predefined signals received during a predefined number of transmission cycles.

In an embodiment the device is operable in accordance with a mesh communication mode.

According to a fifth aspect of the invention there is provided a network system comprising a network device according to the second aspect of the invention and a network device according to the fourth aspect of the invention.

A sixth aspect of the invention provides a method of managing synchronisation between a first network and a second network, wherein the first network includes a parent co-ordinator node and the second network comprises a plurality of network nodes and a dependent network co-ordinator node, the method comprising a network node of the second network: being designated by the dependent network co-ordinator node as a time synchronisation reference node for the second network; providing to the dependent network co-ordinator node a time correction value for application to the local clock of the dependent network co-ordinator node to synchronise the dependent network co-ordinator node with the parent co-ordinator node; wherein the time correction value is determined based on a first time drift measured between the local clock of the parent co-ordinator node and the local clock of said network node.

In an embodiment the method according to the sixth aspect further includes providing to the other network nodes of the dependent network the time correction value.

In an embodiment the method includes operating as a proxy device between the dependent network co-ordinator node and the parent co-ordinator node.

A seventh aspect of the invention provides a network device for managing synchronisation between a first network and a second network, wherein the fiist network includes a parent co-ordinator node and the second network comprises a plurality of network nodes including the network device and a dependent network co-ordinator node, the network device comprising: measurement means for measuring a first time drift between the local clock of the parent co-ordinator node and the local clock of said network device; reception means for receiving a notification that the network device has been designated as a time synchronisation reference node; and means for providing to the dependent network co-ordinator node a time correction value for application to the local clock of the dependent network co-ordinator node to synchronise the dependent network co-ordinator node with the parent co-ordinator node.

A further aspect of the invention provides a method of synchronising a first network and a second network, wherein the first network includes a parent co-ordinator node and the second network comprises a plurality of network nodes and a designated co-ordinator node, the method comprising a step of managing synchronisation in accordance with the method of any one of the above described embodiments: and a step of synchronising the parent co-ordinator of the first network and the designated co-ordinator of the second network by applying the time correction value.

A further aspect of the invention provides a device for synchronising a first network and a second network, wherein the first network includes a parent co-ordinator node and the second network comprises a plurality of network nodes H and a designated co-ordinator node, the method comprising a network device for managing synchronisation in accordance with the network device of any one of the described embodiments; and synchronisation means for synchronising the parent co-ordinator of the first network and the designated co-ordinator of the second network by applying the time correction value.

At least parts of the methods according to the invention may be computer implemented. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a "circuit", "module" or "system". Furthermore, the present invention may take the form of a computer program product embodied in any tangible medium of expression having computer usable program code embodied in the medium.

Since the present invention can be implemented in software, the present invention can be embodied as computer readable code for provision to a programmable apparatus on any suitable carrier medium. A tangible carrier medium may comprise a storage medium such as a floppy disk, a CD-ROM, a hard disk drive, a magnetic tape device or a solid state memory device and the like. A transient carrier medium may include a signal such as an electrical signal, an electronic signal, an optical signal, an acoustic signal, a magnetic signal or an electromagnetic signal, e.g. a microwave or RF signal.

Embodiments of the invention will now be described, by way of example only, and with reference to the following drawings in which:-Figure 1 is a schematic diagram of a wireless communication network in which one or more embodiments of the invention may be implemented; Figure 2 is a graphical representation of a transmission cycle of a dependent wireless network according to one or more embodiments of the invention; Figure 3 is a graphical representation of a transmission cycle of a parent wireless network according to one or more embodiments of the invention; Figure 4 is a schematic block diagram of a wireless communication device according to at least one embodiment of the invention; Figure 5 is a graphical representation of clock drift between wireless devices of a the communication network of Figure 1; Figure GA is a flow chart illustrating steps of a method of synchronisation between a first network and a second network for a network device of the second network according to an embodiment of the invention; H Figure 6B is a flow chart illustrating steps of a method of synchronisation between a first network and a second network for a designated co-ordinator node of the second network according to an embodiment of the invention; Figure 6C is a communication diagram illustrating steps of the method of synchronisation between a first network and a second network of Figures 6A and 66; Figure 7 is a flow chart illustrating steps of a method of synchronisation by a selected time synchronisation reference device according to an embodiment of the invention; and Figure 8 is a schematic representation of an information signal for synchronisation of a first network and a second network according to an embodiment of the invention.

Figure 1 illustrates a wireless communication network 100 in which one or more embodiments of the invention may be implemented. The wireless communication network 100 comprises a plurality of wireless communication devices 111, 112, 113, 114, 115, 121, 122, 123, 124, 125 and 126. According to a first embodiment of the present invention, the wireless communication devices 111, 112, 113, 114 and 115 belong to a first network, referred to as a parent wireless communication network 110. The wireless communication devices 121, 122, 123, 124, 125 and 126 belong to a second network, referred as a dependent wireless communication network 120. Wireless communication device 111 is referred to as the parent coordinator device of the parent wireless communication network 110. Its role within the parent wireless communication network 110 will be further described with reference to Figure 3.

Wireless communication device 121 operates as a coordinator device of the dependent wireless communication network 120, and is referred to as the dependent coordinator device. Its role within the dependent wireless communication network 120 will be further described with reference to Figure 2.

According to the first embodiment of the present invention, the wireless communication device 121 is also part of the parent wireless communication network 110. The overall wireless communication network 100 is considered as the union of the parent wireless communication network 110 and the dependent wireless communication network 120.

According to a first embodiment of the invention, the wireless communication network 100 operates as a Time Division Multiple Access (TDMA) network. A transmission cycle, also referred to as TDMA cycle, is divided into time slots.

Only one wireless communication device, configured in transmission mode, wirelessly transmits radio data during each time slot.

Figure 2 graphically represents TDMA transmission cycles, as setup in the dependent wireless communication network 120 of Figure 1, according to the first embodiment of the invention. Time is divided into TDMA cycles 210 (cycle n, cycle n+1) and access to the physical medium for data transmission is shared over time. Each TDMA cycle 210 comprises a first communication perIod 260 and a second communication period 270. The first communication period comprises a plurality of time slots 220, and the second communication period comprises at least one time slot 240.

Each time slot 220 and 240 is allocated to a single wireless communication device configured in transmission mode, referred to hereinafter as a transmission device. During its allocated time slot 220 the respective transmission device transmits a radio frame 230.

In the first embodiment of the invention, the first time slot 220 within a cycle 210 is allocated to the coordinator device of the wireless communication network.

During a time slot 220 the co-ordinator device transmits a radio frame 230. The coordinator device provides within its radio frame 230, data representative of reference information for the timing, duration and allocation scheme for each of the time slots 220 and 240. In the first embodiment of the invention, the other wireless communication devices in the wireless communication network relay, within the respective radio frame 230 they transmit during their allotted time slot 220, the reference information the coordinator device issued in its radio frame 230.

Some timeslots, such as time slots 240 (more than one may exist per TDMA cycle), may be of longer duration than the time slots 220. During a time slot 240 a transmission device transmits a radio frame 250. The time slots 240 are allocated to transmission devices according to application requirements. For instance, time slots 240 may be used to transmit a large amount of data in real-time, such as video data. Audio data or control data which require much less bandwidth than video data are preferably transmitted during time slots 220. In some embodiments of the invention several time slots 220 may be allocated to a single transmission device of the wireless communication network 100. In other embodiments, at least one time slot 220 is not allocated to any particular device and may be considered as a contention access period. Wireless communication devices that wish to access the physical medium for data transmission during such a contention time slot 220 may use collision detection and avoidance schemes, such as CSMA/CA (Carrier Sense Multiple Access With Collision Avoidance) for instance, to obtain access to the wireless medium.

Each time slot, whether it be a timeslot 220 of the first communication period or a timeslot 240 of the second communication period is separated from a previous time slot 220 or 240 by an interframe time interval 280. The interframe time interval 280 is used to mitigate the effects of clock drift occurring at each network device level. Indeed, such an interframe time interval 280 allows one device to perform data transmission within its allocated time slot 220 for some time without performing any clock drift correction.

Each wireless communication device belonging to the wireless communication network is allocated a unique network identifier by the coordinator device of the corresponding wireless communication network.

In the first embodiment, time slots 220 of the first communication period are used for a mesh communication mode, which will be further described with reference to Figure 5. A mesh communication mode involves setting up point-to-multipoint communications between the wireless communication devices, enabling for instance data to be broadcast throughout the wireless network (e.g. control data); or data to be relayed from one wireless communication device to another (one communication device acts as a relay of radio data, from a transmission device to a receiving device) according to a relaying scheme, to ensure that any data is indirectly received by its addressee at least once.

In the mesh communications mode, the transmission device preferably uses an isotropic antenna or the like (wide beam) and the receiving device preferably uses a directive antenna (pointing towards the transmission device). Use of a directive antenna is simple to implement but can be highly subject to shadowing phenomena. Indeed, under such circumstances, an obstacle may easily block or alter the transmission path from the transmission device to the receiving device, resulting in disruption of communication between the two devices.

Directive antenna configuration is therefore well adapted to the mesh communication mode in which data may be repeated or relayed, but not to a point-to-point communication mode in which data cannot be repeated or relayed without significantly impacting the end-to-end quality (due to the necessary compression, in view of the large amount of data to be transferred in real-time).

The settings used for the receiving device to setup a directive antenna may be obtained during an initialization period, during which each receiving device applies a beam steering technique for scanning until receiving a predefined pattern from each transmission device.

Several acceptable directive antenna settings may be found by the receiving device during this initialization period, corresponding to either a direct transmission path (also referred to as line-of-sight or LOS path) line of sight and one or more indirect transmission paths (also referred to as non line-of-sight or NLOS paths. In a NLOS path, the relaying of data from the sending device to the receiving device can achieved by reflection of the radio signal on walls, objects or obstacles. Transmission of data from a sending device to a receiving device by an LOS path or an NLOS path is typically referred to as a point-to-point communication method. According to a particular embodiment of the present invention, a receiving device may dynamically adapt, from one TDMA cycle 210 to another, its antenna configuration, switching between the aforementioned acceptable directive antenna settings found during the initialization period.

The first communication period consisting of all the time slots 220 is hereinafter referred to as the mesh communications period 260. The second communication period consisting of all the time slots 240 is hereinafter referred to as the point-to-point communication period 270.

Figure 3 schematically represents a transmission cycle, as it may be setup in a parent wireless communication network, such as the wireless communication network 110 of Figure 1 or in a dependent wireless communication network, such as the wireless communication network 120 of Figure 1.

Each transmission cycle 310 is divided into time slots 320, 340 and 360. Time slot 320 is reserved for the coordinator device of the corresponding wireless communication network, either a parent coordinator device or a dependent coordinator device. The time slot 320 is used by the corresponding co-ordinator device to broadcast a beacon frame 330, transmitted periodically at the beginning of each transmission cycle 310, to announce the presence of a wireless communication network, as well as the timing, duration and allocation scheme for each of the time slots 340 and 360. The beacon frame.30 may also contain other information concerning the corresponding wireless communication network, such as the duration of the whole transmission cycle 310 or the power saving scheme to be applied by some of the network devices. In one embodiment of the invention, the instant of the transmission of the beacon frame 330 is also used by the wireless communication devices belonging to the corresponding wireless communication network to synchronize themselves to the coordinator device, thus avoiding interferences occurring when transmitting within their own time slot 360.

Time slot 340 is not allocated to any particular device and may be considered as a contention access period. Devices that wish to access the physical medium for transmission of data frames 350 during such a contention time slot 340 may use collision detection and avoidance schemes, such as CSMNCA for instance, to get access to the wireless medium.

Time slots 360 are used for allowing the devices belonging to the wireless communication network to access the physical medium for data transmission.

Such a wireless shared medium access scheme may also be referred to as Time Division Multiple Access, or IDMA. In one embodiment of the present invention, each time slot 360 is allocated to a single transmission device.

During a time slot 360, the transmission device transmits a radio frame 370.

Some timeslots may be longer than others since the time slots 360 can be allocated to transmission devices according to application requirements.

In another embodiment, several time slots 360 may be allocated to a single transmission device of the wireless communication network.

In the first embodiment of the invention, the transmission cycle 310 may be applied to the parent wireless communication network 110 of Figure 1. In a particular embodiment of the invention, the transmission cycle is compliant with IEEE 802.15.3-2003 and IEEE 802.15.3c-2009 standards.

The coordinator device 111 of the parent wireless communication network 110 shares the wireless channel bandwidth with devices belonging to the dependent wireless communication network 120 by allocating a dedicated time slot 360 for this purpose.

In one embodiment of the present invention, the dependent wireless communication network 120 operates a transmission cycle 310, co-ordinated in the same way as the transmission cycle 310 of the parent wireless communication network 110. In such a case, the dependent wireless communication network 120 is referred as a child wireless communication network. In this embodiment of the invention, the transmission cycle operated by the devices belonging to the dependent wireless communication network is compliant with the IEEE 802.15.3-2003 and IEEE 802.153c-2009 standards.

In another embodiment of the present invention, the dependent wireless communication network 120 operates a transmission cycle 210, as described with reference to Figure 2 and different to the transmission cycle 310 scheme of Figure 3, In such a case, the dependent wireless communication network 120 is referred to as a neighbour wireless communication network.

The parent coordinator 111 may change the duration or location of a time slot 360 that it formerly allocated for operating a dependent wireless communication network 120. The parent coordinator 111 may also release a time slot 360 it formerly allocated for operating a dependent wireless communication network 120. Such time slot 360 adaptations are notified by the parent coordinator device 111 to the dependent coordinator device 121 through the beacon frame 330.

The dependent coordinator device 121 also relies on the timing of reception of the beacon frame 330 to perform clock drift correction, will be described with reference to Figure 5.

If the dependent coordinator device 121 does not receive a beacon frame 330 for a maximum period of time, it will no longer be able to perform a clock drift correction. This may lead to interference phenomenon between transmissions issued by wireless communication devices belonging to the dependent wireless communication network 120 and transmissions issued by wireless communication devices belonging to the parent wireless communication network 110.

Furthermore, if the dependent coordinator device 121 misses consecutives beacon frames up to a maximum number (for instance, this number may be equal to 8 when the transmission cycle operated by the parent wireless communication network is compliant with the IEEE 802.15.3-2003 and IEEE 802.15.3c-2009 standards) it will no longer be able to know whether the parent coordinator device has applied some changes to the time slot 360 allocated for operating the dependent wireless communication network 120. In such a case, the IEEE 802.15.3-2003 and IEEE 802.15.3c-2009 standards mandate that the dependent coordinator 121 device should shut down the dependent wireless communication network 120 of which it is in charge.

Each device belonging to the parent wireless communication network 110 is allocated a unique network identifier by the parent coordinator device 111. Each device belonging to dependent wireless communication network 120 is allocated a unique network identifier by the dependent coordinator device 121.

Since in the first embodiment the dependent coordinator device 121 belongs to both the parent wireless communication network 110 and the dependent wireless communication network 120, it has two unique network identifiers: one identifier for when it is being operated as a device belonging to the parent wireless communication network 110, and one identifier for when it is operated as a device belonging to the dependent wireless communication network 120.

Figure 4 schematically illustrates the configuration of a wireless communication device according to an embodiment of the invention. The wireless communication device may either belong to the parent wireless communication network 110, of Figure 1, or to the dependent wireless communication network, of Figure 1.

The wireless communication device is adapted to perform wireless communication and comprises: -a micro-controller or Control Process Unit (denoted CPU) 410; -a Random Access Memory (denoted RAM) 420, whose capacity can be extended by an additional Random Access Memory connected to an expansion port (not shown in Figure 3); -a Read-Only Memory (denoted ROM) 430; and -a wireless communication interface 440, enabling communication with the other wireless communication devices of the network 100.

The CPU 410, RAM 420, ROM 430 and the wireless communication interface 440 exchange data and control information via a communication bus 460.

The wireless communication device 120 can either be a transmission device, a receiving device or both.

CPU 410 is capable of executing instructions loaded from ROM 430 into RAM 420. After the communication device 120 has been powered on, CPU 410 is capable of executing, from RAM 420, instructions of a computer program, once these instructions have been loaded from ROM 430 or from an external memory (not shown in Figure 3). A computer program of this kind causes CPU 410 to perform some or all of the steps of the algorithms described hereinafter in relation to Figures 5 to 8.

The CPU 410 controls the overall operation of the communication device. CPU 410 acts as a data analyzer unit, which analyses useful data payload (also referred as MAC payload) of a packet received from another communication device, once processed by the wireless communication interface 440.

The wireless communication interface 440 further comprises: -a medium access controller (denoted MAC) 441; -a baseband processor (denoted BBP) 442; -an RF module (denoted RE) 443; -a smart antenna 445; and -an antenna controller 446; and The RF module 443 processes a signal output by the baseband processor 442 before it is transmitted by means of the smart antenna 445. For example, the processing can be done by frequency transposition and power amplification processes. Conversely, the RF module 443 is also responsible for processing a signal received by the smart antenna 445 before it is provided to the baseband processor 442.

The baseband processor 442 is responsible for modulating and demodulating the digital data exchanged with the RF module 443. For instance, the modulation and demodulation scheme applied by the baseband processor 442 is of Orthogonal Frequency-Division Multiplexing (OFDM) type.

MAC 441 manages the accesses to the wireless medium. MAC 441 also acts as a synchronization control unit, which controls synchronization relative to a superirame (as described in relation to Figure 2), and scheduling the transmissions via the network. MAC 441 schedules the beginning and the end of data transmission in the network by an antenna 445, which may be a smart antenna, as well as the beginning and the end of a reception of data from the network by the smart antenna 445. MAC 441 also manages input data required to determine the antenna parameters provided by the antenna controller 446 for configuring the antenna 445.

Figure 5 graphically illustrates an example of clock drift phenomenon which may occur at several wireless communication devices belonging to the wireless communication network 100 of Figure 1.

At an instant of time T0 521, the parent coordinator device 111 of the parent wireless communication network 110 issues its beacon frame 330. Based upon its own clock, it determines the instant of time T' 531 when it issues a new beacon frame 330, such that one cycle 310 has elapsed since instant of time T0521.

Since the clock of the dependent coordinator device 121 does not run at exactly the same speed as the clock of the parent coordinator device 111, a clock drift phenomenon occurs, and the dependent coordinator device 121 estimates, based upon its local clock timing, that the reception of the beacon frame 330 will occur at instants of time T1 522 and T'1532, which differ slightly to instants of time T0 521 and T'3 531. Since the dependent coordinator device 121 knows the duration of the cycle 310, because the value of the duration of the cycle is indicated within the beacon frame 330, it can deduce the actual drift 541 of its own clock compared to that of parent coordinator device 111.

In the same way, since the clock of a wireless communication device belonging to the dependent wireless communication network 120 does not run at the exact right speed compared to the clock of the dependent coordinator device 121 of the said dependent wireless communication network 120, a clock drift phenomenon occurs between a device belonging to the dependent wireless communication network 120 and its dependent coordinator device 121.

Since a wireless communication device belonging to the dependent wireless communication network 120 knows the duration of the cycle used for operating the dependent wireless communication network 120, because the value of the cycle duration is indicated through the radio frame sent by the dependent coordinator device 121, the device belonging to the dependent wireless communication network 120 can determine the actual drift 542 of its own clock compared to that of parent coordinator device 111.

In one embodiment of the invention, the transmission cycle scheme applied to the dependent wireless communication network 120 is based on the cycle 210 described in Figure 2. In such a case, the value of the duration of cycle 210 is embedded within the radio frame 220 allocated to the dependent coordinator device 121.

In another embodiment of the invention, the transmission cycle scheme applied to the dependent wireless communication network 120 is based on the cycle 310 described in Figure 3. In such a case, the value of the duration of cycle 310 is embedded within the beacon frame 330 issued by the dependent coordinator device 121 at the beginning of each cycle 310. The transmission cycle scheme applied to the dependent wireless communication network 120 may be compliant with the IEEE 802.15.3-2003 and IEEE 802.15.3c-2009 standards.

In the case where no clock drift correction is performed, the cumulated clock drift 543 between the clock of a device belonging to the dependent wireless communication network 120 and the clock of a parent coordinator device 111 corresponds to the sum of clock drift values: the drift in time 541 between the parent co-ordinator device and the dependent co-ordinator device and the drift in time 542 between the dependent co-ordinator device and the said wireless device of the dependent wireless network.

Figure GA and Figure 6B are flow diagrams illustrating steps of a method according to a first embodiment of the invention for maintaining synchronization between a parent wireless communication network 110 and a dependent wireless communication network 120 in a versatile wireless environment. A wireless communication network is considered as being operated in a versatile environment when unpredictable shadowing phenomena are likely to occur inside the wireless communication network coverage area.

Figure 6A illustrates the steps of the method from the viewpoint of a network node 122-126 of the dependent wireless network 120 and Figure 6B illustrates the steps of the method from the viewpoint of the dependent co-ordinator device 121 of the dependent wireless network 120. Figure 6C is a communication diagram illustrating the interaction between the parent network co-ordinator device1 the dependent network co-ordinator device, a network node of the second network and the selected time synchronisation reference device.

Any step of the method shown in Figure 6A, 6B or 6C may be implemented in software by execution of a set of instructions or program by a programmable computing machine, such as a PC ("Personal Computer"), a DSP ("Digital Signal Processor") or a microcontroller; or else implemented in hardware by a machine or a dedicated component, such as an FPGA ("Field-Programmable Gate Array") or an ASIC ("Application-Specific Integrated Circuit").

The various steps of the algorithm shown in Figure 6A may be performed by any one of a plurality of communication devices of the wireless communication network 120 in order to enable a dependent wireless communication network to be operated regardless of the actual communication link quality between the parent coordinator device 111 and the dependent coordinator device 121.

In a first step 5600, all or some of the wireless communication devices belonging to the dependent wireless communication network 120 during each transmission cycle 310 of a parent wireless communication network 110, determine the start time and the end time of the time slot 360 allocated by parent coordinator device 111 for operation of the dependent wireless communication network 120, as described with reference to Figure 3.

During the time interval defined by the end of such time slot 360 and the start of the next one, the wireless communication devices belonging to the dependent wireless communication network 120 listen to the wireless medium in order to try and receive the beacon frame 330 issued by the parent coordinator device 111 at the beginning of each transmission cycle 310. Techniques employed by the wireless communication devices belonging to the dependent wireless communication network 120 for performing such a listening process, including the way their antenna pattern is adjusted, or performing antenna tracking, are well-known by persons skilled in the art and consequently no further description is needed here for an understanding of the present invention.

In a subsequent step 5601, each wireless communication device belonging to the dependent wireless communication network 120 determines its ability to receive the beacon frame 330 issued by the parent coordinator device 111. The dependent co-ordinator device 121 may also determine its ability to receive the beacon frame 330 issued by the parent coordinator device 111.

In one embodiment of the invention, a wireless communication device of the dependent network estimates the Signal To Noise Ratio (SNR), or the Received Signal Strength Indication (RSSI) of its communication link with the parent wireless communication network 110, and compares the estimated SNR or RSSI value to a plurality of thresholds, in order to determine its level of ability of receiving the beacon frame 330 from the parent coordinator device 111.

In another embodiment, a device belonging to the dependent wireless communication network 120 may consider the robustness of its communication link with the parent coordinator device 111 by considering the antenna pattern used for receiving the beacon frame 330. For instance, if the device needs to use a directive antenna pattern to receive such beacon frame 330, this would indicate that its communication rink with the parent coordinator device 111 is more fragile than it would have been if the device had used a wide antenna pattern. Indeed, using a directive antenna pattern for receiving data implies that the communication path with the source device is likely to be very sensitive to shadowing phenomena that may occur in between the source and the receiver device. On the contrary, if the device belonging to the dependent wireless communication network 120 is able to receive the beacon frame 330 while relying on a wide antenna pattern, the communication link with the parent coordinator device 111 may be considered as particularly robust since the receiver device is then able to collect energy of the signal issued by the source device from several directions.

In another embodiment, the device belonging to the dependent wireless communication network 120 may perform statistics on the number of occurrences of the beacon frame 330 it received during a predefined number of past transmission cycles 310, and derive from such statistics a level of ability at receiving said beacon frame 330 from the parent coordinator device 111.

In a further embodiment at least two of the three aforementioned techniques may be combined for determining the ability of one wireless communication device belonging to the dependent wireless communication network 120 at receiving the beacon frame 330 from the parent coordinator device 111.

In step S602 when a wireless communication device belonging to the dependent wireless communication network 120 (including the dependent coordinator device 121) receives two consecutive occurrences of the beacon frame 330 issued by the parent coordinator device 111, and computes a clock drift 543 between its own clock and the clock of the parent coordinator device 111, in the same way the dependent coordinator device 121 would do so, as described with reference to Figure 5.

Based on the radio frame issued by the dependent coordinator device 121, each device belonging to the dependent wireless communication network 120 can also compute in step S603 the value of the clock drift 542 between its own clock and the clock of the dependent coordinator device 121, as described in relation to Figure 5. The wireless communication device belonging to the dependent wireless communication network 120 is then able to deduce in step 5604 a clock drift correction value equal to the time difference between clock drift value 543 and clock drift value 542. This clock drift correction value corresponds to the deduced value by the said wireless communication device of the clock drift 541 between the clock of the dependent coordinator device 121 and the clock of the parent coordinator device 111.

In a subsequent step S605, each wireless communication device 122-126 belonging to the dependent wireless communication network 120 shares its level of ability to receive the beacon frame 330 from the parent coordinator device 111 with at least the dependent coordinator device 121. In one particular embodiment of the invention, each wireless communication device 122-126 belonging to the dependent wireless communication network 120 shares its level of ability at receiving the beacon frame 330 from the parent coordinator device 111 with all of the other wireless communication devices 122-126 belonging to the dependent wireless communication network 120.

In one particular embodiment, the wireless communication devices 122-126 may rely on a mesh communication scheme in order to ensure robust and low-latency exchange of the devices' level of ability at receiving the beacon frame 330 from the parent coordinator device 111, using a signalling mode as will be described with reference to Figure 8.

The mesh communication scheme may be applied through the channel access scheme described in Figure 2. In another embodiment, this mesh communication scheme is applied through the channel access scheme described in Figure 3. In a further embodiment, this mesh communication scheme is applied through a channel access scheme compliant with the IEEE 802.15.3-2003 and IEEE 802.15.3c-2009 standards.

In step S606 a wireless communication device belonging to the dependent wireless communication network 120 shares, with the other devices belonging to the dependent wireless communication network 120, the value of the clock drift correction value 543 that was determined in step S602 along with the level of ability to receive the beacon frame 330 from the parent coordinator device 111 determined in step S601. Additionally or alternatively, in some embodiments of the invention the wireless communication devices of the dependent wireless communication network may share the clock drift correction value determined in step S604 with other wireless communication devices of the wireless communication network. The dependent co-ordinator device 121 may share the time drift 541 measured between the parent co-ordinator device 111 and the dependent co-ordinator device with other network nodes of the wireless communication dependent network. 120 With reference to Figure 6B, in step 8610 the dependent co-ordinator device 121 receives reception capability information from the other wireless communication devices 122-126 of the dependent wireless network 120.

In the following step S611, the dependent coordinator device 121, based upon the reception capability information received from the wireless communication devices of the dependent wireless communication network 120 in step 611, selects from among the plurality of wireless communication devices 122-126 and the dependent co-ordinator device 121 the wireless communication device:1 to be used as a time synchronization reference device for the dependent wireless communication network 120. In one particular embodiment, the time synchronization reference device is chosen from amongst the devices considered as being capable of receiving the beacon frame 330 issued by the parent coordinator device 111. For instance, the device with the higher level of ability at receiving the beacon frame issued by the parent coordinator is selected as the time synchronization reference device.

The dependent coordinator device 121 then notifies in step 8612 the wireless communication devices 122-126 belonging to the dependent wireless communication network 120 of the identifier of the wireless communication device that has been selected as the time synchronization reference device. It may rely on the mesh communication scheme as used in step S605 or 8606 of Figure 6A or as described in relation to Figure 2, or it may rely on the signalling scheme described in relation to Figure 8.

With reference to Figure 6A the wireless communication device of the plurality of wireless communication devices 122-1 26 of the dependent wireless network receive in step S607 the notification from the dependent co-ordinator identifying the selected time synchronisation reference device.

In step 8608 of Figure 6A and step S613 of Figure 6B the wireless communication devices 122-126 of the dependent wireless network and the dependent co-ordinator device 121 respectively receive from the selected time synchronization reference device the time drift value 543 between the selected time synchronisation reference device and the parent co-ordinator device determined by the selected time synchronization reference device in step 8602.

Additionally or alternatively, in some embodiments of the invention the wireless communication devices of the dependent wireless communication network may receive the clock drift correction value determined in step S604 by the selected time synchronization reference device in step S602.

In a particular embodiment, only the dependent coordinator device 121 of nodes of the dependent wireless communication network 120 receives the clock drift correction value 543 from the selected time synchronisation reference device.

In the case where the wireless communication devices 122-126 belonging to the dependent wireless communication network 120 transmit, in step S606 of Figure 6A, the value of the clock drift 543 they computed in step S602 or the clock drift correction value determined in step 8604 along with their level of ability to receive the beacon frame 330 from the parent coordinator device 111, step S608 may be skipped. The algorithm can then move from step S607 directly to step 8609.

In the last step S609 of Figure GA, clock drift compensation is performed by all the other wireless devices belonging to the dependent wireless communication network 120.

The other wireless communication devices belonging to the dependent wireless communication network 120 may continue performing their clock drift compensation based on the value of the clock drift 542 computed using the instants of reception of two consecutive frames issued by the dependent coordinator device 121, or from another same device belonging to the dependent wireless communication network 120, when the cycle 210 channel access scheme described in Figure 2 is used within the dependent wireless communication network 120.

With reference to Figure 66 the dependent coordinator device 121, upon reception in step 5613 of a clock drift correction value based on time drift 543 from the time synchronization reference device, applies this clock drift correction value 541 to its own clock value so as to perform clack drift compensation in step 8614.

Figure 7 represents a flow diagram illustrating steps of an algorithm to be applied by a synchronization reference device b&onging to a dependent wireless communication network 120, for operation as a proxy device between the dependent coordinator device 121 of its dependent wireless communication network 120 and the parent coordinator device 111 of a parent wireless communication network 110, A wireless communication network is considered as being operated in a versatile environment when unpredictable shadowing phenomena are likely to occur inside the wireless communication network coverage area.

Any step of the algorithm shown in Figure 7 may be implemented in software by execution of a set of instructions or program by a programmable computing machine, such as a PC ("Personal Computer"), a DSP ("Digital Signal Processor') or a microcontroller; or else implemented in hardware by a machine or a dedicated component, such as an FPGA ("Field-Programmable Gate Array') or an ASIC ("Application-Specific Integrated Circuit").

The various steps of the algorithm shown in Figure 7 may be performed by a plurality of communication devices of the wireless communication network 100 in order to allow a device belonging to the dependent wireless communication network 120 to behave as a proxy device between the parent coordinator device 111 and the dependent coordinator device 121.

In a first step S700, a wireless communication device belonging to the dependent wireless communication network 120 receives a notification, by the dependent coordinator device 121, that it has been selected as the new time synchronization reference device for the dependent wireless communication network 120, as described in step S607 of the algorithm described in Figure 6A.

In step S701, the time synchronization reference device obtains the unique network identifier of the dependent coordinator device 121 within the parent wireless communication network 110. In a particular embodiment, the dependent coordinator device 121 communicates its unique network identifier within the parent wireless communication network 110 to each new device being associated with the dependent wireless communication network 120, in order that a device being selected as the new time synchronization reference device is made aware of the unique network identifier of the dependent coordinator device 121 within the parent wireless communication network 110.

This enables the time synchronization reference device to operate as a proxy device between the parent coordinator device 111 and the dependent coordinator device 121 with less latency.

Next, the time synchronization reference device acts as a proxy device between the dependent coordinator device 121 and the parent coordinator device 111.

Tasks undertaken by the selected time synchronization reference device as a proxy device of the dependent co-ordinator device include relaying within the radio frame 370 that it sends during its allocated timeslot 360, the information of each beacon frame 330 received from the parent coordinator device 111 to the dependent coordinator device 121; and periodically transmitting a specific message to the parent coordinator device 111 within a contention access time slot 340, using the unique network identifier of the dependent coordinator device 121 within the parent wireless communication network 110, so as to inform the parent coordinator device 111 that the dependent wireless communication network 120 is still in operation, i.e. it is still coordinated by the dependent coordinator device 121. When considering an IEEE8O2.15.3 type network, the specific message sent by the time synchronization device 111 may actually be any kind of message, such as, for instance, a Probe Request command, as defined in IEEE8O2.15.3-2003 standard document. Indeed, a parent coordinator compliant with the IEEE8O2.15,3 standard resets the timer it uses for managing the membership of one particular device within the network (also referred as the ATP timer) each time it receives a frame from said device, regardless of the nature of the frame. Otherwise, the parent coordinator device disassociates a device if said timer reaches a predefined value, referred as the ATP (Association Timeout Period).

Figure 8 schematically illustrates a configuration of a wireless medium access information descriptor according to an embodiment of the invention, sent by a wireless communication device in its radio frame, for the management of the time synchronization reference device selection and clock drift correction in a dependent wireless communication network 120.

In one particular embodiment of the present invention, a radio frame, either radio frame 230 of Figure 2 or radio frame 370 of Figure 3, transmitted by a wireless communication device 122-126 belonging to the dependent wireless communication network 120, embeds a medium access data element 800, comprising the following information: -an identifier Sllof the selected time synchronization reference device, managed by the dependent coordinator device 121; -an indicator of relevance 812 for the information 811; -information 821 representing the clock drift correction value 542, managed by the time synchronization reference device; -an indicator of relevance 822 for the information 821; When the dependent coordinator device 121 selects a new time synchronization reference device, excluding itself, it sets the information 811 with the unique network identifier within the dependent wireless communication network 120 of said new time synchronization reference device.

The dependent co-ordinator device also sets the associated relevance indicator 812 to an initial value. At the end of each cycle 210 of Figure 2 or 310 of Figure 3, each wireless communication device belonging to the dependent wireless communication network 120, checks the occurrences of information 811 and relevance indicator 812 that it received from either the dependent coordinator device 121 or another device belonging to the dependent wireless communication network 120.

In the case where a wireless communication device 122-126 belonging to the dependent wireless communication network 120 receives a frame issued by the dependent coordinator device 121 containing the information 811 and relevance indicator 812, the said wireless communication device retransmits within the next radio frame to be sent during the next cycle 210 or 310, the information 811 It also decrements the associated relevance information 812 and sends the decremented value along with the information 811 within its next radio frame.

In the case where a device belonging to the dependent wireless communication network 120 does not receive the frame issued by the dependent coordinator device 121 that contains the information 811 and relevance indicator 812, the said wir&ess communication device selects from amongst all previously received information occurrences, the information 811 for which associated relevance information 812 is the highest. It then decrements this highest relevance information 812 and retransmits it, along with the selected information 811, within the next radio frame it sends during the next cycle 210 or 310. As a network node may receive several occurrences of information 811 and 812, this ensures that the network node will select the most relevant one.

At each cycle 210 or 310, the time synchronization reference device updates the value of the clock drift correction information 821. It also sets the associated relevance indicator 822 to an initial value.

At the end of each cycle 210 or 310, each device belonging to the dependent wireless communication network 120, checks the occurrences of information 821 and 822 it received directly from either the time synchronization reference device or via another device belonging to the dependent wireless communication network 120.

In the case where a device belonging to the dependent wireless communication network 120 received the frame issued by the selected time synchronization reference device containing the information 821 and relevance indicator 822, it retransmits, within the next radio frame to be sent during the next cycle 210 or 310, the information 821. It also decrements the associated relevance information 822 and sends the decremented value along with the information 821 within its next radio frame.

In the case where a device belonging to the dependent wireless communication network 120 does not receive the frame issued by the time synchronization reference device that contains the information 821 and relevance indicator 822, it selects from amongst all said previously received information occurrences, the information 821 in which associated relevance information 822 is the highest. It shall then decrement this highest relevance information 822 and retransmit it, along with the selected information 821, within the next radio frame to be sent during the next cycle 210 or 310.

Although the present invention has been described hereinabove with reference to specific embodiments, the present invention is not limited to the specific embodiments, and modifications will be apparent to a skilled person in the art which lie within the scope of the present invention.

Many further modifications and variations will suggest themselves to those versed in the art upon making reference to the foregoing illustrative embodiments, which are given by way of example only and which are not intended to limit the scope of the invention, that being determined solely by the appended claims. In particular the different features from different embodiments may be interchanged, where appropriate.

In the claims, the word comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that different features are recited in mutually different dependent claims does not indicate that a combination of these features cannot be advantageously used.

Claims

<claim-text>CLAIMS1. A method of managing synchronisation between a first network and a second network, wherein the first network includes a parent co-ordinator node and the second network comprises a plurality of network nodes and a designated co-ordinator node, the method comprising a network node of said plurality of network nodes performing the steps of: determining the capability of reception of a predefined signal transmitted from the parent co-ordinator node of the first network; and providing an indication of the determined reception capability to the designated co-ordinator node of the second network to enable the designated coordinator node to select a network node from among the plurality of network nodes and the designated co-ordinator node as a time synchronisation reference node based on the respective reception capability of each of the plurality of network nodes and a reception capability of the designated co-ordinator node.</claim-text> <claim-text>2. A method according to claim 1 further comprising determining a first time drift between the local clock of the parent co-ordinator node and the local clock of said network node to enable a time correction value between the local clock of the designated co-ordinator node and the parent co-ordinator node to be provided in the case where said network node is selected as the time synchronisation reference node.</claim-text> <claim-text>3. A method according to claim 2 wherein the time correction value is determined based on the first time drift and an estimated second time drift between the local clock of the network node and the local clock of the designated co-ordinator node.</claim-text> <claim-text>4. A method according to claim 2 or 3 wherein the first time drift is determined based on the time of reception of at least two consecutive predefined signals received from the parent co-ordinator node of the first network, and a duration of a transmission cycle of said parent co-ordinator node.</claim-text> <claim-text>5. A method according to claim 3 or 4 wherein the second time drift is determined based on the reception of at least two consecutive predefined signals received from the designated co-ordinator node and a duration of a transmission cycle of said designated co-ordinator node.</claim-text> <claim-text>6. A method according to any preceding claim further comprising providing the indication of the determined reception capability to at least one of the other network nodes of the second network.</claim-text> <claim-text>7. A method according to any preceding claim further comprising providing the first time drift, the second time drift and/or the time correction value to at least one of the other network nodes of the second network, 8. A method according to any preceding claim wherein the capability of reception of a predefined signal is determined by measuring at least one of the signal to noise ratio and the received signal strength indication of the predefined signal.9. A method according to any preceding claim wherein the capability of reception of a predefined signal is determined by consideration of the antenna pattern used to receive the predefined signal.10. A method according to any preceding claim wherein the capability of reception of a predefined signal is determined by determining the number of predefined signals received during a predefined number of transmission cycles.11. A method according to any preceding claim wherein each network operates in accordance with a mesh communication mode.12. A method according to any preceding claim further comprising receiving a notification from the designated co-ordinator node indicating the selected time H synchronisation reference node.13. A method according to any preceding claim further comprising receiving a notification from the designated co-ordinator node designating the network node receiving the notification as a time synchronisation reference node.14. A method according to claim 13 further comprising providing to the designated co-ordinator node the time correction value for application to the local clock of the designated co-ordinator node.15. A method according to claim 13 or 14 further comprising operating as a proxy device between the designated co-ordinator node and the parent co-ordinator node.16. A network device for managing synchronisation between a first network and a second network, wherein the first network includes a parent co-ordinator node and the second network comprises a plurality of network nodes including the network device and a designated co-ordinator node, the network device comprising: receiving means for receiving a predefined signal from the parent co-ordinator node of the first network wherein the receiving means is operable to determine the capability of reception of the predefined signal; and indication means for providing an indication of the determined reception capability to the designated co-ordinator node of the second network to enable the designated coordinator node to select a network node from among the plurality of network nodes and the designated co-ordinator node as a time synchronisation reference node based on the respective reception capability of each of the plurality of network nodes and a reception capability of the designated co-ordinator node.17. A device according to claim 16 further comprising processing means operable to determine a first time drift between the local clock of the parent co-ordinator node and the local clock of said network node to enable a time correction value between the local clock of the designated co-ordinator node and the parent co-ordinator node to be provided in the case where said network node is selected as the time synchronisation reference node.18. A device according to claim 17 wherein the processing means is operable to determine the time correction value based on the first time drift and an estimated second time drift between the local clock of the network node and the local clock of the designated co-ordinator node.19. A device according to claim 17 or 18 wherein the processing means is operable to determine the first time drift based on the time of reception of at least two consecutive predefined signals received from the parent co-ordinator node of the first network, and a duration of a transmission cycle of said parent co-ordinator node.20. A device according to claim 18 or 19 wherein the processing means is operable to determine the second time drift based on the reception of at least two consecutive predefined signals received from the designated co-ordinator node and a duration of a transmission cycle of said designated co-ordinator node.21. A device according to any one of claims 16 to 20 wherein the indication means is operable to provide the indication of the determined reception capability to at least one of the other network nodes of the second network.22. A device according to any one of claims 16 to 21 wherein the indication means is operable to provide the first time drift, the second time drift and/or the time correction value to at least one of the other network nodes of the second network.23. A device according to any one of claims 16 to 22 wherein the reception means is operable to determine the capability of reception of a predefined signal by measuring at least one of the signal to noise ratio and the received signal strength indication of the predefined signal.24. A device according to any one of claims 16 to 23 wherein the reception means is operable to determine the capability of reception of a predefined signal by consideration of the antenna pattern used to receive the predefined signal.25. A device according to any one of claims 16 to 24 wherein the reception means is operable to determine the capability of reception of a predefined signal by determining the number of predefined signals received during a predefined number of transmission cycles.26. A device according to any one of claims 16 to 25 wherein the network device is operable in accordance with a mesh communication mode.27. A device according to any one of claims 16 to 26 wherein the reception means is operable to a receive a notification from the designated co-ordinator node indicating the selected time synchronisation reference node.28. A device according to any one of claims 16 to 26 wherein the reception means is operable to a receive a notification from the designated co-ordinator node designating the network node receiving the notification as a time synchronisation reference node.29. A device according to claim 28 wherein the processing means is operable to provide to the designated co-ordinator node the time correction value for application to the local clock of the designated co-ordinator node.30. A device according to claim 25 or 29 wherein the device is operable as a proxy device between the designated co-ordinator node and the parent co-ordinator node. :1 31. A method of managing synchronisation between a first network and a second network, wherein the first network includes a parent co-ordinator node and the second network comprises a plurality of network nodes and a designated co-ordinator node, the method comprising the designated co-ordinator node performing the steps of: receiving, from each of the plurality of network nodes an indication of a capability of the respective network node to receive a predefined signal from the parent co-ordinator node of the first network; and selecting a network node from among the plurality of network nodes and the designated co-ordinator node as a time synchronisation reference node based on the respective reception capability of each of the plurality of network nodes and a reception capability of the designated co-ordinator node.32. A method according to claim 31 further comprising; determining if the reception capability of the designated co-ordinator node of the second network is sufficient to receive timing information directly from the parent co-ordinator node of the first network, and wherein if it is determined that the reception capability of the designated co-ordinator node of the second network is sufficient, selecting the designated co-ordinator device of the second network as the time synchronisation reference node, otherwise, selecting another network node of the plurality of network nodes second network as the time synchronisation reference node.33. A method according to claim 31 or 32 further comprising applying, to the local clock of the designated co-ordinator node, a time correction value determined based on a first time drift between the local clock of the selected time synchronisation node and clock of the parent co-ordinator node.34. A method according to claim 33 wherein the time correction value is determined based on the first time drift and an estimated second time drift between the local clock of the selected time synchronisation reference node and the local clock of the designated co-ordinator node.35. A method according to any one of claims 31 to 34 further comprising transmitting a notification to each network node of the second network indicating the selected time synchronisation reference node, 36. A method according to any one of claims 31 to 35 wherein the received indication of a capability of the respective network node to receive a predefined signal comprises a value indicative of at least one of the signal to noise ratio and the received signal strength indication of the received predefined signal.37. A method according to any one of claims 31 to 36 wherein the indication of a capability of the respective network node to receive a predefined signal comprises a value indicative of the antenna pattern used to receive the predefined signal.38. A method according to any one of claims 31 to 37 wherein the indication of a capability of the respective network node to receive a predefined signal comprises a value indicative the number of predefined signals received during a predefined number of transmission cycles.39. A method according to any one of claims 31 to 38 wherein the designated co-ordinator node operates in accordance with a mesh communication mode.40. A network device for managing synchronisation between a first network and a second network, wherein the first network includes a parent co-ordinator node and the second network comprises a plurality of network nodes and the network device operable as a designated co-ordinator node, the network device comprising: reception means for receiving, from each of the plurality of network nodes an indication of a capability of the respective network node to receive a predefined signal from the parent co-ordinator node of the first network; and selection means for selecting a network node from among the plurality of network nodes and the designated co-ordinator node as a time synchronisation reference node based on the respective reception capability of each of the plurality of network nodes and a reception capability of the designated co-ordinator node.41. A device according to claim 40 further comprising; processing means for determining if the reception capability of the designated co-ordinator node of the second network is sufficient to receive timing information directly from the parent co-ordinator node of the first network, and wherein if it is determined that the reception capability of the designated co-ordinator node of the second network is sufficient, the selection device selects the designated co-ordinator device of the second network as the time synchronisation reference node, otherwise, the selection device another network node of the plurality of network nodes second network as the time synchronisation reference node.42. A device according to claim 40 or 41 further comprising clock regulation means for applying, to the local clock of the designated co-ordinator node, a time correction value determined based on a first time drift between the local clock of the selected time synchronisation node and clock of the parent co-ordinator node.43. A device according to claim 42 wherein the time correction value is determined based on the first time drift and an estimated second time drift between the local clock of the selected time synchronisation reference node and the local clock of the designated co-ordinator node.44. A device according to any one of claims 40 to 43 further comprising notification means for providing a notification to each network node of the second network indicating the selected time synchronisation reference node.45. A device according to any one of claims 40 to 44 wherein the received indication of a capability of the respective network node to receive a predefined signal comprises a value indicative of at least one of the signal to noise ratio and the received signal strength indication of the received predefined signal.46. A device according to any one of claims 40 to 44 wherein the received indication of a capability of the respective network node to receive a predefined signal comprises a value indicative of the antenna pattern used to receive the predefined signal.47. A device according to any one of claims 40 to 46 wherein the received indication of a capability of the respective network node to receive a predefined signal comprises a value indicative the number of predefined signals received during a predefined number of transmission cycles.48. A device according to any one of claims 40 to 47 operable in accordance with a mesh communication mode.49. A method of managing synchronisation between a first network and a second network, wherein the first network includes a parent co-ordinator node and the second network comprises a plurality of network nodes and a dependent network co-ordinator node, the method comprising a network node of the second network being designated by the dependent network co-ordinator node as a time synchronisation reference node for the second network; providing to the dependent network co-ordinator node a time correction value for application to the local clock of the dependent network co-ordinator node to synchronise the dependent network co-ordinator node with the parent co-ordinator node; wherein the time correction value is determined based on a first time drift measured between the local clock of the parent co-ordinator node and the local clock of said network node.50. A method according to claim 49 further comprising providing to the other network nodes of the dependent network the time correction value.51. A method according to claim 49 or 50 further comprising operating as a proxy device between the dependent network co-ordinator node and the parent co-ordinator node.52. A network device for managing synchronisation between a first network and a second network, wherein the first network includes a parent co-ordinator node and the second network comprises a plurality of network nodes including the network device and a dependent network co-ordinator node, the network device comprising; measurement means for measuring a first time drift between the local clock of the parent co-ordinator node and the local clock of said network device reception means for receiving a notification that the network device has been designated as a time synchronisation reference node; and means for providing to the dependent network co-ordinator node a time correction value for application to the local clock of the dependent network co-ordinator node to synchronise the dependent network co-ordinator node with the parent co-ordinator node.53. A method of synchronising a first network and a second network, wherein the first network includes a parent co-ordinator node and the second network comprises a plurality of network nodes and a designated co-ordinator node, the method comprising a step of managing synchronisation in accordance with the method of any one of claims 2 to 15, 33 to 39, or 49 to 51; and a step of synchronising the parent co-ordinator of the first network and the designated co-ordinator of the second network by applying the time correction value.54. A device for synchronising a first network and a second network, wherein the first network includes a parent co-ordinator node and the second network comprises a plurality of network nodes and a designated co-ordinator node, the method comprising a network device for managing synchronisation in accordance with the network device of any one of claims 17 to 30, 42 to 48, or 52 to 53; and synchronisation means for synchronising the parent co-ordinator of the first network and the designated co-ordinator of the second network by applying the time correction value.56. A computer program product for a programmable apparatus, the computer program product comprising a sequence of instructions for implementing a method according to any one of claims 1 to 15; any one of claims 31 to 39, any one of claims 49 to 51, any one of claims 36 to 45 or any one of claims 53 to 54 when loaded into and executed by the programmable apparatus.57. A computer-readable storage medium storing instructions of a computer program for implementing a method, according to any one of claims Ito 15; any one of claims 31 to 39, any one of claims 49 to 51, any one of claims 36 to 45 or any one of claims 53 to 54 58. A network system comprising a network device according to any one of claims 16 to 30 and a network device according to any one of claims 40 to 48.59. A method of synchronisation substantially as hereinbefore described with reference to, and as shown in Figure 6A, 6B, 6C or 7. :1</claim-text>