GB2558551A - Method and device for managing a communication system, communication system - Google Patents

Abstract

A communication system 100 comprising multiple mobile nodes 104 105 and a plurality of receiving nodes 110-116 sharing the same RF channel is managed by first obtaining signal quality metrics for the communication between the mobile and receiving nodes. A control function is then assigned to a predetermined number of the receiving nodes based on these metrics, and a network cell is formed with each of these nodes which further comprises a mobile node. This scheme is directed for use with millimetre wave, 60GHz networks and relates to clustering. The network cells may be personal basic service sets (PBSS) and the control function may be the role of PBSS Control Point (PCP) according to the 802.11ad standard. The predetermined number may be based on two values: the required level of redundancy for a multi-copy transmission involving several receiving nodes, and the number of wireless MAC layers of the mobile nodes. Receiving nodes without a control function may join a network cell to facilitate further redundancy.

Description

(54) Title of the Invention: Method and device for managing a communication system, communication system Abstract Title: Managing spatial diversity in millimetre wave 802.11 ad networks (57) A communication system 100 comprising multiple mobile nodes 104 105 and a plurality of receiving nodes 110-116 sharing the same RF channel is managed by first obtaining signal quality metrics for the communication between the mobile and receiving nodes. A control function is then assigned to a predetermined number of the receiving nodes based on these metrics, and a network cell is formed with each of these nodes which further comprises a mobile node. This scheme is directed for use with millimetre wave, 60GHz networks and relates to clustering. The network ceils may be personal basic service sets (PBSS) and the control function may be the role of PBSS Control Point (PCP) according to the 802.11ad standard. The predetermined number may be based on two values: the required level of redundancy for a multi-copy transmission involving several receiving nodes, and the number of wireless MAC layers of the mobile nodes. Receiving nodes without a control function may join a network cell to facilitate further redundancy.

5/6

5Qg For considered mobile node:

Request a number N2-N1 of receiving nodes without PCP function having the best LQ, to join the PBSS

6/6

Fig. 6

009

METHOD AND DEVICE FOR MANAGING A COMMUNICATION SYSTEM, COMMUNICATION SYSTEM

FIELD OF THE INVENTION

The present invention relates in general to high data rate wireless transmission of data between mobile nodes and receiving nodes sharing a same RF channel. In particular, the present invention provides a method for managing a communication system comprising two or more mobile nodes and a plurality of receiving nodes sharing a same RF channel for data transmission over a wireless communication network. The present invention also provides a device implementing such a method and a communication system.

BACKGROUND OF THE INVENTION

Audio/Video applications using High Definition (HD) video or images are now increasingly numerous and require even higher data bit rates and higher quality of service.

For instance, a mobile source node, such as a video camera or a Head Mounted Display (HMD) may exchange uncompressed HD data with a sink node, such as a video storage (or display) device providing a high resolution image capturing facility or a Computer Graphic capable of adding virtual images to a video received from the HMD as a function of the location and the positioning of the HMD. Generally, for comfort and design reasons, such device is intended to be worn by the user preferably without physical link to any fixed node.

Therefore, a wireless network system using the millimetre wave frequency band (e.g., 60GHz) which enables freedom of movement without being hindered by cables is particularly well-adapted to the transmission of such uncompressed HD data, for example using a short distance technology defined in the 802.11 ad standard. The authorized 60GHz band is divided in four RF channels. Each RF channel offers a wide bandwidth thus enabling a large quantity of data to be transmitted with a high data rate (>3Gbps).

However, it has been noticed that the wave propagation in the 60GHz band is significantly more sensitive to path loss than others 2.4GHz or 5GHz bands used in the legacy 802.11a/b/g/n/ac standards. For illustration purposes, the path loss is at least 20dB worse for 60GHz than 5GHz. In order to achieve an efficient communication with MultiGigabits performance up to several meters distance, the mobile and receiving nodes preferably use communication modules with high gain directional antennas to compensate for attenuation.

The use of such directional antennas makes the 60GHz communication highly directional but also highly subject to masking phenomena. Static or moving obstacles such as furniture, objects, and human beings, can interrupt or disturb the communication link and thus cause transmission errors.

In order to reduce the impact of physical obstacles, multi-copy data transmission is performed based on wireless network systems comprising several fixed receiving nodes spaced apart to create space diversity so that when an obstacle arises on the path between the mobile node and one of the receiving nodes, said obstacle has less chance to be also on the path between the mobile node and another receiving node. These receiving nodes may act as relay nodes between the mobile source node and the sink node and allow several copies of the same data to be transmitted from/to the mobile node so that the chances of successful reception of these data are increased.

In some contexts, there may be several mobile nodes moving independently in the same coverage area of the wireless system and sharing the same set of receiving nodes, thus the same RF channel.

The 802.11 ad standard proposes to organise wireless networks into network cells called Personal Basic Service Set (PBSS). Each network cell comprises a set of stations including a PBSS Control Point (PCP) which is a station assigned with a specific control function. The PCP controls the other station(s) belonging to the network cell.

As the mobile nodes move independently over time, it is difficult to ensure that they will always be in the wireless coverage of a same PCP. Indeed, due to the characteristics of the 60GHz frequency band, there is a high probability that the mobile nodes will have to deal with coverage or masking issues with the PCP. For these reasons, it is preferable that the mobile nodes each belong to a different cell.

In practice, each beacon interval (defined as a transmission period set for all the nodes communicating through the wireless network) is divided according to the number of cells in the wireless network and each PCP manages the scheduling of transmission for its own cell. A clustering mechanism defined in the standard notably permits the allocation of the cells periods and the synchronisation of the cells by assigning a specific role to one PCP of the system called Synchronization PCP (SPCP). The S-PCP is in charge of synchronisation with the other PCP(s) called Member

PCP (M-PCP). This clustering mechanism allows interferences between cells using the same RF channel to be avoided.

However, an issue is that the efficiency of the clustering mechanism depends on whether the S-PCP “sees” the M-PCPs that all have to deal with coverage or masking issues, because otherwise, their synchronisation cannot be achieved and there will be interferences. Unfortunately, the 802.11 ad standard does not specify how to assign the PCP functions among the devices.

Therefore, there is a need for improving scheduling of communications in a wireless network in which there are several concurrent multi-path communications implying independent mobiles nodes sharing the same RF channel.

More generally, there is a need of improving existing methods of managing a wireless system including several mobile nodes and receiving nodes sharing the same RF channel. Also, there is a need for mitigating interferences while ensuring a good connectivity of the mobile nodes.

SUMMARY OF THE INVENTION

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

In this context, according to a first aspect of the invention, there is provided a method for managing a communication system comprising two or more mobile nodes and a plurality of receiving nodes sharing a same RF channel for data transmission over a wireless communication network, the method comprising, at a managing node of the communication system:

obtaining quality metrics representing the quality of wireless communication links between mobile nodes and receiving nodes;

assigning a control function to a predetermined number of receiving nodes selected based on the obtained quality metrics; and for each receiving node assigned with a control function, forming a network cell comprising said receiving node and at least one of the mobile nodes, thereby limiting interferences between network cells thus formed when using the same RF channel.

The communication system is typically based on a wireless network compliant with the 802.11 ad standard and comprising network cells referred to as Personal Basic Service Sets (PBSS) in the 802.11 ad standard.

Thanks to embodiments of the invention, interferences are more limited and the connectivity of the mobile nodes is improved.

This is because the control function is assigned to some selected receiving nodes and not to the mobile nodes. This is advantageous since the mobility of the mobile nodes makes them more sensitive to masking and coverage issues (and makes it difficult to maintain the network cluster because synchronization between PBSSs cannot be achieved correctly and thus there are interferences between them) than receiving nodes that are fixed.

This is also because the control function is assigned based on the quality of the links between the receiving nodes and the mobile nodes.

Optional features of the invention are further defined in the dependent appended claims.

According to embodiments, the data transmission is a multi-copy transmission involving several receiving nodes and the predetermined number is based on a level of redundancy to be achieved for the multi-copy data transmission and on a number of wireless MAC layers of the mobile nodes.

Typically, the level of redundancy corresponds to the number of copies of the same data to transmit in order to achieve a good robustness.

According to embodiments, the method further comprises requesting a second predetermined number of receiving nodes to join at least one of the formed network cells, the second predetermined number of receiving nodes being selected among the receiving nodes not assigned with a control function.

For example, when the number of MAC layer(s) in a mobile node is smaller than the level of redundancy, the number of control nodes to set for this mobile node is set equal to the number of wireless MAC layer(s) of the mobile node and at least some of the network cells formed with this mobile node must then be joined by enough stations to achieve the level of redundancy.

On the contrary, when the number of MAC layers in a mobile node is equal or larger than the level of redundancy, the number of control nodes for this mobile node may be set equal to this level of redundancy. This means that all copies of data from the considered mobile node will be transmitted to control nodes (and not mere stations) and thus, there is no need for supplemental stations joining the network cells. As a consequence, the robustness of the multi-copy transmission is improved since even if a link with the control node is broken, this will not impact the transmission of other copies (in the other cells).

For illustration purposes, if a mobile node has two MAC layers and if the level of redundancy is equal to three copies, only two cells can be formed and thus only one of them must be joined by an additional station so that the total number of copies to be transmitted is three (two copies transmitted to the control nodes and one copy transmitted to the additional station).

According to embodiments, the second predetermined number depends on both a level of redundancy to be achieved for the multi-copy data transmission and a number of wireless MAC layers of the mobile nodes.

According to embodiments, the second predetermined number corresponds to a difference between the level of redundancy and the number of wireless MAC layers of the mobile nodes.

According to embodiments, the method further comprises, for each mobile node, selecting the receiving node(s) having the link(s) with the considered mobile node of best quality among the receiving nodes not assigned with a control function.

According to embodiments, the step of assigning a control function comprises, for each mobile node, selecting the receiving node(s) having the link(s) with the considered mobile node of best quality.

According to embodiments, none of the mobile nodes is assigned a control function.

According to embodiments, the quality metrics are obtained in response to ping commands sent from the receiving nodes to the mobile nodes.

In this way, the robustness of the multi-copy transmission is improved since the vulnerability of the control function due to the mobility of these nodes that makes them very sensitive to masking and coverage issues, is reduced. This is an important issue since when a link with the control node of a network cell is broken, communications within the network cell are all impacted.

According to embodiments, the quality metrics comprise a received signal strength indicator (RSSI), a received channel power indicator (RCPI), a throughput metric, a signal-to-noise ratio (SNR), a bit error rate (BER), a packet error rate (PER), and/or modulation and coding scheme (MCS) metric.

According to embodiments, the formed network cell operates at high data rate in the millimeter wave spectrum.

According to embodiments, the control function is a PCP function and the network cell is a PBSS according to the 802.11 ad standard.

According to embodiments, the formed network cells are synchronized according to the 802.11 ad standard.

Correspondingly, according to a second aspect of the present invention, there is provided a device for managing a communication system comprising two or more mobile nodes and a plurality of receiving nodes sharing a same RF channel for data transmission over a wireless communication network, the device being configured for:

obtaining quality metrics representing the quality of wireless communication links between mobile nodes and receiving nodes;

assigning a control function to a predetermined number of receiving nodes selected based on the obtained quality metrics; and for each receiving node assigned with a control function, forming a network cell comprising said receiving node and at least one of the mobile nodes, thereby limiting interferences between network cells thus formed when using the same RF channel.

According to a third aspect of the present invention, there is provided a communication system comprising two or more mobile nodes and a plurality of receiving nodes sharing a same RF channel for data transmission over a wireless communication network, the communication system also comprising a device for managing as aforementioned.

According to embodiments, the communication system further comprises a sink node interconnected with the receiving nodes via a second communication network, more robust than the wireless communication network.

According to embodiments, the communication system is configured to implement a mixed-reality application, the mobile node being a head mounted display and the sink node being configured to generate virtual images based on real images received by the receiving nodes.

The device and communication system according to the second and third aspects have similar advantages and features to the method aforementioned.

The invention also concerns a method substantially as described herein with reference to Figure 5 of the accompanying drawings, a device substantially as described herein with reference to Figures 1, 2, 3, 4 and 6 of the accompanying drawings, and a communication system substantially as described herein with reference to Figures 1, 2, 3 and 4 of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example only, and with reference to the following drawings in which:

Figure 1 comprises Figure 1a and Figure 1b that illustrate respectively a communication system according to a first example of embodiment of the present invention and a beacon interval corresponding to the configuration of Figure 1a; Figure 2 comprises Figure 2a and Figure 2b that illustrate respectively the communication system of Figure 1 after a movement of one of the mobile nodes and a beacon interval corresponding to the configuration of Figure 2a;

- Figure 3 comprises Figure 3a and Figure 3b that illustrate respectively a communication system according to a second example of embodiment of the present invention and a beacon interval corresponding to the configuration of Figure 3a;

Figure 4 comprises Figure 4a and Figure 4b that illustrate respectively a communication system according to a variant of Figure 3a, and a beacon interval corresponding to the configuration of Figure 4a;

Figure 5 illustrates steps of a method according to embodiments of the present invention; and

Figure 6 illustrates a possible architecture for a device according to embodiments of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The invention is now described by means of specific non-limiting exemplary embodiments and by reference to the drawings. The elements having the same reference in different figures are similar.

Figure 1 comprises Figure 1a and Figure 1b that illustrate respectively a communication system according to a first example of embodiment of the present invention and a beacon interval corresponding to the configuration of Figure 1a.

Figure 1a shows a communication system 100 (e.g. a mixed reality system) comprising devices, in particular mobile source nodes 104 and 105, and sink nodes 106 and 107.

The mobile source nodes 104 and 105 are for instance mobile HMDs and/or mobile cameras, and sink nodes 106 and 107 are for instance processing devices such as servers configured to merge “real” images coming respectively from the mobile HMDs 104 and 105 with computer-generated images to provide a mixedreality application.

In this first example, it is assumed that the mobile nodes 104, 105 have only one MAC layer each (reference 610 on Figure 6).

The communication system 100 also comprises a plurality of fixed receiving nodes or devices (hereafter “receiving nodes”) 110, 111, 112, 113, 114, 115 and 116 that are respectively interconnected with the mobile nodes 104 and 105 through first wireless point-to-point connections when the mobile nodes 104 and 105 are in their coverage area. The mobile nodes 104 and 105 thus move in a limited area under the coverage of at least some of the receiving nodes 110 to 116.

These wireless links (also called radio paths) form a first wireless network 101. For the sake of readability, only some of these wireless point-to-point connections are represented in this figure: 104a, 104b, 104c, 104d and 105a, 105b and 105c. However, this is not limiting and there may be other wireless links between one of the receiving nodes and one of mobile nodes.

This first wireless network 101 preferably operates at a high data rate in the millimeter wave spectrum, e.g. 60 GHz wireless network such as specified in the 802.11ad standard. For these purposes, the mobile nodes and the receiving nodes all comprise a communication module (not shown) equipped with at least one directional antenna.

It is assumed that all the receiving nodes 110 to 116 are constantly able to communicate with each other through the 60GHz wireless network 101, at least for the exchange of signalling and control messages (e.g. beacon, association messages, etc.) using the lower Modulation and Coding Schemes (MCS) defined in the 802.11 ad standard (e.g. MCS0, MCS1).

The sink nodes 106 and 107 are connected to a switch 103 which is itself connected to each one of the receiving nodes 110 to 116 through second point-to-point connections 120, 121, 122, 123, 124, 125 and 126 forming a second network 102.

This second network 102 may be wired (e.g. Ethernet) or in a variant it may be based on another robust network technology such as described in the 802.11ac standard or 802.11η standard. The network technology used for the second network supports at least the data rate of a video application executed by an external source or device connected to the receiving nodes 110 to 116 and preferably provides more reliable communications than the first network.

The receiving nodes 110 to 116 act as relay nodes between the mobile nodes 104 and 105 and the sink nodes 106 and 107. Thanks to this infrastructure of relay nodes 110 to 116, the coverage of the sink nodes 106 and 107 can be extended.

Thus, communication links between the mobile nodes 104 and 105 and the sink nodes 106 and 107 can be established using paths (or routes) consisting of first wireless point-to-point connections between the mobile nodes and relay nodes, and of second point-to-point connections between these relay nodes and the sink nodes.

As shown in Figure 1a, the receiving nodes are spaced apart to create space diversity so that when an obstacle arises on the path between one of the mobile nodes 104 and 105 and one of the receiving nodes 110 to 116, said obstacle has less chance to be also on the path between this mobile node and another receiving node acting as a relay node. For instance, the receiving nodes 110 to 116 may be installed at each corner of a room.

In this example, the sink nodes do not directly communicate with the mobile nodes, but through the switch (point-to-point connections 127 and 128) and the relay nodes. However, embodiments are not limited thereto. For instance, in some embodiments (not shown), each sink node may be equipped with antenna(s) as for the relay nodes and communicates directly with the mobile nodes through these means as a receiving node. In other words, a sink node may be implemented within a given receiving node.

As mentioned before, in order to provide robustness, data are duplicated and transmitted several times (typically two times but possibly three or four times depending on the architecture of the network system 100) through different paths or routes.

The mobile nodes 104 and 105 and the receiving nodes 110 to 116 are configured to use a same RF channel of the 60GHz frequency band defined in the 802.11ad standard. As a result, apart from coverage and masking issues, the mobile nodes 104 and 105 are able to communicate with any of the receiving nodes 110 to 116 through the 60GHz wireless network 101.

As mentioned before, in order to handle the sharing of the same RF channel, the first wireless network 101 is organised into a cluster of network cells (hereafter PBSS) compliant with the clustering mechanism described in the 802.11 ad standard.

In the given example, there is a cluster gathering two PBSSs 133 and 134 respectively controlled by the receiving nodes 113 and 114 that have been selected according to the quality of their wireless links with the mobile nodes for holding a control function (hereafter S-PCP and M-PCP, respectively).. In this cluster, the receiving node 113 (S-PCP) is in charge of the synchronisation between PBSS 133 and PBSS 134. In the following description, the nodes that have not been assigned a control function (not-PCP) are called station (STA). In practice, the election of S-PCP and M-PCP is performed between the receiving nodes 113 and 114 through communication over the 60GHz wireless network 101, as described in the 802.11 ad standard.

For illustration purposes, the multi-copy transmission of data from the mobile node 104 is done in the PBSS 133 through the receiving nodes 113 (S-PCP) and 112 (STA) respectively via the radio paths 104a and 104b. Still for illustration purposes, the multi-copy transmission of data from the mobile node 105 (STA2) is carried out in the PBSS 134 through receiving nodes 114 (M-PCP) and 115 (STA) respectively via the radio paths 105a and 105b.

In the first example, the maximum number of PCPs that can be assigned within the network cluster is two. This is because the mobile nodes 104 (STA1) and 105 (STA2) support only one MAC layer and thus they are able to belong to only one PBSS at a time.

More generally, the maximum number of PCPs (#PCPmax) that can be assigned within the network cluster may be determined by the following equation:

#PCPmax = #Mobile_nodes x #MAC_layer [equation 1 ] wherein:

#Mobile_nodes is the number of mobile nodes in the wireless network (=2 in Figure 1a);

#MAC_layer is the number of MAC layers supported by a mobile node (=1 in Figure 1a).

According to preferred embodiments, a PBSS of minimum size is made of a mobile node and a receiving node set as a PCP because of its good quality of link with the mobile node. Then, in order to transmit the number of copies necessary to achieve a target robustness, additional receiving nodes are selected, also according to their quality of link with the mobile node, to join the minimum size PBSS.

For illustration purposes, it is assumed that the required number of copies (robustness) is two. In the given example, the minimum size PBSS 133 is made of the mobile node 104 (STA1) and the receiving node 113 (S-PCP). This minimum size PBSS 133 enables there to be a first communication path through the radio path 104a.

In order to provide a robustness of two copies, the additional receiving node 112 (STA) joins the PBSS 133 and enables there to be a second communication path through the radio path 104b.

Still for illustration purposes, the minimum size PBSS 134 is made of the mobile node 105 (STA2) and the receiving node 114 (M-PCP). This minimum size PBSS 134 enables there to be a first communication path through the radio path 105a. In order to provide robustness of two copies, the additional receiving node 115 (STA) joins the PBSS 134 and enables there to be a second communication path through the radio path 105b.

The communication between the various nodes in a common and shared beacon interval BI 150 is now described with reference to Figure 1b. The BI 150 permits to mitigate the interference between the PBSS 133 and 134 by scheduling their transmissions in non-overlapping time periods.

The duration of the BI 150 may be equal to 102.4ms. But other durations may be used.

The beacon interval 150 comprises a first type of time intervals 151 and

153 called Beacon Service Period (SP), and a second type of time intervals 152 and

154 called Data Transfer Interval (DTI).

The S-PCP 113 schedules the various Beacon SPs in function of the maximum number of PCPs within the network cluster (here #PCPmax = 2). The beacon SP 151 is used by the S-PCP 113 for its own Beacon Header Interval (BHI), the beacon SP 153 is used by the M-PCP 114 for its own BHI.

The DTIs 152 and 154 represent the maximum time interval during which data may be exchanged between the nodes of a cell.

In practice, the PCPs 113 and 114 exchange their scheduling information and a re-scheduling of their transmissions is carried out. The PCPs 113 and 114 can schedule their CBAP/SP transmissions in the DTIs 152 and 154, for example on a firstallocate-first-use basis.

As a result, the interferences between the PBSSs 133 and 134 are avoided and the connectivity of the mobile nodes 104 and 105 within the 60GHz wireless network 101 is improved.

It should be noted that the clustering configuration shown in Figure 1a corresponds to a given snapshot of the 60GHz wireless network 101 at a given time t.

At this time t, among the set of receiving nodes 110 to 116, the subset of receiving nodes 112, 113, 114 and 115 has been selected to handle the point to point communications of mobile nodes 104 and 105 within the 60GHz wireless network 101.

According to embodiments, the selection of this subset has been performed through the monitoring of Link Quality (LQ) of the radio paths available between the various receiving nodes 110 to 116 and each of the mobile nodes 104 and 105.

For example, the LQ may be a RSSI (Receive Signal Strength Indicator) or a RCPI (Receive Channel Power Indicator) metric, a throughput metric, a MCS metric or else.

It is assumed that at the time t, the best LQ have been obtained for the radio paths 104a, 104b between the mobile node 104 and respectively the receiving nodes 113 (S-PCP) and 112 (STA), and for the radio paths 105a, 105b between the mobile node 105 and respectively the receiving nodes 114 (M-PCP) and 115 (STA).

At a next time t’, the configuration of the 60GHz wireless network 101 may be different, for example, due to a displacement of mobile node(s) or due to an obstacle cutting a radio path. As a result, at the time t’, the clustering configuration, i.e. the receiving nodes assigned with a PCP function and the corresponding PBSSs may have to be updated.

Figure 2 precisely represents the system at the later time t’ (Figure 2a) and the corresponding beacon interval (Figure 2b).

It is assumed that only the mobile node 105 has moved between Figure 1a (former position shown in dotted line) and Figure 2a (new position in full line).

At this time t’, from among the set of receiving nodes 110 to 116, an updated subset of receiving nodes 112, 113, 115 and 116 has been selected to handle the point-to-point communications of mobile nodes 104 and 105 within the 60GHz wireless network 101.

Within this updated subset, the receiving nodes 113 and 115 are assigned a PCP function and handle the point-to-point communications of the mobile node 104 (STA1) within the PBSS 133 and of the mobile node 105 (STA2) within the new PBSS 234 respectively. The receiving nodes 112 and 116 join the PBSS 133 and 234 respectively in order to achieve the robustness of two copies.

According to embodiments, the selection of this subset is performed through the monitoring of the Link Quality (LQ) of the radio paths available between the various receiving nodes 110 to 116 and each of the mobile nodes 104 and 105.

It is assumed that at this time t’, the best LQs are obtained for the radio paths 104a, 104b between the mobile node 104 and respectively the receiving nodes 113 (S-PCP) and 112 (STA), and for the radio paths 105b, 105c between the mobile node 105 and respectively the receiving nodes 115 (M-PCP) and 116 (STA).

The steps performed to select PCPs and to form the corresponding PBSSs are described hereafter with reference to Figure 4.

Figure 2b shows the beacon interval 250 shared at time t’ for the configuration described with reference to Figure 2a which is now described.

It is similar to the BI 150 shown in Figure 1 b except that the beacon SP 253 is used by the M-PCP 115 for its own PBSS 234.

The duration of the BI 250 may also be equal to 102.4ms. But other durations may be used.

In practice, the PCPs 113 and 115 exchange their scheduling information and a re-scheduling of their transmissions is carried out. The PCPs 113 and 115 can schedule their CBAP/SP transmissions in the DTIs 152 and 154, for example on a firstallocate-first-use basis.

The example described above with reference to Figures 1 and 2 may be easily adapted to any configuration where there are not enough MAC layers supported by each mobile node to achieve the multi-copy transmission with the targeted robustness (i.e. number of copies higher than the number of available MAC layers of the mobile node).

Embodiments of the present invention are not limited to the represented configuration. For instance, embodiments may imply more than two mobile nodes and a different number of receiving nodes.

Figure 3 comprises Figure 3a and Figure 3b that illustrate respectively a communication system according to a second example of embodiment of the present invention and a beacon interval corresponding to the configuration of Figure 3a.

In this second example shown in Figure 3a, it is assumed that the mobile nodes 304, 305 have two MAC layers each (reference 610 in Figure 6) and can thus belong to two PBSS. The elements having the same reference as in Figure 1a are similar to the corresponding elements of this figure.

In the given example, there are four PBSSs 332, 333, 334 and 335 respectively controlled by the receiving nodes 112, 113, 114 and 115 that have been selected according to the quality of their wireless links with the mobile nodes for holding a control function (hereafter PCP). These four PBSSs form a network cluster.

More specifically, the receiving node 113 (S-PCP) is in charge of the synchronisation between PBSSs. The receiving nodes 112, 114 and 115 (M-PCP) are synchronized by the receiving node 113 (S-PCP).

In the second example, it should be pointed out that the maximum number of PCPs that can be assigned within the network cluster is four since the mobile nodes have two MAC layers and are thus able to belong to two PBSSs at a time.

In the given example, the mobile node 304 (STA1) belongs to PBSS 332 and 333, and the mobile node 305 (STA2) belongs to PBSS 334 and 335.

Thus, in this second example, in order to achieve a robustness of two copies, it is not necessary that an additional receiving node joins the minimum size PBSSs (made of a mobile node and a PCP) since the minimum size PBSS 333 permits a first communication path through the radio path 104a and the minimum size PBSS 332 permits a second communication path through the radio path 104b. Correspondingly, the minimum size PBSS 334 permits a first communication path through the radio path 105a and the minimum size PBSS 335 permits a second communication path through the radio path 105b.

Figure 3b represents the beacon interval (BI) 350 corresponding to the clustering configuration shown in Figure 3a. The BI 350 is built similarly to the BI 150 of Figure 1a, but is slightly different because of the higher number of PBSSs in the wireless network 101.

More specifically, the beacon interval 350 comprises four Beacon SPs 151, 353, 355 and 357 and four DTIs 352, 354, 356 and 358 permitting to mitigate the interference between the PBSSs 332, 333, 334 and 335 by scheduling their transmissions in non-overlapping time periods.

The duration of the BI 350 may also be equal to 102.4ms. But other durations may be used.

In practice, the PCPs 112, 113, 114 and 115 exchange their scheduling information and a re-scheduling of their transmissions is carried out. The PCPs 112, 113, 114 and 115 can schedule their CBAP/SP transmissions in the DTIs 352, 354, 356 and 358, for example on a first-allocate-first-use basis.

It should be noted that when the link between the control node (PCP) of a PBSS and a mobile node is broken, communications involving this mobile node within this network cell are all impacted.

Therefore, since robustness of two copies can be achieved using two minimum size PBSS, i.e. without need of an additional receiving node joining the cells, the robustness of the multi-copy transmission is improved.

The example described above with reference to Figure 3 may be easily adapted to any configuration where there are enough MAC layers supported by each mobile node to achieve the multi-copy transmission with the targeted robustness (i.e. number of copies equal to or smaller than the number of available MAC layers of the mobile node).

Figure 4 comprises Figure 4a and Figure 4b that illustrate respectively a communication system according to a variant of Figure 3a, and a beacon interval corresponding to the configuration of Figure 4a.

Similarly to the second example shown in Figure 3a, it is assumed that the mobile nodes 304, 305 have two MAC layers each (reference 610 in Figure 6) and can thus belong to two PBSSs. As a consequence, the maximum number of PCPs that can be assigned within the network cluster is four since the mobile nodes have two MAC layers and are thus able to belong to two PBSSs at a time (See [equation 1] above). However, a lower number of PCPs may be assigned. The elements having the same references as in Figures 1a and 3a are similar to the corresponding elements of these figures.

In the given example, it is considered that the mobile devices 304 and 305 are still at a same distance from the receiving nodes as in Figure 3a. There is a nonreflective obstacle 440 between the mobile device 305 and the receiving node 115, such that the mobile node 305 cannot use the receiving node 115 for its communications.

In the given example, the mobile node 304 (STA1) belongs to two PBSSs 332 and 433, and the mobile node 305 (STA2) belongs to two PBSSs 433 and 334.

Thus, in this variant, in order to achieve a robustness of two copies, it is not necessary that an additional receiving node joins the PBSSs (made of at least one mobile node and a PCP) since the PBSS 433 permits a first communication path through the radio path 104a and the minimum size PBSS 332 permits a second communication path through the radio path 104b. The PBSS 433 also permits a first communication path through the radio path 105d and the minimum size PBSS 334 permits a second communication path through the radio path 105a.

Although a maximum number of four different PCPs could be assigned within the network cluster, only three are considered, since the PBSS 433 comprises the two mobile devices 304 and 305.

Figure 4b represents the beacon interval (BI) 450 corresponding to the clustering configuration shown in Figure 4a. The BI 450 is built similarly to the BI 350 of Figure 3a, but is slightly different because of the lower number of PBSSs in the wireless network 101.

More specifically, the beacon interval 450 comprises three Beacon SPs 151, 453 and 455 and three DTIs 452, 454 and 456 permitting to mitigate the interferences between the PBSSs 332, 433 and 334 by scheduling their transmissions in non-overlapping time periods.

The duration of the BI 450 may also be equal to 102.4ms. But other durations may be used.

In practice, the PCPs 112, 113 and 114 exchange their scheduling information and a re-scheduling of their transmissions is carried out. The PCPs 112, 113, and 114 can schedule their CBAP/SP transmissions in the DTIs 452, 454 and 456, for example on a first-allocate-first-use basis.

It should be noted that when the link between the control node (PCP) of a PBSS and a mobile node is broken, communications involving this mobile node within this network cell are all impacted.

Therefore, since robustness of two copies can be achieved using two PBSSs, i.e. without need of an additional receiving node joining the cells, the robustness of the multi-copy transmission is improved.

The example described above with reference to Figure 4 may be easily adapted to any configuration where there are enough MAC layers supported by each mobile node to achieve the multi-copy transmission with the targeted robustness (i.e. number of copies equal to or smaller than the number of available MAC layers of the mobile node).

Figure 5 illustrates steps of a method according to embodiments of the present invention. These steps can be applied to both examples described previously, i.e. irrespective of the number of MAC layers supported by each mobile node and the targeted robustness (number of copies to transmit).

These steps are executed by a managing device (or manager) located, for instance, in one of the sink devices 106 or 107.

At step 500, the network system starts.

At step 501, the value of two parameters N1 and N2 relating to the 60GHz wireless network 101 are retrieved for instance from the ROM memory of the managing device (603 on Figure 6).

The parameter N1 corresponds to the number of MAC layer(s) (610 on Figure 6) supported by the mobile nodes 104 and 105.

It should be noted that in the first example described with reference to Figures 1 and 2, this parameter is equal to 1, while in the second example described with reference to Figures 3 and 4, this parameter is equal to 2.

Even though, in these examples, both mobile nodes have the same number of MAC layers, the present invention is not limited thereto. In other embodiments, the mobile nodes may support a different number of MAC layers (for example one mobile node may support only one MAC layer while another mobile node may support two MAC layers) and there may be a dedicated parameter N1 for each mobile node.

The parameter N2 corresponds to the number of copies (level of redundancy) of the same data to transmit for achieving good robustness. It should be noted that in both the first example described with reference to Figures 1 and 2 and in the second example described with reference to Figures 3 and 4, this parameter is equal to 2. However, a different number may be contemplated if the wireless network 101 requires a higher redundancy of data.

At step 502, the 60GHz wireless network 101 is initialised. The network initialisation comprises assigning a default PCP function to all the receiving nodes 110 to 116.

In practice, a message indicating that clustering according to the 802.11 ad standard is enabled as well as the number of the PCP nodes (variable “ClusterMaxMem”) is sent to all the receiving nodes 110 to 116. At this step, this number is equal to the number of receiving nodes in the wireless network 101 since all the receiving nodes have been assigned a PCP function.

The purpose of this step is to discover the number and the location of each mobile node currently in use in the 60GHz wireless network 101. Assigning a PCP function to all the receiving nodes 110 to 116 allows the transmission of several beacon frames within the entire area covered by the infrastructure of receiving nodes. In this way, any mobile node in use within the coverage area will be able to receive at least one beacon frame and to reply to the corresponding PCP in order to join the corresponding PBSS.

At step 503, the subset of receiving nodes associated with a mobile node is identified among the set of all receiving nodes assigned with a PCP function. Then, a list of the mobile nodes (STA1, STA2) currently in use in the 60GHz wireless network 101 is established. In practice, only the receiving nodes of the subset, i.e. the receiving nodes connected to at least one of the mobile nodes keep their PCP function. The PCP function on other receiving nodes is released (i.e. they are once again mere stations, without PCP function).

At step 504, Link Quality (LQ) metrics for the links between the receiving nodes and the mobile nodes are obtained.

In practice, it is tested whether LQ metrics of receiving nodes have been measured for all possible mobile nodes (STA1, STA2). If there are LQ metrics missing, a mobile node is selected among the list established at step 503 and a PBSS to which this mobile node belongs, is arbitrarily selected (if the mobile node has several MAC layers, it may belong to several PBSS). The receiving node for which LQ metrics are needed is required to join the selected PBSS and to send a ping command to the selected mobile node in order to measure the LQ with it and then to leave the joined PBSS. The fact to leave the joined PBSS after the LQ measure allows limiting the overhead in said PBSS and avoiding the data communications currently occurring to be disturbed.

In practice, the scheduling of these various ping commands within the beacon interval is managed by the receiving node for which a PCP (S-PCP or M-PCP) function is assigned within the selected PBSS. The ping command can thus help to measure LQ metrics such as a RSSI (Received Signal Strength Indicator) or a RCPI (Received Channel Power Indicator) metric, a throughput metric, a MCS metric or else.

Receiving nodes having a PCP function are connected to at least one mobile node thus forming a PBSS, and can thus measure LQ metrics with it at any time while it is connected. A receiving node having a PCP function may also have several MAC layers, and the number of possible PBSS connections for this receiving node depends on its number of MAC layers. In this case, it may have to join another PBSS with a second mobile node to which it is not connected, in order to get LQ metrics with this second mobile node (while still being connected with a first mobile node).

Similarly, a receiving node without PCP function and comprising several MAC layers may be associated with several minimum size PBSS.

It should be noted that when a receiving node having only one MAC layer is already involved in a communication with a mobile node in a PBSS, it cannot quit said

PBSS to measure its LQ with the mobile node of another PBSS. However, if said receiving node has another MAC layer, i.e. another MAC layer which is not already engaged in a PBSS, it is able to measure its LQ with the mobile node of another PBSS.

Next, all receiving nodes, including the PCPs, are requested to provide their LQs for all possible mobile nodes listed (STA1, STA2) and the obtained LQs are processed. For example, such process may comprise sorting, for each mobile node, the received LQs in decreasing order, i.e. from the LQ having the best quality to the LQ having the worst quality.

For illustration purposes, it is assumed that the receiving nodes shown in Figure 1 have only one MAC layer each. Thus, an example of list of LQs that can be obtained in this case is provided in the following table:

	110	111	112	113	114	115	116
104 (STA1)	OK	OK	OK	OK	/	/	OK
105 (STA2)	OK	OK	/	/	OK	OK	OK

In this case, the receiving nodes 112, 113 which are in used in the PBSS 133 with the mobile node 104 cannot join the PBSS 134 to get their LQ with the mobile node 105 and similarly, the receiving nodes 114, 115 which are in used in the PBSS134 with the mobile node 105 cannot join the PBSS 133 to get their LQ with the mobile node 104.

Still for illustration purposes, it is now assumed that the receiving nodes shown in Figure 1 have two MAC layers each. Thus, an example of list of LQs that can be obtained in this case is provided in the following table:

	110	111	112	113	114	115	116
104 (STA1)	OK	OK	OK	OK	OK	OK	OK
105 (STA2)	OK	OK	OK	OK	OK	OK	OK

In this case, the receiving nodes 112, 113 and 114, 115 are respectively able to join the PBSS 134 and PBSS 133 in order to get their LQ with the mobile node 105 and 104.

Next, the LQs obtained for each mobile node from the receiving nodes are analysed. For example, the analysis comprises comparing the received LQs with the previously received LQs.

At step 505, it is checked whether an update of the network cluster (i.e. of PCPs and PBSSs) is needed. For instance, it is decided that an update is needed when there is another receiving node having a better LQ than the current PCP with the considered mobile node.

If the response is no, the algorithm loops to step 504.

If the response is yes, the algorithm goes on to step 506.

At step 506, it is checked, for each mobile node, whether the value of the parameter N1 is greater than or equal to the value of the parameter N2, i.e. whether there are enough MAC layer(s) in the considered mobile node to transmit the number of copies necessary to achieve the desired level of redundancy (and robustness).

If the response is no, the algorithm goes on to step 507. It should be noted that an example of this case has been described with reference to Figures 1 and 2.

At step 507, for each mobile node, the N1 receiving nodes having the best LQs with it are assigned a PCP function. A PBSS is thus set for each PCP node with the corresponding mobile node.

At step 508, for each mobile node, a number equal to the difference between the values of parameters N2 and N1 of receiving nodes having the next best LQs without PCP function are requested to join the PBSS thus created.

For illustration purposes, in the example of Figure 1a, a number N1 = 1 of MAC layers and thus of connections with PCPs is set for each mobile node: receiving node 113 having the best LQ with mobile node 104 and receiving node 114 having the best LQ with mobile node 105. Thus two PBSS 133 and 134 are created: the PBSS 133 comprising the PCP 113 and the mobile node 104 and the PBSS 134 comprising the PCP 114 and the mobile node 105. In this way, one copy may be transmitted from/to the mobile node 104/105 to the PCP 113/114. Since two copies of data from/to each mobile node are needed (N2 = 2) whereas each mobile node can belong to only one PBSS at the same time (only one MAC layer), one (N2-N1 = 1) additional receiving node is requested to join the PBSS so that the second copy may be provided. More specifically, in this example, the receiving node 112, which has the best LQ with the mobile node 104 among the receiving nodes without PCP function, is requested to join the PBSS 133. Similarly, the receiving node 115, which has the best LQ with the mobile node 105 among the receiving nodes without PCP function, is requested to join the PBSS 134.

The algorithm then loops to step 504.

If the response to test 506 is yes, the algorithm goes to step 509. It should be noted that an example of this case has been described with reference to Figure 3.

At step 509, for each mobile node, the N2 receiving nodes having the best LQs with it are assigned a PCP function. A PBSS is thus set for each PCP node with the corresponding mobile node.

For illustration purposes, in the example of Figure 3a, a number N1 = 2 of PCPs is set for each mobile node: receiving nodes 112 and 113 having the best LQs with mobile node 304 and receiving nodes 114 and 115 having the best LQs with mobile node 305. Thus four PBSSs 332, 333, 334 and 335 are created: the PBSS 332 comprising the PCP 112 and the mobile node 304, the PBSS 333 comprising the PCP 113 and the mobile node 304, the PBSS 334 comprising the PCP 114 and the mobile node 305 and the PBSS 335 comprising the PCP 115 and the mobile node 305. In this way, two copies may be transmitted from/to the mobile node 304 to the PCPs 112 and 113 and two copies may be transmitted from/to the mobile node 305 to the PCPs 114 and 115. Since two copies of data from/to each mobile node are needed (N2 = 2) and each mobile node can belong to two PBSSs at the same time (two MAC layers), no additional receiving node is needed.

The algorithm then loops to step 504.

Even though, in these examples, both mobile nodes have the same number of MAC layers, the present invention is not limited thereto. In other embodiments, the mobile nodes may support a different number of MAC layers, for example one mobile node may support only one MAC layer while another mobile node may support two MAC layers. The described algorithm is adapted to these other embodiments since the test 506 is performed for each mobile node individually, as well as the following steps 507 and 508, or 509. Therefore, assuming that a number N2 = 2 copies is needed, the steps 507 and 508 are performed for the mobile node supporting only one MAC layer and the step 509 is performed for the mobile node supporting two MAC layers.

Figure 6 illustrates a possible architecture for a device or node 600 according to embodiments of the present invention, such as nodes 104, 105, 110, 111, 112, 113, 114, 115 or 116 shown in Figure 1a.

In this exemplary architecture, the device 600 comprises a communication bus 608 to which there are connected:

a micro-controller or Control Process Unit (denoted CPU) 601; a Random Access Memory (denoted RAM) 602, working as a main memory, in which instructions and temporary variables and parameters for implementing steps of a method according to some embodiments may be loaded from a non-volatile memory, and whose capacity may be extended by an additional Random Access Memory connected to an expansion port (not shown);

a Read-Only Memory (denoted ROM) 603 in which instructions for implementing steps of a method according to embodiments may be stored;

a first communication interface 604, wireless, enabling first point-to-point connections with the other wireless nodes through the first network 101; and a second communication interface 605, wired (Ethernet for example) or wireless, enabling second point-to-point connections with at least some of the devices (here nodes 110, 111, 112, 113, 114, 115 or 116) through the second network 102. It should be noted that this second communication interface 605 is optional for the mobile nodes.

The communication bus 608 provides communication and interoperability between the various elements included in the device 600 or connected to it. For instance, the CPU 601, the RAM 602, the ROM 603 and the communication interface(s) 604, 605 exchange data and control information via the communication bus 608. The representation of the bus is not limiting and in particular the CPU 601 is operable to communicate instructions to any element of the device 600 directly or by means of another element of the device 600.

After the device 600 has been powered on, the CPU 601 is capable of executing, from the RAM 602, instructions pertaining to a computer program, once these instructions have been loaded from the ROM 603 or from an external memory (not shown in Figure 6). A computer program of this kind causes the CPU 601 to perform some or all of the steps of the algorithm described with reference to Figure 5.

In embodiments, the CPU 601 controls the overall operation of the device 600. It acts as a data analyser unit, which analyses useful data payload (also referred as MAC payload) of a packet received from another device, either received through 60 GHz wireless network (first network 101) and processed by the first wireless communication interface 604, or received through the second network 102 and processed by the second communication interface 605.

The first communication interface 604 comprises: a Wireless Physical Layer Module (denoted WPHY) 609; at least one Medium Access Controller (denoted MAC) 610; at least one antenna 611 (here, only one antenna is represented but the present invention is not limited thereto), for instance a directional antenna or several high gain antennas configured to communicate in several different directions.

In the example described with reference to Figures 1 and 2, the mobile nodes have only one MAC layer whereas on the example described with reference to Figures 3 and 4, the mobile nodes have two MAC layers sharing the same WPHY module 609 and the same antenna 611. A reference model for support of multiple MAC layers is provided in the 802.11 ad standard, in particular § 4.9.3 “Reference model for supporting multiple MAC sublayers”.

The WPHY 609 is configured for processing a signal output by the MAC 610 before it is sent out through the antenna 611. For example, the processing comprises modulation, frequency transposition and power amplification processes. In embodiments, the WPHY 609 may also be configured for processing a signal received by the antenna 611 before it is provided to the MAC 610.

The MAC 610 manages access to the wireless medium (first network 101). It is also configured as a synchronization control unit, which controls the synchronization of data for scheduling the transmissions through the first wireless network 101, based on a beacon interval. More specifically, the MAC 610 schedules the beginning and the end of an emission of data by the antenna 611, through the first network 101, as well as the beginning and the end of a reception of data from the first network 101, by the antenna 611.

The antenna 611 supports Directional Multi Gigabit (DMG) data transfers. It is adapted to select a sector for transmitting and receiving signals.

The second communication interface 605 comprises: a Physical Layer Module (denoted PHY) 612; a Medium Access Controller (denoted MAC) 606;

an interface connection 614, for example comprising a physical cable (if the second network 102 is wired) or an antenna (if the second network 102 is wireless).

The PHY 612 is configured for processing a signal output by the MAC 606 before it is sent out through the interface connection 614. For example, the processing aims at adapting the signal to the electrical specification and to the access mode of the interface connection 614. In embodiments, the PHY 612 may also be configured for processing a signal received by the interface connection 614 before it is provided to the MAC 606, for instance according to the IEEE 802.3 (Gigabit Ethernet).

The device 600 may be connected to an external source or device through the interface 615, and may exchange data with it. The external source or device may execute an application generating application data, such as a compressed video stream, a file storage output, a video camera output, or data to be displayed.

The device 600 may comprise a video application module 607 configured to convert these application data in packets suitable for being transmitted over a network (e.g. first wireless network 101). The module 607 is thus configured to packetize the application data and transmits the packets to a Link Layer Controller (LLC) 606. In embodiments, the module 607 is also configured to convert the received packets from the LLC 606 into application data to be transmitted through the interface 615.

In preferred embodiments, the data packets managed by the module 607 are TCP/IP or UDP/IP video lossless compressed data with a data rate around 100 to

400 Mbps.

The LLC 606 is configured to establish the link between the source and sink nodes in order to transmit and receive the packets between the video application module 607 and the communication interfaces 604 and/or 605.

Although the present invention has been described hereinabove with 10 reference to specific embodiments, the present invention is not limited to the specific embodiments, and modifications which lie within the scope of the present invention will be apparent to a person skilled in the art. 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 as determined by the appended claims. In particular different features from different embodiments may be interchanged, where appropriate.

Claims (17)

1. A method for managing a communication system comprising two or more mobile nodes and a plurality of receiving nodes sharing a same RF channel for data transmission over a wireless communication network, the method comprising, at a managing node of the communication system:

obtaining quality metrics representing the quality of wireless communication links between mobile nodes and receiving nodes;

assigning a control function to a predetermined number of receiving nodes selected based on the obtained quality metrics; and for each receiving node assigned with a control function, forming a network cell comprising said receiving node and at least one of the mobile nodes, thereby limiting interferences between network cells thus formed when using the same RF channel.

2. A method according to claim 1, wherein the data transmission is a multi-copy transmission involving several receiving nodes and wherein the predetermined number is based on a level of redundancy to be achieved for the multi-copy data transmission and on a number of wireless MAC layers of the mobile nodes.

3. A method according to claim 1 or 2, further comprising requesting a second predetermined number of receiving nodes to join at least one of the formed network cells, the second predetermined number of receiving nodes being selected among the receiving nodes not assigned with a control function.

4. A method according to claim 3, wherein the second predetermined number depends on both a level of redundancy to be achieved for the multi-copy data transmission and a number of wireless MAC layers of the mobile nodes.

5. A method according to claim 3 or 4, wherein the second predetermined number corresponds to a difference between the level of redundancy and the number of wireless MAC layers of the mobile nodes.

6. A method according to any one of claims 3 to 5, comprising, for each mobile node, selecting the receiving node(s) having the link(s) with the considered mobile node of best quality among the receiving nodes not assigned with a control function.

7. A method according any one of the preceding claims, wherein the step of assigning a control function comprises, for each mobile node, selecting the receiving node(s) having the link(s) with the considered mobile node of best quality.

8. A method according any one of the preceding claims, wherein none of the mobile nodes is assigned a control function.

9. A method according any one of the preceding claims, wherein the quality metrics are obtained in response to ping commands sent from the receiving nodes to the mobile nodes.

10. A method according to any one of the preceding claims, wherein the quality metrics comprise a received signal strength indicator (RSSI), a received channel power indicator (RCPI), a throughput metric, a signal-to-noise ratio (SNR), a bit error rate (BER), a packet error rate (PER), and/or modulation and coding scheme (MCS) metric.

11. A method according to any one of the preceding claims, wherein the formed network cell operates at high data rate in the millimeter wave spectrum.

12. A method according to any one of the preceding claims, wherein the control function is a PCP function and the network cell is a PBSS according to the 802.11 ad standard.

13. A method according to any one of the preceding claims, wherein the formed network cells are synchronized according to the 802.11 ad standard.

14. A device for managing a communication system comprising two or more mobile nodes and a plurality of receiving nodes sharing a same RF channel for data transmission over a wireless communication network, the device being configured for:

obtaining quality metrics representing the quality of wireless communication links between mobile nodes and receiving nodes;

assigning a control function to a predetermined number of receiving nodes selected based on the obtained quality metrics; and for each receiving node assigned with a control function, forming a network cell comprising said receiving node and at least one of the mobile nodes, thereby

5 limiting interferences between network cells thus formed, when using the same RF channel.

15. A communication system comprising two or more mobile nodes and a plurality of receiving nodes sharing a same RF channel for multi-copy data transmission over

10 a wireless communication network, the communication system also comprising a device according to claim 14.

16. A communication system according to claim 15, further comprising a sink node interconnected with the receiving nodes via a second communication network,

15 more robust than the wireless communication network.

17. A communication system according to claim 16, implementing a mixed-reality application, wherein the mobile node is a head mounted display and wherein the sink node is configured to generate virtual images based on real images received

20 by the receiving nodes.

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Application No: Claims searched:

GB 1700032.4 1-17