GB2476967A

GB2476967A - Configuring wireless node antennae beams in a communication tree

Info

Publication number: GB2476967A
Application number: GB1000661A
Authority: GB
Inventors: Norihito Aoki
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 2010-01-15
Filing date: 2010-01-15
Publication date: 2011-07-20
Anticipated expiration: 2030-01-15
Also published as: GB201000661D0; GB2476967B

Abstract

Wireless nodes 401-405 are interconnected by links 451-460 in a wireless network 450. Data is transmitted from a source node to a plurality of destination nodes. Each node comprises a communication antenna. A manager node 401 determines (S730, figure 6) transmission paths from the source node to the plurality of destination nodes, on the basis of a transmission capacity of the links. The manager node then determines (S740, figures 6, 9) a communication tree from the determined transmission paths, on the basis of respective capabilities of the wireless nodes to control a form of a beam of their respective communication smart antennas (S1030, S1050, figure 9). The manager node then configures (S750, figure 6) the wireless nodes for setting up the communication tree for the data transmission. By taking into account the capability of the wireless nodes to control the form of the beam of their antenna when determining the communication tree to set up for the data transmission, the risks of interference are reduced.

Description

Configuring wireless nodes

1. FIELD OF THE INVENTION

The present invention relates to a method and a device for configuring communication devices in the scope of a data transmission via a wireless communication network, a computer program product which causes a computer or processor to carry out the steps of the configuring, and an information storage means storing the computer program product..

The invention falls within the technical field of wireless communication networks and is particularly applicable in the implementation of wireless mesh communication networks.

2. TECHNOLOGICAL BACKGROUND

Determining data paths or broadcasting trees (such as spanning trees) in wireless communication networks, and in communication networks more generally, is a problematic widely addressed in the state of the art.

One major criterion for selecting a data path is to minimize the distance from the source originating the data toward the destinations.

Another major criterion is to limit the cost regarding the use of transmission resources, such as bandwidth or such as processing resources at intermediate communication devices on the data path from the source device to the destination device(s) by limiting the number of hops between the source and the destination(s).

Yet another criterion is to maximize the transmission quality. Under such circumstances, the most robust links are preferred for relaying signals from the source device to the destination device(s). One should for instance refer to the international patent application published with the reference WO 2007/073466.

Indeed this document describes the use of trellis diagram according to Viterbi routing algorithm in order to determine a multi-hop path between a source device and a destination device having a lowest cost metric.

In the context of wireless communications, an additional problematic shall be taken into account. Indeed, wireless communication links are more subject to interferences than wired communication links. For instance, communications around 60 GHz are easily disturbed by other corrirriunications occurring at the same time in the same geographical zone.

Avoidance of transmission interferences can be achieved by using a medium access of TDMA ("Time Division Multiple Access") type. Such a technique allows several transmitter devices to share the same frequency channel by dividing the transmission cycle into different access timeslots. The transmitter devices transmit successively, one after the other, each using a dedicated timeslot (allocated to the transmitter device). However, as the transmitter devices successively access the medium, the bandwidth consumption especially in millimetre wave transmission domain is not efficient.

3. OBJECTIVES OF THE INVENTION In at least one embodiment, it is desirable to overcome these various drawbacks of the state of the art.

In particular, it is desirable to increase the throughput of a wireless network, and in parallel at reduce interference risks.

It is also desirable to contain the latency of transmission throughout the At least one embodiment it is also desirable to provide a technique that is simple to implement and cost-effective.

4. SUMMARY OF THE INVENTION

According to a first aspect, in at least one embodiment, the invention relates to a method for configuring wireless nodes interconnected by links in a wireless network to enable transmission of data from a source node to a plurality of destination nodes, each node comprising a communication antenna. A manager node performs the steps of: -determining transmission paths from said source node to said plurality of destination nodes, on the basis of a transmission capacity of said links; -determining a communication tree from the determined transmission paths, on the basis of respective capabilities of said wireless nodes to control a form of a beam of their respective communication antennas; -configuring the wireless nodes for setting up, for said data transmission, the communication tree determined.

Thus, the invention relies on the principle that once possible paths throughout the wireless network are determined, a communication tree has to be setup in order to perform the data transmission. This communication tree is determined by taking into account the respective capabilities of the nodes of the selected transmission paths to perform bearnforming with their respective antenna. Indeed, a node in a simple and low cost design form can use an isotropic antenna or the like, in transmission and/or in reception. Inappropriate configuration of the communication tree results in generating interferences in the data transmission, which has a consequence of generating errors (synchronization, decoding) at the addressee(s) of the data transmission. By taking into account the capability of the wireless nodes to control the form of the beam of their antenna when determining the communication tree to set up for the data transmission, the risks of interference are therefore reduced.

Preferably, the transmission capacity of a given link is determined on the basis of information about an error rate and/or a signal-to-noise ratio over said given link.

Therefore, a bit error rate (denoted B ER), which can be obtained by a data receiver receiving data over a given link in a simple and cost-effective way, can be used to define link capacity thanks to a model of the transmission channel as a binary symmetric channel (denoted BSC) or a binary erasure channel (denoted BEC. Similarly, a received signal strength indicator (denoted RSSI) representing a signal-to-noise ratio (denoted SNR) indication, which can be obtained by a data receiver receiving data over a given link in a simple and cost-effective way, can be used to define link capacity thanks to a model of the transmission channel as an additive white Gaussian noise channel.

Advantageously, a transmission capacity is determined for each transmission path determined, on the basis of a transmission capacity of said links constituting said transmission path, and among transmission paths from the source node to one destination node, the one with the highest capacity is selected for forming the communication tree.

Therefore the quality of the signal at destination, in the scope of the data transmission, is optimized.

Advantageously, the step of determining a communication tree further comprises a step of associating the origin of each transmission path selected to a same reference starting instant in a transmission cycle.

Therefore, the latency for the data transmission to all destinations via the network is minimized.

Advantageously, the step of determining transmission paths comprises a step of determining for each one of said transmission paths a set of successive vectors, each vector representing one of said links used by the path during a given time slot.

Therefore, such a division of the transmission paths according to predefined time slots allows simplifying the processing of the communication tree in order to prevent situations generating interference risks.

Advantageously, the step of determining a communication tree further comprises the steps of: -a first checking step of checking if the vectors of the transmission paths selected which correspond to a same time slot have a same vector origin; -in case of a negative result of the first checking step, a second checking step of checking if the wireless node corresponding to said vector origin is capable of controlling the form of the beam of its communication antenna.

Therefore, if, according to the communication tree as currently determined, it is necessary to perform the transmission of data from several transmitters in a single time slot, then checking whether they are capable of performing beamforming with their antenna, allows detecting situations in which there is a high risk of interferences, and making appropriate decisions about the communication tree. Narrow beam antenna settings would allow simultaneous transmissions. The interference risks are limited, as the coverage of the transmission antenna radiation is limited to reach desired destinations. Else, a reconfiguration of the communication tree as currently determined is required.

For instance, such a reconfiguration consists in replacing at least one transmission path by one or more other transmission paths, with less capacity, but that would allow containing (or controlling) the data transmission latency.

Advantageously, in case of a negative result of the first checking step, the method further comprises: -a third checking step of checking if the wireless node corresponding to an end of said vectors is capable of controlling the form of the beam of its communication antenna.

Therefore, if, according to the communication tree as currently determined, it is necessary to perform the transmission of data from several transmitters in a single time slot, then checking whether the receivers are capable of performing beamforming with their antenna, allows detecting situations in which there is a high risk of interferences, and making appropriate decisions about the communication tree. Narrow beam antenna settings would allow focusing on a single reception, whereas several transmissions might be active. The interference risks are limited, as the coverage of the reception antenna radiation is limited to receive from a desired source. Else, a reconfiguration of the communication tree as currently determined is required.

Advantageously, in case either at least one end and/or at least one origin of said vectors is not capable of controlling the form of the beam of its communication antenna, the method further comprises a step of relaxing a time constraint on the whole or a part of at least one of the transmission paths selected.

When a reconfiguration of the communication tree is required, relaxing the time constraint allows maintaining the quality of the signal at destination, in the scope of the data transmission.

Advantageously, the first checking step further comprises checking if the vectors of the transmission paths selected which correspond to a same time slot and transmission paths of at least one already configured communication tree have a same vector origin, and in case of a positive result of the first checking step, the method further comprises a step of relaxing a time constraint on the whole or a part of at least one of the transmission paths selected.

Then multicast transmissions of several data contents can occur simultaneously throughout the network, targeting contained transmission latency for the transmission of each one of said data contents, while limiting the risk of interferences.

According to a second aspect, in at least one embodiment, the invention relates to a device for configuring wireless nodes interconnected by links in a wireless network in the scope of a data transmission from a source node to a plurality of destination nodes, each node comprising a communication antenna. The device comprises: -means for determining transmission paths from said source node to said plurality of destination nodes, on the basis of a transmission capacity of said links; -means for determining a communication tree from the determined transmission paths, on the basis of respective capabilities of said wireless nodes to control a form of a beam of their respective communication antennas; -means for configuring the wireless nodes for setting up, for said data transmission, the communication tree determined.

According to a third aspect, in at least one embodiment, the invention relates to a computer program product comprising instructions for implementing the abovementioned method (in any one of its various embodiments), when said program is run on a computer.

According to a fourth aspect, the present invention also proposes an information storage means, storing a computer program comprising a set of instructions that can be run by a computer to implement the abovementioned method (in any one of its various embodiments), when the stored information is read by the computer. In an embodiment, this storage means is totally removable.

Since the particular features and benefits of this device, of this computer program product and of this information storage means, are similar to those of the corresponding configuring method, they are not repeated here.

5. LIST OF FIGURES Other features and benefits of the invention will become more apparent from the following illustrative and non-limiting description, illustrated by the appended drawings, in which: -Figure 1 schematically illustrates a configuration of a wireless communication device; -Figure 2 schematically illustrates a smart antenna, as implemented in the communication device of Figure 1; -Figure 3 schematically illustrates a medium access controller, as implemented in the communication device of Figure 1; -Figure 4 schematically illustrates a format of data packet, as exchanged by the communication device of Figure 1; -Figure 5 schematically illustrates a communication network comprising communication devices, according to one embodiment of the present invention; -Figure 6 schematically illustrates a flow diagram and message exchanges according to a protocol, according to an embodiment of the present invention; -Figure 7 represents a flow diagram of an algorithm for determining the capacity of network links, according to one embodiment of the present invention; -Figure 8 is a trellis diagram corresponding to the communication network of Figure 5; -Figure 9 represents a flow diagram of an algorithm for determining and configuring a communication tree, according to one embodiment of the present invention.

6. DETAILED DESCRIPTION

The method and the device according to the invention are more fully described hereinafter in the context of an implementation of a 60 GHz transmission system. However, the application of the present invention is by no means limited to this implementation scenario. Indeed, the present invention applies generally to wireless communication systems, in which the form of the antenna beams can be controlled.

Figure 1 schematically illustrates a configuration of a wireless communication device.

A communication device 100, as used in at least one embodiment of the present invention and adapted to perform wireless communications, comprises: -a Random Access Memory (denoted RAM) 120, whose capacity can be extended by an additional Random Access Memory connected to an expansion port (not shown in Figure 1); -a Read-Only Memory (denoted ROM) 130; -a micro-controller or Control Process Unit (denoted CPU) 110; and -a wireless communication interface 140, enabling communications with other wireless communication devices of a network.

CPU 110, RAM 120, ROM 130 and the wireless communication interface 140 exchange data and control information via a communication bus 160.

The communication device 100 can either be a transmitter device, a receiver device or both.

CPU 110 is capable of executing instructions loaded from ROM 130 into RAM 120. After the communication device 100 has been powered on, CPU 110 is capable of executing, from RAM 120, instructions pertaining to a computer program, once these instructions have been loaded from ROM 130 or from an external memory (not shown in figure 1). A computer program of this kind causes the CPU 110 to execute some or all of the steps of the algorithms described hereinafter in relation to Figures 6, 7, 8 and 9.

CPU 110 controls the overall operation of the communication device 100.

CPU 110 acts as a data analyzer unit, which analyses useful data payload (also referred to as MAC payload) of a packet received from another communication device, once processed by the wireless communication interface 140.

ROM 130 further contains look-up tables (denoted LUT) used in steps S840 and S860, detailed hereinafter in relation to Figure 7.

The wireless communication interface 140 further comprises: -an RF module (denoted RF) 230; -a baseband processor (denoted BBP) 220; -a medium access controller (denoted MAC) 210; -an antenna controller 250; and -a smart antenna 240; The RF module 230 is responsible for processing a signal output by the baseband processor 220 before it is sent out by means of the smart antenna 240. For example, the processing can be done by frequency transposition and power amplification processes. Conversely, the RF module 230 is also responsible for processing a signal received by the smart antenna 240 before it is provided to the baseband processor 220.

The baseband processor 220 is responsible for modulating and demodulating the digital data exchanged with the RF module 230. For instance the modulation and demodulation scheme applied by the baseband processor 220 is of Orthogonal Frequency-Division Multiplexing (OFDM) type.

MAC 210 manages the accesses to the wireless medium. MAC 110 also acts as a synchronization control unit, which controls synchronization relatively to a superframe, scheduling the transmissions via the network. It means that MAC 210 schedules the beginning and the end of a transmission of data in the network by the smart antenna 240, as well as the beginning and the end of a reception of data from the network by the smart antenna 240. MAC 210 also manages input data required to determined the antenna parameters provided by the antenna controller 250 for configuring the smart antenna 240.

The smart antenna 240 allows controlling the form of a beam (in transmission and/or in reception) by phase adjustments of signals in array antennas (also referred as agile antennas), such as addressed in the international patent application published with the reference WO 2009/022562.

Greater gain is therefore obtained compared to omnidirectional (isotropic) or quasi-omnidirectional antennas. The smart antenna 240 is further detailed in relation to Figure 2.

Figure 2 schematically illustrates a smart antenna, as implemented in the communication device 100.

The srriart antenna 240 corriprises a network (array) of radiating elerrients or elementary antennas 311, 312, 313, distributed on a given support.

The smart antenna 240 shown in figure 2 comprises only three radiating elements. The number of radiating elements represented is deliberately limited so as to simplify the figure and the associated description. In order to obtain narrow beams (of the order of a few degrees), a greater number of radiating elements is necessary.

Each one of the signals transmitted or received via these radiating elements 311, 312, 313, is controlled in phase and/or in power, thanks to the phase shifters and/or amplifiers 301, 302, 303.

When the communication device 100 is configured in transmission mode, the RF module 230 provides to the smart antenna 240 an RF data signal 235, which is then provided to all the phase shifters and/or power amplifiers 301, 302, 303. The radiating element 311 (respectively 312, 313) sends the RF data signal that has been phase-shifted and/or amplified by the phase shifter and/or amplifier 301 (respectively 302, 303).

When the communication device 100 is configured in reception mode, the RF signals received by the radiating element 311 (respectively 312, 313), are phase-shifted and/or amplified by the phase shifter and/or amplifier 301 (respectively 302, 303). The signals output by the phase shifters and/or amplifiers 301, 302, 303, are then summed together in order to form an RF signal 235, which is further provided to the RF module 230.

The smart antenna 240 is controlled via the control signal 255. For instance, the control signal 255 comprises information relating to a set of complex coefficients Wi, W2, W3, to be respectively applied to the phase shifters and/or amplifiers 301, 302, 303. In reception mode, such a set of complex coefficients Wi, W2, W3, enables the reception of radio signals from one or more directions. This set of complex coefficients Wi, W2, W3, makes it possible, by acting on the sensitivity of the beam in reception, to attenuate the radio signal in undesired directions (reducing sensitivity) and to amplify it in the desired directions (increasing sensitivity). Identically, in transmission mode, such a set of complex coefficients Wi, W2, W3, enables the transmission of radio signals in one or more desired directions.

Therefore, the implementation of the smart antenna 240 is achieved by means of a correspondence table allowing, for a given set of transmission or reception angles, to obtain a set of corresponding antenna parameters (phase and/or power) to apply to the signals input or output at the various radiating elements 301, 302, 303.

In order to obtain a set of antenna parameters allowing to set up a communication from a source device to at least one destination device, a test phase can be used in which the each device performs a scan with its wireless communication interface 240 in reception mode configured to form a narrow beam. Such a technique is referred as beamsteering and the orientation angle in reception can be varied, until a radio signal is received from a transmitter device. Then this orientation angle is stored and can be used as orientation angle for transmitting radio data.

Determining the set of antenna parameters can otherwise be performed by applying predefined configurations of respective different sets of antenna parameters and by identifying one configuration (among these) allowing a transmission with a quality level above a predetermined threshold.

As an illustrative example, the predefined configurations can correspond to orientation angles spaced apart by intervals of 5 degrees, in an angular range between 0 and 180 degrees. The orientation angles are in that case defined according to a reference axis of the communication device 100.

Figure 3 schematically illustrates one example of the constitution of the medium access controller 210.

MAC 210 comprises in this example the following sub-modules: -a medium access manager 1210; -a link capacity manager 1220; -a path searcher 1230; -a tree searcher 1240; and -an antenna capability manager 1250.

The medium access manager 1210 is responsible for interfacing MAC 210 with the communication bus 160, with the antenna controller 250 and with the baseband processor 220. The medium access manager 1210 is also responsible for performing the interface between the link capacity manager 1220, the path searcher 1230, the tree searcher 1240 and the antenna capability manager 1250. The link capacity manager 1220, the path searcher 1230, the tree searcher 1240 and the antenna capability manager 1250 access RAM 120 via the medium access manager 1210 and the communication bus 160.

The medium access manager 1210 is further responsible for managing the accesses to the network by the communication device 100. It controls synchronization relative to the superframe and ensures the scheduling of the transmissions via the network.

The medium access manager 1210 in addition analyses the packet data received from the network via baseband processor 220. If the MAC payload of the received data packet comprises link quality information (denoted LQI), this link quality information is provided to the link capacity manager 1220. If the MAC payload of the received data packet comprises antenna capability information (denoted Aol), this antenna capability information is provided to the antenna capability manager 1250. LQI and AOl are stored in RAM 120.

The link capacity manager 1220 performs a step S720, detailed hereinafter in relation to Figure 6, of determining a capacity of the network links by analysis of LQI stored in RAM 120. The capacity of the network links is stored in RAM 120.

The path searcher 1230 performs a step S730, detailed hereinafter in relation to Figure 6, of determining path vectors in the network on the basis of the capacity of the network links determined by the link capacity manager 1220.

The path vectors are stored in RAM 120.

The tree searcher 1240 performs a step S740, detailed hereinafter in relation to Figure 6, of determining a communication tree applicable to the network on the basis of the path vectors determined by the path searcher 1230.

The tree representation is stored in RAM 120. The tree representation is used by the medium access manager 1210 in order to control access to the medium.

The medium access manager 1210 is further responsible for providing the tree representation to the other communication devices in the network.

The antenna capability manager 1240 associates the antenna-related information, collected by means of the data packet exchanges with the communication device 100 with identifiers (denoted ID). The identifiers and the antenna-related information are stored in RAM 120.

Figure 4 schematically illustrates a format of data packet, as exchanged by the communication device 100.

The data packet (also referred as frame) 500 is divided into three parts (in the order of transmission): -a PHY header 522; -a MAC header 523; -the MAC payload 521.

The PHY header 522 is a portion of the data packet 500 that is generated (at a source device side) and treated (at a destination device side) at the baseband processor 220.

The MAC header 523 is a portion of the data packet 500 that is generated (at the source device side) and treated (at the destination device side) at MAC 210.

The PHY header 522 comprises: -a preamble 501, which is used for detecting the transmission of the data packet 500 at the destination device side; the preamble 501 furthermore enables the destination device to estimate the parameters necessary to be synchronized with the source device and to adjust reception parameters, such as Automatic Gain Control (denoted AGC) or coarse and fine frequency estimations.

-a PHY rate field 502, which indicates a physical layer speed that is used for transmitting the data packet 500; -a length field 503, which indicates the length of the data packet 500.

The MAC header 523 comprises: -a frame control field 511, which indicates a data packet type; the packet type can for instance be: beacon, a request to send (denoted RTS), a clear to send (denoted CTS), an acknowledge (denoted ACK). Each packet type defined according to the transmission protocol applicable in the network has a predefined identifier, which is then stored in the control

field 511;

-a source address field 512, which indicates the identifier (ID) of the source device of the data packet 500; -a destination address field 513, which indicates the identifier (ID) of the destination device.

The MAC payload contains, according to the packet type indicated in the frame control field 511, application data (video data, audio data, file transfer data...), link quality information (LQI), antenna capability information (ACI), tree representation...

Figure 5 schematically illustrates a communication network comprising communication devices, according to an embodiment of the present invention.

The communication network 450 comprises communication devices 401, 402, 403, 404. The communication devices 401, 402, 403, 404 are similar to the communication device 100, described in relation to Figure 1. However, one or more communication devices among the communication devices 401, 402, 403, 404 can have a non-programmable antenna. Each such communication device uses an isotropic antenna, at least designed to send and receive radio data in a predefined and non-programmable angular sector (quasi-omnidirectionnal antenna) greater than 90 degrees and for instance equal to 180 degrees.

The communication network 450 comprises a number K (among which only five are represented so as to simplify the figure) of communication devices.

The communication devices are also referred as nodes N1... NK especially with regard to the trellis representation of Figure 8. The communication devices are interconnected by links 451, 452, 453, 454, 455, 456, 457, 458, 459 and 460.

Each link has a capacity, denoted Cxy, X indicating the origin of the link and Y indicating the end of the link (in one given direction). For instance, C12 represents the capacity of the link from the communication device Ni to the communication device N2.

The capacity of the links is derived from (can be equal to) link quality information (LQI) exchanged in between the communication devices in the step S720 described hereinafter in relation to Figure 6. LQI is for instance a bit error rate, a received signal strength indicator (RSSI) or an effective transfer rate after error correction as obtained by a destination device when a predetermined signal is transmitted by a source device.

The capacity of the links can be stored in a two-dimensional table, itself stored in RAM 120, having as a first dimension (index) the identifier of the communication device being the origin of the link and as a second dimension (index) the identifier of the communication device being the end of the link.

It should be noticed that the capacity C is null, as there is no link between a communication device and itself.

In a particular embodiment, in order to speed up the filling of the aforementioned two-dimensional table containing the capacity of the links, it can be considered that the capacity Cxy equals the capacity Cyx.

Figure 6 schematically illustrates a flow diagram and message exchanges according to a protocol, in an embodiment of the present invention.

Any step of the algorithm shown in Figure 6 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").

Figure 6 illustrates message exchanges between the communication devices Nl...NK (among which only three are represented so as to simplify the figure) introduced in Figure 5.

It is supposed that the communication device N1 401 is responsible for configuring the network, in order to make the communication devices of the network adapted for the transmission of a given data content from a source device to a set of destination devices (devices that can effectively be the final destinations of the given data content (video renderer, audio speaker, addressee of a file transfer...) or simply relay devices, which allow increasing the range of the network or increasing the spatial diversity of the transmission).

The communication device N1 401 is called in this context a "manager device" or a "manager (network) node".

In a step S710, the communication device N1 401 requests the K-I other communication devices to provide LQI and AOl. AOl corresponds to predefined information stored in the communication device 402-405, for instance in ROM when the communication device 402-405 has been manufactured, and which indicates whether the communication device 402-405 has a programmable or a non-programmable antenna.

In a first embodiment, the step S710 can take place in a network initialization phase during which an RTS / CTS protocol type is used. The principle of an RTS / CTS protocol type is that a communication device wishing to send data initiates the process by sending a Request-To-Send (RTS) message. The addressee replies with a Clear-To-Send (CTS) message. Any other communication device receiving the RTS and/or CTS messages should refrain from sending data for a given time. The amount of time this other communication device should wait before trying to get access to the medium is included in both the RTS and CTS messages. The RTS / CTS protocol does however assume that all the communication devices of the network have the same transmission range.

In a second embodiment, the step S710 can take place in a network initialization phase during which a time slot for a given number of transmission cycles is allocated (for instance according to a predefined mapping between time slots and communication device identifiers) to each communication device for transmitting its own data. Therefore, each communication device solely accesses the medium for transmitting LQI and AOl. In order to overcome transmission range issues, a relaying scheme can be put in place, so that communication devices receiving LQI and ACI from other communication devices forward them.

Once the communication device N1 401 has obtained LQI and ACI from each communicating device of the network, the step 720 is performed.

In the step S720, the communication device N1 401 determines the capacity of the network links from LQI obtained in the step S71 0. The step S720 is further detailed in relation to Figure 7. Then the step S730 is performed.

In the step S730, the communication device N1 401 determines paths from the source device toward the destination(s), and further determines the capacity of each path on the basis of the link capacities determined. The step S730 is further detailed in relation to Figure 8. Then the step S740 is performed.

In the step S740, the communication device N1 401 determines a communication tree applicable to the network for transmitting the given data content and determines an antenna configuration type (type of antenna directivity) to be applied for transmissions and receptions by the communication devices. The step S740 is further detailed in relation to Figure 9. Then a step S750 is performed.

In the step S750, the communication device N1 401 transmits, to the other communication devices of the network, the communication tree and configuration items determined in the step S740. The transmission of the tree representation can be achieved identically as the transmission of LQI and AOl in the step S710. The step S750 marks the end of the initialization phase.

Figure 7 represents a flow diagram of an algorithm for determining the capacity of the network links, according to one embodiment of the present invention.

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").

Figure 7 details the step S720. The algorithm starts in a step S810 by obtaining LQI associated to a given source device X and a given destination device Y. Then a step S820 is performed.

In the step S820, the communication device N1 401 determines whether LQI already corresponds to a link capacity Cxy or not. This situation occurs for instance when a transformation of RSSI into link capacity Cxy (as further detailed hereinafter in a step S840) or when a transformation of BER into link capacity Cxy (as further detailed hereinafter in a step S860) is performed by the communication devices N2402. ..NK405, before communicating LQI to the communication device N1 401. If LQI already corresponds to a link capacity Cxy, then a step S870 is performed; otherwise a step S830 is performed.

In the step S830, the communication device N1 401 determines whether LQI corresponds to RSSI or not. If LQI corresponds to RSSI, then a step S840 is performed; otherwise a step S850 is performed.

In the step S840, the communication device N1 401 transforms RSSI (as represented by LQI) into link capacity using a dedicated look-up table (LUT) stored in ROM 130. As RSSI represents a signal-to-noise ratio (denoted SNR) indication, a correspondence between link capacity and RSSI is defined by modeling the transmission channel as an additive white Gaussian noise channel. Then the step S870 is performed.

In the step S850, the communication device N1 401 determines whether LQI corresponds to BER or not. If LQI corresponds to BER, then a step S860 is performed; otherwise an error occurs and the process is aborted.

In the step S860, the communication device N1 401 transforms BER (as represented by LQI) into link capacity using a dedicated look-up table (LUT) stored in ROM 1 30. Similarly as for RSSI, a correspondence between link capacity and BER is defined by modeling the transmission channel as a binary symmetric channel (denoted BSC), or a binary erasure channel (denoted BEC).

Then the step S870 is performed.

In the step S870, the communication device N1 401 stores, in the two-dimensional table introduced in relation to Figure 5, the link capacity Cxy obtained in the preceding step. Then a step S880 is performed.

In the step S880, the communication device N1 401 determines whether the last pair (X,Y) of communication devices in the network has been processed. In other words, the communication device N1 401 determines whether the aforementioned two-dimensional table has been completely filled in. If all pairs have been processed, the process ends; otherwise the step S810 is reiterated with another pair (X,Y) of communication devices.

It should be noticed that the link capacity Cxy can also be determined by applying the transformations of the steps S840 and S860, and then combining the results according to a weighting ratio on each of them.

Figure 8 is a trellis diagram corresponding to the communication network 450. The trellis diagram of Figure 8 communication network 450 describes a number K (among which only three are represented so as to simplify the figure) of communication devices over a number of T = K-i instants (among which only four are represented).

In the step S730, the communication device N1 40i builds a trellis diagram to search paths from the source device toward the destination device(s).

A trellis is a graph in which the communication devices (also referred as nodes) are placed into vertical slices, each vertical slice representing an instant in time. In the trellis diagram, each node in a vertical slice (at a given instant) is connected to at least one node in a preceding vertical slice (at an earlier instant) and to at least one node in a following vertical slice (at a later instant). The first and last vertical slices (earliest and latest instants represented) are respectively connected to following and preceding vertical slices.

Considering Figure 8, the first vertical slice (instant t = 0) contains representation of the nodes 90i, 902, 905; the second vertical slice (instant t = 1) contains representation of the nodes 9ii, 9i2, 9i5; the third vertical slice (instant t = T-i) contains representation of the nodes 95i, 952, 955; and, the fourth vertical slice (instant t = T) contains representation of the nodes 96i, 962, 965.

It is considered in the example shown in Figure 8 that the source node is the communication device N1 40i. (0)

Other nodes are therefore ignored in the first vertical slice of the trellis.

The trellis is initialized, with the following condition: (i) C yç=C x!=s0 It means that, for a given link, when the end of the link matches the source node, the associated link capacity Cxy is null. This excludes trellis diagrams for which a loop exists, from the source node to the source node via at least one other node.

As also noted earlier, the capacity C is null, as there is no link between a communication device and itself.

The communication device N1 401 then initializes path metrics C) with the initial condition shown in the following set of equations: (2) O(Nk)k!=l= 0 A path metric represents, for a given path, the capacity of the given path (from a source node to a destination node). The path metric depends on the capacity of the links constituting the path, as well as the capacity of the nodes interconnected by the links constituting the path. For the sake of simplicity, it is considered hereinafter that the nodes have the necessary internal resources to handle the transmission of the given data content.

The trellis is parsed vertical slice after vertical slice and node after node in each vertical slice. At each node the path metric is updated. At the first vertical slice (instant t = 0), the path metrics are always null, (C) = 0), except for the source node. Indeed, the path metric at the source node is 1 (whatever the vertical slice considered), keeping the maximum value of the link capacity. At each node in the other vertical slices, the path metric is updated according to the following equation: (3) R () = nax{min{c 1 (Nk), Ck, 1}.

It means that considering a given node N1, at a given instant t, the path metric computed so far to reach each other node Nk (k=1. . . K) via a given sub-path is each one compared with the capacity Ckl of the link this node Nk (k=1. . . K) has with the node N1. The smallest value obtained for each comparison is kept and is then compared with the results obtained for the nodes Nk (k=1. . . K). The new path metric for the node N1 on the path is then the maximum value among the smallest values obtained for the nodes Nk (k=1 K).

For instance, if from a node N3 to the node N1 the capacity of the link 031 is smaller than the path metric 0t1(N3) computed in the previous instant t-1 for the node N3, then the capacity of the link C31 is kept and further compared with the smallest between the link capacity 021 and the path metric Q1(N2). The maximum among those two values is kept and then further compared with the smallest value between the link capacity 041 and the path metric Q1(N4). The maximum among those two values is kept and so on.

In effect, the capacity of a path is limited by the smallest capacity among the links constituting the path, and the path to be kept for a given node is the one having the highest capacity.

The operation ends once paths (preferably all paths) from the source node to the destination node(s) are obtained.

Each path is represented by a succession of vectors, each vector representing the use of a network link during one time unit (also referred as time slot) of the superirame. Indeed, in a preferred embodiment of the present invention, the superframe is divided into elementary time elements, called time slots. In each such time slot, a radio data frame can be transmitted from a transmitter node N to a receiver node N1.

The path is further expressed with regard to a reference time tk, as the path is a succession of links used in a corresponding succession of time slots, starting from a given reference instant.

The path can therefore be expressed as shown in the following equation: (4) Pk,tk = [ Vktk+2,"] where:

____________

(5) Vk,t = Figure 9 represents a flow diagram of an algorithm for determining and configuring a communication tree, according to one embodiment of the present invention.

Any step of the algorithm shown in Figure 9 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").

Figure 9 details the step S740. The algorithm starts in a step Si 01 0. In the step SlOb, the communication device N1 401 selects a reference time tk in the superirame to be associated to the origin of the selected paths. All the selected paths are thus starting from the same instant.

At the first occurrence of the step Si 010, tk is set to 0. The value of tk can be adapted to a different reference time for each path, or portion of path, in a step Si 070 (described hereinafter) for a further occurrence of the step Si 010.

The communication device N1 401 then determines a communication tree in the network, by the union of paths as shown in equation (4). One path for each destination node is selected in order to form the communication tree. The path selected for a given destination node is the path having the highest capacity among the paths obtained (as explained in relation with Figure 8) for this destination node. Then a step Si 020 is performed.

In the step Si 020, the communication device N1 401 compares the origin of all the vectors of the communication tree for a given time slot [t-i,t], t varying from t1 to tK (move to the next time slot is performed in a step Si 090). If, in the considered time slot, the vectors have a different origin, a step Si 030 is performed, else a step Si 040 is performed.

In another embodiment, a plurality of data contents is transmitted in the network. The communication device N1 401 is therefore in charge of defining communication trees (at least one per data content) allowing the transmission in good conditions of the data contents. Therefore, when performing the step Si 020, the communication device N1 401 compares the origin of all the vectors of the communication trees (the one considered and the one(s) already configured) for the given time slot [t-i,t]. The communication device N1 401 furthermore pays attention that a given communication node cannot send two contents in the same given time slot [t-1,t]. In case such a situation occurs, the communication device N1 401 relaxes (as performed in the step Si 070) a time constraint on the whole or a part of at least one of the transmission paths.

In the step Si 040, the current configuration of the communication tree for the considered time slot is kept (stored in RAM 1 20). The configuration of the communication devices, one being identified as the transmitter node and at least one being identified as the receiver node according to the vector(s) associated with the time slot considered, is of a wide beam type (isotropic, omnidirectional or quasi-omnidirectional antenna). Then a step S1080 is performed.

In the step 1030, the communication device N1 401 checks whether all the communication devices, identified as the transmitter nodes according to the vectors associated with the time slot considered, are capable of achieving a narrow beam antenna (thanks to AOl, as obtained in the step S710). If the communication devices have this capability, a step Si 050 is performed, else the step Si 070 is performed.

In the step Si 050, all the transmitters can achieve a narrow beam antenna and thus limit interference risks. The communication device N1 401 then checks whether all the communication devices, identified as receiver nodes according to the vectors associated with the time slot considered, are capable of achieving a narrow beam antenna (thanks to Ad, as obtained in the step S7i0). If the communication devices have this capability, a step Si060 is performed, else the step Si 070 is performed.

In the step Si 060, the communication device N1 401 the communication tree of the current configuration for the considered time slot is kept (stored in RAM 120). The configuration of the communication devices, identified as transmitter or receiver nodes according to the vectors associated with the time slot considered, is of narrow beam type (smart antenna). Then a step Si 080 is performed.

In the step 1080, the communication device N1 401 checks whether the last time slot has been considered. If the last time has been considered, the algorithm ends. Else, a step S1090 is performed, in which the algorithm moves to the next time slot and then the step Si 020 is reiterated.

In the step S 1070, either one of the communication devices identified as transmitters and/or one of the communication device identified as receivers is not capable of achieving a narrow beam antenna. This might cause interferences in the network communications. It is therefore needed to find another communication tree configuration.

The communication device N1 401 therefore relaxes the time constraint.

Relaxing the time constraint means postponing by at least one time slot the transmission of the data content to at least one receiver.

If the algorithm reached the step S1070 from the step S1030, the time constraint has to be relaxed for the concerned communication device(s) identified as transmitter(s) (the one(s) not capable of achieving narrow beam).

At least one extra time slot is provided for the transmission I relay of the given data content by said communication device(s) identified as transmitter(s).

Therefore tk is increased by one unit for the concerned vector(s), meaning that the concerned vectors are shifted by one time slot. Then the step Si 010 is reiterated in order to obtain a new configuration of the communication tree.

If the algorithm reached the step S1070 from the step S1050, the time constraint for the concerned communication device(s) identified as receiver(s) (the one(s) not capable of achieving narrow beam) has to be relaxed. At least one extra time slot is allowed for the transmission / relay of the given data content to said communication device(s) identified as receiver(s). Therefore tk is increased by one unit for the concerned vector(s), meaning that the concerned vectors are shifted by one time slot. In a variant, the time constraint is relaxed for all the vector(s) starting from this transmitter node in the considered time slot, meaning that the concerned vectors are shifted by one time slot. Then the step SiOlO is reiterated in order to obtain a new configuration of the communication tree.

In another embodiment, the communication tree as currently defined can be reconfigured by replacing at least one transmission path by one or more other transmission path(s) (that has(have) been excluded in the first occurrence of the step Si 010), with less capacity, but that would allow containing (or controlling) the data transmission latency, instead of maintaining the level of quality at reception.

Claims

CLAIMS1. A method for configuring wireless nodes interconnected by links in a wireless network to enable transmission of data from a source node to a plurality of destination nodes, each node comprising a communication antenna, characterized in that a manager node performs the steps of: -determining transmission paths from said source node to said plurality of destination nodes, on the basis of a transmission capacity of said links; -determining a communication tree from the determined transmission paths, on the basis of respective capabilities of said wireless nodes to control a form of a beam of their respective communication antennas; -configuring the wireless nodes for setting up, for said data transmission, the communication tree determined.
2. The method according to Claim 1, characterized in that the transmission capacity of a given link is determined on the basis of information about an error rate and/or a signal-to-noise ratio over said given link.
3. The method according to any one of Claims 1 to 2, characterized in that a transmission capacity is determined for each transmission path determined, on the basis of a transmission capacity of said links constituting said transmission path, and in that, among transmission paths from the source node to one destination node, the one with the highest capacity is selected for forming the communication tree.
4. The method according to any one of Claims 1 to 3, characterized in that the step of determining a communication tree further comprises a step of associating the origin of each transmission path selected to a same reference starting instant in a transmission cycle.
5. The method according to any of Claims 1 to 4, characterized in that the step of determining transmission paths comprises a step of determining for each one of said transmission paths a set of successive vectors, each vector representing one of said links used by the path during a given time slot.
6. The method according to Claim 5, characterized in that the step of determining a communication tree further comprises the steps of: -a first checking step of checking if the vectors of the transmission paths selected which correspond to a same time slot have a same vector origin; -in case of a negative result of the first checking step, a second checking step of checking if the wireless node corresponding to said vector origin is capable of controlling the form of the beam of its communication antenna.
7. The method according to Claim 6, characterized in that, in case of a negative result of the first checking step, it further comprises: -a third checking step of checking if the wireless node corresponding to an end of said vectors is capable of controlling the form of the beam of its communication antenna.
8. The method according to any one of Claims 6 and 7, characterized in that, in case either at least one end and/or at least one origin of said vectors is not capable of controlling the form of the beam of its communication antenna, it further comprises a step of relaxing a time constraint on the whole or a part of at least one of the transmission paths selected.
9. The method according to any one of Claims 6 to 8, characterized in that the first checking step further comprises checking if the vectors of the transmission paths selected which correspond to a same time slot and transmission paths of at least one already configured communication tree have a same vector origin, and in case of a positive result of the first checking step, it further comprises a step of relaxing a time constraint on the whole or a part of at least one of the transmission paths selected.
10. Computer program product, characterized in that it comprises program code instructions for implementing the method according to at least one of Claims 1 to 9, when said program is run on a computer.
11. Computer-readable storage means, storing a computer program comprising a set of instructions that can be run by a computer to implement the transmission method according to at least one of Claims 1 to 9.
12. A device for configuring wireless nodes interconnected by links in a wireless network to enable transmission of data from a source node to a plurality of destination nodes, each node comprising a communication antenna, characterized in that it comprises: -means for determining transmission paths from said source node to said plurality of destination nodes, on the basis of a transmission capacity of said links; -means for determining a communication tree from the determined transmission paths, on the basis of respective capabilities of said wireless nodes to control a form of a beam of their respective communication antennas; -means for configuring the wireless nodes for setting up, for said data transmission, the communication tree determined.
13. A method, program or device for configuring wireless nodes substantially as hereinbefore described with reference to the accompanying drawings.