GB2492093A

GB2492093A - Selecting pairs of receivers, to be used for reception diversity, on the basis of the relative arrival times of a signal

Info

Publication number: GB2492093A
Application number: GB201110440A
Authority: GB
Inventors: Norihito Aoki; Brice Le Houerou
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 2011-06-21
Filing date: 2011-06-21
Publication date: 2012-12-26
Anticipated expiration: 2031-06-21
Also published as: GB2492093B; GB201110440D0

Abstract

The present invention relates to a method of configuring wireless communications between a transmitting node 110 and a plurality of receivers (121, 122), while taking into account possible obstruction of at least one propagation path between the transmitting node and a receiver by an obstacle (140). More particularly, the invention lies in forming pairs of receiving nodes (121/122, 122/124) and determining which pairs meet a predetermined criterion of path diversity for the propagation paths between the transmitting node and the two receiving nodes of each pair. Those which meet the criterion (S804-S806, Fig. 8) are selected to take part in a communication using reception diversity. The determination step involves transmitting a signal from the transmitter, receiving this at each receiver of the pair and comparing the times of arrival (ToA). The arrival times provide an indication of the angular separation between the receivers of a pair. The receivers are preferably distributed physical layers and may be housed together in a single wireless reception device (340â , Fig. 5).

Description

Method and system for configuring wireless communications and corresponding computer program product and storage means

FIELD OF THE iNVENTION

The present invention relates to a method and system for configuring wireless communications in a network.

TECHNOLQGICAL BACKGROUND

Recently 60 0Hz wireless communication attracts more attention because unlicensed band around this frequency is broad enough to transmit a vast amount of data at rates in the order of several gigabits per second.

However, wireless communication in this frequency range is subject to interferences to quite a large extent. For instance, communications around 60 0Hz are easily disturbed by an unexpected obstacle because of the strong directivity of the waves. This phenomenon is called "shadowing". For instance, US patent No. 7,164,932 deals with this issue.

The shadowing effect can lead to degradation of the quality of data received at the destination node, or even a loss of data.

Path diversity can attenuate the effect of shadowing by having several receivers receiving the same data and selecting one of these receivers which has the correctly received data.

For high bandwidth transmission it is preferable that a receiving node is disposed in a direct transmission path (also referred to as line-of-sight or LOS path) with a transmitting node. However, this LOS arrangement does not prevent an unexpected moving obstacle from occupying a position located on the LOS path and, therefore, altering data transmission.

US patent No. 7,554,451 proposes a method of obtaining path diversity. However, if two LOS paths are close to each other, an obstacle can easily disturb both paths if the frequency transmission is around the 60 0Hz range.

SUMMARY OF THEINVENTION

With the foregoing in mind, the invention proposes a method of configuring wireless communications between a transmitting node and a plurality of receiving nodes while taking into account possible obstruction of at least one propagation path between the transmitting node and a receiving node by an obstacle therebetween, comprising: -transmitting a signal from the transmitting node to the plurality of receiving nodes; -obtaining the time of arrival of the same signal at each receiving node; -forming pairs of receiving nodes from the plurality of receiving nodes; -checking, at least on the basis of the obtained time of arrival of the signal at each receiving node of each pair thus formed, whether at least some of the pairs of receiving nodes thus formed meet a predetermined criterion of path diversity for the propagation paths between the transmitting node and the two receiving nodes of each pair; -configuring wireless communications, in accordance with the result of the checking, by deciding as to selecting or not selecting pairs of receiving nodes for being authorized to take part to subsequent wireless communications between the transmitting node and these pairs of receiving nodes.

The method according to the invention makes it possible to rapidly and easily take a decision as to the meeting of a predetermined path diversity criterion by a pair of receiving nodes on the basis of the time of arrival of the signal at each receiving node of a pair.

Thanks to this criterion it is thus possible to determine the pair or pairs of receiving nodes which have not enough separation angle between the antenna beams when viewed from the transmitting node.

Consequently, the pair or pairs of receiving nodes which do not meet the above criterion can be quickly identified and put aside, i.e. they will not be selected as pairs authorized to take part to subsequent wireless communications with the transmitting node when configuring wireless communications within the network.

More particularly, they will be made unoperable to receive subsequent signals. For instance, the unselected pairs, in particular, their receiving circuit(s), will be deactivated.

Path diversity in the network will therefore be improved since lower error rate will be achieved on the receiving side (at the plurality of receiving nodes).

According to one possible feature, the predetermined criterion of path diversity is not met if the respective propagation paths between the transmitting node and the two receiving nodes of a pair extend along two directions that are at a small angle to each other so that these propagation paths may simultaneously be obstructed by an obstacle therebetween.

A too small antenna separation angle between the two propagation paths or links extending between the transmitting node and each respective receiving node of each pair does not provide path diversity.

Put it another way, such a small angle means that when an unexpected obstacle obstructs the propagation path between the transmitting node and a receiving node of a pair the probability that the obstacle also obstructs the other adjacent propagation path between the transmitting node and the other receiving node of the pair is high.

According to one possible feature, the checking is more particularly based on comparing the difference in the times of arrival of the signal respectively at the two receiving nodes of said pair of receiving nodes to the value of the distance between the two receiving nodes divided by the transmission speed of the signal.

In case Litij = Dij/c, the two receiving nodes of a pair are substantially aligned with the transmitting node and the separation angle is either null or small enough to prevent path diversity. Such a pair will therefore not be selected.

According to another possible feature, checking whether the predetermined criterion of path diversity is met by a pair of receiving nodes comprises at least comparing to each other the times of arrival of the signal at the two receiving nodes of said pair respectively.

When the times of arrival of the signal at the respective two nodes are different from each other, and Atij = Dij/c, it can be assumed that the path diversity criterion is met.

Conversely, when the times of arrival are equal or very close to each other and Atij = Dij/c, it cannot therefore be checked/determined whether the path diversity criterion is met or not. A further item of information will be necessary in this respect.

According to another possible feature, the method further comprises obtaining an item of information (RSSI) indicative of the distance between the transmitting node and each receiving node of each pair of receiving nodes.

For example, an appropriate item of information may be a received signal strength indication (RSSI), which corresponds to the strength of the received signal.

The more the signal strength, the shorter the distance between the transmitting node and the node receiving the signal.

Such an item of information may be obtained, e.g. by measurement, at each receiving node of each pair.

It is assumed that the strength of the signal at the transmitting node as well as the emission gain and the reception gain remain unchanged so that the relative distance between the transmitting node and the two receiving nodes of a pair can be assessed. For example, it can be assessed that a receiving node of a pair is closer to the transmitting node than the other receiving node.

According to still another possible feature, checking whether the predetermined criterion of path diversity is met by at least some of the pairs of receiving nodes is also based on the item of information obtained for each receiving node of each pair.

Thanks to this additional parameter (item of information), the method makes it possible to quickly determine in some cases whether the path diversity criterion is met or not by a pair of receiving nodes.

Thus, a pair of receiving nodes for which the transmitting node is at equal distance from the two receiving nodes and the obtained items of information (RSSIs) are indicative of weak signals is determined as not meeting the predetermined criterion of path diversity. Weak signals are to be understood as signals whose strength (obtained item of information) is less than a predetermined threshold.

This is because weak signals are indicative of a relatively great distance between the transmitting node and the two receiving nodes of the pair and, therefore, of a too small antenna separation angle.

Conversely, a pair of receiving nodes for which the transmitting node is at equal distance from the two receiving nodes and the obtained items of information (RSSI5) are indicative of strong signals is determined as meeting the predetermined criterion of path diversity. Strong signals are to be understood as signals whose strength (obtained item of information) is greater than the above predetermined threshold.

This is because strong signals are indicative of a relatively short distance between the transmitting node and the two receiving nodes and, therefore, of a sufficient great antenna separation angle in order to overcome path obstruction.

Thanks to the checking operation, one or several pairs from all the pairs may be selected or not as meeting the path diversity criterion and, therefore, kept or not when configuring wireless communications between the transmitting node and the plurality of receiving nodes.

According to a variant embodiment, at least one other transmitting node may be used in the method according to the invention.

Thus, the process of selecting or not selecting pairs of receiving nodes may be based on several transmitting nodes implementing the method sequentially.

By way of example, if a pair of receiving nodes is selected with respect to one transmitting node then it may no longer be necessary that the other transmitting node(s) implements the method since the first transmitting node will be chosen. Also, if no pair of receiving nodes is selected with respect to the first transmitting node, another transmitting node will implement the method.

Alternatively, the method is sequentially implemented by all the transmitting nodes and one of them will be chosen after comparing their respective configuration results.

For instance, this may make it possible to select the transmitting node having the greatest number of pairs of receiving nodes that meet the path diversity criterion or, alternatively, not to select the transmitting node having the greatest number of pairs that do not meet the path diversity criterion.

According to another variant embodiment, the transmitting node may move. Thus, if after implementing the method the results are not satisfactory enough, the transmitting node may change its position and the method will be implemented again with the transmitting node in its new position.

Unsatisfactory results may be obtained if no pair of receiving nodes is selected (as meeting the diversity criterion) or if an insufficient number of pairs is selected.

ln one embodiment, the receiving nodes are connected to a central node, e.g. through wired connections.

This central node (e. g. a sink receiver) may perform at least some of the method operations and, where applicable, may obtain by calculation the difference in the times of arrival of the signal at the respective nodes of each pair.

According to a second aspect, the invention concerns a method of configuring wireless communications between a transmitting node and a plurality of receiving nodes while taking into account possible obstruction of at least one propagation path between the transmitting node and a receiving node by an obstacle therebetween, pairs of receiving nodes being formed from the plurality of receiving nodes, the method comprising: -checking whether at least some of the pairs of receiving nodes meet a predetermined criterion of path diversity for the propagation paths between the transmitting node and the two receiving nodes of each pair, said checking being made for each pair of receiving nodes at least on the basis of the time of arrival at each receiving node of the same signal sent by the transmitting node to the plurality of receiving nodes, -configuring wireless communications, in accordance with the result of said checking, by deciding as to selecting or not selecting pairs of receiving nodes for being authorized to take part to subsequent wireless communications between the transmitting node and these pairs of receiving nodes.

This method may be operated in an entity that is separate from the transmitting node and may be distinct or not from the receiving nodes. For instance, this method may be implemented by an RX MAC ("Medium Access Controlle?') connected to a plurality of distributed physical layers.

According to other possible features taken alone or in combination: -prior to said checking, the above method comprises receiving from the plurality of receiving nodes the time of arrival of the signal at each receiving node of the plurality of receiving nodes.

-for each pair of receiving nodes, said checking is more particularly based on the difference in the times of arrival of the signal respectively at the two receiving nodes of said pair of receiving nodes.

-prior to said checking, the above method comprises obtaining, for each pair of receiving nodes, the differences in the times of arrival of the signal at the two receiving nodes of said pair of receiving nodes.

-for each pair of receiving nodes, said checking is also based on an item of information (RSSI) indicative of the distance between the transmitting node and each receiving node of said pair of receiving nodes.

-said item of information is indicative of the strength of the signal received by each receiving node.

-prior to said checking, the above method comprises receiving said item of information from each receiving node of the plurality of receiving nodes.

-the method comprises sending deactivating requests to the receiving nodes of the pairs of receiving nodes which have not been selected when configuring wireless communications so that said receiving nodes can be no longer operable to receive any signal.

According to a third aspect, the invention also concerns a system for configuring wireless communications between a transmitting node and a plurality of receiving nodes while taking into account possible obstruction of at least one propagation path between the transmitting node and a receiving node by an obstacle therebetween, comprising: -means for transmitting a signal from the transmitting node to the plurality of receiving nodes; -means for obtaining the time of arrival of the same signal at each receiving node; -means for forming pairs of receiving nodes from the plurality of receiving nodes; -means for checking, at least on the basis of the obtained time of arrival of the signal at each receiving node of each pair thus formed, whether at least some of the pairs of receiving nodes thus formed meet a predetermined criterion of path diversity for the propagation paths between the transmitting node and the two receiving nodes of each pair; -means for configuring wireless communications, in accordance with the result of the checking, by deciding as to selecting or not selecting pairs of receiving nodes for being authorized to take part to subsequent wireless communications between the transmitting node and these pairs of receiving nodes.

According to a fourth aspect, the invention further concerns a device for configuring wireless communications between a transmitting node and a plurality of receiving nodes while taking into account possible obstruction of at least one propagation path between the transmitting node and a receiving node by an obstacle therebetween, pairs of receiving nodes being formed from the plurality of receiving nodes, the device comprising: -means for checking whether at least some of the pairs of receiving nodes meet a predetermined criterion of path diversity for the propagation paths between the transmitting node and the two receiving nodes of each pair, said checking being made for each pair of receiving nodes at least on the basis of the time of arrival at each receiving node of the same signal sent by the transmitting node to the plurality of receiving nodes, -means for configuring wireless communications, in accordance with the result of said checking, by deciding as to selecting or not selecting pairs of receiving nodes for being authorized to take part to subsequent wireless communications between the transmitting node and these pairs of receiving nodes.

According to a fifth aspect, the invention relates to a computer program product comprising instructions for implementing the above-mentioned method (in any one of its various embodiments), when said program is run on a computer.

According to a sixth 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 above-mentioned method (in any one of its various embodiments), when stored information is read by the computer. In an embodiment, this storage means is totally removable.

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

LIST OF DRAWiIiGS Other features and advantages of the invention will become more apparent from the following illustrative and non-limiting description, made with reference to the appended drawings, in which: -Figure 1 schematically illustrates a wireless communication network comprising wireless communication devices, according to one embodiment of the present invention; -Figure 2 schematically illustrates a packet format used in the wireless communication network; -Figure 3 schematically illustrates an architecture of a wireless communication device of Figure 1; -Figure 4 schematically illustrates a wireless communication module of a transmitting device; -Figure 5 schematically illustrates a wireless communication module of a receiving device; -Figure 6 schematically illustrates a timing diagram of a "de-skew" manager; -Figure 7 schematically illustrates a message exchange diagram in the wireless communication network of the present invention; -Figure 8 schematically illustrates an algorithm executed by an RX MAC module of the present invention.

-Figures 9a-d illustrate different possible configurations identified by the Figure 8 algorithm; -Figure 10 schematically illustrates an algorithm executed by an RX PHY module of the present invention.

pETAlLED DESCRIPTION

The invention will be more fully described hereinafter in the context of a 60GHz transmission system. However, the present invention is not limited to this implementation scenario. This is because the present invention generally applies to wireless communication systems.

Figure 1 schematically illustrates a communication network comprising communication devices or nodes which are operable to exchange information/data therebetween.

In a general manner, the network 100 comprises a transmitting node 110 (TX) which can be considered as a source node, operable to transmit signals, e.g. through an antenna or an antenna array, to a plurality (N) of destination or receiving nodes (RX PHYs) operable to receive the signals. It is to be noted that the number of receiving nodes may be greater than that illustrated in Figure 1.

More particularly, transmitting node 110 transmits packets to a receiving node 121 and a receiving node 122. For instance, receiving nodes 121 (RX PHYi) and 122 (RX PHYJ) may be connected to a central node, e.g. a sink receiver.

Figure 1 illustrates one embodiment where all the receiving nodes (only three of them 121, 122, 124 are represented) are several distributed physical layers (PHYs) connected to a MAC ("Medium Access Controlle?') through several links MPI (MAC PHY interface).

Figure 1 also illustrates another embodiment in dotted lines where, all the receiving nodes are connected to a central node or control system 130 through wired connections 130a, 130b, 130c. In this embodiment, each node (the receiving nodes and central node) has physical and MAC layers.

Control system 130 may receive data from the plurality of receiving nodes, proceed with appropriate computations and adjustments based on received data and knowledge of the network architecture (e.g. distances between the receiving nodes, etc.), and send suitable control and/or adjustment information commands to some or all of the receiving nodes.

It is to be noted that pairs of receiving nodes are formed, e.g. by the central node, from the plurality of receiving nodes. For example, the pairs may be formed by taking all the possible mathematical combinations between all the receiving nodes taken two by two. Alternatively, other criteria may be used to form pairs of receiving nodes such as the proximity between the receiving nodes. For example, pairs of receiving may be formed between receiving nodes which are spaced apart from a distance that is less than a predetermined distance.

It is well known that the 60 0Hz range has strong directivity so that an unexpected obstacle 140 can disturb the link or the propagation path between a transmitting node and a receiving node. Even though TX 110 has two links, TX-RX PHYi with length Li and TX-RX PHYj with length U, an obstacle 140 may nevertheless disturb both propagation paths or links at the same time (as represented in Figure 1). This is because the two paths are close to each other.

In order to show how close the two paths are, the angle O, is introduced. This angle is formed between the two propagation paths or antenna beams that respectively extend between the transmitting node and the two receiving nodes which form a pair of receiving nodes.

As represented in Figure 1, the small value of this angle explains the reason why obstacle 140 simultaneously obstructs the two paths. Such a pair of receiving nodes 121 and 122 is too much sensitive to shadowing and, therefore, not suitable for being selected as good candidates for receiving data and communicating with the transmitting node.

If node TX 110 moves towards another position referred to as TX' 111, better path diversity effects can be expected because the new angle 64' is much greater than previous angle 64. Thus, in this new position even though obstacle 140 also moves towards a different position referred to as 141, it will less likely disturb the two paths simultaneously as illustrated in Figure 1. The pair of receiving nodes 121 and 122 is therefore much less sensitive to shadowing From this schematic illustration, it is quite easy to determine that the condition for which there is no transmission diversity effect (i. e. no path diversity) for two receiving nodes RX PHY 1 and RX PHYJ, is met when 9 = 0, with D0 =L1 -L, (1) and the condition for with there is a maximum transmission diversity effect (i. e. maximum path diversity), is met when O= m, with (2) where I <ISN-I, /+1,.y and D0!=O.

The aim of the present invention is to check whether pairs of receiving nodes in the wireless network satisfy or not a predetermined criterion of path diversity. Put it another way, the possibility that the respective transmission or propagation paths between a transmitting node and a pair of receiving nodes may be obstructed simultaneously by an unexpected obstacle will be quickly assessed based on a simple criterion.

Figure 2 schematically illustrates a format of data packet that is exchanged between the communication nodes or devices in Figure 1.

The data packet 200 is divided into three parts (in the order of transmission): -apHYheader2lO; -a MAC header 220; -a MAC payload 230.

The P1-IY header 210 is a portion of data packet (also referred to as the frame) 200 that is generated on a source device side (e. g. transmitting node 110) and processed on a destination device side (any of receiving nodes 121, 122, 124) by a baseband processor.

The MAC header 220 is a portion of data packet 200 that is generated on the source device side and processed on the destination device side by a MAC ("Medium Access Controlle?') 130.

More particularly, PHY header 210 comprises: -a preamble 211, which is used for detecting the transmission of data packet 200 at the destination device; the preamble 211 furthermore makes it possible for the destination device to estimate the parameters that are 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 and the setting coefficients for the elements of a directional antenna with beam forming capability used to determine reception beam direction or adapt the antenna configuration; -a PHY rate field 212, which indicates a physical layer speed that is used for transmitting data packet 200; -a length field 21 3, which indicates the length of data packet 200; -a padding field 214, which may appear or not depending on the length of PHY header 210.

More particularly, MAC header 220 comprises: -a frame control field 221, which indicates a type of data packet; the packet type can for instance be: a beacon, a request to send (denoted RTS), a clear to send (denoted CTS), an acknowledge (denoted ACK); each packet type that is defined according to the transmission protocol applicable in the network has a predefined identifier, which is then stored in the control field 221; a source address field 222, which indicates the identifier (ID) of the source device of data packet 200; -a destination address field 223, which indicates the identifier (ID) of the destination device; -a header check sequence field 224, which indicates the cyclic redundancy check for MAC Header Data 221; this field is generated by a MAC at the source device (transmitting node 110) and its integrity is checked by a MAC at the destination device (receiving node) to determine whether MAC Header Data 221 contains an error or not; -a padding field 225, which may appear or not depending on the length of MAC header 220.

More particularly, MAC frame payload 230 comprises: -a data field 231, which may appear or not depending on the length of MAC payload 230, contains, according to the packet type indicated in frame control field 221, application data (video data, audio data, file transfer data, etc.); -a FCS field 232, which indicates the cyclic redundancy check for MAC Payload Data 231; this field is generated by a MAC at the source device and its integrity is checked by a MAC at the destination device to determine whether MAC Payload Header Data 231 contains an error or not; -a padding field 233, which may appear or not depending on the length of MAC Payload 230.

Figure 3 schematically illustrates a possible configuration of a wireless communication device or node which may be any device represented in Figure 1.

The communication device denoted 300 is operable to perform wireless communications and comprises: -a central processor unit or CPU 310; and -a random access memory or RAM 320; and -a read only memory or ROM 330; and -a wireless communication module (referred to as WCM) 340 enabling communication with other wireless communication devices in the network (or possibly in another network); and -a system bus 350 enabling data to be read and written to and from each unit 310, 320, 330 and 340.

CPU 310 is in charge of controlling the access to all the units in the device 300 through system bus 350. ROM 330 contains a program memory computer storing a program or several programs and is read from CPU 310.

The program memory may contain one or several programs on which the method according the invention is based. However, it is to be noted that the method may be performed in a distributed manner in several distinct devices or nodes in the network. RAM 330 is a working memory, the function of which is to store and load data for data computation and so on.

Figure 4 schematically illustrates a possible configuration of a wireless communication module (WCM) in a transmitting device or node, such as source transmitter (transmitting node) TX 110 or TX' 111 in Figure 1.

The WCM 340 of Figures 3 and 4 is operable to perform wireless communications and comprises: -a Medium Access Controller for transmission (denoted TX MAC) 410;and -a Radio Frequency Physical layer controller for transmission (denoted TX PHY) 420; and -a MAC / PHY interface (denoted MPI) 430.

TX MAC 410 sends to and receives from system bus 350 of Figure 3 data. TX MAC 410 handles encapsulation of the system bus data in keeping with a transmission protocol for transmission purpose and retrieval of system bus data for reception purpose.

TX PHY 420, for its part, is responsible for transforming digital data into modulated analog data, which take the form of a baseband signal, and converting the baseband signal into a radio signal at a carrier frequency for transmission. Also, TX PHY 420 has a quasi-omni directional antenna pattern (antenna configuration) so as to broadcast the radio signal to a plurality of receiving devices or nodes, such as those represented by RX PHYs in Figure 1.

Figure 5 schematically illustrates a possible configuration of a wireless communication module (WCM) in a receiving device or node, such as receivers (receiving nodes) of Figure 1.

The WCM 340' of Figures 3 and 5 is operable to perform wireless communications and, comprises: -a MAC for reception (denoted RX MAC) 510; -a Radio Frequency Physical layer controller for reception (denoted RX PHY); here RX PHYs 121, ..., 122 of Figure 1 have been represented to illustrate that the Figure 5 configuration includes one RX MAC and multiple distributed RX PHYs; and -an MPI (MAC PHY lnterface) 530.

Each of the plurality of RX PHYs such as 121 and 122 is responsible for down converting a received radio signal into a baseband signal, demodulating modulated analog data of the baseband signal into digital data and obtaining therefrom a received signal strength indication (RSSI). In a broader manner, it is possible to obtain from digital data one or more items of information indicative of the strength of the received signal and, therefore, of the distance between transmitting node 110 and the concerned receiving node.

This item or these items of information are also representative of the quality of the propagation path between transmitting node 110 and the concerned receiving node.

Each receiving node (RX PHYi 121 RX PHYj 122) is capable of adapting its antenna configuration (directivity) e.g. through setting or adjustment of its antenna coefficients in order to obtain a greater received signal strength.

The MPI 530 has a differential serial link (DSL) (here two DSLs 531 and 532 have been represented which cooperate respectively with RX PHYi 121 and RX PHYj 122 but one DSL is sufficient per device; thus the multiple RX PHYs such as 121 and 122 are connected to a single RX MAC through multiple DSL5 such as 531 and 532) having a serializer and a deserializer. The DSL (531,..., 532) has a clock recovery mechanism which is used to recover a clock from the serialized symbols such as 8B1OB. The MPI 530 also has a "de-skew" manager (DM) 540 which removes any symbol timing difference between DSLs such as DSL 531 and DSL 532.

Figure 6 schematically illustrates a timing diagram of skews or drifts taking place between DSL 531 and DSL 532.

The DSL 531 and DSL 532 respectively send idle symbols (IDL) 611 and 612 for links synchronization followed by alignment symbols (ALN) 621 and 622 just before the start of Data symbols 631 and 532. DM 540 measures or alternatively estimates, a skew or drift cycle (SKW) by using the DSL_CLOCK cycles and, on this basis, computes a time of arrival (TOA) difference At (/itFSKWy DSL_CLOCK). Thus the two receiving nodes RX PHYi 121 and RX PHYj 122 receive a signal sent by transmitting node TX 110 with a difference in time of arrival TOA. This difference in time of arrival is therefore determined by DM 540 that is common to the plurality of RX PHYs.

It is to be noted that when the multiple RX PHYs are independent from each other and connected to a central node 130 (embodiment illustrated with dotted lines in Figure 1) the difference in time of arrival (TOA) between two receiving nodes is determined in a known manner, e. g. through using common reference event in signals. For instance, the start of MAC frames can be detected at each receiving node.

Other suitable known synchronization methods can be used.

Figure 7 schematically illustrates a message sequence diagram established between a transmitting node or device, such as TX 110, and RX MAC 510 through RX PHYs (plurality of receiving nodes or devices). In the embodiment illustrated in dotted lines in Figure 1, the steps performed by RX MAC 510 and DM 540 are centralised within control node or system 130.

The diagram includes several steps performed by different entities in the network in order to implement the method according to the invention.

Step S700 is an overall step during which RX MAC 510 obtains parameters the plurality (N) of RX PHYs. This step corresponds to a parameter acquisition sequence which is a prerequisite before taking any decision on selecting or not pairs of receiving nodes in the network. Step S700 is subdivided into several steps or sub-steps 8711 to 8750.

In step 8711 RX MAC 510 requests from RX PHYi 121, through a parameter search request, to send a RSSI value obtained by RX PHYi 121 for the optimized antenna configuration (directivity) in reception mode. RX MAC 510 also communicates with the request the time to start sending the RSSI value RX MAC 510 requests from other receiving devices RX PHYs (122 and 124) to send their respective RSSI values and also supplies their appropriate times to start sending tsjarj during steps 8712 and 8714 respectively.

In step 5720 TX 110 broadcasts a reference signal to the plurality of receiving devices RX PHYs.

in next step 8731 RX PHYi 121 sends its RSSI value at time tstarl and the other RX PHYs proceed likewise with their own RSSI values and timing parameters at steps 8732 and S734 respectively.

ln step 8740 DM 540 makes use of the signals received at steps 8731, 8732 and S734 to measure each TOA difference, Zltd. This TOA difference is determined for example by measuring when a data symbol specific to each RX PHY, such as ALN in Figure 6, is received within a predetermined time interval. It is to be noted that all the TOA differences between the different pairs of the plurality of receiving nodes or devices in the network will thus be obtained, In step S750 DM 540 supplies the different values of Ac to RX MAC 510.

In following step 8760 RX MAC 510 checks whether each pair of receiving nodes meet a predetermined path diversity criterion and determines which pair(s) of receiving nodes or devices, if any, has not valid TX-RX path diversity, and therefore, cannot be selected. Step 8760 is more fully detailed in Figure 8.

Pairs of receiving nodes which are not authorized to take part to subsequent wireless communications are not selected. Wireless communications within the network are thus configured.

In step S764 RX MAC 510 requests (data stop request) from unselected RX PHYs to deactivate their receiver circuit(s) so that they are no longer operable to receive subsequent data signals. This step may also be pad of the configuration process.

In step S770 TX 110 starts transmitting data (data signal or useful data) to the RX PHYs which have been previously selected as having valid TX-RX paths diversity.

In following steps S781 and S782 selected RX PHYs (e.g. 121 and 122) respectively transmit demodulated received data to RX MAC 510.

In step S790 RX MAC 510 checks the CRC of the data items received from selected RX PHYs and selects correct data items (received by one RX PHY) from all the possible correct data items received by the other selected RX PHYs.

Figure 8 schematically illustrates a flow diagram detailing how RX MAC 510 decides to select a valid pair of receiving nodes or devices RX PHYs and not select a pair of RX PHYs.

RX MAC 510 intends to select a plurality K(?1) of RX PHYs pairs that have satisfactory path transmission diversity. Before starting the execution of this flow diagram, RX MAC 510 collects the different distances D between the RX PHYs by making use of the skews obtained by DM540 as illustrated in Figure 6. RX MAC 510 will use in particular the different distances between the two receiving nodes of each pair of receiving nodes as represented in Figure 1.

In first step S801 RX MAC 510 resets the counter value for the number of RX PHYs pairs, Ic, to zero and the counter value for the number of RX PHYs selected, m, to zero too.

In step S802 RX MAC 510 resets the counter value for the number of RX PHY Ito one.

In step S803 RX MAC 510 sets the counter value for the number of RX PHYJt0 1+1.

In the following steps checking of pairs of receiving nodes in the network will be performed with respect to a path diversity criterion. This checking operation aims at determining whether the two propagation or transmission paths between a transmitting node and the respective two receiving nodes of a pair are or are not at a small angle to each other so that an unexpected obstacle may simultaneously obstruct or not both propagation or transmission paths. This operation will be first made on the basis of the TOA difference and the distance between the two receiving nodes of each pair, and then on the additional basis of RSSI values. The aim of this method is to be able to easily and quickly take a decision on selecting or not pairs of receiving nodes after checking whether they meet the above criterion.

In step S804 RX MAC 510 checks, for a first pair of receiving nodes, whether At0 is close to D0 Ic, where c is the constant value of speed of light. This decision criterion is based on the equation (1) given above. lf the test of step S804 proves to be true, this means that the path diversity effect cannot be expected. This case is illustrated in figure 9a and shows that the angle between the two transmission paths from transmitting node TX 110 to the receiving nodes RX PHYs of the concerned pair respectively is closed (small) or even null. This pair will therefore not be selected since all the nodes are substantially aligned to each other.

In the negative, a further step S805 is performed by RX MAC 510 to check if At is close to zero. This test is made in order to determine whether the distance between transmitting node TX 110 and each receiving node RX PHY of the concerned pair is the same or not.

In the negative, step S805 is followed by step S807. This case corresponds to Figure 9b where the angle between the two propagations paths from transmitting node TX to the receiving nodes RI and R2 respectively is great enough to provide path diversity.

Thus, the pair (RI, R2) corresponding to Figure 9b case can be selected.

It is to be noted that the order of appearance of steps S804 and S805 may be inverted in a variant embodiment.

In the affirmative, next step S806 is carried out by RX MAC 510 to check whether TX 110 is close enough from each receiving node RX PHY of the concerned pair by using RSSI values (additional information).

In this respect, each RSSI value obtained for each receiving node is compared to a threshold RSSIth indicative of a predetermined distance between TX 110 and a receiving node. If both receiving nodes of the concerned pair are located beyond this predetermined distance (RSSI < RSSIth), the two propagation paths between TX and the receiving nodes respectively are at a small angle to each other so that an unexpected obstacle is very likely to simultaneously obstruct both propagation paths (see the arrangement in phantom lines in Figure 9c). Such a pair of receiving nodes does not provide path diversity and, therefore, will not be selected for subsequent data transmission. Step S806 is then followed by step S810.

If, conversely, both receiving nodes are close to transmitting node TX (RSSI > RSSIth), then the predetermined path diversity criterion is met since the angle 12 between the two propagation or transmission paths is great enough to enable path diversity. In particular, an unexpected obstacle 0 obstructing one of the two paths will not simultaneously obstruct the other adjacent path (Figure 9c in plain lines).

Next step S807 is therefore performed and a RX PHY pair is selected and the number of selected RX PHYs pair is counted as in.

The steps 5808 to 5813 are required to iterate this process.

Step 808 carries out a test on the value of the number of selected pairs k and compares it to the value K representing the whole number of pairs formed in the network.

If k = K, the process comes to an end.

In the negative, step 5808 is followed by step S809 that increments the value kto k+1.

Next step 5810 is then performed to compare the value i of the number of RX PHY to N (whole number of RX PHYs in the network). If i = N, then step 5812 carries out a test by comparing the value j of the number of RX PHY to N-I. In the affirmative, next step S814 which will be described later on is performed. In the negative, next step 5813 is performed and value j is incremented by I before carrying out again step 3803 already described.

Reverting to step S810, i i is different from N, then next step S811 is carried out to increment the value i by I before carrying out again step 5804 already described.

In step S814 if RX MAC 510 cannot choose the desired number of RX PHY pairs, it will select the least ii RX PHYs from the unselected RX PHYs which have higher RSSI values so that the test for n satisfies the following equation: (m+n »=K-k. 2)

Figure 10 schematically illustrates a flow diagram detailing how a receiving node or device RX PHY (121, 122, 124) sends RSSI values and data to RX MAC 510.

Steps S910 to 5940 correspond to the steps provided for in the above-mentioned parameter acquisition sequence S700 in Figure 7.

More particularly, in step S910 receiving node RX PHY (121, 122, 124) is waiting for a parameter search request from RX MAC 510 (test step).

If received, receiving node RX PHY (121, 122, 124) activates its receiver circuit(s) at step S920 so that it is operable to receive signals.

If not, step 8910 is carried out again.

In step S930 receiving node RX PHY (121, 122, 124) is waiting for a reference signal from transmitting node TX PHY (test step).

If received, receiving node RX PHY (121, 122, 124) obtains the RSSI value by measuring it on the received signal and sends it to RX MAC 510 (step 8940). Otherwise, test S930 is carried out again.

In following step 5950 if data stop is requested from RX MACSIO, then receiving node RX PHY (121, 122, 124) deactivates its receiver circuit(s) at step 8990 and process returns to step S910 already described.

If data stop is not requested, thereby meaning that receiving node RX PHY (121, 122, 124) has been selected, the latter is waiting for data signal (useful data) from TX 110 (test step 5960).

If data signal is received, data is sent to RX MAC51O at step S970.

otherwise, test step 8960 is carried out again.

In next step S980 receiving node RX PHY (121, 122, 124) decides about a predetermined timeout. If the predetermined time limit has not yet expired, receiving node RX PHY (1211 122, 124) executes step S960 again.

Otherwise, receiving node RX PHY (121, 122, 124) returns to step S9lOalreadydescribed.

Claims

CLAIMS1. A method of configuring wireless communications between a transmitting node and a plurality of receiving nodes while taking into account possible obstruction of at least one propagation path between the transmitting node and a receiving node by an obstacle therebetween, comprising: -transmitting a signal from the transmitting node to the plurality of receiving nodes; -obtaining the time of arrival of the same signal at each receiving node; -forming pairs of receiving nodes from the plurality of receiving nodes; -checking, at least on the basis of the obtained time of arrival of the signal at each receiving node of each pair thus formed, whether at least some of the pairs of receiving nodes thus formed meet a predetermined criterion of path diversity for the propagation paths between the transmitting node and the two receiving nodes of each pair; -configuring wireless communications, in accordance with the result of the checking, by deciding as to selecting or not selecting pairs of receiving nodes for being authorized to take part to subsequent wireless communications between the transmitting node and these pairs of receiving nodes.
2. The method according to Claim 1, wherein it further comprises deactivating the pairs of receiving nodes which have not been selected when configuring wireless communications so that they can be no longer operable to receive any signal.
3. The method according to Claim 1 or 2, wherein the predetermined criterion of path diversity is not met if the respective propagation paths between the transmitting node and the two receiving nodes of a pair extend along two directions that are at a small angle to each other so that these propagation paths may simultaneously be obstructed by an obstacle therebetween.
4. The method according to any one of Claims 1 to 3, wherein the checking is more particularly based on comparing the difference in the times of arrival of the signal (Atij) respectively at the two receiving nodes of said pair of receiving nodes to the value of the distance (Dii) between the two receiving nodes divided by the transmission speed (c) of the signal.
5. The method according to any one of Claims 1 to 4, wherein checking whether the predetermined criterion of path diversity is met by a pair of receiving nodes comprises at least comparing to each other the times of arrival of the signal at the two receiving nodes of said pair respectively.
6. The method according to anyone of Claims 1 to 5, wherein it further comprises obtaining an item of information (RSSI) indicative of the distance between the transmitting node and each receiving node of each pair of receiving nodes.
7. The method according to Claim 6, wherein said item of information is indicative of the strength of the signal received by each receiving node.
8. The method according to Claim 6 or 7, wherein checking whether the predetermined criterion of path diversity is met by at least some of the pairs of receiving nodes is also based on the item of information obtained for each receiving node of each pair.
9. The method according to Claim 8, wherein a pair of receiving nodes for which the transmitting node is at equal distance from the two receiving nodes and the obtained items of information (RSSls) are indicative of signals whose strength is less than a predetermined threshold is determined as not meeting the predetermined criterion of path diversity.
10. The method according to Claim 8, wherein a pair of receiving nodes for which the transmitting node is at equal distance from the two receiving nodes and the obtained items of information (RSS15) are indicative of signals whose strength is greater than a predetermined threshold is determined as meeting the predetermined criterion of path diversity.
11. The method according to any one of claims 1 to 10, wherein the receiving nodes are connected to a central node.
12. Computer program product, wherein it comprises program code instructions for implementing the method according to any one of Claims 1 to 11, when said program is run on a computer.
13. Computer-readable storage means, storing a computer program comprising a set of instructions that can be run by a computer to implement the method according to any one of Claims I to 11.
14. A method of configuring wireless communications between a transmitting node and a plurality of receiving nodes while taking into account possible obstruction of at least one propagation path between the transmitting node and a receiving node by an obstacle therebetween, pairs of receiving nodes being formed from the plurality of receiving nodes, the method comprising: -checking whether at least some of the pairs of receiving nodes meet a predetermined criterion of path diversity for the propagation paths between the transmitting node and the two receiving nodes of each pair, said checking being made for each pair of receiving nodes at least on the basis of the time of arrival at each receiving node of the same signal sent by the transmitting node to the plurality of receiving nodes, -configuring wireless communications, in accordance with the result of said checking, by deciding as to selecting or not selecting pairs of receiving nodes for being authorized to take part to subsequent wireless communications between the transmitting node and these pairs of receiving nodes.
15. The method according to claim 14, wherein, prior to said checking, it comprises receiving from the plurality of receiving nodes the time of arrival of the signal at each receiving node of the plurality of receiving nodes.
16. The method according to claim 14 or 15, wherein, for each pair of receiving nodes, said checking is more particularly based on the difference in the times of arrival of the signal respectively at the two receiving nodes of said pair of receiving nodes.
17. The method according to any one of claims 14 to 16, wherein, prior to said checking, it comprises obtaining, for each pair of receiving nodes, the differences in the times of arrival of the signal at the two receiving nodes of said pair of receiving nodes.
18. The method according to any one of claims 14 to 17, wherein, for each pair of receiving nodes, said checking is also based on an item of information (RSSI) indicative of the distance between the transmitting node and each receiving node of said pair of receiving nodes.
19. The method according to claim 18, wherein said item of information is indicative of the strength of the signal received by each receiving node.
20. The method according to claim 18 or 19, wherein, prior to said checking, it comprises receiving said item of information from each receiving node of the plurality of receiving nodes.
21. The method according to any one of claims 14 to 20, wherein it comprises sending deactivating requests to the receiving nodes of the pairs of receiving nodes which have not been selected when configuring wireless communications so that said receiving nodes can be no longer operable to receive any signal.
22. A system for configuring wireless communications between a transmitting node and a plurality of receiving nodes while taking into account possible obstruction of at least one propagation path between the transmitting node and a receiving node by an obstacle therebetween, comprising: -means for transmitting a signal from the transmitting node to the plurality of receiving nodes; -means for obtaining the time of arrival of the same signal at each receiving node; -means for forming pairs of receiving nodes from the plurality of receiving nodes; -means for checking, at least on the basis of the obtained time of arrival of the signal at each receiving node of each pair thus formed, whether at least some of the pairs of receiving nodes thus formed meet a predetermined criterion of path diversity for the propagation paths between the transmitting node and the two receiving nodes of each pair; -means for configuring wireless communications, in accordance with the result of the checking, by deciding as to selecting or not selecting pairs of receiving nodes for being authorized to take part to subsequent wireless communications between the transmitting node and these pairs of receiving nodes.
23. A device for configuring wireless communications between a transmitting node and a plurality of receiving nodes while taking into account possible obstruction of at least one propagation path between the transmitting node and a receiving node by an obstacle therebetween, pairs of receiving nodes being formed from the plurality of receiving nodes, the device comprising: -means for checking whether at least some of the pairs of receiving nodes meet a predetermined criterion of path diversity for the propagation paths between the transmitting node and the two receiving nodes of each pair, said checking being made for each pair of receiving nodes at least on the basis of the time of arrival at each receiving node of the same signal sent by the transmitting node to the plurality of receiving nodes, -means for configuring wireless communications, in accordance with the result of said checking, by deciding as to selecting or not selecting pairs of receiving nodes for being authorized to take part to subsequent wireless communications between the transmitting node and these pairs of receiving nodes.
24. A wireless communications network substantially as hereinbefore described, with reference to, and as shown in, Figure 1 of the accompanying drawings.
25. A system for configuring wireless communications between a transmitting node and a plurality of receiving nodes in a wireless communication network substantially as hereinbefore described, with reference to, and as shown in, Figure 1 in the accompanying drawings.
26. A signal substantially as hereinbefore described, with reference to, and as shown in, Figure 2 in the accompanying drawings.
27. A wireless communications device substantially as herein before described, with reference to, and as shown in, Figure 3 in the accompanying drawings.
28. A wireless communications module of a transmitting wireless communications device substantially as hereinbefore described, with reference to, and as shown in, Figure 4 in the accompanying drawings.
29. A wireless communications module of a receiving wireless communications device substantially as hereinbefore described, with reference to, and as shown in, Figure 5 in the accompanying drawings.
30. A device for configuring wireless communications between a transmitting node and a plurality of receiving nodes substantially as hereinbefore described, with reference to, and as shown in, Figure 5 in the accompanying drawings.
31. A method of exchanging messages in a wireless communications network of a transmitting wireless communications device substantially as hereinbefore described, with reference to, and as shown in, Figure 7 in the accompanying drawings.
32. A method of configuring wireless communications between a transmitting node and a plurality of receiving nodes in a wireless communications network substantially as hereinbefore described, with reference to, and as shown in, Figure 7 in the accompanying drawings.
33. A method of configuring wireless communications between a transmitting node and a plurality of receiving nodes substantially as hereinbefore described, with reference to, and as shown in, Figure 8 in the accompanying drawings.
34. A method of operating in a receiving node substantially as hereinbefore described, with reference to, and as shown in, Figure 10 in the accompanying drawings.