FR2961986A1 - Method for communicating data by node of e.g. wireless mesh network, involves determining transmission channel according to number of transmission when number of transmission is lower or equal to threshold - Google Patents

Abstract

The method involves selecting a time interval (52) in a contention window having a set of time intervals, and tuning the time intervals (55) before the selected time interval. The number of transmission is counted (58) during the time intervals before the selected time interval. The data transmission is carry forward or cancelled (60) when the number of the transmission is higher than a threshold. One of transmission channels is transmitted (62, 63) during the selected time interval and is determined according to the number of transmission, when the number is lower or equal to the threshold. Independent claims are also included for the following: (1) a communication node for performing the data transmission in a telecommunication network (2) a computer program comprising a set of instructions for performing a data communicating method (3) a support medium comprising a set of instructions for performing a data communicating method.

Description

BACKGROUND OF THE INVENTION The invention relates to the general field of telecommunications. The invention relates in particular to an access protocol to the medium. In a telecommunications network in which several nodes share the same medium of communication, simultaneous broadcasts can interfere, causing collisions and packet loss. This is particularly the case in wireless networks such as wireless mesh networks, local WiFi networks or low power networks (LLN for "Lossy and Low Power Network"). Many medium access protocols (MAC protocols for "Media Access Contro /") have been designed to deal with this problem. In particular, the IEEE-802.11 family of protocols concerns WiFi local area networks and the IEEE-802.15.4 protocol family concerns wireless personal networks. The development of wireless sensor networks has introduced a new constraint in the design of a MAC protocol, namely efficiency in terms of energy consumption. Thus, MAC protocols called "Low Power Listening" (LPL) have been designed. In this type of protocol, the nodes are dormant for long periods of time, and a pair of transceiver nodes can be selected to communicate during a waking period. The collision avoidance mechanisms proposed by these protocols can be classified in two categories: deterministic mechanisms and probabilistic mechanisms.

Deterministic mechanisms are based on a pre-established schedule in which each logical channel is dedicated to a specific node. These mechanisms do not adapt well to an unpredictable traffic or needing to review the schedule frequently, as this leads to a significant energy expenditure. In addition, extensibility is not well assured because a particular node can only use the channel assigned to it.

Probabilistic mechanisms are mainly based on a Carrier Sens Multiple Access (CSMA) mechanism. In particular, several protocols use a shared knowledge of time by the nodes to determine, during a fixed contention window, the node that can transmit during the next waking period. For example, K. Jamieson, H. Balakrishnan, and Y.C. Tay, "Sift: A MAC Protocol for Event-Driven Wireless Sensor Networks," in EWSN (K.Rômer, H. Karl, and F. Mattern, eds), vol. 3868 of Lecture Notes in Computer Science, pp. 260-275, Springer, 2006, describes a mechanism in which a transmission period is preceded by a contention window divided into CW time intervals. Each node that has data to transmit randomly chooses 2 an interval r among the CW time slots. Then, during the intervals preceding the interval r, the node listens and passes its turn if it hears a transmission. If during the interval r, the node has not passed its turn, it sends a signal to mark the time interval r and verifies that no collision has taken place. At the end of the contention window, the node that was able to transmit during the time interval it chose determines that it can transmit data during the next transmission period. This solution makes it possible to determine the single node that can transmit during the next allocation of the medium, and this locally, that is to say based solely on information available at each node. In addition, the sizing of the mechanism (i.e., the number of intervals of the contention window and the probability function used to choose a random interval) may depend only on the traffic load, not the network properties. Finally, this solution makes it possible to adapt to a variable traffic, burst. However, the use of available bandwidth remains limited. Indeed, if the selected node has little data to transmit relative to the capacity of the medium during the allocation period, this capacity is underutilized because no other node can access the medium during this time.

OBJECT AND SUMMARY OF THE INVENTION The object of the invention is to provide a method of communication which does not present at least some of the aforementioned drawbacks. In particular, the invention aims to allow a good use of the available bandwidth. To this end, the invention relates to a communication method executed by a node of a telecommunication network, said node having a data transmission to be performed, said method comprising: a step of selecting a time interval j in a contention window comprising several time intervals and preceding a transmission period, - a step of listening to the time intervals preceding the time interval j, characterized in that said transmission period has several transmission channels, and In that the method comprises: - a step of counting a number of transmissions during said time intervals preceding the time interval j, - when the number of transmissions is greater than a threshold, a transfer step or canceling said data transmission, when the number of transmissions is less than or equal to the threshold, a transmitting step during the time interval j and a step of determining one of said transmission channels, as a function of said number of transmissions. Thanks to these characteristics, the invention makes it possible to select several nodes to which it gives the authorization to transmit during a transmission period comprising several transmission channels. Indeed, when several nodes execute this process in parallel, all the nodes which have selected a time interval among the first time intervals will count a number of emissions lower or equal to the threshold and will emit during the time interval that they will have selected. Thus, these nodes will be selected to continue the transmission. The other nodes postpone or abandon their data transmission. Thus, even if the transmission time required by one node is smaller than the duration of the transmission period, the available bandwidth can be used by other nodes.

The invention therefore allows a better use of the available bandwidth. In addition, this communication method uses only information available at each node. Thus, the invention allows a local planning of transmissions. The determining step may comprise a step of participating in a selection mechanism using a contention window determined according to said number of transmissions and, if the node is selected during said selection mechanism, determining one of said selection channels. transmission corresponding to said contention window. Thus, if several nodes have selected the same time interval and thus have counted the same number of transmissions, the selection mechanism makes it possible to select one of these nodes for the transmission channel corresponding to the contention window. The determining step may also include, if said node is not selected during said selection mechanism, a second step of participating in a second selection mechanism using a second contention window. This makes it possible to focus on the nodes that participated in the first selection mechanism, allowing them to participate in the second selection mechanism if they have not been selected. The communication method may comprise, after said determining step, a step of sending an announcement message indicating a destination of said data transmission to be performed. The communication method may also comprise, after said sending step, a step of sleeping until said data transmission. The communication method may also comprise, after said step of posting or cancellation, a step of receiving an announcement message indicating a data transmission of which said node is the destination, and a step of sleeping until said data transmission of which said node is the destination.

Thanks to these characteristics, the node saves energy by being put in sleep while waiting for the transmission of data of which it is the source or the destination. The invention also relates to a communication node intended to perform data transmission in a telecommunication network, said node comprising: means for selecting a time interval j in a contention window comprising a plurality of time slots and preceding a transmission period, means for listening to the time intervals preceding the time interval j, characterized in that said transmission period has several transmission channels, and in that the node comprises: counting a number of transmissions during said time intervals preceding the time interval j, - means for deferring or canceling said data transmission when the number of transmissions is greater than a threshold, - means during the time interval j and means for determining one of said transmission channels, as a function of said number of transmissions, when the number b Emissions are less than or equal to the threshold. The invention also relates to a communication network comprising a plurality of nodes according to the invention.

The advantages and features discussed in relation to the communication method are correspondingly applicable to the node and the network. The invention is also directed to a computer program comprising instructions for carrying out the steps of the aforementioned communication method when said program is executed by a computer.

This program can use any programming language, and be in the form of source code, object code, or intermediate code between source code and object code, such as in a partially compiled form, or in any other form desirable shape. The invention also relates to a recording medium or information carrier readable by a computer, and comprising instructions of a computer program as mentioned above. The recording media mentioned above can be any entity or device capable of storing the program. For example, the medium may comprise storage means, such as a ROM, for example a CD ROM or a microelectronic circuit ROM, or a magnetic recording medium, for example a diskette (floppy disc) or a disk hard. On the other hand, the recording media may correspond to a transmissible medium such as an electrical or optical signal, which may be conveyed via an electrical or optical cable, by radio or by other means. The program according to the invention can be downloaded in particular on an Internet type network.

Alternatively, the recording media may correspond to an integrated circuit in which the program is incorporated, the circuit being adapted to execute or to be used in the execution of the method in question. BRIEF DESCRIPTION OF THE DRAWINGS Other features and advantages of the present invention will be apparent from the description given below, with reference to the accompanying drawings which illustrate an embodiment having no limiting character. In the figures

FIG. 1 is a diagrammatic view of a network according to one embodiment of the invention, FIG. 2 represents an example of a flow of a communication in the network of FIG. 1, and FIGS. 3 to 6 are step diagrams that illustrate a communication method according to an embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS FIG. 1 shows a network 2 comprising a plurality of nodes 1. The network 2 is for example a low-power wireless network of sensors, in which the nodes 1 can switch between a sleep state in which they are connected. consume little energy and a waking state in which they can send and receive data, especially data relating to values measured by sensors. However, the invention is not limited to this type of network and may in particular relate to a network of links on any kind of shared medium. Each node 1 presents the hardware architecture of a computer. One of the nodes 1 is shown in more detail in FIG. 1 and comprises a microprocessor 3, a read-only memory 4, a random access memory 5, a communication interface 6 and an input port 7. The microprocessor 3 enables executing programs stored in the read-only memory 4, using the RAM 5. The communication interface 6 makes it possible to communicate by wireless connection with the other nodes 1 of the network 2. Finally, the input port 7 allows to acquire the value of a measurement signal. The read-only memory 4 constitutes an information medium that can be read by the microprocessor 3. It includes instructions from a computer program whose main steps represented in the form of flow charts in FIGS. 3 to 6 allow the execution of the method of FIG. communication according to the invention implemented by the node 1. Periodically or as a function of the value of the measurement signal acquired on its input port 7, each node 1 decides to transmit data on the network 2. To avoid collisions and packet loss, each node 1 implements a collision avoidance mechanism described in more detail hereinafter. FIG. 2 represents, as a function of time, the progress of a communication on the network 2. The nodes 1 have a shared knowledge of the time t. Thus, they can periodically switch to their awake state at times common to all nodes 1. The flow of communication comprises two phases 10, 1: L which precede an instant 12 of switching to the awake state, and two phases 13 and 14 following the moment 12. The phases 10 and 11 are intended to determine the nodes 1 that will be authorized to transmit. Phase 13 is an announcement phase in which the nodes 1 authorized to transmit indicate the nodes 1 of destination of their communication. Finally, phase 14 is a transmission period during which the nodes 1 authorized to transmit transmit the data to be transmitted. The transmission period of phase 14 has several transmission channels. In the example shown in FIG. 2, the transmission period comprises three transmission channels 15, 16 and 17 temporally multiplexed. Alternatively, the transmission period could comprise more or fewer transmission channels. Alternatively also, the transmission channels could be frequency multiplexed. The phases 10 and 11 allow the implementation of a collision avoidance mechanism in two parts, which aims to select the three nodes 1 which will be authorized to transmit respectively in the transmission channels 15, 16 and 17 Of course, if the transmission period comprises more or less than three transmission channels, the number of nodes 1 selected during the phases 10 and 11 is adapted accordingly. FIGS. 3 to 6 are step diagrams representing the communication method carried out by each node 1, allowing the progress of a communication 20 according to FIG. 2. At step 30 of FIG. 3, which precedes the phase 10 , node 1 is in its sleep state, which is represented by the symbol S in the figures. In step 31, node 1 determines whether it has data to transmit. If node 1 has no data to transmit, it proceeds to step 40 of FIG. 4. If it has data to transmit, it proceeds to step 50 of FIG. 5. FIG. 4 represents the steps performed by a node 1 which has no data to transmit. In step 40, node 1 waits for the moment: L2 to switch to its awake state, which is represented by the symbol W. Then, in step 4: L, node 1 listens to possible messages received on its communication interface 6, which is symbolized by RADIO RX. In step 42, node 1 determines whether one of the received messages is a message announcing a communication of which it is the destination, which is symbolized by "ADV? ". If no announcement message indicates a communication of which it is the destination, the node 1 program, in step 43, its next instant 12 switching to the awake state, which is symbolized by "W = .. . " Finally, node 1 switches to the sleep state. If an announcement indicates a communication of which it is the destination, the node 1 program, in step 44, its next switching moment awake according to the transmission channel indicated in the announcement message, which is symbolized by "W = F (ADV)". For example, if the node 1 is the destination of a communication in the transmission channel 17, the node 1 plans to switch to the awake state just before the start of the transmission in the transmission channel 17. In step 45, node 1 switches to sleep while waiting to receive data, which is symbolized by S / D.

Steps 40 to 45 of FIG. 4 correspond, for a node 1 which has no data to transmit, to phase 13 of FIG. 2. FIG. 5 represents the steps performed by a node 1 which has data at During phase 10 of FIG. 2, phase 10 allows the implementation of a first part of the collision avoidance mechanism, by using a contention window 18 divided into several time intervals. In Figure 2, the contention window 18 is divided into seven time slots. Alternatively, the contention window 18 could be divided into more or less time intervals. In step 50, the node 1 initializes a counter c to 1. Then, in the step 51, the node 1 waits a moment corresponding to the beginning of the phase 10 to switch to the awake state.

In step 52, the node 1 randomly selects a time interval j in the contention window 18. The probability function used to select the time interval j is preferably a geometrically increasing distribution, of the type described in FIG. Sift document cited in introduction. Then, in step 53, a counter x representing the current interval is initialized to 1.

Then, in step 54, node 1 determines whether the current interval represented by the counter x corresponds to the selected time interval j. If not, in step 55, node 1 listens for any messages received on its communication interface 6. In step 56, if no message has been received, node 1 goes to step 57, increments the counter x and then loops to step 54.

On the other hand, if a message has been received, the node 1 goes to step 58 and increments the counter c. Then, in step 59, the node 1 compares the counter c with a threshold T. The threshold T corresponds to the number of transmission channels in the transmission period. Thus, T = 3 in the example of FIG. 2. If the counter c is less than or equal to T, node 1 goes to step 57 where the counter x is incremented and then looped to step 54. the counter c is greater than T, the node 1 goes to the step 60 in which it decides to cancel or to postpone the data transmission to be carried out, and then switches to the sleep state in step 61. In step 61, the node 1 is considered as a node 1 having no data to be transmitted and will thus perform the steps 40 to 45 of FIG.

If, at step 54, the current interval represented by the counter x corresponds to the selected time interval j, the node 1 proceeds to the steps 62 and 63 in which it transmits a message. The message is for example a scrambling signal, which is represented by the JAM symbol. Thus, the time interval j is marked by the node 1. 8 By listening to the messages received in step 55 and by incrementing the counters c and x, the node 1 can therefore count the time intervals preceding the one it selected, which have been marked by other nodes 1. Indeed, for each time interval preceding the selected time interval, another node may send a jamming signal JAM. In this case, node 1 goes to step 58 and increments counter c. If more than T time intervals preceding the one it has selected have been marked by other nodes, node 1 considers, in step 59, that it can not transmit its data and proceeds to steps 60 and 61 On the other hand, if in step 54, the current interval represented by the counter x corresponds to the time interval j selected, this means that the counter c is less than or equal to T. In other words, the number of Time intervals marked by other nodes before the time interval j selected by node 1, which corresponds to c-1, is less than T-1. Thus, the node 1 can mark the time interval j in steps 62 and 63 and then continue the course of the collision avoidance mechanism by participating, during phase 11 of FIG. 2, in a second part of the avoidance mechanism collisions.

The nodes 1 which participate in the second part of the collision avoidance mechanism are therefore the nodes 1 which have data to be transmitted and which have been able to mark a time interval j selected during the phase 10. Thus, for each node 1 which part of this second part, the counter ca a value between 1 and T. As shown in Figure 2, the second part of the collision avoidance mechanism uses T contention windows, that is to say three windows of contention 19, 20 and 21 in the example shown. The counter c of each node 1 makes it possible to assign one of the contention windows 19, 20 and 21 for the second part of the collision avoidance mechanism. Thus, according to the invention, a selection mechanism is implemented in each contention window 19, 20 and 21 making it possible to select a single node 1 authorized to transmit in the transmission channel 15, 16 or 17 respectively corresponding to the window This second part of the collision avoidance mechanism is useful because, during the first part, several nodes 1 may have selected the same time slot in step 55 and therefore have the same value of the same. counter c.

Advantageously, a node 1 which has not been selected by the selection mechanism of the contention window 19 can participate in the selection mechanism of the contention window 20, and a node 1 which has not been selected by the mechanism The selection window of the contention window 20 may participate in the selection mechanism of the contention window 21. FIG. 6 represents an example of a selection mechanism implemented during the contention windows 19, 20 and 21. In this example, the selection mechanism is a Binary Countdown Mechanism (BCM), in which each contention window is divided into CW2 time slots, each time interval 9 being considered a selection round. Other mechanisms could be used alternatively. Node 1 participates in the selection mechanism of the contention window 19, 20 or 21, depending on the value of its counter c.

In step 70, node 1 initializes a counter s representing a current interval of the contention window. Then, in step 71, the node: 1 randomly decides whether to send a message to mark the current interval represented by the counter s. If so, in steps 72 and 73, the node 1 sends a JAM scrambling message and, in step 74, increments the counter s.

In step 75, node 1 determines whether the counter s is less than or equal to the number CW2 of time slots in the contention window. If so, it means that the time interval marked in step 73 was not the last time interval of the contention window. Node 1 thus loops to step 71. On the other hand, if the time interval marked in step 73 was the last time interval of the contention window, node 1 considers that it has been selected to transmit using the transmission channel corresponding to its counter c, and therefore goes to step 80. Step 80 corresponds to phase 13 of FIG. 2, in which the nodes 1 selected to transmit send an announcement message indicating the destination of their transmission. Then, the node 1 switches to the sleep state until the beginning of the transmission channel that has been assigned to it. If, in step 71, the node 1 decides not to mark the current interval represented by the counter s, it proceeds to step 76 where it listens to any received interference messages. In step 77, it determines whether a scrambling message has been received. If, in step 77, an interference message has been received, node 1 considers that it has not been selected to transmit by the selection mechanism corresponding to the current contention window. In step 82, it compares the counter c with T. If the counter c is less than T, it means that the contention window in progress was not the last contention window. Thus, node 1 increments its counter c in step 83 and then loops to step 70 to participate in the selection mechanism of the next contention window. On the other hand, if the contention window was the last one, node 1 considers that it was not selected to emit collisions by the collision avoidance mechanism. Thus, in step 84, it decides to cancel or postpone the data transmission to be performed, and in step 85, it plans to switch to the awake state at the instant 12 before switching to sleep state. After step 85, the node 1 is considered as a node 1 having no data to be transmitted and will thus perform the steps 40 to 45 of FIG. 4. On the other hand, if, at the step 77, no message of scrambling has been received, node 1 continues the selection mechanism of the current contention window. Thus, in step 78, it increments the counter s and then determines, in step 79, whether the current interval was the last of the contention window. If not, that is, if the current time interval is not the last time interval of the contention window, node 1 loops at step 71. However, if the interval current time was the last time interval of the contention window, node 1 considers that it was selected to transmit and therefore goes to step 81 identical to step 80 above. Referring again to FIG. 2, a more detailed description of the flow of the illustrated communication is now given. Five nodes 1 are considered to have data to transmit. During the first part of the collision avoidance mechanism, that is to say during the phase 10 and the steps of FIG. 5, these five nodes 1 respectively select, in step 52 of FIG. time slots 2, 4, 5, 6 and 7. The time slots 2, 4 and 5 are therefore marked by the corresponding nodes 1, which is represented by the letters A, B and C. On the other hand, , the two nodes 1 which have selected the time intervals n ° 6 and 7 will have three time intervals marked before their, and will therefore decide to cancel or to postpone their transmission then to pass into the state of sleep, according to the steps 59, 60 and 61 of Fig. 5. After step 63, the three nodes 1 that marked the time slots 2, 4 and 5 have their counter c being 1, 2 and 3 respectively. node 1 having marked the time interval n ° 2 with its counter c equaling 1 and thus participates, during phase 11, in the selection mechanism n of the contention window 19. Correspondingly, the node 1 having marked the time slot No. 4 has its counter c equaling 2 and thus participates, during phase 11, in the selection mechanism of the contention window 20 , and the node 1 having marked the time interval # 5 has its counter c equaling 3 and thus participates, during phase 11, in the selection mechanism of the contention window 21.

Each of these three nodes 1 being alone to participate in the selection mechanism of its respective contention window, it will be selected as node authorized to issue. Of course, if several nodes 1 had selected the same time interval during phase 10, they would all participate in the selection mechanism of the corresponding contention window of phase 11, thus leading to the elimination of one or more nodes.

During the step of announcing phase 13, each of its three nodes 1 sends an announcement message indicating the destination node 1 of the data it has to transmit. Then, each of the three nodes 1 authorized to transmit transmits its data on the transmission channel 15, 16 and 17 corresponding to its contention window 19, 20 and 21. Thus, in the example shown, the node 1 which selected the time slot 2 during phase 10 and participated in the selection mechanism of the contention window 19 during phase 11 transmits its data in the transmission channel 15. It can be seen that the method described above makes it possible to select several nodes allowed to transmit during a transmission period comprising several transmission channels. Thus, even if the transmission time required by one node is smaller than the duration of the transmission period, the available bandwidth can be used by other nodes. On the other hand, the two-part collision avoidance mechanism enables efficient selection of the nodes allowed to transmit locally, i.e. relying solely on information available at each node. The collision avoidance mechanism also makes it possible to switch each node between its sleep state and its waking state, as needed. In particular, thanks to the step of announcing phase 13, only the nodes participating in a transmission are in the awake state during transmission. The other nodes therefore consume little energy.

Claims (10)

REVENDICATIONS1. A method of communication executed by a node (1) of a telecommunication network (2), said node (1) having a data transmission to be performed, said method comprising: - a step (52) of selecting an interval of time j in a contention window (18) comprising a plurality of time intervals and preceding a transmission period; - a step (55) for listening to the time intervals preceding the time interval j, characterized in that said period of time transmission has a plurality of transmission channels (15, 16, 17), and in that the method comprises: - a step (58) of counting a number of transmissions during said time intervals preceding the time interval j, - when the number of transmissions is greater than a threshold, a step (60) of postponement or cancellation of said data transmission, - when the number of transmissions is lower than or equal to the threshold, a transmission step ( 62, 63) during the interval time and a step of determining one of said transmission channels, as a function of said number of transmissions. The communication method according to claim 1, wherein said determining step comprises a step of participating in a selection mechanism using a contention window (19, 20, 21) determined according to said number of transmissions and, if the node is selected during said selection mechanism, determining one of said transmission channels (15, 16, 17) corresponding to said contention window. The communication method according to claim 2, wherein said determining step comprises, if said node is not selected during said selection mechanism, a second step of participating in a second selection mechanism using a second contention window ( 20, 21). 4. The communication method according to claim 1, comprising, after said determining step, a step (80, 81) of sending an announcement message indicating a destination of said data transmission to be performed. 5. The communication method according to claim 4, comprising, after said sending step (80, 81), a step of sleeping until said data transmission. 6. The communication method as claimed in claim 1, comprising, after said step (60) of postponement or cancellation, a step (41) for receiving an announcement message indicating a data transmission of which said node is the destination. , and a step (45) of sleeping until said data transmission of which said node is the destination. 7. Communication node (1) for transmitting data in a telecommunication network (2), said node (1) comprising means for selecting a time interval j in a contention window (18) comprising several time intervals and preceding a transmission period, means for listening to the time intervals preceding the time interval j, characterized in that said transmission period has several transmission channels (15, 16, 17 ), and in that the node (1) comprises: means for counting a number of transmissions during said time intervals preceding the time interval; means for deferring or canceling said transmission of data when the number of transmissions is greater than a threshold, - transmission means during the time interval j and means for determining one of said transmission channels, as a function of said number of transmissions, when e the number of emissions is less than or equal to the threshold. 20 8. Communication network (2) comprising a plurality of nodes (1) according to claim 7. A computer program comprising instructions for performing the steps of the communication method according to claim 1 when said program is executed by a computer. A computer-readable information carrier having instructions of a computer program according to claim 9.