EP2359646A1

EP2359646A1 - Communication device and method, and system including such a device

Info

Publication number: EP2359646A1
Application number: EP09793560A
Authority: EP
Inventors: Olivier Coutelou
Original assignee: Schneider Electric Industries SAS
Current assignee: Schneider Electric Industries SAS
Priority date: 2008-12-18
Filing date: 2009-12-03
Publication date: 2011-08-24
Anticipated expiration: 2029-12-03
Also published as: FR2940558A1; WO2010076406A1; CN102326431B; EP2359646B1; FR2940558B1; CN102326431A

Abstract

The invention relates to a communication device for wireless communication networks having one or more frequencies. The device comprises a control module (23) for the transmission of repetitive messages (45, 55) to reception devices having at least two reception frequencies (Fl, F2, F3), at least one reception frequency being common with the transmission frequency (F2) of the repetitive messages. Upon reception of the repetitive messages, a polling module (5) changes the reception frequency according to at least one polling period (TS). At least one predetermined transmission period (TE) has a value different from the said polling periods. The communication system comprises a device for transmitting and receiving the repetitive messages. The method processes the transmission and the reception of the repetitive messages in a multi-frequency network.

Description

COMMUNICATION DEVICE AND METHOD AND SYSTEM COMPRISING SUCH A DEVICE

TECHNICAL AREA

The invention relates to a communication device for wireless communication networks with one or more frequencies.

The invention also relates to a communication system for wireless communication networks comprising:

at least one communication device that can communicate on one or more frequencies, and

at least one communication device communicating with at least one common frequency with said communication means.

The invention also relates to a method of communication between at least a first communication device and at least a second communication device that can communicate on one or more frequencies.

STATE OF THE ART

In existing installations such as that shown in FIG. 1, wireless communication devices IA, IB and 2 generally interact with communication protocols on one or more frequencies F1, F2, F3. More recent short message communication devices 3A, 3B and 4 communicate with each other at a frequency F2 but require a gateway 5 for the passage of information to networks 7 at several frequencies. Such gateways allow upward compatibility between old multi-frequency networks and one-frequency networks. Thus, existing functions with multi-frequency devices will still be able to operate even when interacting with devices at a frequency. Of the one-frequency devices, some 3Cs and 3Ds are short-message and unidirectional. They are generally integrated into self-powered wireless communication devices that must operate at very low energy. For example, wireless remote control switches or sensors with built-in electric generator or energy-independent. The self-powered remote control switches will be named SPS (Self Powered Switch).

A first example of gateways with wireless communication devices is shown in FIG. 2. This gateway comprises a first radio transmitter / receiver circuit 8 operating on three frequencies F1, F2 and F3, and a second radio transmitter / receiver circuit 9 operating on a frequency F2. These circuits are connected to a processing circuit 10 for the transmission and reception of data D.

Another example of a communication bridge between wireless communication networks is described in patent application EP 1858203.

Some communication networks operate in a synchronized manner as described in WO00 / 18150. However these systems are very expensive and can not be used in devices without a permanent power source such as SPS.

Known multifrequency communication devices do not securely receive short messages transmitted in a single frequency. Thus gateways between the reception of short messages on a single frequency and a multifrequency installation is necessary. Gateways or communication devices operating with two rates, two protocols or two types of demodulation or two frequency modes are very energy consuming. For example, when the communication devices are associated with SPS type switches, they must be able to be arranged in control devices and be fed through the load. Thus, known communication devices that can receive two types of multi-frequency or uni-frequency networks or having gateway functions can not be used in very low-power applications. In addition, the cost of bridges known compatible with communication networks already installed or having to work with multiple frequencies is high.

SUMMARY OF THE INVENTION

The object of the invention is a device and a method of wireless communication operating on one or more frequencies and having compatibility with existing systems and very low power consumption, as well as a system integrating such a device.

A communication device according to the invention for wireless communication networks at one or more frequencies comprises repetitive message transmission control means for reception devices having:

at least two reception frequencies with at least one common reception frequency with a repetitive message transmission frequency, and reception frequency change polling means according to at least one polling period, said reception control means issuing repetitive messages controlling the transmission of messages according to transmission periods between the messages of predetermined duration, at least one predetermined transmission period having a value different from the said scanning periods of the said scanning means.

Advantageously, said repetitive message transmission control means are fed intermittently and said repetitive messages are out of synchronization.

Advantageously, said repetitive message transmission control means transmit messages according to transmission periods between the messages of durations substantially identical to each other and different in value from said scanning periods of said scanning means.

Preferably, said repetitive message transmission control means emits at least three repetitive messages, said transmission period of said repetitive messages having a duration substantially equal to 2/3 or 4/3 of said duration of the scanning periods of said scanning means.

In a particular embodiment, said repetitive message transmission control means transmit messages according to transmission periods between messages of different durations between them and different values of said scanning periods of said scanning means.

Advantageously, said repetitive message transmission control means transmit messages according to first transmission periods between the messages having at least one duration less than the duration of said scanning periods of said scanning means and at least second periods of time. emission having durations longer than the duration of said scanning periods.

Preferably, said repetitive message transmission control means emit at least four repetitive messages, said transmission periods between repetitive messages having a first duration substantially equal to 4/3 of the duration of the polling periods, a second duration substantially equal to 2.5 / 3 of the duration of the scanning periods and a third period substantially equal to 5/3 of the duration of the scanning periods.

A communication system for wireless communication networks comprising:

at least one communication device communicating with at least one common frequency with said communication means comprises:

- at least one communication device

communicating on at least two reception frequencies and with at least one common reception frequency with a repetitive message transmission frequency, and

comprising polling means with reception frequency change according to at least one polling period, and

at least one communication device as defined above for transmitting repetitive messages on at least one common frequency with said reception frequency change scanning means

In a preferred embodiment, said frequency change scanning means includes a scan cycle having a first period at a first frequency, a second period at a second common frequency, a third period at a third frequency, and a fourth period. at said second common frequency.

In a particular embodiment, said frequency change scanning means includes a scan cycle having a first period at a first frequency, a second period at a second common frequency, and a third period at a third frequency.

A communication method between at least a first communication device and at least a second communication device that can communicate on one or more frequencies comprises:

the scanning according to a frequency scan cycle having a change of frequency at each predefined scanning period, and

the transmission by a communication device having a common frequency of repetitive messages according to transmission periods between the messages of predetermined durations, at least one predetermined transmission period having a value different from the said scanning periods.

In a first variant, the method comprises:

- scanning according to a scanning cycle having a first period at a first frequency, a second period at a second common frequency, a third period at a third frequency, and a fourth period at said second common frequency, - transmitting to said second common frequency of repetitive messages spaced apart from a transmission period of different duration of the periods of said scanning cycle. Preferably, in this process: said first communication device transmits at least three repetitive messages,

said period of transmission of said repetitive messages has a duration substantially equal to 2/3 or 4/3 of a duration of the scanning periods.

In a second variant, the method comprises:

scanning according to a scanning cycle having a first period at a first frequency, a second period at a second common frequency and a third period at a third frequency,

the transmission at said second frequency of repetitive messages spaced apart from several periods of different durations.

Preferably, in this process:

said first communication device transmits at least four repetitive messages,

said periods of the scanning cycle have a first duration, and the transmission periods between repetitive messages have a first duration substantially equal to 4/3 of a duration of the scanning periods, a second duration substantially equal to 2, 5/3 of said duration of the scanning periods and a third duration substantially equal to 5/3 of said duration of the scanning periods.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages and features will emerge more clearly from the following description of particular embodiments of the invention, given by way of non-limiting examples, and represented in the accompanying drawings in which:

FIG. 1 represents a diagram of frequency and multi-frequency communication networks comprising known communication devices,

FIG. 2 represents a known communication device,

FIG. 3 represents a diagram of a communication device according to a first embodiment of the invention,

FIG. 4 represents a diagram of a communication device according to a second embodiment of the invention, FIG. 5 represents a diagram of a communication device according to a third embodiment of the invention,

FIG. 6 represents a diagram of an apparatus comprising a communication device according to one embodiment of the invention, FIG. 7 represents a diagram of communication networks at a frequency and in multifrequencies comprising at least one communication device. according to one embodiment of the invention,

FIG. 8 represents a flow diagram of repetitive messages,

FIG. 9 represents a first operating chronogram showing the frequency shift scanning sequences of a receiver and the transmission periods of an emitter in a method according to one embodiment of the invention,

FIG. 10 represents a second operating chronogram showing the frequency change scanning sequences of a receiver and the transmission periods of an emitter in a method according to one embodiment of the invention, FIG. 11 represents a second flowchart comprising steps of a method according to the invention with a change of frequency, and

- Figure 12 shows a third flowchart comprising steps of a method according to the invention with frequency change.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In communication devices for wireless communication networks, transmission and reception is generally done with long messages whose duration is generally greater than 15 ms (milliseconds). The preamble of the message during synchronization detection is often greater than 3 ms. These devices can operate on several frequencies Fl, F2, F3.

Self-powered remote control switches called SPS (Self Powered Switch) can emit short messages whose duration is less than 1 millisecond, for example. These devices operate on a single frequency F2. In the known devices, two communication circuits, of which a first in multifrequencies and a second at a frequency make it possible to communicate information or data between the different protocols and different frequencies.

To avoid risks of loss of message, high costs of certain gateways and the high consumption of these devices, devices 20 according to embodiments of the invention comprise a transmission and / or reception circuit 21 and a module. of 22 processing to communicate with repetitive messages. Advantageously, the communication between the transmitter and the receiver is not synchronized.

In an embodiment shown in FIG. 3, a communication device comprises a repetitive message sending control module 23 with at least one frequency F2 intended for frequency-tuned reception devices such as that represented in FIG. 4. A communication device 24 of FIG. 4 can receive at least two reception frequencies F1, F2, F3 with at least one common receiving frequency F2 with a repetitive message transmission frequency. In the communication device 24, a polling module 25 periodically changes its reception frequency according to at least one polling period TS. In the communication device 20, the module 23 controls the transmission of repetitive messages according to transmission periods TE between the messages of predetermined durations, at least one transmission period having a value different from the scanning periods of the module 25. For example, the repetitive message transmission control module 23 transmits messages according to transmission periods TE between the messages of durations substantially identical to each other and of different value of the scanning periods TS of the scanning module 25.

The device 20 may be self-powered SPS type (Self Powered Switch) or autonomous sensor configured transmission for transmitting on a frequency F2 short repetitive messages for a device 24 that can scan several frequencies Fl, F2 and F3 in reception. The processing module 22 exchanges data D with a transmission and / or reception circuit 21. The module 23 for sending repetitive messages is associated with the module 22 for processing the repetitive messages to be sent. The modules 22 and 23 are preferably associated in one and the same circuit 22A. microcontroller or microprocessor. In this example, the module 23 provides a signal repetition control signal R. In other preferred embodiments, the processing circuit 22A repeatedly sends the repetitive message to be transmitted through the data link D.

In order to be able to receive at least one repetitive message on the frequency F2 as well as other messages, especially on other frequencies F1, F2 and F3, the device 24 of FIG. 4 comprises a scanning module 25 controlling a receiver with several frequencies F1. , F2 and F3 of a transmission and / or reception circuit 21B. The processing module 22 exchanges data D with a transmission and / or reception circuit 21. In this example, the module 25 provides a signal F frequency or frequency change. The modules 22 and 25 are preferably associated in the same microcontroller or microprocessor processing circuit 22B. The signals of frequency F and data D can also be carried by the same link. In this particular embodiment, the circuit 21B provides a message receiving signal M for blocking or delaying the frequency change while a message is being received.

In Figure 5, a device according to another embodiment of the invention operates in gateway mode. It comprises a module 23 for transmitting repetitive messages on a frequency F2 and a reception frequency scanning module 25 for receiving several frequencies F1, F2 and F3. An emission and / or reception circuit 2 IC is controlled by the frequency change module 25 and by the module 23 in message repetition. The modules 22, 23 and 25 are preferably associated in the same microcontroller or microprocessor processing circuit 22C.

FIG. 6 represents a diagram of an apparatus 27 comprising a communication device 28 according to one embodiment of the invention able to receive and / or transmit short messages in single frequency or long messages in multifrequency. In the device 27, a transmission and / or reception circuit 21D is controlled by a frequency change and message repetition processing circuit 22D, a link between the circuits 21D and 22D carries D data signals, the repetitive message commands R to be sent and the frequency setting commands F of reception and in some cases a signal M of message reception. The electrical apparatus 27 includes an application control circuit 29 connected to the device 28 for receiving and / or transmitting control signals and for providing a power supply thereto. The circuit 29 may be associated with an actuator and powered through an electric load 30. The power consumption of a device according to the invention and very small to avoid disturbing the control of the load.

FIG. 7 represents a diagram of a system with a communication network 6A at a frequency F2 and a communication network 7A at several frequencies F1 F2 and F3 comprising at least one communication device 26 according to an embodiment of the invention. In this communication system, at least one communication device 26 can communicate on one or more frequencies F1, F2 and F3 with ID and IC devices, and with communication devices 3E, 3F, 31, 3J communicating with at least a common frequency F2 and repetitive short messages with said multifrequency communication devices and / or long messages. In this case, the device 26 is in a communication gateway fully compatible with other existing communication devices. In the exchanges between the transmitter / receiver circuit 21C and the processing circuit 22C, the signals can be carried by the same lines. For example, the data signal D and the frequency change signal F can travel on the same line.

In this system, a communication device 26 capable of communicating over one or more frequencies F1, F2, F3 comprises a frequency scanning module 25 operating according to a scanning cycle having a change of frequency at each predefined scanning period. This system also comprises at least one device 20, 26 for transmitting repetitive messages on at least one common frequency F2 with a frequency scanning module 25. The communication devices 20 are notably integrated in devices of the SPS 31 and 3J type shown in FIG. 7.

Without departing from the scope of the invention, the transmission of messages can also be done on other frequencies Fl and F3 in gateways. A flowchart shown in Fig. 8 shows the issuing of repetitive messages in embodiments of a device, method or system according to the invention. In a step or a module 32 the message to be transmitted repeatedly is defined. Then at a step or module 33, a first message is sent and a control of a first transmission period TE, TE1 is started. After the first transmission period, at a step or a module 34, the message is returned and a control of a second transmission period TE, TE2 is started. Depending on the number of expected shipments, a step or module sends the message and initiates a check for the last transmission period TE, TE3. Finally, a step or module 36 sends the last repetitive message. Transmission periods are different from polling periods TS of communication devices that can receive several frequencies F1, F2, F3.

FIG. 9 represents a first operating chronogram of a device, a method or a system according to the invention. This flowchart shows a first polling sequence by frequency change Fl, F2 and F3 of a receiver and transmission periods of a transmitter. In this scan, the common frequency F2 returns once in two with a sequence F1, F2, F3, F2 ... as represented on the first part 40 of FIG. 9. Thus, a scan cycle has a first period 41. at a first frequency F1, a second period 42 at a second frequency F2, and a third period 43 at a third frequency F3 and a fourth period 44 at said second frequency F2. Step 44 is therefore identical to step 42. To be picked up quickly and reliably by a receiver according to the first scanning sequence, a transmitter of a communication device transmits at said second common frequency F2 repetitive messages 45 spaced apart from each other. a transmission period TE of different duration TS periods of said scan cycle.

In this case, a communication device 20, 26, 28, 3E, 3F, 31 and / or 3J emits at least three repetitive messages 45. By taking as a reference the duration of the periods TS of the scanning cycle, preferably the emission period TE of the repetitive messages has a duration substantially equal to 2/3 or 4/3 of said duration of the scanning periods TS. In FIG. 9 the messages are represented several times in offset in part 46. In the window of the frequency F2, the messages 47 are received since it is sufficient that the beginning of the message is detected. Other messages 48 outside the period with F2 are not received.

FIG. 10 represents a second operating chronogram of a device, a method or a system according to the invention. This flowchart shows a second polling sequence by frequency change Fl, F2 and F3 of a receiver and transmission periods of a transmitter. In this scan, the common frequency F2 returns once in three with a sequence F1, F2, F3, F1, F2, F3 ... as represented on the first part 50 of FIG. 10. Thus, a scanning cycle has a first period 51 at a first frequency F1, a second period 52 at a second frequency F2 and a third period 53 at a third frequency F3.

To be picked up quickly and reliably by a receiver according to the second scanning sequence, a transmitter of a communication device 20, 26, 28, 3E, 3F, 31 and / or 3J transmits at said second frequency F2 repetitive messages spaced from each other. several periods of different durations TE1, TE2 and TE3.

In this case, the communication device 20, 26, 28, 31 and / or 3 J emits at least four repetitive messages. By taking as reference the duration of the periods TS of the scanning cycle, preferably the transmission periods between repetitive messages have a first duration TE1 substantially equal to 4/3 of the duration of the polling periods TS, a second duration TE2 substantially equal to 2.5 / 3 of the duration TS of the scanning periods and a third TE3 duration substantially equal to 5/3 of the duration TS of the scanning periods. In FIG. 10 the messages are represented several times in offset in the part 56. In the window of the frequency F2, messages 57 are received since it is sufficient for the beginning of the message to be detected. Other messages 58 out of the period with F2 are not received.

FIG. 11 represents a second flowchart comprising steps of a method according to the invention with a change of frequency as represented in the timing diagram of FIG. 9 to receive repetitive messages having a substantially constant transmission period. At a step 60, a transmitter / receiver is configured on the frequency F1. Then, at a step 61, a radio message is expected during a polling period TS. If a message appears, the demodulation of the message is started. Then, a step 63 configures the transceiver at a frequency F2. A step 64 controls the processing of receiving long or short messages during a polling period TS. In a step 65, a transmitter / receiver is configured on the frequency F3 to wait for a radio message during a polling period TS in step 66. If a message appears, the demodulation of the message is started. Steps 68 and 69 perform the same functions as steps 63 and 64 respectively.

Fig. 12 shows a third flowchart comprising steps of a method according to the invention with a frequency change as shown in the timing diagram of Fig. 10 for receiving repetitive messages having different transmission periods. In a step 70 a transmitter / receiver is configured on the frequency Fl. Then, in a step 71, a radio message is expected during a polling period TS. If a message appears, the demodulation of the message is started. Then, a step 73 configures the transceiver at a frequency F2. A step 74 controls the processing of receiving long or short messages during a polling period TS. In a step 75, a transceiver is configured on the frequency F3 to wait for a radio message during a polling period TS in step 76. If a message appears, the demodulation of the message is started.

In the flowcharts of Figures 11 and 12, the short messages are always broadband while the long can be high speed or low speed.

Preferably, the polling periods TS have durations greater than short message durations and much shorter than long message durations and / or the preamble of the long messages. For example the change of frequency is done with TS periods of 3 mS. These periods are interrupted or staggered when a message is being received. At the end of the reception, the frequency change scan resumes.

The polling periods TS may be of different durations for example 1 mS, 2 mS and 3 mS. In the examples shown above, the high speed and short message devices emit bursts of repetitive messages having three or four messages. Of course, the invention also relates to different numbers of messages.

Claims

1. Communication device for wireless communication networks at one or more frequencies, characterized in that it comprises means (22, 22A, 22C, 22D, 23, 32-36) for transmitting control on a frequency (F2 ) repetitive messages (45, 55) for reception devices having: - at least two receiving frequencies (F1, F2, F3) with at least one common reception frequency with a message transmission frequency (F2) repetitive, and - scanning means (25, 22B, 22C, 22D, 2 IB, 2 IC, 2 ID, 60-69, 70-76) receiving frequency change according to at least one period (TS) of scanning said repetitive message sending control means (45, 55) controlling the transmission of messages (45, 55) according to transmission periods (TE, TE1, TE2, TE3) between the messages of predetermined durations, at least one predetermined transmission period having a value different from said periods (TS) of scanning said m scan means, said repetitive messages being randomly received in time by the receiving devices.

2. Communication device according to claim 1 characterized in that said transmission control means (22, 22A, 22C, 22D, 23, 32-36) of repetitive messages are fed intermittently and said repetitive messages are desynchronized.

3. Communication device according to one of claims 1 or 2 characterized in that said transmission control means (22, 22A, 22C, 22D, 23, 32-36) of repetitive messages (45, 55) emit messages according to transmission periods (TE) between the messages of durations substantially identical to each other and of different value of said periods (TS) of scanning of said scanning means (25, 22B, 22C, 22D, 2 IB, 2 IC, 21D , 60-69, 70-76).

4. The communication device as claimed in claim 3, characterized in that said transmission control means (22, 22A, 22C, 22D, 23, 32-36) for repetitive messages transmit at least three repetitive messages (45), said period (TE) for transmitting said repetitive messages having a duration substantially equal to 2/3 or 4/3 of said duration of the scanning periods (TS) of said scanning means (25, 22B, 22C, 22D, 2 IB, 2 IC, 2ID, 60-69).

5. Communication device according to one of claims 1 or 2 characterized in that said transmission control means (22, 22A, 22C, 22D, 23, 32-36) of repetitive messages transmit messages (55) according to transmission periods (TE1, TE2, TE3) between the messages of different durations between them and different values of said scanning periods (TS) of said scanning means (25, 22B, 22C, 22D, 2 IB, 2 IC, 2 ID, 70-76).

6. The communication device as claimed in claim 5, characterized in that said transmission control means (22, 22A, 22C, 22D, 23, 32-36) for repetitive messages transmit messages (55) at first periods of time. transmission (TE2) between the messages having at least one duration less than the duration of said scanning periods (TS) of said scanning means and at least second transmission periods (TE1, TE3) having durations longer than the duration of said periods of scanning (TS).

7. Communication device according to claim 6 characterized in that said repetitive message transmission control means emit at least four repetitive messages (55), said transmission periods (TE1, TE2, TE3) between repetitive messages having a first duration substantially equal to 4/3 of the duration of the periods (TS) of scanning, a second duration substantially equal to 2.5 / 3 of the duration of the periods (TS) of scanning and a third duration substantially equal to 5 / 3 of the duration of the periods (TS) of scanning.

8. Communication system for wireless communication networks comprising: - at least one communication device (IC, ID) capable of communicating over one or more frequencies (F1, F2, F3), and at least one communication device (3E, 3F, 31, 3J) communicating with at least one frequency (F2) common to said communication means, characterized in that it comprises:

at least one communication device (24, 26, 28) communicating on at least two receiving frequencies (F1, F2, F3) and with at least one common reception frequency with a message transmission frequency (F2) repetitive and

comprising polling means (25, 22B, 22C, 22D, 2IB, 2CI, 2ID, 60-69, 70-76) with a reception frequency change according to at least one scanning period (TS), and

at least one communication device (20, 26) according to any one of claims 1 to 7 for transmitting repetitive messages (45, 55) on at least one frequency (F2) common with said polling means (25, 22B, 22C, 22D, 2IB, 2CI, 2ID, 60-69, 70-76) with receive frequency change.

9. Communication system according to claim 8 characterized in that said scanning means (25, 22B, 22C, 22D, 2 IB, 2 IC, 2 ID, 60-69, 70-76) frequency change comprise a cycle with a first period (41, 60, 61, TS) at a first frequency (F1), a second period (42, 63, 64, TS) at a second common frequency (F2), a third period (43, 65, 66, TS) at a third frequency (F3), and a fourth period (44, 68, 69, TS) at said second common frequency (F2).

10. Communication system according to claim 8 characterized in that said scanning means (25, 22B, 22C, 22D, 2 IB, 2 IC, 2 ID, 60-69, 70-76) frequency change comprise a cycle with a first frequency (51, 70, 71, TS) at a first frequency (F1), a second period (52, 73, 74, TS) at a second common frequency (F2) and a third period (53, 75, 76, TS) at a third frequency (F3).

11. A method of communication between at least a first communication device and at least a second communication device that can communicate on one or more frequencies, characterized in that it comprises: the scanning according to a frequency scanning cycle (F1, F2, F3) having a change of frequency at each preset scanning period (TS), and

the transmission by a communication device having a common frequency (F2) of repetitive messages (45, 55) according to transmission periods (TE, TE1, TE2, TE3) between the messages of predetermined duration, at least one period predetermined transmission having a value different from said scanning periods (TS).

12. The communication method as claimed in claim 11, characterized in that it comprises: the scanning according to a scanning cycle having a first period (41, 60, 61, TS) at a first frequency (F1), a second period ( 42, 63, 64, TS) at a second common frequency (F2), a third period (43, 65, 66, TS) at a third frequency (F3), and a fourth period (44, 68, 69, TS) at said second common frequency (F2),

transmitting, at said second common frequency (F2), repetitive messages (45) spaced apart from a transmission period (TE) of duration different from the periods (TS, 41, 42, 43, 44) of said scanning cycle.

13. The communication method as claimed in claim 12, characterized in that:

said first communication device transmits at least three repetitive messages (45), said transmission period (TE) of said repetitive messages has a duration substantially equal to 2/3 or 4/3 of a duration of the periods (TS) ) of scanning.

14. A method of communication according to any one of claims 9 to 11 characterized in that it comprises: - scanning according to a scan cycle having a first period (51, 70, 71, TS) at a first frequency (F1 ), a second period (52, 73, 74, TS) at a second common frequency (F2) and a third period (53, 75, 76, TS) at a third frequency (F3),

the emission at said second frequency (F2) of repetitive messages spaced apart by several periods (TE1, TE2, TE3) of different durations

15. The communication method as claimed in claim 14, characterized in that

said first communication device transmits at least four repetitive messages (55), said periods (TS) of the scanning cycle have a first duration, and

the transmission periods (TE1, TE2, TE3) between repetitive messages have a first duration substantially equal to 4/3 of a duration of the scanning periods (TS), a second duration substantially equal to 2.5 / 3 of said duration of the scanning periods (TS) and a third duration substantially equal to 5/3 of said duration of the scanning periods (TS).