FR2839593A1 - RADIO FREQUENCY COMMUNICATION METHOD BETWEEN MULTIPLE DEVICES AND MONITORING SYSTEM IMPLEMENTING SUCH A METHOD - Google Patents

Abstract

The method includes, in normal functioning mode, to synchronise at regular intervals, the compatibility modules of the different devices (1 and 2) and establishing a discontinuous radio communication link, during the consecutive separated temporal windows, between this central device (1) and the peripheral devices (2) corresponding to the cyclical limited activation periods of the central device and of these peripheral devices, repeated at regular intervals, with a frequency greater than the repetition frequency of the emission of the synchronisation message.

Description

first Node B.

DESCRIPTION

  The present invention relates to the field of communication by radio transmission between several separate elements, in particular but not limited to in the case of monitoring or alarm systems, and relates to an improved communication method and a monitoring or monitoring system. alarm implementing such a process. In numerous applications based on the cooperation of several separate electronic devices located at a distance from each other, it is necessary to provide for wireless communication by radio link between these devices as well as an autonomous power supply for each of them. . These provisions may be mandatory for reasons of installation, security and / or independence from the network, in particular

  particularly in the case of surveillance and alarm systems.

  However, systems of this type currently proposed generally use, for reasons of ease of development and development, as well as cost, one-way radio links

between the sensors and the control unit.

  As a result, the sensors or other peripherals may cause them to transmit frequently for all the detections observed, regardless of the system activation mode (weapon or disarm), because they are not aware of the state of the system defined at the central level. On the other hand, due to the limited capacity of the autonomous power sources of the power plant and of the sensors, reception at the level of the cenkale can only be intermittent and transmission at the level of the sensors also. To ensure correct transmission, it is essential that the transmission time from the sensor side is greater than the duration of the rhythm.

listening (reception) central side.

  If you choose a slow listening rhythm, you prefer the autonomy of the control panel to the detriment of the autonomy of the sensors (each transmission must be greater than the listening periods of the control panel). On the contrary, the increase in the listening rate of the central unit penalizes the autonomy of

  this behind in favor of that of the sensors.

  - 2 In practice, the values retained are a compromise between the two, while ensuring the system an acceptable reaction time (time

  means to inform the central office of a detection observed by a sensor).

  However, such a compromise, constitute the least worst solution produced by the state of the art, is not satisfactory, neither from an autonomous point of view, nor from a reactivity, ability or even adaptability point of view. The purpose of the present invention is to meet at least some of the needs expressed above and to provide a suitable solution.

  has at least some of the above limitations.

  To this end, the present invention relates to a two-way communication method by transmission of radio frequency messages in the form of digital frames frequency modulated between a central or primary master device and several peripheral or secondary slave devices, these devices all being physically independent, provided with autonomous energy sources and at least equipped with a radio transmission / reception circuit, as well as a time accounting module providing a local time reference, a process characterized in that it consists, in normal operation, to synchronize at predetermined intervals the accounting modules of the different devices by sending a radio synchronization message from the central device to the peripheral devices and to establish a discontinuous radio communication link, during predetermined separate time windows, between said central device and the peripheral devices correspond to limited periods of cyclic activation of said central device and of at least some of said peripheral devices, repeated at regular and / or predetermined intervals, of duration (s) less than that (s) of the interval separating two successive transmissions of the synchronization message, each activation period comprising a first phase of authorization or obligation to transmit message (s) for one of the peripheral devices and simultaneously listening, at least during a first part of this first phase, for the central device and a second phase of authorization of transmission of message (s) for the central device and simultaneously listening for at least one of the peripheral devices, program recipient (s) ( s) of such a possible message from the central device, said second phase immediately following said first phase and the synchronization message being sent at predetermined intervals during ing

such a second phase.

  The repetition of the synchronization phases will preferably be regular, that is to say with a given frequency (simple and robust procedure). However, this repetition can also be irregular and follow an identical scheme given for the device.

  central and the peripheral devices concerned.

  The precise synchronization between devices, periodically refreshed, makes it possible to reduce the transmission and listening windows (reception state) to minimum values, ideally around the same order of

greatness than the messages exchanged.

  In addition, the definition of limited activation periods affecting only some of the peripheral devices and grouping transmission and listening phases which are temporally adjacent leads, in association with the above-mentioned arrangement, to a significant reduction in consumption at the level of central device, but especially at the level of peripheral devices. Consumption can be further reduced by providing for the transmission of messages from the central device to the devices

  peripherals only when necessary.

  In order to guarantee a reception of messages free of koncature due to a possible offset between simultaneous transmission and listening phases, each message exchanged between master device and slave device (s) comprises a first part forming a preamble of which the time duration is greater than the maximum drift of synchronization between the central device and the peripheral devices during the interval separating two successive synchronization messages and the device (s) in listening phase remain active at least during the duration of this preamble, continuously or discontinuously, said device or devices being deactivated or put on standby in the absence of detection of

  message after this period has elapsed.

  If there is an advantageous variant of real is ati on of the invention, the body of the preamble may be constituted by a portion of digital message in the form of a repeating pattern comprising as many as 1 as 0, preferably present in a regularly alternating manner, said preamble ending with a pattern of particular numeric characters different from said repeating pattern, preferably an extended sequence of a

  plural of 1, followed by an extended sequence of plural 0.

  - 4 In addition, it can be advantageously provided that, for each message sent, the preamble is followed by a synchronization byte for the activation of the asynchronous radio transmission interface of the transmission / reception circuit. of the cenkal or peripheral device (s) or recipient (s), and that said peripheral devices carry out, after each reception of a synchronization radio message, a verification of the validity of said message, then an exploitation of its information time by its comparison with the local time reference of the peripheral device concerned and the subsequent modification, by advance or delay, of the local time reference provided by the accounting module correspond as a function of the difference observed or of a fraction of the latter , evaluated taking into account at least the last two

previous deviations noted.

  In any event, the length of the messages sent will be calculated in such a way that, in any case, there is an overshoot of the

  emission authorization phase assigned.

  In accordance with a preferred embodiment of the invention, corresponding to an optimized operation, the central device is systematically listening during the first phase of each period of cyclic activation. Furthermore, the peripheral devices are authorized to transmit, one by one, in a predetermined cyclic order, for example the link to their address for identification and recording with the central device, and with a repetition frequency, occurrence or realization correspond to a soul-multiple of the frequency of repetition of the limited periods of activation and the listening phases of said peripheral devices repeat with a frequency of repetition or of occurrence correspond to a soul-multiple of the frequency of repetition of the limited activation periods, said repetition frequencies being different for each type or each of the peripheral devices, the frequencies of the listening phases being, for the same peripheral devices, higher than the frequencies, of the emission phases every peripheral devices listening for each transmission of a radio message from

  synchronization sent by the central device.

  In order to avoid as far as possible total or partial collisions between messages transmitted simultaneously or in a partially overlapping manner by two different devices, it can be provided that, immediately before each phase of transmission of a message by the central device or the one of the peripheral devices, the device concerned puts itself in a listening position, and is only authorized to transmit in the absence of

  any radio message being transmitted.

  In general, in current operation, the messages addressed by the peripheral devices to the central device consist either of predetermined routine messages indicating a normal situation at the level of the peripheral device concerned and obligatorily addressed to the central device repetitively at successive instants to each peripheral device, that is to say random messages for signaling an incident, an event or an abnormal situation, each signaling message being transmitted to the central device during the authorization phase of transmission of the immediately consecutive activation period upon the occurrence of an incident, event or abnormal situation and its emission beginning before the start of the emission authorization phase, said signaling messages being provided with extended preambles. The method according to the invention thus implements a method of active monitoring of the radio link between the peripherals and the central unit.

  link of presence messages cyclically.

  The peripherals send their respective messages sequentially using their individual address to determine the time of transmission in relation to their local time reference, itself periodically wedged on the sequencing of the central unit. Likewise, the central unit determines the times during which it is supposed to receive the

  presence messages from different registered devices.

  In order to be able to maintain communication between the central device and all the peripheral devices, despite poor radio frequency transmission conditions, interfering or jamming signals or a charged electromagnetic environment, the various devices are quick to transmit and to receive radio signals on at least two frequency channels, namely a main channel used in normal operation and at least one fallback, fold-down or emergency channel used in the event of transmission difficulties on the main channel, or by time distribution communications on

  several channels used alternately.

  Thus, in accordance with a first embodiment of the invention, said method may consist in switching radio transmissions - 6 between devices of the main channel to the or a fallback channel on the initiative of a peripheral device, after this the latter diagnosed a break in its radio frequency link with the central device, either due to the absence of reception, possibly repeated, of a radio synchronization message at one or more predetermined time (s), or due to [ 'absence of response message or acknowledgment of receipt from the central system following a previous link, repeatedly, radio messages, in particular messages signaling an incident, an event or an abnormal situation, of the peripheral device concerned

versleditdispositifcentral.

  According to another characteristic of the invention, the switching of transmissions between devices on the or a fallback channel consists, for the peripheral device on the initiative of said tilting, of switching on the or a fallback channel at the time of the advent a phase of authorization or obligation to send messages that is assigned to it in the order established for the various peripheral devices, to then put itself in a listening position for a first duration at least equal to the sum of the durations of the interval separating two periods of cyclic activation and of such a period, then possibly, in a repetitive manner, during the estimated consecutive emission phases of the central device, until receiving a delayed synchronization message emitted by the central device and fixing the new rhythm of emission and listening between said

  peripheral device and said central device on said fallback channel.

  According to yet another characteristic of the invention, the switching of transmissions between devices on the or a fallback channel consists, for the central device, after having noted the repeated absence of reception of any message, in particular a routine message, during several successive authorization or transmission obligation phases allocated to the flip-flop peripheral device, to be transmitted during the next listening phase provided to said peripheral device a synchronized synchronization message on the fallback channel, or successively on the different possible fallback channels, possibly repeating this transmission during several successive corresponding listening phases of the peripheral devices on the fallback channel or channels, until receiving a return message from said peripheral device having toggled , and to send one or more messages, in one or more emission authorization phases to said central device, requiring the switching 7 of the other peripheral devices on the considered fallback channel, the case falling in the order of addressing of said other peripheral devices, the successive phases of transmission / reception of the various devices on the main channel and on the fallback channel being shifted in time, the addressing order of the peripherals, after their tilting, will be the fallback channel being either identical to that prevailing on the main channel, or different from the latter, the new order being in this

  last case indicated by the central device to the peripheral devices.

  This rear arrangement allows the central device to communicate simultaneously with all of the distributed peripheral devices.

  on both transmission channels.

  In accordance with a second embodiment of the invention, the wind devices capable of transmitting and receiving radio signals on at least two different frequency channels and at each successive time window the central device and the peripheral devices are switched on a different channel of that used for the immediately preceding time window, according to a predetermined order of succession of said channels, which is identical for each device and which takes place from

  synchronously for all said devices.

  Thus, a jump is made at each activation period

  frequency according to a deterministic scheme identical for all devices.

  Preferably, the latter use at least four different communication channels and the order of succession of said channels.

  is selected when these devices are started up.

  The repetition sequence of the different channels will preferably be odd when the number of usable channels is even

  and will present a number of steps greater than the number of usable channels.

  For marginal cases where it is necessary to implement a recovery procedure (for example after a failure, a shutdown of the power plant, ...), a fallback channel can be provided which will be fixed and known to the various devices , in addition to the various current channels used during

  normal communication procedures.

  As part of an initialization phase of the communication or integration process of a new peripheral device, the pairing of such a new peripheral device or the re-pairing of a peripheral device having been disconnected with respect to the central device, consists, by exchanging asynchronous radio messages, of sending to the central device a message indicating the characteristics of said new peripheral device, in particular the frequency of its activation for transmission and listening, then of transmitting to this latter an address , also fixing its order in the sequence of the phases of authorization of transmission of the various peripheral devices in connection with the central device, an initial synchronization message and a

  possible site identifier used for secure transmissions.

  Likewise, the method according to the invention can consist of a mobile peripheral device, having been disassembled outside the field of coverage of the central device and having received a reactivation and / or reconnection signal or having made [' object of this type of solicitation, to be sent continuously for a duration greater than the sum of the durations of a period of activation of the devices and of an interval separating two such periods, a signaling frame containing the address or the identifier assigned to said device, then to put itself in a listening situation with a view to receiving a response from the central device, in the form of an initial synchronization message accompanied by a request for authentication, to repeat the two previous operations for the different possible transmission channels, starting with the last channel used by said peripheral device before its disconnection from the central unit, until reception of a response e on the part of the central device or reaching the predetermined maximum number of attempts, with standby or deactivation consecutive to said peripheral device considered in the event

  failure to reestablish communication with the central device.

  Typically these last measurements can be implemented in relation to a non-fixed peripheral device, ointment, such as

than a remote control or the like.

  In order to increase the reactivity and the efficiency of the process according to the invention, while keeping a current low activation rate, each peripheral device can have two different frequencies of repetition of its period of cyclic activation and communication. radio with the central device, namely a low frequency and a high frequency, said peripheral device operating normally with the low repetition rate and said peripheral device switching to the high repetition rate when said device is requested or active or, in an anticipated manner , when said device determines the next occurrence of an action likely to solicit it or to necessitate

  establishing communication with the central system.

  In accordance with a particularly advantageous application, the communication method according to the invention can be implemented by a monitoring or alarm system, the central device consisting of a microprocessor-based alarm center for the execution of the management and piloting said system and provided with an external communication interface and the peripheral devices consist of one or more sensor (s), control organ (s), organ (s) for taking images and / or sounds, siren ( s), horn (s), actuators (s), detector (s) and / or

  communication device (s) to a network.

  The invention also relates to a monitoring or alarm system comprising a central unit and peripherals, forming independent devices and with autonomous power supply, characterized in that it

  implements the communication process as described above.

  The invention will be better understood, thanks to the description below.

  after, which relates to a mode of real i sati one prefers, gives a tike of nonlimiting example, and explains with reference to the annexed diagrammatic drawings, in which: Figure 1 represents chronograms showing the signals emitted / received at central device level during two successive activation periods; FIG. 2A represents timing diagrams illustrating the offsets that can be generated when transmitting and receiving messages sent by the devices during the TPP due to the drift of the local clock; Figure 2B illustrates a variant embodiment of the invention according to which the activation of the central device in the listening phase is intermittent during the TPP; Figure 3 is a flowchart representing the steps performed by a peripheral device that has not received a synchronization message (top desynchro) sent by the central device at a predetermined time; Figure 4 is a representation in the form of a timing diagram of an example of constitution of a signaling frame emitted by a mobile peripheral device wishing to resume the link with the central device; - 10 Figure 5 shows an example of possible structure of the current frame used in the context of the method according to the invention, Figure 6 is a schematic representation of an assembly comprising a central device and several peripheral devices communicating with the latter according to the method object of the present; Figure 7 shows in diagram form the different possible states for peripheral devices in relation to the first embodiment of the invention described above, and, Figure 8 shows in diagram form the different possible states for devices peripherals related to the second

  embodiment of the invention described above.

  The invention will now be described more precisely in relation to a practical embodiment in the form of a monitoring or alarm system consisting of at least one central or central device 1 with microprocessor (in some cases called base) cooperating with at least one peripheral device or peripheral device 2 chosen from the list comprising the sensors, control devices, sirens, alarms, actuators and the devices for communication to a network by means of distance-race radio communications (also called SRD) using a free band Of type

ISM).

  Each element of this system, shown diagrammatically in FIG. 6, is fitted with a radio transmission / reception circuit 1 ′, 2 ′ (alternating) and has an autonomous energy source (cell or battery), as well as a module 1 ", 2" of time recording associated with a time reference (typically a quartz with a counting chain) again

called "local reference".

  The control unit 1 periodically emits a radio signal containing information representative of the temporal sequencing of said control unit 1 and the peripherals 2 receive this information so as to calibrate their internal functioning at a rhythm identical or multiple to that of the control unit 1 or at least try to approach it. When control unit 1 sends the temporal information, it precedes it by a series of characters (called preamble) whose emission duration is greater than the maximum drift observable between a peripheral 2 and control unit 1 (taking into account the uncertainties related to crystal precision, temperature deviations, crystal aging and differing uncertainties), increased by the number of characters required to ensure reception synchronization, allowing devices 2 in reception mode to detect transmission of [ time information despite the derivatives of time references, knowing that the rate and time of transmission of wind are predetermined both in the central unit 1 and in the peripherals 2 considered. Said peripherals 2 exploit this temporal information after verification of the validity of the latter (use of an electronic "signature" system or authentication) by modifying their counting chain in advance or delay of this behind according to the observed gap between the local reference (peripheral 2) and the temporal information transmitted, of a value equal to this deviation or to a fraction of this deviation, weighted by the average value calculated in a sliding manner on the

previous deviations.

  According to an example of practical implementation without limitation of a monitoring and alarm system, the central unit 1 can operate on a reception rate of one second (interval separating two successive listening phases), for a duration of approximately ms in ['no message and

  ms in the presence of a message from a synchronized device 2.

  The window or listening phase of control panel 1 starts 125 ms (1/8 s) before its speech window. This window is called peripheral speaking time

(TPP).

  This listening period of the control unit 1 is followed by a time of

  40 ms speech for the latter called TPC (central speaking time).

  It is used in particular to synchronize the devices every 64 seconds (repeated sending of synchronization message). TPC talk times are only used if the control panel has information to transmit. Synchronized devices are not allowed to transmit during TPC (see

figure 1).

  When non-synchronized peripherals 2 transmit, they may accidentally do so during the talk time of the control panel, and for a duration of up to one second. The central must therefore verify

  before transmitting, the presence or absence of an already committed program.

  Thus, energy saving is obtained by reducing the listening and transmission times for the various devices 1 and 2 constituting the alarm system. This reduction is only possible thanks to the

  synchronization of the peripherals to the rhythm of the central unit.

  - 12 The inevitable physical inaccuracy of synchronization on which the simulations carried out by the inventors were based gives a delta () of 12 ms per minute, when a quartz of 32.768 kHz is used as a reference. When the initial precision of the quartz is +/- 30 ppm and the temperature drift is given at +/- 50 ppm in the range -10 to + 55, the overall tolerance adopted will be +/- 100 ppm to take account of 'other

  factors (aging, dispersion of resynchro, ...).

  As indicated above, the set of peripherals 2 (with the possible exception of a nomadic peripheral of the remote control type) is synchronized on the central unit. When the system is started up, after the installation phase, the peripherals v cale at the rate of 60 s. This synchronization is maintained by the repeated (systematic) acquisition of the synchronization signal (synchronization message) sent by the control panel. As the control panel is in reception every second, peripherals with a message to send to the control panel must

  do in the scheduled TPP interval (see Figure 1).

  The address messages in normal operation can be of two types: - signaling or alert message (intrusion, self protection, power failure, ...) - presence message (with possible indication

  stack level and field level).

  The first type being unpredictable and exceptional, there is no collision in the vast majority of cast A mechanism

  particular to manage rare collisions is explained further.

  The second type is predictable because the peripherals are configured to emit a presence signal at regular intervals (every 600 s for example). Two possible wind solutions: - systematic call of the peripherals by the central unit (drawback: increased consumption for the central unit) - automatic sending of the presence message by the peripheral initiated by a first call (the central unit can thus leave the peripherals over 600 seconds and therefore avoid subsequent collisions). This automation can be stopped by the sending of a "silence" command by the central unit. - 13 For reasons of energy saving and functionality, the peripherals are also tuned in according to a predetermined alternate cycle. While for the power plant this cycle is one second, it

  may vary from 2 to 30 seconds depending on the devices.

  In practice, this means that the control panel cannot communicate at any time, with any device, and that it must therefore manage

  predictively its listening periods of the peripherals.

  For reasons of simplicity, all the peripherals will be wedged on the same soul-multiples: - cycle at 2 seconds: awakening on the second padres (0,2,4,)

  - cycle at 10 seconds: 0, 10, 20, 30, 40, ...

  - cycle at 30 seconds: 0 and 30 seconds.

  All of the peripherals are therefore listening to at least two

  times per minute (simultaneously for at least some of them).

  When the control unit needs to communicate with several peripherals (after collision detection, sending an order to several contacts, ...) or just one (rapid entry of several parameters with the control unit), the control unit informs the peripherals concerned with the activation of this mode of communication, which will have the consequence for the peripherals concerned to keep the reception active until the transaction or communication in progress

  either ended or this mode is deactivated by the control panel.

  In practice, the control panel activates the mode by specifying the peripherals concerned, namely: - a particular peripheral - the peripherals having initiated a communication (or during dialogue) with the central

- all peripherals.

  As indicated above, such a discontinuous mode of communication requires precise synchronization between the control unit 1 and the ..,.

perlpnerlques f.

  In the practical example mentioned above, the central unit and the peripherals have a time base of 32768. Thus, every 64s, the central unit sends a synchronization signal (message) which allows the peripherals to reset the channels. counting their modules

counting 2 ".

  - 14 The sync top coincides with the end of the word in the synchronization message (but another convention can be used). The control unit must therefore anticipate the length of the preamble to be "on time". When a TPC is superimposed with the sending of the sync (once per 64s), the peripherals go into reception mode at the same rate

  than the one used by the central during the TPP.

  The synchronization message can take the form of any message. One can imagine that to reduce the effect of a loss of synchronization, the peripherals adjust their clock by software based on the deviations observed at the time of synchronization. In the absence of correction, a measurement of the difference observed (including the sync signal and the local clock) can help to maintain a satisfactory level of performance in the event of "prolonged" sync loss, because the

  necessary activation anticipations can be minimized.

  In this context of synchronized transmission / reception, two main problems may arise: the drift of local time references and the lack of synchronization due to the absence of reception of the cyclic synchronization message forming "synchro-top", which may arise from a loss of connection between cenkale and peripheral. Concerning the derivatives (local clock derivatives), the error will be, in the practical case mentioned above, of 6 ms or a delta of 12 ms

as mentioned above.

  In a practical way, this means that when the control panel starts listening, a peripheral could have started a transmission 6 ms longer.

  early, or can start 6 ms later.

  In the extreme case, the control panel activates first, a device can transmit 12 ms later. These 12 ms are advantageously absorbed by the presence of a preamble signal preceding the message.

proper (see Figure 2A).

  This preamble allows in particular: - to manifest / detect radio activity while preserving the message of a truncation, - to perform an AFC (automatic frequency control) if the average frequency is f0 (numbers of 0 and 1 identical) - 15 - to synchronize the receiver to activate the UART (asynchronous transmission / reception interface) at the appropriate time, - to absorb the clock differences between the elements

constitutive of the system.

  As the speech window of devices 2 is limited to ms, the message sent by a "late" device should not exceed the limit of the TPP. If the preamble is 14 ms (dispersion delta) + 3 characters (i.e. 3 ms), the message will be a maximum: 125 - 12 - (14 + 3) = 99 ms (99 bytes at 9600 teds). Advantageously, we will limit ourselves to 31 ms for the length of the message to avoid any risk of overflow

(figure 2).

  Advantageously, the preamble contains as much 1 as 0 so that, in frequency modulation code, the average value of the radio signal corresponds to the central value of the radio channel used, thus allowing the activation of an automatic servo-control device of the frequency

  (AFC) receiver side, at the start of the call.

  Preferably, the preamble is made up of a series of 55h characters (101010 ...) allowing faster exploitation of the frequency control and can be followed by a pattern made up of two characters FFh and OOh used to mark the end of the preamble and the beginning

  data transmitted in the message or frame concerned 2.

  Receiving FFh before OOh indicates that synchronization

  character was carried out from the first 55h.

  In practical terms, said preamble can, for example, be

  composed of 15 characters, i.e. 15.6 ms of duration (at 9600 teds).

  Alternatively, the first 14 characters can be the same and be OxFO (0000011111 in binary). The 15th is worth Ox9c (0001110011 in binary). The beginning of the preamble materializes in the form of positive and negative pulses of equal length (521, us). The last character Ox9C

indicates the end of the preamble.

  To optimize the consumption of the receiving device, the activation of the latter can be cut in two periods of 4 ms (instead

  15 ms continuous), as shown in Figure 2B.

  In addition, a synchronization fault can occur when a device 2 misses one or more synchronization message (s) sent by

control unit 1.

  - 16 The first time, the device retains its internal reference, but during the next minute, it will have to anticipate the TPC so

  be able to receive the synchronization message even in the event of delay.

  If synchronization is missed a second time, the device concerned must initiate a procedure to regain its synchronization, such as

  than that represented for example in FIG. 3.

  To implement such a procedure, the system according to the invention will, for example, implement a method of managing transmissions on multiple channels with drawdown in the event of failure.

of the usual radio link.

  Thus, during the installation of the system, the control unit 1 requests the different recorded peripherals 2 to measure the quality of the radio signal on the set of usable channels (measurement of the noise floor using the RSSI - power indicator signal received), so as to be able to determine in a second time which will be respectively the main channel and the backup channel (or fallback). After having made the selection, the control unit 1 indicates to all the peripherals the settings

on the choice of channels.

  Radio link faults can be noted, on the one hand, by the peripherals, when the time registration is no longer received at the scheduled time or when there is no acknowledgment following the transmission of an event and, on the other hand on the other hand, by the central office, by the repeated absence of presence messages or the absence of acknowledgment following a request. This observation is put to good use: - by the device (s) concerned, to switch to the rep channel linked after a predetermined number of registration absences (non reception of several synchronization messages) or successive repetitions of transmission of event signaling messages that remained unanswered, and, - by the central unit, to search for the device (s) for absent "subscribers" (absence of presence message or of

non-response to a request).

  In all cases, one of the peripherals 2 of the system will initiate the channel change when the required conditions are met, and the control unit 1 will emit a form of radio beacon on the fallback channel (after the required conditions) , while retaining the management of

main channel.

  Each device 2 having rocked on the channel of reduction modifies its rhythm and its chronology of reception. Indeed, while the peripherals operating on the main channel activate at different rhythms (depending on the nature of the peripherals), the rhythm

  is identical for all of them that they have rocked on the fallback channel.

  Advantageously, the instants of the listening phases on the channel

  fallback, wind shifted from nominal operation.

  Thus, for example, in nominal operation (main channel), exchanges (excluding alerts) are made on second padres and, in emergency operation (drawdown channel) and the radio beacon is transmitted by the central unit 1 to odd seconds (which allows it to

  continue to manage the other peripherals 2 on the main channel).

  In the practical example discussed, the link loss procedure is initiated after two synchronization losses (two synchronization messages not received). At first, the isolated peripheral of the control panel continues to listen for synchronization every minute on the initial channel. Anticipation of the TPP and TPC wind intervals anticipated (or delayed) by the value: (Number of minutes elapsed since behind synchro) x

(average error observed).

  In a second step, the isolated device switches to the fallback channel when it was supposed to send its presence message and returns to reception mode for a second to try to capture a synchro (the control panel having noted the absence of signal presence, it is programmed to send a status request (synchronized) on the

drawdown channel.

  If this procedure is not successful, the peripheral concerned will fall asleep for 32 seconds, then reactivate reception for 40 ms on the fallback channel (during the TPC) and so on (sleep, Rx, ...). These ms are divided into periods of 4 ms of Rx separated by

2 ms standby.

  It should be noted, in this regard in particular, that the presence of a mobile device, such as a remote control, in the surveillance or alarm system will constitute a special case since it could be outside the coverage area at the time of migration (tilting of the - 18 peripherals on the fallback channel). Therefore, if it is not synchronized, it transmits asynchronously successively on the four channels, starting with the channel that has been used most recently. The show on

  each channel must eke a second to allow listening by the control panel.

  The different communication channels that can be used are preferably

located in the 868 MHz band.

  In fact, a mobile device such as a remote control will have to be managed in a specific way, in particular as regards its communication with the central, since it is likely to leave the

  radio coverage area of the plant.

  It will therefore be necessary to plan some special provisions for this peripheral, with repercussions on the

general functioning of the system.

  Thus, it can be provided that: - in the absence of synchronization signal, the remote control falls asleep and is reactivated only at the press of a button, - a button press "wakes up" the remote control which is therefore no longer Synchronized; to be sure of being heard, it will have to transmit for one second on each of the four possible communication channels, starting with the last one (in date) used - each transmission is followed by a listening time to detect a possible response from the control panel for a determined period before going to the next channel to indicate this phase to the user, you can flash a diode quickly until the connection with the control panel is established when the control panel detects the remote control, it responds by an authentication request accompanied by synchronization parameters As the frame sent by the remote control can be picked up at any stage, it is proposed to establish the connection in two stages: - signaling frame transmitted continuously (1 second) containing only simp l ifiee information of linker dentificati on (to allow the interpretation of the message with a reduced number of bytes received), response from the central by a e authentication request, - 19 - sending the authentication certificate by remote control with the parameters of the latter (id of the button pressed,

battery level, ...).

  A proposal for a transmission frame for the remote control is shown in Figure 4. The proposed frame contains 4 bytes repeated 241 times to obtain a second transmission: The first byte is a preamble byte, the 2nd is a sync byte identical to the preamble of the messages and is worth OxfO (0000011111 in binary. The 3rd and 4th bytes are a value fixed at the time of

the remote control pairing.

  Furthermore, it is also worth mentioning the problems linked to possible collisions of radio messages that may occur in the system, namely: - simultaneous response of two devices during the TPP; superimposition of a remote control emission (asynchronous)

  with a central-peripheral dialogue.

  The first case is identified by the central unit by the observation of the envelope of the superimposed carriers: the signal indicating the level of field must in principle indicate at the end of the TPP ['absence of signal, consequently with an impossibility of decoding viable data during the TPP. In this case the control panel quits by sending in the TPC a message requesting a prolonged listening of the peripherals to allow

a call from two.

  In the second case, the remote control emission is detected by the control panel, at the earliest at the time of the TPP, if not during dialogue. At the end of TPP, the field level signal will indicate a pros of the presence of the emission, and during dialogue, the intervals of silence will not be respected. From these observations, the control unit interrupts the dialogues in progress to listen to (and decode as soon as possible) the frame of the remote control. It would be desirable that the peripherals involved can also detect this case for

cancel a scheduled program.

  At the end of the remote control frame, the control panel responds with a message (in priority to what was in progress) intended for the remote control to initiate a dialogue. This response must take place within the standard delay provided so that such a remote control does not switch over to the next radio channel - 20. It would be desirable that, if this collision occurs at the time of a synchro, that the peripherals having noted either the absence of sync, or the remote control frame, postpone to the next second the attempt at sync. In case of failure (i.e. impossibility for the control panel to send the synchro), this will be done for the next

  minute (at this point in 63 seconds).

  Finally, the monitoring or alarm system may also implement an initial synchronization method for each

  new device 2 (also known as pairing).

  In this case, before a device can integrate into the system, it will have to exchange information on its characteristics (type of sensor, identifier, etc.) and receive in return an address code allowing to identify it within of the system, as well as a "time setting" of its reference

local to central 1.

  This is achieved by sending an asynchronous request for a pairing request by the peripheral concerned, successively scanning the different radio channels likely to be used at the time of the

initial synchronization.

  The transmission periods (peripheral side) are interspersed with racing reception periods in order to test a possible response from control unit 1 (and initiate dialogue ...). Said central unit 1 will be previously placed in a specific mode used to install new peripherals 2, so as not to accidentally take into account a peripheral being installed in another system located within range

radio.

  This initial synchronization mode can also apply to peripherals which have left the radio coverage area of control panel 1 (remote control, alert medallion, etc.). Indeed, if one wishes to solicit them after having returned to the perimeter of the central 1, they must resynchronize in order to be able to dialogue. Likewise, a peripheral 2 having

  been stopped (battery replacement) must re-engage this procedure.

  To complete the description of the example implementation

  practice of the invention set out above, a possible constitution will be described below, as well as an associated format, for the usual messages (synchronization, routine, signaling) in the form of digital frames, exchanged between the devices 1 and 2 forming the system

alarm or monitoring.

  - 21 A tell th frame is represented in FIG. 5 of the accompanying drawings, and is normally preceded by a preamble and a byte of

  synchronization as mentioned above (not shown).

  The "signaling" fields (signaling_1 and signaling_2) indicate to the device (s) receiving the frame (s) the conditions and

  the enchantment of the transmission in progress.

  These fields can for example indicate the situation of the frame in a transmission (first, behind), the number of recipients (frame intended for a specific device or all the devices), the type of recipients (device having a transmission in progress) , whether or not to write encryption or authentication, and

  synchronized or asynchronous nature of the frame.

  The length (coded on 6 bits) indicates the number of bytes of the

"data" area.

  The Ack flag is an acknowledgment flag indicating that

  the frame is also used to acknowledge the received frame.

  The "type" field identifies the nature of the message

  ("Rfa" is a free bit for possible subsequent assignments).

  Valid addresses range from Olh to 3Eh, the value 00 being used for broadcast commands and the value 3Fh for

  peripherals not paired. The address of the central office is your default name.

  In the peripheral direction towards the central, the address represents the sender,

  in the opposite direction, it is the recipient.

  The "data" field forms the zone containing the useful information. Most frames have a fixed length, that is, the data is 32-bit. To standardize the formats, the length is shown

done in all messages.

  The "MAC" zone is used to authenticate the message and the calculation of its content can be carried out in different ways, in particular according to those known to those skilled in the art, for example of the type

known as the AES designation.

  Finally, the "CRC" is a cyclic redundancy zone making it possible to ensure that the frame has not suffered any error during radio transmission. Its calculation complies with the CCIR standard. The data taken into account in the calculation include all the fields (from

signaling_1 has MAC included).

  - 22 It should be noted that there are two sequences whose format differs from the format described above. Wiles are employed in situations where synchronism is not guaranteed between the sender of the message and the recipient. The first non-standard sequence is used by this remote control (and all other mobile devices) to indicate its intention to send a status kame. Indeed, a prolonged distance from the control unit causes synchronization to be lost. The remote control sends a particular sequence for one second on the last channel used and tries to get a response from the control panel. A failure begins with the transmission of the same sequence on another channel, and so on until the exhaustion of

four possible channels.

  The other non-standard sequence is used by the control panel to resynchronize peripherals whose radio link has been interrupted for an extended period (typically> 512 s). This case does not concern mobile devices (remote controls, medallions, etc.). Indeed, after 128 seconds without synchronization and a synchro request in failure, a device goes into a sleep mode from which it will only come out on request from the central unit, this in order to preserve the energy of the batteries. In practice, times will be fine so as not to obtain an overly sensitive system. Figures 7 and 8 show schematically the different possible states for the peripheral devices 2, respectively in relation to the first and second embodiments. In these figures, the following terms have the meanings indicated below: - Rx: reception; - Tx: emission; - "time-out": expiry of the time limit); - "timing": sequencing or repetition cycle; - P_stat: device status frame; - C_app: pairing frame sent by the central unit; - P_init: pairing request frame; - P_txt: text entry frame; - synchro or sync: synchronization frame; - 23 - C_chan: channel change frame sent by the control panel; - C_stat: status request frame sent by the central; - C_xxx: indeterminate frame; S "burst": burst;

- "tst": test.

  Of course, the invention is not limited to the embodiments described and shown in the accompanying drawings. Modifications remain possible, in particular from the point of view of the constitution of the various elements or by substitution of technical equivalents, without leaving for

  as much of the protection field of the invention.

-24

Claims (14)

  1) Method of bidirectional communication by transmission of radio frequency messages in the form of digital frames frequency modulated between a central or primary master device and several peripheral or secondary slave devices, these devices all being physically independent, provided with energy sources autonomous and at least equipped with a radio transmission / reception circuit, as well as a time recording module providing a local time reference, a process characterized in that it consists, in normal operation, in synchronizing the modules at predetermined intervals for accounting for the different devices (1 and 2) by sending a radio synchronization message from the central device (1) to the peripheral devices (2) and for establishing a discontinuous radio communication link, during separate repetitive time windows predetermined, between said central device (1) and the peripheral devices es (2), correspond to limited periods of cyclic activation of said central device (1) and of at least some of said peripheral devices (2), repeated at regular and / or predetermined intervals, of duration (s) less than (s) that (s) of the intervals separating two successive transmissions of the synchronization message, each activation period comprising a first phase of authorization or obligation to transmit message (s) for one of the peripheral devices (2) and simultaneously listening, at least during a first part of this first phase, for the central device (1) and a second authorization phase for sending messages (s) for the central device (1) and simultaneously listening for at at least one of the peripheral devices (2), program recipient (s) of such a possible message from the central device (1), said second phase immediately following said first phase and the synchronization message being sent at intervals   predetermined during such a second phase.   2) Method according to claim 1, characterized in that each message exchanged between master device (1) and slave device (s) (2) comprises a first part forming a preamble whose time duration is greater than the maximum drift of synchronization between the central device (1) and the peripheral devices (2) during the interval separating two successive synchronization messages and in that the device (s) in listening phase remain active (s) at least for the duration of this preamble, in a continuous or dis continuous manner, said device (s) being active (s) or partially on standby   ['absence of message detection after this period has elapsed.   3) Method according to claim 2, characterized in that the body of the preamble is constituted by a portion of digital message in the form of a repeating pattern comprising as many as 1 than 0, preferably present in a regularly alternating manner, said preamble ending in a pattern of particular numeric characters different from said repeating pattern, preferably an extended sequence of a plurality of 1, followed   of a sequence extended by a plurality of 0.   4) Method according to claim 3, characterized in that, for each message sent, the preamble is followed by a synchronization byte for ['activation of [' interface of asynchronous radio transmission of the transmission / reception circuit (1 ' , 2 ') of the central device (s) (1) or peripheral (s) (2) recipient (s), and in that the said peripheral devices (2) realize, after each reception of a synchronization radio message , a verification of the validity of said message, pods an exploitation of its temporal information by its comparison with the local temporal reference of the peripheral device (2) concerned and the consecutive modification, by advance or delay, of the local temporal reference provided by the module of corresponding accounting (2 ") according to the observed ltec or a fraction of the latter, evaluated   taking into account at least the last two previous deviations noted.   5) Method according to any one of claims 1 to 4,   characterized in that the central device (1) is systematically tuned during the first phase of each period of cyclic activation, in that the peripheral devices (2) are authorized to transmit, one by one, in a cyclic order predetermined, for example linked to their identification and registration address with the central device (1), and with a frequency of repetition, occurrence or realization correspond to a soul-multiple of the frequency of repetition of the limited periods activation and in that the listening phases of said peripheral devices (2) are repeated with a frequency of repetition or occurrence correspond to a soul-multiple of the frequency of repetition of the limited periods of activation, said frequencies of repetition being different for each type or each of the peripheral devices (2), the frequencies of the -26 listening phases being, for the same peripheral devices (2), higher than the frequencies of s transmission phases, all peripheral devices (2) listening to each message transmission   synchronization radio emitted by the central device (1).   6) Method according to any one of claims 2 to S.   characterized in that, immediately before each phase of transmission of a message by the central device (1) or one of the peripheral devices (2), the device (1 or 2) concerned puts itself in a listening situation, and is only allowed   to emit in the absence of any radio message during transmission.   7) Method according to any one of claims 1 to 6,   characterized in that the messages addressed by the peripheral devices (2) to the central device (1) consist either of predetermined routine messages indicating a normal situation at the level of the peripheral device (2) concerned and necessarily addresses to the central device (1) in a repetitive manner at successive instants specific to each peripheral device (2), either in random messages for signaling an incident, an event or an abnormal situation, each signaling message being transmitted to the central device (1 ) during the emission authorization phase of the activation period immediately following the occurrence of the incident, event or abnormal situation and its emission starting before the start of the authorization phase 'emiss ion, the so-called generalization messages being provided with extended preambles.   8) Method according to any one of claims 1 to 7,   characterized in that the various devices (1 and 2) are able to transmit and receive radio signals on at least two frequency channels, namely a main channel used in normal operation and at least one fallback, drawdown or backup used in the event of a transmission failure on the main channel, and in that the said method consists in switching radio transmissions between devices (1 and 2) of the main channel to the or a fallback channel on the initiative of a device peripheral (2), after the latter has diagnosed a cut in its radio frequency link with the central device (1), either due to the absence of reception, possibly repeated, of a synchronization radio message at one or more timescale (s) ) predetermined (s), either because of the absence of a response message or acknowledgment of receipt from the central device (1) following the prior sending, repeatedly, of radio messages, in particular messages -27 - by signali of an incident, an event or an abnormal situation, from the peripheral device (2) concerned towards said device central (1).   9) Method according to claim 8, characterized in that the switching of transmissions between devices (1 and 2) on the or a fallback channel consists, for the peripheral device (2) at ['initiative at said switching, to switch to the or a fallback channel at the time of the advent of an authorization or obligation phase for sending messages that is allocated to it in the order established for the various peripheral devices (2), has then to put in listening situation during a first duration at least equal to the sum of the durations of the interval separating two periods of cyclic activation and such a period, then possibly, in a repetitive way, during the emission phases estimated consecutives of the central device (1), until receiving a delayed synchronization message sent by the central device (1) and fixing the new transmission and listening rhythm between said peripheral device (2) and said central device (1) on said c fallback anal.   ) Method according to any one of claims 8 and 9,   characterized in that the switching of the transmissions between devices (1 and 2) on the or a fallback channel consists, for the central device (1), after having noted the repeated absence of reception of any message, in particular of a routine message, during several successive phases of authorization or of obligation of emission allocated to the peripheral device (2) having toggled, to emit during the next listening phase provided for said peripheral device (2) a synchronization message shifted on the rep channel linked, or successively on the different possible fallback channels, to possibly repeat this emission during several successive corresponding listening phases of the peripheral devices (2) on the fallback channel (s), until receiving a message in return on the part to said peripheral device (2) having toggled, and to send one or more messages, in one or more phases of authorization of transmission to said central device ( 1), requiring the switching of the other peripheral devices (2) to the considered fallback channel, if necessary in the order of addressing of said other peripheral devices (2), the successive transmission / reception phases of the different devices on the main channel and on the fallback channel being shifted in time, the order -28 of addressing of the peripherals (2), after their tilting, will be the fallback channel being either identical to that prevalent on the main channel, or different from this last, the new order being in the latter case indicated by   the central device (1) to the peripheral devices (2).   ll) Method according to any one of claims 1 to 7,   characterized in that the devices (1 and 2) are capable of transmitting and receiving radio signals on at least two different frequency channels and in that at each successive time window the central device (1) and the peripheral devices (2 ) wind switched to a different channel from that used for the immediately preceding time window, according to a predetermined order of succession of said channels, which is identical for each device (1, 2) and which takes place synchronously for all said channels devices (1 and 2).   12) Method according to claim 11, characterized in that the devices (1 and 2) use at least four different communication channels and in that the order of succession of said channels is selected   during the start-up of said devices (1 and 2).   13) Method according to any one of claims 8 to 10,   characterized in that the pairing of a new peripheral device (2) or the re-pairing of a peripheral device (2) having been disconnected with respect to the central device (1), consists, by exchanging asynchronous radio messages, of addressing to the central device (1) a message indicating the characteristics of said new peripheral device (2), in particular the frequency of its activation for transmission and listening, then to transmit to the latter an identification address, also fixing its order in the sequence of the emission authorization phases of the various peripheral devices (2) in connection with the central device (1), an initial synchronization message and a possible site identifier used for the secure transmissions.   14) Method according to any one of claims 1 to 13,   characterized in that it consists for a mobile peripheral device (2), having been moved outside the field of coverage of the central device (1) and having received, or a reactivation and / or reconnection signal or having been the subject of '' a request of this type, to be sent continuously for a duration greater than the sum of the durations of a period of activation of the devices (1 and 2) and an interval separating two such periods, a signaling frame containing identification address or identifier assigns -29 to said device (2), then to put itself in a listening situation with a view to receiving a response from the central device (1), in the form of a message initial synchronization accompanied by an authentication request, to repeat the two previous operations for the different possible transmission channels, starting with the last channel used by said peripheral device (2) before its disconnection from the central unit (1), until receipt of a no response from the central device (1) or reaching the predetermined maximum number of attempts, with standby or deactivation consecutive to the peripheral device (2) considered in the event   failure to reestablish communication with the central device (1).   ) Method according to any one of claims 1 to 14,   characterized in that it is implemented by a monitoring or alarm system, the central device (1) consists of a microprocessor-based alarm center for the execution of the management and piloting program at said system and provided with an external communication interface, in that the peripheral devices (2) consist of one or more sensor (s), control organ (s), organ (s) for taking images and / or sounds, siren (s) ), horn (s), actuators (s), detector (s) and / or device (s) communication to a network.   16) Method according to any one of claims 1 to 15,   characterized in that each peripheral device (2) has two different frequencies for repeating its period of cyclic activation and radio communication with the central device (1), namely a low frequency and a high frequency, said peripheral device (2) operating normally with the low repetition rate and said peripheral device (2) switching to the high repetition rate when said device (2) is requested or active or, in an anticipated manner, when said device (2) determines the next occurrence of '' an action likely to solicit him or necessitate the establishment of a communication with central device (1).   17) Surveillance or alarm system comprising a central unit and peripherals, forming independent devices and with autonomous power supplies, characterized in that it implements the method of