EP1363260B1 - Method for radio frequency communication among multiple devices and monitoring system using the 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

The present invention relates to the field of communication by radio transmission between several separate elements, in particular but not exclusively in the case of surveillance or alarm systems, and relates to an improved communication method and a monitoring or control system. alarm using such a method.

In many applications based on the cooperation of several separate electronic devices and located at a distance from each other, it is necessary to provide a wireless communication over the air between these devices and an independent power supply for each of them . These provisions may be mandatory for reasons of installation, security and / or independence from the network, particularly in the case of surveillance and alarm systems.

However, the systems of this type currently proposed generally use, for reasons of ease of development and development, as well as cost, unidirectional radio links between the sensors and the central.

As a result, the sensors or other peripherals are frequently transmitted for all the detections observed, regardless of the activation mode of the system (armed or disarmed), because they are not aware of the system status defined at the plant.

On the other hand, because of the limited capacity of the stand-alone power sources of the plant and the sensors, the reception at the plant can only be intermittent and the emission at the level of the sensors also.

To ensure correct transmission, it is essential that the transmission time on the sensor side be greater than the duration of the listening rhythm (reception) on the central side.

If one chooses a slow listening rhythm, one privileges the autonomy of the power station to the detriment of the autonomy of the sensors (each emission must be superior to the periods of listening of the power station). On the contrary, the increased listening rate of the plant penalizes the autonomy of the latter in favor of that of the sensors.

In practice, the values retained are a compromise between the two, while ensuring the system an acceptable reaction time (average time to inform the central unit of a detection observed by a sensor).

However, such a compromise, constituting the least worst solution produced by the state of the art, is not satisfactory, either from the point of view of autonomy, or from the point of view of reactivity, reliability or adaptability.

EP 0 676 733 describes a synchronization system between sensors and a central unit, for bidirectional radio links.

The present invention aims to meet at least some of the needs expressed above and to provide a solution meeting at least some of the above limitations.

To this end, the subject of the present invention is a method of bidirectional communication by transmission of radio frequency messages in the form of frequency-modulated digital frames between a master central or primary device and several slave peripheral or secondary devices, these devices being all physically independent , provided with autonomous power sources and at least equipped with a radio transmission / reception circuit, as well as a time accounting module providing a local time reference, a method consisting, in normal operation, of synchronizing at intervals predetermined the accounting modules of the various devices by transmitting a synchronization radio message from the central device to the peripheral devices and to establish a discontinuous radio communication link, during predetermined repetitive separate temporal windows, between said disp central ositive and peripheral devices, corresponding to limited periods of cyclic activation of said central device and at least some of said peripheral devices, repeated at regular and / or predetermined intervals, of duration (s) lower than that ( s) intervals separating two successive transmissions of the synchronization message, characterized in that each activation period comprises a first phase or time interval of authorization or obligation of transmission of message (s) for one of the peripheral devices and at the same time listening, at least during a first part of this first phase, for the central device and a second phase or time interval for authorizing transmission of message (s) for the central device and simultaneously listening for least one of the peripheral devices, recipient (s) programmed (s) of such a possible message of the central device, said secon next phase immediately said first phase and the synchronization message being transmitted at predetermined intervals during 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 may also be irregular and follow a given pattern identical for the central device and the peripheral devices concerned.

The precise synchronization between devices, periodically refreshed, makes it possible to reduce the transmission and listening windows (reception status) to minimum values, ideally about the same order of magnitude as the messages exchanged.

In addition, the definition of limited periods of activation affecting only some of the peripheral devices and grouping temporally adjacent transmission and listening phases lead, in association with the aforementioned provision, to a significant reduction in the consumption at the level of the device. central device, but especially at the level of peripheral devices. Consumption can be further reduced by providing messages from the central device to the peripheral devices only when necessary.

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

According to an advantageous embodiment of the invention, the body of the preamble may consist of a portion of a digital message formed of a repeating pattern comprising as many as 1 as 0, preferably present in a regularly alternating manner, said preamble ending in a a particular digital character pattern different from said repeating pattern, preferably an extended sequence of a plurality of 1, followed by a prolonged sequence of a plurality of 0's.

Furthermore, it can be advantageously provided that, for each transmitted message, the preamble is followed by a synchronization byte for the activation of the asynchronous radio transmission interface of the transmission / reception circuit of the device (s) central or recipient device (s), and that said peripheral devices perform, after each reception of a synchronization radio message, a verification of the validity of said message, then an exploitation of its time information by its comparison with the local time reference of the peripheral device concerned and the subsequent change, in advance or delay, of the local time reference provided by the corresponding accounting module as a function of the difference observed or a fraction thereof, evaluated taking into account at least the last two previous deviations noted.

In any case, the length of messages sent will be calculated in such a way that in no case is the allocated emission authorization phase exceeded.

According to a preferred embodiment of the invention, corresponding to an optimized operation, the central device is systematically listening during the first phase of each cyclic activation period. In addition, the peripheral devices are allowed to transmit, one by one, in a predetermined cyclic order, for example linked to their identification and registration address with the central device, and with a repetition frequency, occurrence or embodiment corresponding to a sub-multiple of the repetition frequency of the limited activation periods and the listening phases of said peripheral devices are repeated with a repetition or occurrence frequency corresponding to a sub-multiple of the repetition frequency limited periods of activation, 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, transmission phases all the peripheral devices listening during each transmission of a synchronous radio message onisation issued by the central device.

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

Generally speaking, 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 peripheral device concerned and necessarily addressed to the central device repeatedly at successive clean times. to each peripheral device, either in random messages for signaling an incident, an event or an abnormal situation, each signaling message being transmitted to the central device during the transmission authorization phase of the period d activation immediately following the occurrence of the incident, the event or the abnormal situation and its issuing beginner before the start of the transmission authorization phase, said signaling messages being provided with extended preambles.

The method according to the invention thus implements a method of actively monitoring the radio link between the peripherals and the central unit by sending presence messages cyclically.

The devices send their respective message sequentially by using their individual address to determine the time of emission with respect to their local time reference, itself periodically calibrated on the sequencing of the plant. Similarly, the control unit determines for its part the times during which it is supposed to receive the presence messages of the various registered devices.

In order to be able to maintain communication between the central device and all the peripheral devices, despite poor radiofrequency transmission conditions, interfering signals or interference or a charged electromagnetic environment, the various devices are capable of transmitting and receiving radio signals on at least two frequency channels, namely a main channel used in normal operation and at least one folding, folding or emergency channel used in case of difficulty of transmission on the main channel, or by time distribution communications on several channels used alternately.

Thus, according to a first embodiment of the invention, said method may consist of switching radio transmissions between devices of the main channel on the or a fallback channel at the initiative of a peripheral device, after the latter has diagnosed a cut of its radiofrequency link with the central device, either because of the absence of reception, possibly repeated synchronization radio message to one or more predetermined deadline (s), either because of the absence of response message or acknowledgment of receipt of the central device following the prior sending, repeatedly , radio messages, in particular messages signaling an incident, an event or an abnormal situation, of the peripheral device concerned to said central device.

According to another characteristic of the invention, the switching of the transmissions between devices on the or a fallback channel consists, for the peripheral device at the initiative of said tilting, to switch on the or a fallback channel at the time of the advent a phase of authorization or obligation to issue messages (s) assigned to it in the order established for the various peripheral devices, to then put in listening situation for a first period at least equal the sum of the periods of time between two cyclic activation periods and of such a period, and possibly, repetitively, during the estimated consecutive transmission phases of the central device, until a message is received; shifted synchronization emitted by the central device and setting the new transmission and listening rhythm between said peripheral device and said central device on said channel downturn.

According to another characteristic of the invention, the switching of the 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 of a routine message, during several successive phases of authorization or transmission obligation allocated to the peripheral device having switched, to emit during the next scheduled listening phase of said peripheral device a synchronization message shifted on the fallback channel, or successively on the various possible fallback channels, possibly repeating this transmission during several successive corresponding listening phases of the peripheral devices on the fallback channel (s), until receiving a message back from said peripheral device having switched over , and to address one or more messages, in one or more phases of authorization of transmission of said central device, requiring the switching of the other peripheral devices on the foldback channel considered, if necessary in the order of addressing of said other peripheral devices, the successive transmission / reception phases of the different devices on the main channel and on the foldback channel being shifted temporally, the order of addressing devices, after their switching, 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 the latter case indicated by the central device peripheral devices.

This latter arrangement allows the central device to simultaneously communicate with all the peripheral devices distributed on the two transmission channels.

According to a second embodiment of the invention, the devices are 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 to a different channel. of the one 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 synchronously for all said devices.

Thus, at each activation period, a frequency jump is carried out according to an identical deterministic scheme for all the devices.

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

The repetition sequence of the different channels will preferably be odd when the number of usable channels is even and will have a greater number of steps 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 plant, ...), it will be possible to provide a fallback channel which will be fixed and known to the various devices. , in addition to the different common channels used during normal communication procedures.

In the context of an initialization phase of the method of communication or integration of a new peripheral device, the pairing of such a new peripheral device or the re-pairing of a peripheral device having been disconnected from the device exchange, consists of exchanges of asynchronous radio messages to be sent 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, and then to transmit to the latter an identification address, also setting its order in the sequence of phases of authorizing 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.

Similarly, the method according to the invention may consist of a mobile peripheral device, having been moved outside the coverage field of the central device and having received a reactivation and / or reconnection signal or having been the subject of a solicitation of this type, to transmit continuously for a duration greater than the sum of the durations of a period of activation of the devices and an interval between two such periods, a signaling frame containing the identification address or the identifier assigned to said device, then to be in a listening situation in order to receive a response from the central device, in the form of an initial synchronization message 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 before its disconnection from the central, ju until a response from the central device has been received or the predetermined maximum number of attempts has been reached, with said peripheral device being put on standby or subsequently deactivated if communication with the central device is not restored.

Typically these latter measurements may be implemented in connection with a peripheral device not fixed, nomadic, such as a remote control or the like.

In order to increase the reactivity and efficiency of the method according to the invention, while maintaining a low activation rate, each peripheral device may have two different frequencies of repetition of its cyclic activation period and of radio communication 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 swinging to the high repetition rate when said device is solicited or activated or, in advance, when said device determines the occurrence next action that may require it or require the establishment of a communication with the central device.

According to a particularly advantageous application, the communication method according to the invention can be implemented by a surveillance or alarm system, the central device consisting of a microprocessor alarm central for the execution of the management program and driving said system and provided with an external communication interface and the peripheral devices consisting of one or more sensor (s), control organ (s), organ (s) for taking pictures and / or sounds, siren (s), buzzer (s), actuator (s), detector (s) and / or device (s) for communication to a network.

The invention also relates to a surveillance or alarm system comprising a central unit and peripherals, forming independent devices and autonomous power supply, characterized in that it implements the communication method as described above. .

• La figure 1 représente des chronogrammes montrant les signaux émis/reçus au niveau du dispositif central au cours de deux périodes d'activation successives ;
• La figure 2A représente des chronogrammes illustrant les décalages pouvant être générés à l'émission et à la réception des messages envoyés par les périphériques pendant le TPP du fait de la dérive de l'horloge locale ;
• La figure 2B illustre une variante de réalisation de l'invention selon laquelle l'activation du dispositif central en phase d'écoute est intermittente pendant le TPP ;
• La figure 3 est un ordinogramme représentant les étapes effectuées par un dispositif périphérique n'ayant pas reçu un message de synchronisation (top desynchro) émis par le dispositif central à un instant prédéterminé ;
• La figure 4 est une représentation sous forme d'un chronogramme d'un exemple de constitution d'une trame de signalisation émis par un dispositif périphérique mobile souhaitant reprendre la liaison avec le dispositif central ;
• La figure 5 représente un exemple de possible structure de la trame courante utilisée dans le cadre du procédé selon l'invention ;
• La figure 6 est une représentation schématique d'un ensemble comprenant un dispositif central et plusieurs dispositifs périphériques communiquant avec ce dernier selon le procédé objet de la présente ;
• La figure 7 montre sous forme de diagramme les différents états possibles pour les dispositifs périphériques en relation avec le premier mode de réalisation de l'invention décrit ci-dessus, et,
• La figure 8 montre sous forme de diagramme les différents états possibles pour les dispositifs périphériques en relation avec le second mode de réalisation de l'invention décrit ci-dessus.

The invention will be better understood, thanks to the following description, which refers to a preferred embodiment, given by way of non-limiting example, and explained with reference to the attached schematic drawings, in which:

• The figure 1 represents timing diagrams showing signals transmitted / received at the central device during two successive activation periods;
• The Figure 2A represents timing diagrams illustrating the offsets that can be generated when transmitting and receiving messages sent by the peripherals during the TPP due to drift of the local clock;
• The Figure 2B illustrates an alternative embodiment of the invention according to which the activation of the central device during the listening phase is intermittent during the TPP;
• The figure 3 is a flowchart showing the steps performed by a peripheral device that did not receive a synchronization message (top desynchro) transmitted by the central device at a predetermined time;
• The figure 4 is a representation in the form of a timing diagram of an example of constitution of a signal frame transmitted by a mobile peripheral device wishing to resume the connection with the central device;
• The figure 5 represents an example of a possible structure of the current frame used in the context of the method according to the invention;
• The 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 of the present invention;
• The figure 7 shows in diagrammatic form the different possible states for the peripheral devices in relation to the first embodiment of the invention described above, and,
• The figure 8 shows in diagrammatic form the different possible states for the peripheral devices in relation 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 a microprocessor (in some cases called a base) cooperating with at least one peripheral or peripheral device 2 selected from the list comprising sensors, control elements, sirens, horns, actuators and communication devices to a network using short-distance radio communications (also called SRD) using a free band of ISM type).

Each element of this system, shown schematically in figure 6 , is equipped with a radio transmitting / receiving circuit 1 ', 2' (alternating) and has an autonomous power source (battery or battery), as well as a module 1 ", 2" associated time accounting a time reference (typically a quartz with a counting chain) also called "local reference".

The central unit 1 transmits periodically a radio signal containing information representative of the temporal sequencing of said central unit 1 and the peripherals 2 capture this information so as to block their internal operation at a rate identical to or multiple from that of the central unit 1 or at all. less are trying to get close to it. When the central unit 1 sends the temporal information, it precedes it with a series of characters (called preamble) whose duration of emission is greater than the maximum drift observable between a peripheral 2 and the central 1 (taking into account the uncertainties precision of quartz, temperature differences, aging of quartz and various uncertainties), increased by the number of synchronization of the reception, allowing the peripherals 2 in reception mode to detect the transmission of the temporal information despite the drifts of the time references, knowing that the timing and the moment of transmission are predetermined both in the central 1 and in the peripherals 2 considered.

Said peripherals 2 exploit this temporal information after verifying the validity thereof (use of an electronic "signature" or authentication system) by modifying their counting chain in advance or delay of the latter according to the difference observed between the local reference (device 2) and the temporal information transmitted, of a value equal to this difference or a fraction of this difference, weighted by the average value calculated in a sliding manner on the previous deviations.

According to an exemplary non-limiting practical embodiment of a monitoring and alarm system, the unit 1 can operate on a reception rate of one second (interval separating two successive listening phases), for a duration of about 8 ms in the absence of message and 30 ms in the presence of message from a synchronized device 2. The window or listening phase of the panel 1 starts 125 ms (1/8 s) before its speech window. This window is called Peripheral Speech Time (TPP).

This listening period of the central 1 is followed by a 40 ms talk time for the latter called TPC (central speaking time). It is used to synchronize 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 the TPC (see figure 1 ).

When unsynchronized 2 devices are transmitting, they may accidentally do so during the talk time of the panel, and for up to one second. The plant must therefore check before issuing, the presence or absence of a program already engaged.

Thus, the energy saving is obtained by reducing the listening and transmission times for the different devices 1 and 2 constituting the alarm system. This reduction is only possible thanks to the synchronization of peripherals on the rhythm of the plant.

The inevitable physical inaccuracy of synchronization on which the simulations carried out by the inventors were based gives a delta (Δ) of 12 ms per minute, when a quartz of 32.768 kHz is used as a reference.

When the initial accuracy of the quartz is +/- 30 ppm and the drift in temperature is given at +/- 50 ppm in the range -10 ° to + 55 °, the overall tolerance retained will be +/- 100 ppm to hold account other factors (aging, dispersion of resynchro, ...).

As indicated above, all the peripherals 2 (with the possible exception of a mobile device of the remote control type) are synchronized on the control unit. When the system is turned on, after the installation phase, the devices are calibrated at the rate of 60 s. This synchronization is maintained by the repeated (systematic) acquisition of the sync signal (synchronization message) transmitted by the central unit. Since the control unit is receiving every second, the devices having a message to be sent to the control panel must do so within the planned TPP interval (see figure 1 ).

• message de signalisation ou d'alerte (intrusion, auto protection, défaut d'alimentation, ...)
• message de présence (avec éventuellement indication niveau de pile et niveau de champs).

Messages sent in normal operation can be of two types:

• signaling or warning message (intrusion, auto protection, power failure, ...)
• presence message (possibly with stack level and field level indication).

The first type being unpredictable and exceptional, there is no collision in the vast majority of cases. A particular mechanism for managing the rare collisions is explained further.

• appel systématique des périphériques par la centrale (inconvénient : consommation accrue pour la centrale)
• envoie automatique du message de présence par le périphérique initié par un premier appel (la centrale peut ainsi répartir les périphériques sur les 600 secondes et de ce fait éviter les collisions ultérieures). Cet automatisme peut s'arrêter par l'envoi d'une commande "silence" par la centrale.

The second type is predictable because the devices are set to emit a presence signal at regular intervals (every 600 s for example). Two solutions are possible:

• systematic call of peripherals by the central (disadvantage: increased consumption for the power station)
• automatic sending of the presence message by the device initiated by a first call (the control unit can thus distribute the devices over 600 seconds and thus avoid subsequent collisions). This automation can stop by sending a command "silence" by the central.

For reasons of energy saving and functionality, the devices are also listening in a predetermined alternating cycle. While for the plant this cycle is one second, it can vary from 2 to 30 seconds depending on the devices.

In practice, this means that the control panel can not communicate at any time, with any device, and that it must therefore manage its listening periods for devices in a predictive manner.

• cycle à 2 secondes : réveil sur les secondes paires (0,2,4,...)
• cycle à 10 secondes : 0, 10, 20, 30, 40, ...
• cycle à 30 secondes : 0 et 30 secondes.

For the sake of simplicity, all devices will be keyed to the same sub-multiples:

• cycle to 2 seconds: waking up on the second pairs (0,2,4, ...)
• cycle at 10 seconds: 0, 10, 20, 30, 40, ...
• cycle at 30 seconds: 0 and 30 seconds.

All devices are listening at least twice a minute (simultaneously for at least some of them).

When the central unit needs to communicate with several devices (after collision detection, sending a command to several interlocutors, ...) or only one (quick entry of several parameters with the control box), the control panel informs the peripherals of the activation of this communication mode, which will have the consequence for the concerned devices to keep the reception activated until the current transaction or communication is completed or this mode is deactivated by the control panel.

• un périphérique particulier
• les périphériques ayant initiés une communication (ou en cours de dialogue) avec la centrale
• tous les périphériques.

In practice, the control unit activates the mode by specifying the devices concerned, namely:

• a particular device
• devices that initiated a communication (or ongoing dialogue) with the central
• all devices.

As indicated above, such a discontinuous communication mode requires precise synchronization between the central unit 1 and the peripherals 2.

In the practical example mentioned above, the control panel and the peripherals have a time base of 32768. Thus, every 64s, the control unit sends a synchronization signal (message) which allows the devices to reset the counting channels of their counting modules 2 ".

The sync top coincides with the end of the synchronization message word (but another convention can be used). The plant 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 devices go into receive mode at the same rate as that used by the panel during the TPP.

The synchronization message can take on the appearance of any message. One can imagine that to reduce the effect of a loss of synchronization, the devices software adjust their clock based on the discrepancies noted at the time of synchronization. Without correction, a measure of the observed difference (between the sync signal and the local clock) can contribute to maintaining a satisfactory level of performance in the event of loss of "extended" sync, because the necessary activation anticipations can be minimized.

In this context of synchronized transmission / reception, two main problems may arise: the drift of the local time references and the synchronization fault due to the absence of reception of the cyclic synchronization message forming "sync top", which may come from a loss of connection between central and peripheral.

Concerning the drifts (local clock drifts), the error will, in the practical case mentioned above, be 6 ms or a delta of 12 ms as mentioned previously.

In a practical way, this means that when the control panel starts to listen, a device could start a transmission 6 ms earlier, or it could start 6 ms later.

In the extreme case, the control unit is activated first, a device can emit 12 ms later. These 12 ms are advantageously absorbed by the presence of a preamble signal preceding the actual message (see Figure 2A ).

• de manifester/détecter une activité radio tout en préservant le message d'une troncature,
• d'effectuer un AFC (contrôle automatique de la fréquence) si la fréquence moyenne vaut f₀ (nombres de 0 et de 1 identiques)
• de synchroniser le récepteur pour activer l'UART (interface d'émission / réception asynchrone) au moment opportun,
• d'absorber les écarts d'horloge entre les éléments constitutifs du système.

This preamble allows in particular:

• to manifest / detect a radio activity while preserving the message of a truncation,
• to perform an AFC (automatic frequency control) if the average frequency is worth f ₀ (numbers of 0 and 1 identical)
• to synchronize the receiver to activate the UART (asynchronous transmit / receive interface) at the appropriate time,
• to absorb the clock differences between the components of the system.

Since the device 2 speech window is limited to 125 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 (ie ~ 3 ms), the message will be at most: 125 - 12 - (14 + 3) = 99 ms (~99 bytes to 9600 bds) 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 both 1 and 0 so that, coded in frequency modulation, the average value of the radio signal corresponds to the central value of the radio channel used thus enabling the activation of an automatic control device of the radio frequency. Frequency (AFC) receiver side, at the beginning of the communication.

Preferably, the preamble consists of a sequence of characters 55h (101010 ...) allowing a faster operation of the frequency servo and can be followed by a pattern consisting of two characters FFh and 00h used to mark the end of the preamble and the beginning of the data transmitted in the message or the frame concerned 2.

The reception of FFh before 00h indicates that the character synchronization was carried out from the first 55h.

In practice, said preamble may, for example, be composed of 15 characters or 15.6 ms duration (at 9600 bds).

As a variant, the first 14 characters may be identical and be worth 0xF0 (0000011111 in binary). The ^15th is 0x9C (0001110011 in binary). The beginning of the preamble materializes in the form of positive and negative pulses of equal length (~521 μs). The last character 0x9C 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 of 15 ms continuous), as shown in FIG. Figure 2B .

In addition, a synchronization fault may occur when a device 2 misses one or more synchronization message (s) issued by the central unit 1.

The first time, the device retains its internal reference, but the next minute, it must anticipate the TPC so as to receive the synchronization message even in case of delay.

If the synchronization is missed a second time, the device concerned must initiate a procedure to find its synchronization, such as that represented for example on the figure 3 .

To implement such a procedure, the system according to the invention will, for example implement a method for managing transmissions on multiple channels with folding in case of failure of the conventional radio link.

Thus, during the installation of the system, the unit 1 asks the various registered devices 2 to measure the quality of the radio signal on all the exploitable channels (measurement of the noise floor using the RSSI - power indicator of the received signal), so as to determine in a second time what will be respectively the main channel and the backup channel (or fallback). After making the selection, the unit 1 indicates to all the devices the instructions on the choice of channels.

• par le(s) périphérique(s) concerné(s), pour basculer sur le canal de repli après un nombre prédéterminé d'absence de recalage (non réception de plusieurs messages de synchronisation) ou de répétitions successives d'émission de messages de signalisation d'événement restés sans réponse, et,
• par la centrale, pour rechercher le(s) périphérique(s) aux "abonnés" absents (absence de message de présence ou de non-réponse à une requête).

The radio link faults can be detected, on the one hand, by the peripherals, when the time adjustment is no longer received at the scheduled time or when there is no acknowledgment following the transmission of an event and, d on the other hand, by the central unit, by the repeated absence of presence messages or the absence of acknowledgment following a request. This observation is exploited:

• by the device (s) concerned, to switch to the fallback channel after a predetermined number of no registration (no receipt of several synchronization messages) or successive repetitions of transmission of signaling messages event that remained unanswered, and,
• by the central unit, to search for the device (s) to the "subscribers" absent (absence of message of presence or non-response to a request).

In any case, one of the devices 2 of the system will initiate the change of channel when the required conditions are fulfilled, and the central 1 will emit a form of radio beacon on the channel of fallback (after the requirements), while maintaining the management of the main channel.

Each device 2 having switched to the draw channel changes its timing and reception timeline. Indeed, while the devices running on the main channel are activated at different rates (depending on the nature of the devices), the rhythm is identical for all as soon as they have switched to the fallback channel.

Advantageously, the instants of the listening phases on the fallback channel are offset with respect to the nominal operation.

Thus, for example, in nominal operation (main channel), the exchanges (excluding alerts) are made on second pairs and, in emergency operation (draw channel) and the radio beacon is transmitted by the central 1 on odd seconds (which allows it to continue to manage other devices 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 device of the plant continues to listen for a synchronization every minute on the initial channel. Anticipation of TPP and TPC intervals are anticipated (or delayed) of the value:
(Number of minutes since last sync) x (average error found).

In a second step, the isolated device switches to the fallback channel at the moment when it was supposed to send its presence message and goes into reception mode for a second to try to capture a sync (the control unit having noted the absence of a signal presence, it is programmed to send a status request (synchronized) to the draw channel.

If this procedure does not succeed, the device concerned will fall asleep for 32 seconds, then reactivate the reception for 40 ms on the fallback channel (during the TPC) and so on (sleep, Rx, ...). These 40 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 be a special case since it could be outside the coverage area at moment of migration (switchover of devices on the fallback channel). Therefore, if it is not synchronized, it transmits asynchronously successively on the four channels starting with the most recently used channel. The program on each channel must be one second to allow the station to listen. 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 plant, since it is likely to leave the radio coverage area of the plant.

It will therefore be necessary to provide some special provisions for this device, with repercussions on the general operation of the system.

• en l'absence de signal de synchronisation, la télécommande s'endorme et ne se réactive que sur appui d'un bouton,
• un appui bouton "réveille" la télécommande qui n'est donc plus synchronisée ; pour être sûre d'être entendue, elle devra émettre durant une seconde sur chacun des quatre canaux possibles de communication en commençant par le dernier (en date) utilisé
• chaque émission est suivie d'un temps d'écoute pour détecter une possible réponse de la centrale pendant une durée déterminée avant de passer au canal suivant
• pour indiquer cette phase à l'usager, on peut faire clignoter une diode de manière rapide jusqu'à ce que la liaison avec la centrale soit établie
• lorsque la centrale détecte la télécommande, elle répond par une demande d'authentification accompagnée des paramètres de synchronisation

Thus, it can be expected that:

• in the absence of a synchronization signal, the remote control falls asleep and is reactivated only at the touch of a button,
• a button press "wakes" the remote control which is no longer synchronized; to be sure of being heard, it will have to transmit for one second on each of the four possible channels of communication starting with the last one (in date) used
• each transmission is followed by a listening time to detect a possible response of the control unit during a determined duration before moving on to the next channel
• to indicate this phase to the user, it is possible to flash a diode quickly until the link with the plant is established
• when the control unit detects the remote control, it responds with an authentication request accompanied by the synchronization parameters

• trame de signalisation transmise en continu (1 seconde) ne contenant qu'une information simplifiée d'identification de l'envoyeur (pour permettre l'interprétation du message avec un nombre réduit d'octets reçus),
• réponse de la centrale par une demande d'authentification,
• envoi du certificat d'authentification par la télécommande avec les paramètres de celle-ci (id du bouton appuyé, niveau pile, ...).

Since the frame transmitted by the remote control can be picked up at any stage, it is proposed to establish the link in two stages:

• signaling frame transmitted continuously (1 second) containing only simplified information of identification of the sender (to allow interpretation of the message with a reduced number of bytes received),
• response of the central by an authentication request,
• sending the authentication certificate by the remote control with the parameters of the remote control (id of the button pressed, battery level, ...).

A transmission frame proposal for the remote control is shown on the figure 4 .

The proposed frame contains 4 bytes repeated 241 times to obtain a second of emission:

The first byte is a preamble byte, the ^2nd is the same sync byte preamble messages and is 0xf0 (0000011111 in binary. The 3 ^rd and 4 ^th bytes are a fixed value at the time of pairing the remote control .

• réponse simultanée de deux périphériques lors du TPP ;
• superposition d'une émission télécommande (asynchrone) avec un dialogue centrale-périphérique.

Moreover, it is also worth mentioning the problems related to possible collisions of radio messages that may occur in the system, namely:

• simultaneous response of two devices during the TPP;
• superposition of a remote control program (asynchronous) with a central-peripheral dialogue.

The first case is identified by the central unit by the observation of the envelope of superimposed carriers: the signal indicating the field level must in principle indicate at the end of the TPP the absence of a signal, following an impossibility to decode viable data during the TPP. In this case the control unit continues by sending in the TPC a message requesting a prolonged listening of the peripherals to allow a call of two-ci.

In the second case, the transmission of the remote control is perceived by the central, 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 continuation of the presence of the emission, and during dialogue, the silence intervals will not be respected. From these observations, the control unit interrupts the current dialogues to listen (and to decode as soon as possible) the frame of the remote control. It would be desirable for the devices involved to also be able to detect this case to cancel a scheduled broadcast.

At the end of the remote control frame, the control unit responds with a message (in priority on what was in progress) to the remote control to initiate a dialogue. This response must occur within the standard timeout period so that the remote control does not switch to the channel next radio. It would be desirable, if this collision occurs at the time of a sync, that the devices having found either the absence of synchro or the remote control frame, postpones to the next second the synchro attempt. In the event of failure (that is to say of impossibility for the central one to emit the synchro), this one will be carried out for the next minute (at this stage, in 63 seconds).

Finally, the monitoring or alarm system may also implement an initial synchronization method for each new device 2 (also called pairing).

In this case, before a device can integrate into the system, it will exchange information on its characteristics (type of sensor, identifier, ..) and receive back an address code to identify it within of the system, as well as a "setting time" of its local reference in relation to the central 1.

This is achieved by asynchronously sending a pairing request by the device concerned successively scanning the different radio channels that may be used at the time of the initial synchronization.

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

This initial sync mode can also be applied to devices that have left the radio coverage area of Central Station 1 (remote control, alert locket, etc.). Indeed, if one wishes to solicit them after having returned in the perimeter of the central 1, they must resynchronize to be able to dialogue. Similarly, a device 2 that has been stopped (battery replacement) will have to re-engage this procedure.

To complete the description of the exemplary practical embodiment of the invention set out above, a possible constitution, as well as an associated format, for the usual messages (synchronization, routine, signaling) will be described below. in the form of digital frames, exchanged between the devices 1 and 2 forming the alarm or monitoring system.

Such a frame is represented on the figure 5 appended drawings, and is normally preceded by a preamble and a synchronization byte as evoked above (not shown).

The "signaling" fields (signaling _1 and signaling _2) indicate to the recipient device (s) of the frame the conditions and the sequence of the transmission in progress.

These fields can, for example, indicate the situation of the frame in a transmission (first, last), the number of recipients (frame destined for a specific device or all peripherals), the type of recipients (device having a transmission in progress). , the writing or not of an encryption or an authentication, and the synchronized or asynchronous nature of the frame.

The length (coded on 6 bits) indicates the number of bytes of the "data" zone.

The Ack flag is an acknowledgment flag indicating that the frame is also used to acknowledge the received frame.

The "type" field makes it possible to identify the nature of the message ("Rfa" is a free bit for possible subsequent assignments).

Valid addresses are from 01h to 3Eh, with 00 being used for broadcast commands and 3Fh for unpaired devices. The address of the control panel is always implicit. In the peripheral direction towards the central, the address represents the sender, in the opposite direction, it is about the addressee.

The field "data" forms the area containing the useful information. Most frames are of fixed length, that is, the data is 32 bits long. To homogenize the formats, the length appears in all the messages.

The "MAC" zone is used to authenticate the message and the calculation of its content can be done in various ways, in particular according to those known to those skilled in the art, for example of the type known as AES.

Finally, the "CRC" is a zone of cyclic redundancy making it possible to ensure that the frame has not undergone an error during the radio transmission. Its calculation complies with the CCIR standard. The data taken into account in the calculation include all the fields (from signaling_1 to MAC included).

It should be noted that there are two sequences whose format differs from the format described above. They are used in situations where synchronism is not ensured between the sender of the message and the recipient.

The first nonstandard sequence is used by the remote (and all other mobile devices) to indicate its intention to emit a status frame. Indeed, a prolonged distance from the central causes loss of synchronization. The remote sends a particular sequence for one second on the last channel used and tries to get a response from the panel. Failure causes the same sequence to be broadcast on another channel, and so on until all four channels are exhausted.

The other non-standard sequence is used by the control panel to resynchronize devices whose radio link has been interrupted for an extended period (typically> 512 s). This case does not concern mobile devices (remotes, 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 solicitation of the central, this in order to preserve the energy of the batteries. In use, times will be refined to not get a too sensitive system.

The figures 7 and 8 show schematically the different possible states for the peripheral devices 2, respectively in relation to the first and second embodiments.

• Rx : réception ;
• Tx : émission ;
• "time-out" : écoulement du délai imparti ;
• "timing" : séquencement ou cycle de répétition ;
• P_stat : trame de statut du périphérique ;
• C_app : trame d'appairage émise par la centrale ;
• P_init : trame de demande d'appairage ;
• P_txt : trame de saisie de texte ;
• synchro ou sync : trame de synchronisation ;
• C_chan : trame de changement de canal émise par la centrale ;
• C_stat : trame de demande de statut émise par la centrale ;
• C_xxx : trame indéterminée ;
• "burst" : salve ;
• "tst" : test.

In these figures, the following terms have the meanings given below:

• Rx: reception;
• Tx: emission;
• "time-out": expiration of the time limit;
• "timing": sequencing or repetition cycle;
• P_stat: device status frame;
• C_app: the pairing frame sent by the plant;
• P_init: pairing request frame;
• P_txt: text entry frame;
• sync or sync: synchronization frame;
• C_chan: channel change frame sent by the plant;
• C_stat: status request frame sent by the central;
• C_xxx: indeterminate frame;
• "burst": salvo;
• "tst": test.

Of course, the invention is not limited to the embodiments described and shown in the accompanying drawings. Modifications are possible, particularly from the point of view of the constitution of the various elements or by substitution of technical equivalents, without departing from the scope of the invention as defined by the claims.

Claims (17)

1. Method of bidirectional communication by transmitting radio frequency messages in the form of digital frames which are modulated in frequency between a central device or primary master and several peripheral devices or secondary slaves, said devices all being physically independent, provided with independent sources of energy and equipped at least with a radio transmission/reception circuit, as well as a module for counting time, which provides a local time reference, which method consists, in normal functioning, of synchronising at predetermined intervals the modules for counting different devices (1 and 2) by the transmission of a radio synchronisation message from the central device (1) to the peripheral devices (2) and establishing a discontinuous radio communication link during predetermined repetitive separate time windows between said central device (1) and the peripheral devices (2), corresponding to limited periods of cyclical activation of the said central device (1) and at least some of said peripheral devices (2), repeated at regular and/or predetermined intervals of shorter duration than the intervals separating two consecutive transmissions of the synchronisation message, the method being characterised in that each activation period comprises a first authorisation phase or requirement of transmission of a message(s) for one of the peripheral devices (2) and simultaneous monitoring, at least during the first part of this first phase, for the central device (1) and a second authorisation phase of transmission of the message(s) for the central device (1) and simultaneous monitoring for at least one of the destination programmed peripheral devices (2) of such a message from the central device (1), the said second phase immediately following the said first phase and the synchronisation message being transmitted at predetermined intervals during such a second phase.
2. Method according to claim 1, characterised in that each message exchanged between the master device (1) and the slave device(s) (2) comprises a first part forming the preamble of which the time duration is greater than the maximum derivative of synchronisation between the central device (1) and the peripheral devices (2) during the interval separating two successive synchronisation messages, and in that the device or devices in a monitoring phase remain active at least for the duration of this preamble, in a continuous or discontinuous manner, the said device or devices being deactivated or put on standby in the absence of detecting a message after the completion of this period.
3. Method according to claim 2, characterised in that the body of the preamble is formed by a portion of the digital message formed by a repetitive pattern comprising as many 1s as 0s, preferably in a regularly alternating manner, the said preamble terminating in a particular pattern of digital characters differing from said repetitive pattern, preferably a prolonged sequence of a plurality of 1s, followed by a prolonged sequence of a plurality of 0s.
4. Method according to claim 3, characterised in that for each transmitted message, the preamble is followed by a synchronization octet for activating the interface of asynchronous radio transmission of the transmission/reception circuit (1', 2') of the central device(s) (1) or destination peripheral devices (2), and in that the said peripheral devices (2) verify each time after receiving a radio synchronisation message the validity of said message, then use its time information by comparing with the local time reference of the peripheral device (2) concerned and the following modification, in advance or in retrospect, of the local time reference provided by the corresponding counting module (2") as a function of the recorded interval or a fraction of the latter, evaluated by taking into account at least the two previous picked up intervals.
5. Method according to any one of claims 1 to 4, characterised in that the central device (1) systematically in monitoring mode during the first phase of each cyclical activation period, in that the peripheral devices (2) are authorised to transmit, one by one, in a predetermined cyclical order, for example linked to their identification and registration address to the central device (1) and with a repetition, occurring or realisation frequency corresponding to a sub-multiple of the repetition frequency of limited periods of activation, and in that the monitoring phases of said peripheral devices (2) are repeated with a repetition or occurrence frequency corresponding to a sub-multiple of the repetition frequency of limited periods of activation, the said repetition frequencies being different for each type or each of the peripheral devices (2), the frequencies of the monitoring phases being for the same peripheral devices (2) greater than the frequencies of the transmission phases, all of the peripheral devices (2) monitoring at each transmission a synchronisation radio message transmitted by the central device (1).
6. Method according to any one of claims 2 to 5, characterised in that immediately prior to each transmission phase of a message by the central device (1) or one of the peripheral devices (2), the device (1 or 2) concerned is put into a monitoring mode and is only authorised to transmit in the absence of any radio message during transmission.
7. Method according to any one of claims 1 to 6, characterised 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 of the peripheral device (2) concerned and necessarily addressed to the central device (1) in a repetitive manner at successive instances for each peripheral device (2), or random messages for signalising an incident, an event or abnormal situation, each signalling message being transmitted to the central device (1) during the phase of authorizing a transmission of the period of activation immediately following the occurrence of the incident, the event or abnormal situation and its transmission prior to the start of the transmission authorisation phase, whereby the said signalling messages are provided with extended preambles.
8. Method according to any one of claims 1 to 7, characterised in that the different 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 functioning and at least one fold channel, fold down or backup channel used in case of problems with transmission on the main channel, and in that the said method consists of swinging the radio transmissions between devices (1 and 2) from the main channel to the or a fold channel on the initiative of a peripheral device (2), after the latter has diagnosed an interruption in its radiofrequency link with the central device (1), either due to the lack of reception, possibly repeated, of the synchronisation radio message at one or more predetermined times, or the absence of the response message or acknowledgement of the central device (1) following the preceding transmission, in a repeated manner, of radio messages, in particular messages for signalling an incident, an event or an abnormal situation of the peripheral device (2) concerned towards the said central device (1).
9. Method according to claim 8, characterised in that the swinging of transmissions between devices (1 and 2) on the or a fold channel consists, for the peripheral device (2) initiating said swinging, of swinging to the or a fold channel at the time of an authorisation phase or requirement of transmission of messages which is attributed thereto according to the established order for the different peripheral devices (2), then putting itself into a monitoring situation for a first period at least equal to the sum of the periods of the interval separating two cyclical activation periods and such a period, then possibly, in a repetitive manner, during estimated consecutive transmission phases of the central device (1), until receiving an error synchronisation message transmitted by the central device (1) and fixing the new transmission and monitoring rhythm between the said peripheral device (2) and the said central device (1) on said fold channel.
10. Method according to any one of claims 8 and 9, characterised in that the swinging of transmissions between devices (1 and 2) to the or a fold channel consists, for the central device (1), having picked up the repeated absence of reception of any message, in particular a routine message, during several consecutive phases of authorisation or requirement of transmission allocated to the peripheral device (2) having swung, of transmitting during the following monitoring phase of said peripheral device (2) an error synchronization message to the fold channel, or consecutively to different possible fold channels, repeating this transmission during several corresponding successive monitoring phases of the peripheral devices (2) to the fold channel or channels, until receiving a message in return from said peripheral device (2) which has swung, and addressing one message or messages, in one or more transmission authorisation phases of said central device (1), requiring the swinging of other peripheral devices (2) to the fold channel in question, if necessary in the address order of the said other peripheral devices (2), the consecutive transmission/receiving phases of different devices on the main channel and on the fold channel being shifted in time, the address order of the peripheral devices (2), after swinging, being the fold channel either identical to that of the one on the main channel or different from the latter, the new order being in this latter case indicated by the central device (1) to peripheral devices (2).
11. Method according to any one of claims 1 to 7, characterised 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) are switched to a different channel than 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 progresses in a synchronous manner for all of said devices (1 and 2).
12. Method according to claim 11, characterised 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 at the time of starting up said devices (1 and 2).
13. Method according to any one of claims 8 to 10, characterised in that the pairing of a new peripheral device (2) or the repairing of a peripheral device (2) which has been disconnected from the central device (1), consists via asynchronous exchanges of radio messages, of addressing to the central device (1) a message indicating the characteristics of the said new peripheral device (2), in particular the frequency of its activation for transmission and monitoring, then transmitting to the latter an identification address, also fixing its order in the sequence of the transmission authorisation phases of different peripheral devices (2) in association with the central device (1), an initial synchronisation message and a possible identifier of the site used for trusted transmissions.
14. Method according to any one of claims 1 to 13, characterised in that for a mobile peripheral device (2), which has been placed outside the range of the central device (1) and has received a reactivation and/or reconnection signal or has been subject to an activation of this kind, it consists of transmitting continuously for a period which is greater than the sum of the periods in an activation period of the devices (1 and 2) and an interval separating two such periods, a signalling frame containing the identification address or the identifier attributed to the said device (2), then putting itself in a situation of monitoring in view of receiving a response from the central device (1), in the form of a suitable initial synchronisation message of an authentication request, repeating the two preceding operations for the different possible transmission channels, starting with the last channel used by the said peripheral device (2) prior to its disconnection from the central unit (1), until receiving a response from the central device (1) or achieving the maximum predetermined number of attempts, including putting on standby or the consecutive deactivation of said peripheral device (2) considered in case of not re-establishing communication with the central device (1).
15. Method according to any one of claims 1 to 14, characterised in that it is used by a surveillance or alarm system, whereby the central device (1) consists of a microprocessor central alarm unit for executing the management and control program of said system and is provided with an external communication interface, in that the peripheral devices (2) consist of one or more sensor(s), control element(s), image and/or sound recording elements, siren(s), alarm(s), actuator(s), detector(s) and/or devices for communicating with a network.
16. Method according to any one of claims 1 to 15, characterised in that each peripheral device (2) has two different repetition frequencies of its cyclical activation period and radio communication with the central device (1), namely a low frequency and a high frequency, whereby said peripheral device (2) functions normally with the low repetition rhythm and said peripheral device (2) swings towards the high repetition rhythm, when said device (2) is actuated or activated or, in an anticipated manner, when said device (2) determines the next occurrence of an action likely to actuate it or to necessitate establishing communication with the central device (1).
17. Surveillance or alarm system comprising a central device and peripheral devices, which form independent devices and are powered autonomously, characterised in that it applies the method of communication according to any one of claims 1 to 16.

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