Alarm system with a peer-to-peer backup communication link

Abstract

The invention relates to an alarm system (10-1) and a monitoring method. The alarm system comprises at least one intrusion detector (11), a central unit (13-1) configured to communicate with a remote monitoring server (20) via a first communication protocol, and a backup module (12-1). The method comprises the following steps: detecting an intrusion, determining that the central unit is unable to reliably transmit an alert message to the remote monitoring server via the first communication protocol, transmitting an alert message, by the backup module (12-1), to a peer backup module (12-2) of another alarm system (10-2), via a second communication protocol, transmitting the alert message to the remote monitoring server (20) by the other alarm system (10-2). Figure for abstract: Fig. 1

Description

Title of the invention: Alarm system with a peer-to-peer backup communication link Field of the invention

[0001] The present invention belongs to the field of alarm systems for sending an alert to a remote monitoring server in the event of an intrusion. More particularly, the invention relates to an alarm system, as well as the associated monitoring method, using a backup communication link with another alarm system on a neighboring site. State of the art

[0002] Many alarm systems are available on the market to protect a site against intrusion. These systems are designed to detect and signal an unauthorized intrusion into the site to be protected (this may be a house, an apartment, a building, a room within a building, a garden, etc.). Their purpose is to contribute to the monitoring and protection of property and people present on the site.

[0003] Alarm systems are generally equipped with intrusion detectors (infrared sensors, radars, volumetric sensors, shock detectors, etc.). In response to the detection of the intrusion, the alarm system can trigger deterrent means (for example a siren or a smoke generator) and transmit an alert message from a central unit of the alarm system to a remote monitoring server.

[0004] The alert message is generally sent to the remote monitoring server through a wireless cellular communication network, such as for example an LTE network (an acronym for "Long Term Evolution", in French "long term evolution", this is the fourth generation standard, or 4G, specified by the 3GPP consortium) or a 5G-NR network (an acronym for "5G - New Radio", in French "5G - Nouvelle radio", this is the fifth generation 3GPP standard).

[0005] To prevent the alarm system from transmitting the alert message, a malicious person can use a radio jammer. This is a radio transmitter designed to disrupt the reception of radio frequency signals by other devices. A radio jammer works by emitting a noise signal at a higher radio power level than the useful signals, on one or more frequency bands. The useful signals are then no longer detected by the receivers of devices close to the jammer. The jammer can break the radio links between both the central unit of the alarm system and the remote monitoring server than between an intrusion detector and the central unit.

[0006] To overcome this problem, it is known to transmit an alert message via a wireless communication network that uses radio transmission techniques that are not very sensitive to frequency jamming. Patent EP3716242B1 describes a method of secure radio communication between an intrusion detector and the central unit of an alarm system. Patent EP3477611B1 gives an example of an alarm system whose central unit includes a radio communication module configured to send an alert message to the remote monitoring server via an LPWAN (Low Power Wide Area Network) network with ultra-narrow band (UNB for "Ultra Narrow Band" in English) in unidirectional mode when radio jamming is detected.

[0007] However, an LPWAN network implementing jamming-resistant radio technology is not always available. Furthermore, this requires a subscription to the LPWAN network operator. Statement of the invention

[0008] The present invention aims to remedy all or part of the drawbacks of the prior art, in particular those set out above.

[0009] To this end, and according to a first aspect, the present invention proposes a method for monitoring a site by an alarm system. The alarm system comprises at least one intrusion detector, a central unit configured to communicate with a remote monitoring server via a first communication protocol, and a backup module. The method comprises: - detection of an intrusion, by the intrusion detector or by the backup module, - a determination, by the intrusion detector or by the backup module, that the central unit is not able to reliably transmit an alert message to the remote monitoring server via the first communication protocol, - transmission of an alert message, by the backup module, via a second communication protocol, to a peer backup module of another alarm system used to monitor another site, - transmission of the alert message to the remote monitoring server by the other alarm system.

[0010] In particular embodiments, the monitoring method may further comprise one or more of the following characteristics, taken in isolation or in all technically possible combinations.

[0011] In particular embodiments, the second communication protocol is a peer-to-peer communication protocol whose physical layer is based on low-power wireless wide area communication technology. The second communication protocol uses an ISM frequency band and a spread spectrum technique. The transmission of the alert message is done asynchronously between the backup module and the peer backup module, or in a time slot agreed between the two backup modules before the intrusion is detected.

[0012] In particular embodiments, the determination that the central unit is not able to reliably transmit an alert message to the remote monitoring server comprises a detection by the backup module of the presence of radio jamming likely to affect the first communication protocol.

[0013] In particular embodiments, the intrusion detection is carried out by the intrusion detector, and the method comprises sending an alert message by the intrusion detector to the backup module via a third communication protocol.

[0014] In particular embodiments, the transmission of the alert message by the intrusion detector to the backup module via the third communication protocol comprises a transmission of a series of several frames in a channel of an ISM band. Each frame comprises at least two sub-parts each comprising a different modulation, while having the same power and the same spectral band.

[0015] In particular embodiments, the determination that the central unit is not able to reliably transmit an alert message to the remote monitoring server comprises a detection, by the backup module, of an absence of response to a transmission of an alert message by the backup module to the central unit.

[0016] In particular embodiments, the determination that the central unit is not able to reliably transmit an alert message to the remote monitoring server comprises a detection, by the intrusion detector, of an absence of response to the transmission of an alert message by the intrusion detector to the central unit via a fourth communication protocol.

[0017] In particular embodiments, the determination that the central unit is not able to reliably transmit an alert message to the remote monitoring server comprises a detection, by the intrusion detector, of the presence of radio jamming likely to affect the first communication protocol.

[0018] In particular modes of implementation, the monitoring method comprises, prior to intrusion detection, pairing between the backup module and the peer backup module. Pairing is implemented according to the second communication protocol and includes: - a broadcast, by the backup module, of a pairing request to one or more neighboring backup modules, - for each neighboring backup module having received the pairing request, a transmission of a pairing response, to the backup module, after a wait whose duration depends on a received power level measured by the neighboring backup module upon receipt of the pairing request, - an identification, by the backup module, of the peer backup module corresponding to the neighboring backup module whose pairing response is received first.

[0019] In particular embodiments, the pairing comprises: - a determination, by the backup module, of communication parameters to be used for subsequent communications with the peer backup module, based on a pairing quality determined by the backup module from the pairing response received from the peer backup module, - a transmission, by the backup module, to the peer backup module, of a configuration message indicating said communication parameters.

[0020] In particular embodiments, the communication parameters comprise at least one of the following elements: a transmission power level, a spectrum spreading factor, a bandwidth, a transmission frequency.

[0021] In particular embodiments, the pairing comprises: - a recurrent transmission of a test message by the backup module to the peer backup module, using current communication parameters, - a transmission, by the peer backup module, of a response message to the test message, - a determination, by the backup module, of new communication parameters to be used for subsequent communications with the peer backup module, based on a pairing quality determined by the backup module from the response message received, - a transmission, by the backup module, to the peer backup module, of a configuration message indicating the new communication parameters.

[0022] In particular embodiments, the communication parameters to be used for subsequent communications are determined as a function of a received power level measured by the peer backup module upon receipt of a message sent by the backup module and / or as a function of a received power level measured by the backup module upon receipt of a message sent by the peer backup module.

[0023] According to a second aspect, the present invention relates to an alarm system for monitoring a site. The alarm system comprises at least one intrusion detector, a central unit configured to communicate with a remote monitoring server via a first communication protocol, and a backup module. The alarm system is configured to implement the following steps: - detection of an intrusion, by the intrusion detector or by the backup module, - a determination, by the intrusion detector or by the backup module, that the central unit is not able to reliably transmit an alert message to the remote monitoring server via the first communication protocol, - transmission of an alert message, by the backup module, via a second communication protocol, to a peer backup module of another alarm system used to monitor another site.

[0024] In particular embodiments, the alarm system may further comprise one or more of the following features, taken individually or in any technically possible combination.

[0025] In particular embodiments, the backup module is configured to implement, prior to the detection of an intrusion, a pairing with the peer backup module. The pairing is implemented according to the second communication protocol and comprises: - a broadcast of a pairing request to one or more neighboring backup modules, - reception of at least one pairing response from neighboring backup modules having received the pairing request, - an identification of the peer backup module corresponding to the neighboring backup module whose pairing response is received first.

[0026] In particular embodiments, in response to the pairing response received from the peer backup module, the backup module is configured to implement the following steps: - a determination of communication parameters to be used for subsequent communications with the peer backup module, - a transmission, to the peer backup module, of a configuration message indicating said communication parameters.

[0027] In particular embodiments, the backup module is configured to implement the following steps: - a recurrent transmission of a test message to the peer backup module, using current communication parameters, - upon receipt of a response message to the test message, a determination of new communication parameters to be used for subsequent communications with the peer backup module, based on a pairing quality determined by the backup module from the response message received, - a transmission, to the peer backup module, of a configuration message indicating the new communication parameters. Presentation of figures

[0028] The invention will be better understood upon reading the following description, given as an example which is in no way limiting, and made with reference to figures 1 to 12 which represent:

[0029] [Fig-1] a schematic representation of the operation of the alarm system according to the invention in case of radio jamming,

[0030] [Fig.2] a schematic representation of the main stages of the method of monitoring according to the invention,

[0031] [Fig.3] a sequence diagram illustrating a first example of implementation of the monitoring method,

[0032] [Fig.4] a sequence diagram illustrating a second example of implementation of the monitoring method,

[0033] [Fig.5] a sequence diagram illustrating a third example of implementation of the monitoring method,

[0034] [Fig.6] a sequence diagram illustrating a fourth example of implementation of the monitoring method,

[0035] [Fig.7] a sequence diagram illustrating a fifth example of implementation of the monitoring method,

[0036] [Fig.8] a sequence diagram illustrating a sixth example of implementation of the monitoring method,

[0037] [Fig.9] a sequence diagram illustrating a pairing between the backup module of the alarm system and a peer backup module belonging to another alarm system,

[0038] [Fig. 10] a schematic representation of an exemplary embodiment of an intrusion detector of the alarm system according to the invention,

[0039] [Fig. 11] a schematic representation of an exemplary embodiment of a backup module of the alarm system according to the invention,

[0040] [Fig. 12] a schematic representation of an exemplary embodiment of a central unit of the alarm system according to the invention.

[0041] In these figures, identical references from one figure to another designate identical or similar elements. For reasons of clarity, the elements represented are not necessarily on the same scale, unless otherwise stated. Detailed description of the invention

[0042] [Fig. 1] illustrates, by way of example, the general operation of an alarm system 10-1 according to the invention in a case of radio jamming. More particularly, [Fig. 1] illustrates an example in which a malicious person equipped with a radio jammer 31 intrudes on a site monitored by the alarm system 10-1.

[0043] As illustrated in [Fig.l], the alarm system 10-1 comprises at least one intrusion detector 11, a central unit 13-1, and a backup module 12-1. In the figures, the intrusion detector 11 of the alarm system 10-1 is named “ISi”, the backup module 12-1 of the alarm system 10-1 is named “EMi” and the central unit 13-1 of the alarm system 10-1 is named “CUi”. The alarm system 10-1 is named “ASi”.

[0044] The central unit 13-1 is configured to be able to communicate, under normal operating conditions, with a remote remote monitoring server 20 via a first communication protocol. This first communication protocol is a conventional wide area communication protocol based for example on a 3G, 4G, 5G or NB-IoT type cellular access network, or on communication by ADSL cable (acronym for “Asymmetric Digital Subscriber Line”) or by optical fiber. The first communication protocol provides access to a WAN (acronym for “Wide Area Network”) to communicate with the remote monitoring server 20.

[0045] The intrusion can be detected by the intrusion detector 11. For example, the intrusion detector 11 can comprise an intrusion sensor of the infrared sensor or shock sensor type making it possible to detect an opening or a break-in of a door or a window. According to another example, the intrusion sensor can be a radar or a volumetric sensor making it possible to detect the presence of a person. No.

[0046] The intrusion may, however, also be detected directly by the backup module 12-1. For example, the backup module may include a radio jamming detector, and the detection of an intrusion by a malicious person may correspond to the detection of radio jamming likely to affect the first communication protocol. According to another example, the backup module 12-1 could also include an intrusion sensor. According to yet another example, the intrusion detector 11 and the backup module 12-1 could be a single entity (in other words, the intrusion detector 11 could be part of the backup module 12-1, i.e., the intrusion detector 11 could be implemented in the same housing as the backup module 12-1).

[0047] Due to radio jamming, the central unit 13-1 is not able to reliably transmit an alert message to the remote monitoring server 20 via the first communication protocol.

[0048] To circumvent this problem, the backup module 12-1 transmits an alert message, via a second communication protocol, to a peer backup module 12-2 of a second alarm system 10-2 used to monitor another site. The second alarm system 10-2 is substantially identical to that of the first alarm system 10-1. The site monitored by the first alarm system 10-1 and the site monitored by the second alarm system 10-2 may be several kilometers, or even several tens of kilometers, apart. In the figures, the backup module 12-2 of the second alarm system 10-2 is named “EM2” and the central unit 13-2 of the second alarm system 10-2 is named “CU2”. The second alarm system 10-2 is named “AS2”.

[0049] Advantageously, the second communication protocol is a peer-to-peer wide-area communication protocol resistant to radio interference. More particularly, the physical layer of this peer-to-peer communication protocol may be based on a low-power wireless wide-area communication technology, using for example a spread spectrum technique in an ISM frequency band (acronym for "industrial, scientific and medical", these are frequency bands defined by the IUT which may in particular be used for domestic use, such as for example the 868 MHz band). The spread spectrum technique is particularly resistant to radio interference. By way of non-limiting example, the physical layer of the second communication protocol may be based on LoRA technology (acronym for "Long Range", this is a proprietary physical layer technology).However, nothing would prevent us from considering other technologies for the physical layer of the second communication protocol.

[0050] Advantageously, the transmission of the alert message between the backup module 12-1 and the peer backup module 12-2 is done asynchronously, or in a time slot agreed between the two backup modules before the detection of the intrusion. Also, the radio resources that the backup module 10-1 must use to transmit the alert message to the peer backup module 10-2 are predetermined before the detection of the intrusion. Thus, after the detection of the intrusion (i.e. at the time when the radio jamming is present), the backup module 10-1 does not need to receive a message on a downlink communication link before transmitting the alert message to the peer backup module 10-2.

[0051] Upon receipt of the alert message by the backup module 10-2, the second alarm system 10-2 can then transmit the alert message to the remote monitoring server 20.

[0052] In the example illustrated in [Fig.l], the transmission of the alert message to the remote monitoring server 20 is carried out by the central unit 13-2 of the second alarm system 10-2, via the first communication protocol. In this case, initially the backup module 12-2 even transmits the alert message to the central unit 13-2, and in a second step the central unit 13-2 transmits the alert message to the remote monitoring server 20. The communication between the backup module 12-2 even and the central unit 13-2 of the second alarm system can be implemented according to a third communication protocol corresponding to a local communication protocol resistant to radio jamming. According to another example, this communication can be implemented according to a fourth communication protocol corresponding to a conventional local communication protocol, such as for example Bluetooth or Wi-Fi.

[0053] According to another example, the transmission of the alert message by the second alarm system 10-2 can be carried out directly by the backup module 10-2 if the latter supports an extended communication protocol allowing it to communicate with the remote monitoring server 20 (this can be an LPWAN type communication protocol, for example via an NB-IoT network). This communication protocol is subsequently called the “fifth communication protocol”.

[0054] [Fig.l] illustrates an example where the central unit 13-1 of the first alarm system 10-1 is not operational due to radio jamming. However, it should be noted that other events could result in the central unit 13-1 not being able to send an alert message to the remote monitoring server 20, such as for example in the event of a power outage (power outage and / or battery fault in the central unit 13-1) or in the event of a wired communication link (ADSL or optical fiber) being cut off.

[0055] [Fig. 2] schematically represents the main steps of the monitoring method 100 according to the invention, an example of implementation of which has been described previously with reference to [Fig. 1]. The method 100 comprises the following steps: - a detection 110 of an intrusion, by the intrusion detector 11 or by the backup module 12-1 of the first alarm system 10-1, - a determination 120, by the intrusion detector 11 or by the backup module 12-1 of the first alarm system 10-1, that the central unit 13-1 is not able to reliably transmit an alert message to the remote monitoring server 20 via the first communication protocol, - a transmission 140 of an alert message, by the backup module 12-1 of the first alarm system 10-1, via the second communication protocol, to the backup module 12-2 of the second alarm system 10-2, - a transmission 150 of the alert message to the remote monitoring server 20 by the second alarm system 10-2.

[0056] Optionally, and as will be seen subsequently in some of the implementation examples described below with reference to FIGS. 3 to 8, the monitoring method 100 may also comprise a step 130 of sending an alert message by the intrusion detector 11 to the backup module 12-1.

[0057] It is important to note that the order of steps 110, 120 and 130 is not necessarily fixed as in [Fig. 2]. For example, the step 120 of determining that the central unit 13-1 is not operational could take place before the step 110 of detecting an intrusion, or after the step 130 of transmitting an alert message by the intrusion detector.

[0058] Figures 3 to 8 illustrate different examples of implementation of the method 100 according to the invention. Figures 10 to 12 illustrate different embodiments of the intrusion detector 11 (in [Fig. 10]), the backup module 12-1 (in [Fig. 11]) and the central unit 13-1 (in [Fig. 12]) to implement the different examples of Figures 3 to 8.

[0059] As illustrated in [Fig. 10], the intrusion detector 11 comprises an intrusion sensor 33 (for example an infrared sensor, a shock detector, a radar or a volumetric sensor). In certain embodiments, the intrusion detector 11 may also comprise one or more of the following elements: a radio jamming detector 32, a communication module 43 configured to send or receive messages according to the third communication protocol, a communication module 44 configured to send or receive messages according to the fourth communication protocol.

[0060] The radio jamming detector 32 is configured to detect the presence of radio jamming likely to affect the first communication protocol. The detection of the presence of radio jamming may in particular comprise a measurement, for different frequency bands, of a received radio power level (RSSI for “Received Signal Strength Indication”). A jamming detection criterion may then be evaluated based on the measurements obtained. For example, the jamming detection criterion is satisfied if the RSSI of at least one frequency band is greater than a threshold, or if the average of the RSSIs of the different frequency bands is greater than a threshold.

[0061] As illustrated in [Fig. 11], the backup module 12-1 comprises a communication module 42 configured to send or receive messages according to the second communication protocol. In certain embodiments, the backup module 12-1 may also comprise one or more of the following elements: a radio jamming detector 32, a communication module 43 configured to send or receive messages according to the third communication protocol, a communication module 44 configured to send or receive messages according to the fourth communication protocol, a communication module 45 configured to send or receive messages according to the fifth communication protocol.

[0062] As illustrated in [Fig. 12], the central unit 13-1 comprises a communication module 41 configured to send or receive messages according to the first communication protocol. In certain embodiments, the backup module 12-1 may also comprise one or more of the following elements: a communication module 43 configured to send or receive messages according to the third communication protocol, a communication module 44 configured to send or receive messages according to the fourth communication protocol.

[0063] The backup module 12-2 pair can be implemented as in [Fig. 11]. The central unit 13-2 of the second alarm system 10-2 can be implemented as in [Fig.12],

[0064] It should be noted that the backup module 12-1 and the central unit 13-1 can be part of the same physical entity (same box) or correspond to two distinct physical entities (in this case the backup module 12-1 is implemented in an additional box which can be integrated into an existing alarm system).

[0065] Even if this is not shown in the figures, the intrusion detector 11, the backup module 12-1 and the central unit 13-1 also comprise, in a conventional manner, a control circuit (comprising for example a processor, a microcontroller, or a programmable logic circuit of the FPGA type) to implement the different steps of the monitoring method 100 according to the invention.

[0066] [Fig. 3] is a sequence diagram illustrating a first example of implementation of the monitoring method 100. This first example also corresponds to the example previously described with reference to [Fig. 1]. In this first example, it is the backup module 12-1 which implements the steps of detecting 110 the intrusion and determining 120 that the central unit 13-1 is not operational (i.e. it is not able to reliably transmit an alert message to the remote monitoring server 20 via the first communication protocol). These steps may for example both correspond to the detection of radio jamming by the jamming detector 32 of the backup module 12-1.According to another example, the intrusion detection 110 is performed using an intrusion sensor 33 of the backup module 12-1, and the determination 120 that the central unit 13-1 is not operational is performed using the jamming detector 32 of the backup module 12-1. In the first example illustrated in [Fig. 3], the transmission 150 of the alert message to the remote monitoring server 20 by the second alarm system 10-2 is carried out in two stages: in a first stage (step 151) the alert message is transmitted to the central unit 13-2 of the second alarm system 10-2 by the backup module 12-2 (for example via the second communication protocol, or via the fourth communication protocol) and in a second stage (step 152), the alert message is transmitted by the central unit 13-2 of the second alarm system 10-2 to the remote monitoring server 20 (for example via the first communication protocol).

[0067] [Fig.4] is a sequence diagram illustrating a second example of implementation of the monitoring method 100. This second example is identical to the first example described previously with reference to [Fig.1], with the difference that the transmission 150 of the alert message to the remote monitoring server 20 by the second alarm system 10-2 is carried out directly by the backup module 12-2 (for example via the fifth communication protocol).

[0068] [Fig. 5] is a sequence diagram illustrating a third example of implementation of the monitoring method 100. In this third example, the detection 110 of the intrusion is carried out by the intrusion detector 11 (using the intrusion sensor 33) and the determination 120 that the central unit 13-1 is not operational is carried out by the backup module 12-1 (using the jamming detector 32). The method 100 then comprises a transmission 130 of an alert message by the intrusion detector 11 to the backup module 12-1. The transmission 130 of the alert message is triggered by the detection 110 of the intrusion. As already mentioned previously, the determination 120 that the central unit 13-1 is not operational could take place before the transmission 130 of the alert message by the intrusion detector 11.

[0069] [Fig. 6] is a sequence diagram illustrating a fourth example of implementation of the monitoring method 100. This fourth example is substantially identical to the third example described previously with reference to [Fig. 5], with the difference that the determination 120 that the central unit 13-1 is not able to reliably transmit an alert message to the remote monitoring server 20 is not based on the detection of radio jamming (in this example of implementation, it is therefore not necessary for the intrusion detector 11 or the backup module 12-1 to include a radio jamming detector 32). In this fourth example, the determination 120 that the central unit 13-1 is not operational includes the detection of a lack of response to a transmission 121 of an alert message by the backup module 12-1 to the central unit 13-1.This lack of response corresponds to an indication that the central unit 13-1 was unable to transmit the alert message to the remote monitoring server 20. This may be due, for example, to a failure of the central unit 13-1 to receive the alert message (for example, due to radio interference), or to an inability for the central unit 13-1 to transmit the alert message to the remote monitoring server 20 (for example, due to a power supply fault, a cut in a wired communication link (ADSL or optical fiber) of the central unit 13-1, or the presence of radio interference). This transmission 121 of the alert message by the backup module 12-1 to the central unit 13-1 is, for example, carried out according to the third communication protocol (local communication protocol resistant to radio interference) or according to the fourth communication protocol (conventional local communication protocol).

[0070] [Fig. 7] is a sequence diagram illustrating a fifth example of implementation of the monitoring method 100. In this fifth example, the determination 120 that the central unit 13-1 is not operational is implemented by the intrusion detector 11, and it comprises the detection of an absence of response to a transmission 111 of an alert message by the intrusion detector 11 to the central unit 13-1. As in the fourth example, this absence of response corresponds to an indication that the central unit 13-1 was unable to transmit the alert message to the remote monitoring server 20. The transmission 111 of the alert message by the intrusion detector 11 to the central unit 13-1 may in particular be carried out according to the fourth communication protocol.Again, this fifth implementation example does not necessarily require that the intrusion detector 11 or the backup module 12-1 include a radio jamming detector 32.

[0071] [Fig.8] is a sequence diagram illustrating a sixth example of implementation of the monitoring method 100. In this sixth example, it is the intrusion detector 11 which implements the determination 120 that the central unit 13-1 is not not operational, by detecting the presence of radio jamming likely to affect the first communication protocol. In this sixth, the intrusion detector 11 therefore comprises a radio jamming detector 32.

[0072] Advantageously, in the examples described above with reference to FIGS. 5 to 8, the transmission 130 of the alert message by the intrusion detector 11 to the backup module 12-1 is carried out according to the third communication protocol (local communication protocol resistant to radio jamming). The transmission 130 of the alert message may in particular comprise the transmission of a series of several frames in a channel of an ISM band, each frame comprising at least two sub-parts each comprising a different modulation, while having the same power and the same spectral band. The different modulations of a frame are difficult to perceive for a spectrum analyzer. Despite the sequence of the different modulations, the spectrum analyzer sees a single frame occupying a fixed bandwidth, with a constant power.The third communication protocol can advantageously be based on a spread spectrum technique, with a variable spreading factor. It can advantageously be used over a relatively narrow bandwidth, for example less than 30 kHz. Such arrangements provide better resistance to radio interference.

[0073] As illustrated in [Fig.9], prior to the detection 110 of an intrusion, the method 100 may comprise a preliminary pairing phase 200 between the backup module 12-1 and the peer backup module 12-2. This pairing is implemented according to the second communication protocol.

[0074] The pairing 200 notably comprises a broadcast 210, by the backup module 12-1, of a pairing request to one or more neighboring backup modules 12-2 to 12-5. The broadcast 210 of the pairing request is made with predefined default communication parameters known by all the backup modules. The backup modules of all the alarm systems which are located at a reasonable distance (for example up to a few kilometers, or even a few tens of kilometers) from the alarm system 10-1 are likely to receive the pairing request.

[0075] A pairing request is for example made up of several identical frames repeated successively. Each neighboring backup module is for example configured to recurrently enter a listening period, for example every ten seconds (it is assumed that the total transmission duration of the four frames is then at least equal to ten seconds). The listening period is of a predetermined duration long enough to make it possible to determine whether a frame of a pairing request is currently being transmitted. If this is the case, the neighboring backup module continues its listening period to fully receive at least one of the frames of the pairing request. Otherwise, the neighboring backup module may return to a standby phase until a next listening period.

[0076] For each neighboring backup module having received the pairing request, the pairing phase 200 comprises a transmission 220 of a pairing response, intended for the backup module 12-1, after a wait 211 whose duration depends on a received power level (RSSI) measured by the neighboring backup module upon receipt of the pairing request. For example, the higher the measured RSSI level, the shorter the wait duration 211.

[0077] The pairing phase 200 then comprises an identification 230, by the backup module 12-1, of the neighboring backup module 12-2 whose pairing response is received first. The backup module thus identified then becomes the peer backup module 12-2. It corresponds to the neighboring backup module with which the communication quality is a priori the best (in general, the higher the RSSI level, the better the communication quality).

[0078] In the example illustrated in [Fig.9], only backup modules 12-2, 12-3 and 12-4 received the pairing request. Backup module 12-5 is for example too distant to receive the pairing request. The RSSI level measured by backup module 12-2 is the highest, and the RSSI level measured by backup module 12-4 is the lowest.

[0079] The pairing 200 described above makes it easier to install the alarm system 10-1 on the site to be protected. Indeed, there is no need to resort to manual configuration to pair the backup module 12-1 with a peer backup module. The pairing 200 is done automatically.

[0080] As illustrated in [Fig.9], the pairing 200 may also comprise a determination 240, by the backup module 12-1, of communication parameters to be used for subsequent communications with the peer backup module 12-2. These communication parameters may in particular be defined as a function of a pairing quality determined by the backup module 12-1 from the pairing response received from the peer backup module 12-2. The communication parameters may then be sent to the peer backup module 12-2 (step 250 in [Fig.9]) in a configuration message. The configuration message is for example sent with the default communication parameters, then any subsequent message is then exchanged between the backup module 12-1 and the peer backup module 12-2 using the new communication parameters.

[0081] The communication parameters may comprise one or more of the following elements: a transmission power level, a spectrum spreading factor, a bandwidth, a transmission frequency.

[0082] The transmission frequency may be chosen randomly. According to another example, the transmission frequency may be chosen by determining a noise level in different frequency channels, and choosing a frequency of the frequency channel having the lowest noise level.

[0083] When the pairing quality is deemed insufficient, higher values ​​may be chosen for the transmission power level and for the spectrum spread factor, in order to guarantee sufficient communication reliability between the backup modules 12-1 and 12-2.

[0084] Conversely, smaller values ​​may be chosen for the transmission power level and for the spectrum spread factor when the pairing quality is deemed too high, in order to limit the energy consumption of the backup modules 12-1 and 12-2.

[0085] The pairing quality may be determined based on an RSSI level measured by the backup module 12-2 peer upon receipt of the pairing request and / or based on an RSSI level measured by the backup module 12-1 upon receipt of the pairing response. The RSSI level measured by the backup module 12-2 peer is for example transmitted to the backup module 12-1 in the pairing response.

[0086] The pairing phase 200 may also comprise a regular verification of the pairing quality. For this purpose, and as illustrated in [Fig.9], the pairing 200) may comprise - a transmission 260 of a test message, recurrently, by the backup module 12-1, to the peer backup module 12-2, using the current communication parameters. - a transmission 270, by the backup module 12-2 even, of a response message to the test message, - a determination 280, by the backup module 12-1, of new communication parameters to be used for subsequent communications with the peer backup module 12-2, based on a pairing quality determined by the backup module 12-1 from the response message received, - a transmission 290, by the backup module 12-1, to the peer backup module 12-2, of a configuration message indicating the new communication parameters (the configuration message is transmitted with the current communication parameters, before moving on to the new communication parameters).

[0087] Here again the pairing quality can be determined as a function of the RSSI level measured by the backup module 12-2 even upon receipt of the test message, and / or in function of the RSSI level measured by the backup module 12-1 upon receipt of the response to the test message.

[0088] When the backup module does not receive a response to a test message, it can reinitiate a discovery of a peer backup module by issuing a pairing request with the default communication parameters (return to step 210).

[0089] The method according to the invention thus demonstrates scalability, by automatically adapting to the addition or deletion of neighboring alarm systems, and to the evolution of the quality of pairing between two alarm systems. The alarm system 10-1 can therefore adapt to the evolution of the environment automatically.

Claims

Claims

1. Method (100) for monitoring a site by an alarm system (10-1), the alarm system (10-1) comprising at least one intrusion detector (11), a central unit (13-1) configured to communicate with a remote monitoring server (20) via a first communication protocol, and a backup module (12-1), the method (100) comprising: - a detection (110) of an intrusion, by the intrusion detector (11) or by the backup module (12-1), - a determination (120), by the intrusion detector (11) or by the backup module (12-1), that the central unit (13-1) is not able to reliably transmit an alert message to the remote monitoring server (20) via the first communication protocol, - a transmission (140) of an alert message, by the backup module (12-1), via a second communication protocol,to a backup module (12-2) of another alarm system (10-2) used to monitor another site, - a transmission (150) of the alert message to the remote monitoring server (20) by the other alarm system (10-2).,

2. Method (100) according to claim 1 wherein the second communication protocol is a peer-to-peer communication protocol, the physical layer of which is based on a low-power wireless wide area communication technology, using an ISM frequency band and a spread spectrum technique, and for which the transmission (140) of the alert message is made asynchronously between the backup module (12-1) and the peer backup module (12-2), or in a time slot agreed between the two backup modules (12-1 and 12-2) before the detection (110) of the intrusion.

3. Method (100) according to any one of claims 1 to 2 in which the determination (120) that the central unit (13-1) is not able to reliably transmit an alert message to the remote monitoring server (20) comprises a detection by the backup module (12-1) of a presence of radio jamming likely to affect the first communication protocol.

4. Method (100) according to any one of claims 1 to 3 in which the intrusion detection (110) is carried out by the intrusion detector (11), and the method comprises a transmission (130) of an alert message by the intrusion detector (11) to the emergency module (12-1) via a third communication protocol.

5. Method (100) according to claim 4 in which the transmission (130) of the alert message by the intrusion detector (11) to the emergency module (12-1) via the third communication protocol comprises a transmission of a series of several frames in a channel of an ISM band, each frame comprising at least two sub-parts each comprising a different modulation, while having the same power and the same spectral band.

6. Method (100) according to any one of claims 4 to 5 in which the determination (120) that the central unit (13-1) is not able to reliably transmit an alert message to the remote monitoring server (20) comprises a detection, by the backup module (12-1), of an absence of response to a transmission (121) of an alert message by the backup module (12-1) to the central unit (13-1).

7. Method (100) according to any one of claims 4 to 5 in which the determination (120) that the central unit (13-1) is not able to reliably transmit an alert message to the remote monitoring server (20) comprises a detection, by the intrusion detector (11), of an absence of response to the transmission (111) of an alert message by the intrusion detector (11) to the central unit (13-1) via a fourth communication protocol.

8. Method (100) according to any one of claims 4 to 5 in which the determination (120) that the central unit (13-1) is not able to reliably transmit an alert message to the remote monitoring server (20) comprises a detection by the intrusion detector (11) of a presence of radio jamming likely to affect the first communication protocol.

9. Method (100) according to any one of claims 1 to 8 comprising, prior to the detection (110) of intrusion, a pairing (200) between the backup module (12-1) and the backup module (12-2) pair, the pairing being implemented according to the second communication protocol and comprising: - a broadcast (210), by the backup module (12-1), of a pairing request to one or more neighboring backup modules (12-2 to 12-5), - for each neighboring backup module (12-2 to 12-5) having received the pairing request, a transmission (220) of a pairing response, to the backup module (12-1), after a wait (211) the duration of which depends on a received power level measured by the neighboring backup module upon receipt of the pairing request, - an identification (230), by the backup module (12-1), of the peer backup module (12-2) corresponding to the neighboring backup module whose pairing response is received first.

10. Method (100) according to claim 9 in which the pairing (200) comprises: - a determination (240), by the backup module (12-1), of communication parameters to be used for subsequent communications with the peer backup module (12-2), as a function of a pairing quality determined by the backup module (12-1) from the pairing response received from the peer backup module (12-2), - a transmission (250), by the backup module (12-1), to the peer backup module (12-2), of a configuration message indicating said communication parameters.

11. Method (100) according to claim 10 wherein the communication parameters comprise at least one of the following elements: a transmission power level, a spectrum spreading factor, a bandwidth, a transmission frequency.

12. Method (100) according to any one of claims 9 to 11 in which the pairing (200) comprises: - a transmission (260) of a test message, recurrently, by the backup module (12-1), to the peer backup module (12-2), using current communication parameters, - a transmission (270), by the peer backup module (12-2), of a response message to the test message, - a determination (280), by the backup module (12-1), of new communication parameters to be used for subsequent communications with the peer backup module (12-2), as a function of a pairing quality determined by the backup module (12-1) from the response message received, - a transmission (290), by the backup module (12-1), to the peer backup module (12-2), of a configuration message indicating the new communication parameters.

13. Method (100) according to any one of claims 10 to 12 in which the communication parameters to be used for subsequent communications are determined as a function of a received power level measured by the peer backup module (12-2) upon receipt of a message transmitted by the peer backup module (12-1) and / or as a function of a received power level measured by the peer backup module (12-1) upon receipt of a message transmitted by the peer backup module (12-2).

14. Alarm system (10-1), for monitoring a site, comprising at least one intrusion detector (11), a central unit (13-1) configured to communicate with a remote monitoring server (20) via a first communication protocol, and a backup module (12-1), the alarm system (10-1) being configured to implement the following steps: - a detection (110) of an intrusion, by the intrusion detector (11) or by the backup module (12-1), - a determination (120), by the intrusion detector (11) or by the backup module (12-1), that the central unit (13-1) is not able to reliably transmit an alert message to the remote monitoring server (20) via the first communication protocol, - a transmission (140) of an alert message, by the backup module (12-1), via a second communication protocol communication,to a backup module (12-2) paired with another alarm system (10-2) used to monitor another site.,

15. Alarm system (10-1) according to claim 14 wherein the backup module (12-1) is configured to implement, prior to the detection (110) of an intrusion, a pairing (200) with the peer backup module (12-2), the pairing being implemented according to the second communication protocol and comprising: - a broadcast (210) of a pairing request to one or more neighboring backup modules (12-2 to 12-5), - a reception of at least one pairing response from the neighboring backup modules (12-2 to 12-5) having received the pairing request, - an identification (230) of the peer backup module (12-2) corresponding to the neighboring backup module whose pairing response is received first.

16. Alarm system (10-1) according to claim 15 wherein, in response to the pairing response received from the peer backup module (12-2), the backup module (10-1) is configured to implement the following steps: - a determination (240) of communication parameters to be used for subsequent communications with the peer backup module (12-2), - a transmission (250), to the peer backup module (12-2), of a configuration message indicating said communication parameters.

17. Alarm system (10-1) according to claim 16 wherein the backup module (10-1) is configured to implement the following steps: - a transmission (260) of a test message, recurrently, to the peer backup module (12-2), using current communication parameters, - upon receipt of a response message to the test message, a determination (280) of new communication parameters to be used for subsequent communications with the peer backup module (12-2), based on a pairing quality determined by the backup module (12-1) from the response message received, - a transmission (290), to the peer backup module (12-2), of a configuration message indicating the new communication parameters.

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