Alarm system with a backup communication link between peers

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 not able 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).

Description

[0001] Alarm system with a peer-to-peer backup communication link

[0002] Scope of the invention

[0003] The present invention relates to the field of alarm systems that send an alert to a remote monitoring server in the event of an intrusion. More specifically, the invention concerns an alarm system, as well as the associated monitoring method, using a backup communication link with another alarm system at a neighboring site.

[0004] State of the art

[0005] Numerous alarm systems are available on the market to protect a site against intrusion. These systems are designed to detect and signal unauthorized entry into the protected site (which could be a house, apartment, building, room within a building, garden, etc.). Their purpose is to contribute to the monitoring and protection of property and people on the site.

[0006] Alarm systems are generally equipped with intrusion detectors (infrared sensors, radar, volumetric sensors, shock detectors, etc.). In response to intrusion detection, the alarm system can trigger deterrents (for example, a siren or a smoke generator) and send an alert message from a central unit of the alarm system to a remote monitoring server.

[0007] The alert message is usually sent to the remote monitoring server through a wireless cellular communication network, such as an LTE network (English acronym for "Long Term Evolution", in French "évolution à long terme", this is the fourth generation, or 4G, standard specified by the 3GPP consortium) or a 5G-NR network (English acronym for "5G - New Radio", in French "5G - Nouvelle radio", this is the fifth generation 3GPP standard).

[0008] To prevent the alarm system from sending an alert, a malicious individual 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 intended signals, on one or more frequency bands. The intended signals are then no longer detected by the receivers of devices near the jammer. The jammer can disrupt the radio links between the alarm system's central unit and the monitoring server, as well as between an intrusion detector and the central unit.

[0009] To overcome this problem, it is known to transmit an alert message via a wireless communication network that uses radio transmission techniques that are relatively insensitive to frequency jamming. Patent EP3716242B1 describes a secure radio communication method between an intrusion detector and the central unit of an alarm system. Patent EP3477611 B1 provides an example of an alarm system whose central unit includes a radio communication module configured to send an alert message to the monitoring server via a unidirectional, ultra-narrowband (UNB) LPWAN (Low Power Wide Area Network) when radio jamming is detected.

[0010] However, an LPWAN network using jam-resistant radio technology is not always available. Furthermore, it requires a subscription with the LPWAN network operator.

[0011] Description of the invention

[0012] The present invention aims to remedy all or part of the drawbacks of the prior art, in particular those set out above.

[0013] To this end, and according to a first aspect, the present invention proposes a method for monitoring a site using 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:

[0014] - detection of an intrusion, either by the intrusion detector or by the backup module,

[0015] - a determination, by the intrusion detector or the backup module, that the central unit is unable to reliably transmit an alert message to the remote monitoring server via the primary communication protocol,

[0016] - the 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,

[0017] - transmission of the alert message to the remote monitoring server by the other alarm system. In specific implementation modes, the monitoring method may also include one or more of the following characteristics, taken individually or in all technically possible combinations.

[0018] In specific implementation modes, the second communication protocol is a peer-to-peer communication protocol whose physical layer relies on a low-power wireless extended communication technology. This second communication protocol uses an ISM frequency band and a spread-spectrum technique. The alert message is transmitted asynchronously between the backup module and the peer backup module, or within a pre-arranged time slot between the two backup modules before intrusion detection.

[0019] In specific implementation modes, the determination that the central unit is unable to reliably transmit an alert message to the remote monitoring server involves detection by the backup module of the presence of radio interference likely to affect the first communication protocol.

[0020] In specific implementation modes, intrusion detection is performed by the intrusion detector, and the method includes the issuance of an alert message by the intrusion detector to the backup module via a third communication protocol.

[0021] In specific implementation modes, the transmission of the alert message by the intrusion detector to the backup module via the third communication protocol involves the transmission of a series of frames in an ISM band channel. Each frame comprises at least two sub-parts, each with a different modulation, while having the same power and spectral band.

[0022] In specific implementation modes, the determination that the central unit is unable to reliably transmit an alert message to the remote monitoring server involves the detection, by the backup module, of a lack of response to an alert message sent by the backup module to the central unit.

[0023] In specific implementation modes, determining that the central unit is unable to reliably transmit an alert message to the remote monitoring server involves the intrusion detector detecting a lack of response to the alert message sent by the intrusion detector to the central unit via a fourth communication protocol. In specific implementation modes, determining that the central unit is unable to reliably transmit an alert message to the remote monitoring server involves the intrusion detector detecting radio interference that could affect the first communication protocol.

[0024] In certain implementation modes, the monitoring method includes, prior to intrusion detection, pairing between the backup module and its peer backup module. This pairing is implemented, for example, according to the second communication protocol.

[0025] In specific implementation modes, pairing includes:

[0026] - a broadcast, by the backup module, of a pairing request to one or more neighboring backup modules,

[0027] - for each neighboring backup module that has received the pairing request, a pairing response is sent to the backup module after a waiting period whose duration depends on a received power level measured by the neighboring backup module upon receiving the pairing request,

[0028] - identification, by the backup module, of the peer backup module corresponding to the neighboring backup module whose pairing response is received first.

[0029] In specific implementation modes, pairing includes:

[0030] - 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,

[0031] - an emission, by the backup module, to the peer backup module, of a configuration message indicating said communication parameters.

[0032] In particular modes of implementation, the communication parameters include at least one of the following: a transmit power level, a spread spectrum factor, a bandwidth, a transmit frequency.

[0033] In specific implementation modes, pairing includes:

[0034] - a recurring transmission of a test message by the backup module to the peer backup module, using standard communication parameters, - a transmission, by the peer backup module, of a reply message to the test message.

[0035] - 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 received reply message,

[0036] - an emission, by the backup module, to the peer backup module, of a configuration message indicating the new communication parameters.

[0037] In particular implementation modes, the communication parameters to be used for subsequent communications are determined based on a received power level measured by the peer backup module upon receiving a message emitted by the peer backup module and / or based on a received power level measured by the backup module upon receiving a message emitted by the peer backup module.

[0038] 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:

[0039] - detection of an intrusion, either by the intrusion detector or by the backup module,

[0040] - a determination, by the intrusion detector or the backup module, that the central unit is unable to reliably transmit an alert message to the remote monitoring server via the primary communication protocol,

[0041] - a 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.

[0042] In particular embodiments, the alarm system may further include one or more of the following features, taken individually or in all technically possible combinations.

[0043] In specific implementation modes, the backup module is configured to establish a pairing with the peer backup module prior to intrusion detection. This pairing is implemented, for example, using the second communication protocol. In specific implementation modes, the pairing includes:

[0044] - the broadcast of a pairing request to one or more neighboring backup modules,

[0045] - receipt of at least one pairing response from neighboring backup modules that received the pairing request,

[0046] - an identification of the peer backup module corresponding to the neighboring backup module whose pairing response is received first.

[0047] In specific implementation modes, in response to the pairing response received from the peer backup module, the backup module is configured to implement the following steps:

[0048] - a determination of communication parameters to be used for subsequent communications with the peer backup module,

[0049] - an emission, to the peer backup module, of a configuration message indicating said communication parameters.

[0050] In specific implementation modes, the backup module is configured to implement the following steps:

[0051] - the recurring transmission of a test message to the peer backup module, using standard communication parameters,

[0052] - upon receipt of a reply 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 received reply message,

[0053] - a transmission, to the peer backup module, of a configuration message indicating the new communication parameters.

[0054] Presentation of the figures

[0055] The invention will be better understood upon reading the following description, given by way of non-limiting example, and made with reference to Figures 1 to 12 which represent:

[0056] [Fig. 1] a schematic representation of the operation of the alarm system according to the invention in the event of radio jamming,

[0057] [Fig. 2] a schematic representation of the main steps of the monitoring method according to the invention,

[0058] [Fig. 3] a sequence diagram illustrating a first example of the implementation of the monitoring method, [Fig. 4] a sequence diagram illustrating a second example of the implementation of the monitoring method,

[0059] [Fig. 5] a sequence diagram illustrating a third example of implementation of the monitoring method,

[0060] [Fig. 6] a sequence diagram illustrating a fourth example of implementation of the monitoring method,

[0061] [Fig. 7] a sequence diagram illustrating a fifth example of implementation of the monitoring method,

[0062] [Fig. 8] a sequence diagram illustrating a sixth example of implementation of the monitoring method,

[0063] [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,

[0064] [Fig. 10] a schematic representation of an example of an embodiment of an intrusion detector of the alarm system according to the invention,

[0065] [Fig. 11] a schematic representation of an example of an embodiment of a backup module of the alarm system according to the invention,

[0066] [Fig. 12] a schematic representation of an example of an embodiment of a central unit of the alarm system according to the invention.

[0067] In these figures, identical references from one figure to another designate identical or analogous elements. For clarity, the elements shown are not necessarily to the same scale, unless otherwise stated.

[0068] Detailed description of the invention

[0069] Figure 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 specifically, Figure 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.

[0070] As illustrated in Figure 1, the alarm system 10-1 comprises at least one intrusion detector 11, one control unit 13-1, and one backup module 12-1. In the figures, the intrusion detector 11 of the alarm system 10-1 is labeled "ISi", the backup module 12-1 of the alarm system 10-1 is labeled "EMi", and the control unit 13-1 of the alarm system 10-1 is labeled "CUi". The alarm system 10-1 is labeled "ASi".

[0071] The central unit 13-1 is configured to communicate, under normal operating conditions, with a remote monitoring server 20 via a primary communication protocol. This primary communication protocol is a conventional wide area network (WAN) protocol based, for example, on a 3G, 4G, 5G, or NB-LoT cellular access network, or on ADSL (Asymmetric Digital Subscriber Line) cable communication or fiber optic cable. The primary communication protocol provides access to a wide area network (WAN) for communication with the monitoring server 20.

[0072] Intrusion can be detected by the intrusion detector 1. For example, the intrusion detector 1 may include an intrusion sensor such as an infrared sensor or a shock sensor, enabling the detection of an opening or forced entry of a door or window. As another example, the intrusion sensor may be a radar or a volumetric sensor, enabling the detection of the presence of a person.

[0073] However, the intrusion can 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 individual may correspond to the detection of radio jamming likely to affect the primary communication protocol. In another example, the backup module 12-1 could also include an intrusion sensor. In yet another example, the intrusion detector 11 and the backup module 12-1 could be a single unit (in other words, the intrusion detector 11 could be part of the backup module 12-1, meaning that the intrusion detector 11 could be implemented in the same housing as the backup module 12-1).

[0074] Due to radio interference, the central unit 13-1 is unable to reliably transmit an alert message to the remote monitoring server 20 via the first communication protocol.

[0075] 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 essentially 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 tens of kilometers, apart. In the figures, the backup module 12-2 of the second alarm system 10-2 is labeled "EM2" and the central unit 13-2 of the second alarm system 10-2 is labeled "CU2". The second alarm system 10-2 is labeled "AS2".In general, we can consider the case where an intrusion detector 1 1 of the first alarm system 10-1 is not able to communicate directly with an element of the second alarm system 10-2 because of the distance that separates the two alarm systems 10-1 and 10-2.

[0076] Advantageously, the second communication protocol is a wide-area peer-to-peer communication protocol resistant to radio interference. More specifically, the physical layer of this peer-to-peer communication protocol can be based on a low-power wireless wide-area communication technology, using, for example, a spread spectrum technique in an ISM frequency band (an acronym for "Industrial, Scientific, and Medical," which are frequency bands defined by the ITU that can be used for domestic purposes, such as the 868 MHz band). The spread spectrum technique is particularly resistant to radio interference. As a non-limiting example, the physical layer of the second communication protocol can be based on LoRa technology (an acronym for "Long Range," a proprietary physical layer technology).However, nothing would prevent us from considering other technologies for the physical layer of the second communication protocol.

[0077] Advantageously, the transmission of the alert message between the backup module 12-1 and the backup module 12-2 is done asynchronously, or within a time slot agreed upon between the two backup modules before intrusion detection. Also, the radio resources that the backup module 12-1 must use to transmit the alert message to the backup module 12-2 are predetermined before intrusion detection. Thus, after intrusion detection (i.e., when radio jamming is present), the backup module 12-1 does not need to receive a message on a downlink before transmitting the alert message to the backup module 12-2 (radio jamming primarily affects the receive, not the transmit, capabilities of the backup module 12-1).

[0078] Upon receiving the alert message by the backup module 12-2 pair, the second alarm system 10-2 can then transmit the alert message to the remote monitoring server 20.

[0079] In the example shown in Figure 1, the alert message is transmitted to the monitoring server 20 by the central unit 13-2 of the second alarm system 10-2, via the first communication protocol. In this case, the backup module 12-2 even first transmits the alert message to the central unit 13-2, and then the central unit 13-2 transmits the alert message to the monitoring server 20. Communication between the backup module 12-2 even and the central unit 13-2 of the second alarm system can be implemented using a third communication protocol, corresponding to a local communication protocol resistant to radio jamming. In another example, this communication can be implemented using a fourth communication protocol, corresponding to a conventional local communication protocol, such as Bluetooth or Wi-Fi.

[0080] In another example, the transmission of the alert message by the second alarm system 10-2 can be carried out directly by the backup module 12-2 pair if the latter supports an extended communication protocol allowing it to communicate with the remote monitoring server 20 (this could be an LPWAN type communication protocol, for example via an NB-LoT network). This communication protocol is subsequently referred to as the "fifth communication protocol".

[0081] Figure 1 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 prevent the central unit 13-1 from sending an alert message to the remote monitoring server 20, such as a power outage (power failure and / or battery failure of the central unit 13-1) or a break in a wired communication link (ADSL or fiber optic).

[0082] Figure 2 schematically represents the main steps of the monitoring method 100 according to the invention, an example of which was described previously with reference to Figure 1. Method 100 comprises the following steps:

[0083] - a detection 1 10 of an intrusion, by the intrusion detector 11 or by the backup module 12-1 of the first alarm system 10-1,

[0084] - 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 unable to reliably transmit an alert message to the remote monitoring server 20 via the first communication protocol,

[0085] - 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 even of the second alarm system 10-2,

[0086] - a transmission 150 of the alert message to the remote monitoring server 20 by the second alarm system 10-2. Optionally, and as will be seen later in some of the implementation examples described below with reference to figures 3 to 8, the monitoring method 100 may also include a step of sending 130 an alert message by the intrusion detector 11 to the backup module 12-1.

[0087] It is important to note that the order of steps 110, 120 and 130 is not necessarily fixed as in Figure 2. For example, step 120 of determining that the central unit 13-1 is not operational could take place before step 110 of detecting an intrusion, or after step 130 of issuing an alert message by the intrusion detector.

[0088] Determining whether the central unit 13-1 can reliably transmit an alert message to the monitoring server 20 via the first communication protocol allows us to know whether this first communication protocol can be used or whether it is necessary to involve the backup module 12-1 and the backup module 12-2, along with the second communication protocol. In the absence of interference, it is generally preferable to use the first communication protocol (better reliability, better throughput). However, in the presence of interference, it becomes necessary to use the backup modules and the second communication protocol to guarantee the delivery of the alarm message to the monitoring server 20.

[0089] Figures 3 to 8 illustrate different examples of implementation of method 100 according to the invention. Figures 10 to 12 illustrate different embodiments of the intrusion detector 11 (in Figure 10), the backup module 12-1 (in Figure 11), and the central unit 13-1 (in Figure 12) for implementing the various examples in Figures 3 to 8.

[0090] As illustrated in Figure 10, the intrusion detector 11 includes an intrusion sensor 33 (for example, an infrared sensor, a shock detector, a radar, or a volumetric sensor). In some embodiments, the intrusion detector 11 may also include one or more of the following: 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.

[0091] The radio interference detector 32 is configured to detect the presence of radio interference that could affect the primary communication protocol. Radio interference detection may include measuring the Received Signal Strength Indication (RSSI) level for different frequency bands. An interference detection criterion can then be evaluated based on the measurements obtained. For example, the interference detection criterion is met if the RSSI of at least one frequency band is above a threshold, or if the average RSSI of the different frequency bands is above a threshold.

[0092] As illustrated in Figure 11, the backup module 12-1 includes a communication module 42 configured to send or receive messages according to the second communication protocol. In some embodiments, the backup module 12-1 may also include one or more of the following: 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.

[0093] As illustrated in Figure 12, the central unit 13-1 includes a communication module 41 configured to send or receive messages according to the first communication protocol. In some embodiments, the backup module 12-1 may also include one or more of the following: 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.

[0094] The backup module 12-2 pair can be implemented as in Figure 11. The central unit 13-2 of the second alarm system 10-2 can be implemented as in Figure 12.

[0095] 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 separate 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).

[0096] Although not shown in the figures, the intrusion detector 11, the backup module 12-1 and the central unit 13-1 also conventionally include a control circuit (comprising for example a processor, a microcontroller, or an FPGA-type programmable logic circuit) to implement the various steps of the monitoring method 100 according to the invention.

[0097] Figure 3 is a sequence diagram illustrating a first example of the implementation of monitoring method 100. This first example also corresponds to the example previously described with reference to Figure 1. In this first example, the backup module 12-1 implements the steps of intrusion detection 110 and determination 120 that the central unit 13-1 is not operational (i.e., it is unable to reliably transmit an alert message to the remote monitoring server 20 via the first communication protocol). These steps could, for example, both correspond to the detection of radio jamming by the jamming detector 32 of the backup module.

[0098] 12-1. According to another example, 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 Figure 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: first (stage 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 second (stage 152) the alert message is transmitted by the central unit

[0099] 13-2 of the second alarm system 10-2 to the remote monitoring server 20 (for example via the first communication protocol).

[0100] Figure 4 is a sequence diagram illustrating a second example of the implementation of monitoring method 100. This second example is identical to the first example described previously with reference to Figure 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).

[0101] Figure 5 is a sequence diagram illustrating a third example of the implementation of monitoring method 100. In this third example, the intrusion detection 110 is performed by the intrusion detector 11 (using the intrusion sensor 33), and the determination 120 that the central unit 13-1 is not operational is performed by the backup module 12-1 (using the jamming detector 32). Method 100 involves the 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 intrusion detection 110. As mentioned previously, the determination 120 that the central unit 13-1 is not operational could occur before the transmission 130 of the alert message by the intrusion detector 11.

[0102] Figure 6 is a sequence diagram illustrating a fourth example of the implementation of monitoring method 100. This fourth example is substantially identical to the third example described previously with reference to Figure 5, with the difference that the determination 120 that the central unit 13-1 is unable to reliably transmit an alert message to the remote monitoring server 20 is not based on the detection of radio jamming (in this implementation example, 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 involves the detection of a lack of response 121 to an alert message transmitted by the backup module 12-1 to the central unit 13-1.This lack of response indicates 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 the central unit 13-1 failing to receive the alert message (for example, due to radio interference), or to the central unit 13-1 being unable to transmit the alert message to the remote monitoring server 20 (for example, due to a power outage, a break in a wired communication link (ADSL or fiber optic) to the central unit 13-1, or the presence of radio interference). This transmission of the alert message 121 by the backup module 12-1 to the central unit 13-1 is carried out, for example, according to the third communication protocol (radio interference-resistant local communication protocol) or according to the fourth communication protocol (conventional local communication protocol).

[0103] Figure 7 is a sequence diagram illustrating a fifth example of the implementation of 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 involves detecting a lack of response 11 to an alert message transmitted by the intrusion detector 11 to the central unit 13-1. As in the fourth example, this lack of response indicates 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 can, 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. Figure 8 is a sequence diagram illustrating a sixth implementation example of monitoring method 100. In this sixth example, it is the intrusion detector 11 that implements the determination 120 that the central unit 13-1 is not operational, by detecting the presence of radio jamming likely to affect the first communication protocol. In this sixth example, the intrusion detector 11 therefore includes a radio jamming detector 32.

[0104] Advantageously, in the examples described above with reference to Figures 5 to 8, the transmission of the alert message 130 by the intrusion detector 11 to the backup module 12-1 is carried out according to the third communication protocol (a local communication protocol resistant to radio jamming). The transmission of the alert message 130 may, in particular, consist of a series of several frames in an ISM band channel, each frame comprising at least two sub-parts, each with a different modulation, while having the same power and spectral band. The different modulations of a frame are difficult for a spectrum analyzer to detect. Despite the sequence of different modulations, the spectrum analyzer sees a single frame occupying a fixed bandwidth, with constant power.The third communication protocol can advantageously be based on a spread spectrum technique, with a variable spreading factor. It can be used effectively over a relatively narrow bandwidth, for example, less than 30 kHz. Such arrangements provide better resistance to radio interference.

[0105] As illustrated in Figure 9, prior to the detection 1 10 of an intrusion, the method 100 may include a preliminary pairing phase 200 between the backup module 12-1 and the paired backup module 12-2. This pairing is implemented, for example, according to the second communication protocol.

[0106] In the example considered, pairing 200 includes, in particular, 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 to all the backup modules. The backup modules of all alarm systems located within a reasonable distance (for example, up to a few kilometers, or even a few tens of kilometers) of the alarm system 10-1 are likely to receive the pairing request.

[0107] A peering request, for example, consists of several identical frames repeated successively. Each neighboring backup module is configured to repeatedly enter a listening period, for example, every ten seconds (assuming the total transmission time of the different frames is at least ten seconds). The listening period is of a predetermined duration long enough to determine whether a frame of a peering request is currently being transmitted (in other words, the listening period is at least equal to the interval between two frames). If so, the neighboring backup module continues its listening period to receive at least one of the frames of the peering request in its entirety. Otherwise, the neighboring backup module can return to a standby phase until the next listening period.

[0108] For each neighboring backup module that has received the peering request, the peering phase 200 involves the transmission 220 of a peering response to 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 receiving the peering request. For example, the higher the measured RSSI level, the shorter the wait 211 duration.

[0109] The pairing phase 200 then involves 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 (generally, the higher the RSSI level, the better the communication quality).

[0110] In the example shown in Figure 9, only standby modules 12-2, 12-3, and 12-4 received the peering request. Standby module 12-5, for example, is too far away to receive the peering request. The RSSI level measured by standby module 12-2 is the highest, and the RSSI level measured by standby module 12-4 is the lowest.

[0111] The 200 pairing described above simplifies the installation of the 10-1 alarm system at the site to be protected. In fact, there is no need for manual configuration to pair the 12-1 backup module with a peer backup module. The 200 pairing is performed automatically.

[0112] As illustrated in Figure 9, the pairing step 200 can also include the determination, 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 can be defined based on 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 can then be sent to the peer backup module 12-2 (step 250 in Figure 9) in a configuration message. The configuration message is, for example, sent with the default communication parameters, and any subsequent messages are then exchanged between the backup module 12-1 and the peer backup module 12-2 using the new communication parameters.

[0113] Communication parameters may include one or more of the following: a transmit power level, a spread spectrum factor, a bandwidth, a transmit frequency, a time slot scheme in which the 12-2 pair backup module can expect to receive a message transmitted by the 12-1 backup module, etc.

[0114] The transmission frequency can be chosen randomly. As another example, the transmission frequency can be chosen by determining the noise level in different frequency channels and selecting a frequency from the channel with the lowest noise level.

[0115] When the pairing quality is deemed insufficient, higher values ​​can be chosen for the transmit power level and for the spectrum spreading factor, in order to ensure sufficient communication reliability between the 12-1 and 12-2 backup modules.

[0116] Conversely, smaller values ​​can be chosen for the transmit power level and for the spectrum spreading factor when the matching quality is deemed too high, in order to limit the energy consumption of the backup modules 12-1 and 12-2.

[0117] Peering quality can be determined based on an RSSI level measured by the 12-2 peer backup module upon receiving the peering request and / or based on an RSSI level measured by the 12-1 peer backup module upon receiving the peering response. The RSSI level measured by the 12-2 peer backup module is, for example, transmitted to the 12-1 peer backup module in the peering response.

[0118] The pairing phase 200 may also include regular verification of pair quality. For this purpose, and as illustrated in Figure 9, pairing 200 may include

[0119] - a 260 transmission of a test message, on a recurring basis, by the backup module 12-1, to the backup module 12-2 pair, using the current communication parameters.

[0120] - an emission 270, by the backup module 12-2 pair, of a reply 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 backup module 12-2 pair, based on a pairing quality determined by the backup module 12-1 from the received reply message,

[0121] - an emission 290, by the backup module 12-1, to the backup module 12-2 pair, of a configuration message indicating the new communication parameters (the configuration message is emitted with the current communication parameters, before switching to the new communication parameters).

[0122] Here again, the pairing quality can be determined based on the RSSI level measured by the 12-2 peer backup module upon receiving the test message, and / or based on the RSSI level measured by the 12-1 backup module upon receiving the response to the test message.

[0123] When the standby module does not receive a response to a test message, it can re-initiate a discovery of a peer standby module by issuing a peering request with the default communication parameters (return to step 210).

[0124] The method according to the invention thus demonstrates scalability, automatically adapting to the addition or removal of neighboring alarm systems and to changes in the pairing quality between two alarm systems. The 10-1 alarm system can therefore adapt automatically to changes in the environment.

[0125] Peering 200 is implemented prior to the detection of jamming. In other words, peering 200 is intended to be implemented in the absence of jamming. In the absence of jamming, the backup module 12-1 is capable of receiving messages transmitted by the peer backup module 12-2; in particular, the backup module 12-1 is capable of receiving a peering reply or a reply to a test message. However, in the presence of jamming, it is not guaranteed that the backup module 12-2 will be able to receive a message transmitted by the peer backup module 12-2. Advantageously, according to the invention, once pairing 200 has been performed, the transmission 140 of an alert message by the backup module 12-1 to the backup module 12-2 pair no longer requires the backup module 12-1 to be able to receive a message.It is important to note that radio interference primarily affects reception capabilities, not transmission capabilities. Pairing between the backup module 12-1 and the backup module 12-2 pair could not occur in the presence of interference because the backup module 12-1 would be unable to receive a pairing reply message from the backup module 12-2 pair. Once pairing 200 has been established, the backup module 12-2 pair is configured, for example, to repeatedly enter a listening period to receive any alert messages from the backup module 12-1. This listening period may correspond to a time slot defined in the communication parameters established during the pairing process.In another example, the alert message might consist of several identical frames repeated successively, and the listening period is of a predetermined duration long enough to determine whether a frame of the alert message is being transmitted (for example, it is assumed that the duration of a listening period is at least equal to the interval between two successive frames and that the total transmission time of the different frames is at least equal to the interval between two listening periods). If so, the peer backup module continues its listening period to receive at least one of the frames of the alert message in its entirety. Otherwise, the peer backup module can return to a standby phase until the next listening period.

Claims

Demands 1. Method (100) of 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: - 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 unable 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 peer 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 extended communication technology, using an ISM frequency band and a spread spectrum technique, and wherein 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 an agreed time slot 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 wherein the determination (120) that the central unit (13-1) is unable to reliably transmit an alert message to the remote monitoring server (20) comprises a detection by the backup module (12-1) of the presence of radio interference likely to affect the first communication protocol.

4. Method (100) according to any one of claims 1 to 3 wherein the intrusion detection (110) is performed by the intrusion detector (11), and the method comprises an emission (130) of an alert message by the intrusion detector (11) to the backup module (12-1) via a third communication protocol.

5. Method (100) according to claim 4 wherein the transmission (130) of the alert message by the intrusion detector (11) to the backup module (12-1) via the third communication protocol comprises the transmission of a series of several frames in a channel of an ISM band, each frame comprising at least two sub-parts each having 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 wherein the determination (120) that the central unit (13-1) is unable to reliably transmit an alert message to the remote monitoring server (20) comprises a detection, by the backup module (12-1), of a lack of response to an emission (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 wherein the determination (120) that the central unit (13-1) is unable to reliably transmit an alert message to the remote monitoring server (20) comprises a detection, by the intrusion detector (11), of a lack 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 wherein the determination (120) that the central unit (13-1) is unable to reliably transmit an alert message to the remote monitoring server (20) comprises a detection by the intrusion detector (11) of the presence of radio jamming capable of affecting the first communication protocol.

9. Method (100) according to any one of claims 1 to 8 comprising, prior to intrusion detection (1 10), a pairing (200) between the backup module (12-1) and the backup module (12-2) pair.

10. Method (100) according to claim 9 wherein the pairing is implemented according to the second communication protocol and 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), - for each neighbouring backup module (12-2 to 12-5) having received the pairing request, an emission (220) of a pairing response, to the backup module (12-1), after a wait (211) whose duration depends on a received power level measured by the neighbouring backup module upon receipt of the pairing request, - an identification (230), by the backup module (12-1), of the backup module (12-2) corresponding to the neighboring backup module whose pairing response is received first.

11. Method (100) according to claim 10 wherein 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), based on a pairing quality determined by the backup module (12-1) from the pairing response received from the peer backup module (12-2), - an emission (250), by the backup module (12-1), to the even backup module (12-2), of a configuration message indicating said communication parameters.

12. Method (100) according to claim 1 1 wherein the communication parameters include at least one of the following: a transmit power level, a spread spectrum factor, a bandwidth, a transmit frequency.

13. Method (100) according to any one of claims 10 to 12 wherein the pairing (200) comprises: - a recurring transmission (260) of a test message by the backup module (12-1) to the peer backup module (12-2), using standard communication parameters, - an emission (270), by the backup module (12-2) even, of a reply 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 received reply message, - an emission (290), by the backup module (12-1), to the even backup module (12-2), of a configuration message indicating the new communication parameters.

14. Method (100) according to any one of claims 11 to 13 wherein the communication parameters to be used for subsequent communications are determined as a function of a received power level measured by the backup module (12-2) even upon receipt of a message transmitted by the backup module (12-1) and / or as a function of a received power level measured by the backup module (12-1) upon receipt of a message transmitted by the backup module (12-2) even.

15. 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: - 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 unable 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 peer backup module (12-2) of another alarm system (10-2) used to monitor another site.

16. Alarm system (10-1) according to claim 15 in which the backup module (12-1) is configured to implement, prior to the detection (110) of an intrusion, a pairing (200) with the backup module (12-2) pair.

17. Alarm system (10-1) according to claim 16 wherein pairing is implemented according to the second communication protocol and comprises: - a broadcast (210) of a pairing request to one or more neighboring backup modules (12-2 to 12-5), - receipt of at least one pairing response from neighboring backup modules (12-2 to 12-5) that received the pairing request, - an identification (230), of the backup module (12-2) corresponding to the neighboring backup module whose pairing response is received first.

18. Alarm system (10-1) according to claim 17 wherein, in response to the pairing response received from the backup module (12-2) pair, 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 backup module (12-2) pair, - an emission (250), to the backup module (12-2) even, of a configuration message indicating said communication parameters.

19. Alarm system (10-1) according to claim 18 wherein the backup module (10-1) is configured to implement the following steps: - a recurring transmission (260) of a test message to the backup module (12-2) using standard communication parameters, - upon receipt of a reply message to the test message, a determination (280) of new communication parameters to be used for subsequent communications with the backup module (12-2) peer, based on a pairing quality determined by the backup module (12-1) from the received reply message, - an transmission (290), to the backup module (12-2) pair, of a configuration message indicating the new communication parameters.

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