ES2972084T3 - Security monitoring system - Google Patents

Abstract

A security monitoring system comprising: - a central unit, having at least one radio frequency transceiver, and a control unit for controlling the at least one radio frequency transceiver, the central unit being configurable to provide a first RF communication mode and an alternative long range communication mode, the first communication mode supporting a higher maximum bit rate than the long range mode, and the long range mode supporting a greater transmission range than the first mode; - a node comprising a node radio frequency transceiver operable in the first communication mode, for direct communication with the central unit, and in the long range communication mode for direct communication with the central unit, and a controller for controlling the node radio frequency transceiver. (Automatic translation with Google Translate, no legal value)

Description

DESCRIPTION

Security monitoring system

Technical field

The present invention relates to a security monitoring system for monitoring facilities, a node and a central unit for said system, methods of operation of the security monitoring system, the node and the central unit, and a method for compensating for differences between the operating frequency of a crystal oscillator of a central unit of a security monitoring system and a crystal oscillator of a node of the security monitoring system.

Background

Security monitoring systems for monitoring facilities generally provide a means to detect the presence and/or actions of people in the facilities and react to detected events. Commonly, such systems include sensors of various types to detect the opening and closing of doors and windows, or their attempt to force or break, motion detectors to monitor spaces for signs of movement, microphones to detect sounds such as breaking glass, and sensors images to capture still or moving images of monitored areas. Such systems can be autonomous, with alarm indicators, such as sirens and flashing lights, that can be activated if an alarm condition is detected. Such installations normally include a central unit that is coupled to sensors, detectors, cameras, etc. (here generally referred to as "nodes"), and which processes received notifications and determines a response. The central unit is normally connected to the various nodes wirelessly, rather than via cables, as this makes installation easier (making it faster and therefore potentially cheaper) and also provides some safeguards against effectively disabling sensors/detectors by disconnecting them from the central unit. Similarly, to facilitate installation and improve security, nodes in such systems typically have a self-contained power source, such as a battery, rather than mains power.

Alternatively, a security monitoring system may include such an installation in a premises, domestic or commercial, that is linked to a Central Monitoring Station (CMS) where normally human operators manage the responses required by different types of alarms and notifications. In such centrally monitored systems, the central unit at the facility's facility generally processes the notifications received from the nodes at the facility and notifies the Central Monitoring Station only some of them, depending on the system configuration and the nature of the detected events. In such a configuration, the central unit of the installation effectively acts as a gateway between the nodes and the central monitoring station.

With wireless connectivity between the nodes and the central unit, the area that can be protected by a security monitoring system will depend on the range of the wireless signals. As homes become larger and there is a need to also protect building annexes, the range of wireless signals becomes the limiting factor.

In both centrally managed and stand-alone security surveillance systems, one of the most important issues, from a practical perspective, is the battery life of the nodes in the installation, that is, the battery life of the different detectors, sensors, cameras, etc. Obviously, if a node's battery loses enough power, the node may not be able to detect a change of state or contact the central unit and, consequently, the security installation develops a weak point where an intruder can access the installations without being detected. In the case of centrally managed systems, it is normally the responsibility of the company managing the system, and not the owner or occupier of the premises, to change the batteries and, obviously, the shorter the battery life in the nodes, the more frequent the visits to the site will be and the higher the administrative cost will be. Consequently, controlling power consumption at the nodes is a high priority.

In both centrally managed and stand-alone security monitoring systems, it is also desirable that nodes and other system elements have a long useful life, for example at least 10 to 15 years, even though computer-controlled oscillators Crystals used in both nodes and the central unit can be expected to significantly change their resonant frequency over this time scale.

In addition to this, it is very important to ensure fast and timely delivery of notifications and alarms from the node to the CMS.

Document EP2542011A1 refers to an agile listen-before-talk radio frequency synchronization technique. A radio frequency communication system includes a transmitter that selects a frequency channel from multiple frequency channels available to the transmitter and a receiver, listens to ensure that a selected channel is not used before transmitting, and sends a preamble longer than the receiver scan time during which the receiver is operational to scan all frequency channels available to the transmitter and receiver for preamble. This allows receivers to scan all channels to find the preamble and lock on to the new channel to receive subsequently transmitted data while the preamble is being transmitted without prior knowledge of the transmitter's new frequency. In a further example, the transmitted preamble data comprises encoded data that receivers can read and recognize as directed to the intended receiver, ensuring that the transmitter reestablishes a communications link with the intended receiver(s).

Using scanning radios in a frequency-agile listen-before-talk radio environment is said to allow the transmitting radio to determine if a channel is busy or has a high level of noise or interference before changing frequencies, so that the transmitter can simply select another frequency or channel and transmit once it has been determined that a channel is available. Another advantage of using a listen-before-talk system is said to be that it exempts the transmitter from this duty cycle limitation "since the listen-before-talk system is supposed to impose some fairness in the use of the time available in a Limited time". “This makes 868MHz radios that employ listen-before-talk technologies desirable because they are not subject to the duty cycle limitations imposed to ensure that other devices have the opportunity to use the same frequency channels.”

Compendium

The invention is defined by independent claims 1,3 and 8 and by claim 13.

According to a first aspect, the present invention provides a method for compensating for differences between the operating frequency of a crystal oscillator of a central unit of a security monitoring system and a crystal oscillator of a node of the security monitoring system. , understanding the method:

tuning a receiver of the central unit to a first frequency subchannel of multiple frequency subchannels that together form a predetermined broader frequency channel;

listening to a preamble from the node on the first frequency subchannel;

in the event that no valid preamble is received on the first frequency subchannel within a predetermined period, tuning the receiver to one second of the multiple frequency subchannels and listening to a preamble from the node on the second frequency subchannel; and repeating the tuning and listening process until a valid preamble is received or until all multiple frequency subchannels have been used;

in the event that a valid preamble is received on one of the multiple frequency subchannels, listen for a synchronization word, and upon detecting a valid synchronization word, cause a radio frequency transceiver of the central unit to transmit an acknowledgment in a radio frequency within the predetermined frequency channel;

detecting an offset between the radio frequency of the carrier on which the valid preamble was received and the center frequency of the predetermined frequency channel;

in the event that the offset exceeds a predetermined threshold, transmitting information relating to the offset from the central unit to allow the node to adjust the operating frequency of a transceiver of the node based on the information.

Said method may further comprise adjusting the operating frequency of the node (114, 118, 125, 126) based on information related to the offset.

According to a second aspect, the present invention provides a central unit for a security monitoring system, the central unit having at least one radio frequency transceiver, and a controller for controlling at least one radio frequency transceiver, the central unit being configurable to provide a first RF communication mode and an alternative long-range communication mode, the first communication mode supporting a maximum bit rate greater than the long-range mode, and the long-range mode supporting a transmission range greater than the first mode; The controller is configured to:

control a radio frequency transceiver of the central unit to tune to one of the multiple different radio frequency subchannels that together form the long range communication channel and to listen to a preamble transmitted by a node of the security monitoring system, and in the case of that no preamble is detected within a predetermined period to control said radio frequency transceiver of the central unit to tune another of the multiple different radio frequency subchannels to listen to a preamble transmitted by the node, and repeat this procedure until all have been used multiple different radio frequency subchannels or a preamble has been detected;

and, in the event that a preamble is detected, listen for a synchronization word, and upon detection of a valid synchronization word cause a radio frequency transceiver of the central unit to transmit an acknowledgment on a radio frequency within the transmission channel. long-range communication and subsequently communicate with the node using a radio frequency within the long-range communication channel; in which the central unit is configured, based on the frequency at which the preamble of the node was received, to estimate the precision of a crystal oscillator of the node, and if the estimated precision is less than a predetermined level to provide a signal of feedback to the node, based on that estimate, to allow the node to compensate for the inaccuracy of the crystal oscillator by tuning the node's radio frequency transceiver.

In central units according to the second aspect, the central unit controller may be configured to transmit the acknowledgment on the radio frequency subchannel on which the valid synchronization word was received.

In such central units, the multiple different radio frequency subchannels may be contiguous virtual subchannels within a long range communications channel that is defined by a pair of guard bands.

Said central units can be configured to use the same radio frequency transceiver to transmit messages using the first RF communication mode and using the long range communication mode.

In such central units, the radio frequency transceiver that is used to tune to the multiple different radio frequency subchannels and to listen to a preamble transmitted by the node can be configured to use Digital Signal Arrival (DSA) to detect a valid preamble pattern.

The central units according to any variant of the second aspect may be configured to determine the RSSI for communications received from the node (114, 118, 125, 126) using the long range communication mode, and optionally in the case that the determined RSSI is above a predetermined threshold, the central unit (110) can be configured to issue an instruction to the node (114, 118, 125, 126) to switch from the long-range communication mode to the first communication mode.

According to a third aspect, the present invention provides a node for a security monitoring system, the node having a node radio frequency transceiver configurable to provide a first RF communication mode and an alternative long range communication mode, supporting the first communication mode a higher maximum bit rate than the long range mode, and the long range mode supports a larger transmission range than the first mode;

the node driver being configured to:

attempt to establish communication with a central unit of the security monitoring system using long-range communication mode by:

transmit a message comprising a preamble followed by a synchronization word on a frequency within a long-range communications channel, and

listening to an acknowledgment from the central unit on a frequency within the long range communications channel;

and, in the event that an acknowledgment is received from the central unit on one of the multiple different frequencies, communicating with the central unit using a frequency within the long range communication channel; wherein the node controller (350) is configured to use a crystal oscillator feedback signal from the central unit to compensate for the inaccuracy of the crystal oscillator (360) in tuning the node radio frequency transceiver (340).

With the node of the third aspect, the node controller can be configured to control the node transceiver to communicate with the central unit using the frequency on which an acknowledgment was received from the central unit.

The node of the third aspect may be configured, upon initial activation, to attempt to establish direct communication with the central unit using the first RF communication mode and, if the node cannot establish direct communication with the central unit using the first configuration, to attempt to establish direct communication with the central unit using long range communication mode.

The third aspect node may further be configured, when attempting to establish direct communication with the central unit using the first RF communication mode, to first attempt communication using the frequency on which the node last received an acknowledgment from the unit. central.

The node may further be configured by establishing direct communication with the central unit to receive an acknowledgment from the central unit to exchange security keys and system settings using the communication mode that was used by the node to establish direct communication with the central unit. central unit, and subsequently communicate with the central unit directly using that communication mode.

According to a fourth aspect, a security monitoring system is provided comprising a central unit according to the second aspect and one or more nodes according to the third aspect.

In the security monitoring systems of the fourth aspect, the central unit controller may be configured to transmit the acknowledgment on the radio frequency subchannel on which the preamble and the valid synchronization word were received, the node controller being configured to control the node transceiver to transmit on the center frequency of the long range communications channel.

In fourth aspect security monitoring systems, the node controller may be configured to control the node transceiver to transmit on the center frequency of the long range communications channel.

In security monitoring systems of the fourth aspect, the multiple different radio frequency subchannels may be contiguous virtual subchannels within a long range communications channel that is defined by a pair of guard bands.

The multiple different radio frequency subchannels may be provided by at least 6 different virtual radio subchannels, for example 8 or 10 subchannels.

Each of the subchannels can cover a frequency range of no more than 5 kHz, for example each of the subchannels can cover a frequency range of between 1.5 and 3 kHz.

In any of these security monitoring systems, the node can be configured to attempt to establish communication with the central unit using the first communication mode before attempting to establish communication with the central unit using the long range communication mode, and only if it does not communication with the central unit can be established using the first communication mode to attempt to establish communication with the central unit using the long range communication mode.

In any of these security monitoring systems, the central unit can be configured to use the same radio frequency transceiver to transmit messages using the first RF communication mode and using the long range communication mode.

In any of these security monitoring systems, the preambles transmitted by the node in long range mode may be at least 10 bytes long, for example at least 12 bytes or at least 15 or 16 bytes long.

In any of these security monitoring systems, the data rate of the long range communication mode may be 20% or less, for example 10%, of the data rate of the first RF communication mode.

In any of these security monitoring systems, the long range communication mode can operate in the ISM band g3 of 869.4 - 869.65 MHz, in the ISM band of 869.65 to 869.7 MHz or in the ISM g4 band from 869.7 to 870.0 MHz.

In any of these security monitoring systems, the first RF communication mode can operate in the ISM g1 band of 868.0 - 868.6 MHz or in the ISM g2 band of 868.7 to 869.2 MHz.

In any of these security monitoring systems, the radio frequency transceiver of the central unit which is used to tune to one of the multiple different radio frequency subchannels and to listen to a preamble transmitted by the node that is preferably configured to use Digital Signal Arrival (DSA). to detect a valid preamble pattern. This allows the central unit to recognize preamble patterns quickly, meaning that frequency locking between the central unit and the node can be achieved more quickly.

According to a fifth aspect, an unclaimed example provides a method for operating a security monitoring system, the system comprising:

a central unit, having at least one radio frequency transceiver, and a control unit for controlling at least one radio frequency transceiver, the central unit being configurable to provide a first RF communication mode and an alternative long range communication mode, the first communication mode supporting a higher maximum bit rate than the long range mode, and the long range mode supporting a higher transmission range than the first mode;

a node comprising a node radio frequency transceiver operable in the first communication mode, for direct communication with the central unit, and in the long range communication mode for direct communication with the central unit, and a controller for controlling the transceiver radio frequency node;

the method that includes:

attempt, using the node controller, to establish communication with the central unit using long-range communication mode by:

transmit a message comprising a preamble followed by a synchronization word on a frequency within the long-range communication channel, and

listening to an acknowledgment from the central unit on a frequency within the long range communication channel;

and, in the event that an acknowledgment is received from the central unit on a frequency within the long-range communication channel, communicating with the central unit using a frequency within the long-range communication channel; and

control, using the control unit of the central unit, a radio frequency transceiver of the central unit to tune to one of the multiple different radio frequency subchannels that together form the long range communication channel and listen to a preamble transmitted by the node and in In the event that no preamble is detected within a predetermined period, control the radio frequency transceiver of the central unit to tune another of the multiple different radio frequency subchannels to listen to a preamble transmitted by the node, and repeat this procedure until no preamble is detected. all multiple different radio frequency subchannels have been used or a preamble has been detected;

and, in the event that a preamble is detected, listening for a synchronization word and, upon detection of a valid synchronization word, causing a radio frequency transceiver of the central unit to transmit an acknowledgment on a radio frequency within the channel long-range communication; The method further comprises that the central unit estimates, based on the frequency at which the message from the node was received, the precision of a crystal oscillator of the node, and if the estimated precision is less than a predetermined level, it provides a signal of feedback to the node, based on that estimate; and the node controller uses the feedback signal provided by the central unit to compensate for the inaccuracy of the crystal oscillator in tuning the node's radio frequency transceiver.

According to a sixth aspect, an unclaimed example provides a method for operating a central unit of a security monitoring system,

the central unit having at least one radio frequency transceiver, and a controller for controlling at least one radio frequency transceiver, the central unit being configurable to provide a first RF communication mode and an alternative long range communication mode, supporting the first mode communication a higher maximum bit rate than the long range mode, and the long range mode supports a larger transmission range than the first mode;

the method that includes:

control a radio frequency transceiver of the central unit to tune to one of the multiple different radio frequency subchannels that together form a long range communication channel and listen to a preamble transmitted by the node, and in the event that no preamble is detected within a predetermined period control said radio frequency transceiver of the central unit to tune to another of the multiple different radio frequency subchannels and listen to a preamble transmitted by the node, and repeat this procedure until all the multiple different radio frequency subchannels have been used or are has detected a preamble;

and, in the event that a preamble is detected, listen for a synchronization word, and upon detecting a valid synchronization word, cause a radio frequency transceiver of the central unit to transmit an acknowledgment on a radio frequency within the communication channel long-range, and subsequently communicate with the node using a radio frequency within the long-range communication channel; The method further comprises estimating, based on the frequency at which the node's preamble was received, the precision of a crystal oscillator of the node, and whether the estimated precision is less than a predetermined level to provide a feedback signal to the node, based on that estimate, to allow the node to compensate for the inaccuracy of the crystal oscillator by tuning the node's radio frequency transceiver.

In the method of any of the fifth or sixth aspects of the invention, the multiple different radio frequency subchannels are preferably contiguous virtual subchannels within a communications channel that is defined by a pair of guard bands.

According to a seventh aspect, an unclaimed example provides a method for operating a node of a security monitoring system, the node having a node radio frequency transceiver configurable to provide a first RF communication mode and an alternative long-range communication mode. range, the first communication mode supporting a maximum bit rate greater than the long range mode, and the long range mode supporting a transmission range greater than the first mode;

the method that includes:

try to establish communication with the central unit using long range communication mode by:

transmit a message comprising a preamble followed by a synchronization word on a frequency within the long-range communication channel, and

listening to an acknowledgment from the central unit on a frequency within the long range communication channel;

and, in the event that an acknowledgment is received from the central unit on a frequency within the long-range communication channel, communicating with the central unit using a frequency within the long-range communication channel; The method further comprises the node controller using a crystal oscillator feedback signal from the central unit to compensate for the inaccuracy of the crystal oscillator in tuning the radio frequency transceiver of the node.

In any of the first to seventh aspects, the node's attempt to communicate with the central unit may result from the node being activated by an event such as detection of the opening of a door or window, motion detection, etc. Alternatively, the node's attempt to communicate may occur when it registers with the central unit, for example a periodic registration for updates or synchronization.

Brief description of the drawings

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is an overview of a security monitoring system according to a first aspect of the invention;

Figure 2 is a schematic drawing showing in more detail features of the gateway or central unit of Figure 1; and

Figure 3 is a schematic drawing showing features of a node of the security monitoring system according to an embodiment of the invention.

Detailed description of embodiments

Hereinafter, certain embodiments will be described more fully with reference to the accompanying drawings. However, the invention can be embodied in many different ways and should not be considered limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this description is thorough and complete, and fully conveys the scope of the invention, as defined in the appended claims, to those skilled in the art.

Specific description

Generally, in high security systems, the nodes are in bidirectional contact with the central unit, being able to receive information from, as well as send information to, the Central Unit 110. For example, some security monitoring facilities may operate synchronously, with each node having an internal clock that must be kept synchronized with the master clock in Central Unit 110. To maintain synchronization, the central unit can send periodic beacon signals, and the nodes periodically listen to these and adjust their clock synchronization as necessary. Such synchronization can help ensure that multiple nodes can communicate with the central unit, should an incident be detected, without the nodes' transmissions colliding. Typically, these low-power radio systems use ISM radio channels and protocols designed to reduce power consumption.

When synchronization beacons are not heard and when an event notification is not sent, the nodes' radios are typically in a low-power sleep state. Some detectors and sensors, such as magnetic switches used in doors and windows and PIR detectors, consume virtually no power while waiting to detect an event. But other detectors, such as cameras, need to have high-power functionality and be turned off to avoid consuming power; They typically only turn on when activated due to the detector's low battery functionality, or when they or another associated sensor detects motion or when instructed to turn on by Central Unit 110.

In general, nodes can notify events to the central unit with only very modest amounts of data. The main exceptions are sensors that provide image data, image sensors (usually cameras of some type), and those that provide sound data (microphones), each of which can produce significant amounts of data. Although it is of course possible to send such large amounts of data over a low bitrate channel, this requires considerable time, meaning that the transceiver must be on at least during transmission and consequently consumes A lot of energy. Additionally, on many frequencies there are regulations that control how long a device is allowed to transmit wirelessly within a certain time period. If a sensor such as a PIR or door/window opening sensor has detected an event and there is, for example, a video camera capable of monitoring an area that includes the location of the event, it would be desirable to be able to transfer usable images and frames of video to the central unit as soon as possible so that the nature and scale of the threat can be determined - and so that in a centrally monitored system the images/video stream can be sent to the CMS 200 for analysis and action.

Security monitoring systems typically include many nodes. In general, when one node in a system detects an incident, most other nodes in the system do not detect an incident but remain armed ready to detect another incident. The central unit receives a signal from the node that has detected an incident and may respond to this by signaling to the node or adjacent nodes, as well as possibly communicating with the CMS 200. But it is desirable that the central unit continue to listen for reports of other incidents of other nodes, as well as to send signals to the other nodes for control and other purposes, while exchanging communications with the node(s) at the site of the reported incident. To this end, in embodiments of the invention, the central unit preferably includes at least two transceivers for simultaneous communication with the nodes of the monitoring system to provide diversity. Preferably, each of the at least two transceivers is tunable. Preferably, one of the transceivers is dedicated to the long-range communication mode, while another of the transceivers is dedicated to providing a higher data rate channel (e.g., a standard communication link).

Figure 1 is an overview of a security monitoring system according to a first aspect of the invention. The figure shows a stylized home installation 100 of a monitoring system according to an embodiment of the invention, and a monitoring center (Central Monitoring Station) 200 that supports the home installation. The facility 100 includes a gateway or central unit, 110, also called a control unit, which is connected to the monitoring center 200 via a data connection 150. The data connection 150 may be provided via a telephone line, a broadband Internet connection, Ethernet, a dedicated data connection, or wirelessly, for example using an LTE or GSM network, and generally there will be multiple of these. options for any installation, so that there is security and diversity of connection between the gateway 110 and the monitoring center 200. For additional security, the Central Unit 110, the system sensors and nodes, and the monitoring center may all be provided with means to support an ISM radio connection, for example in the European frequency band of 863 to 870MHz, preferably a configured to resist interference.

The domestic installation 100 involves a typical arrangement where the exterior doors 120 and windows 124 are equipped with sensors 114, for example magnetic contact sensors, to detect the opening of the door or window, and/or magnetic contact and shock sensors ( which also include an accelerometer, for example to detect attempts to break the window or door). Each room in the building containing the facility may be provided with a combined fire/smoke detector 116. Additionally, several rooms have motion detectors 118, such as passive infrared (PIR) detectors, to detect motion within an observed area within the room. The entrance door 120 of the building leads to a hall that also has internal doors to several rooms in the house. The room is monitored by a video camera 125 that has an associated or integrated motion detector. Similarly, the kitchen accessed through rear door 121 is monitored by a video camera 126 that includes a motion detector. Each of the sensors, detectors and video cameras, which throughout this specification may be generically referred to as nodes, includes a wireless interface through which it can communicate with the Central Unit 110. The Central Unit 110 preferably includes a first and a second transceivers (not shown) with associated antennas 130 and 132 for communication with the sensors, detectors and video cameras. Additionally, the Central Unit 110 may include at least one additional transceiver with an antenna 134 for wireless communication with the monitoring center. Additionally, the Central Unit 110 may include a dedicated antenna arrangement, and an associated transmitter/receiver or transceiver, for Wi-Fi, for example for connecting to a home Wi-Fi access point 180. The Wi-Fi access point may also provide one of the means of access to the monitoring center 200. Optionally, the Central Unit 110 may itself function as a Wi-Fi access point, with a connection (e.g., a cable connection) to an Internet service provider, to provide Wi-Fi coverage within the building in place of Wi-Fi access point 180. One or more of the system nodes, for example nodes that include an image sensor such as a video camera, may also include Wi-Fi functionality in addition to an ISM or similar transceiver.

Some installations may include more than one central unit (CU), such as two mainframes, to provide fail-safe backup. Generally, in this type of multi-CU installations, the two CUs work together in parallel. However, in some installations the two CUs may work in parallel in communication with some of the nodes of the domestic installation and individually in communication with other nodes of the domestic installation. The latter may be the case when CU is used as a range extender in home installations covering larger installations. That is, if there are two CUs, they work in parallel but a node is only connected to one of the CUs at a time, and that CU is responsible for all communications with the node, while the other CU can listen to all and understand all communications between the other two, if it is not a scope expansion scenario.

In a home installation 100, the Central Unit 110 typically has knowledge of all nodes comprised in the installation 100. Each node may have a unique node identifier or a serial number that is used to identify the node. Each node can have different associated functionalities, such as. video capabilities, motion detection, still images, audio recording, communication rates, etc. Some or all of the capabilities may be communicated from the node to the Central Unit during a login procedure during setup configuration 100. Alternatively and/or additionally, some or all of the capabilities may be communicated to the Central Unit from the node to request from Unit 110 Central.

Alternatively and/or additionally, some or all of the capabilities may be recovered, by Central Unit 110, from CMS 200.

Figure 2 is a schematic drawing showing in more detail features of the gateway or Central Unit 110 of Figure 1. The gateway 110 includes a first transceiver 230 coupled to the first antenna 130 and, optionally, a second transceiver 232 coupled to a second antenna 132. Each of the transceivers 230 and 232 can transmit and receive, but a transceiver cannot transmit and receive at the same time. Therefore, each of the transceivers 230, 232 operates in half-duplex. Preferably, one transceiver will use the same frequency to transmit and receive (although, of course, if the two transceivers are to operate simultaneously but in opposite modes, they will operate on different frequencies). The transceivers 230, 232 may be arranged such that one transceiver 230 uses a first frequency to transmit and receive and the second transceiver 232 uses the same first frequency to transmit and receive, that is, the transceivers are arranged to operate in an arrangement similar to the diversity. Alternatively, the second transceiver may, depending on the configuration, be arranged to use a second frequency for transmitting and/or receiving. Transceivers 230 and 232 are coupled to a controller 250 via a bus. The controller 250 is also connected to a network interface 260 through which the controller 250 can be provided with a wired connection to the Internet and therefore the monitoring center 200. The controller 250 is also coupled to a memory 270 that can store data received from the various nodes of the installation, for example event data, sounds, images and video data. Central Unit 110 also includes a crystal oscillator 251, which is preferably a temperature or oven controlled crystal oscillator. This is used for system synchronization and also for frequency control of the transceivers. The gateway 110 includes a power source 262 that is coupled to a home power source, from which the gateway 110 generally draws power, and a backup battery pack 264 that provides power to the gateway 110. in case of main power supply failure. Optionally, as shown, the Central Unit 110 includes a Wi-Fi transceiver 240 and an associated antenna arrangement 242, which may be used for communication with any of the nodes that are Wi-Fi enabled. The Wi-Fi enabled node may be a remote control or control panel that may, for example, be located near the main entrance of the building to allow the occupant to arm or disarm the system from near the main entrance, or may, for example, being an image capturing device, such as a video camera. Similarly, an interface may optionally be provided that allows bidirectional communication over a Public Land Mobile Network (PLm N), such as GSM or LTE. Optionally, a third antenna 134 and an associated ISM transceiver 234 may be provided, for example, for communication with the monitoring center 200 over, for example, the European 863MHz to 870MHz frequency band.

Both the first and second transceivers may be tunable ISM devices, operating, for example, in the European frequency band 863 MHz to 870 MHz or in the 915 MHz band (which may cover 902-928 MHz or 915-928 MHz depending on the country). In particular, both devices can be tuned, that is, tuned, to frequencies within the regulatory agreed sub-bands within this defined frequency band. Alternatively, the first transceiver and the second transceiver, if present, may have different tuning ranges and, optionally, there is some overlap between these ranges.

Additionally, at least the second transceiver 232 may be used to support a long range channel, having a significantly lower symbol rate or bit rate than the other, that is not offered by the first transceiver, but this does not require that the transceivers first and second are technically different, as they may share the same inherent technical capabilities. But the gateway controller is configured to provide one or more communication channels operated through the second transceiver that can provide a longer range than that provided by the communication channels operated through the first transceiver. Note that the second transceiver can also be used as a diversity transceiver operating on the same channels as the first transceiver, but at any instant the first and second transceiver will operate on frequencies that are different enough not to interfere with each other. . In particular, the second transceiver can be used to support what can be called a long range channel according to a second configuration, while the first transceiver is used to support a normal range channel according to a first configuration. If the central unit only has one transceiver for communication with the security monitoring system nodes, that transceiver can switch between the first and second configurations as necessary, under the control of a central unit controller, as will be explained.

To help understand some embodiments, the following sections will briefly describe some general information about wireless communication. Within wireless communications there are several parameters that determine the possibility of successful transmission and reception of a packet. The possibility that a packet will not be received and/or decoded successfully is known as the Packet Error Rate (PER) and the corresponding bit-level measure is the Bit Error Rate (BER). The PER and BER are stochastic distributions and a specific level, for example BER of 2.4% for GSM, is defined as the sensitivity limit. The sensitivity limit may be different depending on the protocol and standard. In the case of ISM communications in the sub-GHz band, the maximum allowable sensitivity is specified in ETSI EN300220-1 v3.1.1. according to the equation. 1:

In the equation. 1, RBW is the receiver bandwidth. The maximum allowable sensitivity will increase with increasing receiver bandwidth and the reason for this is that the thermal noise power N introduced into the receiver increases as the receiver bandwidth increases, Eq. 2:

N = k - T<■>RBW<Eqn. 2>Where k is the Boltzmann constant in joules per Kelvin (approx. 1.381 x10<-23>J/K) and T is the temperature in Kelvin. A received signal S, with most modulation techniques, will need to be above thermal noise and a signal-to-noise ratio, SNR, is defined according to equation 3:

SNR = -<Eqn. 3>As mentioned above, the receiver will decode a received signal S into bits and the sensitivity is usually defined in BER. An alternative measure of received signal quality may be the received energy per bit E<b>versus noise equation 5:

Eb

NEqn. 5 The relationship between BER and E<b>/N is known in the art and can be accurately modeled, see for example "Analyze VER Performance of Wireless FSK System", Hamood Shehab Hamid et al., Microwaves &RF; November 2009, vol. 48, number 11, p80.

To maximize the link budget of a wireless communication, the fraction presented in equation 5 above must be maximized. This is achieved by increasing the energy per bit E<b>or by decreasing the noise N. A simple approach would be to increase the energy per bit E<b>by increasing the transmit power, but this is not always possible due to regulatory limitations; For example, regulations governing the use of ISM bands in Europe specify a maximum transmit power. Energy is power over time and if a transmission burst of a power P consists of n bits and the transmission time is t<trans>, the energy per bit E<b>can be described according to equation 6:

As seen in equation 6, increasing the transmission time t<trans>is an alternative way to increase the energy per bit E<b>. This is achieved by simply decreasing the transmission bit rate, since doing so will require a longer transmission time t<trans> to transfer the same number of bits n.

Equation 2 teaches that noise will increase with receiver bandwidth, RBW, and equation 6 teaches that decreasing the bit rate will increase the energy per bit, E<b>. Consequently, a low bit rate received over a narrow bandwidth will increase the link budget, thus potentially increasing the link range. Generally, electronic devices in general and electronic devices comprising radio frequency circuits in particular use one or more oscillators to generate base frequencies used for, for example, internal clock. The oscillator is usually connected to a frequency synthesizer which is used to generate signals of relevant frequencies for the electronic device. Consequently, the oscillator is usually the most important source of frequency errors in an electronic device. The following section will detail this and from the above explanation it is clear that regardless of the terminology used, for example clock, oscillator, etc., it refers to the same basic group of components and functions.

Having a narrow receiver bandwidth will make the receiving node more sensitive to frequency drift (both its own and that of the central unit transmitter). Frequency drift arises from the inaccuracy of the oscillator that powers the RF circuit synthesizer. Typically this is a crystal oscillator, XO, or in less price sensitive devices, a temperature controlled crystal oscillator, TCXO, or even a furnace controlled crystal oscillator, OCXO. The oscillator frequency will have an inherent error of a first Parts Per Million, PPM, a temperature drift of a second PPM, and an aging drift of a third PPM. The worst-case frequency error is the sum of the first, second, and third PPM. If the operating frequency is for example 869.5 MHz, the bit rate is 2.4 kbps (as might be used for a long range channel) and the receiver bandwidth is 5 kHz (as might also used for a long-range channel), an inaccuracy of the oscillator frequency of just over 5 PPM would be enough for the RBW to fall outside the band of interest. Typically, the central unit of the security monitoring system comprises a relatively precise oscillator (and therefore clock) compared to the node, which is usually temperature or oven controlled, but with receiver bandwidths. Below 5 kHz it will be challenging, or at least expensive, for the Central Unit to have a precise enough oscillator to ensure a precise enough transmit frequency to fit within the receiver window given its narrow bandwidth of the receiver. receiver (RBW). The frequency error, as the expert understands, in the worst case will be the sum of the worst frequency error of the node added to the worst frequency error of the central unit (when the two frequencies have been separated). To further complicate matters, commercial limitations mean that nodes must be produced cheaply, while high-precision oscillators are expensive. Furthermore, and very significantly, security monitoring system installations are typically expected to have a useful life of 10 years or more, for example 15 years. On this type of time scale, even the most expensive crystal-controlled oscillators can be expected to exhibit significant frequency drift, due to crystal aging, particularly, for example, in facilities where air quality is poor. Consequently, during the design life of a facility, something needs to be done to address oscillator frequency drift.

Consequently, something needs to be done to address the problem of frequency drift, especially that arising from crystal aging, in systems with narrow receiver bandwidths, to allow installed systems to operate reliably over a lifetime of between 10 and 15 years.

Figure 3 is a schematic drawing showing features of a node of the security monitoring system according to an embodiment of the invention. In this case, the node is a video camera such as the video camera 126 that is mounted in the kitchen, as shown in Figure 1. The node includes a radio frequency node transceiver 340 coupled to an antenna 330. A controller 350 is coupled to the transceiver and also to the image sensor 310 of the video camera. The controller 350 is coupled to a crystal controlled oscillator 360, which may also be coupled to the transceiver. The controller is also coupled to an integral motion sensor 320 and a memory 370. A battery 380 provides power to the node, in particular powering the controller, the image sensor and the motion detector. The video camera includes a lens arrangement 315 for forming an image on the image sensor 310. Optionally, the node includes an infrared light source 325 suitable for illuminating images detectable by the image sensor. The node transceiver 340 is tunable. In particular, node transceiver 340 can be tuned to frequencies to match those transmitted or received by the first and second transceivers of gateway 110.

In security monitoring systems according to embodiments of the invention, the central unit is capable of using at least two communication modes to communicate with the system nodes: a normal range communication protocol (with a first configuration) and a long range communication (with a second configuration). The normal range communication protocol comprises one or more normal range communication channels, and the long range communication protocol comprises one or more long range communication channels. Security monitoring systems according to embodiments of the invention may be configured to use only one of the normal range communication channels for the normal range communication protocol and only one of the long range communication channels for the communication protocol. long range. The long-range communication channels defined by the long-range communication protocol have a lower bit rate and smaller receiver bandwidth than the corresponding normal-range communication channels defined by the normal-range protocol.

The most effective way to improve range is to increase sensitivity. If one aims to improve sensitivity over that provided by a standard, for example for a 38.4 kbit/s data rate channel by 10 dB, it is usually necessary to reduce the bit rate considerably. To obtain an adequate improvement in sensitivity, a low bit rate of kilobits per second, for example 5 kbps or less, for example 2.4 kbps, will generally be required. To give a receiver, such as a receiver in the central unit, optimal sensitivity, the modulation index is preferably kept close to h=1, so with a bit rate of 2.4 kbps the deviation could be set to around 1.2 kHz. This gives a fairly narrow occupied bandwidth of approximately 3.9 kHz.

This rather narrow bandwidth places strict requirements on the accuracy of clock synchronization between the nodes and the central unit. Using 2.4 kbps we would need to have an accuracy of 0.5-1 ppm or better than 600-900 Hz. This would require expensive and precise oscillators and there are still real challenges in managing aging and long term stability. Later there will also be a rapid decrease in sensitivity depending on the receiver's ability to track the carrier and adjust the filters.

Problems with high clock synchronization requirements mean that it would be difficult or even impossible to achieve clock synchronization between the mainframe and the nodes, even with the most precise oscillators. Therefore, a different approach would seem necessary.

A standard narrowband channel of 25 kHz was defined and the approximate occupied BW of the signal was set to 4 kHz.

The solution adopted for the embodiments of the present invention was to implement a kind of asynchronous automatic frequency hopping in a long range receiver (generally, of course, this is the receiver function of a transceiver) in the central unit. A certain number of channels were defined that would cycle constantly. The receiver's task is to quickly find the channel that corresponds to the frequency offset between the node transceiver and that of the central unit, without any prior knowledge other than the target center frequency of the narrowband channel (at which the node transceiver would be nominally tuned). By making the preamble long enough to catch the worst case in which the transmission channel was simply lost, the asynchronous jump scheme should not lose any packets.

A target channel frequency was set at the center of the long-range channel, and depending on the accuracy of clock synchronization between the node clock and the central unit clock, there is an unknown frequency offset. We want to translate this unknown offset to a known subchannel. To achieve this, the long-range channel is divided into several virtual channels (virtual in the sense that they are contiguous analog subchannels that are not separated by guard bands), based on the channel resolution needed to obtain sufficiently good sensitivity. . The long-range communication mode uses a narrowband frequency modulated signal. System nodes will typically use a standard crystal and will generally attempt to transmit as close as possible to the center of the long range channel being used (of course, determined based on the frequency of their own crystal oscillator). The central unit's (long range) receiver will continually search for preambles on the subchannels and as soon as there is a lock on a preamble, the central unit will attempt to find a valid sync word. If the central unit's (long-range) receiver manages to receive the message, it will send an acknowledgment to the node, preferably on the same subchannel that was used to receive the valid synchronization word. This confirmation can be sent quickly and it is assumed that the node's crystal oscillator will be stable in this period of time and the node should be able to receive the confirmation (packet) from the central unit. With the bandwidth chosen to cover set to approximately 20 kHz, 10 subchannels with 2 kHz channel spacing can be used to cover the entire bandwidth. Clearly, these parameters can be appropriately tuned based on the particular system and required system performance. So, for example, less than 10 subchannels, for example 5, 6, 7, 8 or 9 subchannels can be used. Likewise, more than 10 subchannels can be provided, for example 11, 12, 13, 14 or 15 channels can be provided. Similarly, the channel spacing need not be 2 kHz but can be, for example, anywhere in the range 1.5 to 3 kHz.

In this way, the central unit is controlled to continuously scan through the set of pseudo channels and attempt to detect the channel that the node is using based on the individual offset and inaccuracy of its crystal. When a valid preamble is found, the host cycles through the channels, a clock synchronization is performed, and the synchronization word is checked to see if it is a system message (that is, it is determined whether the synchronization word is valid or not for the system). Upon detection of a valid packet, or that the preamble, synchronization, CRC are correct, an acknowledgment is sent, for example according to ETSI regulations, on the same frequency and on the actual channel/frequency of the received packet.

The biggest challenge here is that the channels are not well defined with guard bands, but are simply a collection of analog channels scattered over the discrete channel we have defined, and the central unit (long range) receiver has to decide which is the strongest channel and be able to set the preamble of that channel. The challenge with this approach is the time it takes to scan all virtual subchannels and quickly determine whether there is a valid preamble or not. To solve this we use the digital signature (sometimes called Digital Signal Arrival DSA) of a valid preamble so that the receiver in just two bits can decide if the preamble is valid or not, and if not, the receiver must jump to the next subchannel . The lack of guard bands is a challenge, but we mitigate it by restricting the dynamics to only use long range on weak signals. After a valid preamble detection, we still have enough preamble bits to perform a full clock recovery and frequency offset measurement.

The configured normal range communication channels can be used by all nodes whose link budgets allow normal range communication. This will often be possible for those nodes corresponding to the interior of a given facility, for example a house or an apartment. But nodes that are placed too far from the central unit, or for which signal attenuation is likely to be greater than normal for other reasons (e.g. as a result of attenuation by walls/floors, etc.) the central unit and the relevant node), in order to communicate using the normal range communication protocol can be arranged to communicate using the configured long range communication channel. This can be for example nodes mounted in a detached or attached garage, latrine, pool house, etc. There are also situations where, although the central unit and all nodes in a facility are within 10, 20, or 30 meters, one or more of the nodes may be located such that RF signals between the node and the unit central unit suffer considerably greater attenuation compared to signals passing between the central unit and most other nodes in the installation. For example, the affected nodes may be on another floor of the central unit, for example in a basement or attic, and the construction of the intermediate ceilings/floors may be such that RF signals are significantly attenuated when passing through the nodes. themselves. Typically, this can occur when construction includes metal framing or reinforcement, high-density concrete, or similar. Similar problems can occur even between rooms on the same floor, whether through the use of metal structures or reinforcements, high-density concrete, or even with intervening walls lined with books or files, for example. Additionally, there may be particular use cases for certain nodes that cause the link balance to deteriorate; A non-limiting example could be sensors placed inside refrigerators, freezers or other appliances that have a shielding effect against radio waves.

In security monitoring systems according to embodiments of the invention that have both a long range transceiver and a normal range transceiver, the Central Unit will generally be arranged to continuously monitor the configured long range communication channel and the configured long range communication channel. configured normal range (unless the corresponding transceiver is transmitting). This means that in such systems there is at least one receiver (usually a transceiver operating in receive mode) of the Central Unit(s) in the security monitoring system listening to each configured channel.

When a new node is installed in a security monitoring system, it typically needs to log in to the system's Central Unit. A login procedure usually comprises exchanging security keys and system settings, etc. The login procedure is generally initiated by the node wishing to log in, with the node transmitting, sequentially on each of the communication channels available to the node, a login beacon (a "HELLO" message) comprising a message composed of a preamble, a synchronization word, and a payload. After each login beacon is transmitted, the node waits (in receive mode) for a response from the Central Unit; If no response is received, the node changes the communication channel and sends a new login beacon. If a response is received from the Central Unit, the node continues the login procedure on the communication channel on which the response was received.

The initial login is, from a frequency perspective, open loop. The node has no concept of its frequency relative to the Central Unit other than perhaps, for example, a factory calibrated offset. If the RBW of the receiving device is in the region above 50 kHz, this is usually not a major problem, but if the RBW is below 10 kHz, there is a risk of the login beacon being transmitted to a frequency outside the intended communication channel. It should be noted that the node and central unit transceivers do not need to operate with the same receiver bandwidth. For example, if the central unit increases its transmitted power, the node can reduce its RBW. The node/CU of the Rx/Tx link budgets must be balanced with respect to the entire receiver chain.

An attempt can be made to log in using a node on the configured long range channel if the available normal range channels cannot be logged in. Alternatively, the Central Unit may instruct a node (which is already logged into the Central Unit) to switch to the configured long-range communication channel, in which case a frequency or frequency offset related to the currently frequency may be communicated. busy from the Central Unit to the node. For example, the central unit can order the change based on instructions from the CMS. For example, when an alarm system suffers from recurring monitoring problems with a particular node (the node fails to communicate with the central unit for a certain period of time), the CMS service staff can highlight this and a possible solution would be switch to a long range setting.

Additionally, the CU may have functionality itself to determine if there should be a protocol change. In particular, the central unit can be configured to determine the RSSI of signals received from the different nodes of the system. If the central unit determines that the RSSI of a node using the long-distance communication mode is greater than a certain threshold (meaning a higher than expected received signal strength), the central unit may instruct the corresponding node to switch from long range mode to standard mode. Of course, such a transition means that the relevant node will benefit from a higher bandwidth communication channel to the central unit, meaning that alerts and other messages can be sent from that node to the central unit in less time, thereby resulting in lower battery consumption on the node and therefore potentially longer battery life.

In embodiments of the invention, a node can be configured to "remember" long range as the preferred protocol, for example, having learned it on initial installation. This would mean that in the case of battery change or loss of communication with the mainframe, these cases trigger a new login sequence from the node, the node in this case would initiate the new login sequence using long range (second setup) instead of a normal channel (first setup). Additionally, or alternatively, system nodes can be configured to "remember" the communication parameters from their last communication session, whether long range or standard, and to use those remembered parameters the next time they attempt to communicate with the central unit. .

Generally the Central Unit is the master and the frequency it uses as a long-range communication channel is the one that should be used. The nodes that receive messages on the long-range communication channel are configured to adjust their frequency to that of the Central Unit, for example this would be the case where communication and login are established but the node detects a small error of frequency when receiving the CU transmission. This error is compensated at the node, with each transceiver having a register indicating the frequency offset between the center frequency of the tuned RBW and the measured frequency of the received message.

If the Central Unit receives a message from a node, it may optionally acknowledge the message on the same core frequency on which the message was received, but have the acknowledgment specify a frequency offset from the current frequency that the node should use for all future communications. This can be used as a typical acknowledgment on all acknowledgments sent from the Central Unit on the long range communication channel.

Alternatively, and preferably, the central unit can be configured to use the narrow modulation bandwidth of long range signals from the nodes. When the central unit's long-range receiver is connected to the node preamble, the receiver obtains a rough estimate of the accuracy of the node crystal compared to the central unit's crystal. You can also determine an estimate of the distance in Hz between the center frequency of the central unit's long-range transceiver and the center frequency of the node transceiver. This information can be stored and compared to a predetermined threshold value, and if it is outside certain limits, the discrepancy can be returned to the node with a hint (or instruction) to update its crystal offset (to reduce the frequency offset between the node transceiver and the corresponding transceiver of the central unit). Importantly, this technique can be used both to track and improve communication in semi-rapid crystal changes, and to more generally compensate for crystal aging. Aging occurs in all crystals, in the nodes and in the central units, but it is the difference between the receiver and the transmitter that is critical and by aligning all the nodes with the central unit crystal the effects of aging are no longer They would be a problem. The inaccuracy of the mainframe crystal would not affect the system, only the accuracy in the frequency measurement compensated by the mainframe and the resolution of the frequency compensation and the ability of the nodes to handle rapid changes in the environment, like the temperature. It will be appreciated that this approach to compensating for the effects of crystal aging, and in particular the differences between the effects of crystal aging in the nodes and in the central unit, is of general relevance and is not limited in its application to systems that include multiple modes of communication (i.e., not only applicable to systems that provide both standard and long-range communication channels).

Installation limitation

Typically, in conventional security monitoring systems a minimum received signal strength (RSSI) limit is set, and for a node to be installed in the system, the node must be close enough to the central unit to receive signals from the central unit above that signal level. For example, such a limit may be set to, for example -82 dBm. Most importantly, we want to have a margin of at least 20 dB to cope with link fading conditions.

The power budgets can be set so that the standard and long range operation overlap, for example by about 10 dB, so there would be a high probability that the standard mode operates most of the time and therefore the long range could be used largely as recoil. Since the long-range channel not only has a lower bit rate, but also adds frequency diversity, it effectively adds some additional robustness to the link.

Frequency band

The 869.4-869.65 MHz band allows for a 10% duty cycle and a maximum power of 500 mW ERP, which is 12 dB above the other alarm channels used. Although the use of only one long range channel has been described, more than one channel can be provided if necessary.

Energy budget

One of the main challenges with a lower bitrate is meeting the target power budget. The lower bitrate will consume more power for the same traffic data, so essentially there is a need to decrease the amount of data that needs to be transferred to meet the power budget. A sensible battery life target for nodes is 5 years of service, with the main limiting factors being: background current consumption in sleep mode, periodic refresh, and tamper detection. By comparison, alarm interactions are rare.

Frequency band and additional channels

Although the described long range implementation uses only one 869.4-869.425 MHz channel, it could be beneficial to implement support for more channels, for example to limit the impact on other systems in areas where there are many competing RF sources. For example, it should be possible to run up to 10 channels on the same band. The 869.65-869.7 MHz band is an alarm band restricted to 25 mW ERP and this band would be suitable for running the long range channel, and two channels should be supported in this band.

The packet structure of the communications described herein are known structures comprising preamble, synchronization word and data. Depending on the transmission structure used, e.g. block transmission, etc., the data messages may contain packet identifiers, sender ID, recipient identifier and/or counters and the length of the packets may be, e.g. default, configurable, negotiable, etc. Packets may be encrypted and there may be a Cyclic Redundancy Check, CRC, included in the packet. The skilled person will know how to form packages that will allow the implementation of the embodiments described herein.

Long packets should only be allowed under good network conditions, at least unless direct error correction is implemented. Since the long-range channel targets weak link conditions, it is reasonable to accept a limitation on the maximum payload length.

When choosing frequencies and transmission rate, the regulations in force in the region where the security system is implemented must be taken into account. In Europe, radio systems for security monitoring systems commonly use ISM (Industrial Scientific and Medical) radio frequencies around 868 MHz (the 863-870 MHz band). Similar bands, but centered on different frequencies, are similarly allocated for the same purposes in other territories. For example, in the USA, Canada, Chile, Colombia, Costa Rica, Mexico, Panama and Uruguay the 915 MHz band covers between 902-928 MHz, while in Australia, Peru and Brazil it covers between 915-928 MHz, and in other countries other parts of a 915-928 MHz bands are available. In Europe, duty cycles in the ISM bands are regulated by the relevant sections of the latest harmonized revision of the ETSI standard EN300220. This standard defines, at the time of this application, the following subbands and their permitted duty cycles:

g(863.0 - 868.0 MHz): 1%

g1(868.0 - 868.6 MHz): 1%

g2(868.7 - 869.2 MHz): 0.1%

g3(869.4 - 869.65 MHz): 10%

g4(869.7 - 870.0 MHz): 1%

Embodiments of the invention implemented in Europe can make use of the g1 and g2 subbands, where the allowed Effective Radiated Power (ERP) is 25 mW (+14 dBm), with a 1% duty cycle for communication between the Unit 110 Central. and the nodes. Typically, systems are configured to offer predefined frequency options in each of the g1 and g2 bands. In such systems, high-speed channels and other channels offered in the g3 subband can be offered, which has an allowed ERP of 500 mW (+27 dBm) with a 10% duty cycle. Again, more than one frequency in this band can be preselected to enable alternative options. But it will be appreciated that the invention is not based on the use of the g3 subband; channels could be reserved within subbands g1 or g2. If the security monitoring system is deployed in another territory, it is anticipated that the RF bands assigned to security and alarm systems, or available for such use even if not specifically assigned, will also provide opportunities to preselect some frequencies for speed. normal, control and messaging functions, while allowing others to be preselected for use as long-range channels in the context of the invention.

Typically, channels or normal speed settings can operate between 30 and 45 kbit/s; 38.4 kbit/s. "Long range" can be equivalent to 0.6 to 14.4 kbit/s, for example 4.8 kbit/s or 2.4 kbit/s.

Sending the same amount of data over long-range radio will take longer due to, among other reasons, the lower bit rate. The longer the radio is active, the more battery it will consume. This means that, in general, if we can transmit packets over standard radio, we should use it.

Channel agility

To support fast switching to long-range channels, the system must be configured to support channel switching without requiring login, since a complete login sequence typically requires many packets to be sent in both directions. Thus, for example, a node change channel (or subchannel) should continue its operation on the new channel as if nothing had changed. And a gateway (mainframe) must accept a node change channel without logging in.

Node behavior

Optional Hello Cycle/Cold Start Scheme: When a node enters its hello cycle to search for host units, it must include its available long-range channels.

Channel fixation: It is preferable that a node be configured to remain on the channel where it last received an ACK, that is, on the channel where it last had a functional link.

Optional node fallback scheme: When a node does not receive the required ACK in response to the transmission of a message (preamble, sync word, data), it will use the following sequence to attempt to send the message (packet). The list starts on a standard channel:

1. Retry the packet x times (e.g. 10 times) on the current channel

2. Retry the packet and times (for example, 3 to 5 times) on the available node long range channels 3. Retry once on all standard channels

4. Restart Hello cycle

Central Unit Behavior

Normally there are different requirements during installation and normal operation mode.

Mode of operations

During normal system operation, the preference is always to use Standard rates, if possible. This is mainly to conserve battery, but will also have other benign effects, such as polluting the frequency band less and logging back in faster if necessary.

If a node is in long range, but the RSSI (measured by the central unit) indicates that it should operate at Standard rates, the central unit can be configured to issue a pulse to move that node to Standard.

Installation mode

One of the benefits of the long-range approach is that it can make the system installation experience (and the installation experience of new nodes) easier and less complicated for installers. This means that systems can be configured in such a way that the process of installing a long-range node does not differ significantly for the installer from installing a standard-range node.

Therefore, during installation, the mainframe and the long-range node can be configured to work together automatically to direct the node to the best protocol based on the acceptance criteria. Therefore, it is possible that the node will predictably follow the behavior outlined above, while the Central Unit will try to make more informed decisions.

A node with RSSlnode < the lowest RSSI level acceptable for installing a standard range node (Sinst) will be forced to Long Range, to ensure that the RSSI acceptance criteria are met and receives Long Range RSSI values.

When the Central Unit exits Installation mode it will run an evaluation on the current RSSI if the node is on a Long Range channel:

evaluates standard RSSI<Long Range Strength, if RSSI < Sinst>

No action - otherwise

Although generally security monitoring systems according to embodiments of the invention will be configured such that the nodes will initially attempt to communicate with the central unit using a standard communication channel rather than a long range channel, they may instead be configured so initially try to communicate using a long-range channel. Subsequently, the central unit can move such a node to a standard communication channel if the measured RSSI indicates an appropriately high signal strength. But due to the higher bit rate provided by standard communication channels, it is generally preferred to configure the system and nodes so that the nodes always try to communicate initially using a standard communication channel.

Additionally, nodes that last successfully communicated with the central unit using a long-range channel may, due to channel rigidity, also initially attempt to communicate with the central unit using the stored long-range channel and then frequency hop. through the other long-range channels to establish communication through any long-range subchannels. Subsequently, the central unit can move such a node to a standard communication channel if the measured RSSI indicates an appropriately high signal strength.

Interactive mode

Let us now consider the provision of long-range functionality in the case of a magnetic contact node. Typically, magnetic contact nodes can be configured as listen-after-talk (LAT) nodes. This means that the central unit can only talk to this node after the node has first spoken to the central unit, and only for a short period after the node spoke to the central unit.

LAT stands for Listening After Speaking. Which means that the node listens for packets from the Central Unit a short period after it has sent its own packets to the Central Unit.

A LAT-based node will only communicate with the Central Unit under two main conditions:

1. If something happens to the node, that is, magnetic contact is violated.

2. During periodic updates to verify that the node is still alive.

The periodic update for a magnet can be around 7 minutes, but for a Long Range node it will have to be less frequent due to battery consumption.

With the introduction of Long Range, there is now a requirement for more frequent RSSI reporting, as well as being able to issue the push command to nodes if they need to be moved between Long Range and Standard.

To solve this, it is proposed to introduce a mode for the node that could be called interactive mode. During the installation of nodes where this requirement is valid, the central unit will reduce the periodic reporting rate on the nodes to ensure that the central unit can communicate with them in a timely manner.

This method can also be used for the same type of nodes to allow for faster and more deterministic FOTA (Firmware Over The Air) updates.

In order for the Central Unit to make the switch between Long Range and Standard, the central unit can issue instructions to the nodes according to one or the other of the following two options, although of course alternative methods can be used instead:

Maintain credentials

This option allows the node to not perform a full login to the new channel. Instead, it will simply change frequencies and continue as if nothing happened. This can be enabled using the channel agility functionality.

Immediate shipping enablement

This option requires the node to immediately send a periodic status report once it has changed frequency. This can be configured by the Central Unit as a way to immediately verify that a switch has operated. A failed confirmation of the periodic state will force the node to enter its hello cycle.

It will be appreciated that according to the unclaimed alternatives, the security monitoring system does not need to include a central monitoring station 200, although it normally will. The gateway or Central Unit 110 may have or be associated with one or more screens for displaying images, moving or still, and audio output devices such as speakers. So that an operator can be alerted by state changes detected by nodes such as motion sensors, magnetic switches and the like, and can view images and listen to audio signals received from the nodes.

Claims (15)

1. A method for compensating differences between the operating frequency of a crystal oscillator (251) of a central unit (110) of a security monitoring system and a crystal oscillator (360) of a node (114, 118, 125, 126) of the security monitoring system, the method comprising: tuning a receiver (230, 232, 234) of the central unit (110) to a first frequency subchannel of multiple frequency subchannels that together form a frequency channel widest default; listening to a preamble from the node (114, 118, 125, 126) on the first frequency subchannel; In the event that no valid preamble is received on the first frequency subchannel within a predetermined period, tune the receiver (230, 232, 234) to within one second of the multiple frequency subchannels and listen to a preamble from the node ( 114, 118, 125, 126) in the second frequency subchannel; and repeating the tuning and listening process until a valid preamble is received or until all multiple frequency subchannels have been used; in the event that a valid preamble is received on one of the multiple frequency subchannels, listen for a synchronization word, and upon detecting a valid synchronization word, activate a radio frequency transceiver (230, 232, 234) of the unit (110) central for transmitting an acknowledgment on a radio frequency within the predetermined frequency channel; detecting an offset between the radio frequency of the carrier on which the valid preamble was received and the center frequency of the predetermined frequency channel; In the event that the displacement exceeds a predetermined threshold, transmit from the central unit (110) information related to the displacement to allow the node (114, 118, 125, 126) to adjust the operating frequency of a transceiver (340) of the node based on the information. 2. The method of claim 1, further comprising adjusting the operating frequency of the node (114, 118, 125, 126) based on the displacement information. 3. A central unit (110) for a security monitoring system, the central unit having at least one radio frequency transceiver (230, 232, 234), and a controller (250) for controlling at least one transceiver (230, 232). , 234) of radio frequency, the central unit (110) being configurable to provide a first RF communication mode and an alternative long-range communication mode, the first communication mode supporting a maximum bit rate greater than the long-range mode , and the long-range mode supporting a greater transmission range than the first mode; the controller (250) being configured to: control a radio frequency transceiver (230, 232, 234) of the central unit to tune to one of the multiple different radio frequency subchannels that together form the long range communication channel and listen to a preamble transmitted by a node (114,118, 125, 126 ) of the security monitoring system, and in the event that no preamble is detected within a predetermined period to control said radio frequency transceiver (230, 232, 234) of the central unit (110) to tune another of the multiple different radio frequency subchannels to listen to a preamble transmitted by the node (114, 118, 125, 126), and repeat this procedure until all multiple different radio frequency subchannels have been used or until a preamble has been detected; and, in the event that a preamble is detected, listen for a synchronization word, and upon detection of a valid synchronization word cause a radio frequency transceiver (230, 232, 234) of the central unit (110) to transmit a acknowledge receipt on a radio frequency within the long-range communication channel and subsequently communicate with the node using a radio frequency within the long-range communication channel; wherein the central unit (110) is configured, based on the frequency at which the preamble of the node (114, 118, 125, 126) was received, to estimate the precision of a crystal oscillator (360) of the node, and if the estimated accuracy is less than a predetermined level to provide a feedback signal to the node (114, 118, 125, 126), based on that estimate, to allow the node (114, 118, 125, 126) to compensate for the inaccuracy of the crystal oscillator (360) when tuning the node's radio frequency transceiver (340). 4. The central unit of claim 3, wherein the controller unit (250) of the central unit (110) is configured to transmit the acknowledgment on the radio frequency subchannel on which the valid synchronization word was received. 5. The central unit of claim 3 or claim 4, wherein the central unit (110) is configured to use the same radio frequency transceiver (230, 232, 234) to transmit messages using the first RF communication mode and using long range communication mode. 6. The central unit of any of claims 3 to 5, wherein the radio frequency transceiver (230, 232, 234) of the central unit (110) is used to tune the multiple different radio frequency subchannels and to listen to the preamble transmitted by the node (114, 118, 125, 126) is configured to use Digital Signal Arrival, DSA, to detect a valid preamble pattern. 7. The central unit of any of claims 3 to 6, wherein the central unit (110) is configured to determine the RSSI for communications received from the node (114, 118, 125, 126) using the communication mode long range, and optionally wherein in the event that the given RSSI is above a predetermined threshold, the central unit (110) is configured to issue an instruction to the node (114, 118, 125, 126) to change from long range communication mode to first communication mode. 8. A node (114, 118, 125, 126) for a security monitoring system, the node having a configurable node radio frequency transceiver (340) to provide a first RF communication mode and an alternative long-range communication mode. range, the first communication mode supporting a higher maximum bit rate than the long range mode, and the long range mode supporting a greater transmission range than the first mode; the node controller (350) being configured to: attempt to establish communication with a central unit (110) of the security monitoring system using the long-range communication mode by: transmit a message comprising a preamble followed by a synchronization word on a frequency within a long-range communications channel, and listening to an acknowledgment from the central unit (110) on a frequency within the long-range communications channel; and, in the event that an acknowledgment is received from the central unit (110) on one of the multiple different frequencies, communicating with the central unit (110) using a frequency within the long range communication channel; wherein the node controller (350) is configured to use a crystal oscillator feedback signal from the central unit to compensate for the inaccuracy of the crystal oscillator (360) in tuning the node radio frequency transceiver (340). 9. The node of claim 8, wherein the node controller (350) is configured to control the node transceiver (340) to communicate with the central unit (110) using the frequency on which an acknowledgment was received. receipt of the central unit (110). 10. The node of claim 8 or claim 9, wherein the node is configured, upon initial activation, to attempt to establish direct communication with the central unit (110) using the first RF communication mode, and, if the node (114, 118, 125, 126) cannot establish direct communication with the central unit (110) using the first configuration, to try to establish direct communication with the central unit using the long-range communication mode. 11. The node of claim 10, the node (114, 118, 125, 126) being further configured, when attempting to establish direct communication with the central unit (110) using the first RF communication mode, to first attempt communication using the frequency at which the node (114, 118, 125, 126) last received an acknowledgment from the central unit (110). 12. The node of any of claims 8 to 11, the node further being configured to establish direct communication with the central unit (110) to receive an acknowledgment of receipt from the central unit to exchange security keys and system configurations using the communication mode that was used by the node to establish direct communication with the central unit, and subsequently to communicate with the central unit directly using that communication mode. 13. A security monitoring system comprising a central unit according to any of claims 3 to 7, and one or more nodes according to any of claims 8 to 12. 14. A security monitoring system according to claim 13, a central unit according to any of claims 3 to 7, or a node (114, 118, 125, 126) according to any of claims 8 to 12, wherein the Multiple different radio frequency subchannels are contiguous virtual subchannels within a long-range communications channel that is defined by a pair of guard bands. 15. A central unit, node or security monitoring system of any of claims 3 to 14, wherein the data rate of the long range communication mode is 20% or less, for example 10%, of the data rate. data from the first mode of RF communication.