Field

The present invention relates generally to security monitoring systems for premises, and in particular to such installations including radio-based location sensing arrangement to detect human presence based on detecting perturbations of radio signals, control units and nodes for such systems, and corresponding methods.

Background

Security monitoring systems for monitoring premises, often referred to as alarm systems, typically provide a means for detecting the presence and/or actions of people at the premises and reacting to detected events. Commonly such systems include sensors to detect the opening and closing of doors and windows, movement detectors to monitor spaces (both within and outside buildings) for signs of movement, microphones to detect sounds such as breaking glass, and image sensors to capture still or moving images of monitored zones. Such systems may be self- contained, with alarm indicators such as sirens and flashing lights that may be activated in the event of an alarm condition being detected. Such installations typically include a control unit (which may also be termed a central unit or local management device), generally mains powered, that is coupled to the sensors, detectors, cameras, etc. (“peripherals” or “nodes”), and which processes received notifications and determines a response. The local management device or central unit may be linked to the various nodes by wires, but increasingly is instead linked wirelessly, rather than by wires, since this facilitates installation and may also provide some safeguards against sensors/detectors effectively being disabled by disconnecting them from the central unit. Similarly, for ease of installation and to improve security, the nodes of such systems typically include an autonomous power source, such as a battery power supply, rather than being mains powered.

As an alternative to self-contained systems, a security monitoring system may include an installation at a premises, domestic or commercial, that is linked to a remotely located monitoring station where, typically, human operators manage the responses required by different alarm and notification types. These monitoring stations are often referred to as Central Monitoring Station (CMS) because they may be used to monitor a large number of security monitoring systems distributed around the monitoring station, the CMS located rather like a spider in a web. In such centrally monitored systems, the local management device or central unit at the premises installation typically processes notifications received from the nodes in the installation, and notifies the Central Monitoring Station of only some of these, depending upon the settings of the system - in particular whether it is fully or only partially armed, and the nature of the detected events. In such a configuration, the central unit at the installation is effectively acting as a gateway between the nodes and the Central Monitoring Station. Again, in such installations the central unit may be linked by wires, or wirelessly, to the various nodes of the installation, and these nodes will typically be battery rather than mains powered.

An issue that arises particularly with monitored alarms, whether remotely monitored at a monitoring station or linked to a local police department, is false alarms - the triggering of alarm events that are reported to the remote monitoring station or the police, but which are not the result of an intrusion or burglary. False alarms, needlessly occupy the human operators in the monitoring station so that extra staff need to be provided to compensate for this, in order to maintain possibly contractually specified response times. False alarms that lead to the call out of security staff add extra expense, and if false alarms are reported to the police there may be penalties of various kinds.

The remote monitoring station, or more usually the staff of the remote monitoring station, will generally try to verify that an alarm report is in respect of a “real” alarm rather than a false alarm using information received from the relevant security monitoring installation - in particular using images/video from any cameras at the installation, using sound files from microphones, or using data from a combination of sources, but it is not always possible to eliminate false alarms. A key contributor to this problem is that many domestic installations have no more than one camera, and some have no camera at all, in part because customers may be reluctant to live with perceived surveillance in their own homes - and because they may worry about their domestic lives being observed by means of security system cameras. There is also the issue of expense or cost, with system suppliers typically charging extra for each camera included in an installation. But of course, the lack of cameras means that monitoring centre staff often cannot see much of the internal space protected by an installation - at least where the space is divided into multiple rooms. And even in those installations that do have more than one camera, it is extremely rare for the sleeping accommodation of a home to include camera coverage - due to understandable concerns about privacy.

There therefore exists a need to improve verification of security events or incidents reported by security monitoring systems.

Summary

According to a first aspect, there is provided a premises security monitoring system comprising a system control unit and at least one sensor node to detect security events, each sensor node including a first transceiver to receive control signals from, and to report security events to, the control unit, the control unit being configured to operate as an access point for a Wi-Fi network; at least one of the sensor nodes being powered by an autonomous power supply and including in addition to the first transceiver a Wi-Fi transceiver for communication with the control unit over the Wi-Fi network; wherein the control unit is further configured to respond to a report of a security event by: reporting the security event to a remote monitoring station; sending an instruction to the first transceiver of the autonomously powered node for the autonomously powered node to activate its Wi-Fi transceiver to transmit Wi-Fi signals that function as illumination signals in a Wi-Fi sensing function for a sensing area of the premises; activating the Wi-Fi sensing function for the sensing area; using Wi-Fi illumination signals transmitted by the autonomously powered node in the Wi-Fi sensing function to perform a determination of whether there is human presence in the sensing area; and transmitting the result of the determination to the remote monitoring station.

In this way the controller of the security monitoring system can implement a Wi-Fi sensing function even if there are no other Wi-Fi devices available to act as illuminators for the sensing area. And if there are other Wi-Fi devices to act as illuminators, this aspect enables the controller to enhance the available illumination - possibly to extend the sensing area or to improve the coverage of or resolution within the sensing area.

It should be understood that the precise order in which the control unit performs the various tasks is not important.

Optionally, the autonomously powered node comprises a video camera having an associated motion sensor.

Optionally the autonomous power supply of the sensor node(s) is a battery power supply.

Optionally, the Wi-Fi transceiver of the autonomously powered node is only activated upon instruction from the control unit. In this way the power of the autonomous power supply is not wasted.

Optionally, the autonomously powered node has an operating mode in which its Wi-Fi transceiver is only activated upon instruction from the control unit. The node may for example have another operating mode in which activation of a sensor, such as a motion or presence detector (e.g. a PIR detector or a thermal MOS “TMOS” sensor), automatically activates, the WiFi transceiver - for example so that a camera of the autonomously powered node can supply images/video automatically upon the motion/presence sensor of the node being activated. This may be of interest to the premises owner/occupants so that they can “keep an eye on” the premises while they are away even if no other sensor has been triggered (and thus potentially in the absence of a potential security event).

Optionally, when human presence is detected, transmitting the result of the determination includes transmitting a location of the detected human presence. If the Wi-Fi presence sensing is able to provide a location of an assumed intruder, this can enable personnel of the remote monitoring station to make better-informed decisions, and also enable them to provide relevant advice to the police or other security personnel (and optionally to the owner/occupier of the premises, e.g. via messages pushed from the monitoring station).

Optionally, the first transceiver uses single-sideband modulation, Bluetooth low energy, Matter, or a channel in a dedicated ISM band. These techniques all avoid the use of communication protocols according to any of the IEEE 802.11 standards, and in this way the power consumption of the autonomously powered node can be reduced, thereby facilitating a desirably long lifetime for the autonomous power supply.

Optionally in a premises security monitoring system as claimed in any one of the preceding claims, wherein the autonomously powered node is configured to power down the first transceiver after a predetermined time if it has not received an instruction to power down the transceiver down before that time. In this way the power of the autonomous power supply can be preserved.

According to a second aspect there is provided a method of processing a security event reported by a sensor node of a premises security monitoring system, performed by a control unit of the security monitoring system, the method comprising: receiving at the control unit a report of a security event; reporting the security event to a remote monitoring station; sending an instruction to a first transceiver of an autonomously powered node for the autonomously powered node to activate its Wi-Fi transceiver to transmit Wi-Fi signals; activating a Wi-Fi sensing function for a sensing area of the premises, the Wi-Fi sensing function using Wi-Fi signals transmitted by the autonomously powered node; performing a determination, using the Wi-Fi sensing function, of whether there is human presence in the sensing area; and transmitting the result of the determination to the remote monitoring station.

In this way the controller of the security monitoring system can implement a Wi-Fi sensing function even if there are no other Wi-Fi devices available to act as illuminators for the sensing area. And if there are other Wi-Fi devices to act as illuminators, this aspect enables the controller to enhance the available illumination - possibly to extend the sensing area or to improve the coverage of or resolution within the sensing area.

It should be understood that the precise order in which the steps of the method are performed is not critical. Steps may be performed simultaneously or in a different order and yet still provide the benefits of the invention.

In the method of the second aspect the result of the determination includes, in the event that human presence is detected, a location of the detected human presence. If the Wi-Fi presence sensing is able to provide a location of an assumed intruder, this can enable personnel of the remote monitoring station to make better-informed decisions, and also enable them to provide relevant advice to the police or other security personnel (and optionally to the owner/occupier of the premises, e.g. via messages pushed from the monitoring station).

Optionally, the report of the security event is received from a sensor node other than the autonomously powered node. In this way, even though an event is detected by the triggering of a sensor other than for example a motion sensor of a camera, the control unit lis able both to activate the camera and the associated Wi-Fi transceiver so that both images and Wi-Fi sensing data may be provided to the remote monitoring station.

Optionally, the report of the security event may be received from the autonomously powered node.

The method of the second aspect may further comprise sending an instruction to the autonomously powered node to power down its Wi-Fi transceiver. In this way, the control unit is able to minimise unnecessary use of power from the autonomous power supply.

Optionally the method of the second aspect may further comprise transmitting to the remote monitoring station images or video captured by the autonomously powered node.

In a third aspect there is provided a control unit for a premises security monitoring system, the security monitoring system including at least one sensor node to detect security events, the control unit including: a first transceiver to transmit control signals to, and to receive reports of security events from, the at least one sensor node; a Wi-Fi transceiver to receive data transmissions from at least one of the sensor nodes; and the control unit being configured to operate as an access point for a Wi-Fi network using the Wi-Fi transceiver, wherein the control unit is further configured to respond to a report of a security event by: reporting the security event to a remote monitoring station; sending an instruction for a sensor node to activate its WiFi transceiver to transmit Wi-Fi signals that function as illumination signals in a Wi-Fi sensing function for a sensing area of the premises; activating the Wi-Fi sensing function for the sensing area; using Wi-Fi illumination signals transmitted by the activated Wi-Fi transceiver of the node in the Wi-Fi sensing function to perform a determination of whether there is human presence in the sensing area; and transmitting the result of the determination to the remote monitoring station.

The control unit according to the third aspect may further comprise a controller that is configured to use the first transceiver to send a status update message to the sensor node on the arming and disarming of the security monitoring system. Optionally the controller is configured, in the event of receiving video sent by the sensor node other than in consequence of an instruction from the control unit, to forward the received video to a remote server rather than to the remote monitoring station. Optionally the first transceiver of the control unit according to the third aspect may use single-sideband modulation to receive reports of security events from, the at least one sensor node - and optionally also to transmit control messages to the at least one sensor node. 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 a schematic plan of a dwelling in which a first security monitoring system has been installed;

Figure 2 illustrates schematically the principles of radio-based presence and location sensing; Figure 3 is a schematic timing diagram illustrating a method according to an aspect of the invention; and

Figure 4 illustrates schematically features of a local management device of the system of Figure 1.

Specific description

Figure 1 shows schematically a plan of a dwelling in which a security monitoring system 100 has been installed. In this example, the dwelling is in the form of a one-bedroom apartment with an internal floor area of, for example, 50 to 80 square metres. The dwelling has a front door 102, a rear door 104 that leads out onto a balcony 106, and a rear window 108. Each of the doors and windows includes a sensor node 110 to detect whether the door or window is open or closed, each sensor node 110 for example being based on the combination of a magnet and a magnetic contact or magnetometer. Optionally, the rear door 104 is a glazed door, and both the rear door 104 and the window 108 are preferably also provided with a sensor node 112 to detect shocks - such as might be experienced during a break-in attempt, using either a combination of one or more magnets and a magnetometer, or using an accelerometer. Each sensor node 110, 112 includes a first transceiver to receive control signals from, and to report security incidents to, a control unit 114. The control unit 114, includes a first transceiver to transmit control signals to, and to receive reports of security incidents from, the first transceiver of the sensor nodes 110, 112. In addition, the control unit 114 includes a Wi-Fi transceiver and is configured to operate as an access point for a Wi-Fi network using its Wi-Fi transceiver.

In a domestic installation 100, the central unit 114 typically has knowledge of all nodes comprised in the installation 100. Each node may have a unique node identifier or serial number that is used to identify the node. Each node may have different functionalities associated with it, such as e.g. video capabilities, motion detection, still imaging, audio recording, communication speeds etc. Some or all capabilities may be communicated from the node to the central unit during a login procedure during setup of the installation 100. Alternatively and/or additionally, some or all capabilities may be communicated to the central unit from the node upon request from the central unit 114. Alternatively and/or additionally, some or all capabilities may be retrieved, by the central unit 114, from a remote monitoring station 120.

The sensor node(s) for the usual point of entrance to the premises is/are typically treated rather differently from sensor nodes of other points of entry so that the security monitoring system differentiates between “normal” entrance and “unusual” entrance. Entrance at the usual point of entrance, which in this case is the front door 102 is detected by the front door node 110, and when this is triggered, it does not initially give rise to an alarm event in the same way that the triggering of the corresponding nodes 110 of the rear door 104 and rear window 108. Rather, the control unit 114 of the security monitoring system starts a disarm timer of between 30 seconds and one minute within which the system can be disarmed by entering a code or presenting a dongle or token at a disarm node or control panel 118. Only if there is a failure to input an appropriate code or present an authorised dongle or token within the disarm period is an alarm event determined. The sensor node(s) for the usual point of entrance to the premises may include a magnetically activated sensor as described above, and/or a movement or presence sensor such as a PIR sensor or a thermal MOS “TMOS” sensor, or another type of sensor.

There are generally two categories of nodes, and these may be termed wakeup nodes and non-wakeup nodes. The non-wakeup nodes are nodes with which communication can be initiated only by the node itself, and not by the central unit. Examples of non-wakeup nodes are e.g. switches such as magnetically controlled contacts used on doors and windows, e.g. sensors 110 of Figure 1. Should the central unit 114 need to communicate with a non-wakeup node, the central unit 114 has to wait until it receives a message from the non-wakeup node and acknowledge that message with a message saying that the central unit 114 has additional message(s) to send to the non-wakeup node. This design of the communication protocol enables non-wakeup nodes to stay in a sleep or hibernation state for extended periods of time. Consequently, they only have to wake up on e.g. external events that are communicated to the central unit 114 or the expiry of an internal wakeup-timer that requires a periodic communication with the central unit 114. The internal wakeup-timer may be configurable and is typically in the range of 5-60 minutes. The communication protocol allows for extended battery life (e.g. at least 5 years from a single small battery cell) of non-wakeup nodes.

Conversely, wakeup nodes are nodes that can be woken from a monitoring state (in which their power consumption is less than in a fully awake state) to a fully awake state by the central unit 114, so that the central unit 114 can initiate communication with wakeup nodes (albeit that this requires the wake up node to enter a partially awake state - the monitoring state - in order to be able to detect the presence of a message from the central unit. Examples of wakeup nodes, i.e. nodes that can be triggered from the central unit 114 include e.g. camera-PIRs (or camera TMOS), nodes with video functionality, nodes with audio functionality, etc.. The wakeup nodes have to wake up (that is move from a sleep state and enter a (low power consumption) monitoring state) periodically to determine if the central unit 114 needs to communicate with them. Because a central unit generally only needs to communicate with a wakeup node rather infrequently, the battery life of wakeup nodes is largely dependent on how often they have to listen for communications from the control unit 114 and for how long the wakeup nodes have to stay awake before they can determine that there is no communication for them.

The design of wake-up units of embodiments of the invention may conveniently be in accordance with the teachings of W02020/039044, in particular as described in conjunction with Figures 5 to 10 of the patent application - the content of which is hereby incorporated by reference.

The security monitoring system 100 of Figure 1 further comprises an additional sensor node 116 which is a wakeup node that includes a first transceiver to receive control signals from, and to report security incidents to, the control unit 114. The first transceiver is preferably a wakeup transceiver configured to have very low energy consumption and hence is configured to use a protocol, other than one according to any of the IEEE 802.11 standards, and preferably one using single-sideband channel communication, optionally one operating on an ISM band such as the European 863MHz to 870MHz frequency band (e.g. around 868MHz). The first transceiver may for example use a protocol such as BLE, Matter, or another low energy protocol that uses an ISM channel. The additional sensor node 116 additionally includes a Wi-Fi transceiver to transmit data such as images or video to the control unit 116. The additional sensor unit 116 is preferably an image source, such as a camera or video camera, with an integrated or associated motion sensor, that is capable of capturing still or moving images of the interior of the dwelling. We use Wi-Fi, rather than our low power channel, for transmitting video, because low power typically also means lower bandwidth - and hence if one wants to send (or even stream) high resolution images or video in a timely fashion (such as to a remote monitoring station where the images are needed so that decisions about intervention can be made in a timely manner) one needs to use a much higher bandwidth channel. The security monitoring system 100 further comprises a control panel or user interface, 118, that is typically mounted within the apartment close to the front door, and by means of which the security monitoring system can be armed or disarmed. The control panel 118 typically includes a display panel, optionally a touch sensitive display, and at least one microphone and loudspeaker by means of which a user may interact with personnel (or automated systems) in a remote monitoring centre 120. The additional sensor node 116, like the other sensor nodes, has an autonomous power supply, such as a battery power supply, and is not connected to mains electricity. In order to ensure a long enough battery life (typically at least three years, but preferably longer), the first transceiver of the sensor nodes is engineered for very low energy consumption, optionally using single-sideband modulation channels as these typically use lower power per bit, and may use wake on radio technology, for example in accordance with the teachings of W02020/039044 incorporated above.

Unfortunately, Wi-Fi transceivers tend to be very power hungry - so that it is not possible to achieve an acceptably long battery life with a battery powered sensor if its Wi-Fi transceiver is used anything other than sporadically. Because of this, the additional sensor node 116 may be configured only to activate its Wi-Fi transceiver on command from the control unit (using a low power radio signal received by the additional sensor node’s first transceiver, e.g. using BLE, Matter, or a channel in an ISM band - optionally using a sideband channel). Assuming that the additional sensor node 116 is a video camera, the control unit may be configured only to instruct the use of the node’s Wi-Fi transceiver when the security monitoring system is armed (typically only in an armed away state) and the control unit 114 has received a report of a security incident (either reported by the motion sensor of the additional sensor node 116 or some other sensor). In response to a command from the control unit 114, the additional sensor node 116 will use its Wi-Fi transceiver to transmit images/video to the control unit 114 which in turn transmits them to the remote monitoring station 120 using a wired data network 122 or using radio. At the remote monitoring station 120 human agents 124 review the information supplied by the control unit 114, including any information received from the various sensor nodes 110, 112, together with images/video from the additional sensor node 116, and any sound files from any microphones (such as one installed in the control panel 118).

Alternatively, the additional sensor node 116 may include a Wi-Fi camera and a motion sensor and be configured to have three operating modes: a first in which the camera and the motion sensor are disabled (turned off); another in which the camera and Wi-Fi are both turned on; and a third in which the motion sensor is active, the node being configured to activate the camera and Wi-Fi upon triggering of the motion sensor. In the second or third modes, the Wi-Fi camera node may be configured to transmit any captured images/video to a remote server via the control unit 114 which acts as a Wi-Fi access point. In this way, captured images/video may be accessed by or pushed to a device of an owner/occupier of the premises. The central unit 114 may be configured to send a signal to the Wi-Fi camera node (116) informing it of the status of the security monitoring system - that is, whether it is armed (armed away) or disarmed. The Wi- Fi camera node may be configured to switch automatically into its third mode of operation on receiving a message from the central unit that the security monitoring system has been armed.

The Wi-Fi network of which the control unit 114 serves as Access Point (AP) may be considered to provide network coverage within at least the zone 130 marked by the dashed and dotted line. The presence of this Wi-Fi network means that, with the provision of a suitable extra source of Wi-Fi signals, a Wi-Fi sensing function may be provided to enable a determination to be made whether there is human presence in a sensing area of the premises. For example, by using the Wi-Fi transceiver of the additional sensor node 116 to transmit Wi-Fi signals that function as illumination signals in the Wi-Fi sensing function, human presence may be detected anywhere within the sensing area indicated by the dashed line 132.

The control unit 114 may be configured to respond to a report of a security incident, for example following the triggering of one of the sensor nodes 110 or 112 (or even sensor node 116), by reporting the security incident to the remote monitoring station 120, sending an instruction for the additional sensor node 116 to activate its Wi-Fi transceiver to transmit Wi-Fi signals that function as illumination signals in a Wi-Fi sensing function for the sensing area 132. By activating the Wi-Fi sensing function for the sensing area 132 the control unit 114 can use Wi-Fi illumination signals transmitted by the activated Wi-Fi transceiver of the additional sensor node 116 in the Wi-Fi sensing function to perform a determination of whether there is human presence in the sensing area 132. The control unit 114 can then transmit the result of the determination to the remote monitoring station 120. The control unit 114 therefore constitutes an embodiment of the third aspect of the invention.

The installation of Figure 1 also provides a premises security monitoring system according to the first aspect of the invention, and the controller of the security monitoring system can implement a Wi-Fi sensing function even if there are no other Wi-Fi devices available to act as illuminators for the sensing area. And if there are other Wi-Fi devices to act as illuminators, this aspect enables the controller to enhance the available illumination - possibly to extend the sensing area or to improve the coverage of the sensing area.

The described installation also enables a method according to the second aspect of the invention.

Before going into details of the operation of the security monitoring system using radiobased presence detection, we will provide here a brief introduction to radio-based presence detection, which may for example be based on analysing the signal dynamics and signal statistics of radio signals and/or detecting changes in channel state information (CSI). A radio (or wireless) signal as used herein refers to a signal transmitted from a radio transmitter and received by a radio receiver, wherein the radio transmitter and radio receiver operate according to a standard or protocol. Such standards include, but are not limited to, IEEE 802.11. (which includes the Wi-Fi standards), IEEE 802.15 (which includes Zigbee), Bluetooth SIG, IEEE 802.16, IEEE 802.20, UMTS, GSM 850, GSM 900, GSM 180, GSM 19011, GPM ITU-R 5.13, GPM ITU-R 5.150, ITU-R 5.280, 3GPP 4G (including LTE), 3GPP 5G, 3GPP NR, AND IMT- 2000. However, the radio transmitters and receivers may operate in non-telecommunications or Industrial, Scientific and Medical (ISM) spectral regions without departing from the scope of the invention.

Essentially the idea is to use radio signals to probe a zone or zones of interest, and to analyse and extract statistics from these signals, in particular looking at the physical layer and/or data link layer such as MAC address measurements that expose the frequency response of a radio channel (e.g., CSI or RSSI measurements). These measurements are processed to detect anomalies and variations over time, and in particular to detect changes signifying the entrance of a person and/or movement of a person within a monitored zone. The zone(s) to be monitored need to be covered sufficiently by radio signals, but the sources of the radio signals may either already be present before a monitoring system is established - for example from the plurality of Wi-Fi or Bluetooth capable devices that are now dotted around the typical home or office, or the sources may be added specifically to establish a monitoring system. Often some established (i.e., already located or installed) radio devices are supplemented by some extra devices added as part of establishing a radio-based presence detection system. Among the types of devices (preinstalled or specifically added) that may be used as part of such a detection system are Wi-Fi access points, Wi-Fi routers, smart speakers, Wi-Fi repeaters, as well as video cameras and video doorbells, smart bulbs, etc. Because presence (or intrusion) is detected by detecting a change in the properties or character of radio signals compared to some previous reference signal(s), it is preferred to establish what might be termed the monitoring network between radio devices that are essentially static (i.e., that remain in the same position for extended periods) rather than relying on devices that are repeatedly moved - such as smart phones, headphones, laptops, and tablet devices. It is not strictly speaking essential for all the devices whose signals are used by the monitoring system to be part of the same network - for example, signals from Wi-Fi access points of neighbouring premises could be used as part of a monitoring system in different premises. Again, a primary consideration is the stability of the signals from the signal sources that are used. Wi-Fi access points provided by broadband routers are seldom moved and rarely turned off, consequently they can generally be relied upon as a stable signal source - even if they are in properties neighbouring the property containing the zone or zones to be monitored.

The idea is illustrated very schematically in Figure 2, here with an installation 200 including just a single source (or illuminator) 202 and just a single receiver 204, for simplicity, although in practice there will commonly be multiple sources (illuminators) and sometimes plural receivers. The installation 200 has been established to monitor a monitored zone 206. In Figure 2A we see that in steady state, and in the absence of a person, radio signals are transmitted from the source 202, spread through the monitored zone 206, and are received by the receiver 204. Of course, in most installations there will be walls, ceilings, floors, and other structures that will tend to reflect, at least in part, signals from the source. Furniture and other objects may block and attenuate the signals, the reflected signals will give rise to multiple paths, and the signals may interfere with each other, and there may be scattering and other behaviours, such as phase shifts, frequency shifts, all leading to complexity in the channels experienced by the radio signals that arrive at the receiver 204. But while the environment is static and unchanging, the receiver will tend to see a consistent pattern of radio signals. And this is true whether or not the source transmits continuously or transmits periodically. But this consistent pattern of received signals is changed by the arrival of an intruder 208, as shown in Figure 2B. From Figure 2B we see that, at the very least, the presence of a person in the monitored zone blocks at least some of the signals from the source, and that affects the pattern of radio signals received by the receiver 204. The changed pattern of signals received by the receiver enables the presence of the intruder to be detected by a presence monitoring algorithm that is supplied with information derived from the received signals. It will be appreciated that the nature and extent of the perturbation of the signals passing from the source 202 to the receiver 204 is likely to change as the intruder 208 enters, passes through, and leaves the monitored area 206, and that this applies also to reflected, refracted, and attenuated signals. These changes may enable the location of a person within the zone, and their speed of movement, to be determined.

It will be realised that signals that are received from an illuminator device (or from more than one illuminator device) after having passed through a monitored space (or volume), have in effect been filtered by the environment to which they have been exposed. We can therefore imagine the monitored volume as a filter having a transfer coefficient, and we can see that a received signal is at least in part defined by the properties, or channel response, of the wireless channel through which it is propagated. If the environment provided by the monitored volume changes, for example by the addition of a person, then the transfer coefficient of the filter, and the channel response or properties, will also change. The changes in the transfer coefficient, and that in the channel response, consequent on the change in the environment of the monitored space, can be detected and quantified by analysing radio signals received by the wireless sensing receiver(s). Both the introduction of an object, e.g., a person, into the monitored space and movement of that object within the monitored space will change the environment and hence change the effective transfer coefficient and the channel response. The radio-based sensing system may be trained by establishing a base setting in which the monitored zone is unoccupied, which is then labelled as unoccupied for example using a smartphone app or the like, and then training occupied states by a person entering, standing, and then walking through each of the zones one by one. Presence at different locations in each of the zones may be captured and labelled in the system in the same way. This process may be repeated with two people, and then optionally with more people. In essence this is a supervised machine learning approach, but other approaches to training may be used. Alternatively, the radio-based sensing system may store a limited rolling view of the radio environment and look for identifiable variations in that view. In effect this involves the assumption that in the absence of presence, there should be minimal deviation in the environment. The presence of object should cause a deviation to the “baseline”. If someone walks into a room they’ll be detected. If they stand there and don’t move, they’ll eventually become part of the background and they’ll no longer be seen as “present”, but as soon as they move, they’ll be picked up again.

The system may need to be retrained for the base setting if bulky furniture (or if a large metal object) is added to or moved within the monitored space, because these can be expected to change the propagation properties of the relevant zone/space. The data for unoccupied states is preferably retained within a database of “unoccupied” states, even when there are changes to the arrangement of furniture etc. It may not be necessary to retrain for the occupied states, if the system can determine a delta function between the previous base state and the new one, because the delta function may also be applicable in occupied states. But if not, it may be sufficient to retrain only a subset of the occupied states previously learnt. The system may also be configured to self-learn to accommodate changes in the characteristics of the zones when unoccupied, and to add newly determined unoccupied state data to the database.

Although the Figure 2 example uses just a single source (illuminator) and a single receiver, which corresponds to the arrangement shown in Figure 1, as already mentioned often multiple sources (illuminators) will be used in order to achieve satisfactory coverage of the zone or zones to be monitored. Multiple zones may be monitored by a single receiver through the use of multiple strategically placed sources, but each zone, or some zones of multiples zones may have a dedicate receiver that does not serve other zones. Likewise, a radio signal source (illuminator) may provide illuminating signals for a single monitored zone or for multiple monitored zones. Also, a presence monitoring system (and a security monitoring system including such a presence monitoring system) may use mesh network arrangement, for example a Wi-Fi mesh network, in which multiple devices act as receivers for illuminating signals - either for a single monitored zone or for multiple monitored zones. The radio-based presence sensing, which may conveniently be based, as here, on the monitoring of Wi-Fi signals, and which for convenience we will refer to as WFS, is here performed by the central unit 114 which operates as a Wi-Fi Access Point (AP) and which serves as a Wi-Fi sensing receiver.

Consider now Figure 3 which is a timeline that illustrates a method 300 of processing a security event according to an aspect of the invention. The security monitoring system is in an armed away state - meaning that the apartment is meant to be unoccupied. At 302 one of the event sensors 110 (other than that for the main entrance, here front door 102), 112 reports a security event to the control unit 114 using its first transceiver. In response to receiving the report the central unit 114 sends 304 an instruction to the additional sensor node 116, to be received by that node’s first transceiver, to cause the node 116 to activate 308 its Wi-Fi transceiver, and also reports 306 the incident to the remote monitoring station 120. The incident report will typically include the identity of the sensor node making the report, together with any incident data, and an event time. If other security events are reported by the same or another event sensor - for example a shock sensor reporting repeated shocks, or an anti-tamper on an event sensor or another device (such as the control panel 118) reporting repeated events, these will also be reported by the control unit 114 to remote monitoring station 120, again with an event time, sensor node ID, and all the reported event data.

The central unit 114 also activates 310 the Wi-Fi sensing function - and this may happen before, after, or simultaneously with the sending of the instruction to the node 116 to activate its Wi-Fi transceiver. The control unit 114 then uses the Wi-Fi illumination signals transmitted by the node 116 in the Wi-Fi sensing function to determine 312 whether there is human presence in the sensing area 132 and transmits 314 the result of the determination to the remote monitoring station. The determination preferably includes both presence information and a motion score that indicates the degree of any detected motion.

If the presence information shows that there is human presence, the remote monitoring station 120 may send a trigger command 316 to the central unit 114 to cause the central unit 114 to activate 318 a siren and/or to instruct 320 a video camera, such as Wi-Fi device 116 to send 322 images or video files, or to stream video, which the control unit 114 then sends 324 on to the remote monitoring station 120. The remote monitoring station may also, in the event that a positive presence indication is received, send 326 a report of the detected intrusion to the local police or to private security personnel. The remote monitoring station may also instruct 328 the control unit 114 to activate 330 an intervention device, such as a smoke generator 128 (or a very loud siren or klaxon) if not already activated at 318, to drive the intruder from the premises. The monitoring station 120 may have no information about the layout of the premises - only being concerned with determining whether or not an assumed intruder is or is not still on the premises. However, the various sensors of the system may be named so that there is an indication as to the location (kitchen, hall, etc.) of the sensor that triggered an alarm. But it is also possible for Wi-Fi sensing, particularly if it uses multiple illuminators, to “locate” a human presence within a monitored zone - and in such a case it is useful for the monitoring station to be aware of the layout of the monitored premises (and hence the remote monitoring station may store details of the layouts of premises protected by security monitoring installations, the details being made available to operatives of the monitoring station when incident reports come in).

At the remote monitoring station 120 a human operator, or an automated system, uses the presence information and optional motion score to verify whether the reported security incident is a “real” incident (because the presence information/motion score indicate that there is a human presence), or a false alarm (because the presence information/motion score indicate that there is no human presence). This means that verification of incidents can be done more quickly than may happen for comparable installations that do not use wireless sensing. For example, if an intruder enters through the bedroom window 108, they can ransack the bedroom - where typically most people store their valuables such as jewellery, passports, etc., and also the storage area, while remaining out of sight of the video camera 116.

The sensor node 116 that was instructed by the control unit 114 to turn on its Wi-Fi transceiver may be configured to power down the transceiver after a predetermined time (e.g. one or two minutes, or more) if it has not received an instruction 332 to power the transceiver down before that.

The use of security monitoring systems that provide presence information and optional motion scores can also mean that remote monitoring stations can be configured to prioritize incident reports for which presence information and optional motion scores show that there is human presence. Thus, a signal sent to the remote monitoring station, based on the triggering of one of the sensor nodes 110, 112, can be prioritised based on Wi-Fi sensing information. The existence of a “presence” or “no presence” signal allows false positive classifications when no human presence is detected (for example when a motion sensor has been triggered by a pet, moving branches or leaves of a plant, or even a spider moving across the motion sensor), and will therefore reduce the cost and procedural burden that would otherwise arise through the deployment of police or security personnel. In the case of confirmed events, the provision of the “presence” or “no presence” signal may enable quicker intervention - for example the activation of an intervention device such as the smoke generator 128 or a siren, and enabling valuable information (human presence detected, and the location of the human presence - intruder still there, etc) to be passed to the police, other security personnel, as well as to the owner(s)/occupier(s) of the premises (thereby enabling the owner/occupier to be warned against entering the premises because a believed intruder is still present).

All this may be achieved for small apartments or the like using just one Wi-Fi illuminator (such as sensor node (video camera) 116) working in conjunction with the control unit Access Point 114. Of course, as already mentioned, it may be helpful to use more than one illuminator device, and preferably any extra illuminator devices are also stations on the Wi-Fi network provided by the control unit Access Point 114. Smart plugs and the like are particular convenient for use as illuminator devices because they are small and discreet, simply plugging in to a convenient power outlet, but there are many other device types that can readily be accommodated even in small apartments to enhance the coverage of the Wi-Fi sensing system - e.g. smart speakers, smart TVs, etc.

Although the installation shown in Figure 1 includes only one Wi-Fi station, node 116, which functions as an illuminator in the Wi-Fi sensing function, in addition to the Wi-Fi access point 114, the use of more illuminators is attractive as this can be expected to improve the performance of the Wi-Fi sensing function. If additional Wi-Fi stations are used as illuminators, any that rely on autonomous power sources (e.g., relying on a battery power supply) are preferably turned on upon instruction from the central unit 114 following the arrival of a report of a security incident. Conveniently, however, additional Wi-Fi stations may be mains powered.

Figure 4 is a schematic drawing showing in more detail features of the gateway or central unit 114 of Figures 1. The gateway 114 includes a first transceiver 430 coupled to the first antenna 480, and optionally a second transceiver 432 coupled to a second antenna 482. The transceivers 430 and 432 can each both transmit and receive, but a transceiver cannot both transmit and receive at the same time. Thus, the transceivers 430, 432 each operate in half duplex. Preferably a 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 430, 432 may be arranged such that one transceiver 430 uses a first frequency for transmit and receive and the second transceiver 432 uses the same first frequency for transmit and receive, i.e. the transceivers are arranged to operate in a diversity-like arrangement. Alternative, the second transceiver may, depending on configuration, be arranged to use a second frequency for transmit and/or receive. The transceivers 430 and 432 are coupled to a controller 450 by a bus. The controller 450 is also connected to a network interface 460 by means of which the controller 450 may be provided with a wired connection to the Internet and hence to the remote monitoring centre 120. The controller 450 is also coupled to a memory 470 which may store data received from the various nodes of Y1 the installation for example event data, sounds, images and video data. The central unit 114 also includes a crystal oscillator 451, which is preferably a temperature controlled or oven-controlled crystal oscillator. This is used for system clocking and also frequency control of the transceivers. The gateway 114 includes a power supply 362 which is coupled to a domestic mains supply, from which the gateway 114 generally derives power, and a backup battery pack 464 which provides power to the gateway in the event of failure of the mains power supply. The central unit 114 also includes a Wi-Fi transceiver 440, and associated antenna arrangement 442, which may be used for communication with any of the nodes that are Wi-Fi enabled., such as node 116. The Wi-Fi enabled node may be a remote control or control panel that may for example be located close to the main entrance to the building (e.g., control panel 118) to enable the occupier to arm or disarm the system from near the main entrance, or it may for example be an image-capture device such as a video camera (e.g. camera 116). Similarly, an interface enabling bidirectional communication over a Public Land Mobile Network (PLMN), such as GSM or LTE, may optionally be provided. Optionally, a third antenna 484 and associated ISM transceiver 434 may be provided, for example for communication with the remote monitoring centre 120 over, for example, the European 863MHz to 870MHz frequency band. Optionally, the third transceiver 434 may be a Sigfox transceiver configured to use the Sigfox network to contact the central monitoring station especially if jamming of other radio channels is detected.

The first 430 and second 432 transceivers may both be tuneable ISM devices, operating for example in the European 863MHz to 870MHz frequency band or in the 915MHz band (which may span 902-928MHz or 915-928MHZ depending upon the country). In particular, both of these devices may be tuned, i.e. may be tuneable, to the frequencies within the regulatorily 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. Similar transceivers are preferably used as the first transceivers in the sensor nodes 110, 112, and 116. The first 430 and second 432 transceivers are both configured to use a protocol other than one according to any of the IEEE 802.11 standards, and preferably one using single-sideband channel communication, optionally one operating on an ISM band such as the European 863MHz to 870MHz frequency band or in the 915MHz band.

The controller 450 is configured to run a sensing application using a WFS software agent 800, which may be stored in memory 470. The WFS software agent 400 uses WFS radio APIs in the Wi-Fi transceiver 440 to interact with the Wi-Fi radio, the APIs enabling extraction of desired channel environment measurement information and provides the ability to assert any related controls to configure WFS features. This behaviour will be described in more detail shortly. The sensing application on the CU will report a presence state change when the appropriate thresholds are triggered, along with the address of the device whose received data triggered the algorithm. The WFS agent provides a monitoring system which enables the security monitoring system to detect presence and movement in a monitored space, without the necessity to use line of sight motion detectors.

As an alternative to incorporating the radio sensing application into the central unit, this functionality can be provided on a separate access point, e.g. a Wi-Fi access point, AP such as a router, of the premises, with the AP configured to report the result of presence detection to the central unit 114. In another example, a Wi-Fi range extender could instead be used as sensing master for its connected nodes, but would be configured to report to the central unit 114 which would be the overall master in terms of reporting the “alarm”.

A brief explanation will now be given of how WFS works, and how WFS can be integrated into a security monitoring system, and in particular how WFS can be integrated into a central unit of a security monitoring system.

Wi-Fi Sensing can be performed with any Wi-Fi device and can be used on any available communication path. Each communication path between two devices gives the chance to extract information about the surrounding environment. Wi-Fi sensing is based on an ability to estimate the wireless channel and hence the surrounding environment. Because Wi-Fi networks comprise many devices spread throughout a geographical area, they are well suited to exploiting these devices’ transmissions in effect to provide a radar system. Depending on the number of devices, the radar system may be monostatic, bistatic, or multistatic. In monostatic WFS, a single device measures its own transmitted Wi-Fi signals. In bistatic WFS, the receiver and transmitter are two different devices (for instance, an AP and a STA in infrastructure mode). In multistatic WFS, the received signals from multiple Wi-Fi transmitters are used to learn about a shared environment.

At least one Wi-Fi transmitter and one Wi-Fi receiver are required to perform WFS measurements, and these can be located in the same device (to create a kind of monostatic radar) or in different devices. The measurement is always performed by a Wi-Fi Sensing-enabled receiver on the Wi-Fi signal transmitted by a transmitter, and which may or may not originate from a Wi-Fi sensing-capable device. The device that transmits the signal that is used for measurements is called the “illuminator,” as its transmissions enable collection of information about the channel - that is, it illuminates the channel.

Different modes of Wi-Fi Sensing measurements are recognised - Passive, Triggered, Invoked, and Pushed, and these depend upon what triggers the illuminator device to transmit a Wi-Fi signal. Preferably the agent improves the usefulness of the standard beacon interval by using optimised timings. In passive mode, WFS relies on transmissions that are part of regular Wi-Fi communication. The Wi-Fi Sensing receiver(s) rely only on transmissions between itself and the illuminator device(s). Passive transmissions do not introduce overhead, but the Wi-Fi sensing device lacks control over the rate of transmissions, transmission characteristics (bandwidth, number of antennas, use of beamforming), or environmental measurements.

Triggered measurement happen when a Wi-Fi Sensing device is triggered to transmit a Wi-Fi packet for the purpose of WFS measurements, either in response to a received Wi-Fi packet or by the higher layers (for instance, in WFS software).

Invoked measurement involves utilizing a packet transmission that is in response to a packet received from the Wi-Fi Sensing receiver device.

In pushed mode, a transmission is initiated by the illuminator device for measurement. A pushed transmission can be either a unicast or a multicast/broadcast message.

Multicast/broadcast messages can be used for measurements by multiple WFS receivers simultaneously if the devices are not in power-save mode.

Triggered transmissions introduce overhead because additional over-the-air transmissions are required. Pushed transmissions introduce less overhead compared to invoked transmissions, because the exchange is unidirectional rather than bidirectional. Triggered transmissions allow for a system to control both the rate and occurrence of measurements.

A WFS network is made up of one or more WFS illuminators and one or more WFS receivers. A WFS system is made up of three main components and that are present in Wi-Fi Sensing illuminators and receivers: first is the Wi-Fi radio, which encompasses the radio technology specified in IEEE 802.11 standards, the interfaces and the APIs connecting the radio to the higher layers; second is the Wi-Fi Sensing software agent, consisting of a signal processing algorithm and interfaces, the agent interacting with the Wi-Fi environment, and turning radio measurement data into motion or context-aware information; and thirdly, an application layer operates on the Wi-Fi sensing output and forms the services or features which are ultimately presented to an end user - such as a security monitoring service provided by a security monitoring system that detects presence using WFS.

A WFS system can be built based on existing Wi-Fi standards, hardware, software and infrastructure.

The fundamental component required to enable Wi-Fi sensing on the radio is the interface to enable control and extraction of periodic channel or environmental measurement data. Regardless of device type, operating band or Wi-Fi generation, the core APIs to enable WiFi sensing are similar, as the required data and control are common. The WFS software Agent can reside on any Wi-Fi device; for example, in the infrastructure mode, the agent may reside on the AP, in which case channel measurements from all the STAs associated with the AP can be collected. The software agent may also be located on a STA. But in the security management system applications this would mean that the STA would either need to be the controller of the security management system (e.g. the CU), or would have to be reporting to the controller of the security management system (e.g. the CU). Generally, we therefore prefer to run the software agent on the CU, and given that the CU is conveniently also an access point, it makes sense for us to run the software agent on the CU acting as AP rather than merely as an STA.

The WFS software Agent uses the WFS radio APIs to interact with the Wi-Fi radio, the APIs enabling extraction of desired channel environment measurement information, and providing the ability to assert any related controls to configure WFS features.

The WFS Agent has two main subsystems: Configuration and Control; and a Sensing Algorithm. The Configuration and Control subsystem interact with the radio, using a standard set of APIs. The Configuration and Control subsystem performs tasks including sensing capability identification, pushed illumination coordination, and radio measurement configuration. The sensing algorithm subsystem includes intelligence needed to extract the desired features from the radio measurement data and may differ according to the desired sensing application.

The WFS software Agent is needed on any sensing receiver, but is merely optional on an illuminator - only being required if the illuminator also acts as a receiver. If included on an illuminator, only the configuration and control subsystem is needed. By having the agent on the illuminator, additional enhancements are enabled, including sensing capability identification and co-ordinated pushed illumination. If the illuminator is not running an agent, it is still technically able to participate in the sensing network, but only the most basic features that currently exist in Wi-Fi standards will be supported.

The WFS software Agent processes and analyses the channel measurement information and makes sensing decisions, such as detecting motion. This information is then shared with the application layer via the Wi-Fi Sensing agent I/O interface. As well as interfacing with the radio and the application layer, the Wi-Fi Sensing agent also interfaces with the existing Wi-Fi services on the system. This interface is necessary for the agent to provide feedback for sensing optimizations that can be used in radio resource management decisions, such as band steering or AP selection requests.

The application layer of a WFS system creates the sensing service and in effect presents the information to the end user (in our case to the security management system). The application layer can potentially reside on any networked device: in some embodiments of the present invention it will reside in the central unit 114 along with the WFS agent, but in other embodiments the application layer may exist in an external server or even in the central monitoring station. We prefer, however, to provide the application layer on the central unit to avoid potential problems with signalling delays (for example due to accidental or deliberate network interruption) between the central unit (or other WFS receiver) and a remotely located entity. The application layer receives input from one or multiple Wi-Fi sensing software agents. It combines the information and delivers it to the security management system which may then in turn provide it to the CMS and/or to a cloud service by means of which push notifications may be sent to a registered user device such as a smartphone - allowing users to receive real-time notifications and the ability to view historic data.

A typical Wi-Fi home network follows one of two common deployment scenarios. The first consists of a single AP that serves as the internet gateway for all the devices in the house. The second consists of multiple APs forming an ESS and extending coverage throughout the home. Depending on the use case, the Wi-Fi Sensing receiver may be the AP and/or other devices in the network. Not all the devices in a home deployment need to be Wi-Fi Sensing capable.

Wi-Fi Sensing can be deployed in all types of Wi-Fi networks and topologies, operating in different frequency bands (2.4, 5, 6, and 60 GHz) and different bandwidths. The sensing resolution and performance depends on the use case requirements. In general, it is enhanced with the increase in the number of participating devices and higher bandwidths. Applications that require lower resolutions and longer range, such as home monitoring, can be deployed using WiFi networks operating in 2.4GHz and 5GHz. Applications that require higher resolutions and lower range, such as gesture recognition, require 60GHz Wi-Fi networks.

In multi- AP and/or multi-band deployments, there may be an advantage to having a WiFi sensing device connected to a specific AP or operating in a specific frequency band. Radio resource management (RRM) events, such as AP and/or band steering, should be conducted in coordination with the Wi-Fi Sensing agent/operation.

The devices involved with Wi-Fi Sensing will depend upon the deployment environment and the specific use case. The sensing measurements also need to be processed by the device with enough computation power. The coordination of sensing, including participating devices, is a role particularly suited to an AP. Typically the central unit of a security monitoring system will have ample processing power, as well as being able to function as an AP, to handle this task efficiently and speedily. The nature of Wi-Fi networks is such that it should be possible able to add additional WiFi sensing capable devices to the network to enhance accuracy, coverage and/or localization. These additional devices do not necessarily need to be Wi-Fi Sensing capable or dedicated Wi-Fi sensing devices to participate; however, optionally they may also identify their Wi-Fi sensing capabilities and supported features to the AP. Internet of Things (loT) devices for home deployment can typically also be used as part of a WFS installation supporting a WFS-enabled security monitoring system: example include Wi-Fi controllable plugs and sockets, light bulbs, thermostats, smart speakers, and video door bells. However, even when a device connects to the AP and reports that it is Wi-Fi sensing capable, the Wi-Fi Sensing agent may elect not to make use of that device.

WFS for a security monitoring system may be run over a dedicated Wi-Fi network, the premises having at least one other Wi-Fi network for other purposes. But for reasons of simplicity and economy it may often be preferred to operate a single Wi-Fi network to serve all a household’s (or small business’s) needs including WFS for a security monitoring service. If a single-network solution is adopted, performance degradation due to airtime usage and sensing overhead must be minimized and hence Wi-Fi transactions required for conducting sensing measurements and sensing management and processing must be optimized for efficiency.

For each Wi-Fi Sensing application, at least one network device executes the sensing software, or Wi-Fi Sensing Agent. The Wi-Fi Sensing agent is typically placed on the AP, but it can be placed on any STA (although, as previously mentioned, we prefer to run the Wi-Fi Sensing agent on the AP). Following authentication and association of a device with the Wi-Fi network, the Wi-Fi Sensing agent should discover the device and its sensing capabilities. Depending on the capabilities of the device, its role in the Wi-Fi sensing network would be determined. If the new device is another Wi-Fi Sensing-capable AP, then coordination among the agents is required.

The WFS agent needs to have a mechanism to determine which devices are capable and needs to participate in the sensing for each application on a device-specific basis.

A WFS agent also needs to be capable of configuring the radio for measurements and triggering transmissions on a periodic basis for sensing measurements, and to enable/disable measurements or adjust configuration parameters for Wi-Fi sensing-capable devices. Optionally, the Wi-Fi Sensing agent is also able to request specific radio resource management operations, such as AP or band steering. The WFS agent is also preferably able to detect and process specific sensing events and communicate the relevant information to the application layer (e.g., the security monitoring system) for specific handling and user presentation. One of the parameters that impacts the quality of the received signal in a wireless network is the amount of interference present. Interference can be caused by other Wi-Fi devices operating in the same band, which causes cochannel interference, or in an adjacent channel, which causes adjacent channel interference. It can also be caused by non-W-Fi devices, which can be other communication systems or unintentional transmissions that create electromagnetic noise in the band. Interference can impact Wi-Fi Sensing performance in two ways. Firstly, it may interfere with the sensing transmissions and thereby reduce the number of measurements made in a given time interval. As such, it introduces jitter in time instants during which the measurements are made. Secondly channel-state measurements may capture the impact of transient interference, such as for a non-Wi-Fi device, as opposed to motion in the environment.

Wireless systems deploy various techniques to avoid or reduce the impact of interference, and these techniques also help to improve WFS performance. These techniques aim at maximizing the reuse of spectrum, while minimizing the overlap of spectrum used by nearby networks: for example, Dynamic Channel Allocation (DCA); Auto Channel Selection (ACS); optimized RF planning; (e.g., non-overlapping channels and use of reduced channel width when applicable), and power control.

As already mentioned, increasing the number of illuminators may result in a higher sensing performance: with more transmitters that are located sufficiently apart from one another, motion in a larger area can be detected; when motion is detected using transmissions on one or more transmitters, information is provided that can be used to determine localization of the motion; and sensing accuracy is improved with a higher number of measurements taken across a larger number of transmitters in most scenarios.

The IEEE 802.11a preamble is useful for Wi-Fi Sensing. The preamble contains a short training field (STF), a guard interval and a long training field (LTF). The STF is used for signal detection, automatic gain control (AGC), coarse frequency adjustment and timing synchronization. The LTF is used for fine frequency adjustment and channel estimation. Since only 52 subcarriers are present, the channel estimation will consist of 52 frequency points. Newer OFDM PHY versions (HT/VHT/HE) maintain the IEEE 802.11a preamble for backward compatibility and refer to it as the legacy preamble. The legacy preamble spans a 20MHz bandwidth and consists of a legacy STF (L-STF) and legacy LTF (L-LTF). As more recently defined OFDM PHY versions (HT/VHT/HE) introduce wider channel bandwidths (up to 160MHz) for backward compatibility, the legacy preamble is duplicated on each 20MHz channel. This allows the receiver to compute 52, 104, 208 or 416 valid L-LTF frequency points, which represent the channel estimation between the two devices. Also potentially useful for Wi-Fi Sensing are the MIMO training fields present in HT, VHT and HE LTFs. The MIMO fields are modulated using the full bandwidth (20MHz to 160MHz) and are traditionally used by the receiver to estimate the mapping between the constellation outputs and the receive chains. Since these fields span the full bandwidth, they provide more frequency points. For example, a 20MHz E-ETF contains 52 subcarriers, while a 20MHz HT/VHT-ETF contains 56 subcarriers. The latest introduction of the HE PHY has the potential to enhance WiFi Sensing. In addition to enabling operation in the 6GHz spectrum, the HE PHY has increased the number of subcarriers per 20MHz bandwidth by 4x, which effectively allows for better object resolution.

The IEEE 802.1 lad amendment defines a Directional-Multi-Gigabit (DMG) PHY for operation in the 60GHz band. While there are three different modulation schemes (Control, Single-Carrier and OFDM) defined, Control and the Single Carrier PHY are the primary PHY used in 802. Had (and is also part of the subsequent 802.11ay amendment). Regardless of the modulation scheme, every packet starts with a preamble that consists of a short training field (STF) and a channel estimation field (CEF). The STF is used for timing estimation and AGC adjustment. CEF is used for channel estimation. Similar to the OFDM -based PHYs, the necessary channel estimation for Wi-Fi Sensing is available following successful reception and processing of the preamble of a packet and can be provided to the higher layers. The wide channel bandwidth available in 802.11ad/ay can significantly improve the performance of Wi-Fi Sensing in terms of the resolution; however, the limited communication range in 60GHz band restricts the sensing range and coverage. As such, in many situations the central unit of a security monitoring system may relay instead on frequency bands with longer range, sufficient to cover the majority of households. However, for smaller-scale installations the use of the 60GHz band may be attractive and therefore embodiments of the invention may use this band for WFS.

When it comes to identifying peer devices in a WFS installation, the MAC layer mechanisms may be used to obtain information about the connected devices and the roles they play in Wi-Fi sensing. The MAC layer also initiates and drives transmissions required for channel estimation among the devices in the Wi-Fi Sensing network.

Various aspects of peer identification arise with Wi-Fi Sensing. The first is identifying the devices and the channel estimation mapped to the physical environment between any two devices. Typically, an STA is identified by a 48-bit MAC address. A MAC address is sufficient identification for STAs associated with a Wi-Fi network; however, if the association is lost during the lifetime of the application, then randomized MAC addresses may be used. In this case, a different or more involved mechanism would be required to identify each STA. This identification must match the corresponding channel estimate measurement obtained from the PHY. The second is identifying the device network role and its connection type, such as whether it is an AP or an STA, or whether it is part of a mesh or a P2P connection. This information is used by the Wi-Fi Sensing agent to decide the best method for conducting measurements.

The third aspect is the identification of WFS device capabilities, such as sensing capabilities, supported measurement rate, and the availability and willingness of the device to participate in sensing measurements. This information is required from all devices in the network for the Wi-Fi Sensing agent to select devices participating in the sensing measurements.

As already noted, there are different types of transmissions that can be used for illumination of the Wi-Fi channel and obtaining measurements between two devices. Passive transmissions rely on existing Wi-Fi traffic and do not introduce any new MAC layer requirements. Triggered transmissions, however, rely on additional transmissions. Depending on whether existing packet exchange procedures are used for triggered transmissions or new exchanges are defined, the requirements on the MAC layer will be different. An example of one existing packet exchange that can be used for triggering invoked transmissions is null data packet (NDP) and ACK exchange. NDP transmission by the Wi-Fi Sensing receiver can be used to invoke a Wi-Fi Sensing transmitter to respond with an ACK, which may then be used to compute a channel estimation. The disadvantage of using ACK packets for channel estimation, in 2.4/5GHz bands, is that the ACKs are only transmitted in legacy mode. Another example of how an invoked measurement can be triggered is by use of the implicit unidirectional beamforming procedure, first defined in the IEEE 802.1 In standard. In this procedure, an STA requests beamforming training by sending a MAC frame with the training request (TRQ) bit set to 1. This triggers the receiving device to send an NDP announcement, followed by an NDP to illuminate the channel. The benefit of this invoked measurement is that it is not limited to the legacy preamble for channel measurements and uses the MIMO training fields, as well.

In pushed measurements, a transmission is triggered by the illuminator to be received by one or multiple Wi-Fi Sensing receivers. Beacon frames are an example of using existing MAC packet exchanges for pushed measurements.

Also as already noted, to support different use cases, either the AP or STA may take the role of sensing receiver; additionally, there may be multiple sensing receivers required to support the application. Moreover, there may be multiple illuminators involved in the measurements. MAC layer coordination is used to coordinate the sensing transmissions among the illuminators and the sensing receivers in an efficient way. MAC layer scheduling may also be used to enable periodic measurements on which some use cases rely. Coordination and scheduling at the MAC layer should enable different options for conducting sensing measurements among multiple illuminators and sensing receivers, with minimal added overhead, while accounting for the power save state of the devices.

To interact with the MAC and PHY, the WFS agent has an interface to pass the WFS control information to the radio and extract the measurement data. The interface should be PHY agnostic and is, therefore, defined in a generic manner and extendable to cover different radio driver implementations, including drivers from different chipset vendors. The interface definition should allow for potential additional features or capabilities provided by a specific PHY or a chipset, as well as a path for growing the technology. Definition of a standard interface/ API enables radio firmware and driver developers to ensure compliance and enables reuse of components or common codes, which may be placed into a library. Most Wi-Fi drivers are based on either the wireless-extensions framework or the more recent and actively developed cfg80211 I nl80211 framework. As the system integration components are largely provided, these frameworks enable Wi-Fi driver developers to focus on the hardware aspects of the driver. These frameworks also offer significant potential as a location for defining a WFS API. The WFS interface should provide the WFS agent with STA identification and enable the WFS agent to track the physical device in the network (i.e., the AP to which it is connected), as well as the device’s capability and availability to participate in the measurements.

The WFS agent requires control of the STAs that will participate in the sensing measurements, as well as what measurement type (passive vs triggered) will be performed. The WFS interface should provide such control, either on a global system scale or on a per STA basis so that the WFS agent can conduct WFS measurements in the most efficient manner.

Based on the specific WFS application or use case, different measurement rates may be required. The measurement rate is typically decided by the WFS agent, and the interface should support its control. However, to provide the lowest jitter and best efficiency possible, it is best to rely on the MAC layer for scheduling. WFS applications may have different measurement parameter requirements (bandwidth, antenna configuration, etc.). The configuration of measurement parameters allows the application to obtain only the data it requires to maintain efficiency. The measurement parameters should be configurable independently for each STA.

The WFS interface should be flexible enough for the radio to specify whether the data payload is in time-domain or frequency-domain, the numerical format, etc. By having this knowledge, the Wi-Fi Sensing agent can correctly interpret the data.

WFS can be used not only to detect the presence and location of humans, also enabling their counting, but it may also be used to detect respiration (which can be used in people counting) and even orientation - e.g. whether a person is standing up or lying down.