TECHNICAL FIELD

The present disclosure relates to a method and system for tracking a target device that broadcasts or receives a beacon signal. BACKGROUND

Beacon transmitting devices (“beacons”), also sometimes referred to as asset tags, are small hardware transmitters that broadcast a unique identifier which can be picked up by nearby beacon receiving devices. Typically, the beacons transmit their identifier over a wireless technology standard, such as Bluetooth or Zigbee. A receiving device can use the identifier to determine the beacon’s physical location, track packages, trigger a location- based action, etc. For example, the beacon maybe attached to an item, such as keys, a wallet, luggage, or even a pet. If a beacon signal is received by, for example, a mobile phone, then software installed on the mobile phone can determine an approximate location of the beacon and display this location to a user.

US 2013/0342131 Al discloses devices and applications for the use of wireless control and wireless power in lighting devices and further discloses a centralized power outage system bridged to a networked lighting system. The centralized power outage control may come in the form of a module that detects a disruption in the AC power source and transmits to a system of bulbs, tubes, lamps, fixtures, retrofit fixtures, battery powered fixtures, and the like, to turn on, switch to backup power or change their mode of operation in some manner in response to the detected disruption in power.

DE 102015119627 A in turn discloses a lighting system comprising a plurality of lighting devices each equipped to emit a radio signal beacon and preferably also emitting an identification signal embeded in the emitted light of the lighting device, for reception by a mobile device for localization purposes.

Beacon transmitters or beacon receivers can be integrated with the lighting fixtures of a professional lighting system for various commercial applications. In previous applications, the beacon transmitting devices are integrated within the lighting fixtures and a beacon signal receiving device is used to detect the transmitted signals. One such application uses a beacon transmitting device, which is powered by a respective lighting fixture in a retail store such as a supermarket, to transmit a unique identifier. This identifier, possibly combined with the received signal strength received by a user device of a customer inside the store, can be used to determine the user’s location within the store - e.g. using tri-literati on or triangulation using multiple non co-located receivers. Additionally, the identifier may transmit product-specific information related to a product located near (e.g. underneath) the lighting fixture.

In other systems the beacon receivers are integrated in the lighting fixtures and the device to be tracked emits the beacon signal to be detected by the lighting fixtures.

SUMMARY

In previous beacon tracking lighting systems, the beacon receivers are integrated with and powered by mains-powered lighting devices. For example, continuously- powered lighting fixtures in retail stores, warehouses, hospitals and the like are capable of continuously powering beacon receivers for professional and/or commercial applications. However, for residential or personal applications, the beacon tracking performance of, for example, a home lighting system will be hampered by residents intentionally or

unintentionally de-powering the lighting fixtures which power the beacon receivers integrated therein. For example, the lighting fixtures may be powered off during the day or when a user goes to sleep, leaves the room, etc. When the lighting fixtures and therefore the beacon receivers are depowered, the system loses the ability to track the beacons. This could even happen in other scenarios such as the aforementioned professional or commercial systems, for instance due to a power outage, or due to electricity-cabinet based timer switching which de-powers the lighting infrastructure based on a pre-defmed time schedule in order to save energy at periods when no light is needed in a certain space, (e.g. to turn off a window row of lighting fixtures in an open plan office during the daytime, or to turn off all lights during the weekend).

According to a first aspect disclosed herein, there is provided a method of controlling a lighting system for tracking a target device configured to transmit and/or receive beacon signals, wherein the lighting system comprises at least one mains-powered lighting device and at least one battery-powered device, wherein the mains-powered lighting device comprises a first beacon signal interface configured to perform a first monitoring of beacon signals transmitted by the target device or a first emitting of beacon signals to be received by the target device for determining a location of the target device, and wherein the method comprises: determining, by the battery-powered device, whether or not the mains- powered lighting device is performing said first monitoring or first emitting of the beacon signals; and in response to determining that the mains-powered lighting device is not performing said first monitoring or first emitting of the beacon signals, controlling a second beacon signal interface of the battery-powered device to perform a second monitoring of the beacon signals transmitted by the target device or a second emitting of beacon signals to be received by the target device for determining a location of the target device.

By selectively enabling a battery-powered beacon receiver to monitor for beacon receivers when the mains-powered lighting device is powered off, the lighting system as a whole retains the ability to track the beacon signals. This ensures that at all times there is a receiving device in a monitoring state ready to receive an identifier or information transmitted by a beacon within the locality of the lighting system, even if the user of the system switches off the power to the lighting devices, such as by turning off a wall-switch, or by an automatic time-scheduling switch relay or other such means (e.g. a power MOSFET).

The determining by the battery-powered device may comprise the battery- powered device autonomously detecting the relevant state of the mains-powered device, or the battery-powered device being instructed by another entity such as the mains-powered device or a central controller.

The beacon signals may be transmitted by the target device and monitored by the mains-powered device and/or the battery-powered device. Alternatively or additionally, the beacon signals may be emitted by the mains-powered lighting device and/or battery- powered device and received by the target device. Either way the monitoring device is configured to output the received beacon signals, or measurements thereof, to a localization function configured to determine a position of the target device based on said beacon signals. The idea here is that the mobile target device location is established based on the known locations of the fixed beacon receivers or of fixed beacon transmitters, depending on the case.

The localization function may be implemented locally on the monitoring devices or elsewhere, e.g. a control component such as a lighting bridge, lighting controller or server. Wherever implemented, the localization function may be implemented in the form of software stored on computer-readable storage of the relevant device(s) and arranged to run on one or more processors of the device(s). Alternatively, a hardware implementation is not excluded, neither is a combination of hardware and software.

ln an example, the localization function is implemented across one or more of the mains-powered lighting device, the battery-powered device and the target device. The localization function may for example be implemented in a distributed manner, wherein the target device receives/monitors beacons from beacon transmitters and subsequently identifies the transmitter (e.g. from an embedded identifier) and communicates such finding e.g. in the form of the beacon transmitter identifiers and/or possibly the received signal strength to another component in the tracking system, e.g. hosted in the cloud. A back end tracking system may then subsequently use the known fixed beacon transmitter locations and/or signal strength report to establish the target device position. The beacon signal monitoring device may filter multiple received beacon signals from the same beacon transmitter and transmits an aggregated beacon signal to the localization function. This may result in better resolution of the location of the target device and fewer messages transmitted to the back-end tracking system.

In the event the localization function is implemented fully at the mobile target device, the mobile target device may have access to the non-moving beacon transmitter locations. These may be provided e.g. in a database linking beacon transmitter IDs with locations, or such location information may be embedded directly in the beacon itself, e.g. a hospital room identifier string. The mobile target device can subsequently determine its position based thereon and share its determined position with a back-end tracking system so as to enable tracking of the asset. Such position could be communicated directly to the back end tracking system, or indirectly by communicating through one or more beaconing transceivers towards the back-end tracking system. Alternatively, the mobile target device may determine only the unique identifier of the top N (N>=l) received beacon signals, and forward that information to another device, e.g. the back-end tracking system. Here, the location is defined as "the unique identifier(s) closest to the target device". That is, the location can be real coordinates to a certain level of accuracy, but can also be more coarse such as, for example, a room identifier (which could be included in the beacon signal).

In an example, the respective beacon signal interfaces of the mains-powered lighting device and the battery-powered device are beacon signal receivers configured to monitor for beacon signals transmitted by the target device, wherein the battery-powered device is configured to: determine whether or not the mains-powered lighting device is performing said monitoring of the beacon signals; and in in response to determining that the mains-powered lighting device is not performing said monitoring of the beacon signals, monitor for beacon signals transmitted by the target device.

In an example, the respective beacon signal interfaces of the mains-powered lighting device and the battery-powered device are beacon signal emitters configured to emit beacon signals to be received by the target device, wherein the battery-powered device is configured to: determine whether or not the mains-powered lighting device is performing said emitting of the beacon signals; and in response to determining that the mains-powered lighting device is not performing said emitting of the beacon signals, emit beacon signals to be received by the target device.

In an example, the beacon signal interface of the mains-powered lighting device is a beacon signal receiver configured to monitor for beacon signals transmitted by the target device and the beacon signal interface of the battery-powered device is a beacon signal emitter configured to emit beacon signals to be received by the target device, wherein the battery-powered device is configured to: determine whether or not the mains-powered lighting device is performing said monitoring of the beacon signals; and in in response to determining that the mains-powered lighting device is not performing said monitoring of the beacon signals, emit beacon signals to be received by the target device.

In an example, the beacon signal interface of the mains-powered lighting device is a beacon signal emitter configured to emit beacon signals to be received by the target device and the beacon signal interface of the battery-powered device is a beacon signal receiver configured to monitor for beacon signals transmitted by the target device, wherein the battery-powered device is configured to: determine whether or not the mains-powered lighting device is performing said emitting of the beacon signals; and in response to determining that the mains-powered lighting device is not performing said emitting of the beacon signals monitor for beacon signals transmitted by the target device.

In an example, the battery-powered device is configured to determine: a) whether or not the target device has switched from a state of transmitting beacon signals to a state of receiving beacon signals; or b) whether or not the target device has switched from a state of receiving beacon signals to a state of transmitting beacon signals.

In an example, the method comprises: in response to determining that the mains-powered lighting device is not performing said first monitoring or first emitting of the beacon signals, controlling the battery-powered device to switch from a state of not performing said second monitoring or second emitting of the beacon signals to a state of performing said second monitoring or second emitting of the beacon signals.

In an example, the method comprises: if the battery-powered device is in the state of performing said second monitoring or second emitting of the beacon signals and if it is determined that the mains-powered lighting device is performing said first monitoring or first emitting of the beacon signals, controlling the battery-powered device to discontinue performing said second monitoring or second emitting of the beacon signals.

In an example, when in the state of not performing said second monitoring or second emitting of the beacon signals, the battery-powered device is controlled to operate in a reduced beacon monitoring or emitting state, wherein the reduced beacon monitoring or emitting state comprises periodically monitoring or emitting the beacon signals.

In an example, the method comprises controlling the battery-powered device to periodically monitor a received signal strength value of the beacon signals.

In an example, the method comprises: receiving, at the battery-powered device, an indication of a beaconing frequency of the beacon signals; and controlling a monitoring rate of the battery-powered device based on the received indication of the beaconing frequency of the beacon signals.

In an example, said determining whether or not the mains-powered lighting device is performing said first monitoring or first emitting of the beacon signals comprises determining whether or not the mains-powered lighting device is transmitting a signal that indicates the mains-powered lighting device is performing said first monitoring or first emitting of the beacon signals.

In an example, said determining whether or not the mains-powered lighting device is performing said first monitoring or first emitting of the beacon signals comprises determining whether or not the mains-powered lighting device has transmitted a message indicating that the mains-powered lighting device is not performing said first monitoring or first emitting of the beacon signals.

In an example, said determining whether or not the mains-powered lighting device is performing said first monitoring or first emitting of the beacon signals comprises determining whether or not the mains-powered lighting device is powered on such that the mains-powered lighting device can perform said first monitoring or first emitting of the beacon signals.

In an example, said determining whether or not the mains-powered lighting device is performing said first monitoring or first emitting of the beacon signals comprises determining whether a lighting control device has been operated to switch off the mains- powered lighting device. In an example, the lighting control device is a mains-powered light switch.

In an example, the method comprises maintaining the battery-powered device in the state of monitoring for the beacon signals if at least one of the following conditions is met: i) a new target device is detected; ii) a target device is moving at a speed above a predetermined value; iii) a target device is classified as a high-priority target device; iv) an emergency monitoring state is activated; v) a target device is within a predetermined distance of another target device; and vi) a target device is outside a predetermined distance of another target device.

According to a second aspect disclosed herein, there is provided a system for tracking a target device configured to transmit and/or receive beacon signals, the system comprising: at least one mains-powered lighting device comprising a first beacon signal interface configured to perform a first monitoring of beacon signals transmitted by the target device or a first emitting of beacon signals to be received by the target device for determining a location of the target device; and at least one battery-powered device comprising a second beacon signal interface configured to perform a second monitoring of beacon signals transmitted by the target device or a second emitting of beacon signals to be received by the target device for determining a location of the target device, the battery-powered device being configured to: determine that the mains-powered lighting device is not performing said first monitoring or first emitting of the beacon signals, and perform said second monitoring of beacon signals transmitted by the target device or said second emitting of beacon signals to be received by the target device if the mains-powered lighting device is determined to not be performing said first monitoring or first emitting of the beacon signals.

In an example, the system comprises a localization function arranged to determine the location of the target device based on said monitored or received beacon signals.

In an example, the system comprises a beacon signal monitoring component configured to determine whether or not the mains-powered lighting device is performing said first monitoring or first emitting of the beacon signals.

In an example, the battery-powered device comprises the beacon signal monitoring component.

In an example, said determining comprises determining that the mains- powered device has switched from a state of performing said first monitoring or emitting of the beacon signals to a state of not performing said first monitoring or emitting of the beacon signals, wherein the battery-powered device is configured to switch from a state of not performing said second monitoring or emitting of the beacon signals to a state of performing said second monitoring or emitting of the beacon signals if the mains-powered lighting device has switched from a state of performing said first monitoring or emitting of the beacon signals to a state of not performing said first monitoring or emitting of the beacon signals.

In an example, the battery-powered device is configured to: determine that the mains-powered lighting device has switched from a state of not performing said first monitoring or emitting of the beacon signals to a state of performing said first monitoring or emitting of the beacon signals; and switch from a state of performing said second monitoring or emitting of the beacon signals to a state of not performing said second monitoring or emitting of beacon signals if the mains-powered lighting device has switched from a state of not performing said first monitoring or emitting of the beacon signals to a state of performing said first monitoring or emitting of the beacon signals.

In an example, the battery-powered device is at least one of: i) a battery- powered lighting device, ii) a battery-powered lighting control device configured to control the mains-powered lighting device, and iii) a battery operated building-control device.

For example, the battery-powered lighting control device may be configured to control the mains-powered lighting device via a wireless connection.

For example, the battery operated building-control device may be a C0 ₂ environmental sensor of an HVAC system or a battery-powered employee-badge reader of the building entrance system.

In an example, the mains-powered lighting device is a lighting device connected (wired or wirelessly) to a mains-powered lighting control device, wherein the mains-powered lighting control device is configured to control a mains-power supplied to the lighting device.

In an example, the mains-powered lighting control device is a mains-powered light switch.

According to a third aspect disclosed herein, there is provided a computer program product for controlling at least one battery-powered device in a lighting system, wherein the lighting system comprises a target device configured to transmit and/or beacon signals and at least one mains-powered lighting device, and wherein the mains-powered lighting device comprises a first beacon signal interface configured to perform a first monitoring of the beacon signals transmitted by the target device or a first emitting of beacon signals to be received by the target device for determining a location of the target device, the computer program product comprising code embodied on computer-readable storage and/or being downloadable therefrom, and being configured so as when run on a processing apparatus comprising one or more processing units to: determine whether or not the mains- powered lighting device is performing said first monitoring or emitting of the beacon signals; and in response to determining that the mains-powered lighting device is not performing said first monitoring or first emitting of the beacon signals, control a second beacon signal interface of the battery-powered device to perform a second monitoring of the beacon signals transmitted by the target device or a second emitting of beacon signals to be received by the target device for determining a location of the target device.

According to a fourth aspect disclosed herein, there is provided a method of controlling a lighting system for tracking a target device configured to transmit beacon signals, wherein the lighting system comprises at least one mains-powered lighting device and at least one battery-powered device, wherein the mains-powered lighting device and the battery-powered device each comprise a respective beacon signal receiver configured to receive the beacon signals transmitted by the target device for determining a location of the target device, and wherein the method comprises: determining, by the battery-powered device, whether or not the mains-powered lighting device is monitoring for the beacon signals; and in response to determining that the mains-powered lighting device is not monitoring for the beacon signals, controlling the battery-powered device to monitor for the beacon signals for determining a location of the target device.

BRIEF DESCRIPTION OF THE DRAWINGS

To assist understanding of the present disclosure and to show how embodiments may be put into effect, reference is made by way of example to the

accompanying drawings in which:

Figure 1 shows schematically an example of an environment comprising a lighting system for tracking a target device;

Figure 2 shows schematically a block diagram of a system for tracking a target device; and

Figure 3 shows schematically four different ways of tracking a target device using a mains-powered lighting device and a battery-powered device.

DETAIFED DESCRIPTION

Embodiments of the invention are described in detail below. First, some useful context to such embodiments is provided.

Fighting infrastructure based beacon tracking systems are often applied in professional applications such as hospitals, where the continuously powered lights also act as beacon receivers. However, for residential applications, the beacon tracking performance will be negatively affected by consumers intentionally or unintentionally actuating, for example, wall switches and hence de-powering the lights within the lighting system. Lights are typically switched off for power saving reasons, or because the lights are not required at a particular time (e.g. during the day in a well-lit room). Lights may be switched off for other reasons such as, for example, during repair or maintenance of the lighting infrastructure (safety of the workers). Lights may be also switched based on pre-defmed schedules using relays in the electricity cabinet. Lights may also be switched off during demand response events to aid the electricity utility during periods of extreme electricity consumption. In all such cases, the asset tracking function is still desired, e.g. to protect against theft, or to know the location of the asset (e.g. a critical device such as an automated external defibrillator, AED).

Furthermore, standby power consumption is a particular concern for wireless lighting systems. Wireless lights can be depowered using a wireless relay in order to eliminate standby power consumption. For example, a wirelessly-controlled relay can be inserted in the mains wires of the lighting system. In addition to or instead of using a wireless relay, the lights may be powered and de-powered using alternative electronic power switching such as, for example, a power MOSFET or other power semiconductor devices.

The relay is typically mounted onto a junction-box or embedded within a wall-switch.

However, the de-powering of the lights in order to eliminate standby power losses also disables the lights’ ability to function as beacon receivers and/or transmitters. The overall performance of the beacon tracking system is negatively impacted when the lights are de powered as the resulting system has fewer or even no active beacon receivers and/or transmitters.

The invention provides means to selectively activate a battery-powered beacon receiving device whenever a mains-powered lighting device is depowered, e.g. by a consumer. That is, the beacon receiver functionality is (temporarily) handed over to the battery-powered device. For example, battery-powered motion sensors or remote controls which are present in the same room or area of a house can be used to track beacon signals when the main lights are switched off. These devices can retain the beacon tracking coverage until the main lights regain power. It would however also be advantageous to enable the monitoring by battery-powered beacon receivers only when it is needed, in order to optimize their battery life. In residential applications, beacon tracking can be used, for example, to track a device such as a smartphone, to track keys, a wallet, children, pets, etc. Battery-powered devices can serve as temporary backup beacon-receivers to enable accurate beacon tracking in an environment whenever one or more mains-voltage lights are de-powered by, for example, the user toggling a wall switch or during a power outage (in case of power outage, the gateway may be powered by a UPS, Uninterrupted Power Supply). The invention is also beneficial for professional lighting systems which may be depowered at night or at the weekend by lighting relay panels with time clocks.

Figure 1 illustrates an example environment 100 in which embodiments disclosed herein may be employed. The environment 100 is a space which maybe occupied by one or more users 102. The environment 100 may take the form of an indoor space such as one or more rooms of a home, office or other building; an outdoor space such as a garden or park; a partially covered space such as a gazebo; or a combination of such spaces such as a campus or stadium or other public place that has both indoor and outdoor spaces.

The environment 100 is equipped with one or more lighting devices 104 installed or otherwise disposed at different locations throughout the environment 100. A lighting device 104 may refer to any kind of illumination device for illuminating an environment 100 or part of the environment 100 occupied by a user 102, whether providing for example ambient lighting or specific task lighting. Each of the lighting devices 104 may take any of a variety of possible forms, such as a ceiling or wall mounted luminaire, a free standing floor or table lighting device, or a less traditional form such as a lighting device embedded in a surface or an item of furniture. The different lighting devices 104 in the environment 100 need not take the same form as one another. Whatever form it takes, each lighting device 104 comprises at least one lamp (illumination element) and any associated housing, socket and/or support. Examples of suitable lamps include LED-based lamps, or traditional filament bulbs or gas discharge lamps.

Whilst not shown in Figure 1, in some scenarios the environment 100 maybe divided into a plurality of different zones or localities, such as different rooms, each illuminated by a different respective subset of one or more of the lighting devices 104. For example, a zone may correspond to e.g. a living room, kitchen, hall, and bathroom, multiple bedrooms in a home; or multiple offices, hallways, a reception and a canteen or breakroom in an office building.

In the environment, at least some of the lighting devices 104 are mains- powered lighting devices 104. That is, a mains-powered lighting device 104 is powered by mains-voltage electricity. A mains-powered lighting device 104 may, for example, have a plug which is connected to a socket to draw mains power. Alternatively, a mains-powered lighting device 104 may be connected to the mains power via a mains-powered lighting control. The environment 100 may be equipped with one or more mains-powered lighting controls 106 disposed at one or more locations throughout the environment 100. For example, each zone or locality may comprise a single respective mains-powered control apparatus 106. Alternatively, each zone or locality may comprise more than one respective mains-powered control apparatus 106. Each mains-powered lighting controls 106 may take the form of a stand-alone lighting control 106 such as a smart light switch or an actuator device such as a button, switch, dial or slider device, or wall panel comprising one or more buttons, switches, dials and/or sliders etc.

The environment 100 also contains at least one battery-powered device 108. That is, a device that can operate without drawing mains power. The battery-powered device 108 may be any device with a constrained amount of power available. The battery-powered device 108 maybe powered by traditional (disposable) non-rechargeable batteries such as zinc-carbon batteries and alkaline batteries. Alternatively, the battery-powered device 108 may be powered by rechargeable batteries such as nickel-cadmium (NiCd), nickel-zinc (NiZn), nickel metal hydride (NiMH), and lithium-ion (Li-ion) cells. Other types of batteries are well known to the skilled person. The battery-powered device 108 maybe, for example, a battery-powered lighting device such as, for example, indoor lanterns, outdoor lamps, night lights, etc. In some examples, the battery-operated device 108 is a solar-powered device. A battery-powered device 108 may also be, for example, a lighting control device, such as a smart switch, a remote control, a motion sensor, etc. In general, the battery-powered device 108 may be any electrical device not reliant on mains power for operation. A battery- powered device 108 may sometimes be connected to mains power and/or to a charging point (e.g. a wired or wireless charging point, such as a laptop or charging pad respectively), in order to charge its battery. When connected to the mains power and/or charging point, the battery-powered device 108 may temporarily function as a mains-powered device 104 in addition to, or instead of, functioning as a battery-powered device 108.

The environment 100 also contains a target device 110. The target device 110 may be in the form of a small tag which can be attached to a device or object, e.g. via a mechanical, adhesive or magnetic connection. For example, the target device 110 may be clipped onto a set of keys. Alternatively, the target device 110 may be integrated within a parent device, such as a user device (e.g. a smartphone, smartwatch, laptop, etc.). In these examples, the target device 110 maybe a target function 110, e.g. software implemented on hardware (e.g. a Bluetooth chip) of the parent device. The target device 110 may also be integrated within a piece of luggage, a package, a pet collar, an item of clothing, etc.

The environment 100 may also contain at least one user device (not shown) having a user interface for outputting information to a user 102.

Figure 2 illustrates an example of a lighting system 200 for tracking a target device 110. The target device 110 contains a wireless transmitter/transceiver 202 for transmitting (e.g. broadcasting) an identifier of the target device 110. The identifier may be unique to an individual target device 110. The wireless transmitter 202 may be a radio transmitter for communicating via a radio channel (though other forms are not excluded, e.g. infrared transceiver, coded light). The wireless transmitter 202 may comprise for example a ZigBee, Bluetooth, Wi-Fi, Thread, JupiterMesh, Wi-SUN, 6L0WPAN, etc. interface for broadcasting information. The wireless transmitter 202 is operatively coupled to a controller 204 configured to control the wireless transmitter 202. For example, the controller may control the transmission frequency of the wireless transmitter 202.

The system 200 also contains one or more mains-powered lighting devices 104. The mains-powered lighting device 104 is shown to receive mains-voltage power from a mains power supply 206, i.e. an AC or DC power supply. In the example of Figure 2, the mains-powered lighting device 104 is operatively coupled to a mains-powered lighting control apparatus 106. The mains-powered lighting control apparatus is configured to control the power supplied to the mains-powered lighting device 104. In examples where the system 200 contains more than one mains-powered lighting device 104, each lighting device 104 may all be connected to a single mains-powered lighting control apparatus 106. Alternatively, each lighting device 104 may all be connected to its own respective mains-powered lighting control apparatus 106, or a subset of the lighting devices 104 maybe controlled by one or more control apparatus 106. For example, a light switch 106 may control all of the lighting devices 104 in a particular room.

The mains-powered lighting device 104 contains a controller 208 operatively coupled to a wireless transceiver 210. The lighting control device 108 comprises the wireless transceiver 210 for communicating via any suitable wireless medium, e.g. a radio transceiver for communicating via a radio channel (though other forms are not excluded, e.g. an ultrasound or infrared transceiver). The wireless transceiver 210 may comprises a Wi-Fi, ZigBee, Bluetooth, Thread etc. interface for communicating with other lighting devices 104 and/or the battery-powered device 108. Each lighting device 104 is configured to be able to communicate over a wireless channel in order to perform the respective control operations disclosed herein, preferably a radio channel (though the possibility of other media such as visual light communications, ultrasound or infrared are not excluded). For instance the radio channel may be based on a radio access technology such as ZigBee, Bluetooth, Wi-Fi,

Thread, JupiterMesh, Wi-SUN, 6L0WPAN, etc. The radio channel can be used by the lighting control device 108 to control the lighting devices 104.

In some examples, the wireless transceiver 210 may communicate with other lighting devices 104 and/or the battery-powered device 108 via a wireless network and/or via the central lighting bridge 212, for example, over a local area network or a wide area network such as the internet. It is also not excluded that a wired connection could alternately, or additionally, be provided between the lighting devices 104 themselves, or between a central lighting bridge 212 and the lighting devices 104 for control purposes, e.g. an Ethernet or DMX connection.

In examples the functionality of the central lighting bridge 212 is implemented in the form of software stored in memory and arranged for execution on a processor (the memory on which the software is stored comprising one or more memory units employing one or more storage media, e.g. EEPROM or a magnetic drive, and the processor on which the software is run comprising one or more processing units). Alternatively it is not excluded that some or all of the functionality of the central lighting bridge 212 could be implemented in dedicated hardware circuitry, or configurable or reconfigurable hardware circuitry such as a PGA or FPGA. Also note again that the central lighting bridge 212 may be implemented locally within the environment 100 or at a remote location, and may comprise one or more physical units at one or more geographic sites.

The central lighting bridge 212 may contain a control module 214. Note that the control module 214 need not be contained within the central lighting bridge 212. Indeed, the environment 100 may not contain a central lighting bridge 212 and instead the control module 214 may be implemented across one or more lighting devices 104, one or more lighting control apparatus 106, or across one or more servers (not shown). The central lighting bridge 212 and/or the lighting control module 214 may comprise a wireless transceiver 216. The wireless transceiver 216 may comprise a Wi-Fi, ZigBee, Bluetooth, Thread etc. interface for communicating with the mains-powered lighting devices 104 or the battery-powered devices 108 over a local and/or wide area network. For instance a radio channel may be based on a radio access technology such as ZigBee, Bluetooth, Wi-Fi,

Thread, JupiterMesh, Wi-SUN, 6L0WPAN, etc. Alternatively or additionally, in some examples the central lighting bridge 212 may comprise a wired connection for

communicating with the lighting devices 104 or the battery-powered devices 108.

As discussed, the system 200 also contains one or more battery-powered devices 108. In the example of Figure 2, the battery-powered device 108 is shown separately from the mains-powered lighting device. For example, the battery-powered device 108 may be a motion sensor. However, it is not excluded that the mains-powered device and the battery-powered device 108 can be situated within the same housing, e.g. within a luminaire. In some examples, the mains-powered lighting device 104 may recharge a rechargeable battery of the battery-powered device 108 whilst the mains-powered lighting device 104 is powered on and the battery-powered device 108 is not powered on or does not have a dedicated connection to mains power.

The battery-powered device 108 contains a controller 218 operatively coupled to a wireless transceiver 220. The wireless transceiver 220 maybe of the kind described in relation to the wireless transceiver of the mains-powered lighting device 104 and/or the central lighting bridge 212.

The controllers 218, 208, of the battery-powered device 108 and the mains- powered lighting device 104 respectively, may be implemented in the form of software stored in memory and arranged for execution on a respective processor (the memory on which the software is stored comprising one or more memory units employing one or more storage media, e.g. EEPROM or a magnetic drive, and the processor on which the software is run comprising one or more processing units). Alternatively it is not excluded that some or all of the controllers 218, 208 could be implemented in dedicated hardware circuitry, or configurable or reconfigurable hardware circuitry such as a PGA or FPGA. Whatever form it takes, in examples the controller 218, 208 may be implemented internally in a single battery- powered device 108 or the mains-powered lighting device 104 respectively, along with the wireless transceiver 210, 220, i.e. in the same housing. Alternatively the controllers 218, 208 could, partially or wholly, be implemented externally such as on the central lighting bridge 212.

Both the mains-powered lighting device 104 and the battery-powered device 108 contain a respective beacon signal interface222a, 222b (e.g. a receiver, transmitter or transceiver). Each beacon signal receiver 222 is configured to receive beacon signals transmitted by the wireless transmitter 202 of the target device 110. For example, the beacon receiver 222 may be a wireless receiver such as a radio receiver for receiving information via a radio channel (though other forms are not excluded, e.g. infrared transceiver). The beacon receiver 222 may comprise for example a ZigBee, Bluetooth, Wi-Fi, Thread, JupiterMesh, Wi-SU , 6L0WPAN, etc. interface. The beacon receivers 222a, 222b are operatively coupled to the controller 218, 208 respectively. The controllers 218, 208 are configured to control the beacon receivers 222a, 222b respectively. For example, the controller 218 may activate the wireless receiver 222a.

Each controller 218, 208 may be configured to receive the beacon signals and determine a received signal strength indication (RSSI) of the received beacon signals. RSSI is a measurement of the power present in a received (radio) signal. Each controller 218, 208 can use the RSSI of received beacon signals to determine, for example, a distance between the receiving device (i.e. the mains-powered lighting device 104 or the battery-powered device 108) and the target device 110. In an example system 200 containing multiple receiving devices, the RSSI of the beacon signals received at multiple devices may be used to locate the target device 110 in two or three dimensions, e.g. via triangulation or trilateration of the signals. Another technique that may be used to determine the location of the target device 110 is“fingerprinting”, which relies on mapping a received signal strength from multiple devices at each of a plurality of locations throughout the environment in a preliminary commissioning phase. When the beacon signals are later received from the target device in day-to-day operation, the RSSI measurement can be compared to the“mapped”

measurements.

Whatever technique is used, in order to compare or combine the received signals, each receiving device may transmit the RSSI of the beacon signals to each other device, or to a central lighting bridge 212 or other such central component, via their respective wireless transceiver. Additionally or alternatively, the controller may determine an identifier contained of a specific target device 110 if it is present in the received signals.

Using the RSSI measurements is just one example way of tracking the target device 110. Another example includes using the time-of- flight (ToF) or angle of arrival of the received signals. For example, the distance between the target device 110 and the battery- powered device 108 can be directly calculated from the time-of- flight (or time-of-arrival) as the beacon signals travel with a known velocity. ToF data from two receiving devices (e.g. two battery-powered devices 108) will narrow a position to a position circle; data from a receiving devices allows a precise position to be resolved as a single point. Angle-of-arrival (AoA) measurements may be used to determine the direction by measuring the Time Difference of Arrival (TDOA) at individual elements of a receiving array of the receiving device - from these delays the AoA can be calculated. Like ToF measurements, a location in three dimensions can be determined by using multiple receiving devices.

In another example, the localization is based on a beacon identifier of the target device 110 being received (or not) by one or more mains-powered lighting devices 104 and/or battery-powered lighting devices 108. For example, receiving a beacon identifier of the target device may be enough to determine that the target device 110 is in the same room as the mains-powered lighting device 104 that receives the identifier.

The determination of location of the target device 110 is performed by a localization function 226 based on the monitored beacon signals. The localization function 226 may be implemented in the form of software stored in memory and arranged for execution on a respective processor (the memory on which the software is stored comprising one or more memory units employing one or more storage media, e.g. EEPROM or a magnetic drive, and the processor on which the software is run comprising one or more processing units). Alternatively it is not excluded that the localization function could be implemented in dedicated hardware circuitry, or configurable or reconfigurable hardware circuitry such as a PGA or FPGA. The localization function 226 may be implemented locally on the monitoring devices or elsewhere, e.g. a control component such as a lighting bridge, lighting controller or server.

For example, the localization function 226 may be implemented on a master one of the mains-powered lighting devices 104 or as a distributed function across more than one of the mains-powered lighting devices 104, and/or on a master one of battery-powered devices 108 or as a distributed function across more than one of the battery-powered devices 108. As another example, the localization function may be implemented on the target device itself or on the central lighting bridge 212 or on one or more servers, or across a combination of any of the aforementioned devices. The respective controllers 208, 218 of the mains- powered lighting device 104 and the battery-powered device 108 are configured to communicate the monitored beacon signals (or a processed version thereof) to the localization function 226 via any suitable communication channel, e.g. via a wireless network such as a Wi-Fi, ZigBee, 6L0PAN network or other wireless local area network or a mobile cellular network such as a 3 GPP network; and/or via a wired network such as an Ethernet network, DALI network or other wired local area network, and/or a wide area network such as the Internet.

The system 200 may optionally contain a determining component 224 configured to determine whether or not the mains-powered lighting device 104 is monitoring for the beacon signals. In the example of Figure 2, the determining component 224 is contained within the battery-powered device 108 and operatively coupled to the controller 218. However the determining component 224 may instead be contained within the mains- powered lighting device 104 or the central lighting bridge 212. As another example, the determining component 224 maybe replicated or distributed across two or more of the battery-powered device(s) 108, the mains-powered device(s) 104 and the central lighting bridge 212. The determining component 224 is configured to receive information from which it can determine whether or not the mains-powered lighting device 104 is monitoring for beacon signals. The determining component 224 is also configured to inform the battery- powered device 108 of the result of the determination, e.g. by causing a message to be transmitted to the battery-powered device 108.

Some particular embodiments of the invention will now be described by way of example only.

As discussed above, in previous lighting systems, when the mains-powered lighting devices 104 containing a beacon receiver, powered by the lighting devices 104, are de-powered either intentionally or unintentionally, the lighting system loses the ability to monitor or track a target device 110. To ensure that the target device 110 can be continually monitored, the present invention uses a battery-powered device 108 that is configured to determine whether or not one, some, or all of the mains-powered lighting devices 104 in the environment 100 are monitoring for beacon signals transmitted by one or more target devices. If one, some or all of the mains-powered lighting devices 104 are not monitoring for the beacon signals, the battery-powered is controlled to monitor for the beacon signals.

For example, the battery-powered device 108 may determine if all or some of the ceiling lights in a particular room (e.g. in the same room as the battery-powered device 108) are monitoring for the beacon signals. In another example, determining that a single mains-powered lighting device 104 is not monitoring for the beacon signals is enough for the battery-powered device 108 to monitor for the beacon signals.

An advantage of this is that the system 200 retains the ability to track target devices 110 even when the mains-powered lighting devices 104 (and in turn a respective wireless receiver configured to receive the beacon signals) are switched off.

The battery-powered device 108 may switch between operating in a beacon- receiver mode, in which the battery-powered device 108 monitors for beacon signals, to operating in a non-beacon-receiver mode, in which the battery-powered device 108 does not monitor for beacon signals. The battery-powered device 108 may switch between the two modes based on whether or not the mains-powered lighting device(s) are determined to be monitoring for beacon signals. That is, the battery-powered device 108 may switch back and forth between the two modes whenever the mains-powered lighting device 104 starts and stops monitoring for the beacon signals. For example, the battery-powered device 108 may begin monitoring for beacon signals every time the mains-powered lighting device 104 stops, and vice versa. Put another way, in some examples, the battery-powered device 108 only monitors for beacon signals when the mains-powered lighting device 104 is not monitoring for beacon signals, e.g. because the mains-powered lighting device 104 has been switched off. An advantage of this is that the battery supply of the battery-powered device 108 is conserved when the battery-powered device 108 is not required (due to the mains-powered lighting device 104 tracking the target device 110).

For example, at time T=0, the mains-powered lighting devices 104 are powered on and monitoring for beacon signals and the battery-powered device 108 is not monitoring for beacon signals. The battery-powered device 108 may be powered off or it may be powered on and performing a function other than monitoring for beacon signals, e.g. acting as a motion sensor or a remote control. At a later time T=Tl>T0, the battery-powered device 108 determines that the mains-powered lighting devices 104 are not monitoring for the beacon signals. For example, the mains-powered lighting devices 104 may have been depowered. In another example, the mains-powered lighting devices 104 have not been depowered but are not monitoring for beacon signals for a different reason, e.g. because the beacon signal receiver 222b has developed a fault. The battery-powered device 108 determines that the mains-powered lighting devices 104 are not monitoring for the beacon signals and is controlled to start monitoring for the beacon signals. This may involve activating the beacon signal receiver 222a from an inactive state. At a later time T2>Tl, the mains-powered lighting devices 104 are determined to once again be monitoring for the beacon signals (e.g. the lights have been switched on) and in response, the battery-powered device 108 discontinues monitoring for the beacon signals.

The battery-powered device 108 may, in some examples, operate in a reduced beacon monitoring state. That is, the battery-powered device 108 may not simply switch between two states of continuously monitoring and not monitoring for beacon signals. For example, the battery-powered device 108 may use a low duty cycle to scan for the beacon signals. For instance, the target device 110 may be required to transmit beacon signals ten times per second. The battery-powered device 108 may scan for a sufficiently long period of time in which several beacon signal transmissions occur (e.g. 0.5 to ls), every thirty seconds. An advantage of this is that this is that the battery-powered device 108 continues to contribute to the beacon tracking ability of the system 200 without draining the battery resources of the battery-powered device 108 as quickly as if the battery-powered device 108 was constantly scanning for the beacon signals.

In additional or alternative examples, when operating in a reduced beacon monitoring state the battery-powered device 108 may record a received signal strength indicator (RSSI) value of the target device 110. The battery-powered device 108 may monitor and record the RSSI value at regular or irregular intervals. An advantage of this is that when the mains-powered lighting devices 104 are determined not to be monitoring for beacon signals, the battery-powered device 108 can immediately take over the tracking of the target device 110 using a recent (e.g. most recent) RSSI reference value. In some examples, the beacon payload (i.e. a beacon signal) can include an indication of the transmission power of the target device 110. The receiver can compensate the RSSI reading by using this indication.

As an optional feature, the battery-powered device 108 may be configured to receive an indication of the frequency of beacon signal transmissions. For example, the mains-powered lighting device 104 and/or the battery-powered device 108 may determine the beacon frequency by monitoring the rate at which the beacon signals are received at the mains-powered lighting device 104 and/or the battery-powered device 108 respectively. The mains-powered lighting device 104 may transmit the indication directly to the battery- powered device 108 (e.g. via a radio connection) or via the central lighting bridge 212. In another example, the beacon signals transmitted by the target device 110 may include the beacon frequency. Note that the beacon frequency is the number of beacon signals by the target device 110 per unit time (i.e. beaconing rate) and not the modulation frequency of the beacon signals. In some examples, the battery-powered device 108 may receive, as well as or instead of the beacon frequency, a beacon period of the beacon signals. That is, the (average) period of time between each transmitted beacon signal.

The battery-powered device 108 may adjust the rate at which it (or rather the beacon signal receiver 222a) monitors for beacon signals based on the indication of the beacon signal transmission frequency. If, for example, the transmission frequency is ten transmissions per second, the battery-powered device 108 may scan for beacon signals for a limited time period during which several beacon signals will be transmitted, e.g. 0.5s. The scan duration maybe less than or greater than 0.5s depending on the beacon signal transmission frequency. By minimizing the scanning duration, the power consumption of the battery-powered device 108 can be reduced. Furthermore, it is advantageous for the battery- powered device 108 to scan for beacon signals for longer than the minimal time period since beacon signals can be lost in transmission, e.g. due to interference issues.

As an option, the battery-powered device 108 may predict when the next beacon signal will arrive at the device, e.g. based on the transmission frequency or observed rate of received signals) and scan for the predicted signal for a short period either side of the predicted arrival time. As another option, battery-powered device 108 may be provided with the expected arrival time of the next beacon signal(s) from another device such as, for example, the target device itself, e.g. in addition to the received indication of the frequency of beacon signal transmissions

In some examples, the target device may comprise a motion detector configured to detect movement of the target device. Once the target device moves, the target device may increase the frequency of the beacon transmissions to enable more accurate (real time) tracking of the target device. When movement is detected, the target device may transmit a message (to be received by the mains-powered lighting device and/or battery- powered device) indicating that movement has occurred. The receiving device can then deduce that the frequency of the beacon transmissions will increase. The message may include the interval and/or expected pattern of the beacon signal transmissions. For example, as it is known that the target device has just moved, the target device will transmit a series of ten beacons during the next one minute from the time of movement.

There are several mutually compatible ways in which the battery-powered device 108 may determine whether or not the mains-powered lighting device 104 is monitoring for beacon signals. As a first option, the mains-powered lighting device 104 may be configured to transmit a signal that indicates the lighting device 104 is monitoring for the beacon signals. For example, the signal may contain a message indicating that the lighting device 104 is monitoring for beacon signals. The battery-powered device 108 maybe configured to receive this signal and optionally extract the message. The battery-powered device 108 maybe controlled to monitor for beacon signals based on the presence or absence of the signal. The signal may be received by the battery-powered device 108 itself or via the central lighting bridge 212.

As another option, when a mains-powered lighting device 104 is de-powered (and hence no longer monitoring for beacon signals), it transmits a message indicating that it is no longer monitoring for beacon signals. This“last gasp” message may be received by the battery-powered device 108 itself or another device in the system 200, e.g. the central lighting bridge. The bridge 212 may then notify the battery-powered device 108 that the mains-powered device is no longer monitoring for beacon signals so that the battery-powered device 108 can take over the functionality of listening for the signals. As another option, the mains-powered lighting device 104 and the battery-powered device 108 periodically exchange a“handshake” message with each other, wherein the handshake indicates that the mains-powered lighting device 104 is monitoring for the beacon signals. If the battery- powered device 108 does not receive the handshake, this is enough for the battery-powered device 108 to determine that the mains-powered device 104 is not monitoring for the beacon signals.

As another option, the determination may be performed by the battery powered device 108 having a connection to the mains power to check whether mains power is present, e.g. in emergency lighting fixtures, when battery-powered devices are connected to mains power for charging the battery and providing power during normal operation. When the mains power is removed, the battery-powered device 108 can conclude that the mains- powered lighting devices 104 have lost power and use this conclusion itself and/or notify (other) battery-powered devices 108.

As a further option, a device, e.g. the battery-powered device 108, the central lighting bridge 212 or another device in the system 200 such as, for example, a remote control, may attempt and fail to communicate with the mains-powered lighting device 104 when it is de-powered. For example, the battery-powered device 108 or central lighting bridge 212 may regularly poll the mains-powered lighting device 104 to determine whether it is still active. This failure is interpreted as indicating that the mains-powered lighting device 104 is no longer monitoring for beacon signals and therefore the battery-powered device 108 is controlled to monitor for the beacon signals. When the mains-powered lighting-device 104 switches again to a state of monitoring for the beacon signals, the battery-powered device 108 is notified (e.g. via the central bridge) and subsequently stops monitoring for the beacon signals.

In some examples, when powered, the mains-powered lighting device 104 will regularly report received beacon signals or processed version thereof to the lighting bridge 212. If the lighting bridge 212 does not receive these signals for more than a predetermined period of time, it can instruct the battery-powered device 108 to start monitoring for beacon signals (irrespective of the cause of non-reception of reports from the mains-powered lighting device 104).

As another example, the battery-powered device 108 is notified whenever the mains-powered lighting device 104 is powered on and/or off by a lighting control device 106 such as, for example, a wall-switch. For example, when the wall-switch is operated, a signal is transmitted to the central lighting bridge 212 indicating the change in state of the mains- powered lighting device. The bridge 212 then transmits a message to the battery-powered device 108 to switch on or off depending on the change in state. As an example, if a central building unit decides to de-power a mains-powered lighting device 104 by way of a wireless relay, it can instruct the battery-powered device 108 to start monitoring. This may be combined in a single message "power down ceiling lights" which is interpreted by the battery-powered device 108 as "start monitoring".

In some situations, the battery-powered device 108 may continue monitoring for beacon signals even when the mains-powered lighting device 104 is monitoring for beacon signals. For example, if beacon signals from a new target device 110 (i.e. a target device 110 not previously tracked by the system 200) are detected, the battery-powered device 108 may assume beacon tracking functionality in order to generate a more accurate location than otherwise possible just with the mains-powered lighting device 104.

In another example, the battery-powered device 108 is maintained in the beacon monitoring state at the same time as the mains-powered lighting device 104 when a target device 110 is detected as moving at high speeds and/or if the target device 110 is classified as a high-priority target device 110. For example, a high-priority target device 110 may be attached to an automated external defibrillator (AED) in hospitals so that there precise real-time location can be determined. The determined RSSI change of a target device 110 may be used to determine that a target device 110 is moving at high speeds (e.g. large changes in RSSI over short amounts of time). As an option, the battery-powered device 108 may only monitor the beacon signals from high-priority target devices.

Furthermore, the battery-powered device 108 may, in some examples, operate in an emergency monitoring state. In this state, the battery-powered device 108 monitors for beacon signals until the emergency monitoring state is deactivated. For example, the battery- powered device 108 may switch to and from the emergency monitoring state in response to receiving a message from the mains-powered lighting device 104, central lighting bridge 212, etc. informing the battery-powered device 108 of the beginning or ending of the emergency state. As an example, an emergency monitoring state may be entered in response to a building fire, a school shooter, an earthquake, etc. An advantage of this is that one or more of the battery-powered devices 108 can be used by first responders to track the target devices worn by the building’s inhabitants, e.g. on the bags, jackets, smartphones emitting BLE beacons, etc.. The inhabitants could for example be school children, workers in an enterprise, or patients in a hospital, etc.

As an optional feature, the beacon-receiver functionality of the battery- powered device 108 may be selectively activated based on one or more events. For example, the battery-powered device 108 maybe controlled to monitor for beacon signals in response to a motion sensor (e.g. within the same room as the battery-powered device 108) being triggered. Another example of selectively activating the beacon-receiver functionality is in response to a monitoring schedule. That is, the battery-powered device 108 maybe controlled to monitor for beacon signals depending on the time of day and/or day of the week, or based on machine-learned building usage patterns. In some examples, the monitoring rate of the battery-operated device 108 may be context-dependent. That is, it may be adjusted based on one or more events. For example, the monitoring rate maybe increased when selectively activated, e.g. when a motion sensor has been triggered. As another example, the monitoring rate may be adjusted based on the time of day or based on machine- learned building usage patterns.

As an example use case, the invention can be used to track children outside of the house via battery-operated solar garden lights acting as beacon receivers. The beacon receivers can be used to create a geo-fence around the garden which causes an alert to be output (e.g. via a connected device such as a speaker) when the children move outside of the garden (i.e. the target device is above a pre-determined distance threshold from the geo- fenced area). The geo-fenced area may also be set up around one or more rooms within the environment, e.g. a child’s bedroom. Alternatively, the target device being below a pre determined distance threshold from the geo-fenced area may also trigger the beacon tracking, e.g. a child is approaching the perimeter if the garden. The beacon tracking functionality may be activated either by a parent or based on certain time windows (e.g. after school and before bedtime) or by context awareness. For instance, the beacon receiver functionality in the garden lights may be activated based on a motion sensor detecting activity in the garden.

The beacon-receiver functionality of the battery-powered device 108 may also be selectively activated if the target device 110 is above or below a predetermined distance of another target device (or another known device or object). For example, the tracking may be activated if two forklifts in a warehouse equipped with target devices are approaching each other, or an employee wearing a badge (target device) is approaching a dangerous piece of machinery, upon which the machinery is controlled to stop. As another example, the tracking may be activating if a high value item (equipped with a target device) is stolen or if a parcel falls off a delivery robot.

As another example use case, the beacon functionality of battery-powered devices 108 may be activated in response to a smartphone being detected in the environment 100. For example, the location of the smartphone (determined based on the received beacon signals emitted by the smartphone) may be used to control the garden lights which are closest to the smartphone (and therefore the user 102).

The accuracy of beacon tracking is dependent on the number of beacon receivers and their distribution across the environment 100. Whilst a mains-voltage wireless relay (e.g. a mains powered ZigBee wall-switch) may feature permanent beacon receiver functionality, utilizing the wireless relay as a singular beacon receiver within the

environment 100 may not yield sufficiently accurate beacon tracking results. The invention therefore proposes that when mains-powered lighting device 104 (e.g. ceiling lights) are de- powered by the wireless relay (e.g. in order to save standby power), the battery-operated device (e.g. sensor or switch) which is present in the environment 100 takes over the RSS1 beacon receiver functionality. The system 200 may re-apply power to the mains-powered lighting devices 104 if, for example, the environment 100 becomes occupied by a user 102 and therefore requires light, the system 200 desires to (temporarily) increase the beacon tracking accuracy and hence requires a higher density of beacon receivers, and/or the remaining battery life of the battery-powered device 108 is insufficient to allow for them to act as beacon receivers in addition to their usual mode of operation. The system 200 may also provide power to the mains-powered lighting device(s) 104 so they can receive beacon signals but also instruct the luminaires to stay in a standby state (i.e. emit no light) to track assets even if no user is detected (so therefore no light is needed). This may be done once in a while (e.g. after a predetermined period of time) to get a more accurate fix than possible solely with the wireless relay - while still retaining the majority of the power savings.

Next to depowering lights for reasons such as, for example, saving standby power or during maintenance, in some scenarios it may be desirable to temporarily fully depower certain wireless devices for privacy reasons. For example, it may be desirable to depower lighting network devices such as, for example, occupancy sensors, presence sensors, motion sensors, image sensors, ultrasound sensors, actuators, etc. that are each mains powered and have a wireless receiver / transceiver. For example, a wireless receptacle may be used to fully depower a luminaire-based voice-recognition system, luminaire-powered cameras or distributed thermopile imaging system. Optionally, the voice recognition system and internet camera when powered up may act, on top of its core functionality, as one of the beacon receivers within a beacon tracking system.

For example, some parts of a digital ceiling or lighting infrastructure (e.g. certain mains-powered lighting devices with embedded microphones) may be consciously temporarily depowered (e.g. using a wireless relay) at certain moments for privacy reasons. When these mains-powered lighting devices are de-powered, the tracking functionality of the system decreases, since the tracking is dependent on the number of beacon receivers and their equal distribution across the building space. Therefore selectively activating a battery- powered device 108 to monitor for beacon signals when the mains-powered device(s) 104 are de-powered for privacy reasons ensures that target devices 110 can be continually tracked.

ft will be appreciated that the embodiments above have been described only by way of example. For example, the examples describe determining that a mains-powered lighting device 104 is not monitoring for beacon signals transmitted by the target device 110 and in response, controlling a battery-powered device 108 to monitor for the beacon signals. However, three other implementations are envisaged, with the examples above applying to each implementation. These implementations, along with the first implementation (shown in Figure 3a), are described below in relation to Figure 3.

Battery-operated devices 108, which are assigned to act as beacon receiver, will likely consume more battery charge than a battery-operated device 108 acting as a beacon transmitter ft hence may be advantageous in Figure 3 (upon the mains powered device losing power) to select whether the battery-powered device 108 or the target device 110 acts as beacon receiver based on the remaining battery life of 108 and 110.

ln the second implementation (shown in Figure 3b), the mains-powered lighting device 104 emits beacon signals , such that the position of the target device 110 can be determined based on the signals received by the target device 110. lf the mains-powered device is determined not to be emitting beacon signals, the battery-powered device 108 is controlled to emit beacon signals to be received by the target device 110, such that the target device 110 can continue to be tracked.

ln the third implementation (shown in Figure 3 c), the mains-powered lighting device 104 emits beacon signals to be received by the target device 110. lf the mains- powered lighting device 104 is determined not to be emitting beacon signals, e.g. because it has been de-powered, the target device 110 switches from receiving beacon signals to transmitting beacon signals. If the battery-powered device 108 determines that the mains- powered lighting device 104 is not emitting beacon signals, the battery-powered device 108 monitors for the beacon signals that are transmitted by the target device 110. The battery- powered device 108 may conclude that the mains-powered device is not emitting beacon signals based on the battery-powered device 108 receiving beacon signals from the target device.

In the fourth implementation (shown in Figure 3d), the mains-powered lighting device 104 monitors for beacon signals transmitted by the target device 110. If the mains-powered lighting device 104 is determined not to be monitoring for the beacon signals, e.g. because it has been de-powered, the target device 110 switches from transmitting beacon signals to receiving beacon signals. If the battery-powered device 108 determines that the mains-powered lighting device 104 is not monitoring for beacon signals, the battery-powered device 108 emits beacon signals to be received by the target device 110.

The beacon signals received by the target device 110, the mains-powered lighting device 104 and/or the battery-powered device 108 are output to a determining function (implemented at one or more of said devices) to determine the position of the target device. For example, when the beacon signals are received by the target device 110, the position determination (e.g. via RSSI values) may be performed by the target device.

Alternatively, the target device may share the RSSI values with a different device, such as the central lighting bridge (either via a direct single-hop wireless link to the bridge or by using another device in the environment as a router node).

In some luminaire electronics architectures, the LED driver provides low- voltage DC Power to controls accessories. For instance, an LED driver may provide up to 500mW of power of the DALI wires towards controls accessories. An example of such luminaire electronics architecture is the Philips Lighting SR bus architecture or Sensor Ready bus architecture. Several controls components can be powered on the same SR bus. As an example, one wireless Zigbee radio unit may be powered which consumes 300mW of DC power. In addition, a separate target device tracking unit is added on the same SR bus. As only 200mW of spare DC power is available from the 500mW generated by the SR driver, the target device tracking unit may have insufficient power budget to allow for beacon signal receiving. Hence, even when the luminaire is mains-powered, it is advantageous to act as beacon transmitter (second and third implementations, see Figures 3b and 3c). As another example, where the radio unit temporarily needs more power e.g. during configuration or software update, it is advantageous to act as a beacon transmitter. For situations where no sufficient power is available for the beacon module to be in receiving mode, using a beacon transmitter in the luminaire (needing less power than a beacon receiver) would be a viable option.

If the SR power supply for the target device tracking unit is unlimited (e.g. no Zigbee unit in the luminaire, or the power need from the modules can be handled by the supply), it is advantageous for the luminaire-based asset tracking unit to act as beacon receiver (first and fourth implementations, see Figures 3a and 3d).

In a case where the battery-powered device 108 has sufficient power budget (or the period that it has to listen to beacons are sufficiently short), it can listen to beacons in the same way as the mains-powered lighting device 104 would do (first and third implementations, see Figures 3a and 3c). For example, a battery powered luminaire which gets recharged regularly.

However, if the power budget of the battery-powered device 108 is limited, it would be a beacon transmitter, independent of the choice for mains-powered lighting device 104 (second and fourth implementations Figures 3b and 3d).

In summary, the beacon tracking functionality of battery-powered devices 108 may be selectively activated to ensure that there is sufficient beacon tracking performance of a target device 110. Furthermore, the examples describe how the redundancy of the beacon tracking system can be enhanced in the case of reliability issues of the mains-powered lighting devices 104. The interaction between the wireless relay and the battery-powered device 108 is used to dynamically optimize the trade-off between system standby power, battery life, privacy and beacon tracking performance (e.g. improving the real-time nature and location accuracy).

Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may fulfil the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. A computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems. Any reference signs in the claims should not be construed as limiting the scope. Although at least some aspects of the embodiments described herein with reference to the drawings comprise computer processes performed in processing systems or processors, the invention also extends to computer programs, particularly computer programs on or in a carrier, adapted for putting the invention into practice. The program may be in the form of non-transitory source code, object code, a code intermediate source and object code such as in partially compiled form, or in any other non-transitory form suitable for use in the implementation of processes according to the invention. The carrier may be any entity or device capable of carrying the program. For example, the carrier may comprise a storage medium, such as a solid-state drive (SSD) or other semiconductor-based RAM; a ROM, for example a CD ROM or a semiconductor ROM; a magnetic recording medium, for example a floppy disk or hard disk; optical memory devices in general; etc.