Receiver for a radio frequency (RF) based presence sensing arrangement

Abstract

The present invention relates to a receiver (100) for an RF presence sensing arrangement (150). The receiver is configured to receive a first intra-network RF sensing signal (102) from a first transmitter (104) belonging to a first local area RF communication network (106) spanning a first presence sensing volume (114), and additionally receive an inter-network RF sensing signal (108) from a second transmitter (110) belonging to a second local area RF communication network (112), spanning a third presence sensing volume (120) and provide first and inter-network signal strength signals (S1, S3) indicating respective received signal strengths. In the RF presence sensing arrangement, a presence detection unit (122) is configured to provide a presence detection signal (S1) based on the signal strength signal. DET ), the presence detection signal (S DET ) indicates a change in the presence of a subject or object in the first or third presence sensing volume, thereby increasing the accuracy of the presence determination.

Description

Technical Field

[0001] The present invention relates to a receiver for a radio frequency (RF) presence sensing arrangement, an RF transceiver for an RF presence sensing arrangement, a method for operating an RF transceiver in an RF presence sensing arrangement, a method for operating an RF presence sensing arrangement and a computer program for implementing these methods. Background Art

[0002] Radio frequency presence sensing is a presence sensing mechanism that infers the presence of a subject (human) or object in a given presence sensing volume based on how the RF sensing signal is affected by the presence or motion of the subject or object within the presence sensing volume.

[0003] US 9474042 B1 describes an RF presence sensing arrangement and method for detecting the presence of a body using signal absorption caused by the presence of biological matter and signal forward and reflected backscattering of the RF sensing signal.

[0004] US 2012 / 146788 A1 discloses a method for device-free motion and presence detection within a region of interest. A plurality of nodes arranged around the region of interest form a wireless network and are arranged to transmit and receive wireless signals. A computing device receives reported values ​​of the measured RSS of the received wireless signals and tracks the reported values ​​over time. The computing device processes the reported values ​​using an aggregated interference calculation to detect motion and presence within the region of interest. Summary of the Invention

[0005] It would be desirable to provide an RF presence sensing arrangement, an RF transceiver for an RF presence sensing arrangement, a receiver for use in such an RF transceiver and corresponding methods and computer programs which allow a particularly low hardware outlay in the RF presence sensing arrangement.

[0006] The present invention includes different aspects, which particularly include device aspects and method aspects. Hereinafter, before turning to various embodiments of these different device aspects, the different device aspects of the present invention will be described. Subsequently, the different method aspects of the present invention will be described, followed by the computer program aspects of the present invention.

[0007] Turning to the equipment aspect, a first aspect of the present invention is formed by an RF presence sensing arrangement. The RF presence sensing arrangement comprises:

[0008] - a first set of RF transceivers belonging to a first local area RF communication network spanning the first presence sensing volume, wherein the first set of RF transceivers is configured to transmit and receive first intra-network RF sensing signals within the first local area RF communication network;

[0009] - a second set of RF transceivers belonging to a second local area RF communication network spanning a second presence sensing volume different from the first presence sensing volume, wherein the second set of RF transceivers is configured to transmit and receive second-network intra-RF sensing signals within the second local area RF communication network;

[0010] -At least one RF transceiver of the second group of RF transceivers is further configured to transmit an inter-network RF sensing signal for receipt by at least one RF transceiver of the first group of RF transceivers, and the at least one RF transceiver of the first group is arranged and configured to additionally receive the inter-network RF sensing signal, thereby spanning a third presence sensing volume bridging space between the first presence sensing volume and the second presence sensing volume.

[0011] At least one RF transceiver of the first group includes a receiver having a signal strength determination unit configured to determine a first quantity indicative of a received signal strength of a first intra-network RF sensing signal received, and provide a first signal strength signal indicative of the first quantity. The receiver is additionally configured to determine a second quantity indicative of a received signal strength of an inter-network RF sensing signal received, and provide an inter-network signal strength signal indicative of the second quantity.

[0012] The RF presence sensing arrangement further includes at least one presence detection unit configured to receive the first signal strength signal and the inter-network signal strength signal from the receiver, and to use the first signal strength signal and the inter-network signal strength signal to provide a presence detection signal indicating the presence or absence of a subject or object in the first or third presence sensing volume.

[0013] The first aspect of the RF presence sensing arrangement is based on the recognition that, because the quality of presence detection (i.e., reliability, latency, repeatability, accuracy, etc.) depends on the interaction of the human body with the RF sensing signal, the directivity of the antennas of the RF transceivers in the local area RF communication network and their placement within a given space play a significant role in RF-based sensing. Detection sensitivity is highest within the direct line of sight of the RF transceivers of a given local area RF communication network, but is subject to variations in RF design and antenna directivity. Due to reflections and the resulting multipath propagation, the presence sensing volume extends to some extent beyond the line of sight. However, such a relatively limited presence sensing volume would require a large number of RF transceivers distributed throughout the local area RF communication network to fully cover the desired overall sensing space.

[0014] Furthermore, the RF presence sensing arrangement of the first aspect exploits the further recognition that most RF presence sensing arrangements are based on using multiple different groups of RF transceivers, each group covering a different sensing volume, for covering a desired overall sensing space.

[0015] Utilizing these insights, the RF presence sensing arrangement of the first aspect further comprises at least two different groups of RF transceivers, each group forming part of a respective different local area RF communication network for presence sensing across a respective presence sensing volume. Of course, depending on the application, more than two groups of RF transceivers, each group forming part of a respective different local area RF communication network, may be used in the arrangement.

[0016] The first and second presence sensing volumes spanned by the first and second local area RF communication networks are distinct from one another. Thus, each of the first and second presence sensing volumes forms a corresponding volume in space that may overlap with, but typically does not overlap with, other presence sensing volumes. These presence sensing volumes are spanned by the respective local area RF communication networks of presence-sensing RF transceivers and are defined until a received RF sensing signal (transmitted within the respective local area RF communication network) permits the determination of human presence. For a given pair of two RF transceivers within a local area RF communication network, the corresponding presence sensing volume spanned by the pair of RF transceivers has a geometric shape that typically resembles an oval, or in other words, an American football, with the RF transceivers positioned at the ends of the shape. However, the shapes of such presence sensing volumes mentioned are merely exemplary and may vary depending on the directivity of the antennas of a given type of RF transceiver. The presence sensing volume of a given local area RF communication network corresponds to the combination of the presence sensing volumes of the paired RF transceivers within that local area RF communication network. For a given RF sensing signal transmission energy, the reliability, or even the likelihood, of presence sensing typically decreases beyond a certain distance between the two RF transceivers in question. Thus, depending on a given arrangement of RF transceivers, and in particular their radiation patterns and the distribution of objects arranged in a given environment, not all possible pairs of RF transceivers may contribute to the sensing volume.

[0017] This arrangement of multiple local area RF communication networks covering a single presence sensing volume enables presence sensing in different areas of the space to be monitored, such as, for example, different floors or areas in a building.

[0018] Advantageously, the sensing arrangement of the first aspect additionally enables signal communication of inter-network RF sensing signals, i.e., beyond the technical and spatial network boundaries defined by the association of an RF transceiver to the respective first or second local area RF communication network. This creates a third presence sensing volume bridging space between the first and second presence sensing volumes, increasing the overall sensing volume of the RF presence sensing arrangement. The present invention improves intra-network presence sensing by extending intra-network presence sensing with inter-network presence sensing. This additional third presence sensing volume allows an RF transceiver to be positioned further away from the next adjacent RF transceiver in the same local area RF communication network, thereby reducing the hardware expenditure required to implement a given RF presence sensing arrangement compared to known arrangements that only provide intra-network RF sensing signals. Of course, the arrangement of the RF transceivers in the first and second local area RF communication networks that receive and transmit the inter-network RF sensing signals is selected based on a given transmission energy or transmit power requirement for the inter-network RF sensing signals in a given application, so as to allow at least one RF transceiver to receive the inter-network RF sensing signals and subsequently perform RSSI determination.

[0019] Even if, in a given RF presence sensing arrangement, the sensing volumes of the first and second local area RF communication networks overlap, the RF presence sensing arrangement advantageously increases the accuracy of detecting the presence of a subject or object by enabling detection in the first and third presence sensing volumes based on providing additional sensing information for detecting said presence.

[0020] For the sake of clarity, it is noted that the presence detection unit is typically configured to provide a presence detection signal indicating whether any subject is present in the first or third presence sensing volume. Certain embodiments, which will be described further below, additionally enable detecting changes in a plurality of subjects in the first or third presence sensing volume.

[0021] For simplicity and clarity of description, this specification assigns certain functionality associated with inter-network presence sensing to different sets of RF transceivers associated with the first and second local-area RF communication networks. For example, the inter-network RF sensing signal is described as being generated and provided by the second set of RF transceivers forming the second local-area RF communication network. However, it should be understood that, throughout this specification, the roles of the first and second sets of RF transceivers in transmitting and receiving inter-network RF signals are interchangeable. In fact, in some embodiments, both sets of RF transceivers assume the receiving role of the RF transceiver for the first local-area RF communication network and the transmitting role of the RF transceiver for the second local-area RF communication network, enabling bidirectional exchange of inter-network RF signals between the first and second local-area RF communication networks.

[0022] In a preferred embodiment, at least one of the first set of RF transceivers is an RF transceiver according to the third aspect of the present invention, which will be described further below.

[0023] In an embodiment of the RF presence sensing arrangement of the first aspect, the transceivers of the second group of RF transceivers are configured to transmit the inter-wireless network RF sensing signal to be received by at least one RF transceiver of the first group of RF transceivers at a controllable amount of signal power.

[0024] In a preferred embodiment, the first and second groups of RF transceivers are configured to provide a first intra-network RF sensing signal and an inter-network RF signal, wherein the first intra-network RF sensing signal and the inter-network RF signal include data indicative of an RF transceiver identifier suitable for identifying the RF transceiver that has provided the received first intra-network RF sensing signal or the inter-network RF signal.

[0025] As a further device aspect, a second aspect of the present invention comprises an RF transceiver for an RF presence sensing arrangement. The RF transceiver is configured to exchange first intra-network RF sensing signals within a first group of RF transceivers, the first group of RF transceivers belonging to a first local area RF communication network spanning a first presence sensing volume. The RF transceiver includes a receiver for the RF sensing signals. The receiver for the RF sensing signals includes an RF signal receiving unit configured to receive wireless first intra-network RF sensing signals transmitted within the first local area RF communication network spanning the first presence sensing volume from a first transmitter. The RF signal receiving unit is further configured to receive inter-network RF sensing signals from a second transmitter belonging to a second local area RF communication network (different from the first local area RF communication network and spanning a second presence sensing volume different from the first presence sensing volume), thereby spanning a third presence sensing volume bridging space between the first presence sensing volume and the second presence sensing volume. The receiver further includes a signal strength determination unit configured to determine a first quantity indicative of a received signal strength of the received first intra-network RF sensing signals and to provide a first signal strength signal indicative of the first quantity. Additionally, the signal strength determination unit is configured to determine a second quantity indicative of an amount of received signal strength of the received inter-network RF sensing signal and provide an inter-network signal strength signal indicative of the second quantity.

[0026] The RF transceiver of the second aspect of the present invention provides the functionality required for an RF transceiver to implement the RF presence sensing arrangement according to the first aspect of the present invention. The transceiver includes an RF sensing signal receiver having an RF signal receiving unit that is capable of receiving and processing not only intra-network RF sensing signals received from one or more first RF transceivers within a first local area RF communication network to which the RF transceiver belongs, but also inter-network RF signals provided by one or more second RF transceivers that do not form part of the first local area RF communication network defining the first presence sensing volume, but instead form part of a second presence sensing volume. As such, the RF transceiver of the second aspect of the present invention shares the advantages achieved by the RF presence sensing arrangement of the first aspect.

[0027] As a further apparatus aspect, a third aspect of the present invention comprises a receiver for RF sensing signals for use in an RF transceiver of an RF presence sensing arrangement. The receiver for RF sensing signals according to the third aspect comprises an RF signal receiving unit configured to receive a wireless first intra-network RF sensing signal transmitted within a first local area RF communication network spanning a first presence sensing volume from a first transmitter. The RF signal receiving unit is further configured to receive an inter-network RF sensing signal from a second transmitter belonging to a second local area RF communication network (different from the first local area RF communication network and spanning a second presence sensing volume different from the first presence sensing volume), thereby spanning a third presence sensing volume bridging space between the first presence sensing volume and the second presence sensing volume. The receiver further comprises a signal strength determination unit configured to determine a first quantity indicating a received signal strength of the received first intra-network RF sensing signal and provide a first signal strength signal indicating the first quantity. Additionally, the signal strength determination unit is configured to determine a second quantity indicating a received signal strength of the received inter-network RF sensing signal and provide an inter-network signal strength signal indicating the second quantity.

[0028] The receiver of the third aspect of the invention provides the receiver functionality required by an RF transceiver to implement the RF presence sensing arrangement according to the first aspect of the invention. As such, the receiver particularly forms a component suitable for incorporation in the RF transceiver of the second aspect. The receiver for RF sensing signals has an RF signal receiving unit which is capable of receiving and processing not only intra-network RF sensing signals received from one or more first RF transceivers within a first local area RF communication network to which the RF transceiver belongs. Additionally, the RF signal receiving unit is also capable of receiving and processing inter-network RF signals provided by one or more second RF transceivers which do not form part of the first local area RF communication network defining the first presence sensing volume but form part of a second local area RF communication network defining the second presence sensing volume.

[0029] The receiver of the third aspect of the invention shares the advantages achieved by the RF transceiver of the second aspect and the RF presence sensing arrangement of the first aspect.

[0030] Hereinafter, embodiments of the RF presence sensing arrangement, RF transceiver, and receiver of the above-mentioned device aspects of the present invention will be described. For the sake of simplicity of description, embodiments will be described only in the context of a specific device aspect. However, it should be understood that all embodiments described below are generally applicable to all three device aspects and therefore also refer to corresponding embodiments of other device aspects not mentioned in a specific context.

[0031] The first and second local area RF communication networks are each formed from respective sets of RF nodes, wherein communication links (in this case RF communication links) are established to enable payload data transmission between the RF nodes within a given local area RF communication network.

[0032] As is well known, RF communication links between RF nodes belonging to the same local RF communication network also enable presence sensing capabilities between these RF nodes. RF nodes suitable for presence sensing purposes are sometimes referred to herein as sensing nodes. Depending on their communication capabilities, they can generally be implemented in different ways, such as as separate RF receivers, separate RF transmitters, or preferably, as RF transceivers, i.e., sensing nodes configured to transmit and receive the RF sensing signals referred to herein.

[0033] Preferred embodiments of the RF presence sensing arrangement of the first aspect of the invention advantageously comprise at least one RF transceiver of the second aspect of the invention.

[0034] Preferred embodiments of the RF presence sensing arrangement of the first aspect of the invention comprise at least one RF transceiver having a receiver according to the third aspect.

[0035] Thus, preferred embodiments of the RF transceiver of the second aspect of the invention advantageously comprise a receiver according to the third aspect.

[0036] In the following, embodiments of a receiver of the third aspect of the invention will be described, occasionally accompanied by implementation examples forming part of embodiments of the other apparatus aspects.

[0037] In some embodiments, the first and second local area RF communication networks utilize different wireless communication protocols in the context of their respective intra-network RF sensing.

[0038] In other embodiments, different local area RF communication networks use the same wireless communication protocol for their respective intra-network RF sensing. However, in this case, to distinguish intra-network RF communication from inter-network RF communication, each local area RF communication network has a different network identifier, such as, for example, a service set identifier (SSID) associated with an 802.11 wireless local area network. Other types of network identifiers may be used in the context of other communication protocols.

[0039] For example, therefore, in certain embodiments, the RF signal receiving unit of the receiver of the first aspect is configured to receive and process the first intra-network RF sensing signal and the inter-network RF sensing signal using the same wireless communication protocol. Exemplary embodiments communicate according to alternative wireless communication protocols, such as WiFi, Bluetooth, Bluetooth Low Energy (BLE), Z-wave, 6LoWPAN, Thread, or another known suitable wireless communication protocol.

[0040] In a preferred embodiment, the wireless communication protocol is an IEEE 802.15.4 based wireless communication protocol, such as ZigBee.

[0041] Different embodiments utilize different implementations of signal exchange, and in particular, employ different channelization schemes for receiving intra-network RF sensing signals and inter-network RF sensing signals. For example, in one embodiment of an RF presence sensing arrangement, a first local area RF communication network and a second local area RF communication network are implemented, and presence sensing is performed using different signal frequencies within their respective local area RF communication networks. However, at least one RF transceiver of the second local area RF communication network uses the same signal frequency as that used in the first local area RF communication network to provide the inter-network RF sensing signal for reception by at least one RF transceiver of the first local area RF communication network. In one specific example, channelization for distinguishing the inter-network RF sensing signal is implemented using a time-division scheme for transmitting and receiving the two RF sensing signals. Specifically, in this variation, the receiver of the third aspect in the RF transceiver of the first local area RF communication network is configured to receive the first intra-network RF sensing signal in a predetermined first time slot and to receive the inter-network RF sensing signal in a predetermined second time slot that is different from and does not overlap with the first time slot. Other channelization schemes may also be used.

[0042] In an alternative embodiment implementing other schemes for exchanging RF sensing signals, the RF signal receiving unit of the receiver of the first aspect is configured to receive the inter-network RF sensing and first intra-network RF sensing signals via respective different communication channels (defined by the wireless communication protocol).

[0043] Configurations according to wireless communication protocols based on IEEE 802.15.4 are also suitable. Some of these protocols require a PAN (Personal Area Network) identifier using a 16-bit identifier. It is used by the MAC (Media Access Control) layer of the protocol stack, for example, to filter out received data packets that do not belong to the same local RF communication network but are exchanged using the same wireless communication protocol (such as ZigBee). In one embodiment, where the wireless communication protocol is a wireless communication protocol based on IEEE 802.15.4, the receiver of the third aspect is configured to receive and process the inter-network RF sensing signal according to inter-PAN transmission under the protocol. Inter-PAN transmission refers to a situation where a message is sent to network nodes in different PANs with different PAN IDs. In this embodiment, the inter-network RF sensing signal is sent as part of such an inter-PAN message. Advantageously, in this particular embodiment, the RF transceiver of the second local RF communication network provides the inter-network RF sensing signal.

[0044] In an alternative embodiment, the RF signal receiving unit of the receiver of the third aspect is configured to receive the first intra-network RF sensing signal according to a first wireless communication protocol, and to receive the inter-network RF sensing signal according to a second wireless communication protocol different from the first communication protocol. This receiver embodiment advantageously reduces RF interference between the first and second local area RF communication networks. As a non-limiting example, in one such embodiment, the first and second wireless communication protocols are the IEEE802.15.4 communication protocol and the IEEE 802.15.1 communication protocol, respectively. In another embodiment of this type, the first and second intra-network RF sensing signals are exchanged according to the ZigBee communication protocol, and the inter-network RF sensing signals are exchanged according to the BLE communication protocol. Other alternative wireless communication protocols that can be used to exchange payload data within the first and second local area RF communication networks include, but are not limited to, WiFi, Bluetooth, Bluetooth Low Energy (BLE), Z-wave, 6LoWPAN, and Thread.

[0045] In an embodiment of the RF transceiver of the second aspect, the RF transceiver is configured to additionally associate with a second local area RF communication network and receive a second intra-network RF sensing signal within the second local area RF communication network from a second transmitter belonging to the second local area RF communication network as an inter-wireless network RF sensing signal. Thus, with respect to corresponding embodiments of the RF presence sensing arrangement, at least one RF transceiver of the first group forming part of the first local area RF communication network is configured to operate in both the first and second local area RF communication networks, thereby spanning a third sensing volume. However, in terms of spatial arrangement, such RF transceivers are preferably arranged to contribute to the first and third sensing volumes, but not to the second sensing volume.

[0046] In the following, further embodiments of the RF presence sensing arrangement of the first aspect will be described.

[0047] Different embodiments utilize the determined first signal strength signal and the inter-network signal strength signal to implement different ways of determining presence. In one embodiment, the presence detection unit is configured to compare the respective signal strengths provided therein with predetermined reference signal strength information, which indicates, in the form of respective thresholds, an expected received signal strength indicator value when no object or subject is present in the respective presence sensing volume. In one variation, additional thresholds are pre-stored to allow comparison with the expected received signal strength indicator values ​​for different predetermined numbers of subjects in the respective presence sensing volume. In this way, changes in the number of people present in the respective presence sensing volume can be determined.

[0048] In another embodiment of the RF presence sensing arrangement, the presence sensing unit is a standalone device that, in one variation of this embodiment, is associated with the first local area RF communication network to form a further network node of the first local area RF communication network. In another variation, the presence sensing unit is not associated with any local area RF communication network, but is part of a superordinate local area network (LAN) or wide area network (WAN), with which the first and second local area RF communication networks communicate using respective gateway devices.

[0049] In yet another alternative embodiment, the presence sensing unit is an integral part of an RF transceiver of the first set of RF transceivers. With respect to the corresponding embodiment of the RF transceiver of the second aspect, the RF transceiver embodiment therefore additionally comprises at least one presence detection unit, the presence detection unit preferably being configured to generate and provide a presence detection signal using the first signal strength signal and the inter-network signal strength signal, the presence detection signal indicating the presence or absence of a subject or object in the first or third presence sensing volume.

[0050] For intra-network presence sensing within a second local area RF communications network, further embodiments of the RF presence sensing arrangement of the third aspect include a second set of at least one RF transceiver configured to determine a quantity indicative of the amount of received signal strength of a received second intra-network RF sensing signal and to provide a second signal strength signal indicative of the quantity. Suitably, in such embodiments, the presence sensing unit is further configured to receive the second signal strength signal and use it to determine the presence or absence of a subject or object within the second presence sensing volume. In alternative embodiments, the second local area RF communications network includes a dedicated second presence detection unit to perform this task.

[0051] In another embodiment, the at least one RF transceiver of the second group is configured to additionally receive inter-network RF sensing signals from an external RF transceiver belonging to an external local area RF communication network different from the second local area RF communication network, determine a quantity indicative of a received signal strength of the received inter-network RF sensing signals, and provide a corresponding signal strength signal indicative of the quantity. In an embodiment, the external local area RF communication network is the first local area RF communication network. Alternatively or additionally, in another embodiment, the external local area RF communication network is a network different from the first and second local area RF communication networks. In this way, the overall sensing volume can be further expanded.

[0052] In another embodiment, a first set of RF transceivers is arranged on one floor of a building, and a second set of RF transceivers is arranged on another adjacent floor of the building. In particular, the RF transceivers of a given local RF communication network are arranged only on one given floor, and for example in the ceiling structure of the corresponding floor. Thus, in this RF presence sensing arrangement, each floor has a corresponding local RF communication network, and the third sensing volume spans the space extending vertically between the two floors. In principle, placing the first set of RF transceivers on a single plane, such as in the ceiling of a building floor, results in the object or subject to be detected (which is typically standing on the floor of the building floor) presenting a significantly smaller detection target. This is especially true in the case of high ceiling heights. This means that when detection is performed based solely on the first signal strength signal, the probability of false negatives increases due to insufficient interaction or due to an increase in blind spots in the corresponding presence sensing volume. However, by placing a second set of RF transceivers on the ceiling of another, next adjacent building floor in the building, and enabling transmission and reception of inter-network RF sensing signals, the accuracy of detection of objects or subjects on the intervening building floors is increased because the third detection volume provides an additional presence sensing volume where detection based solely on the first signal strength signal is less accurate or even impossible.

[0053] It is particularly advantageous to arrange the RF transceivers of different local area RF communication networks at corresponding or nearly corresponding lateral positions so as to establish at least an approximately vertical line of sight for communication of RF sensing signals between the networks, which line of sight corresponds to the shortest distance between RF transceivers arranged at the same lateral position but on different floors.

[0054] In another embodiment, the RF transceivers of two different local RF communication networks are arranged on different sides of a firewall or other highly absorbing but not completely shielding wall with respect to RF signals. In another embodiment, the RF transceiver of one of the different local RF communication networks is arranged in the elevator shaft.

[0055] In an embodiment of the RF presence sensing arrangement, the RF transceivers of the first and second sets of RF transceivers are included in respective lighting devices. This is particularly advantageous in embodiments where the first and second sets of RF transceivers are arranged in respective ceilings of respective building floors. Suitably, the intra-network RF sensing signal may be provided in the form of, or as a signal component of, an RF operational control signal exchanged between RF transceivers of a given local area RF communication network, for controlling the operation of the lighting device using payload data exchanged within the local area RF communication network.

[0056] In a preferred embodiment, a first set of RF transceivers is included in the corresponding troffer fixtures, and a second set of RF transceivers is included in the corresponding downlight fixtures. Downlight fixtures typically utilize a wireless driver located on top of the downlight fixture, facing downward toward the ventilation area. The metal can of the downlight fixture can obstruct the wireless downlink path. Therefore, the downlight fixtures are preferably assigned to the lower of the two building floors, while the troffer fixtures are preferably assigned to the higher of the two building floors.

[0057] In another embodiment of the RF presence sensing arrangement, the RF transceivers of the second group of RF transceivers are also configured to receive inter-network RF sensing signals provided by RF transceivers belonging to an additional local area RF communication network that is different from the second local area RF communication network. In a variation of this embodiment, the additional local area RF communication network is the first local area RF communication network. In other preferred embodiments, the additional local area RF communication network is different from the first and second local area RF communication networks.

[0058] The following description turns to the method and computer program aspects of the invention.

[0059] According to a fourth aspect of the present invention, a method for operating a receiver is disclosed. The method comprises:

[0060] - receiving a wireless first-network intra-RF sensing signal transmitted within the first local area RF communication network from the first transmitter;

[0061] - determining a quantity indicative of a quantity of a received signal strength of the received first intra-network RF sensing signal;

[0062] - providing a first signal strength signal indicative of the quantity;

[0063] - receiving an inter-network RF sensing signal from a second RF transceiver belonging to a second local area RF communications network different from the first local area RF communications network;

[0064] - determining a quantity indicative of an amount of received signal strength of the received inter-network RF sensing signal; and - providing an inter-network signal strength signal indicative of the quantity.

[0065] Therefore, the method of the third aspect shares the advantages of the receiver of the first aspect or any embodiment thereof.

[0066] Similarly, the method of the fourth aspect may be implemented to operate an RF transceiver according to the second aspect of the invention.

[0067] Furthermore, according to a fifth aspect, a method for operating an RF presence sensing arrangement is described, the RF presence sensing arrangement comprising a first set of RF transceivers forming a first local area RF communication network spanning a first presence sensing volume and a second set of RF transceivers forming a second local area RF communication network spanning a second presence sensing volume, the second presence sensing volume being separated from the first presence sensing volume by a sensing gap. The method comprises:

[0068] - performing the steps of the method of the third aspect;

[0069] - comparing the signal strength provided by the first and inter-network signal strength signals with predetermined corresponding reference signal strength information;

[0070] - Based on the comparison, providing a presence detection signal, the presence detection signal indicating a change in the presence of a subject or object in the first or third presence sensing volume.

[0071] According to a sixth and seventh aspect of the present invention, corresponding computer programs are presented. The computer programs comprise instructions which, when executed by a computer, cause the computer to perform the steps of the method of the third and fourth aspects, respectively.

[0072] It shall be understood that the receiver, the RF transceiver, the RF presence sensing arrangement, the method of operating a receiver, the method of operating an RF presence sensing arrangement and the computer program have similar and / or identical preferred embodiments, in particular the defined preferred embodiments.

[0073] It should be understood that a preferred embodiment of the present invention may also be any combination of the above embodiments.

[0074] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

[0075] In the following figures:

[0076] Figure 1 Shown is a schematic representation of an embodiment of an RF presence sensing arrangement.

[0077] Figure 2 A schematic representation of another embodiment of an RF presence sensing arrangement is shown.

[0078] Figure 3 A schematic block diagram of an embodiment of a receiver is shown.

[0079] Figure 4 A schematic block diagram of another embodiment of a receiver is shown.

[0080] Figure 5 A flow chart of an embodiment of a method for operating a receiver is shown.

[0081] Figure 6 A flow chart of an embodiment of a method for operating an RF presence sensing arrangement is shown. DETAILED DESCRIPTION

[0082] Figure 1 A schematic representation of an embodiment of an RF presence sensing arrangement 150 is shown. The RF presence sensing arrangement 150 includes a first set of RF transceivers 100, 104 forming a first local area RF communication network 106 spanning a first presence sensing volume 114. The first set of RF transceivers 100 is configured to receive a first intra-network RF sensing signal 102 from a first transmitter 104. Both RF transceivers 100 and 104 belong to the first local area RF communication network 106. The RF transceivers 100 are further configured to determine a quantity indicative of a received signal strength RSSI1 of the received first intra-network RF sensing signal and to provide a first signal strength signal S1 indicative of the quantity.

[0083] Furthermore, the RF transceiver 100 is configured to additionally receive the inter-network RF sensing signal 108 from the external RF transceiver 110 belonging to the second local area RF communication network 112. The second local area RF communication network 112 is different from the first local area RF communication network 106. The RF transceiver 100 is further configured to determine a quantity indicative of an amount of received signal strength of the received inter-network RF sensing signal (SSI3) and provide an inter-network signal strength signal S3 indicative of the quantity.

[0084] The RF presence sensing arrangement 150 also includes a second group of RF transceivers 110, 111 forming a second local area RF communication network 112, the second local area RF communication network 112 spanning a second presence sensing volume 116 separated from the first presence sensing volume 114 by a sensing gap. Each RF transceiver of the second group is configured to transmit and receive second intra-network RF sensing signals 118 within the second local area RF communication network 112, to determine a quantity indicative of a received signal strength RSSI2 of the received second intra-network RF sensing signals, and to provide a second signal strength signal S2 indicative of the quantity.

[0085] Additionally, the RF transceiver of the first group is configured to receive the inter-network RF sensing signal 108 from the at least one RF transceiver 110 of the second group, thereby spanning the third presence sensing volume 120 bridging the first presence sensing volume 114 and the second presence sensing volume 116, to determine a quantity indicative of a quantity of a received signal strength RSSI3 of the received inter-network RF sensing signal, and to provide an inter-network signal strength signal S3 indicative of the quantity.

[0086] The RF presence sensing arrangement further comprises at least one presence detection unit 122 configured to receive the first and inter-network signal strength signals, compare the respective signal strengths provided therein with predetermined reference signal strength information, and provide a presence detection signal S based thereon. DET , which indicates a change in the presence of a subject or object in the first or third presence sensing volume.

[0087] The RF presence sensing arrangement of the present invention allows the RF transceivers of the first and second local area RF communication networks to be placed on a respective single plane, in particular on a ceiling, e.g. as viewed from above. In principle, considering only intra-RF network sensing signals, this arrangement results in the human body presenting a considerably smaller target, particularly for higher ceiling heights, compared to placing the RF transceivers at chest height on the walls of a room. As explained previously, most of the detection sensitivity is primarily within the direct line of sight of the RF transceivers of a given local area RF communication network. The RF presence sensing arrangement of the present invention compensates for this unfavorable sensing characteristic in a local area RF communication network having such a spatial arrangement of its RF transceivers. By providing inter-RF network sensing between the local area RF communication networks of the RF presence sensing arrangement, a third presence sensing volume is established in the space, thereby bridging the space or volume between the first and second presence sensing volumes. In this way, the provision of a large number of RF transceivers within a given local area RF communication network can be avoided.

[0088] Figure 2 A schematic representation of another embodiment of an RF presence sensing arrangement is shown, wherein a first group 202, 204 of RF transceivers are arranged on one building floor 206 in a building 250, and a second group 208, 210 of RF transceivers are arranged on another, next lower building floor 212 in the building 250. In particular, the first group 202, 204 of RF transceivers are arranged at a ceiling 214 of the building floor 206, and the second group 208, 218 of RF transceivers are arranged at a ceiling 216 of the building floor 212.

[0089] In a particularly advantageous RF presence sensing arrangement, the RF transceivers of the first and second sets of RF transceivers are integrated into respective lighting devices. More preferably, the lighting devices can be wirelessly controlled using the respective first and second local area RF communication networks by exchanging payload data within the respective local area RF communication networks.

[0090] As an example, building 250 is equipped with RF sensing via its ceiling light fixtures, which include RF transceivers configured to exchange RF sensing signals according to a predetermined wireless communication protocol. A first set of RF transceivers is arranged at ceiling 214 of building floor 206 and forms a first local RF communication network spanning a first presence sensing volume 218. RF transceivers 202 and 204 are configured to transmit and receive first-network RF sensing signals within the first local RF communication network, determine a quantity indicating the received signal strength of the first-network RF sensing signals, and provide a first signal strength signal indicating the quantity. Based on the RSSI value of the first-network RF sensing signals, the presence of an object or subject 220 in building floor 206 can be determined if the object or subject enters the first presence sensing volume.

[0091] Thus, RF transceivers 208 and 210 belong to a second group of RF transceivers and are arranged at ceiling 216 of building floor 212, forming a second local area RF communication network spanning second presence sensing volume 222. RF transceivers 208 and 210 are configured to transmit and receive second intra-network RF sensing signals within the second local area RF communication network, determine a quantity indicative of an amount of received signal strength of the received second intra-network RF sensing signals, and provide a second signal strength signal indicative of the quantity.

[0092] Based on the RSSI value of the RF sensing signal within the second network, the presence of the object or subject in the floor 212 may be determined if the object or subject enters the second presence sensing volume 222 .

[0093] To more accurately determine the presence of subject 220 on building floor 206, RF transceivers 202 and 204 are additionally configured to receive inter-network RF sensing signals from RF transceivers 208 and 210 belonging to a second local RF communication network, determine a quantity indicative of the amount of received signal strength of the received inter-network RF sensing signals, and provide an inter-network signal strength signal indicative of the quantity. This is particularly advantageous in situations where it is not possible or feasible to add additional RF transceivers to the first local RF communication network, which results in increased accuracy in determining presence.

[0094] Reference above Figure 2In the depicted exemplary presence sensing arrangement, the accuracy of presence determinations in a building floor 206 is enhanced by having the RF transceivers 202 and 204 in that floor establish additional sensing links with corresponding RF transceivers 208 and 210 in a building floor 212, which are positioned in substantially the same location relative to those RF transceivers 202, 204 in the building floor 206. Thus, the RF transceivers 202 and 204 are able to combine information from their own floor and use the vertical space between them and the corresponding RF transceivers 208 and 210 in the building floor 212 as an additional third presence sensing volume, thereby resolving the issue of a single-plane detection area.

[0095] In this particular example, where each RF transceiver 202, 204 of the first local area RF communication network receives an inter-network RF sensing signal from a corresponding one of the RF transceivers 208, 210 of the second local area RF communication network, there is almost no overhead and additional network traffic when compared to the local state of each layer, i.e., when sensing is limited within the corresponding local area RF communication network.

[0096] For the sake of clarity and conciseness, Figure 2 In the example, the number of RF transceivers is limited to two per local RF communication network. However, there are RF presence sensing arrangements in which the number of RF transceivers in each local RF communication network is greater than two. Additionally or alternatively, each RF transceiver on a higher building floor can establish a sensing link with more than one, or even all, RF transceivers installed on lower building floors. If more granular presence detection is required, this will result in an increase in coverage area at the expense of additional traffic in the local RF communication network. The additional network traffic can be addressed by placing additional gateways in the local RF communication network.

[0097] This use of RF transceivers on two consecutive building floors results in a certain asymmetry, as, for example, RF transceivers on the lower floor may not have corresponding transceivers in the floor below them to sense relative to them. However, the RF transceivers in the lower floor can use the information gathered by the sensing cross-link provided by the inter-network RF sensing signals between the local area RF communication networks on the upper floor and the lower floor to appropriately discern whether detections picked up solely by nodes on the lower floor are due to entities present there, or due to unwanted interference from entities present on the upper floor. In this way, the RF transceivers of the lower floor local area RF communication network also partially benefit from the inter-network RF sensing. For example, and by way of non-limiting example, if a shared-use building has offices on the first floor and a data center on the second floor, an RF-based RF presence sensing arrangement would be selected to ensure maximum presence detection reliability on the second floor, which houses the data center, and thereby allow, for example, accurate sensing of intruders.

[0098] In another exemplary RF presence sensing arrangement (not shown) implemented in a building with intermediate floors, RF transceivers on the intermediate floors participate in multiple inter-floor RF sensing schemes. For example, if the building has three floors, each floor including a respective local area RF communication network spanning a respective presence sensing volume, the RF transceivers in the second floor are configured to participate in the inter-floor RF sensing scheme along with those of the first and third floors. In this particular example, the primary improvement in detection quality for the second-floor RF transceivers comes from their interaction with the first-floor RF transceivers, with some discriminating information from their interaction with the third-floor RF transceivers. In some cases, such as with an RF transceiver having a powerful Wi-Fi radio that penetrates both ceilings, a node on the first floor may contribute to RF-based sensing on the third floor of a building.

[0099] In another exemplary presence sensing arrangement, the location, number, or density of RF transceivers on each local area RF communication network may differ from one another; that is, the placement of RF transceivers across floors may be inconsistent when viewed horizontally. Consequently, not all RF transceivers may have the same corresponding links. In a particular presence sensing arrangement, this situation is addressed by filtering inter-network RF sensing signals based on the distance between an RF transceiver of a first local area RF communication network and an RF transceiver of a second local area RF communication network, thereby avoiding reliance on inter-network RF sensing signals provided by RF transceivers that are simply too far away.

[0100] In another RF presence sensing arrangement, the RF transceivers of the first local-area RF communication network are further configured to select which corresponding RF transceivers to interact with based on, for example, the RSSI values ​​of inter-network sensing signals received from the RF transceivers of the second local-area RF communication network, regardless of their relative locations. This is advantageous because it avoids evaluating the RF sensing link, i.e., the inter-network RF sensing signal, when, for example, large furniture pieces, such as cabinets, are located between the corresponding RF transceivers. The presence of large furniture not only reduces the signal-to-noise ratio but also, from an application perspective, suggests that these locations are less likely to be occupied. It also avoids evaluating the RF sensing link in areas where occupancy detection has a low value, such as busy hallways where lights are always on and therefore latency is minimal, and highly reliable presence detection is not required. Similarly, locations exhibiting large fluctuations in RSSI over time should be favored, as they may indicate areas frequently occupied by users, such as desks.

[0101] In another presence sensing arrangement, and in order to limit network traffic and inaccessibility of some RF transceivers, the RF presence sensing arrangement is configured to select those RF transceivers that are not used or those that are less used within each floor for inter-floor RF sensing. This ensures that the overall traffic is properly balanced.

[0102] RF-based sensing is difficult for high ceiling heights because the wireless path / distance from the ceiling luminaire containing the RF transceiver to the ground where the subject to be detected is located, and then to other ceiling luminaires, is too long. For example, in warehouses, ceiling heights are often 15 meters and above. Therefore, for multi-story warehouse buildings, it may be advantageous to utilize wireless lighting nodes in the ceilings of the second and first floors. In addition, emergency lights or digital signage can be used at multiple wall heights within a floor, which can be utilized to connect to the floors below.

[0103] In a typical RF presence sensing arrangement (not shown), a predetermined wireless communication protocol is used to exchange corresponding intra-network RF sensing signals, and the RF transceivers in each local area RF communication network are commissioned to use different channels (e.g., Zigbee channels) to avoid radio interference between building floors. However, it is desirable to install RF transceivers on different building floors, sharing the same Zigbee channel, but not necessarily the same Zigbee local area RF communication network, so that RF transceivers on different floors can listen to each other's messages, i.e., the inter-network RF sensing signals, and determine their RSSI.

[0104] Another exemplary presence sensing arrangement performs RF-based sensing in walkways between buildings. ZigBee lighting installations are known to be susceptible to wireless interference from windows penetrating neighboring buildings. Therefore, lighting fixtures located on buildings on either side of the walkway are utilized. In addition to presence sensing, this highly spatially distributed presence sensing arrangement also enables the counting and tracking of people without the need for cameras.

[0105] Figure 3 A schematic block diagram of a receiver 300 that can be implemented in any of the RF transceivers described above is shown. The receiver includes an RF signal receiving unit 302 configured to receive a first intra-network RF sensing signal 304 from a first transmitter belonging to a first local area RF communication network. The RF signal receiving unit 302 is further configured to additionally receive an inter-network RF sensing signal 306 from a second transmitter belonging to a second local area RF communication network that is different from the first local area RF communication network. The receiver includes a signal strength determination unit 308 configured to determine a quantity indicating a received signal strength of the received first intra-network RF sensing signal and provide a first signal strength signal S1 indicating the quantity. The signal strength determination unit 308 is further configured to determine a quantity indicating a received signal strength of the received inter-network RF sensing signal and provide an inter-network signal strength signal S3 indicating the quantity.

[0106] Figure 4 A schematic block diagram of another receiver 400, which can be implemented in any of the RF transceivers described above, is shown. Receiver 400 is configured to receive a first intra-network RF sensing signal 404 according to a first wireless communication protocol and to receive an inter-network RF sensing signal 406 according to a second wireless communication protocol different from the first communication protocol. The RF signal receiving unit includes two subunits 402.1 and 402.2, each configured to receive a respective one of the first intra-network RF sensing signal 404 and the inter-network RF sensing signal 406. Receiver 400 also includes a signal strength determination unit 408 configured to determine a quantity indicating a received signal strength of the received first intra-network RF sensing signal 404 and provide a first signal strength signal S1 indicating the quantity. Signal strength determination unit 408 is further configured to determine a quantity indicating a received signal strength of the received inter-network RF sensing signal 406 and provide an inter-network signal strength signal S3 indicating the quantity.

[0107] Figure 5A flow chart illustrating an embodiment of a method 500 for operating a receiver is shown. The method includes, in step 502, receiving a wireless first intra-network RF sensing signal transmitted within a first local area RF communication network from a first transmitter. The method also includes, in step 504, determining a quantity indicating a quantity of received signal strength of the received first intra-network RF sensing signal. Furthermore, the method includes, in step 506, providing a first signal strength signal indicating the quantity. The method also includes, in step 508, receiving an inter-network RF sensing signal from a second RF transceiver belonging to a second local area RF communication network different from the first local area RF communication network. The method includes, in step 510, determining a quantity indicating a quantity of received signal strength of the received inter-network RF sensing signal, and, in step 512, providing an inter-network signal strength signal indicating the quantity.

[0108] Steps 508, 510, and 512 may be performed in this order before steps 502, 504, and 506. Therefore, it is not necessary to provide an inter-network signal strength signal after providing the first signal strength signal.

[0109] Figure 6 A flow chart illustrating an embodiment of a method 600 for operating an RF presence sensing arrangement includes a first set of RF transceivers forming part of a first local area RF communication network spanning a first presence sensing volume and a second set of RF transceivers forming part of a second local area RF communication network spanning a second presence sensing volume, the second presence sensing volume being separated from the first presence sensing volume by a sensing gap. The method includes performing the steps of method 500. Furthermore, the method includes, in step 602, comparing a signal strength provided by the first and inter-network signal strength signals with predetermined corresponding reference signal strength information. Finally, the method includes, in step 604, providing a presence detection signal based on the comparison, the presence detection signal indicating a change in the presence of a subject or object in the first or third presence sensing volume.

[0110] In summary, the present invention is directed to a receiver for an RF presence sensing arrangement. The receiver is configured to receive a first intra-network RF sensing signal from a first transmitter belonging to a first local area RF communication network spanning a first presence sensing volume, and additionally receive an inter-network RF sensing signal from a second transmitter belonging to a second local area RF communication network spanning a third presence sensing volume, and provide first and inter-network signal strength signals indicating respective received signal strengths. In the RF presence sensing arrangement, a presence detection unit is configured to provide a presence detection signal based on the signal strength signal, the presence detection signal indicating a change in the presence of a subject or object in the first or third presence sensing volume, thereby improving the accuracy of the presence determination.

[0111] 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.

[0112] 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.

[0113] A single unit or device may fulfill 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.

[0114] The computer program may be stored / distributed on a suitable medium, such as an optical storage medium or solid-state medium, provided 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.

[0115] Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. A receiver for RF sensing signals for use in an RF transceiver of an RF presence sensing arrangement, the receiver comprising: - an RF signal receiving unit configured to receive, from a first transmitter, a wireless first intra-network RF sensing signal transmitted within a first local area RF communication network spanning a first presence sensing volume, and to receive, from a second transmitter belonging to a second local area RF communication network that is different from the first local area RF communication network and spans a second presence sensing volume that is different from the first presence sensing volume, an inter-network RF sensing signal, thereby spanning a third presence sensing volume that bridges a space between the first presence sensing volume and the second presence sensing volume; and a signal strength determination unit configured to determine a first quantity indicative of a quantity of received signal strength of the received first intra-network RF sensing signal and provide a first signal strength signal indicative of the first quantity, and additionally determine a second quantity indicative of a quantity of received signal strength of the received inter-network RF sensing signal and provide an inter-network signal strength signal indicative of the second quantity, - wherein the first and second transmitters are installed on different floors of a building and transmit on the same communication channel, while the respective first and second local area RF communication networks to which they belong are different. 2 . The receiver according to claim 1 , wherein the RF signal receiving unit is configured to receive and process the first intra-network RF sensing signal and the inter-network RF sensing signal according to the same wireless communication protocol.

3. The receiver according to claim 2, wherein The wireless communication protocol is an IEEE 802.15.4 wireless communication protocol, and wherein the receiver is further configured to receive the inter-network RF sensing signal according to an inter-PAN transmission.

4. The receiver according to claim 1, wherein The RF signal receiving unit is further configured to receive the first intra-network RF sensing signal according to a first wireless communication protocol, and receive the inter-network RF sensing signal according to a second wireless communication protocol different from the first wireless communication protocol.

5. An RF transceiver for an RF presence sensing arrangement, configured to exchange a first intra-network RF sensing signal as a member of a first local area RF communication network spanning a first presence sensing volume and formed by a first group of RF transceivers, wherein the RF transceiver includes a receiver for RF sensing signals according to claim 1.

6. The RF transceiver according to claim 5 is configured to additionally associate with the second local area RF communication network and receive a second intra-network RF sensing signal within the second local area RF communication network from the second transmitter belonging to the second local area RF communication network as an inter-wireless network RF sensing signal.

7. An RF presence sensing system comprising - a first group of RF transceivers belonging to a first local area RF communication network spanning a first presence sensing volume, wherein the first group of RF transceivers is configured to transmit and receive first intra-network RF sensing signals within the first local area RF communication network, the first group comprising at least one RF transceiver, the at least one RF transceiver comprising a receiver according to claim 1; - a second set of RF transceivers belonging to a second local area RF communication network spanning a second presence sensing volume different from the first presence sensing volume, wherein the second set of RF transceivers is configured to transmit and receive second-network intra-RF sensing signals within the second local area RF communication network; - at least one RF transceiver of the second set of RF transceivers is further configured to transmit an inter-wireless network RF sensing signal for receipt by the first set of RF transceivers including the receiver according to claim 1; thereby spanning a third presence sensing volume bridging space between the first presence sensing volume and the second presence sensing volume; The RF presence sensing system further comprises: - at least one presence detection unit configured to receive the first signal strength signal and the inter-network signal strength signal from the receiver according to claim 1, and use the first signal strength signal and the inter-network signal strength signal to provide a presence detection signal, the presence detection signal indicating the presence or absence of a subject or object in the first or third presence sensing volume.

8. The RF presence sensing system of claim 7, wherein: at least one RF transceiver in the second group is configured to determine a quantity indicative of an amount of received signal strength of the received second intra-network RF sensing signal and provide a second signal strength signal indicative of the quantity; and - wherein the presence detection unit is further configured to receive the second signal strength signal, compare the signal strength provided therein with predetermined reference signal strength information, and based thereon provide the presence detection signal additionally indicating a change in the presence of a subject or object in the second presence sensing volume.

9. The RF presence sensing system of claim 7, wherein: The first set of RF transceivers is arranged on one building floor in a building, and the second set of RF transceivers is arranged on another next lower building floor in the building.

10. The RF presence sensing system of claim 7, wherein the RF transceivers in the first and second groups of RF transceivers are included in respective lighting devices.

11. A method for operating a receiver according to claim 1, the method comprising - receiving a wireless first-network intra-RF sensing signal transmitted within the first local area RF communication network from the first transmitter; - determining a quantity indicative of a quantity of a received signal strength of the received first intra-network RF sensing signal; - providing a first signal strength signal indicative of said quantity to a presence detection unit; - receiving an inter-network RF sensing signal from a second RF transceiver belonging to a second local area RF communications network different from the first local area RF communications network, thereby spanning a third presence sensing volume; - determining a quantity indicative of a quantity of received signal strength of the received inter-network RF sensing signal; and - providing an inter-network signal strength signal indicative of said number to a presence detection unit.

12. A method for operating an RF presence sensing system, the RF presence sensing arrangement comprising a first set of RF transceivers forming a first local area RF communication network spanning a first presence sensing volume and a second set of RF transceivers forming a second local area RF communication network spanning a second presence sensing volume, the second presence sensing volume being separated from the first presence sensing volume by a sensing gap, the method comprising: - performing the steps of the method of claim 11; - comparing the signal strength provided by the first and inter-network signal strength signals with predetermined corresponding reference signal strength information; - Based on the comparison, providing a presence detection signal, the presence detection signal being indicative of a change in the presence of a subject or object in the first or third presence sensing volume.

13. A computer-readable storage medium comprising instructions, which, when executed by a computer, cause the computer to perform the steps of the method of claim 11.

14. A computer-readable storage medium comprising instructions, which, when executed by a computer, cause the computer to perform the steps of the method of claim 12.

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