FIELD OF THE INVENTION

The present invention relates to a wireless system and method, a wireless transmitter for use in a wireless system, a wireless transmission method, an electronic device for use in a wireless system and a wireless reception method.

BACKGROUND OF THE INVENTION

The paper Vamsi Talla, Bryce Kellogg, Benjamin Ransford, Saman

Naderiparizi, Shyamnath Gollakota and Joshua R. Smith: "Powering the Next Billion Devices with Wi-Fi", University of Washington, 25 May 2015, arXiv: 1505.06815 describes how to achieve power over WiFi to charge IoT (Internet of Things) devices or, more generally, electronic devices. The paper describes a power over WiFi system that delivers power and works with existing WiFi chipsets. Specifically, it is shown that a ubiquitous piece of wireless communication infrastructure, the WiFi router, can provide far field wireless power without compromising the network's communication performance. Battery- free temperature and camera sensors are prototyped that are powered using WiFi chipsets with ranges of 20 and 17 feet respectively. Further, the ability to wirelessly recharge nickel-metal hydride and lithium-ion coin-cell batteries at distances of up to 28 feet is described.

The authors of the above cited paper further observe that the connection of a WiFi antenna to a harvester does not manage to achieve the required output to actually power a device, due to (i) discontinuous WiFi transmissions, providing only bursts of energy and (ii) leak currents, causing continuous drop in the energy. Therefore, the authors propose a system in which the router introduces additional broadcast traffic in different WiFi channels in such a way that one channel is active almost at any time (95%), and that the antenna and harvester have such a design that they can collect power over the whole WiFi spectrum. This means that the impedance coupling between antenna and harvester needs to be suitable over the whole frequency spectrum. With such a system, a router transmitting at +23 dBm can power exemplary WiFi sensor applications located at up to 28 feet in US indoor environment.

US 2013/0234536 Al discloses a method and apparatus for controlling radio- frequency (RF) energy for wireless devices. In one embodiment, the method comprises determining to increase radio -frequency (RF) energy available to power a wireless tag and controlling the RF energy delivered to the wireless tag to provide tag energy, using one or more of: a) increasing transmission RF power of one or more wireless communication devices, b) increasing a duty cycle associated with wireless transmissions of one or more wireless communication devices, and c) decreasing path loss of the power to the wireless tag.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a wireless system and method, a wireless transmitter for use in a wireless system, a wireless transmission method, an electronic device for use in a wireless system and a wireless reception method, which are improved compared to the known components as described in the above cited paper, in particular to enable localization and/or tracking of electronic devices.

In a first aspect of the present invention a wireless system is presented, said wireless system comprising:

- a wireless transmitter for wirelessly transmitting a tracking signal to an electronic device comprising a wireless receiver, said tracking signal including an identifier for identifying the electronic device and/or the type of electronic device and being configured to provide electrical power to the electronic device for powering the electronic device to enable the electronic device to transmit a response signal, and

- an electronic device comprising a wireless receiver for receiving a tracking signal from the wireless transmitter and a power module for extracting electrical power from the received tracking signal enabling the electronic device identified by the identifier to transmit a response signal for reception by the wireless transmitter allowing the wireless transmitter to locate the electronic device,

wherein said electronic device is configured to check the received tracking signal if an included identifier identifies said electronic device and/or the type of said electronic device and to transmit the response signal if the included identifier identifies said electronic device and/or the type of said electronic device, and

wherein said wireless transmitter is configured to evaluate one or more parameters of a received response signal and/or response information included in a received response signal for determining the location of the electronic device or to evaluate the presence or absence of a response signal with particular characteristics to locate the electronic device. In a further aspect of the present invention a wireless transmitter for use in a wireless system is presented, said wireless transmitter comprising:

a transmission unit for wirelessly transmitting a tracking signal to an electronic device comprising a wireless receiver, said tracking signal including an identifier for identifying the electronic device and/or the type of electronic device and being configured to provide electrical power to the electronic device for powering the electronic device to enable the electronic device to transmit a response signal,

a reception unit for receiving a response signal from an electronic device allowing the wireless transmitter to locate the electronic device, and

- a location unit for locating the electronic device based on the received response signal by evaluating one or more parameters of a received response signal and/or response information included in a received response signal for determining the location of the electronic device or evaluating the presence or absence of a response signal with particular characteristics.

In a further embodiment of the present invention an electronic device for use in a wireless system is presented, said electronic device comprising:

a wireless receiver for receiving a tracking signal from a wireless transmitter, said tracking signal including an identifier for identifying the electronic device and/or the type of electronic device and being configured to provide electrical power to the electronic device for powering the electronic device to enable the electronic device to transmit a response signal,

a power module for extracting electrical power from the received tracking signal enabling the wireless receiver,

wherein the electronic device is configured to check the received tracking signal if an included identifier identifies said electronic device and/or the type of said electronic device and to transmit, if if the included identifier identifies said electronic device and/or the type of said electronic device, a response signal for reception by the wireless transmitter allowing the wireless transmitter to locate the electronic device.

In yet further aspects of the present invention, there are provided corresponding methods.

Preferred embodiments of the invention are defined in the dependent claims. It shall be understood that the claimed methods, transmitting device and electronic device have similar and/or identical preferred embodiments as the claimed system, in particular as defined in the dependent claims and as disclosed herein. The present invention addresses extensions for power over WiFi systems that enable the localization and tracking of power over WiFi devices (generally called electronic devices herein). Tracking devices remains a problem, either in buildings or outdoors. If WiFi is ubiquitous, the proposed wireless system can make the localization and tracking feasible, providing high accuracy and even despite lack of direct line of sight. Such tracking and localization is currently possible using WiFi tags; however, these tags are battery powered and may thus run out of power and they need to be specifically deployed on tracked objects. This then necessitates strategies to track power status, and replace batteries, which is very inconvenient, especially in high volume applications. Using WiFi to power the tags as well as detecting them solves this disadvantage of the known system and devices. Further, the WiFi communication interface of the electronic devices can be used for communication, powering and tracking purpose.

Further, because such tags are battery powered, the communication with the tags is by nature very limited. Firstly, the tags must duty cycle and the latency of responses to queries is slow. Secondly, it is not possible to deploy advanced search strategies with many packet exchanges, as that will rapidly drain the battery. Using WiFi powered WiFi tags solves this disadvantage and allows for refined search strategies (using the many different features of WiFi, including different frequency bands and directional signals) that allows for faster and more accurate localization of the devices.

The present invention proposes devices, systems and methods, in which a user can use the router (i.e. the wireless transmitter) used to power WiFi devices to discover and locate electronic devices. In a simple embodiment the router sends a request message (such as a "Where are you?"), to which the electronic device replies with response message (such as "I am here").

Some device identification, e.g. device address, serial number, type of device, device status (e.g. in use/idle), battery/power status, etc., is included as identifier in the tracking signal so that only the specific device or devices of a specific type will reply. For instance, a particular searched electronic device (e.g. a particular sensor) may be identified or a type of electronic device (e.g. all sensors of a certain type) may be identified by the device identifier (both being understood herein by the check "if the electronic device is identified by the identifier"). In an embodiment, device characteristics can be included in addition to the device identifier, so that the device will only respond if it is in a particular condition or fulfills a particular characteristic. In another embodiment, the electronic device can be configured to only respond to the request if it was able to harvest at least a minimum amount of power from the request. This prevents from responding the devices with additional power sources or devices with sufficient energy storage, which are located too far away from the wireless transmitter.

In yet another embodiment, the electronic device which already responded to one wireless transmitter would not answer a search request from another transmitter unless a particular condition is fulfilled, e.g. the received signal strength of the subsequently received request is stronger or a frequency band preferred by the electronic device is used. This way, the search may be restricted to yet undiscovered devices or devices with insufficient power over WiFi coverage.

In yet another embodiment, the response of the electronic device to a particular wireless transmitter or request type could be made dependent on the wireless transmitter type. For example, the request signal could include some transmitter

characteristics, e.g. the information whether the transmitter is fixed or portable/mobile. This way, the electronic devices could only "lock" themselves (e.g. accept security keys) to fixed elements of the infrastructure, like access points and luminaires, rather than a temporarily present portable device, which may have a stronger signal due to proximity, such as commissioning tool or a user device. The electronic device could still accept particular request types from all types of wireless transmitters.

According to a preferred embodiment said wireless transmitter is configured to subsequently transmit tracking signals in different search areas and/or search areas of decreasing size and to listen for a response signal in response to the transmitted tracking signal. Initially, the direction in which a searched electronic device is located is unknown. Thus, e.g. by use of a directional antenna different directions can be searched step by step. Further, by stepwise decreasing the size of the search area the search can be improved step by step.

In another embodiment said wireless transmitter is configured to subsequently transmit tracking signals with increasing power, different frequencies and/or different bandwidths. This can further improve and accelerate the search of the electronic device(s).

The wireless transmitter may further be configured to evaluate one or more parameters of a received response signal and/or response information included in a received response signal for determining the location of the electronic device, said one or more parameters including received signal strength, time-of- flight, signal-to-noise ratio, and said response information including information about the quality of reception of signals by the wireless receiver, including received signal strength, time-of- flight and/or signal-to-noise ratio, or to evaluate the presence or absence of a response signal with particular

characteristics, said characteristics including direction, signal strength, and/or radio frequency. This allows the wireless transmitter to better assess the distance and/or direction and whether obstacles are located between the wireless transmitter and the electronic devices.

The wireless system may further comprise two or more wireless transmitters and a coordinator for coordinating the transmission of tracking signals from said wireless transmitters and evaluating response signals received by two or more wireless transmitters to locate the electronic device and/or to assign the electronic device to one or more wireless transmitters for further powering and/or communication. In this way accuracy of location determination may be increased. Hereby, the coordinator may be at least one of the wireless transmitters or a separate entity, such as a computer or server.

The coordinator may particularly be configured to evaluate response signals transmitted by two or more electronic devices and received by two or more wireless transmitters to create a location map of said two or more electronic devices. Such a location map may also be used in future location and tracking of electronic device. For instance, a known location of an electronic device, as recorded in the location map, can be used in a subsequent localization.

Furthermore, the coordinator may further be configured to assign electronic devices to wireless transmitter devices, at least in part based on the result of the evaluation of the response signals as received by the wireless transmitter devices. This assignment can be done based on the derived location of the electronic device, physical proximity to the wireless transmitters, signal strength between the electronic device and the wireless transmitters, in one or both directions, communication pattern of the electronic device and/or the wireless transmitters, number of electronic devices already assigned to the wireless transmitters and their characteristics, etc.

The location map can be stored in any level of detail, from the binary information if any electronic devices were found in range of the wireless transmitter, in general or per search area, to storing the available device details like identifier, type and status together with the location information; for all electronic devices found or those electronic devices that were assigned to that wireless transmitter, e.g. based on the decision made by a coordinator device.

In an embodiment, based on the initial discovery information, the electronic devices may be configured with information related to their physical location, such as relative topographic information (e.g. building A, room3, floor 2, on the window side, etc.) or related to the type of the location (e.g. office, storage room, shop, meeting room, coffee corner, etc.). That information can subsequently be used as device identification or type for the search (e.g. to find all the temperature sensors on floor 5).

A possible result is also that there are no electronic devices requiring power over WiFi in the range of said wireless transmitter, or in particular direction sector. The wireless transmitter may then be configured to completely stop power over WiFi

transmissions, incl. power over WiFi discovery, until explicitly triggered by the user; or to stop power over WiFi transmissions, but for occasional power over WiFi discovery.

The wireless transmitter may further be configured to include a transmitter key in the tracking signal and wherein said wireless receiver (of said electronic device) is configured to verify the received tracking signal by checking a receiver key against the transmitter key. In another embodiment the wireless transmitter is configured to include a tag in the tracking signal and said wireless receiver is configured to verify the received tracking signal by checking if the received tag is stored in the wireless receiver. In still another embodiment the wireless transmitter is configured to encrypt the tracking signal by an encryption key and said wireless receiver is configured to verify the received tracking signal by decrypting the received tracking signal by use of a decryption key. These embodiments help to ensure privacy-awareness of the localization and tracking. In particular, it ensures that an attacker cannot easily eavesdrop the communication between wireless transmitter and wireless receiver so that later another user can find back the same electronic devices or can find electronic devices of the same user. The key may be preconfigured, configured out of band or established over the air following the initial discovery of electronic devices.

The electronic device may be configured to issue a visible and/or audible feedback signal in response to reception of a tracking signal, if said electronic device is identified by the received tracking signal. This may assist the user in the location and identification of the physical electronic device.

In another embodiment said wireless receiver is configured to ignore the identifier and to transmit a response signal even if the identifier included in a received tracking signal does not identify said wireless receiver. Thus, also unknown electronic devices at unknown locations can be detected. In an embodiment of the claimed system, method and transmitter identifiers are generally not or even never used. The proposed wireless transmitter generally comprises a transmission unit, a reception unit, and a location unit. The transmission unit and the reception may comprise one or more (common or separate) antennas. The location unit may be implemented in soft- and/or hardware, e.g. by a dedicated or programmed processor or computer.

The proposed electronic device generally comprises a wireless receiver and a power module for extracting electrical power from the received tracking signal. The wireless receiver may comprise a reception unit, e.g. one or more antennas. The power module (also called power extraction unit) may be configured as known in the art, e.g. as described in the above cited paper "Powering the Next Billion Devices with Wi-Fi" of Vamsi Talla et al. Other configurations that may be used are described in Jean-Pierre Joosting:

"HARVESTING ENERGY FROM ELECTROMAGNETIC WAVES", April 15, 2015 (currently available at http://www.analog-eetimes.com/news/harvesting-energy- electromagnetic-waves), or Tony Armstrong: "AN INFLEXION POINT FOR ENERGY HARVESTING AND THE INTERNET OF THINGS", July 14, 2014 (currently available at http://www.analog-eetimes.com/content/inflexion-point-energy -harvesting-and- internet- things), or Dixon, B. (2010): "Radio Frequency Energy Harvesting", currently available at http://rfenergyharvesting.com/, or Raju, M. (2008): "Energy Harvesting", currently available at http://www.ti.com corp/docs/landing/cc430/graphics/slyy018_20081031.pdf

One or more wireless transmitters may be included in a respective user device, in particular in a luminaire or lamp or power outlet, and said one or more electronic devices may include one or more sensors, switches, movement detectors and/or presence detectors.

Generally, one potential field of application of the present invention is lighting systems. Due to the ubiquity of lighting end points as well as their access to power, the lighting systems may evolve from "merely providing light" to becoming the last meter network in the IoT. This creates enormous business opportunities and adds value to the lighting systems. Specifically, the lighting network may evolve to provide wireless connectivity and wireless power over relatively short distances to very constrained devices in the IoT. These may have an extremely limited capacity to store power. Examples for such devices are e.g. environmental sensors (presence or movement, light, temperature, humidity, C02, door opening sensors, window opening sensors, ...) and light switches or other controllers, e.g. for operating blinds, setting temperature in the thermostats, etc. Such devices will be very cheap to produce, green, and flexibly deployed, but need external sources of power and connectivity to function. BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter. In the following drawings

Fig. 1 shows a schematic diagram of a first embodiment of a wireless system including a wireless transmitter and an electronic device according to the present invention,

Fig. 2 shows a schematic diagram of the layout of an electronic device as disclosed in the above cited paper "Powering the Next Billion Devices with Wi-Fi" of Vamsi Talla et al., which layout may also be used according to the present invention,

Fig. 3 shows an exemplary more detailed schematic diagram of the electronic device shown in Fig. 2, as disclosed in said paper of Vamsi Talla et al, which may generally also be used in an electronic device according to the present invention,

Fig. 4 shows a schematic diagram of a second embodiment of a wireless system including a wireless transmitter and an electronic device according to the present invention, and

Fig. 5 shows a schematic diagram of a third embodiment of a wireless system including a wireless transmitter and an electronic device according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Fig. 1 shows a schematic diagram of a first embodiment of a wireless system 1 including a wireless transmitter 10 and one or more electronic devices 20, 30 according to the present invention. The wireless system may be a WiFi system, wherein the wireless transmitter 10 may be included in or represent an access point or router and the electronic devices 20, 30 may be included in or represent any kind of user device having no or only minimum electrical power supply or power storage capacity and being able to communicate via WiFi with the wireless transmitter 10 by use of a wireless receiver. The electronic devices 20, 30 are herein also called harvesting device; a particular example of such electronic devices 20, 30 are IoT (Internet of Things) devices.

Notably, WiFi systems as described herein are understood to at least include systems operating according to the publicly available IEEE 802.1 la, 1 lb, 1 lg, 1 In, and/or 1 lac specifications which may operate in the 2.4 GHz and the 5.0 GHz band.

The wireless transmitter 10 is generally configured to transmit a tracking signal to an electronic device (e.g. the electronic device 20) comprising a wireless receiver. Said tracking signal includes an identifier for identifying the electronic device 20 and/or the type of electronic device and is configured to provide electrical power to the electronic device 20 for powering the electronic device 20 to enable the electronic device 20 to transmit a response signal.

The wireless transmitter 10 particularly comprises a transmission unit 11 for wirelessly transmitting a tracking signal to an electronic device. The transmission unit 11 particularly comprises one or more transmitting antennas, as e.g. used in a conventional wireless transmitter of a WiFi system. Further, the wireless transmitter 10 comprises a reception unit 12 for receiving a response signal from an electronic device allowing the wireless transmitter 10 to locate the electronic device. The reception unit 12 particularly comprises one or more reception antennas, as e.g. used in a conventional wireless receiver of a WiFi system. The transmitting antennas and the reception antennas may, but need not be identical. The wireless transmitter 10 further comprises a location unit 13 for locating the electronic device based on the received response signal. The location unit 13 may e.g. be a signal processor. It shall be noted here that the response signal may further contain location- related data, e.g. RSSI of the tracking signal or status information (e.g. measured sensor data itself or data about the amount of energy harvested or available).

The electronic device 20 (the electronic device 30 is generally constructed accordingly, which is not shown explicitly in Fig. 1) comprises a wireless receiver 21 for receiving a tracking signal from the wireless transmitter 10 (or another wireless transmitter in reach of the electronic device 20). The wireless receiver 21 particularly comprises one or more receiving antennas, as e.g. used in a conventional wireless receiver of a WiFi system. The electronic device 20 further comprises a power module 22 for extracting electrical power from the received tracking signal enabling the wireless receiver 21 of the electronic device 20 identified by the identifier to transmit a response signal (e.g. by the antenna(s) of the wireless receiver 21 or a separate transmission unit including one or more separate antenna(s)) for reception by the wireless transmitter 10 allowing the wireless transmitter 10 to locate the electronic device 20. As indicated for the wireless transmitter 10, here too the wireless receiver 21 could be implemented as a wireless transceiver powered by means of the power module 22. The power module 22 may be constructed as electronic circuit, as e.g. described in the above cited paper "Powering the Next Billion Devices with Wi-Fi" of Vamsi Talla et al.

Fig. 2 shows a schematic diagram of the layout of an electronic device 40 as disclosed in the above cited paper "Powering the Next Billion Devices with Wi-Fi" of Vamsi Talla et al., which layout may also be used according to the present invention. In this exemplary embodiment three WiFi channels shall be used for power harvesting by the electronic device.

A receiving antenna 21 representing the wireless receiver is followed by a rectifier 221 that converts the 2.4 GHz signal into DC power. This power is fed into a DC- DC converter 222 that increases the voltage of the DC signal to match the voltage

requirements of the task execution unit 23, e.g. a sensor and/or micro-controller. The rectifier hardware 221 is extremely non- linear with input power, operational frequency and the parameters of the DC-DC converter 222, making it challenging to achieve good harvester sensitivity and efficiency across the 72 MHz band that spans e.g. three WiFi channels. Hence, a matching network 223 is arranged between the receiving antenna 21 and the rectifier 221 to transform the rectifier's impedance to match that of the receiving antenna 21. Since the rectifier's impedance varies significantly with frequency and is dependent on the DC-DC converter 222, all components of the power module 22 (sometimes also called RF harvester) are co-designed to achieve good impedance matching across the 72 MHz WiFi band. The input of the DC-DC converter 222 affects the input impedance of the rectifier 221. Thus, if the rectifier 221 can be co-designed with the DC-DC converter 222, the constraints on the matching network 223 can be relaxed.

Fig. 3 shows an exemplary more detailed schematic diagram of the electronic device 40 shown in Fig. 2, which may generally also be used in an electronic device according to the present invention.

At a high level, the rectifier 221 tracks twice the envelope of the incoming signal and converts it into power. Specifically, it adds the positive and negative cycles of the incoming sinusoidal carrier signal to double the amplitude. To do this, it uses a specific configuration of diodes and capacitors as shown in Fig. 3. However, in practice, diodes and capacitors have losses that limit the output voltage of the rectifier. Diodes having low losses, i.e., loss threshold voltage, low junction capacitance and minimal package parasitics and high-quality factor, low-loss UHF-rated capacitors that minimize losses and maximize the rectifier's efficiency and sensitivity are preferred.

Two different embodiments of the DC-DC converter are shown in Fig. 3: a battery recharging version 222a and a battery- free version 222b. The DC-DC converter generally serves two purposes: i) boost the voltage output of the rectifier 221 to the levels required by the task execution unit 23, and ii) make the input impedance of the rectifier 221 less variable across three WiFi channels. The key challenge is the cold-start problem: in a battery- free design, as shown for DC-DC converter 222b, all the hardware components must boot up from 0 V. Practical DC-DC converters, however, have a non-zero minimum voltage threshold. Hence, a DC-DC conversion unit 224b may be used, which can start from input voltages as low as 300 mV, which the rectifier 221 can provide, and boost the output on a storage capacitor Cs to 2.4V. Once the 2.4 V threshold is reached, the DC-DC converter 222 (acting as charge pump) connects the storage capacitor Cs to the output, powering a task execution unit 23 for executing a task, e.g. measuring a sensor signal, actuating a switch, etc.

The DC-DC converter 222a is optimized while recharging a battery 225. Specifically, the battery 225 can provide a minimum voltage level and hence the hardware components need not boot up from 0 V. Hence, a DC-DC conversion unit 224a may be used that contains a boost converter, a battery charger, voltage monitoring solutions and a buck converter. The rechargeable battery 225 is connected to the battery charging node, Vbat, of the DC-DC conversion unit 224a. The boost is used as DC-DC converter to achieve the voltage required to charge the battery 225. Finally, the maximum power point tracking (MPPT) mode of the DC-DC conversion unit 224a is leveraged to tune the input impedance of the DC-DC converter so as to minimize the variation of the rectifier's impedance across WiFi channels. Specifically, the buck converter's MPPT reference voltage may be set to 200 mV.

With such rectifier and DC-DC converter designs, the constraints on the impedance-matching network 223 have been relaxed. The resulting circuit can match impedances between the rectifier 221 and a 50 Ω antenna 21 across WiFi channels, using a single-stage LC matching network 223. In LC matching networks, inductors are the primary source of losses. To mitigate this, high-frequency inductors may be used which have minimal parasitics and a quality factor of 100 at 2.45 GHz. The resulting matching network 223 consumes less board area than traditional transmission lines and distributed-element based matching networks and can be modified to meet different system parameters without any loss.

Further details about the design and function of the electronic device 40 shown in Figs. 2 and 3 can be found in the cited paper. The general layout of this electronic device 40 can also be used in the electronic device 20, 30 according to the present invention, in particular the design and function of the power module 22.

In a simple exemplary use scenario a user enters, in a first step, a command in a PC or the like with the request to find a particular device. In step 2, the PC communicates with the router (i.e. the wireless transmitter) that will send over WiFi a message (i.e. the "tracking signal"), e.g. an "Are you there?" message. In step 3, the electronic device, that harvests energy over WiFi will pick up the signal and reply with a response message, e.g. an "I am here" response. In step 4, the electronic device may then be shown on the screen of the user's PC.

Hereby, the user can provide some device identification, e.g. device address, serial number, type of device, device status (e.g. in use/idle), battery/power status, etc., which will be included in the "Where are you?" message so that only the specific device or devices of a specific type will reply. In a further modification, the device characteristics can be included in addition to the device identifier, so that the device will only respond if it is in a particular condition.

Alternatively, the request message is generic, the characteristics of the electronic device (incl. e.g. device address, serial number, type of device, device status (e.g. in use/idle), battery/power status) are included in the "I am here" (i.e. response) message, and displayed to the user, so that the user can select devices of particular type, group them, etc. In addition, there may be different types of request signals, e.g. in addition to the "where are you?" command (i.e. the tracking signal), resulting in over-the-air "I am here" command, there may also be e.g. a "show yourself command, resulting in the electronic device using the harvested energy for any user-perceivable feedback such as beeping, buzzing, flashing light, starting a fan, etc. so that the user can identify the physical location of that electronic device. Yet another signal can trigger the device to respond with their status, e.g. the measured value.

The above described embodiment will enable any user to find the devices of any other user. In some cases, a user might want that only he or she can find (track or locate) his/her devices. To this end, the tracking signal (e.g. the message "Where are you?") may include the name of the user or use a user- specific security key.

Further, in an embodiment the user-rights related filtering - instead of being performed by the electronic devices responding to the tracking signal - may be performed by the wireless transmitter or the user device/application.

Further, not only the identity of a user can be used, but the system may also filter by class of user (e.g. worker, guest, admin, etc.), where different user classes may have different rights.

Fig. 4 shows a schematic diagram of a second embodiment of a wireless system 2 according to the present invention. In this embodiment the wireless system is integrated into a lighting system, i.e. the wireless transmitter 10 is integrated or coupled with a luminaire 50 and the electronic devices are e.g. represented by an occupancy sensor 60 and a wall switch 70. In a practical system one or more luminaires include a respective access point (i.e. a wireless transmitter), which are thus distributed in space, e.g. in a room or building.

In such an integrated lighting system 2 (i.e. including power transfer capability) the wireless transmitter 10 can be easily integrated with the luminaire 50. A typical luminaire 50 comprises the optical part with light generation means 51 which is operated by the lamp driver 52 which is e.g. powered from mains 53. The wireless transmitter 10 can even be powered from the power supply of the lamp driver 52 via supply line 54 and optionally, in extension, provide control information to the driver via signal line 55. The exemplary occupancy sensor 60 and wall switch 70 get powered over WiFi and need no cable connection or battery. The wireless transmitter 10 can be a built-in part of the luminaire 50. Alternatively, it can be a plug-and-play extension to the luminaire 50, which simplifies the installation and planning, particularly if the luminaires are identical and only some of them are only later extended with the required power extraction functionality. This also simplifies wireless transmitter 10 location changes, e.g. when changing room layout. The powering of the occupancy sensor 60 and wall switch 70 over WiFi is made by means of the above described modification to the transmission using powering burst signal(s) and allowing for energy and RF noise optimized operation. Alternatively, each luminaire can still be equipped with a wireless transmitter, and all of the transmitter functionality or selectively its power over WiFi functionality can be enabled and disabled for selected luminaires, e.g. with the goal to achieve the required power coverage with minimal energy waste.

In an exemplary use scenario the wireless transmitter 10 (e.g. under control of a luminaire controller; not shown) polls the related in-range light switch(es) 70 and sensor(s) 60 (i.e. the electronic devices) by sending a tracking signal that is not only used to locate the light switch(es) 70 and sensor(s) 60 but also to provide sufficient energy to supply the battery-less electronic device(s) for a specific task. One task can be polling the sensor 60 or the light switch 70. The wirelessly powered electronic device only has to power-up for reading out the sensor or switch status and sending an response message to the wireless transmitter 10 (and, thus, to the optional luminaire controller). The wireless transmitter 10 (and the optional luminaire controller) has the ability of powering and thus polling as well as locating the wirelessly powered electronic devices in range, which are of relevance to itself. It may ignore any communication not intended for itself. Similarly, the electronic device may only accept polling signals from known wireless transmitters; for accepting new transmitters, a discovery may be required. Generally, the above described embodiments do not provide information about the direction in which the electronic device is located. This can be solved if the wireless transmitter uses a directional antenna (e.g., comprising multiple spatially separated antennas or phased arrays) so that power can be selectively beamed in different directions and the electronic device will only be able to reply if the power is directed in its direction, which allows finding out the direction where the electronic device is located. Alternatively, the wireless transmitter may also start transmitting with maximum power and in all directions to check whether the electronic device is there at all and then start beaming power in a directional manner. The wireless transmitter can also beam with beams of different widths to speed up the search (e.g., a type of binary search in space).

To additionally get any information of how far the electronic device is the wireless transmitter may be adapted to use different features of signal propagation. In one embodiment, the wireless transmitter can transmit the tracking signal (e.g. the message "Where are you?") with an increasing power level. In this way, the wireless transmitter can assess the distance. A simple approach is to assume propagation in free space so that the received power decreases with the square of the distance. Alternatively, the wireless transmitter may also start transmitting with maximum power to check whether the electronic device is there at all and then start decreasing the power. This provides the user with fastest feedback. Alternatively, the RSSI of the response signal of the electronic devices and/or time-of- flight of the response time can be measured.

In another embodiment the wireless transmitter may also use different frequencies to transmit the tracking signal. For instance, messages sent at a high frequency (e.g. in the 5.0 GHz band) will be attenuated more/blocked by walls. Using different frequencies, e.g. in the 2.4 GHz and/or 5.0 GHz band, may therefore provide additional valuable information as to the locations of the electronic devices to be searched. This may require the electronic devices to be capable of receiving signals in (and being powered by) those different frequency bands. This approach can also use building information to better estimate the current location of the electronic device. For instance, it can use the construction materials of the walls to estimate attenuation at the used frequency/power and use this additional information to better estimate the distance to the electronic device.

In another embodiment the wireless transmitter is provided with information about the received signal strength of the response signal (e.g. the "I am here" message) at the to-be-discovered electronic device. This allows the wireless transmitter to better assess the distance and whether obstacles are located between the wireless transmitter and the electronic devices. For instance, if a wireless transmitter beams a very high power, the wireless transmitter could estimate the electronic device to be very far away. But if there is a wall between the electronic device and the wireless transmitter, the wall may absorb much of the power. If the electronic device replies with the received signal strength, the wireless transmitter can then assess the type and amount of material between the wireless transmitter and the electronic device providing the user with better feedback to locate and track the electronic device. This may require the wireless transmitter to have some knowledge about the receiver characteristics of the electronic device (e.g. a correction factor), to compensate for the imperfections of the electronic device's antenna (impedance matching, non-omni- directionality, etc.).

Alternatively, the wireless transmitter may have some knowledge about intended location of the devices, e.g. based on a floor plan, and train its transmitter and receiver, and compensate for the electronic device's antenna characteristics, based on the actual observed signal strengths. Furthermore, the wireless transmitter may combine the location data, e.g. from a floor plan, e.g. distance to the electronic device, with the directional information obtained from directional search. The relative distances and directions can also be calibrated based on exchanges with other wireless transmitters.

In another embodiment, the location information of the electronic device, if known, can be used to make the further communication more efficient. If the wireless transmitter has a directional antenna and knows the location of the electronic device, and it is unique, then the direction can replace the explicit addressing, making the frame received and/or that transmitted by the electronic device more compact and thus conserving the energy. In addition, that may allow for minimizing the spectrum utilization for the power over WiFi communication, thus increasing the throughput of the total system.

In the above described embodiments of the wireless system 1 a single wireless transmitter 10 is considered. Therefore, the wireless transmitter 10 should be able to locate the electronic device 20 based on the direction, transmitted power and feedback from the electronic device 20. In many systems, e.g. indoors or outdoors, there is a network of wireless transmitters, e.g. all using WiFi to provide an ubiquitous WiFi network. An embodiment of such a wireless system 3 is schematically depicted in Fig. 5. In this embodiment the wireless system 3 comprises two (or more) wireless transmitters 10a, 10b and a coordinator 80 for coordinating the transmission of tracking signals from said wireless transmitters and evaluating response signals received by two (or more) wireless transmitters 10a, 10b to locate an electronic device 20, 30. For this purpose, the coordinator 80, which may be a separate device, such as a PC (e.g. the user's PC), or may be integrated in or represented by at least one of the wireless transmitters 10a, 10b, preferably communicates with the wireless transmitters 10a, 10b over the same network (e.g. the WiFi network) that is used for communication between the wireless transmitters 10a, 10b and the electronic device 20, 30. Thus, if the user can communicate with multiple wireless transmitters 10a, 10b, the wireless transmitters 10a, 10b might get information about the location of the electronic device, which information can then be combined providing higher accuracy of the location detection.

In other words, accuracy of location determination may be increased by making use of multiple access points (wireless transmitters) to receive the response signal (e.g. the message "I am here") and allow for a rough triangulation between the receiving access points. Even if the distance for WiFi powering is too far, receiving of the response signal might still be possible.

In an embodiment the tracking signal (with WiFi powering property) may be sent from different wireless transmitters 10a, 10b. This may require additional

communication between the wireless transmitters 10a, 10b.

Another embodiment allows enriching the available distance information and may further enhance location determination. By making use of multiple (or all) WiFi powered nodes (i.e. electronic devices) which report on quality and/or amplitudes of various received tracking signals a network of distances can be recorded even at a relatively distant wireless transmitter. This embodiment may benefit from a dense network like that of a lighting system as illustrated in Fig. 4.

The coordinator 80 is preferably configured to evaluate response signals transmitted by two or more electronic devices 20, 30 and received by two (or more) wireless transmitters 10a, 10b to create a location map of said two or more electronic devices 20, 30. The coordinator 80 and/or the user's PC can then show the results related to the location of the searched electronic device(s) by means of the location map.

As described above, an identifier of the searched electronic device (and, optionally, also of the device type and/or the user) are used to make sure that only a specific electronic device or the electronic devices of a specific user are e.g. shown in the location map. However, an attacker may eavesdrop this communication so that later another user can find back the same electronic device(s) or can find electronic device(s) of the same user. In an embodiment, the electronic device and user may receive a key (e.g., a symmetric key or asymmetric key) and use it to generate a pseudo-identifier so that an attacker cannot learn the actual identifiers. The pseudo-identifier could also change if, e.g., a counter is added. For instance, the wireless transmitter may keep an increasing counter. Furthermore, when a user wants to find his electronic device, the user (or the wireless transmitter) may encrypt (by means of the program running on the PC or the wireless transmitter) its identifier with a key that issued to that electronic device using the current counter as nonce. This is the pseudo- identifier of the user. Analogously, a pseudo-identifier for the electronic device can be generated. Then, the wireless transmitter transmits the pseudo-identifier and counter. When the electronic device receives the message, the electronic device verifies whether the result of decryption of the pseudo-identifier with the key issued by its owner using as nonce the counter in the message is equal to its device identifier and/or a user identifier. If it is, then the electronic device replies with the response signal and also updates in its memory the latest heard counter with the counter that was just received.

In this embodiment, the amount of energy available is limited, and therefore a further embodiment might be used. For instance, the electronic device may store a number of random tags (e.g. as provided by the user). When the user wants to find an electronic device, the user will enter one of the tags assigned to an electronic device. The wireless transmitter then will then include this tag in the tracking signal. An electronic device receiving this message will then only reply to the message, if it has the same tag in memory. In this case, the electronic device will subsequently also remove this tag from its memory since it is already used.

Instead of or in addition to the electronic devices responding with a response signal, they can also use the collected energy to provide local feedback, e.g. start a buzzer or start blinking LED, to assist the user in the location and identification of a physical object (i.e. electronic device).

The present invention can also be used to localize electronic devices already known by the user (e.g. localizing a misplaced keyfob). Alternatively, the present invention can be used to discover unknown electronic devices in unknown locations, e.g. lighting devices, HVAC (Heating, Ventilation and Air Conditioning) control panels in hotel meeting rooms, wireless printers, etc. Exchange of additional capability information can follow. This would enable auto-commissioning. Furthermore, the present invention can also be used to discover the location of mobile or portable devices, specifically, to assure the optimal powering by the wireless transmitter able to provide the strongest power over WiFi signal (i.e. the strongest tracking signal).

In another embodiment, particularly for power conservation, the electronic devices may be woken up by the system to start operation (e.g. backlight a screen on a control panel, start beaming/displaying, etc.) only after discovery of the tracking signal. In a further embodiment, a signal for that purpose may be emitted by a portable user device seeking connection with the surrounding electronic devices (e.g. a smartphone, tablet or laptop searching for a nearby wireless printer), or vice versa.

Thus, in summary, the present invention may be used for localization and/or tracking of any type of electronic devices, such as lighting system assets, portable or mobile devices, objects in a room or building provided with a kind of tag functioning as electronic device and thus enabling to find the object, etc. Devices that have a depleted battery or no battery may thus still be found, particularly using one and the same communication network that is used for power delivery and detection.

In the case where wireless power delivery is spatially selective, a search strategy may be used to provide devices in a particular area with sufficient power in the first place. If there are multiple power delivery devices, these devices can be coordinated. For instance, power delivery can be made in a combined manner with a challenge message, or in a first step devices may be charged in a search area and then in a second step a quick scan may be conducted. The results of the search by multiple devices can also be combined.

As the powering device knows where it has delivered power, it may also prime a receiver. Many different reception strategies are possible, like using one or more directional receiver(s) in combination with one power delivering station, or multiple omnidirectional receivers to pin-point the direction of the transmission. It is also possible to prime the receivers for the receipt of a particular message pattern, because it is known what needs to be received to improve the sensitivity.

Further, there is a possible interaction with the "charge and challenge" message (i.e. the tracking signal) and a corresponding response that allows for coordination between the searches. For example, a device identifier (and optionally the transmitter identifier) and a sequence number may be added into the powering transmission (i.e. the tracking signal). The response would then include the latter one or two allowing the position determination because the transmitter with the transmitter identifier knows where it sent that sequence number.

Further, user interaction is possible by having the user indicate an outline of where to search. For instance, if there are multiple RF power delivery devices, they can be coordinated to divide the search area between them for searching and power transmission (optionally including the transmitter identifier of the respective transmitter and the sequence number), meanwhile making sure that the directional power delivery does not interfere with one another. Further, the search and power transmission may optionally done in parallel. Receivers could be primed for receipt of a response when a search area is energized to make sure they e.g. know what message to receive so as to improve sensitivity.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. 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 element or other unit 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.

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