WO2022117191A1

WO2022117191A1 - Determination of a position of a communication device

Info

Publication number: WO2022117191A1
Application number: PCT/EP2020/084460
Authority: WO
Inventors: Bruno Roberto FRANCISCATTO
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2020-12-03
Filing date: 2020-12-03
Publication date: 2022-06-09
Also published as: CN117044070A; EP4244951A1

Abstract

Embodiments of the invention relate to determining the position of a communication device, e.g. a UE. By broadcasting a Harvested Power (HP) parameter in a control signal a Line-of- Sight (LoS) signal can be identified and distinguished from multipath signals. Based on the LoS signal a distance to the communication device and an angle may be determined. The distance and the angle give the position of the communication device. The position of the communication device may thereby be determined using a single device for determining the position of a communication device. This means reduced implementation cost and complexity. Further, improved position accuracy is also possible implying improved Wireless Power Transfer (WPT) applications.

Description

DETERMINATION OF A POSITION OF A COMMUNICATION DEVICE

Technical Field

Embodiments of the invention relate to a device for determining a position of a communication device and to a wireless power transfer beacon comprising such a device. Furthermore, embodiments of the invention also relate to a communication device, corresponding methods and a computer program.

Background

In the recent years it has been noted a progress in the development and deployment of Internet of Things (loT) devices across different markets such as industry, consumer electronics, aviation, defence, etc. Each market has its own constraints and requirements. However, one common key parameter between these verticals is that the deployed device should have a long battery-life and may even be completely battery-less. The battery replacement cost and environment impact are the main reasons for this requirement. One possible solution to tackle the battery issue is the possibility of recharging the battery or completely replace it by energy harvesting or energy transfer techniques. In this respect there exists several possible energy sources, such as solar, mechanical, thermal, radio frequency (RF), etc.

For wireless energy transfer solution one possible application scenario is an indoor environment, e.g. room, where the user will enter with a smartphone which may automatically start charging without any action from the user, such as plugging a cable into the smartphone or placing the smartphone in a specific charging position. Currently the power required to charge a smartphone can be in the order of magnitude of 1W. To meet such requirements the use of Wireless Power Transfer (WPT) techniques have been proposed. However, transmitting high power wirelessly is not trivial since a high system efficiency is required with very directive antenna beamforming. Further, when using WPT an accurate estimation of the object's position is needed. The direction where the object might be positioned but also the distance to the object is therefore necessary.

Summary

An objective of embodiments of the invention is to provide a solution which mitigates or solves the drawbacks and problems of conventional solutions.

Another objective of embodiments of the invention is to provide a solution with improved positioning accuracy and reduced implementation cost compared to conventional solutions. The above and further objectives are solved by the subject matter of the independent claims. Further advantageous embodiments of the invention can be found in the dependent claims.

According to a first aspect of the invention, the above mentioned and other objectives are achieved with a device for determining a position of a communication device, the device being configured to: broadcast a wireless power transfer signal; receive a set of control signals from a communication device, wherein each control signal comprises a control message indicating an identity of the communication device and a harvested power associated with the wireless power transfer signal; identify a line-of-sight signal among the set of control signals based on the set of control signals; and determine a position of the communication device based on the identified line-of-sight signal.

The communication device may be a stationary communication device or a mobile communication device.

The wireless power transfer signal may be periodically broadcasted so that the position of the communication device can be updated. This may be particularly relevant when the communication device is a mobile communication device.

An advantage of the device according to the first aspect is that only a single device is needed for determining the position compared to conventional solutions which require a plurality of devices. This implies reduced implementation complexity and implementation cost. Further, by considering the harvested power at the communication device as a parameter the positioning accuracy may be improved compared to conventional solutions.

In an implementation form of a device according to the first aspect, each control message further indicates a clock signal associated with the harvested power.

An advantage with this implementation form is that the positioning accuracy is further improved as the identification of the line-of-sight signal is improved by also indicating clock signals in the control messages. In an implementation form of a device according to the first aspect, each control message is received in a link layer protocol.

An advantage with this implementation form is that the present solution may easily be implemented in existing protocols such as WiFi and Bluetooth Low Energy.

In an implementation form of a device according to the first aspect, each control message is embedded in a packet data unit payload.

In an implementation form of a device according to the first aspect, the device further being configured to determine a set of received signal strength indicators, RSSIs, based on the set of control signals, wherein each RSSI is associated with a control signal; and identify the line-of-sight signal based on the set of control signals and the set of RSSIs.

An advantage with this implementation form is that the line-of-sight signal can more accurately be identified.

In an implementation form of a device according to the first aspect, identify the line-of-sight signal further comprises compare for each RSSI an associated RSSI equivalent distance with a harvested power equivalent distance to identify the line-of-sight signal.

It may be understood that each RSSI value corresponds to a certain equivalent distance and each harvested power value corresponds to a certain equivalent distance. Hence, the corresponding equivalent distances may be compared so as to identify the line-of-sight signal.

An advantage with this implementation form is that the line-of-sight signal can be more easily identified.

In an implementation form of a device according to the first aspect, identify the line-of-sight signal further comprises identify a control signal among the set of the set of control signals having the minimum distance between the associated RSSI equivalent distance and the harvested power equivalent distance as the line-of-sight signal.

An advantage with this implementation form is that the line-of-sight signal is identified with higher probability.

In an implementation form of a device according to the first aspect, the device further being configured to determine an angle-of-arrival of the identified line-of-sight signal; and determine the position of the communication device based on the identified line-of-sight signal and its angle-of-arrival.

According to a second aspect of the invention, the above mentioned and other objectives are achieved with a wireless power transfer beacon for a communication system, the wireless power transfer beacon comprising a device according to any one of the preceding claims, and being configured to beam a wireless power transfer signal towards the communication device according to the determined position of the communication device.

An advantage of the wireless power transfer beacon according to the second aspect is that since only a single wireless power transfer beacon is needed implementation complexity and cost is reduced. Further, since the positioning accuracy is improved the power transfer is also improved as the direction of the power transfer beams are more correctly directed during power transfer.

According to a third aspect of the invention, the above mentioned and other objectives are achieved with a communication device for a communication system, the communication device being configured to: receive a wireless power transfer signal; determine a harvested power based on a conversion of the received wireless power transfer signal into a direct current power; and broadcast a set of control signals, wherein each control signal comprises a control message indicating an identity of the communication device and the determined harvested power. In an implementation form of a communication device according to the first aspect, the communication device further being configured to insert a clock signal associated with the determined harvested power into each control message.

An advantage with this implementation form is that the positioning accuracy is further improved as the identification of the line-of-sight signal is improved by also indicating clock signals in the control messages.

In an implementation form of a communication device according to the first aspect, each control message is transmitted in a link layer protocol.

In an implementation form of a communication device according to the first aspect, each control message is embedded in a packet data unit payload.

According to a fourth aspect of the invention, the above mentioned and other objectives are achieved with a method for a device for determining a position of a communication device, the method comprises broadcasting a wireless power transfer signal; receiving a set of control signals from a communication device, wherein each control signal comprises a control message indicating an identity of the communication device and a harvested power associated with the wireless power transfer signal; identifying a line-of-sight signal among the set of control signals based on the set of control signals; and determining a position of the communication device based on the identified line-of-sight signal.

The method according to the fourth aspect can be extended into implementation forms corresponding to the implementation forms of the device according to the first aspect. Hence, an implementation form of the method comprises the feature(s) of the corresponding implementation form of the device. The advantages of the methods according to the fourth aspect are the same as those for the corresponding implementation forms of the device according to the first aspect.

According to a fifth aspect of the invention, the above mentioned and other objectives are achieved with a method for a communication device, the method comprises... receiving a wireless power transfer signal; determining a harvested power based on a conversion of the received wireless power transfer signal into a direct current power; and broadcasting a set of control signals, wherein each control signal comprises a control message indicating an identity of the communication device and the determined harvested power.

The method according to the fifth aspect can be extended into implementation forms corresponding to the implementation forms of the communication device according to the third aspect. Hence, an implementation form of the method comprises the feature(s) of the corresponding implementation form of the communication device.

The advantages of the methods according to the fifth aspect are the same as those for the corresponding implementation forms of the communication device according to the third aspect.

The invention also relates to a computer program, characterized in program code, which when run by at least one processor causes said at least one processor to execute any method according to embodiments of the invention. Further, the invention also relates to a computer program product comprising a computer readable medium and said mentioned computer program, wherein said computer program is included in the computer readable medium, and comprises of one or more from the group: ROM (Read-Only Memory), PROM (Programmable ROM), EPROM (Erasable PROM), Flash memory, EEPROM (Electrically EPROM) and hard disk drive.

Further applications and advantages of the embodiments of the invention will be apparent from the following detailed description. Brief Description of the Drawings

The appended drawings are intended to clarify and explain different embodiments of the invention, in which:

- Fig. 1 illustrates general principals of embodiments of the invention;

- Fig. 2 shows a system according to an embodiment of the invention;

- Fig. 3 shows a flow chart of a method for a device for determining a position of a communication device according to an embodiment of the invention;

- Fig. 4 shows a flow chart of a method for a communication device according to an embodiment of the invention;

- Fig. 5 shows a block diagram of a device for determining a position of a communication device according to an embodiment of the invention;

- Fig. 6 shows a block diagram of a communication device according to an embodiment of the invention;

- Fig. 7 shows a sequence diagram according to an embodiment of the invention;

- Fig. 8 illustrates two alternative RF to DC conversion techniques that may be implemented in conjunction with embodiments of the invention;

- Fig. 9 illustrates a protocol format according to an embodiment of the invention;

- Fig. 10 shows a flow chart of a detailed algorithm for determining the position of a communication device according to an embodiment of the invention;

- Fig. 11 illustrates a reference database for the HP parameter as a function of the distance;

- Fig. 12 illustrates a reference database for the RSSI parameter as a function of the distance;

- Fig. 13 shows a graph in a polar representation of two control signals; and

- Fig. 14 shows a graph in a polar representation of the final position of a harvester.

Detailed Description

In typical indoor scenarios a single transmission from a communication device can generate multiple received signals by the receiver due to multipath effect. A receiver is not intrinsically able to differentiate which signal is a Line-of-Sight (LoS) and which one is from multipath. Hence, estimation of the position of the communication device is not trivial since each received signal could generate different results. In order to locate the communication device with only one beacon at least two parameters are usually necessary, i.e. the distance between the receiver and the communication device and the angle of direction to the communication device. Conventional solutions for indoor location are well known but each of them has their pros and cons regarding the trade-off between positioning accuracy vs number of transmitters sometimes also denoted beacons. Examples of conventional indoor location solutions are proximity location based on Received Signal Strength Indication (RSSI), Time Difference of Arrival (TDOA), and Angle of Arrival (AoA). In general, in order to achieve good accuracy the number of required beacons is high with conventional solutions.

Proximity location is based on the RSSI parameter which basically is the ratio between the received power divided by the transmitted power. This method is strongly dependent on the propagation environment and it is not possible to differentiate the LoS signal from the multipath signal using RSSI.

The TDOA solution is based on the measurement of difference of time of arrival of the same transmitted signal received by at least two beacons. This solution is able to provide a 2D or 3D location. However, at least 3 beacons are necessary for 2D localisation and 4 beacons for 3D localisation. Depending on the RF protocol used for the localization, e.g. Ultra-Wide Band (UWB), good accuracy can be achieved but the installation cost is high since at least 3 beacons are necessary to localise the object and a very precise synchronisation (in the order of nano seconds) between the beacons is mandatory. Additionally, the distance range may be quite limited using TDOA.

The AoA solution is based on the measurement of the phase difference between two consecutive elements of an antenna array. The difference in travelling time of the signal arrival at the receiver generates phase difference on each antenna of an antenna array and its neighbours. Using AoA for indoor positioning remains a good option if only the direction information is necessary since it provides the direction but no distance information. Additionally, the AoA solution is strongly dependent on the multipath behaviour since the receiver could see coherent reflections of the original incident signal coming from different angles.

From the above it is realised that locating a communication device or correspondingly to determine the position of a communication device is not trivial mainly due to the multipath propagation phenomenon. Consequently, one key factor in order to obtain accurate indoor positioning is to be able to differentiate the direct RF signal, i.e. LoS, from the multipath signal(s). Conventional indoor location techniques will not be able to differentiate the LoS signal from the multipath signals and their positioning algorithm will very likely generate inaccurate output resulting in poor accuracy. However, according to the present solution a novel technique for differentiating the LoS signal from multipath signals is provided. By using a Harvested Power (HP) parameter, an identity (ID) of the harvester, and optionally a transmission clock generation, the received signals are more suitable to be used for position estimation. The HP parameters indicates a measure of RF power that is converted from radiofrequency signals to DC power at the harvester. The harvester is able to broadcast a signal indicating the HP parameter and the ID of the harvester. The broadcasted signal will propagate and multipath signals will appear. Hence, the beacon will not only receive the LoS signal but also undirected signals due to multipath. Moreover, the position of an object can be determined with a single beacon thereby reducing installation costs and complexity. Further, the present solution is RF frequency protocol agnostic since it may be used in different protocols in the physical layer such as WiFi, Bluetooth Low Energy (BLE), etc.

The importance of differentiating the LoS signal from the multipath signals is highlighted in Fig. 1 which shows a harvester broadcasting a signal that will reach the beacon as a LoS signal and at least one multipath signal reflected against the obstacle. If the beacon would only use the information in the multipath signal, the estimation of the distance to the harvester and the angle of arrival will be erroneous. On the other hand a beacon according to embodiments of the invention is capable of separating the LoS signal from multipath signals thanks to the use of the HP parameter and the ID comprised or indicated in the broadcast signal of the harvester. Hence, all broadcast signals originating from the same harvester transmission will have the same measurement of HP and the same ID. All signals from the same broadcast transmission will have the same HP value since it is encoded in the framework protocol as the ID of the harvester.

Embodiments of the invention may be used in any indoor or outdoor applications in which the position of a harvester has to be determined or estimated. Especially, WPT applications where knowing the position of the harvester is necessary to beam the energy is suitable. Nevertheless, the solution can be extended to other applications that requires low-cost and practical location solution. Non-limiting examples of other potential applications are:

• Smart-homes: in general most of the smart-homes are equipped with a RF hub (e.g. a WiFi router, 3G/4G/5G relay, smart speakers, etc.), the beacon proposed could be potentially integrated to these existent RF hubs and portable or mobile devices like smartphones, tags, access cards/keys, could be upgraded with a RF harvester.

• Security RF access: with the increase of security aspects related to the different RF protocols available today, embodiments of the invention could be used as additional login security service that guarantees the access to a RF network, e.g. WiFi, GSM, Wireless Private Network, etc. For example, in an office meeting room that has state- of-art wireless audio/video systems, due to the confidentially, only people physically present in the room can have access to the different wireless networks. The beacon proposed in this invention may be located in the room as stand-alone device on embedded into another RF hub and each person would have a small smart-key/card with the harvester. Since the proposed apparatus is able to locate the harvesters, in this case, confirm that the object that belongs to a person is in the room, wireless access can be granted.

• Industry 4.0/industrial tracking: the necessity of locating objects in a real time and in a low-cost manner is one of the key requirements for the industry 4.0. Embodiments of the invention provides a reliable and low-cost indoor location approach that could be deployed in industrial sites.

• Data centres: some data centres require a reliable system that confirm how many server racks are present in a specific room but sometimes they need also the exact location of specific server racks. Embodiments of the invention could potentially to be used providing a low-cost and practical solution to be solve this problem.

Therefore, a system as illustrated in Fig. 2 according to embodiments of the invention is herein disclosed. The system comprises a device 100 for determining a position of a communication device 300 and the communication device 300 itself.

The device 100 for determining a position of a communication device 300 will also be referred to as a beacon 100. Hence, these expressions will be used interchangeably in this disclosure.

The beacon 100 may be a stand-alone device that can be placed on a wall, on a table or could also be hidden in a dropped ceiling. The beacon 100 may also be part of another device such as a base station or an Access Point (AP). In general terms the device 100 or beacon 100 is configured to generate a waveform signal that will power the communication device 300 or harvester 300 wirelessly. The device 100 or beacon 100 is also configured to receive a control signal from the communication device 300 or harvester 300 with at least information elements or parameters HP and ID.

The communication device 300 will also be referred to as a power harvester 300 or simply a harvester 300. Hence, these expressions will be used interchangeably in this disclosure. The harvester herein can be any general communication device such as a smartphone, a smartwatch, an loT device, a smart card/key, and any portable stationary electronic device. The beacon can be any of a WPT transmitter, a RF hub, WiFi router, smart speaker, and any wall-plugged device capable of generating RF signals. The harvester is capable of measuring a conversion of a received RF signal into a DC or AC power. The harvester 300 may be a stand-alone device or be embedded in any other suitable device, e.g. smartphones, smart-home devices, loT devices, a client device, etc. The client device in this disclosure includes but is not limited to: a UE such as a smart phone, a cellular phone, a cordless phone, a session initiation protocol (SIP) phone, a wireless local loop (WLL) station, a personal digital assistant (PDA), a handheld device having a wireless communication function, a computing device or another processing device connected to a wireless modem, an in-vehicle device, a wearable device, an integrated access and backhaul node (IAB) such as mobile car or equipment installed in a car, a drone, a device-to-device (D2D) device, a wireless camera, a mobile station, an access terminal, an user unit, a wireless communication device, a station of wireless local access network (WLAN), a wireless enabled tablet computer, a laptop-embedded equipment, an universal serial bus (USB) dongle, a wireless customerpremises equipment (CPE), and/or a chipset. In an Internet of things (IOT) scenario, the client device may represent a machine or another device or chipset which performs communication with another wireless device and/or a network equipment. The UE may further be referred to as a mobile telephone, a cellular telephone, a computer tablet or laptop with wireless capability. The UE in this context may e.g. be portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile device, enabled to communicate voice and/or data, via the radio access network, with another entity, such as another receiver or a server. The UE can be a station (STA), which is any device that contains an IEEE 802.11 -conformant media access control (MAC) and physical layer (PHY) interface to the wireless medium (WM). The UE may also be configured for communication in 3GPP related LTE and LTE-Advanced, in WiMAX and its evolution, and in fifth generation wireless technologies, such as NR.

The harvester 300 may be a stationary communication device or a mobile communication device. For practical reasons, a downlink (DL) may be defined as all communications protocol on the following direction from the beacon 100 to the harvester 300 and consequently uplink (UL) as all communications form the harvester 300 to the beacon 100.

According to embodiments of the invention and with reference to the system 500 shown in Fig. 2 a device 100 for determining a position of a communication device also known as a beacon 100 is herein disclosed. The device 100 is configured to broadcast a wireless power transfer signal 510. The device 100 is further configured to receive a set of control signals 520a, 520b,... , 520n from a communication device 300 in response to the transmission of the wireless power transfer signal 510. Each control signal 520n comprises a control message 520n' indicating an ID of the communication device 300 also known as a harvester 300 and a HP associated with the wireless power transfer signal 510. The device 100 is further configured to identify a LoS signal among the set of received control signals 520a, 520b,... , 520n based on the set of control signals 520a, 520b,... , 520n. The device 100 is further configured to determine a position of the communication device 300 based on the identified LoS signal. It is noted that only a single beacon 100 is needed in the system 500 to determine the position of the harvester 300.

Fig. 3 shows a flow chart of a corresponding method 200 for a beacon that e.g. may be executed by the beacon 100 as shown in Fig. 2. The method 200 comprises broadcasting 202 a wireless power transfer signal 510. The method 200 further comprises receiving 204 a set of control signals 520a, 520b,... , 520n from a communication device 300. Each control signal 520n comprises a control message 520n' indicating an ID of the communication device 300 and a HP associated with the wireless power transfer signal 510. The method 200 further comprises identifying 206 a LoS signal among the set of control signals 520a, 520b,... , 520n based on the set of control signals 520a, 520b,... , 520n. The method 200 further comprises determining 208 a position of the communication device 300 based on the identified LoS signal.

According to embodiments of the invention and with reference to the system 500 shown in Fig. 2 a communication device 300 also denoted a harvester 300 for a communication system 500 is herein also disclosed. The communication device 300 is configured to receive a wireless power transfer signal 510. The communication device 300 is further configured to determine a HP based on a conversion of the received wireless power transfer signal 510 into a direct current power. The communication device 300 is further configured to broadcast a set of control signals 520a, 520b,... , 520n, wherein each control signal 520n comprises a control message 520n' indicating an ID of the communication device 300 and the determined HP.

Fig. 4 shows a flow chart of a method 400 for a communication device that e.g. may be executed by the communication device 300 shown in Fig. 2. The method 400 comprises receiving 402 a wireless power transfer signal 510. The method 400 further comprises determining 404 a HP based on a conversion of the received wireless power transfer signal 510 into a direct current power. The method 400 further comprises broadcasting 406 a set of control signals 520a, 520b,... , 520n, wherein each control signal 520n comprises a control message 520n' indicating an ID of the communication device 300 and the determined HP.

The beacon 100 may in embodiments of the invention be comprised in a WPT beacon 600 for a communication system 500. The WPT beacon 600 is configured to beam a wireless power transfer signal 530 towards the harvester 300 according to the determined position of the harvester 300. Fig. 5 shows a block diagram of an exemplary WPT beacon 600 according to embodiments of the invention. The WPT beacon 600 may comprise: a WPT transmitter (TX) block 102, an antenna array 110, a Micro Controller Unit (MCU) 106, a Position Determination (PD) block 104 and a database 108, the latter comprising a real-time database and corresponding reference databases (see below). The WPT TX block 102 and the PD block 104 can share the same antenna array or have separate antenna arrays depending on operating frequency and/or application. The database 108 can be stored locally, e.g. being embedded in the beacon 100 or in the cloud or combined i.e. being partially embedded in the beacon 100 and in the cloud. The different blocks of the beacon 100 are coupled to each other using communication means known in the art.

The WPT TX block 102 of the WPT beacon 600 may comprise a frequency synthesizer or a VCO block, bi-directional channels with amplitude and phase variation coupled to the antenna array 110. This block is therefore responsible for creating the waveform signal that will power the harvester 300 wirelessly. The PD block 104 with its own MCU is responsible for demodulating the ID and the HP of each control message. The database 108 may be split into two parts, i.e. a reference database and a real-time database. The reference database is initially constructed based on empirical data and the real-time database stores the currently measurements of the PD parameters. The reference database stores the HP values.

Fig. 6 shows a block diagram of an exemplary harvester 300 according to further embodiments of the invention. The harvester 300 comprises: a WPT receiver (RX) block 302, a MCU 306, an antenna array 310, a RF TX block 304 and a load 308. The WPT RX block 302 additionally to providing power to the load 308, is also responsible for providing a measurement or an estimation of the amount of HP to the MCU 306. The MCU 306 also stores the ID of the harvester 300, and in embodiments generates a clock signal that will be sent for each broadcast transmission in each control message. The RF TX block 304 can operate at the same frequency as the WPT RX block 302 or it can operate at its own operating frequency which in the latter case implies its own antenna array (not shown). Finally, the RF TX block 304 is able to broadcast a control signal comprising a control message indicating the parameters, ID, HP and in embodiments a clock signal. The broadcasted signal will due to the multipath effect result in a set of control signals 520a, 520b,... , 520n at the beacon 100.

Fig. 7 shows a flow chart for determining a position of a harvester 300 according to yet further embodiments of the invention. In step I in Fig. 7, the WPT beacon 600 broadcasts a wireless power transfer signal 510 in WPT scan sweep mode in different directions, e.g. in an organized sequence or in a random sequence. Hence, the procedure starts with the WPT beacon 600 broadcasting energy by broadcasting wireless power transfer signal 510 in a scan sweep mode searching for harvesters able to convert RF power into DC power. The speed and angle step of the WPT scan sweep mode can e.g. be adjusted as a function of the RF transmitter operation frequency.

In step II in Fig. 7, the harvester 300 receives the wireless power transfer signal 510 from the WPT beacon 600 and converts the RF power of the received wireless power transfer signal 510 into DC power. The harvester 300 further measures or estimates the amount of HP derived from the wireless power transfer signal 510 to obtain the HP parameter herein used.

In step III in Fig. 7, the harvester 300 in response to reception of the wireless power transfer signal 510 broadcasts a control signal 520 comprising a control message 520n' indicating its own unique ID and the HP parameter. Additionally, for each broadcast transmission the harvester 300 increments an internal transmission clock. Hence, as previously mentioned in embodiments of the invention each control message 520n' further indicates a clock signal associated with the HP. The clock parameter is used by the WPT beacon 600 to separate different broadcast transmission of the harvester 300 from each other.

Due to the real-world propagation phenomenon, the WPT beacon 600 will not only receive a LoS signal but also one or more multipath signals, hence a set of control signals 520a, 520b, ... , 520n arrives at the WPT beacon 600.

In step IV in Fig. 7, based on the set of received control signals 520a, 520b,... , 520n and their respective control messages from the harvester 300, the WPT beacon 600 is capable of demodulating each received control signal and store information about the received control signal in a real-time database. For each received control signal from the harvester 300, the WPT beacon 600 is configured to demodulate the ID and the HP parameter. Further, the WPT beacon 600 also calculates a RSSI value and an AoA value for each received control signal and stores the values in the real-time database. For the same clock signal, the control signals in the set of control signals will very likely have the same ID, HP, but different AoA and RSSI values.

The WPT beacon 600 has to separate the LoS signal from the multipath signals in the set of control signals 520a, 520b,... , 520n, since the LoS signal is more reliable for position computation. Therefore, based on the received set of control signals 520a, 520b,... , 520n, the WPT beacon 600 is in embodiments of the invention configured to determine a set of RSSIs based on the set of control signals 520a, 520b,... , 520n. Each RSSI in the set of RSSIs is associated with a specific received control signal 520n. Based on the set of control signals 520a, 520b,... , 520n and the set of RSSIs the LoS signal may be identified among the set of control signals 520a, 520b,... , 520n. In embodiments of the invention, to identify the LoS signal further comprises compare for each RSSI an associated RSSI equivalent distance with a HP equivalent distance to identify the LoS signal. It has been realized that each RSSI value corresponds to a certain equivalent distance and each HP value corresponds to a certain equivalent distance. The equivalent distances for the RSSI value and the HP value may be obtained from the HP reference database and the RSSI reference database, respectively.

An non-limiting way of identify the LoS signal is to identify a control signal 520n among the set of the set of control signals 520a, 520b,... , 520n having the minimum distance between the associated RSSI equivalent distance and the harvested power equivalent distance as the LoS signal. This means that the distance d to the harvester 300 may be determined using the set of computed RSSIs. For example, in order to determine the LoS signal, for each sampled control signal, its RSSI equivalent distance is compared with the HP equivalent distance. By e.g. applying a Euclidean minimum absolute approach, the WPT beacon 600 can identify the RSSI candidate that has the estimated distance closest to the estimated HP distance. Based on this calculation, the WPT beacon 600 can confirm which signal is the LoS signal among the set of control signals 520a, 520b,... , 520n. It is noted that other methods than Euclidean minimum absolute approach may be used for identifying the LoS signal.

Moreover, based on the received set of control signals 520a, 520b,... , 520n, the WPT beacon 600 is in embodiments of the invention also configured to calculate the AoAs of the received set of control signals 520a, 520b,... , 520n. Therefore, by having identified the LoS signal previously the WPT beacon 600 can determine the corresponding AoA of the identified LoS signal. Hence, the distance d between the harvester 300 and the WPT beacon 600 has been determined together with the AoA which means that the position of the harvester 300 may be established.

The reference database that may be stored locally in the WPT beacon 600 and/or in a remote machine through the cloud may comprise three reference databases, i.e. a RSSI reference database, a HP reference database and an AoA reference database. Fig. 8 shows examples of a real time database and a HP reference database and a RSSI reference database. The real time database is illustrated in Fig. 8(a) with exemplary entries. For the purpose of the concept demonstration, in this case only two control signals 1 and 2 are shown but is not limited thereto. For each control signal the following entries are stored in the real time database: harvester ID, HP value e.g. in dBm, AoA value e.g. in degrees, RSSI value e.g. in dBm, and a transmission clock.

As can be observed, besides the fact that the WPT beacon 600 is capable of decoding parameters, ID, HP, AoA, RSSI, and clock, it is not enough to directly determine which signal is the LoS or multipath, especially when several signals are received.

The RSSI reference database in Fig. 8(b) initially stores a look-up table of empirical RSSI values versus distance where potentially the harvester 300 is located. By taking into account that the transmitted power P_t of the control signal is known, the WPT beacon 600 is capable of measuring the ratio of the power of the received control signal over the power of the transmitted control signal, P_r/P_t. Therefore, the RSSI can be calculated, since this parameter is the ratio of P_r/P_t. Since, P_r and P_t are known and e.g. based on the Friis equation, for each RSSI value an equivalent distance between the WPT beacon 600 and the harvester 300 may be calculated.

The HP reference database in Fig. 8(c) initially stores a look-up table of empirical HP values versus distance where potentially the harvester 300 is located. In this case the difference is that the P_tand P_r are reversed, i.e. the P s from the WPT beacon 600 and the P_r is at the harvester 300.

The AoA reference database stores a look-up table of AoA values versus angle the direction where the harvester 300 potentially located. In the WPT beacon 600, e.g. an embedded software algorithm may compare real-time measurement of the three parameters RSSI, HP and AoA against the values in the reference databases. As an output, the position of the harvester 300 is hence determined as previously described.

The reference databases may have initial values originated from empirical calculations. However, in embodiments of the invention the values of the database may be based on real world measurements. Also, a calibration process for the database could be implemented to create a baseline between the empirical database and the real-world measurements for improved accuracy. In step V in Fig. 7, the WPT beacon 600 directs a beam for WPT at the harvester 300. Since the WPT beacon 600 with high accuracy has established the position of the harvester 300 the wireless powering of the harvester 300 can be made efficiently.

In step VI in Fig. 7, the harvester 300 receives the directed beam and converts the power in the beam to DC power for powering one or more loads. The converted power may e.g. be used for charging a re-chargeable device and/or directly powering a power consumer of the harvester 300.

The above procedure in Fig. 7 may be repeated in a periodic or a non-periodic manner in order to make sure that the harvester 300 is at the same position or has moved if the harvester 300 is a mobile harvester 300.

In the following disclosure each of the parameters HP, RSSI and AoA will be more thoroughly described and explained in the context of the present solution.

The harvester 300 may comprises a circuit capable of converting RF power into DC power. Once received by the antenna array 310, the RF signal from the WPT beacon 600 may be injected at the input of a rectifier 312 where the RF signal is converted into a DC power. Depending on the topology of the rectifier 312, e.g. half-wave or full-wave, the rectifier 312 is able to convert single or both sides of a sinusoidal signal, as shown in Fig. 9(a) and 9(b). Schottky diodes and transistors are the most used converters in the art. Typical rectifier topologies based on Schottky diodes are shown in 9(a) which shows the single diode topology for half-wave and Fig. 9(b) shows a voltage multiplier topology for full-wave. Once the RF to DC conversion has been performed, a Power Management Module (PMM) (not shown in the Figs.) may be needed in order to boost the voltage level to an acceptable level for charging and/or managing an energy storage element, e.g. a capacitor, a supercapacitor, a rechargeable battery, etc.

The amount of available power delivered to the load 308 of the harvester 300 is dependent on different parameters, such as described in the following equation:

where, P_T is the WPT transmitted power, rj_ant and D_ant are the efficiency and directivity of the receiver/harvester antenna, respectively. The wavelength is A and the distance between the transmitter (i.e. WPT beacon 600) and receiver (i.e. harvester 300) is d. Finally, RF is the DC conversion efficiency RF-DC of the rectifier 312 and TJDC is the DC-DC conversion efficiency. DC

There exists multiple RSSI definitions in the art. For convenience the RSSI may herein be defined as the ratio between the received power by the WPT beacon 600 and the power level of the transmitted signal by the harvester 300. However other definitions of the RSSI may be used in conjunction with embodiments of the invention. It is also noted that the RF channel characteristics, such as power, frequency, etc. of the UL (harvester to WPT beacon 600) is in general different from the one in the DL to avoid interference.

The transmitted power by the harvester Pt_Harv is known by the system, the amount of received power by the beacon Pr_bea is dependent on the path loss. Based on RSSI measurements, an estimation of the distance d between harvester 300 and the beacon 100 could be calculated. However, this estimation is not reliable due to the incertitude related to the multipath. In other words, if the beacon 100 would rely only on the RSSI measurement, it would not be able to differentiate the direct signal (i.e. LoS) from a multipath signal.

The PD block 104 of the WPT beacon 600 is capable of sampling the received signal from the antenna array. These measurements are sampled by taking a number of phase and amplitude measurement at precise intervals. This process is known as In-phase and Quadrature sampling - IQ sampling. For each element of the antenna array, IQ samples are acquired. One can calculate the angle of arrival 0 as following:

where is <t> the phase difference between two elements of the antenna array, A is the wavelength and da is the distance between the elements of the antenna array.

Moreover, Fig. 10 illustrates a proposed packet framework for a harvester 300 according to embodiments of the invention. The packet framework presented herein is based on the standard packet of BLE version 5.1 , which includes direction finding information in the Constant Tone Extension (CTE). It is noted that the present packet framework may be based on other packet formats and is therefore not limited to BLE version 5.1. As disclosed in Fig. 10, each control message 520n' may be transmitted and received in a link layer protocol of a protocol format. The link layer protocol may comprise a Packet Data Unit (PDU) header, PDU payload, a Message Integrity Check (MIC) and a Cyclical Redundancy Check (CRC). In embodiments of the invention, each control message 520n' may be embedded in a PDU payload of the link layer protocol as disclosed in Fig. 10. Hence, any of parameters ID, HP, and clock signal may be embedded in the PDU payload according to such embodiments.

In order to validate the performance of the present solution the following system has been implemented in the downlink, i.e. from WPT beacon 600 to harvester 300: operation frequency = 5.8 GHz, transmitter power = 24.5 dBm, transmitter antenna gain = 15.6 dBi, receiver antenna gain = 5 dBi, harvester conversion efficiency (i.e. RF/DC + DC/DC) = 39%. In the uplink i.e. from harvester 300 to WPT beacon 600: operation frequency = 2.4 GHz, transmitter power = 20 dBm, transmitter antenna gain = 0 dBi, and receiver antenna gain = 0 dBi.

Fig. 11 illustrates the reference database for the HP parameter as a function of the distance, i.e. the x-axis shows the distance between the beacon 100 and the harvester 300 in meters and the y-axis shows the amount of power harvested in dBm. As disclosed in Fig. 11 by considering that the transmitted power P_t of the WPT beacon signal is known, the harvester 300 is capable of measuring the received signal P_r to obtain parameter HP. Since, P_rand P_rare known and e.g. derived based on the Friis equation, for each HP an equivalent distance between the WPT beacon 600 and the harvester 300 may be calculated.

Fig. 12 illustrates the reference database for the RSSI parameter as a function of the distance, i.e. the x-axis shows the distance between the beacon 100 and the harvester 300 in meters and the y-axis shows the RSSI measurement in dBm. As disclosed in Fig. 12 by considering that the transmitted power P_t of the control signal is known, the WPT beacon 600 is capable of measuring the ratio P_r/P_t. Since, as previously mentioned these powers are known and e.g. derived based on the Friis equation, for each RSSI an equivalent distance between WPT beacon 600 and the harvester 300 may be calculated.

Fig. 13 shows a graph in a polar representation, i.e. in angle ° and x distance in m, of first (“Signal 1”) and second (“Signal 2”) control signals and its respective calculations of distance based on HP and RSSI parameters. As may be observed in Fig. 13, based on two received control signals (Signal 1 and 2), the WPT beacon 600 is not able to differentiate directly which signal is the LoS signal and which is a multipath signal, neither to define the exact position or direction of the harvester 300. Further, it may be observed an important discrepancy between the estimated distances for each parameter RSSI and HP. The algorithm will continue the process flow in order to identify the LoS signal and then calculate the position of the harvester 300. In other words, the algorithm will apply the different steps described in order to present a first result, where each control signal is plotted as per the measurement. Any distance calculation to determine the position of the harvester 300 in intermediate steps may be erroneous. However, once the PD algorithm converges to a final calculation, the correct position of the harvester 300 may be found.

Fig. 14 shows a graph in a polar representation of the final position of the harvester 300 generated by the WPT beacon 600. It may be observed that the algorithm has identified the signal denoted “Signal 1” (see Fig. 13) as the LoS signal. As derived from Fig. 14 a single device 100 is able to calculate the distance between itself and the harvester 300 and the angle of arrival of the incident LoS signal. The precise localization of the harvester 300 is feasible since the LoS signal has been correctly identified.

Table 1 below shows some differences of the present solution compared to conventional solutions. As seen in Table 1 using RSSI technique for locating indoor objects such as a communication device 300 is not a suitable option, since for each received signal (i.e. LoS or multipath signals) the value of the RSSI can be very different, consequently different distance estimations will be obtained. The AoA technique offers only the information about the angle of direction of the received signal and no information about the distance. The TDOA technique is one of the most accurate solution for indoor location, but it requires at least 3 beacons increasing the implementation cost considerably. However, with the present solution only a single beacon is needed.

Table 1 : performance comparison.

Furthermore, any method according to embodiments of the invention may be implemented in a computer program, having code means, which when run by processing means causes the processing means to execute the steps of the method. The computer program is included in a computer readable medium of a computer program product. The computer readable medium may comprise essentially any memory, such as a ROM (Read-Only Memory), a PROM (Programmable Read-Only Memory), an EPROM (Erasable PROM), a Flash memory, an EEPROM (Electrically Erasable PROM), or a hard disk drive.

Moreover, it is realized by the skilled person that embodiments of the device 100 for determining a position of a communication device and the communication device 300 comprises the necessary communication capabilities in the form of e.g., functions, means, units, elements, etc., for performing the solution. Examples of other such means, units, elements and functions are: processors, memory, buffers, control logic, encoders, decoders, rate matchers, de-rate matchers, mapping units, multipliers, decision units, selecting units, switches, interleavers, de-interleavers, modulators, demodulators, inputs, outputs, antennas, amplifiers, receiver units, transmitter units, DSPs, MSDs, TCM encoder, TCM decoder, power supply units, power feeders, communication interfaces, communication protocols, etc. which are suitably arranged together for performing the solution.

Especially, the processor(s) of the device 100 for determining a position of a communication device and the communication device 300 may comprise, e.g., one or more instances of a Central Processing Unit (CPU), a processing unit, a processing circuit, a processor, an Application Specific Integrated Circuit (ASIC), a microprocessor, or other processing logic that may interpret and execute instructions. The expression “processor” may thus represent a processing circuitry comprising a plurality of processing circuits, such as, e.g., any, some or all of the ones mentioned above. The processing circuitry may further perform data processing functions for inputting, outputting, and processing of data comprising data buffering and device control functions, such as call processing control, user interface control, or the like. Finally, it should be understood that the invention is not limited to the embodiments described above, but also relates to and incorporates all embodiments within the scope of the appended independent claims.

Claims

1. A device (100) for determining a position of a communication device (300), the device (100) being configured to: broadcast a wireless power transfer signal (510); receive a set of control signals (520a, 520b,... , 520n) from a communication device (300), wherein each control signal (520n) comprises a control message (520n') indicating an identity (ID) of the communication device (300) and a harvested power associated with the wireless power transfer signal (510); identify a line-of-sight (LoS) signal among the set of control signals (520a, 520b, ... , 520n) based on the set of control signals (520a, 520b,... , 520n); and determine a position of the communication device (300) based on the identified line-of- sight (LoS) signal.

2. The device (100) according to claim 1 , wherein each control message (520n') further indicates a clock signal associated with the harvested power.

3. The device (100) according to claim 1 or 2, wherein each control message (520n') is received in a link layer protocol.

4. The device (100) according to claim 3, wherein each control message (520n') is embedded in a packet data unit payload.

5. The device (100) according to any one of the preceding claims, further configured to determine a set of received signal strength indicators, RSSIs, based on the set of control signals (520a, 520b,... , 520n), wherein each RSSI is associated with a control signal (520n); and identify the line-of-sight (LoS) signal based on the set of control signals (520a, 520b,... , 520n) and the set of RSSIs.

6. The device (100) according to claim 5, wherein identify the line-of-sight (LoS) signal further comprises compare for each RSSI an associated RSSI equivalent distance with a harvested power equivalent distance to identify the line-of-sight (LoS) signal.

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7. The device (100) according to claim 6, wherein identify the line-of-sight (LoS) signal further comprises identify a control signal (520n) among the set of the set of control signals (520a, 520b,... , 520n) having the minimum distance between the associated RSSI equivalent distance and the harvested power equivalent distance as the line-of-sight (LoS) signal.

8. The device (100) according to any one of the preceding claims, further configured to determine an angle-of-arrival (AoA) of the identified line-of-sight (LoS) signal; and determine the position of the communication device (300) based on the identified line- of-sight (LoS) signal and its angle-of-arrival (AoA).

9. A wireless power transfer beacon (600) for a communication system (500), the wireless power transfer beacon (600) comprising a device (100) according to any one of the preceding claims, and being configured to beam a wireless power transfer signal (530) towards the communication device (300) according to the determined position of the communication device (300).

10. A communication device (300) for a communication system (500), the communication device (300) being configured to: receive a wireless power transfer signal (510); determine a harvested power based on a conversion of the received wireless power transfer signal (510) into a direct current power; and broadcast a set of control signals (520a, 520b,... , 520n), wherein each control signal (520n) comprises a control message (520n') indicating an identity (ID) of the communication device (300) and the determined harvested power.

11. The communication device (300) according to claim 10, further configured to insert a clock signal associated with the determined harvested power into each control message (520n').

12. The communication device (300) according to claim 10 or 11 , wherein each control message (520n') is transmitted in a link layer protocol.

13. The communication device (300) according to claim 12, wherein each control message (520n') is embedded in a packet data unit payload.

14. A method (200) for a device (100) for determining a position of a communication device, the method (200) comprising: broadcasting (202) a wireless power transfer signal (510); receiving (204) a set of control signals (520a, 520b,... , 520n) from a communication device (300), wherein each control signal (520n) comprises a control message (520n') indicating an identity (ID) of the communication device (300) and a harvested power associated with the wireless power transfer signal (510); identifying (206) a line-of-sight (LoS) signal among the set of control signals (520a, 520b,... , 520n) based on the set of control signals (520a, 520b,... , 520n); and determining (208) a position of the communication device (300) based on the identified line-of-sight (LoS) signal.

15. A method (400) for a communication device (300), the method (400) comprising: receiving (402) a wireless power transfer signal (510); determining (404) a harvested power based on a conversion of the received wireless power transfer signal (510) into a direct current power; and broadcasting (406) a set of control signals (520a, 520b,... , 520n), wherein each control signal (520n) comprises a control message (520n') indicating an identity (ID) of the communication device (300) and the determined harvested power.

16. A computer program with a program code for performing a method according to claim 14 or 15 when the computer program runs on a computer.