Positioning system based on distributed transmission and reception of wi-fi signals

This application claims the benefit of U.S. Provisional Patent Application 62/787,310, filed Jan. 1, 2019, whose disclosure is incorporated herein by reference.

Embodiments described herein relate generally to wireless networks, and particularly to systems and methods for wireless positioning within a wireless network environment.

Techniques that utilize wireless communication signals to perform indoor positioning based on wireless signals were previously proposed in the patent literature. For example, U.S. Patent Application Publication 2017/0212210 describes a time-reversal positioning system includes a storage storing first data representing channel impulse responses derived from probe signals sent from a plurality of positions and second data representing coordinates of the positions. A data processor determines a position of a terminal device based on the stored channel impulse responses and a time-reversed signal determined based on a time-reversed version of a channel impulse response that is estimated based on a channel probing signal sent from the terminal device.

As another example, U.S. Pat. No. 10,031,209 describe a method in which a first distance between a first node and a target node is computed based on a first time-of-flight (ToF) of a communication sequence between the first node and the target node. A second distance between a second node and the target node is computed based on a second ToF of the communication sequence between the first node and the target node, as recorded by the second node. A location of the target node is determined based on the first distance and the second distance.

PCT patent application Publication WO2016/065368 describes systems and methods for determining a location of user equipment (UE) in a wireless system can comprise receiving reference signals via a location management unit (LMU) having two or more co-located channels, wherein the two or more co-located channels are tightly synchronized with each other and utilizing the received reference signals to calculate a location of the UE. Some systems may include multichannel synchronization with a standard deviation of less than or equal 10 ns. Some systems may include two LMUs, with each LMU having internal synchronization, or one LMU with tightly synchronized signals.

An embodiment of the present invention includes a method for estimating a location of a target Wireless Local-Area Network (WLAN) device, the method including obtaining relative locations of three or more WLAN devices. Respective distances are measured between each of the WLAN devices and the target WLAN device. The location of the target WLAN device is estimated based on the locations of the WLAN devices and on the distances between the WLAN devices and the target WLAN device, wherein measuring a distance between a WLAN device and the target WLAN device includes (a) sending a first WLAN signal by a transmitter of the WLAN device and detecting a first leakage signal by a receiver of the WLAN device, (b) detecting the first WLAN signal by a receiver of the target WLAN device and responsively sending a second WLAN signal by a transmitter of the target WLAN device, and detecting a second leakage signal by the receiver of the target WLAN device, (c) detecting the second sent WLAN signal by the receiver of the WLAN device, (d) calculating a first time difference between a time the second WLAN signal was sent and a time the first leakage signal was detected, (e) calculating a second time difference between a time the first WLAN signal was sent and a time the second leakage signal was detected, and (f) subtracting the second time difference from the first time difference to obtain a time-of-flight that corresponds to the distance between the WLAN device and the target WLAN device.

In some embodiments, obtaining the relative locations of the three or more WLAN devices includes (a) obtaining distances among the three or more WLAN devices (b) calculating the relative locations based on the relative distances among the three or more WLAN devices.

In some embodiments, obtaining the distances among the three or more WLAN devices includes calculating each distance, between a first WLAN device and a second WLAN device, by (i) sending a first WLAN signal by a transmitter of the first WLAN device and detecting a first leakage signal by a receiver of the first WLAN device, (ii) detecting the first WLAN signal by a receiver of the second WLAN device and responsively sending a second WLAN signal by a transmitter of the second WLAN device, and detecting a second leakage signal by the receiver of the second WLAN device, (iii) detecting the second sent WLAN signal by the receiver of the first WLAN device, (iv) calculating a first time difference between a time the second WLAN signal was sent and a time the first leakage signal was detected, (v) calculating a second time difference between a time the first WLAN signal was sent and a time the second leakage signal was detected, and (vi) subtracting the second time difference from the first time difference to obtain a time-of-flight that corresponds to the distance between the first WLAN device and the second WLAN device.

In an embodiment, estimating the location of the target WLAN device further includes: (a) detecting, by at least one of the three or more WLAN devices that is further configured as a Wi-Fi radar, a radar-derived location of a user of the target WLAN device, and (b) corroborating the radar-derived location of the user with the location measured using the three or more WLAN devices.

In other embodiments, the three or more WLAN devices are an access point and two repeaters, or three repeaters.

There is additionally provided, in accordance with another embodiment of the present invention, a method for calculating a distance between first and second Wireless Local-Area Network (WLAN) devices, the method including sending a first WLAN signal by a transmitter of the first WLAN device and detecting a first leakage signal by a receiver of the first WLAN device. The first WLAN signal is detected by a receiver of the second WLAN device and responsively a second WLAN signal is sent by a transmitter of the second WLAN device, and a second leakage signal is detected by the receiver of the second WLAN device. The second sent WLAN signal is detected by the receiver of the first WLAN device. A first time difference is calculated between a time the second WLAN signal was sent and a time the first leakage signal was detected. A second time difference is calculated between a time the first WLAN signal was sent and a time the second leakage signal was detected. The second time difference is subtracted from the first time difference to obtain a time-of-flight that corresponds to the distance between the first WLAN device and the second WLAN device.

There is further provided, in accordance with another embodiment of the present invention, an apparatus for estimating a location of a target Wireless Local-Area Network (WLAN) device, the apparatus including three or more WLAN devices which are configured to obtain their relative locations, wherein each of the WLAN devices is further configured to measure a respective distance between the WLAN device and the target WLAN device, so as to estimate the location of the target WLAN device based on the locations of the WLAN devices and on the distances between the WLAN devices and the target WLAN device, wherein each of the WLAN devices is configured to measure a distance between the WLAN device and the target WLAN device by: (i) sending a first WLAN signal by a transmitter of the WLAN device and detecting a first leakage signal by a receiver of the WLAN device, (ii) detecting the first WLAN signal by a receiver of the target WLAN device and responsively sending a second WLAN signal by a transmitter of the target WLAN device, and detecting a second leakage signal by the receiver of the target WLAN device, (iii) detecting the second sent WLAN signal by the receiver of the WLAN device, (iv) calculating in a processor a first time difference between a time the second WLAN signal was sent and a time the first leakage signal was detected, (v) calculating a second time difference between a time the first WLAN signal was sent and a time the second leakage signal was detected, and (vi) subtracting the second time difference from the first time difference to obtain a time-of-flight that corresponds to the distance between the WLAN device and the target WLAN device.

These and other embodiments will be more fully understood from the following detailed description of the embodiments thereof, taken together with the drawings in which:

Indoor positioning using Wi-Fi signals may be used for various applications, such as optimizing a deployment of multiple access points (APs), and to analyze occupancy and traffic volume of humans carrying Wi-Fi enabled personal devices, such as smartphones. Such Wi-Fi enabled devices are also called hereinafter “target Wireless Local-Area Network (WLAN) devices.”

However, Wi-Fi based positioning solutions, which use measured time-of-flight signals between WLAN transmitters and receivers, have limited accuracy. The inaccuracy may result from, for example, delays related to how the AP functions, such as between a time of request to send a packet and the actual time the packet is sent, and/or between actual time of arrival of the packet and the time its detection is registered in the receiver.

An AP is a device that creates a WLAN in a designated area, such as inside a building. An AP typically transmits and receives wireless communication signals to and from WLAN stations (e.g., smartphones and laptops) in the designated area. A common communication standard in use with APs is the IEEE 802.11 standard family for Wi-Fi communication using ultra-high radio frequencies, typically between 1 GHz and 10 GHz.

Embodiments of the present invention that are described hereinafter provide techniques for WLAN systems comprising two or more WLAN devices (e.g., an AP and a repeater) which, using the disclosed techniques on top of their standard use in communication, can measure a distance between the WLAN devices, with highly accurate results, by automatically cancelling the aforementioned delays existing with nominally functioning WLAN devices.

Some embodiments of the present invention provide methods of use and systems comprising three or more WLAN devices which, on top of their standard use, function as (a) accurate Wi-Fi positioning systems of Wi-Fi enabled devices, and optionally (b) a Wi-Fi radar to detect location and movements of physical objects, such as a human subject. Use (b) is also called hereinafter “detecting a radar-derived location of a user of the target WLAN device.”

The disclosed systems can perform either positioning or radar sensing within a designated area (i.e., in the surroundings of the three or more WLAN devices). In some embodiments, the system performs both positioning and radar sensing, in order to, for example, improve positioning reliability of moving targets, such as humans, who carry a Wi-Fi enabled device. Such positioning, which is corroborated using two different methods, may improve robustness in challenging positioning applications.

In some embodiments of the present invention, both the transmitter and the receiver of an AP and a repeater of the system utilize a same Wi-Fi channel, whereby the receiver of an AP is able to receive both the AP's (or the repeater's) own transmitter packets and packets from a Wi-Fi enabled device (e.g., from a station (STA) or a from a smartphone), and compare the time differences between receptions with high accuracy as part of a disclosed high-accuracy positioning method. Furthermore, the transmitter and the receiver operate in parallel, and by removing the need to switch between transmission and reception phases (e.g., states), the AP (or the repeater) can perform positioning measurements at higher rates.

For the disclosed positioning techniques, there is no need for timing synchronization between the transmitter and the receiver of the AP or the repeater. Nor is clock synchronization between transmitter and receiver of the AP or the repeater mandatory, though it may improve positioning accuracy. Typically, the disclosed positioning technique uses fine timing measurement (FTM) packets, but other packet types can be used as well. In some embodiments, the AP used is radar-sensing capable, and which includes timing and clock synchronization, as described below. Such an AP that uses WLAN packets for radar sensing is described in U.S. patent application Ser. No. 16/550,232, filed Aug. 25, 2019, entitled “Wi-Fi Radar Sensing,” which is assigned to the assignee of the present patent application and whose disclosure is incorporated herein by reference.

In radar mode, the disclosed AP device transmits sequences of Wi-Fi channel-sounding packets, e.g., Null Data Packets (NDPs) such as 802.11AX NDP packets, and receives respective sequences of NDPs, also named hereinafter “echoes,” that are physically reflected or scattered by objects in the designated area. The embodiments described herein refer mainly to NDPs by way of example. Generally, however, any other suitable type of WLAN packet, channel-sounding packets or otherwise, can be used for radar processing.

To estimate a range (i.e., a distance) from the AP to a target that causes the echoes, the disclosed AP in use includes synchronization circuitries, so that the same AP device that makes the transmission can analyze the synchronously received echo signals in order to detect moving targets by detecting Doppler shifts.

To measure the very low Doppler shifts, carrier frequency drift and/or jitter between the transmit and receive circuitries of the radar-sensing capable AP are zeroed by driving an RF transmit circuitry and an RF receive circuitry of the AP with an identical RF clock signal.

Typically, each of the disclosed systems comprises a root AP and one or more repeaters. In some embodiments, the processor in the root AP is programmed in software containing a particular algorithm that enables the processor to conduct each of the processor-related steps and functions outlined above. In general, however, any processor can be used for conduct each of the processor-related steps and functions outlined herein, including, by way of example, any of the processors comprised in any of the WLAN devices, or a remote processor (e.g., a cloud processor).

The disclosed techniques provide accurate positioning capabilities to APs using WLAN signals, which may be applied as a standalone solution or in combination with Wi-Fi radar sensing.

is a block diagram that schematically illustrates a Wi-Fi positioning systemthat is further configured as a Wi-Fi radar, in accordance with an embodiment that is described herein. Systemcomprises a root wireless communication access point (AP)that is further configured as a Wi-Fi radar. In the present example, APoperates in accordance with an IEEE Standard of the 802.11 family. In the shown embodiment, root APcommunicates with a repeater, but in general root APcommunicates with two or more repeaters, such as with a repeaterof system, as described below. Repeaterhas transmission and reception capabilities but lacks dedicated radar-sensing capabilities.

APcomprises one or more transmit antennasand one or more receive antennas. The transmit antennas and receive antennas may be the same, or different, antennas. Antennastransmit transmission beams(and the transmit antennas of repeatertransmit transmission beams) that are directed toward the repeater(s) (and back to the root AP).

In the uplink direction, APreceives, via antennasin a WLAN receiver, uplink transmissions (not shown) from one or more repeaters, such as repeater, and extracts information sent to APfrom repeater(s) (in case of repeater, sent () by a transmitterafter receiverof repeaterreceives signals from AP).

The disclosed layout is capable of performing the disclosed distance measurement protocol that begins when root APtransmittersends a packet that triggers the measurement sequence. When repeaterreceiverreceives the trigger packet, repeaterreturns transmission. The distance measurement sequence includes:

The sequence is described in detail in. The measured distance is subsequently used for accurate positioning of Wi-Fi enabled devices, as described in.

After running this sequence several times, removing problematic results, and averaging the remaining results, the distance provided gives an accuracy of up to several centimeters (cm).

Subtracting the longest time difference measured by the two WLAN devices with the time it takes the packet yields the clock difference between devices. Clock synchronization is required, for example, in real time Audio/Video applications.

In radar mode of root AP, WLAN receiverreceives echoesof transmission beams, also termed hereinafter “echo taps.” An echo tap has a time delay due to the accumulated propagation duration of beamto humanand of its echoback to the receiver. In order to perform Wi-Fi radar detection, WLAN transmitterand WLAN receiverare synchronized in time by a timing-synchronization signal: at the beginning of each transmission of an NDP sequence(seen in inset), WLAN transmittersends a timing-synchronization signalto WLAN receiverof AP. The timing-synchronization signal is applied by a synchronization circuitryover an electrical interface.

As further seen in an inset, NDP sequencesare sent by WLAN transmitteronly when allowed by the regular communication stream load, i.e., sent between sequences carrying WLAN communication. In an embodiment, the WLAN transmitter is configured to transmit the communication packets interleaved between the channel-sounding packets, and the WLAN receiver is configured to receive WLAN communication packets from one or more WLAN stations (STAs) interleaved between the echo packets.

WLAN transmitterof root APtransmits NDP sequenceswithout beamforming for the purpose of channel estimation, and therefore NDP sequencesare transmitted more or less omnidirectionally. NDP sequencesand the respective sequences of echoes (not shown) are analyzed by a processorof APto perform radar detection of a human.

Using channel impulse response (CIR) characterization, a delay between a timing of a measured leakage tapand a measured echo tap produced by human is used by processorto estimate the distance of humanfrom AP. The ability of APto detect and analyze echois a prerequisite for estimating a range to human, and it depends on the capability of APto identify micro-Doppler signatures of human.

As noted above, detection of micro-Doppler shifts requires zero drift and/or jitter between RF carrier frequencies of WLAN transmitterand WLAN receiver. The zero drift and/or jitter in an RF frequency is achieved using a single RF carrier frequency source, embodied by a circuitry, that simultaneously drives the two circuitries with synchronized RF clock signals. Typically, circuitryis realized using a single Voltage-Controlled Crystal Oscillator (VCXO) local oscillator (LO).

In some embodiments, WLAN receiverestimates a Multiple-Input Multiple-Output (MIMO) N×N (e.g., 4×4=16 elements) channel configuration between a set of transmit and receive antennas of AP. The MIMO is used to estimate direction and also to improve angular resolving power to separate between targets. The MIMO is also used to improve the tracking estimation of a target object and its Doppler shift estimate. Using MIMO gives an effect of SNR enhancement.

In some embodiments, some of the functions of the APs, e.g., some or all of the functions of processorsand/or, may be carried out by a general-purpose processor, which is programmed in software to carry out the functions described herein. The software may be downloaded to the processor in electronic form, over a network, for example, or it may, alternatively or additionally, be provided and/or stored on non-transitory tangible media, such as magnetic, optical, or electronic memory. In particular, processorruns a dedicated algorithm as disclosed herein, including in, that enables processorto perform the disclosed steps, as further described below.

is a graph that schematically illustrates a method to derive a distance between two WLAN devices of Wi-Fi positioning systemof, in accordance with an embodiment that is described herein. The initial output of the disclosed technique is a net time of flight between root APto repeater, i.e., after all internal latencies (i.e., device related delays) are taken into account, as described below. The time of flight is converted to distance, which by this method is derived to an accuracy of several centimeters, by multiplying it by the speed of light.

The same method can be applied to obtain the distance between APand repeater, and the distance between repeaterand repeater, which are required for systemto position a Wi-Fi enabled device, as described in.

The disclosed derivation of the distance between root APand repeaterbegins with transmitterof root APsending () at a time Ta packet that triggers the measurement sequence. Root receiverdetects () AP's own transmission (i.e., a leakage packet) at a time T. When repeaterreceiverdetects () the sent packet at a time T, repeaterstarts transmitting () at T, e.g., after an unknown delay, a sequence from its side. Repeaterreceiverdetects () its own transmission (i.e., a leakage packet) at a time T. At a time T, root receiver detects () the packet sent by repeaterresponsively to root AP's own transmission, completing the round trip of the packets.

Each WLAN device (i.e., APand repeater) then calculates (e.g., using processorsand) the time difference between arrival of the leakage packet and the respective packet sent by the other WLAN device, i.e., times (T−T) and (T−T). Each WLAN device also records the time of transmission for its packet (i.e., times Tand T) and both WLAN devices share their measurements and timers.

Subtracting one WLAN device time difference from the second WLAN device time difference and dividing by 2 gives the time it takes for one packet to go from one transmitter to the other (T−T), i.e., of the net time of flight from root APto repeater:(T3−T2)=(T6−T5)=((T6−T2)−(T5−T3))/2=(Diff1−Diff2)/2.

The distance between APand repeateris given by:Distance_AP20_REPEATER_22=(Diff1−Diff2)·c/2where c is the speed of light.

Another useful result of the above calculation is the time offset between root APclock to repeaterclock, Δ_clock:Δ_clock=(T6−T2)=Diff1.

is a graph that schematically shows combined Wi-Fi positioning and radar sensing by the Wi-Fi positioning systemof, in accordance with an embodiment that is described herein. Using substantially the same time windows for the two applications saves air time and corroborates positioning of humans carrying Wi-Fi enabled devices, obtained by the Wi-Fi positioning method described in, in dense physical and communication environments.

As seen in, almost immediately after receiving () leakage packets, the root receiver receives () echo packets, which were reflected from targets, such as moving humans. Using the echo packets and analysis of micro Doppler signatures, APidentifies range and direction to moving targets, as described in the aforementioned U.S. patent application Ser. No. 16/550,232. If the same humans are carrying a Wi-Fi enabled device, APmay tag these as a corroborated detection (achieved using the two independent detection methods).

In, radar sensing is performed using the same packets transmitted for the distance measurements. However, dedicated packets may be sent by APfor radar sensing use only.