A WIRELESS SENSING METHOD

Abstract

There is herein provided a provided a method of wireless sensing that can include, at a transmitter which is a component of a transceiver device, transmitting a wireless signal such that the transmitted wireless signal is scattered by an object so as to produce a scattered signal, at a receiver which is a component of the transceiver device, receiving the scattered signal, performing processing on the wireless signal before it is transmitted and/or on the received scattered signal, the processing including an indication of self-coupling occurring at the transceiver device, following the processing, using the received signal to determine information relating to the object, the information including one or more of: a location of the object; a direction of movement of the object; or a speed of the object.

Claims

1. A method of wireless sensing, the method comprising: at a transmitter which is a component of a transceiver device, transmitting a wireless signal such that the transmitted wireless signal is scattered by an object so as to produce a scattered signal, at a receiver which is a component of the transceiver device, receiving the scattered signal, performing processing: on the wireless signal before the wireless signal is transmitted, or on the received scattered signal, or both on the wireless signal before the wireless signal is transmitted and on the received scatter signal, wherein the processing comprises an indication of an extent to which self-coupling is occurring at the transceiver device; following the processing, using the received scattered signal to determine information relating to the object, the information comprising one or more of: a location of the object, a direction of movement of the object, or a speed of the object.

2. The method as claimed in claim 1, further comprising making one or more measurements of the self-coupling at the transceiver device from the transmitter to the receiver.

3. The method as claimed in claim 1, wherein the processing comprises Null-Space Projection (NSP).

4. The method as claimed in claim 1, further comprising: transmitting the wireless signal from a second transmitter such that the transmitted wireless signal is scattered by an object so as to produce a scattered signal; and receiving the scattered signal at a second receiver, wherein the second transmitter and the second receiver are components of the transceiver device and are located on a second aerial of the transceiver device.

5. The method as claimed in claim 1, further comprising multiplying the received scattered signal by a precoding digital spatial filter.

6. The method as claimed in claim 1, the method further comprising multiplying the received scattered signal by a postcoding digital spatial filter.

7. The method as claimed in claim 5, wherein the precoding digital spatial filter comprises eigenvectors of a self-coupling channel function.

8. The method as claimed in claim 7, wherein the eigenvectors are obtained by single-value decomposition of a self-coupling channel function.

9. A wireless sensing transceiver device comprising: a transmitter for transmitting a wireless signal such that the transmitted wireless signal is scattered by an object; a receiver for receiving a signal comprising the scattered signal; a processor for performing processing on: the transmitted wireless signal prior to transmission, or the received signal, or both the transmitted wireless signal prior to transmission and the received signal, wherein the processing comprises an indication of an extent to which self-coupling is occurring at the wireless sensing transceiver device, and wherein the processor is configured to use the processed signal to determine information relating to the object, the information comprising one or more of: a location of the object, a direction of movement of the object, or a speed of the object.

10. The method as claimed in claim 6, wherein the postcoding digital spatial filter comprises eigenvectors of a self-coupling channel function.

11. The method as claimed in claim 10, wherein the eigenvectors are obtained by single-value decomposition of a self-coupling channel function.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Specific embodiments of the disclosure will now be described in detail, for illustration only, with reference to the appended drawings, in which:

[0021] FIG. 1 is a schematic representation of a the method according to the disclosure.

[0022] FIG. 2 is a schematic representation of a time impulse response obtained according to an embodiment of the disclosure.

DETAILED DESCRIPTION

[0023] A MIMO system according to the disclosure is shown generally at 1 in FIG. 1. The MIMO system 1 comprises a router 2 located in a room in a house. The router 2 contains a first aerial 3 and a second aerial 4. The first aerial 3 has a Wi-Fi transmitter 5 and a Wi-Fi receiver 6. The second aerial 4 has a Wi-Fi transmitter 7 and a Wi-Fi receiver 8.

[0024] Embodiments of the present disclosure address, inter alia, a problematic phenomenon known as self-interference. When a transmitter transmits a signal, a portion of the transmitted signal is received by neighboring receiver(s). This occurs because, for example, the transmitted signal reflects from permanent or temporary discontinuities in the atmosphere in the vicinity of the transmitter aerial. The greater the impedance mismatch between the aerial and the atmosphere, the greater the self-interference. Embodiments of the disclosure address this problem by multiplying the signal to be transmitted by a first spatial filter. The resulting signal is then transmitted by both transmitter 5 and transmitter 7. The transmitted signal is scattered from an object 9 (which in this case is a person) in the room. The scattered signal is then received by receivers 6 and 8. The received signal is then multiplied by a second spatial filter. The second spatial filter is related to the first spatial filter. In addition to the scattered signal, receivers 6 and 8 receive the above-described self-interference signals, i.e. reflections of the transmitted signal from discontinuities in the atmosphere. The combined effect of the first and second spatial filters is to remove this self-coupling component from the received signal, leaving only the portion of the received signal which was scattered from the object 9.

[0025] The resulting signal is then analyzed. In particular, the time impulse response of the signal is analyzed. The distance between the receivers 6 and 8 and the object can be estimated from the time at which a peak is seen in the time impulse response. In other words, the time lag between transmission of the signal from transmitters 5 and 7 and reception of the signal at receivers 6 and 8. The sooner a peak is seen, i.e. the smaller the time lag, the closer the object is to the receiver. Furthermore, the time impulse response is measured continuously. A variation in the time impulse response over time indicates that the object is moving. If the variation is such that the time lag between transmission and reception is decreasing, it can be deduced that the object is moving closer to the receivers 6 and 8. If the time lag between transmission and reception is increasing, it can be deduced that the object is moving away from the receivers 6 and 8.

[0026] FIG. 2 shows a schematic plot of the response of a transceiver performing the method of an embodiment of the disclosure against the distance between the transceiver and the object (in this case a person). Distance (time-of flight) runs right to left on the horizontal axis. The receiver response is on the vertical axis. The person is running away from the transceiver (not shown). The person is shown at two locations: 0.75 m from the transceiver and at 4.5 m from the transceiver. It can be seen that the response decreases with increasing separation.

[0027] Time gating is used in receiving the signal at receivers 6 and 8. In particular, the receivers only accept an input signal within a predetermined time window. This ensures that the received signal originates from the scattered transmitted signal and not from e.g. an echo of a previously transmitted signal.

[0028] The signal processing involving the first and second spatial filters will now be described mathematically.

[0029] Consider a router having two antennae (1 and 2) each with a transmitter and receiver. In use, self-coupling (i.e. self-coupling echo) will occur. In particular, the signals transmitted from the transmitter on antenna 1 with be received by the receiver on antenna 1 and also by the receiver on antenna 2. Similarly, the signals transmitted from the transmitter on antenna 2 with be received by the receiver on antenna 1 and also by the receiver on antenna 2. This self-coupling can be represented by the self-coupling matrix:

[00001]$H_{\mathrm{aa}}=\left[\begin{array}{cc}{h}_{11}& h_{12}\\ h_{21}& h_{22}\end{array}\right]$ [0030] where h.sub.ij is the self-coupling of antenna j with antenna i; in particular: [0031] h.sub.11 is the coupling from transmitter on antenna 1 to the receiver on antenna 1; [0032] h.sub.22 is the coupling from transmitter on antenna 2 to the receiver on antenna 2; [0033] h.sub.21 is the coupling from transmitter on antenna 1 to the receiver on antenna 2; [0034] h.sub.12 is the coupling from transmitter on antenna 2 to the receiver on antenna 1.

[0035] Embodiments of the present uses null space projection to remove this self-coupling from the signal received the receiver on antenna 1. This is achieved by precoding the signal to be transmitted from transmitter on antenna 1 using the spatial filter F.sub.a and postcoding the received signal using the spatial filter G.sub.a.

[0036] The two spatial filters F.sub.a and G.sub.a are designed such that:

G.sub.aH.sub.aaF.sub.ax0

[0037] Thus, the combined effect of the spatial filters is to reduce the self-coupling component of the received signal to zero. The filters are designed as follows:

[0038] Firstly, H.sub.aa is decomposed into its eigenvectors and values via singular value decomposition. In particular:

[0039] SVD(H.sub.aa)=U.sub.aa.sub.aaV.sub.aa, where U.sub.aa and V.sub.aa are unitary matrices containing the eigenvectors and .sub.aa is a diagonal matrix containing the eigenvalues.

[0040] F.sub.a is obtained using the eigenvector unitary matrix V.sub.aa as follows:

[00002]$F_a=V_{\mathrm{aa}}*T_a=\left[\begin{array}{cc}{v}_{11}& v_{12}\\ v_{21}& v_{22}\end{array}\right]\left[\begin{array}{c}0\\ 1\end{array}\right]$

[0041] G.sub.a is obtained using the eigenvector unitary matrix U.sub.aa as follows:

[00003]$G_a=W_a*U_{\mathrm{aa}}^H=\left[\begin{array}{cc}1& 0\end{array}\right]\left[\begin{array}{cc}{u}_{11}^{*}& u_{21}^{*}\\ u_{12}^{*}& u_{22}^{*}\end{array}\right]$

where H is the Hermitian (equivalent to transpose conjugate) and * is the conjugate operator.

[0042] The above values for spatial filters F.sub.a and G.sub.a meet the above-mentioned condition:

G.sub.aH.sub.aaF.sub.aX0

[0043] The total received signal at the receiver of antenna 1 is:

[00004]$y=G_a\left(H_{\mathrm{aa}}{F}_a{x}_a+H_{\mathrm{ab}}{F}_b{x}_b+n_r\right)=\stackrel{0}{\stackrel{}{G_a{H}_{\mathrm{aa}}{F}_a}}{x}_a+G_a{H}_{\mathrm{ab}}{F}_b{x}_b+G_a{n}_r$

[0044] As can be seen from the equation immediately above, the self-coupling term (i.e. the component containing H.sub.aa) has been reduced to zero. This means that the self-coupling component of the received signal has been removed by the combined effect of the spatial filters F.sub.a and G.sub.a.