METHOD FOR THE LOCATION OF A BEACON BY ANGLES OF ARRIVAL

Abstract

A method for location of a beacon includes: executing R sequences, wherein R is a whole number equal to or greater than 2, each including reception by a first antenna network and a second antenna network of a signal originating from the beacon, wherein the signals of the R sequences are of different wavelengths; calculating a first estimation function for angles of arrival of the signal on the first antenna network and of a second estimation function for angles of arrival of the signal on the second antenna network; and executing a mutual correlation of the R first estimation functions and the R second estimation functions, for the respective determination of a first angle between the beacon and the first network, and of a second angle between the beacon and the second network.

Claims

1-11. (canceled)

12. A method for location of a beacon, comprising: executing R sequences, wherein R is a whole number equal to or greater than 2, each R sequence comprising: receiving by a first antenna network and a second antenna network a signal originating from the beacon, wherein the signals of the R sequences are of different wavelengths; calculating a first estimation function for angles of arrival of the signal on the first antenna network and of a second estimation function for angles of arrival of the signal on the second antenna network; mutually correlating the R first estimation functions and the R second estimation functions, for respective determining a first angle between the beacon and the first network, and a second angle between the beacon and the second network; a sequence comprising acquiring for the signal, by each receiver of the first receivers connected to first sensors of the first antenna network, at least one acquisition executed by a first receiver comprising a first phase for acquisition of the signal captured by one of the sensors in a pair of first sensors, followed by a second phase for acquisition of the signal captured by the other sensor of said pair, wherein the signal captured by the at least one first sensor is acquired during the first acquisition phase and during the second acquisition phase.

13. The method as claimed in claim 12, wherein acquisition by a first receiver comprises: estimating a frequency drift between the first receiver and the beacon, generating a vector comprising a phase and amplitude of the signal received by a first sensor connected to the first receiver, by the estimated drift, wherein the vectors are employed for calculation of the estimation functions.

14. A device for the location of a beacon, comprising: a first antenna network and a second antenna network configured to receive R signals with distinct carrier frequencies, originating from the beacon; and acquisition and calculation means configured to: calculate estimation functions for angles of arrival of the signals on the first antenna network and on the second antenna network, and correlate the estimation functions to determine a first angle between the beacon and the first network, and a second angle between the beacon and the second network; the acquisition and calculation means comprising: first receivers connected to first sensors on the first antenna network, configured to acquire the signals captured by the first sensors to which they are connected, and at least one switch for connection of a first receiver to one of the sensors of a pair of first sensors during a first phase for the acquisition of a signal, and to the other sensor of the pair during a second phase for the acquisition of the signal, wherein the switch is configured such that the signal captured by at least one first sensor is acquired during a first acquisition phase and during a second acquisition phase.

15. The location device as claimed in claim 14, wherein the acquisition and calculation means is configured to: estimate a frequency drift between a first receiver and the beacon, and generate vectors, wherein each vector comprises a phase and amplitude of a signal received by a first sensor connected to the first receiver, by the estimated drift.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0051] The purposes, advantages and characteristics of the method and device for the location of a beacon will be clarified by the following description, based upon the non-limiting forms of embodiment illustrated by the drawings, in which:

[0052] FIG. 1 shows a schematic representation of a device for the location of a beacon according to one form of embodiment of the invention, comprising a first and a second antenna network,

[0053] FIG. 2 shows a graph of two first estimation functions for angles of arrival of signals emitted by the beacon and incident on the first antenna network,

[0054] FIG. 3 shows a graph of two second estimation functions for angles of arrival of signals emitted by the beacon and incident on the second antenna network,

[0055] FIG. 4 shows a schematic representation of the first antenna network and of an acquisition and calculation unit connected to said first network,

[0056] FIG. 5 shows a schematic representation of the first antenna network during a first acquisition phase and a second acquisition phase, and

[0057] FIG. 6 shows a block diagram of steps in a method for the location of the beacon according to one form of embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0058] The object of the invention is the location of a beacon X in an environment which features a plurality of reflective elements, four of which being represented, for exemplary purposes, by reference symbols P.sub.11, P.sub.12, P.sub.21 and P.sub.22. In any environment, the reflective elements may be of different dimensions, as illustrated in FIG. 1.

[0059] The beacon X is configured to emit R signals (Sg.sub.i).sub.i=1 . . . R of distinct wavelengths (.sub.i).sub.i=1 . . . R, where R is a whole number equal to or greater than 2. In the interests of clarity, only two signals Sg.sub.1 and Sg.sub.2, of respective wavelengths .sub.1 and .sub.2, are represented in FIG. 1. The signals (Sg.sub.i).sub.i=1 . . . R emitted by the beacon X are reflected to a varying degree from the reflective elements, according to their wavelength. A disruptive element of dimensions close to the wavelength of a given signal will in fact specifically reflect said signal, but will only reflect a signal of a wavelength which differs substantially from its dimensions to a limited extent. Naturally, the dimensions of an element thus described are those of the surface of the element upon which the signal is incident.

[0060] Thus, in the example represented in FIG. 1: [0061] The reflective elements P.sub.11 and P.sub.12 strongly reflect the first signal Sg.sub.1, but only weakly reflect the second signal Sg.sub.2. The reflections of the second signal Sg.sub.2 from the reflective elements P.sub.11 and P.sub.12 are thus ignored. [0062] The reflective elements P.sub.21 and P.sub.22 strongly reflect the second signal Sg.sub.2, but only weakly reflect the first signal Sg.sub.1. The reflections of the first signal Sg.sub.1 from the reflective elements P.sub.21 and P.sub.22 are thus ignored.

[0063] A device DISP according to the invention permits the location of the beacon X. The device DISP specifically comprises: [0064] A first antenna network A.sub.1 comprising M sensors (C.sub.1j).sub.j=1 . . . M, where M is a whole number equal to or greater than 2. [0065] A second antenna network A.sub.2 comprising N sensors (C.sub.2k).sub.k=1 . . . N, where N is a whole number equal to or greater than 2.

[0066] Where they propagate in a direct path between the beacon X and the first antenna network A.sub.1, the first signal Sg.sub.1 and the second signal Sg.sub.2 are incident on the first antenna network A.sub.1 according to a first angle .sub.1. Where they propagate in a direct path between the beacon X and the second antenna network A.sub.2, the first signal Sg.sub.1 and the second signal Sg.sub.2 are incident on the second antenna network A.sub.2 according to a second angle .sub.2. A direct path is understood as a path upon which no obstacle is located.

[0067] Moreover: [0068] The first signal Sg.sub.1 is incident on the first antenna network A.sub.1 according to an angle a, where it is reflected from the reflective element P.sub.11. [0069] The second signal Sg.sub.2 is incident on the first antenna network A.sub.1 according to an angle b, where it is reflected from the reflective element P.sub.21. [0070] The first signal Sg.sub.1 is incident on the second antenna network A.sub.2 according to an angle c, where it is reflected from the reflective element P.sub.12. [0071] The second signal Sg.sub.2 is incident on the second antenna network A.sub.2 according to an angle d, where it is reflected from the reflective element P.sub.22.

[0072] The device DISP also comprises acquisition and calculation means (not represented in FIG. 1), comprising two units, each of which is connected to an antenna network A.sub.1, A.sub.2. An acquisition and calculation unit permits the calculation, for a given signal, of the probabilities of the angle of incidence of the signal on the antenna network to which it is connected. Naturally, as a result of reflective phenomena, a number of angles will have high probabilities of incidence.

[0073] FIGS. 2 and 3 illustrate estimation functions for angles of incidence. In the upper part of FIG. 2, an estimation function g.sub.11 is represented for angles of arrival of the first signal Sg.sub.1 on the first antenna network A.sub.1. It will be observed that the estimation function g.sub.11 features two spikes: a first spike for angle a, corresponding to the reflected path of the first signal Sg.sub.t from the reflective element P.sub.11; a second spike for the first angle .sub.1, corresponding to the direct path of the first signal Sg.sub.1 between the beacon X and the first antenna network A.sub.1.

[0074] In the lower part of FIG. 2, an estimation function g.sub.12 is represented for angles of arrival of the second signal Sg.sub.2 on the first antenna network A.sub.1. It will be observed that the estimation function g.sub.12 features two spikes: a first spike for the first angle .sub.1, corresponding to the direct path of the second signal Sg.sub.2 between the beacon X and the first antenna network A.sub.1; a second peak for angle b, corresponding to the reflected path of the second signal Sg.sub.2 from the reflective element P.sub.21.

[0075] In the upper part of FIG. 3, an estimation function g.sub.21 is represented for angles of arrival of the first signal Sg.sub.t on the second antenna network A.sub.2. It will be observed that the estimation function g.sub.21 features two spikes: a first spike for the second angle .sub.2, corresponding to the direct path of the first signal Sg.sub.t between the beacon X and the second antenna network A.sub.2; a second spike for angle c, corresponding to the reflected path of the first signal Sg.sub.t from the reflective element P.sub.12.

[0076] In the lower part of FIG. 3, an estimation function g.sub.22 is represented for angles of arrival of the second signal Sg.sub.2 on the second antenna network A.sub.2. It will be observed that the estimation function g.sub.22 features two spikes: a first spike for the second angle .sub.2, corresponding to the direct path of the second signal Sg.sub.2 between the beacon X and the second antenna network A.sub.2; a second spike for angle d, corresponding to the reflected path of the second signal Sg.sub.2 from the reflective element P.sub.22.

[0077] Accordingly, the estimation functions g.sub.11 and g.sub.12 both feature a spike for the first angle .sub.1, whereas the estimation functions g.sub.21 and g.sub.22 both feature a spike for the second angle .sub.2. Thus, by correlating the estimation functions g.sub.11 and g.sub.12, and respectively the estimation functions g.sub.21 and g.sub.22, it is possible to determine the first angle .sub.1, and respectively the second angle .sub.2.

[0078] FIG. 4 represents the first antenna network A.sub.1 and a first acquisition and calculation unit UT.sub.1 connected to said first network A.sub.1. In the example represented in FIG. 4, the first antenna network A.sub.1 comprises 15 first sensors (C.sub.1j).sub.j=1 . . . 15, and the first unit UT.sub.1 comprises 8 first receivers (R.sub.1p).sub.p=1 . . . 8. More generally, the first unit UT.sub.1 comprises S first receivers (R.sub.1p).sub.p=1 . . . S, where S is a whole number equal to or greater than 2, such that M=2S1.

[0079] The antenna network A.sub.1 comprises one connector, for example of the SMA type, per sensor C.sub.1j. The unit UT.sub.1 further comprises two connectors and one switch S.sub.p per receiver R.sub.1p, with the exception of one receiver (the 8.sup.th receiver R.sub.18 in the example represented in FIG. 4) which is only associated with a single connector. Accordingly, each receiver R.sub.1p is capable of being connected in an alternating manner to two different sensors C.sub.1j via its associated switch S.sub.p, with the exception of one of the receivers R.sub.18. From FIG. 4, it will be observed that only three wired links are represented: the connectors of the 1.sup.st receiver R.sub.11 are shown connected to the connector of the 3.sup.rd sensor C.sub.13 and to the connector of the 5.sup.th sensor C.sub.15; the connector of the 8.sup.th receiver R.sub.18 is shown connected to the connector of the 4.sup.th sensor C.sub.14.

[0080] FIG. 5 represents the states of the 15 first sensors (C.sub.1j).sub.j=1 . . . 15 in FIG. 4 during two acquisition phases. In a first acquisition phase Ph1, the switches (S.sub.p).sub.p=1 . . . 7 are in the state represented in FIG. 3, and the sensors connected to receivers are thus the sensors 4 to 11. In a second acquisition phase Ph2, the position of the switches (S.sub.p).sub.p=1 . . . 7 is modified, and the sensors connected to receivers are thus the sensors 1 to 4 and 12 to 15. It will be observed that the 4.sup.th sensor C.sub.14 is connected to the 8.sup.th receiver R.sub.18 during both the acquisition phases Ph1, Ph2.

[0081] The unit UT.sub.1 also comprises a local oscillator LO, which is capable of delivering a frequency f.sub.p to the first receivers (R.sub.1p).sub.p=1 . . . 8. Indeed, where a sensor C.sub.1j captures a signal Sg.sub.i of frequency f.sub.i originating from the beacon X, said signal Sg.sub.i undergoes the following processing in the receiver R.sub.1p which is connected to the sensor C.sub.1j. Firstly, the signal Sg.sub.i is mixed in parallel with two quadrature signals at a frequency f.sub.p to obtain components at frequencies f.sub.i, f.sub.p and f.sub.i+f.sub.p, and a component at an intermediate frequency |f.sub.if.sub.p|. Thereafter, a polyphase filter only permits the passage of the component at the intermediate frequency, which is lower than the initial frequency f.sub.i of the signal Sg.sub.i. Finally, this low-frequency component undergoes analog-to-digital conversion.

[0082] The unit UT.sub.1 also incorporates memories MEM1, MEM2, for the storage of the samples generated by the first receivers (R.sub.1p).sub.p=1 . . . 8, and a port PO, for example of the USB type, for the retrieval of the samples stored in the memories MEM1, MEM2. The unit UT.sub.1 also comprises calibration means CB for the acquisition channels, in order to standardize the acquisitions executed by the various receivers (R.sub.1p).sub.p=1 . . . 8.

[0083] The unit UT.sub.1 also comprises an emitter-receiver EMR which is capable of communicating with the beacon X, such that the receivers (R.sub.1p).sub.p=1 . . . 8 only acquire the signals (Sg.sub.i).sub.i=1 . . . R originating from the beacon X at the time of transmission thereof by the beacon X, rather than continuously, which would be an exceptionally energy-consuming arrangement. The beacon X transmits, for example, signals (Sg.sub.i).sub.i=1 . . . R in response to a query from the emitter-receiver EMR, or assumes the initiative and notifies the emitter-receiver EMR to this effect.

[0084] The unit UT.sub.1 also comprises a programmable logic circuit PLC, for example of the FPGA type (Field-Programmable Gate Array), for the control of the other components of the unit UT.sub.1.

[0085] Naturally, in a non-limiting form of embodiment, all the above-mentioned elements described with reference to the first antenna network A.sub.1 can be transposed to the second antenna network A.sub.2. A second acquisition and calculation unit (not represented in the figures) is connected to the second network A.sub.2, wherein said second unit comprises T second receivers (R.sub.2q).sub.p=1 . . . T, where T is a whole number equal to or greater than 2, such that N=2T1. Each second receiver R.sub.2q is capable of being connected in an alternating manner to two different sensors C.sub.2k via an associated switch, with the exception of one of the second receivers, which is connected to a single second sensor.

[0086] FIG. 6 represents the steps of a method METH for the location of the beacon X, according to a non-limiting embodiment of the invention. The method comprises a succession of R sequences (Seq.sub.i).sub.i=1 . . . R, wherein each sequence Seq.sub.i comprises the steps described hereinafter.

[0087] According to a step Em_Sg.sub.i in the sequence Seq.sub.i, the beacon X emits a signal Sg.sub.i of wavelength .sub.i. The wavelengths (.sub.i).sub.i=1 . . . R of the R signals (Sg.sub.i).sub.i=1 . . . R in the R sequences (Seq.sub.i).sub.i=1 . . . R are all different. The wavelengths (.sub.i).sub.i=1 . . . R are advantageously selected from the same order of magnitude as the conventional dimensions of the reflective elements in the environment in which beacon X is located. In an interior environment, for example, a signal Sg.sub.i of frequency 2.4 GHz is appropriate, as its wavelength of 12.5 centimeters is likely to correspond to the dimensions of certain objects in this environment. The signals (Sg.sub.i).sub.i=1 . . . R are, for example, continuous wave pulses, whether modulated or unmodulated.

[0088] According to a step Rec_Sg.sub.i in the sequence Seq.sub.i, the signal Sg.sub.i is captured by the first sensors (C.sub.1j).sub.j=1 . . . M of the first antenna network A.sub.1 and by the second sensors (C.sub.1k).sub.1=1 . . . N of the second antenna network A.sub.2.

[0089] According to a step Acq_Sg.sub.i in the sequence Seq.sub.i, acquisition of the signal Sgi is executed by the first receivers (R.sub.1p).sub.p=1 . . . S and the second receivers (R.sub.2q).sub.q=1 . . . T, connected respectively to the first antenna network A.sub.1 and to the second antenna network A.sub.2. Initially, the switches associated with the first receivers (R.sub.1p).sub.p=1 . . . S are configured such that the S first receivers (R.sub.1p).sub.p=1 . . . S are connected to S first sensors (C.sub.1v).sub.v=1 . . . S of the M first sensors (C.sub.1j).sub.j=1 . . . M. Likewise, initially, the switches associated with the second receivers (R.sub.2q).sub.q=1 . . . T are configured such that T second receivers (R.sub.2q).sub.q=1 . . . T are connected to T second sensors (C.sub.2v).sub.v=1 . . . T of the N second sensors (C.sub.2k).sub.k=1 . . . N.

[0090] The acquisition step Acq_Sg.sub.i comprises a first phase Ph1 in which each first receiver R.sub.1p acquires the signal Sg.sub.i captured by the first receiver C.sub.1v to which it is connected, and each second receiver R.sub.2q acquires the signal Sg.sub.i captured by the second receiver C.sub.2v to which it is connected.

[0091] Thereafter, the position of the switches associated with the first receivers (R.sub.1p).sub.p=1 . . . S and of the switches associated with the second receivers (R.sub.2q).sub.q=1 . . . T is modified. The first receivers (R.sub.1p).sub.p=1 . . . S are thus connected to S other first sensors (C.sub.1w).sub.w=1 . . . S of the M first sensors (C.sub.1j).sub.j=1 . . . M, and the second receivers (R.sub.2q).sub.q=1 . . . T are thus connected to T other second sensors (C.sub.2w).sub.w=1 . . . T of the N second sensors (C.sub.2k).sub.k=.sub.1 . . . N. Only one first sensor remains connected to the same first receiver, and one second sensor remains connected to the same second receiver.

[0092] Thereafter, the acquisition step Acq_Sg.sub.i comprises a second phase Ph2 in which each first receiver R.sub.1p acquires the signal Sg.sub.i captured by the first receiver C.sub.1w to which it is connected, and each second receiver R.sub.2q acquires the signal Sg.sub.i captured by the second receiver C.sub.2w to which it is connected.

[0093] Any sensors not used during the first acquisition phase and the second acquisition phase must be connected to 50-ohm resistors, in order to prevent the behavior thereof as reflectors, thereby distorting the radiation pattern of the other sensors.

[0094] As explained above, each acquisition of a signal Sg.sub.i of frequency f.sub.i originating from the beacon X comprises the following: [0095] a parallel mixing of the signal Sg.sub.i with two quadrature signals of frequency f.sub.p, in order to obtain components at frequencies f.sub.i, f.sub.p and f.sub.i+f.sub.p, and one component at an intermediate frequency |f.sub.if.sub.p|, [0096] filtering of components by a polyphase filter, in order to remove components at frequencies f.sub.i, f.sub.p and f.sub.i+f.sub.p, and retain only the component at the intermediate frequency, which is lower than the initial frequency f.sub.i of the signal Sg.sub.i, and [0097] an analog-to-digital conversion of the component at the intermediate frequency, in order to generate a series of samples.

[0098] According to a step Cal_g.sub.1i.sub._g.sub.2i in the sequence Seq.sub.i, a first estimation function g.sub.1i for angles of arrival of the signal Sg.sub.i on the first antenna network A.sub.1, and a second estimation function g.sub.2i for angles of arrival of the signal Sg.sub.i on the second antenna network A.sub.2, are calculated. These functions are generated from the generated samples, for example, by means of the above-mentioned MUSIC algorithm or a Beamforming Spatial Filtering algorithm.

[0099] It will observed that the Beamforming Spatial Filtering algorithm requires, as parameters, vectors comprising the phase and amplitude of each of the signals captured by the sensors of an antenna network. In one form of embodiment, in which the Beamforming Spatial Filtering algorithm is employed for the calculation of the estimation functions, each acquisition of a signal Sg.sub.i therefore comprises a step for the generation of a vector comprised of a phase and amplitude of the signal Sg.sub.i received.

[0100] In one form of embodiment, the phase and amplitude of the received signal Sg.sub.i are calculated by the application of a Fourier transform to the series of samples. The Fourier transform indeed permits the acquisition of a frequency spectrum for phase and a frequency spectrum for the amplitude of a signal. Naturally, in these frequency spectra, the ray corresponding to the signal Sgi must be distinguished from noise. However, if the local oscillators of the receivers and the local oscillator of the beacon are of limited stability, they are likely to show a mutual frequency drift. Acquisition of a signal Sg.sub.i by a receiver thus comprises a step for the estimation of the frequency drift between said receiver and the beacon X, preceding the step for the generation of the phase and amplitude vector. Identification of this drift permits the accurate location of the ray corresponding to the signal in the frequency spectra for phase and amplitude.

[0101] Thereafter, the method METH comprises, further to the R sequences (Seq.sub.i).sub.i=1 . . . R, a step Corr_g.sub.1i.sub._g.sub.2i for the correlation of the R first estimation functions (g.sub.1i).sub.i=1 . . . R, and for the correlation of the R second estimation functions (g.sub.2i).sub.i=1 . . . R. Correlation of the R first estimation functions (g.sub.1i).sub.i=1 . . . R permits the determination of a first angle .sub.i between the beacon X and the first network A.sub.1, whereas correlation of the R second estimation functions (g.sub.2i).sub.i=1 . . . R permits the determination of a second angle .sub.2 between the beacon X and the second network A.sub.2. A correlation is executed, for example, by the calculation, for each angle of a plurality of angles, of a mean for the probabilities associated with said angle by the estimation functions. The angle with the highest mean is thus the angle between the beacon X and the network considered. Indeed, the first estimation functions (g.sub.1i).sub.i=1 . . . R all feature a spike corresponding to the first angle .sub.i, whereas the second estimation functions (g.sub.2i).sub.i=1 . . . R all feature a spike corresponding to the second angle .sub.2.

[0102] Finally, the method comprises a step Loc_X for the location of the beacon X, from the first angle .sub.1 and the second angle .sub.2.

[0103] From the above description, a number of variants of the method and device for the location of a beacon can be inferred by a person skilled in the art, without departing from the scope of the invention defined by the claims.