WO2018115322A1

WO2018115322A1 - Method and system for evaluating a distance between an identifier and a vehicle, associated onboard system and identifier

Info

Publication number: WO2018115322A1
Application number: PCT/EP2017/084160
Authority: WO
Inventors: Eric Leconte
Original assignee: Valeo Comfort And Driving Assistance
Priority date: 2016-12-21
Filing date: 2017-12-21
Publication date: 2018-06-28
Also published as: FR3060766B1; FR3060766A1

Abstract

A method for evaluating a distance (d) between an identifier (20) and a vehicle (10) comprises the following steps: - for each frequency among a plurality of frequencies, measuring an amplitude and a phase on receiving an electromagnetic signal exchanged between the identifier (20) and the vehicle (10) at the frequency concerned; - constructing an autocorrelation matrix on the basis of the amplitudes and phases measured; and - evaluating said distance (d) by processing the autocorrelation matrix. An evaluation system and an associated onboard system and identifier are also described.

Description

FIELD OF THE INVENTION The present invention relates to the evaluation of the distance between an identifier and a vehicle.

It relates more particularly to a method and a system for evaluating a distance between an identifier and a vehicle, as well as an associated embedded system and identifier.

BACKGROUND

We know (especially under the name PEPS for "Passive Entry

- Passive Starf) systems in which a feature of a vehicle (typically the unlocking of vehicle doors) is activated when an identifier (worn by the user of the vehicle) is sufficiently close to the vehicle.

This type of system therefore requires evaluating the distance between the identifier and the vehicle.

In order to be able to use various types of electronic apparatus as an identifier, even when such an electronic apparatus is not specifically designed for this purpose, an attempt has been made to evaluate the distance between the identifier and the vehicle on the basis of electromagnetic signals used elsewhere to exchange data between the identifier and the vehicle.

In the communication systems used today, however, these electromagnetic signals generally have high frequencies (for example of the order of 2.4 GHz in Bluetooth® technology) that do not lend themselves to conventional evaluation techniques. the distance (as the so-called RSSI technique for "Received Signal Strength Indication") because of anisotropy problems and the frequent presence of reflected signals.

OBJECT OF THE INVENTION

In this context, the present invention proposes a method for evaluating a distance between an identifier and a vehicle, characterized in that it comprises the following steps:

for each frequency among a plurality of frequencies, measuring an amplitude and a phase in reception of an electromagnetic signal exchanged between the identifier and the vehicle at the frequency concerned;

- construction of an autocorrelation matrix on the basis of amplitudes and measured phases;

evaluating said distance by processing the autocorrelation matrix.

The distance between the identifier and the vehicle is thus evaluated by means of a method which takes into account the different paths taken by the electromagnetic signals and which therefore gives an accurate result even when relatively high frequencies are used.

For example, the autocorrelation matrix is processed using a high-resolution method (or subspace method); this treatment can include the following steps:

determining a noise subspace associated with the autocorrelation matrix;

for a plurality of possible delays, determining a measurement of the projection in the noise subspace of a vector constructed on the basis of the possible delay concerned;

- selection of possible delays for which said measurement takes the lowest values;

- evaluation of said distance on the basis of the possible possible delays.

According to other characteristics that can be envisaged as optional (and therefore not limiting):

said distance is evaluated by means of the shortest of said selected possible delays;

the frequencies of said plurality of frequencies are included in the 2.4 GHz frequency band;

said plurality of frequencies comprises more than 5 frequencies;

said electromagnetic signals are exchanged between a first communication module fitted to the vehicle and a second communication module fitted to the identifier;

the first communication module and the second communication module are designed to establish a wireless data exchange link.

The invention also proposes an on-board vehicle system comprising: an electromagnetic signal receiving circuit adapted to measure, for each frequency among a plurality of frequencies, an amplitude and a phase of the electromagnetic signal received at the frequency concerned;

an electronic control unit designed to construct an autocorrelation matrix on the basis of the measured amplitudes and phases, and to evaluate the distance separating the identifier and an emitter of the electromagnetic signal by processing the autocorrelation matrix.

In this embodiment, the measurements of the electromagnetic signal and the processing of the measurements made are performed within the vehicle.

The invention also proposes an identifier comprising:

an electromagnetic signal receiving circuit adapted to measure, for each frequency among a plurality of frequencies, an amplitude and a phase of the electromagnetic signal received at the frequency concerned;

a control unit designed to construct an autocorrelation matrix on the basis of the measured amplitudes and phases and to evaluate the distance separating the identifier and an emitter of the electromagnetic signal by processing the autocorrelation matrix.

According to this variant, the measurements of the electromagnetic signal and the processing of the measurements made are carried out within the identifier; the evaluated distance can then be transmitted to the vehicle (possibly in encrypted form), for example via the aforementioned wireless data exchange link.

The invention finally proposes a system for evaluating a distance between an identifier and a vehicle, comprising:

The receiving circuit may be located within the vehicle or in the identifier. The control unit can be located in the vehicle or in the identifier. When the receiving circuit and the control unit are located in two different objects, the amplitudes and the measured phases can be transmitted from the object equipped with the reception circuit to the object equipped with the control circuit, for example via the aforementioned wireless data exchange link.

DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT

The following description with reference to the accompanying drawings, given as non-limiting examples, will make it clear what the invention consists of and how it can be achieved.

In the accompanying drawings:

- Figure 1 schematically shows the main elements of a system in which the invention can be implemented; and

FIG. 2 represents a method for evaluating the distance separating an identifier and a vehicle.

Figure 1 shows schematically the main elements of a system in which the invention can be implemented.

Such a system comprises a vehicle 10, here a motor vehicle, and an identifier 20, for example a vehicle access key or badge 10 (or, alternatively, a user terminal, such as a mobile phone or a smartphone - or "smartphone" according to the English application commonly used, provided with rights of access to the vehicle 10).

The vehicle 10 is equipped with an on-board (electronic) system which notably comprises an electronic control unit 11 and a communication module 12.

The electronic control unit 11 comprises for example a microprocessor and at least one memory, for example a rewritable non-volatile memory. The memory notably stores program instructions which, when executed by the microprocessor, enable the electronic control unit 11 to implement various functionalities, and in particular the method described below with reference to FIG. 2. The memory also stores values or parameters used during these methods, for example measured amplitude and phase values Α ,, Φ, (as explained later).

As a variant, the electronic control unit 1 1 could be made in the form of a specific application integrated circuit (or ASIC for "Application Specifies Integrated Circuit") or a programmable logic circuit (such as a programmable gate array or FPGA for "Field Programmable Gate Arra").

The communication module 12 is designed to establish a wireless data exchange link with other electronic devices, here a connection type "Bluetooth Low Energy (or" BLE "). The communication module 12 is therefore especially designed to send and receive electromagnetic signals (typically of greater than 1 MHz or even 500 MHz), here in the 2.4 GHz band.

The identifier 20 is generally worn by a user of the vehicle 10 and allows the control of certain functionalities of the vehicle 10 (for example the unlocking of the doors of the vehicle 10), especially when approached from the vehicle 10. The identifier 20 may optionally further comprising control buttons, with which the user can control at least some of the aforementioned features or other features of the vehicle 10.

The identifier 20 comprises a control unit 21 and a communication module 22.

The control unit 21 is for example made by means of a microprocessor and at least one memory, for example a rewritable non-volatile memory. The memory notably stores program instructions which, when executed by the microprocessor, enable the control unit 21 to implement certain methods, in particular data exchange methods between the identifier 20 and the control unit. electronic control unit 1 1, as shown below. The memory also stores values or parameters used during these processes.

As a variant, the control unit 21 could be made in the form of a specific application integrated circuit.

The communication module 22 is designed to establish a wireless data exchange link (here of the "Bluetooth Low Energy" or "BLE" type) with other electronic devices, in particular with the electronic control unit 1 1 of the vehicle 10 via the communication module 12 mentioned above, the communication module 22 is also designed to transmit and receive electromagnetic signals (typically with a frequency greater than 1 MHz, or even 500 MHz), here in the band to 2.4 GHz. Thanks to the wireless data exchange link thus established between the communication module 12 of the vehicle 10 and the communication module 22 of the identifier 20, data can be exchanged between the electronic control unit 1 1 of the vehicle 10 and the control unit 21 of the identifier 20.

The electromagnetic signals exchanged between the communication modules 12, 22 may furthermore be used to evaluate the distance d between the identifier 20 and the vehicle 10 as explained at present.

FIG. 2 represents a method for evaluating the distance d between the identifier 20 and the vehicle 10 (precisely the distance between the communication module 22 of the identifier 20 and the communication module 12 of the vehicle 10) .

This method starts in step E2 at which the control unit 21 of the identifier 20 commands the communication module 22 to transmit electromagnetic signals having successively N different frequencies f (these frequencies being noted in the following, f ₂ ,

Typically more than 10 different frequencies are used (ie, N is greater than 10), for example between 50 and 100 different frequencies (ie N is between 50 and 100). Each of these frequencies f, however, is included in the same frequency band (in this case the 2.4 GHz frequency band), the frequencies f being for example between 2.4 GHz and 2.480 GHz. The communication module 22 can use a constant reference phase during these successive transmissions.

Step E2 is for example implemented on reception by the control unit 21 (via the communication module 22) of a specific instruction from the electronic control unit 11 (or upon receipt of a another type of signal emitted by the communication module 12 of the vehicle 10 or by another transmission circuit of the vehicle 10). Alternatively, step E2 could be periodically triggered.

It is thus represented in step E4 in FIG. 2 the transmission of an electromagnetic frequency signal by the communication module 22 of the identifier 20.

This frequency electromagnetic signal is received by the communication module 12 of the vehicle 10 in step E6, which makes it possible to obtain an amplitude measurement Ai and a phase measurement Φι of the electromagnetic signal received. Amplitude and phase measured A _; Φ-ι are received by the electronic control unit 1 1 and stored in step E8.

Steps similar to steps E4 to E8 are performed for each of the frequencies f 1.

FIG. 2 shows the transmission by the communication module 22 of an electromagnetic signal of frequency f _N (last transmission frequency) at step E1 0.

This electromagnetic signal of frequency I N is received by the communication module 1 2 of the vehicle 10 in step E1 2, which makes it possible to obtain a measurement of amplitude A _N and a phase measurement Φ _Ν of the received electromagnetic signal.

The measured amplitude and phase A _N , ΦΝ are received by the electronic control unit 11 and stored in step E14.

The electronic control unit 1 1 thus stores (following the previous steps) amplitudes A, and phases Φ, respectively associated with a plurality of frequencies f 1. Note that, alternatively, instead of amplitude A, and phase Φ, the real part (for "In direct" in English) and the imaginary part Q, (for "In quadrature "in English) with I, = Re (Aie ⁰¹ ) and Q, = lm (Aie ⁰¹ ), where Re (Z) is the real part of the complex number Z and lm (Z) is the imaginary part of the complex number Z .

The electronic control unit 11 may then proceed to step E16 to the construction of an autocorrelation matrix M (or observation covariance matrix) on the basis of the measured amplitudes and phases Α ,, Φ, .

It is recalled that the autocorrelation matrix M is constructed by the product (matrix) of the vector of observations V by its conjugated transposed vector V * ^T :

M = VV * ^T ,

with V = [(Α _{1 Θ} ^Φ1 )) (A ₂ e ⁰² ) ... (A _N e ^0N )] ^T (and therefore ν * ^τ = [(Α _{ι θ} ^"φ1 )) (A ₂ e ^{" 02} ). .. (A _n e ^"0N )]).

The autocorrelation matrix M is a matrix with N rows and N columns. It is proposed to use a high resolution method (or subspace method) to evaluate the distance d by processing the autocorrelation matrix. In the example described here, the method used is a MUSIC type method (for "MUItiple Signal Classification"). However, it would be possible alternatively to use another method, for example a method of the ESPRIT type (for "Estimation of Signal Parameters via Rotational Invariance Techniques"), OPM (for "Orthonormal Propagator Method"), SWEDE (for "Subspace method Without Eigen Decomposition") or ESPRITWED (for "ESPRIT Without Eigen Decomposition").

For further explanations of these methods, reference may be made in particular to the document "Contribution of super and high resolution signal processing techniques to improving the performance of ground radar", Cédric Le Bastard, Signal and Image Processing, University of Nantes, 2007.

According to the method used here, the electronic control unit 11 determines a noise subspace associated with the autocorrelation matrix (step E18).

The electronic control unit 1 1 determines, for example, for this purpose the decomposition of the autocorrelation matrix M on a basis of N eigenvectors E ₁ , E ₂ , E _N with N eigenvalues λ-ι, λ ₂ ,. ., λ _Ν associated (sorted by decreasing values).

The largest eigenvalues λ-ι, ..., λ _κ correspond to the signal subspace (K may be a predetermined value, equal for example to 5, or determined each time as a function of the eigenvalues λ-ι, λ ₂ , ..., λ _Ν ) and the noise subspace determined in step E18 is therefore represented by the eigenvectors E _{K +} i, E _N defining this noise subspace.

The electronic control unit 11 can then determine, for a plurality of delays t _j conceivable, a measurement P _j of the projection in the noise subspace of a directional vector D _j associated with the conceivable delay t _j concerned (step E20).

This measurement uses, for example, the scalar products of the directional vector D _j with each of the eigenvectors E _{K +} 1, E _N defining the noise subspace (here by summation of these scalar products): P _j = D _; -. E _k .

The electronic control unit 1 1 determines in step E21 the delays t _j which correspond to the lowest values of the measurement P _j (or, equivalently, which maximize an increasing function with the inverse of the measurement P _j function sometimes called pseudo-spectrum). This step E21 thus makes it possible to select the delay values t _j which each correspond to a path of the electromagnetic wave transmitted from the communication module 22 of the identifier 20 to the communication module 12 of the vehicle 10 (certain paths involving reflections on neighboring objects or walls of the vehicle 10).

The electronic control unit 1 1 can thus determine in step E22 the distance d as a function of the lowest value τ (which corresponds to the direct line path) of the selected delay values t _j : d = TC, Where is the speed of light?

The electronic control unit 1 1 can then optionally control a vehicle functionality according to the distance d thus evaluated.

In the example described here, the electronic control unit 1 1 determines in step E24 whether the evaluated distance d is less than a predetermined threshold S.

In the negative (arrow N), the identifier 20 is not sufficiently close to the vehicle and the electronic control unit loops in step E8 waiting for other signals received from the identifier 20.

If so in step E24, the identifier 20 is sufficiently close to the vehicle (distance d less than the distance threshold S) and the electronic control unit 11 controls a function such as unlocking the doors of the vehicle 10 (step E26).

In the example just described, the electromagnetic signals (having successively the different frequencies f 1) are emitted by the communication module 22 of the identifier 20.

Alternatively, these electromagnetic signals could be emitted by the communication module 12 of the vehicle 10; the amplitudes A, and the phases Φ, in reception would then be measured at the level of the communication module 22 of the identifier 20. The amplitudes and measured phases Α ,, Φ, in association with each frequency f, could then be transmitted (via the wireless link established between the communication modules 12, 22, possibly in encrypted form) to the electronic control unit 11 for estimating the distance d (as in the steps E16 to E22 described above); the amplitudes A, and phases Φ, measured could also be used within the identifier 20 (and precisely the control unit 21) to estimate the distance d (according to the technique proposed above), in which case the distance d estimated within the identifier 20 would be transmitted to the electronic control unit 1 1 via the wireless link established between the communication modules 12, 22 (possibly in encrypted form).

Claims

1. A method of evaluating a distance (d) between an identifier (20) and a vehicle (10), characterized in that it comprises the following steps:

for each frequency (fi; f _N ) among a plurality of frequencies (f-ι, f _N ), measuring (E6; E12) an amplitude (Ai; A _N ) and a phase (Φι; Φ _Ν) ; ) receiving an electromagnetic signal exchanged between the identifier (20) and the vehicle (10) at the frequency concerned (fi; îN);

- construction (E1 6) of an autocorrelation matrix on the basis of the amplitudes (Ai, A _N ) and phases (Φ-ι, Φ _Ν ) measured;

- Evaluation of said distance (d) by processing the autocorrelation matrix (E18, E20, E21, E22).

The evaluation method according to claim 1, wherein the processing of the autocorrelation matrix comprises the following steps:

determination (E18) of a noise subspace associated with the autocorrelation matrix;

for a plurality of possible delays, determining (E20) a measurement of the projection in the noise subspace of a vector constructed on the basis of the possible delay concerned;

selecting (E21) possible delays for which said measurement takes the lowest values;

evaluation (E22) of said distance on the basis of the possible possible delays.

The evaluation method according to claim 2, wherein said distance is evaluated by means of the shortest of said selected possible delays. 4. Evaluation method according to one of claims 1 to 3, wherein the frequencies (f-ι, f _N ) of said plurality of frequencies are included in the frequency band at 2,

4 GHz.

5. Evaluation method according to one of claims 1 to 4, wherein said plurality of frequencies comprises more than 5 frequencies.

6. Evaluation method according to one of claims 1 to 5, wherein said electromagnetic signals are exchanged between a first communication module (12) equipping the vehicle (10) and a second communication module (22) equipping the identifier (20).

The evaluation method according to claim 6, wherein the first communication module (12) and the second communication module (22) are designed to establish a wireless data exchange link.

8. On-board vehicle system comprising:

- a reception circuit (12) of an electromagnetic signal adapted to measure, for each frequency among a plurality of frequencies, an amplitude and a phase of the electromagnetic signal received at the frequency concerned;

an electronic control unit (1 1) designed to construct an autocorrelation matrix on the basis of the measured amplitudes and phases, and to evaluate the distance separating the identifier and an emitter of the electromagnetic signal by processing the matrix of autocorrelation.

9. Identifier comprising:

a reception circuit (22) for an electromagnetic signal adapted to measure, for each frequency among a plurality of frequencies, an amplitude and a phase of the electromagnetic signal received at the frequency concerned;

a control unit (21) designed to construct an autocorrelation matrix based on the measured amplitudes and phases and to evaluate the distance separating the identifier and an emitter of the electromagnetic signal by processing the autocorrelation matrix.

A system for evaluating a distance between an identifier and a vehicle, comprising:

a reception circuit (12: 22) of an electromagnetic signal adapted to measure, for each frequency among a plurality of frequencies, an amplitude and a phase of the electromagnetic signal received at the frequency concerned;

a control unit (1 1; 21) designed to construct an autocorrelation matrix on the basis of the measured amplitudes and phases and to evaluate the distance separating the identifier and an emitter of the electromagnetic signal by processing the matrix of autocorrelation.