Method for determining a distance between a vehicle and an identifier

Abstract

A method for measuring a distance separating a vehicle and an identifier is disclosed. The method includes transmitting, from the vehicle to the identifier, a first train of first sinusoidal signals, receiving, by the identifier, an image train of second sinusoidal signals corresponding to the first sinusoidal signals, generating, by the identifier, measurements of phases and amplitudes of the second sinusoidal signals that are altered from the first sinusoidal signals by transmission from the vehicle to the identifier, constructing a frequency spectrum based on the measurements and a second image train received by the vehicle from the identifier, where the frequency spectrum is constructed by detecting spectral lines of the first image train and the second image train, performing an inverse Fourier transform of the frequency spectrum to obtain a temporal signature, and calculating the distance on the basis of an intermediate time associated with a maximum of the temporal signature.

Claims

1. A method for measuring a distance separating a vehicle and an identifier for accessing and starting the vehicle, the vehicle and the identifier being synchronized, the method comprising: transmitting, from the vehicle to the identifier, a first train of N first sinusoidal signals with identical amplitudes and with regularly spaced respective frequencies f.sub.p, P[1;N]; receiving, by the identifier, an image train of N second sinusoidal signals corresponding to the N first sinusoidal signals, wherein the N second sinusoidal signals comprise phases and amplitudes that are altered from the N first sinusoidal signals by transmission from the vehicle to the identifier; generating, by the identifier, measurements of the phases and the amplitudes of the N second sinusoidal signals; transmitting the measurments of the phases and the amplitudes of the N second sinusoidal signals, from the identifier to the vehicle; transmitting, from the identifier to the vehicle, a second train of N third sinusoidal signals that are identical to the N first sinusoidal signals of the first train; receiving, by the vehicle from the identifier, a second image train corresponding to the second train altered by transmission from the identifier to the vehicle; constructing a frequency spectrum based on the measurements of the phases and the amplitudes transmitted to the vehicle and the second image train received by the vehicle, wherein the frequency spectrum is constructed by detecting spectral lines of the first image train and the second image train; performing, by a computer processor, an inverse Fourier transform of the frequency spectrum to obtain a temporal signature; determining, by the computer processor, an intermediate time associated with a maximum of the temporal signature; and calculating by the computer processor, the distance on the basis of the intermediate time.

2. The measurement method as claimed in claim 1, wherein the frequencies f.sub.p are such that N=80, f.sub.1=2400 MHz and, for all values of p between 1 and 79, f.sub.p+1f.sub.p=1 MHz.

3. The measurement method as claimed in claim 1, wherein the calculation includes determining a maximum lobe of the temporal signature, and determining a start time of said maximum lobe.

4. The measurement method as claimed in claim 3, further comprising a prior step of synchronizing the identifier and the vehicle using a Bluetooth protocol.

5. The measurement method as claimed in claim 1, wherein the inverse Fourier transform is performed by inverse fast Fourier transform.

6. The measurement method as claimed in claim 5, further comprising adding spectral line samples to the measured image trains.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) The figures are presented only by way of entirely nonlimiting indication of the invention. In the figures:

(2) FIG. 1 shows two transceiver devices belonging to a vehicle and an identifier, respectively, between which it is desired to know the distance, the devices being designed to implement a method according to one embodiment of the invention;

(3) FIG. 2 shows a block diagram showing steps of the method;

(4) FIG. 3 shows signals exchanged between the transceiver devices during steps of the method.

DETAILED DESCRIPTION OF AT LEAST ONE EMBODIMENT OF THE INVENTION

(5) Unless indicated otherwise, one and the same element appearing in different figures has a single reference.

(6) The method described hereinafter makes it possible to calculate a distance R between a vehicle V and what is termed a hands-free identifier I, said identifier I making it possible to control, using a hands-free principle, access to or starting of the vehicle V. The identifier I is for example an electronic key or card, or a smartphone having a suitable application.

(7) The vehicle V includes a first transceiver device Dv, and the identifier I includes a second transceiver device Di. As the first transceiver device Dv and the second transceiver device Di are similar, a general description is given hereinafter.

(8) With reference to FIG. 1, a transceiver device Dp, the index p indiscriminately being v or i, includes: a transmitter TXp of radio signals (with a frequency at least equal to 1 GHz) a receiver RXp of radio signals (with a frequency at least equal to 1 GHz) an antenna Atp to which the transmitter TXp and the receiver RXp are connected a phase-locked loop PLLp for supplying signals of various frequencies to the transmitter TXp a computer Xp for performing calculations on the basis of signals received by the receiver RXp.

(9) It is noted that a smartphone natively has all of the components of the described transceiver device Dp. In one preferred embodiment, the identifier I is therefore a smartphone having a suitable application for the hands-free accessing and starting of the vehicle. The various components of the transceiver device Di are advantageously triggered and controlled by the application installed on the smartphone.

(10) The method according to the invention is implemented by the first transceiver device Dv and the second transceiver device Di. It is noted that the first transceiver device Dv and the second transceiver device Di have been synchronized with one another beforehand, for example via a Bluetooth Low Energy protocol (it is noted that a smartphone natively has a Bluetooth chip). With reference to FIG. 2, the method METH includes the following steps. transmission Em_TS.sub.vp, from the transmitter TXv of the vehicle V to the receiver RXi of the identifier I, of a first train TS.sub.vp of N first sinusoidal signals S.sub.vp with identical phases and amplitudes, and with respective frequencies f.sub.p, p[1;N]. The first train TS.sub.vp is shown in FIG. 3. Advantageously, the frequencies f.sub.p are such that N=80, f.sub.1=2.4 GHz, f.sub.80=2.480 GHz and, for all values of p between 1 and 79, f.sub.p+1f.sub.p=1 MHz. Specifically, these frequencies correspond to the Bluetooth Low Energy channels. It is noted that the first train TS.sub.vp is generated by the phase-locked loop PLLv of the vehicle V. reception Rec_TS.sub.vp, by the receiver RXi of the identifier I, of a first image train TS.sub.vp corresponding to the first train TS.sub.vp altered by the transmission Em_TS.sub.vp. The first image train TS.sub.vp is shown in FIG. 3. The first image train TS.sub.vp is formed of N image sinusoidal signals S.sub.vp with phases .sub.p, amplitudes a.sub.p and frequencies f.sub.p, p[1;N], respectively. If the frequencies f.sub.p of the first signals S.sub.vp are not altered by the transmission, their amplitude and their phase are altered. Specifically, the reflection and refraction phenomena to which the signals are subjected between the transmitter TXv of the vehicle V and the receiver RXi of the identifier I shift phase and modify the amplitude of the signals. measurement Mes_Dat, by the receiver RXi of the identifier I, of phases .sub.p and of amplitudes a.sub.p of the signals S.sub.vp of the first image train TS.sub.vp. transmission Tr_Dat, in the form of data, of the amplitudes a.sub.p and the phases .sub.p measured by the identifier I in the preceding step. These data are for example transmitted using a Bluetooth Low Energy protocol. transmission Em_TS.sub.ip, from the transmitter TXi of the identifier I to the receiver RXv of the vehicle V, of a second train TSi.sub.p identical to the first train TS.sub.vp. It is noted that the second train IS.sub.ip is generated by the phase-locked loop PLLi of the identifier. reception Rec_TS.sub.ip, by the receiver RXv of the vehicle V, of a second image train TS.sub.ip corresponding to the second train TS.sub.ip altered by the transmission Em_TS.sub.ip. measurement, by the receiver RXv of the vehicle V, of phases and of amplitudes of the signals of the second image train TS.sub.ip At a time t4, construction Cons_Sp of a frequency spectrum Sp formed by the first image train TS.sub.vp and the second image train TSi.sub.p, through detection of the spectral lines of the first image train TS.sub.vp and of the second image train TS.sub.ip. an inverse Fourier transform TFI_Sp making it possible to obtain a temporal signature Sg. The temporal signature Sg is equivalent to the one that would have been obtained if a pulse had been transmitted instead of the first and second trains TS.sub.vp and TS.sub.ip. determination Det_t.sub.d of an intermediate time t.sub.d associated with a maximum of the temporal signature Sg. calculation Cal_R, by the computer Xv of the vehicle V, of the distance R on the basis of the intermediate time t.sub.d, using the following formula:

(11) $R=\frac{c}{2}.Math.t_d$
where c is the speed of propagation of the signals exchanged between the vehicle V and the identifier I.

(12) On the basis of the calculated distance R and depending on a specific requested function (opening of a door, closure of a door, starting of the vehicle, for example), the computer Xv of the vehicle V is able to determine whether or not the function should be performed.

(13) As an alternative, the intermediate time t.sub.d could be determined by looking for the value of the start of the maximum lobe of the temporal signature. The start of the lobe may be determined by the difference between the maximum value and a constant (for example 20 dB). As an alternative, the start of the lobe is determined by the difference between the maximum value and a value dependent on the average value of the lobes furthest from the maximum lobe of the temporal signature.

(14) Naturally, the steps of the method could, as an alternative, be performed in another technically feasible order than the one presented above.