Method for assisting in determining the position of an identifier in relation to a vehicle

Abstract

The invention relates to a method (METH) for assisting in determining the position of an identifier (I) for accessing and starting a vehicle (V), relative to the vehicle (V), comprising: transmission (Em_TS.sub.vp), from a first device, either the vehicle (V) or the identifier (I) to a second device, different from the first, either the vehicle (V) or the identifier (I), at a transmission time t0, of an initial train (TS.sub.vp) of N sinusoidal signals, having identical amplitudes and respective frequencies f.sub.p, p[1;N], for any p between 1 and N1; reception (Rec_TS.sub.vp) by the second device of an image train (TS.sub.vp) corresponding to the initial train (TS.sub.vp, TS.sub.ip) altered by the transmission (Em_TS.sub.vp); construction (Cons_Sp.sub.v) of a frequency spectrum (Sp.sub.v) for the image train (TS.sub.vp); inverse Fourier transformation (TFI_Sp.sub.v) of the spectrum (Sp.sub.v), allowing a time signature (Sg.sub.v) to be obtained; first integration (Int1_Sg.sub.v) of the time signature (Sg.sub.v), between the transmission time t.sub.0 and a pre-determined intermediate time t.sub.int, producing a first result (Rlt1); second integration (Int2_Sg v) of the time signature (Sg.sub.v) between the intermediate time t.sub.int and a pre-determined end time t.sub.f, producing a second result (Rlt2); comparison (Comp_1/2) of a ratio (R) of the first result (Rlt1) to the second result (Rlt2) with a threshold value (S), so that it is possible to determine if the identifier (I) is positioned inside the vehicle (V).

Claims

1. A method for assisting in determining a position of an identifier for accessing and starting a vehicle, in relation to said vehicle, the method comprising: transmission, from a first device from among the vehicle and the identifier, to a second device, separate from the first, from among the vehicle and the identifier, at a transmission time t.sub.0, of an initial train of N sinusoidal signals, with identical amplitudes and with respective frequencies f.sub.p, p[1;N], such that, for all values of p between 1 and N1: reception, by the second device, of an image train corresponding to the initial train altered by the transmission, construction of a frequency spectrum of the image train, an inverse Fourier transform of the spectrum to obtain a temporal signature a first integration of the temporal signature, between the transmission time and a predetermined intermediate time t.sub.int, to obtain a first result a second integration of the temporal signature, between the intermediate time and a predetermined final time t.sub.f, to obtain a second result, and comparison of a ratio of the first result to the second result with a threshold value, to determine whether the identifier is positioned inside the vehicle.

2. The method as claimed in claim 1, wherein the intermediate time t.sub.int is such that the temporal signature, between the transmission time and the intermediate time, comprises a first reception lobe corresponding to a direct path between the identifier and the vehicle.

3. The method as claimed in claim 1, wherein the final time is such that the temporal signature, between the intermediate time and the final time, comprises secondary reception lobes corresponding to reflected and/or refracted paths between the identifier and the vehicle.

4. The method as claimed in claim 1, further comprising a step of multiplying the ratio by (t.sub.ft.sub.int)/(t.sub.intt.sub.0), and a step of comparing the result of the multiplication with the threshold value.

5. The method as claimed in claim 1, wherein the threshold value is greater than 10.

6. The method as claimed in claim 1, wherein the frequencies f.sub.p are such that N=80, f1=2400 MHz and, for all values of p between 1 and 79, f.sub.p+1f.sub.p=1 MHz.

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 respective position, 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;

(5) FIG. 4 shows a signature, obtained during a step of the method, characteristic of an identifier positioned inside the vehicle;

(6) FIG. 5 shows a signature, obtained during a step of the method, characteristic of an identifier positioned outside the vehicle.

DETAILED DESCRIPTION OF AT LEAST ONE EMBODIMENT OF THE INVENTION

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

(8) The method described hereinafter makes it possible to determine whether 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 a vehicle V, is positioned inside said vehicle V. The identifier I is for example an electronic key or card, or a smartphone having a suitable application.

(9) The vehicle V includes a first transceiver device Dv, and the identifier I includes a second transceiver device Di.

(10) With reference to FIG. 1, the first transceiver device Dv of the vehicle V includes: a transmitter TXv of radio signals (with a frequency at least equal to 1 GHz) an antenna Atv to which the transmitter TXv is connected a phase-locked loop PLLv for supplying signals of various frequencies to the transmitter TXv.

(11) The second transceiver device Di of the identifier I moreover includes: a receiver RXi of radio signals (with a frequency at least equal to 1 GHz) an antenna Ati to which the receiver RXi is connected a computer Xi for performing calculations on the basis of signals received by the receiver RXi.

(12) It is noted that a smartphone natively has all of the components of the described transceiver device Di. 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.

(13) 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).

(14) With reference to FIG. 2, the method METH includes the following steps. at a time t.sub.0, transmission Em_TS.sub.vp, from the transmitter TXv of the vehicle V to the receiver RXi of the identifier I, of an initial 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 initial 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 initial 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 an image train TS.sub.vp corresponding to the initial train TS.sub.vp altered by the transmission Em_TS.sub.vp. The image train TS.sub.vp is shown in FIG. 3. The 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. construction Cons_Sp.sub.v of a frequency spectrum Sp.sub.v of the image train TS.sub.vp, through detection of the spectral lines of the image train TS.sub.vp. The spectrum Sp.sub.v is shown in FIG. 3. an inverse Fourier transform TFI_Sp.sub.v making it possible to obtain a temporal signature Sg.sub.v. The first temporal signature Sg.sub.v is equivalent to the one that would have been obtained if a pulse had been transmitted instead of the initial train TS.sub.vp. A spectrum characteristic of an identifier inside a vehicle is shown in FIG. 4, while a spectrum characteristic of an identifier outside a vehicle is shown in FIG. 5. It is noted that the amplitudes of the signature in a region close to the time corresponding to the direct travel time of the wave between the transmitter and the receiver are higher when the identifier is inside the vehicle. transmission Tr_t.sub.0, from the transmitter TXv of the vehicle V to the receiver RXi of the identifier I, of the transmission time t.sub.0. a first integration Int1_Sg.sub.v of the temporal signature Sg.sub.v, between the transmission time t.sub.0 and a predetermined intermediate time t.sub.int, giving a first result Rlt1. The intermediate time t.sub.int, in seconds, is advantageously the one corresponding to the direct wave path, that is to say the distance between the transceiver of the vehicle and of the identifier. It is noted that the first integration Int1_Sg.sub.v is performed by the computer Xi of the identifier. a second integration Int2_Sg.sub.v of the temporal signature Sg.sub.v, between the intermediate time t.sub.int and a predetermined final time t.sub.f, giving a second result Rlt2. The final time t.sub.f, in seconds, is advantageously the time allowing all of the reflected and/or refracted waves to arrive at the identifier. It is noted that the second integration Int2_Sg.sub.v is performed by the computer Xi of the identifier. It is noted that the results Rlt1, Rlt2 of the integrations Int1_Sg.sub.v, Int2_Sg.sub.v may possibly be divided by the time t.sub.intt.sub.0 and the time t.sub.ft.sub.int, respectively. This makes it possible to have a basis for comparing the results Rlt1 and Rlt2 that is independent of the intermediate time t.sub.int and the final time t.sub.1. comparison Comp_1/2 of a ratio R of the first result Rlt1 (possibly divided by t.sub.intt.sub.0) to the second result Rlt2 (possibly divided by t.sub.ft.sub.int) with a threshold value S. The threshold value S is a value beyond which the likelihood of the identifier I being positioned inside the vehicle V is high. The greater the threshold value S, the more reliable the result of the positioning via the method METH according to the invention. If the ratio R is greater than the threshold value S, then the identifier I is determined to be positioned inside the vehicle V. The threshold value S is advantageously greater than 10, so the identifier I is determined to be positioned inside the vehicle V if the first result Rlt1 is at least ten times greater than the second result Rlt2.

(15) On the basis of the result of the comparison, and depending on a specific requested function (opening of a door, closure of a door, starting of the vehicle, for example), the computer Xi of the identifier I is able to determine whether or not the function should be performed. This information may then be relayed to the vehicle V.

(16) It is noted that the method METH could, as an alternative, not comprise the step of transmission Tr_t.sub.0, from the transmitter TXv of the vehicle V to the receiver RXi of the identifier, of the transmission time t.sub.0. The method would then comprise a step of transmission, from the transmitter TXi of the identifier I to the receiver RXv of the vehicle V, of the temporal signature Sg.sub.v. The integrations Int1_Sg.sub.v, Int2_Sg.sub.v and the comparison Comp_1/2 would then be performed by a computer Xv of the vehicle V.

(17) Naturally, the steps of the method could, as an alternative, be performed in another technically feasible order than the one presented above. Moreover, the transmission steps Em_TS.sub.vp, Tr_Dat could, as an alternative, be performed from the identifier I to the vehicle V. The other steps would then be performed by the vehicle V. As an alternative, the steps could be performed by both the identifier I and the vehicle V.