METHOD USING ULTRA HIGH FREQUENCY WAVES FOR LOCATING A PORTABLE DEVICE GIVING "HANDS FREE" ACCESS TO A VEHICLE, ASSOCIATED LOCATING DEVICE AND PORTABLE DEVICE

Abstract

Disclosed is a method for locating a portable device giving “hands free” access to a vehicle, by a location device intended to be installed in the vehicle, the portable device communicating with the location device by ultra high frequency waves, the invention consisting at each transmission of an ultra high frequency signal by the location device: of simultaneously transmitting by the location device at least one ultrasonic signal, intended for the portable device; of measuring a delay between a first time of reception of the ultra high frequency signal and un second time of reception of the ultrasonic signal by the portable device; of determining a distance between the portable device and the location device on the basis of the delay thus measured. Also disclosed is a location device and a corresponding portable device.

Claims

1. Method for locating a portable device (P′) for the “hands free” access to a vehicle (V′) by a location device (D′) intended to the installed in the vehicle (V′), the said portable device (P′) communicating with the said location device (D′) by ultra high frequency waves, the method comprising at every transmission of an ultra high frequency signal by the location device (D′): simultaneously transmitting by the location device (D′) at least three successive ultrasonic signals coming from three separate sources, intended for the portable device (P′), measuring a delay (Δt) between each first time of reception (t1) of the ultra high frequency signal and each second time of reception (t2) for each ultrasonic signal transmitted by the portable device (P′), determining a position between the portable device (P′) and the location device (D′) on the basis of the delays thus measured.

2. Device (D′) for the location of a portable device giving “hands free” access to a vehicle (V′), intended to be installed in the said vehicle (V′), the said portable device (P′) communicating with the said location device (D′) by ultra high frequency waves, the location device (D′) comprising: means of sequential transmission (M3) of three ultrasonic signals simultaneously with the transmission of three ultra high frequency signals intended for the portable device (P′), means of reception (M2) of a delay (Δt) between a first time of reception (t1) of each ultra high frequency signal and un second time of reception (t2) of each ultrasonic signal by the portable device (P′), means of computation (M1) of a distance (d) between the portable device (P′) and the location device (D′) on the basis of the delay (Δt) thus received.

3. Portable device (P′) for “hands free” access to a vehicle, intended to be located by a location device (D′), the said portable device (P′) communicating with the said location device (D′) by ultra high frequency waves, the portable device (P′) comprising: means of reception (M6) of three ultrasonic signals, means of measuring (M4) a delay (Δt) between a first time of reception (t1) of each ultra high frequency signal and a second time of reception (t2) of each ultrasonic signal, means of transmission (M5) of the delay (Δt) thus measured to the location device (D′).

4. Device (D′) for locating a portable device giving “hands free” access to a vehicle (V′), intended to be installed in the said vehicle (V′), the said portable device (P′) communicating with the said location device (D′) by ultra high frequency waves, the said location device (D′) comprising: means of sequential transmission (M3) of three ultrasonic signals simultaneously with the transmission of three ultra high frequency signals intended for the portable device, means of reception of a distance (d) between the portable device (P′) and the location device (D′) coming from the portable device (P′).

5. Portable device (P′) giving “hands free” access to a vehicle, intended to be located by a location device (D′), the said portable device (P′) communicating with the said location device (D′) by ultra high frequency waves, the portable device (P′) comprising: means of reception (M6) of three ultrasonic signals, means of measuring (M4) a delay (Δt) between a first time of reception (t1) of each ultra high frequency signal and a second time of reception (t2) of each ultrasonic signal by the portable device (P′), means of computation of a distance (d) between the portable device (P′) and the location device (D′) on the basis of the delay (Δt) thus computed, means of transmission (M5) of the said distance (d) to the location device (D′).

6. “Hands free” access system (100) comprising a location device (D′) according to claim 2 and a portable device (P′) for “hands free” access to a vehicle, intended to be located by a location device (D′), the portable device (P′) communicating with the location device (D′) by ultra high frequency waves, the portable device (P′) comprising: means of reception (M6) of three ultrasonic signals, means of measuring (M4) a delay (Δt) between a first time of reception (t1) of each ultra high frequency signal and a second time of reception (t2) of each ultrasonic signal, means of transmission (M5) of the delay (Δt) thus measured to the location device (D′).

7. “Hands free” access system comprising a location device (D′) according to claim 4 and a portable device (P′) giving “hands free” access to a vehicle, intended to be located by a location device (D′), the said portable device (P′) communicating with the said location device (D′) by ultra high frequency waves, the portable device (P′) comprising: means of reception (M6) of three ultrasonic signals, means of measuring (M4) a delay (Δt) between a first time of reception (t1) of each ultra high frequency signal and a second time of reception (t2) of each ultrasonic signal by the portable device (P′), means of computation of a distance (d) between the portable device (P′) and the location device (D′) on the basis of the delay (Δt) thus computed, means of transmission (M5) of the said distance (d) to the location device (D′).

8. Motor vehicle (V′) comprising a location device (D′) according to claim 2.

9. Motor vehicle (V′) comprising a location device (D′) according to claim 4.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Other features and advantages of the invention will become apparent on reading the following description and on examining the appended drawings in which:

[0048] FIG. 1, is a diagrammatic representation of the location device D equipping a motor vehicle V, of the prior art,

[0049] FIG. 2 is a flowchart showing the location method according to the invention,

[0050] FIG. 3, is a diagrammatic representation of the location device D′ according to the invention,

[0051] FIG. 4 is a diagrammatic representation of the portable device P′ according to the invention,

[0052] FIG. 5 shows a hands free access system 100 according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0053] FIG. 1 shows a motor vehicle V equipped with a device D for the location of a portable device P giving “hands free” access to the said vehicle V according to the prior art.

[0054] The location device D of the prior art comprises four radiofrequency antennas A1, A2, A3, A4 connected to a control unit 10.

[0055] The portable device P of the prior art comprises means of transmission/reception of radiofrequency RF, LF waves, in this case an antenna A5 (cf. FIG. 1) in order to communicate with the location device D.

[0056] As explained above, the method for location of the portable device P of the prior art, based solely on the measurement of the strength of the radiofrequency signal (RSSI measurement) which the portable device P receives from the location device D is no longer applicable when the location device D and the portable device P communicate by ultra high frequency waves, notably by Bluetooth®.

[0057] In fact, the method for determining the position of the portable device P of the prior art does not make it possible to determine the position of the portable device P accurately, the RSSI measurements in Bluetooth® being subject to interference by electromagnetic waves.

[0058] The invention proposes a location device D′ (cf. FIG. 3) as well as a portable device P′ (cf. FIG. 4) communicating by ultra high frequency waves or signals, and allowing the precise location of the portable device P′ with respect to the location device D′.

[0059] According to the invention, the location device D′, shown in FIG. 3, comprises at least one ultra high frequency communication antenna A1′, as well as an associated ultra high frequency transmission/reception circuit 30.

[0060] In the example shown in FIG. 3, are shown four communication antennas A1′, A2′, A3′ and A4′ connected to the ultra high frequency transmission/reception circuit 30.

[0061] The location device D′ (cf. FIG. 3) comprises moreover: [0062] means of transmission M3 of at least one ultrasonic signal to the portable device P′, in the form of an ultrasonic antenna A and an associated ultrasonic transmission/reception circuit 20, [0063] means of reception M2 of a transit time of the ultrasonic signal, [0064] means of computation M1, of a distance between the portable device P′ and the location device D′ on the basis of the transit time of the ultrasonic signal.

[0065] The means of transmission M3 of an ultrasonic signal can consist of audio means installed on the vehicle, such as the reversing radar, the car radio, the horn.

[0066] The means of reception M2 of a transit time are, for example, ultra high frequency means of reception M2 and are connected to at least one ultra high frequency communication antenna A1′ as well as to the ultra high frequency transmission/reception circuit 30.

[0067] The computation means M1 consist of software means.

[0068] With regard to the portable device P′, shown in FIG. 4, this comprises means of reception of ultra high frequency signals in the form of an ultra high frequency antenna A5′ and an associated ultra high frequency transmission/reception circuit 30′.

[0069] The portable device P′ (cf. FIG. 4) comprises moreover: [0070] means of reception M6 of an ultrasonic signal, in the form of an antenna A′ and an associated ultrasonic waves transmission/reception circuit 20′, [0071] means of measuring M4 a delay between the reception of an ultra high frequency signal and the reception of the ultrasonic signal, called the “transit time” of the ultrasonic signal, [0072] means of transmission M5 of the said “transit time” to the location device D′, [0073] a timestamp device, of the electronic clock type,

[0074] The means of reception M6 of the ultrasonic signal can be for example a microphone integrated in the portable device P′ and its associated electronic control circuit.

[0075] The means of measuring M4 the transit time are software means which compute a delay Δt between the reception of the ultra high frequency signal and the reception of the ultrasonic signal. The reception of each signal (ultrasonic and ultra high frequency) is timestamped by an electronic clock comprised in the integrated circuit of the portable device P′ and thus a delay Δt between the reception of the two signals can be computed.

[0076] The means of transmission M5 of the transit time consist, for example of ultra high frequency transmission means M5 connected to the ultra high frequency antenna A5′.

[0077] FIG. 5 shows the location system 100 constituted by the location device D′ installed in the vehicle V′ and the portable device P′ according to the invention.

[0078] In an alternative embodiment of the invention (not shown in FIGS. 3 and 4), the location device D′ comprises, instead of the means of reception M2 of a transit time of the ultrasonic signal, means of reception of the distance d between the portable device P′ and the location device D′ sent by the portable device P′.

[0079] In this embodiment of the invention, the portable device P′ comprises means of computation (not shown) of the distance d, on the basis of the transit time and comprises, instead of the means of transmission M5 of the said transit time to the location device D′, means of transmission of the said distance d (not shown) to the location device D′.

[0080] The location method, shown in FIG. 2, will now be explained.

[0081] During a first step, (E1), the location device 10′ transmits an ultra high frequency signal to the portable device P′.

[0082] This transmission can be carried out periodically, the purpose being to detect the presence of a portable device P′ around the V′. In fact, if the portable device P′ is in the reception zone of the ultra high frequency signal, it responds in its turn by transmitting an ultra high frequency presence signal to the location device D′.

[0083] The invention proposes moreover that, simultaneously with this ultra high frequency transmission, the location device D′ also transmits (step E1) an ultrasonic signal to the portable device P′.

[0084] This ultrasonic signal, which therefore has a frequency which is situated in the ultrasonic frequency band, can be transmitted by the radio, the horn or any acoustic device installed in the vehicle V.

[0085] In a second step (E2), if the ultra high frequency signal has been received by the portable device P′, then the said portable device P′ stores a first time t1 of reception of the said signal or, in other words, the portable device P′, thanks to its internal clock, timestamps (step E3) the time of reception of the ultra high frequency signal.

[0086] If the ultra high frequency signal is not received by the portable device P′, the location method returns to the first step E1.

[0087] Given the difference between the propagation speeds of ultra high frequency waves and ultrasonic waves, the ultra high frequency signal is received chronologically first (if the portable device P′ is in the reception zone of the said waves) by the portable device P′ and then it is followed by the ultrasonic signal which arrives afterwards and is received successively by the portable device P′.

[0088] If the ultrasonic signal is received by the portable device P′ (step E4), then the portable device P′ similarly stores the second time t2 of reception of the said signal (step E5). In other words, the portable device P′, thanks to its internal clock, timestamps (step E5) the time of reception of the ultrasonic signal.

[0089] If the ultrasonic signal is not received by the portable device P′, the location method returns to the first step E1.

[0090] The portable device P′ then computes a delay (step E6) between the second time t2 of reception of the ultrasonic signal and the first time of reception t1 of the ultra high frequency signal, called the “transit time” of the ultrasonic signal, that is to say:

Δt=t2−t1

[0091] The portable device P′ then sends this transit time Δt to the location device D′ (step E7).

[0092] If the location device 10′ receives the said transit time Δt, (step E8), then it deduces the distance d between the portable device P′ and the location device D′ from it, by means of the following formula:

d=(Δt)×v

[0093] where:

[0094] d is the distance between the portable device P′ and the location device D′,

[0095] Δt is the transit time of the ultrasonic wave,

[0096] v is the speed of sound (340 m/s).

[0097] If the location device D′ does not receive the said transit time Δt, the location method restarts at step E1.

[0098] The invention judiciously uses the fact that the propagation speed of ultra high frequency waves is much higher than the propagation speed of ultrasonic waves.

[0099] In fact, the propagation speed of ultra high frequency waves, for example Bluetooth®, is equal to v′=3×10.sup.8 m/s, whereas the propagation speed of ultrasonic waves, v, is equal to v=340 m/s.

[0100] The transit time of the ultra high frequency signal from the location device D′ to the portable device P′ is therefore much shorter than the transit time of the ultrasonic signal, and the location method according to the invention proposes to ignore this transit time of the ultra high frequency signal in comparison with the transit time of the ultrasonic signals from the location device D′ to the portable device P′. By ignoring the transit time of the ultra high frequency signal, a synchronization is achieved between the location device D′ and the portable device P′ without any in the portable device P′ being necessary.

[0101] The location method according to the invention is therefore based on the assumption that the ultra high frequency signal is received by the portable device P′ at the time it is transmitted by the location device D′.

[0102] Since the ultrasonic signal is transmitted simultaneously with the ultra high frequency signal, the timestamped reception of the ultra high frequency signal is considered by the portable device P′ as the start of the transmission of the ultrasonic signal by the location device D′.

[0103] By computing the difference between the second time of reception t2 of the ultrasonic signal and the first time of reception t1 of the ultra high frequency signal, called the “transit time”, that is to say Δt=t2−t1, this is judiciously equivalent, according to the invention, to computing the transit time of the ultrasonic signal between the location device D′ and the portable device P′. The distance d separating the two devices can then be computed according to the formula

d=(Δt)×v

[0104] where:

[0105] d is the distance between the portable device P′ and the location device D′,

[0106] Δt is the transit time of the ultrasonic wave,

[0107] v is the speed of sound (340 m/s).

[0108] The duration of the transit time of the ultrasonic signal therefore makes it possible to determine the distance d separating the location device D′ from the portable device P′.

[0109] In an alternative embodiment, the portable device P′ returns the distance d, computed from the measured transit time according to the equations given above, directly to the location device D′.

[0110] It is also possible in a second embodiment, to determine the position du portable device P′ with respect to the vehicle V′ with more precision and not only the distance d.

[0111] For this purpose, the location device D′ comprises at least three means of transmission of ultrasonic signals, offset in space. In other words, the means of transmission of ultrasonic signals consist of three different sources of signals situated at different places on the vehicle V′.

[0112] The three means of transmission each in their turn sequentially transmit an ultrasonic signal, simultaneously with the transmission of three ultra high frequency signals by the transmission means M2. The portable device P′ receives three ultra high frequency signals and then three ultrasonic signals successively. By computing the transit time between the first time of reception of each ultra high frequency signal and the second time of reception of each corresponding ultrasonic signal, it is possible by triangulation to determine with precision the lateral and longitudinal position of the portable device P′ with respect to the vehicle V′.

[0113] The invention therefore judiciously makes it possible, by the use of existing means (microphone integrated in the portable device P′, acoustic means installed in the vehicle V′) to determine with precision the position around a vehicle V of a portable device P′ communicating by Bluetooth®.