Device for determining the distance between a base and a mobile object by time of flight

Abstract

The invention relates to a device (10) for determining the distance (d) between a base (1) and a moving object (2), the base (1) comprising a time-of-flight distance measuring means (3), wherein the device (10) comprises: - a velocity measuring means capable of determining the velocity (v) of the moving object (2) relative to the base (1), - a control means capable of determining a number of time-of-flight measurements (n), a decreasing function of the velocity (v) of the moving object (2), and of causing the distance measuring means (3) to perform a number of time-of-flight measurements (n) to obtain as many elementary distance measurements (di), - a filtering means capable of determining the distance (d) by calculating the median of the elementary distance measurements (di). Abstract figure: Figure 1

Description

Title of the invention: Device for determining the distance between a base and a moving object by time of flight. Technical field

[0001] The invention relates to a device and a method for determining the distance between a base and a mobile by time of flight. Previous technique

[0002] It is known, to determine a distance between a base and a mobile, to proceed by measuring time of flight.

[0003] For this purpose, a wave, for example radio frequency, is emitted by the base. This wave is reflected by the mobile. The reflected wave is received by the base. The base measures the time interval between the emission and the return of the wave and can thus, knowing the propagation speed, deduce the distance, according to the formula d = (tr - té) / 2v, where d is the distance sought, tr the return time of the wave, té the emission time of the wave and v the propagation speed.

[0004] Distance measurement is subject to errors. Thus, for a time-of-flight device using ULB modulation, the error on a single measurement is + / -20 cm, which is insufficient for some applications.

[0005] One technique for improving the accuracy of distance measurement involves taking multiple measurements and then filtering them, using either the average or median method. The greater the number of measurements, the higher the accuracy, but the longer the response time. Many applications cannot tolerate such an increase in response time.

[0006] Also, an alternative means of determining the distance d between a base and a moving object is sought, allowing an improvement in accuracy without degrading the response time. Summary of the invention

[0007] For this purpose the invention proposes a determination whose accuracy evolves dynamically according to the time available.

[0008] The invention relates to a device for determining the distance between a base and a moving object, the base comprising a time-of-flight distance measurement means, wherein the device comprises: - a speed measurement device capable of determining the speed of the moving object relative to the base, - a control means capable of determining a number of flight time measurements, a decreasing function of the vehicle's speed, and of having these measurements taken by means of measurement distance, a number of flight time measurements, to obtain as many elementary distance measurements, - a filtering means capable of determining the distance by calculating the median of the elementary distance measurements.

[0009] Specific features or embodiments, usable alone or in combination, are: - The decreasing function of velocity is the quotient of a reference velocity to the velocity of the moving object. - the reference speed is the speed that allows a reference distance, preferably equal to 0.5 m, to be covered in a sampling period composed of time-of-flight measurements, preferably equal to an elementary sampling period, equal to 96 ms, - the distance measurement means comprises a plurality of antennas and the distance determination device further comprises a cycling means, capable of cyclically using the antennas to produce as many elementary distance pre-measurements as there are, and determining an elementary distance measurement equal to the minimum value of the elementary distance pre-measurements, - The cycling method cyclically uses the antennas according to the elementary sampling period, and the number of time-of-flight measurements and elementary distance measurements is calculated on the basis of a compound sampling period equal to the elementary sampling period multiplied by the number of antennas. - the speed measurement system includes a radar, positioned on the base, - The speed measurement device comprises a sensor placed on the mobile device, and a communication device capable of transmitting the speed to the base. - the distance measurement means includes a radio frequency transmitter / receiver using ultra-wideband modulation, ULB, - the radar is confused with the radio frequency transmitter / receiver, configured in radar mode, - the means of communication is confused with the radio frequency transmitter / receiver combined with a homologous radio frequency transmitter / receiver, located on the mobile. Brief description of the drawings

[0010] The invention will be better understood upon reading the following description, given solely by way of example, and with reference to the figures in the appendix in which: [Fig. 1] shows, in synoptic view, the context of the invention, [Fig.2] shows a table for determining the number of measurements as a function of the speed of the moving object, according to a first embodiment. [Fig.3] shows, a table for determining the number of measurements as a function of the speed of the moving object, according to another embodiment. Description of the implementation methods

[0011] With reference to [Fig. 1], the invention relates to a device 10 for determining the distance d between a base 1 and a mobile 2.

[0012] In an illustrative application of the invention, the base 1 is a motor vehicle and the mobile device 2 is the user of the motor vehicle, more specifically represented by their smartphone. The application aims to determine the distance between the base 1 and the mobile device 2 in order to perform or not perform certain access control functions to the motor vehicle, depending on the distance between the base 1 and the mobile device 2. Thus, as long as the user is more than 2 m from the vehicle, no authorization should be granted. When the user approaches, and at the latest when they touch the door handle, authorization should be granted.

[0013] For this purpose, the base 1 includes a distance measurement means 3 of the time-of-flight type.

[0014] According to one feature, the device 10 further comprises a speed measurement means, a control means, and a filtering means. The speed measurement means is capable of determining the relative speed v of the mobile 2 with respect to the base 1. The control means is capable of determining a number of flight time measurements n, a decreasing function of the speed v of the mobile 2. The control means is also capable of causing the distance measurement means 3 to perform a number of flight time measurements n. These n flight time measurements allow for obtaining the same number n of distance measurements di, i being between 1 and n. The filtering means is capable of determining the distance d, from n distance measurements di, by calculating the median.

[0015] Since the number of time-of-flight measurements n is a decreasing function of the speed v of the moving object 2, the response time and accuracy of the distance measurement d depend directly on the available time. If the moving object 2 is moving quickly, the available time is short. Therefore, a distance measurement d is performed with few distance measurements di, which guarantees a short response time, at the expense of accuracy. Conversely, if the moving object 2 is moving more slowly, the available time is greater. Therefore, a distance measurement d is performed with a larger number of distance measurements di, which guarantees improved accuracy, at the expense of a longer response time.

[0016] The idea of ​​using a decreasing function of the speed v to determine the number n of time-of-flight measurements allows the number of time-of-flight measurements n to be adapted dynamically. Indeed, the faster the moving object 2 travels, the less time the device 10 has to update the distance d, which changes more rapidly. In this case, the number n decreases and with it the accuracy of the measurement of the distance d. However, an optimized measurement, as accurate as possible in the available time, is provided with a minimum delay.

[0017] Conversely, when the moving object 2 moves more slowly, the device 10 has more time to update the distance d, which changes less rapidly. In this case, the number n increases, and with it, the accuracy of the distance d measurement improves. The device 10 thus provides an optimized distance measurement with increased accuracy, given the greater available time. The update delay is slightly increased, but without adverse consequences, since the distance d also changes less rapidly.

[0018] The decreasing function of the velocity v can be any decreasing function.

[0019] According to another characteristic, the decreasing function of the velocity v is the quotient of a reference velocity v0 to the velocity v of the moving object 2. Thus, the curve of this function is a hyperbola. Written in mathematical terms, this function f of the variable v is given by n = f(v) = vq / v. In this formula, n is the number of measurements per flight time, v is the velocity v of the moving object 2, and v0 is a reference velocity, constant for a given application.

[0020] According to another feature, the reference speed v0 is determined as follows. A reference distance d0 is chosen in relation to the application. The reference speed v0 is then the speed that allows the reference distance d0 to be covered in the time required to determine an elementary distance di, i.e., a time that is called the compound sampling period Te'.

[0021] In the illustrative application for determining the distance between a user and their vehicle, the important event is when the user grasps the vehicle door handle. This event is characterized by a distance d between the mobile device 2 / smartphone, assumed to be carried in a pocket at waist or chest level, and the base 1 / vehicle, approximately equal to the length of the user's forearm. Therefore, in this illustrative application, the reference distance d0 is chosen to be 50 cm.

[0022] Still within the illustrative application, the composite sampling period Te' is a multiple of an elementary sampling period Te. Assuming a single antenna 11, the multiplicity factor is equal to 1, as explained later. The elementary sampling period Te is constrained by compliance with the CCC standard to a value of 96 ms or 0.096 s. Therefore, the composite sampling period Te' is equal to 96 ms here. It follows that the reference velocity v0 = do / Te' is, in this case, equal to 0.5 / 0.096, or 5.2 m / s or 18.75 km / h.

[0023] It follows, in the illustrative application, that the number n of elementary distance measurements di as a function of the speed v, in km / h, of the moving object 2 is given by the table presented in [Fig. 2]. For a speed intermediate between two values, the smaller value of n is retained. Thus, for example, for a speed of 3 km / h, between the limits 3.1 and 2.7 km / h, the number n of measurements is taken to be equal to the lower value, i.e., n = 6.

[0024] According to another feature, the distance measurement means 3 comprises a plurality of antennas 11, 12. The device 10 can operate with a single antenna 11, as described previously. However, one or more additional antennas 12 make it possible to create spatial diversity that improves the accuracy of an elementary distance measurement di. In order to take advantage of this spatial diversity, the distance determination device 10 further includes a cycling means. This cycling means is capable of cyclically using each of the antennas 11, 12 to produce, with each, a preliminary distance measurement dj, with the index j varying from 1 to p, where p is the number of antennas 11, 12. A preliminary distance measurement dj is derived from a time-of-flight measurement, as described previously. For the set of antennas 11, 12, an elementary distance measurement di is determined, equal to the minimum value of the respective pre-distance measurements dj.Indeed, antennas 11 and 12 can be considered sufficiently close for their respective propagation to be considered identical. What distinguishes them from one another is then primarily the presence or absence of multipath propagation. Therefore, the minimum distance is the closest to the actual distance. Subsequently, the elementary distance measurements di are treated essentially as before.

[0025] When there is more than one antenna, each of the antennas 11,12 is used in turn, according to an elementary sampling period Te. It follows that the compound sampling period Te', corresponding to obtaining an elementary measurement di, is equal to an elementary sampling period Te, multiplied by the number p of antennas 11, 12, i.e. Te' = Te * p.

[0026] Therefore, the value of the number of time-of-flight measurements n should be adjusted accordingly. According to another characteristic, the number of time-of-flight measurements n is calculated on the basis of a compound sampling period Te'. This compound sampling period Te' is equal to the elementary sampling period Te multiplied by the number p of antennas 11, 12. It follows that the reference speed v0 = d0 / Te' = d0 / (p.Te) is divided by p. n is modified accordingly.

[0027] Thus, in the illustrative application, the elementary sampling period Te is constrained by compliance with the CCC standard to a value of 96 ms or 0.096 s. Therefore, the compound sampling period Te' is then equal to 192 ms. It follows that the reference speed v0 = d0 / Te', is in this case equal to, 0.5 / 0.192, i.e. equal to 2.6 m / s or 9.4 km / h.

[0028] It follows, in the illustrative application, that the number n of elementary distance measurements di as a function of the speed v, in km / h, of the mobile 2 is given by the table presented in [Fig.3].

[0029] There are at least two ways to determine the speed v of the mobile 2. The first is to use a radar located on base 1. The second is to measure the speed v by a sensor located on the mobile 2. Since all calculations are preferentially performed on base 1, it is then necessary to transmit the speed measurement v obtained on the mobile 2, from the mobile 2 to base 1. This is accomplished by a communication means 6.

[0030] In the first case, the speed measurement means includes a radar 4. This radar 4 can be of any type: radio, ultrasonic, laser, etc. The radar 4 is arranged on the base 1. It emits a wave in the direction of the mobile 2 and analyzes the reflected wave to determine, typically by Doppler effect, the speed v of the mobile 2.

[0031] In the second case, the speed measurement means includes a sensor 5 disposed on the mobile 2. This sensor 5 can be of any type allowing the measurement of a speed v of the mobile 2 which carries the sensor 5. A communication means 6 then transmits the speed v to the base 1. This communication means 6 typically includes a transmitter carried on the mobile 2 and an associated receiver carried on the base.

[0032] According to another feature, in the case where the mobile 2 is a smartphone, the sensor 5 advantageously reuses the position / orientation / speed sensor of said smartphone, or IMU (from the English: "inertial measurement unit").

[0033] According to another feature, the distance measurement means 3 comprises a radio frequency transmitter / receiver 7 using ultra-wideband (ULB) modulation. Such equipment makes it possible to perform time-of-flight measurements.

[0034] According to another feature, the radar 4 reuses said radio frequency transmitter / receiver 7. In this case, the radio frequency transmitter / receiver 7 is configured in radar mode, so as to be able to measure the speed v of the mobile 2 by Doppler effect.

[0035] The communication means 6 can be of any kind and according to any technology capable of transmitting a measurement. According to another characteristic, the communication means 6 reuses the radio frequency transmitter / receiver 7 of the base 1 and combines it with a corresponding radio frequency transmitter / receiver 8, located on the mobile 2.

[0036] The invention has been illustrated and described in detail in the drawings and the preceding description. This description is to be considered illustrative and given by way of example and not as limiting the invention to this single description. Numerous embodiments are possible. List of reference signs

[0037] 1: base, 2: mobile, 3: Time-of-flight measurement device, 4: radar, 5: sensor, 6: means of communication, 7: base transmitter / receiver, 8: Mobile transmitter / receiver, 10: distance determination device, 11, 12: antennas, d: distance between base and mobile device, d0: reference distance, di: elementary distance measure, dj: elementary distance pre-measurement, p: number of antennas, Te: elementary sampling period, Te': compound sampling period, v: relative velocity of the moving part, v0: reference velocity.

Claims

Demands

1. Device (10) for determining the distance (d) between a base (1) and a mobile (2), the base (1) comprising a time-of-flight distance measurement means (3), characterized in that it comprises: - a speed measurement means capable of determining the speed (v) of the mobile (2) relative to the base (1), - a control means capable of determining a number of time-of-flight measurements (n), a decreasing function of the speed (v) of the mobile (2), and of making the distance measurement means (3) perform a number of time-of-flight measurements (n), to obtain as many elementary distance measurements (di), - a filtering means capable of determining the distance (d) by calculating the median of the elementary distance measurements (di).

2. Device (10) according to claim 1, where the decreasing function of the velocity (v) is the quotient of a reference velocity (v0) to the velocity (v) of the mobile (2).

3. Device (10) according to claim 2, wherein the reference speed (v0) is the speed at which a reference distance (d0), preferably equal to 0.5 m, can be covered in a sampling period (Te') composed of time-of-flight measurements, preferably equal to an elementary sampling period (Te) equal to 96 mc

4. ilia. Device (10) according to any one of claims 1 to 3, wherein the distance measuring means (3) comprises a plurality of antennas (11,12) and wherein the distance determining device (10) (d) further comprises a cycling means, capable of cyclically using the antennas (11,12) to produce as many elementary distance pre-measurements (dj), and determining an elementary distance measurement (di) equal to the minimum value of the elementary distance pre-measurements (dj).

5. Device (10) according to claim 4, wherein the cycling means cyclically uses the antennas (11, 12) according to the elementary sampling period (Te) and wherein the number of time-of-flight measurements (n) and elementary distance measurements (di) is calculated on the basis of a compound sampling period (Te') equal to the elementary sampling period (Te) multiplied by the number (p) of antennas (11, 12).

6. Device (10) according to any one of claims 1 to 5, wherein the speed measurement means comprises a radar (4), disposed on the base (1).

7. Device (10) according to any one of claims 1 to 6, wherein the speed measurement means comprises a sensor (5) disposed on the mobile (2), and a communication means (6) capable of transmitting the speed (v) to the base (1).

8. Device (10) according to any one of claims 1 to 7, wherein the distance measuring means (3) comprises a radio frequency transmitter / receiver (7) using ultra-wideband, ULB modulation.

9. Device (10) according to claim 8, wherein the radar (4) is combined with the radio frequency transmitter / receiver (7), configured in radar mode.

10. Device (10) according to claim 8 or 9, wherein the means of communication (6) is combined with the radio frequency transmitter / receiver (7) combined with a corresponding radio frequency transmitter / receiver (8), disposed on the mobile (2).

11. Method for determining the distance (d) between a base (1) and a mobile (2), the base (1) comprising a time-of-flight distance measuring means (3), characterized in that it comprises the following steps: - determination of the speed (v) of the mobile (2) relative to the base (D, - determination of a number of time-of-flight measurements (n), decreasing function of the speed (v) of the mobile (2), - commanding the distance measuring means (3), of a number of time-of-flight measurements (n), to obtain as many elementary distance measurements (di), - determination of the distance (d) by calculating the median of the elementary distance measurements (di).

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