Apparatus for determining distance between base station and mobile entity using time of flight

Abstract

The invention relates to a device (10) for determining a distance (d) between a base station (1) and a mobile entity (2), the base station (1) comprising time-of-flight-based distance measurement means (3), the device (10) comprising:-speed measurement means capable of determining a speed (v) of the mobile entity (2) relative to the base station (1); -control means capable of determining the number (n) of time-of-flight measurements as a decreasing function of the speed (v) of the mobile entity (2) and of causing the distance measuring means (3) to perform a number (n) of time-of-flight measurements in order to obtain the same number of basic distance measurements (di); filtering means capable of determining the distance (d) by calculating a median of the basic distance measurements (di).

Description

TECHNICAL FIELD

[0001] The invention relates to a device and a method for determining the distance between a base station and a mobile entity using time of flight. BACKGROUND

[0002] It is known to determine the distance between a base station and a mobile entity using time of flight measurements.

[0003] To this end, the base station emits a wave, for example a radio frequency wave. This wave is reflected by the mobile entity. The base station receives the reflected wave. The base station measures the time interval between the emission and the return of the wave and is thus able to deduce the distance from this using the formula d = (tr - te) / 2v, where d is the sought distance, tr is the date of return of the wave, te is the date of emission of the wave and v is the propagation speed.

[0004] The distance measurement is affected by errors. Thus, for a time of flight device using UWB modulation, the error on a single measurement is + / - 20 cm, which is not sufficient for some applications.

[0005] One technique that makes it possible to improve the accuracy of the distance measurement consists in performing a plurality of measurements and averaging or median filtering these measurements. The more measurements, the greater the accuracy, but also the longer the response time. Many applications cannot tolerate this lengthening of the response time.

[0006] It is therefore sought to find an alternative way of determining the distance d between a base station and a mobile entity that makes it possible to improve the accuracy without lengthening the response time. SUMMARY

[0007] To this end, the invention proposes a determination process whose accuracy varies dynamically according to the time available.

[0008] One subject of the invention is a device for determining the distance between a base station and a mobile entity, the base station comprising a time of flight based distance measurement means, in which the device comprises:

[0009] - a speed measurement means able to determine the speed of the mobile entity relative to the base station,

[0010] - a control means able to determine the number of time of flight measurements as a decreasing function of the speed of the mobile entity and to cause the distance measurement means to perform a number of time of flight measurements to obtain a same number of elementary distance measurements,

[0011] - a filtering means able to determine the distance by calculating the median of the elementary distance measurements.

[0012] The following are specific features or embodiments that can be used individually or in combination:

[0013] - the decreasing function of the speed is the quotient of the reference speed and the speed of the mobile entity,

[0014] - the reference speed is the speed that enables a reference distance to be travelled in a composite sampling period of time-of-flight measurements, this reference distance preferably being equal to 0.5 m, this composite sampling period preferably being equal to a basic sampling period, equal to 96 ms,

[0015] - the distance measurement device comprises a plurality of antennas, and the device for determining the distance further comprises a cycling device that cyclically uses the antennas to produce the same number of basic distance prediction measurements and to determine a basic distance measurement equal to the minimum of the basic distance prediction measurements,

[0016] - the cycling device cyclically uses the antennas according to the basic sampling period, and the number of time-of-flight measurements and the number of basic distance measurements are calculated on the basis of a composite sampling period, equal to the basic sampling period multiplied by the number of antennas,

[0017] - the speed measurement device comprises a radar arranged on the base station,

[0018] - the speed measurement device comprises a sensor arranged on the mobile entity and a communication device that enables the speed to be transmitted to the base station,

[0019] - the distance measurement device comprises a radio frequency transceiver using ultra-wide band, UWB, modulation,

[0020] - the radar is merged with the radio frequency transceiver, the radio frequency transceiver being configured in radar mode,

[0021] - the communication device is merged with the radio frequency transceiver, the radio frequency transceiver combining with a homologous radio frequency transceiver arranged on the mobile entity. BRIEF DESCRIPTION OF DRAWINGS

[0022] The application will be better understood by reading the following description, provided purely by way of example and with reference to the appended drawings in which:

[0023] [ Figure 1 ] shows an overview of the environment of the application,

[0024] [ Figure 2 ] shows a table for determining the number of measurements as a function of the speed of the mobile entity according to a first embodiment,

[0025] [ Figure 3 ] shows a table for determining the number of measurements as a function of the speed of the mobile entity according to another embodiment. DETAILED DESCRIPTION

[0026] Reference Figure 1 The application relates to a device 10 for determining a distance d between a base station 1 and a mobile entity 2.

[0027] In one illustrative application of the application, the base station 1 is a motor vehicle and the mobile entity 2 is a user of the motor vehicle, more particularly represented by his smartphone. This application aims at determining the distance between the base station 1 and the mobile entity 2 in order to perform or not perform certain motor vehicle access control functions depending on the distance between the base station 1 and the mobile entity 2. Thus, the user should not be granted access as long as he is more than 2 m away from the vehicle. When the user is close and at the latest when he touches the door handle of the vehicle, he should be granted access.

[0028] To this end, the base station 1 comprises a time-of-flight based distance measurement device 3.

[0029] According to one feature, the device 10 further comprises a speed measurement device, a control device and a filtering device. The speed measurement device is able to determine a relative speed v of the mobile entity 2 with respect to the base station 1. The control device is able to determine a number n of time-of-flight measurements as a decreasing function of the speed v of the mobile entity 2. The control device is also able to cause the distance measurement device 3 to perform the number n of time-of-flight measurements. These n time-of-flight measurements make it possible to obtain a same number n of distance measurement values di, with i between 1 and n. The filtering device is able to determine the distance d by computing a median of the n distance measurement values di.

[0030] Since the number n of time-of-flight measurements is a decreasing function of the speed v of the mobile entity 2, the response time directly depends on the accuracy of the distance measurement value d if the speed of movement of the mobile entity 2 is faster, the available time is short. Thus, the measurement of the distance d is performed with few distance measurement values di, guaranteeing a shorter response time at the expense of an accuracy. Conversely, if the speed of movement of the mobile entity 2 is slower, the available time is longer. Thus, the measurement of the distance d is performed with a greater number of distance measurements di, guaranteeing an improved accuracy at the expense of a longer response time.

[0031] The idea of using a decreasing function of the speed v to determine the number n of time-of-flight measurements makes it possible to dynamically adjust the number n of time-of-flight measurements. Indeed, the faster the speed of movement of the mobile entity 2, the less time the device 10 has to update the distance d, the speed of which is faster. In this case, the number n is reduced and the accuracy of the measurement of the distance d is also reduced. However, an optimized measurement as accurate as possible is provided within the available time, with a minimum delay.

[0032] On the other hand, the slower the mobile speed of the mobile entity 2, the more time the device 10 has to update the distance d and the slower the distance d changes. In this case, the number n increases and the measurement accuracy of the distance d improves. Thus, the device 10 provides an optimized distance measurement with improved accuracy taking into account more available time. The delivery delay is slightly increased, but does not produce any adverse consequences since the distance d also changes more slowly.

[0033] The decreasing function of the speed v can be any decreasing function.

[0034] According to another feature, the decreasing function of the speed v is the quotient of a reference speed v0 and the speed v of the mobile entity 2. Thus, the curve of this function is a hyperbola. In mathematical terms, this function f of the variable v can be written n = f(v) = v0 / v. In this formula, n is the number of time-of-flight measurements, v is the speed v of the mobile entity 2, and v0 is a reference speed which is constant for the application.

[0035] According to another feature, the reference speed v0 is determined as follows. A reference distance d0 is chosen which is relevant for the application. Then the reference speed v0 is the speed which makes it possible to travel the reference distance d0 in the time required to determine the elementary distance di, i.e. the time which will be called the composite sampling period Te'.

[0036] In the illustrative application of determining the distance between a user and his vehicle, the significant event is when the user grasps the door handle of the vehicle. This event is characterized by the distance d between the mobile entity 2 / smartphone (assuming it is carried in a pocket at waist or chest level) and the base station 1 / vehicle, which is substantially equal to the length of the user's forearm. Thus, in this illustrative application, the reference distance d0 is chosen to be equal to 50 cm.

[0037] Still in this illustrative application, the composite sampling period Te' is a multiple of the elementary sampling period Te. Assuming there is a single antenna 11, the multiplication factor is equal to 1, as explained below. According to the CCC standard, the elementary sampling period Te is constrained to a value of 96 ms or 0.096 s. Thus, the composite sampling period Te' here is equal to 96 ms. As a result, in this case, the reference speed v0 = d0 / Te' is equal to 0.5 / 0.096, i.e. to 5.2 m / s or 18.75 km / h.

[0038] This means that, in the illustrative application, Figure 2The table shown gives the function between the number n of elementary distance measurements di and the speed v of the mobile entity 2 in km / h. For intermediate speeds between two values, the minimum value of n is chosen. Thus, for example, for a speed of 3 km / h, which is intermediate between the limits 3.1 km / h and 2.7 km / h, the number of measurements n is taken equal to the lower limit value, i.e. n = 6.

[0039] According to another feature, the distance measurement device 3 comprises a plurality of antennas 11, 12. As mentioned above, the apparatus 10 can operate with a single antenna 11. However, one or more additional antennas 12 make it possible to create a spatial diversity which makes it possible to improve the accuracy of the elementary distance measurements di. In order to exploit this spatial diversity, the apparatus 10 for determining the distance d also comprises a cycling device. This cycling device is able to cyclically use each of the antennas 11, 12 in order to produce a distance prediction measurement dj with them respectively, where the index j varies from 1 to p, where p is the number of antennas 11, 12. As mentioned above, the distance prediction measurements dj are obtained from time-of-flight measurements. For all the antennas 11, 12, the elementary distance measurement di is determined which is equal to the minimum of the respective distance prediction measurements dj. In practice, it can be considered that the distances between the antennas 11, 12 are sufficiently close for their respective propagations to be considered as identical. Thus, it is mainly the presence or absence of multipath which distinguishes them from one another. Thus, the minimum distance is the closest to the actual distance. Next, the processing of the elementary distance measurements di is substantially as described previously.

[0040] When there is more than one antenna, each of the antennas 11, 12 is used in turn according to the elementary sampling period Te. This means that the composite sampling period Te' corresponding to the obtaining of the elementary measurements di is equal to the elementary sampling period Te multiplied by the number p of antennas 11, 12, i.e. Te' = Te * p.

[0041] Thus, the number n of time-of-flight measurements should be adjusted accordingly. According to another feature, the number n of time-of-flight measurements is calculated on the basis of the composite sampling period Te'. This composite sampling period Te' is equal to the elementary sampling period Te multiplied by the number p of antennas 11, 12. From this, the reference speed v0 = d0 / Te' = d0 / (p.Te) is divided by p. n is modified accordingly.

[0042] Thus, in the illustrative application, the elementary sampling period Te is constrained to a value of 96 ms or 0.096 s according to the CCC standard. Thus, the composite sampling period Te' is then equal to 192 ms. As a result, in this case, the reference speed v0 = d0 / Te' is equal to 0.5 / 0.192, i.e. equal to 2.6 m / s or 9.4 km / h.

[0043] This means that, in the illustrative application,Figure 3 The table shown gives the functional relationship between the number n of elementary distance measurements di and the speed v of the mobile entity 2, in km / h.

[0044] There are at least two ways of determining the speed v of the mobile entity 2. The first is to use a radar arranged on the base station 1. The second is to use a sensor arranged on the mobile entity 2 to measure the speed v. Since all the calculations are preferably performed on the base station 1, it is necessary to transmit the speed measurement v obtained on the mobile entity 2 from the mobile entity 2 to the base station 1. This is done using the communication means 6.

[0045] In the first case, the speed measurement means comprise a radar 4. This radar 4 can take any type: radio, ultrasound, laser, etc. The radar 4 is arranged on the base station 1. It emits waves in the direction of the mobile entity 2 and analyses the reflected waves to determine the speed v of the mobile entity 2, generally using the Doppler effect.

[0046] In the second case, the speed measurement means comprise a sensor 5 arranged on the mobile entity 2. This sensor 5 can take any type that makes it possible to measure the speed v of the mobile entity 2 carrying the sensor 5. The communication means 6 then transmit the speed v to the base station 1. This communication means 6 generally comprises a transmitter embedded in the mobile entity 2 and an associated receiver embedded in the base station.

[0047] According to another feature, in the case where the mobile entity 2 is a smartphone, the sensor 5 advantageously reuses the position / orientation / speed sensor or IMU (Inertial Measurement Unit) of said smartphone.

[0048] According to another feature, the distance measurement means 3 comprise a radio frequency transceiver 7 using ultra-wide band, UWB, modulation. Such a device makes it possible to perform time-of-flight measurements.

[0049] According to another feature, the radar 4 reuses said radio frequency transceiver 7. In this case, the radio frequency transceiver 7 is configured in radar mode so as to be able to measure the speed v of the mobile entity 2 using the Doppler effect.

[0050] The communication means 6 can take any type and use any technology that makes it possible to transmit the measurements. According to another feature, the communication means 6 reuse the radio frequency transceiver 7 of the base station 1 and combine it with a homologous radio frequency transceiver 8 arranged on the mobile entity 2.

[0051] The application has been shown and described in detail in the drawings and the foregoing description. This should be considered as illustrative in nature, and is provided by way of example only, and not limiting the application to the specification. Many alternative embodiments are possible.

[0052] List of reference signs

[0053] 1: base station,

[0054] 2: mobile entity,

[0055] 3: time-of-flight based measuring device,

[0056] 4: radar,

[0057] 5: sensor,

[0058] 6: communication device,

[0059] 7: base station transceiver,

[0060] 8: mobile entity transceiver,

[0061] 10: distance determining device,

[0062] 11, 12: antenna,

[0063] d: base station / mobile entity distance,

[0064] do: reference distance,

[0065] di: basic distance measurement value,

[0066] dj: basic distance prediction value,

[0067] p: number of antennas,

[0068] Te: basic sampling period,

[0069] Te': composite sampling period,

[0070] v: relative speed of the mobile entity,

[0071] v0: reference speed.

Claims

1. An apparatus (10) for determining the distance (d) between a base station (1) and a mobile entity (2), the base station (1) including a time-of-flight distance measurement device (3), the apparatus comprising: - A speed measuring device capable of determining the speed (v) of the moving entity (2) relative to the base station (1), The device also includes: - A control device capable of determining the number of flight time measurements (n) as the quotient of the reference speed (v0) and the speed (v) of the moving entity (2), and capable of enabling the distance measuring device (3) to perform a certain number (n) of flight time measurements to obtain the same number of basic distance measurement values ​​(di). - A filtering device that can determine the distance (d) by calculating the median of these basic distance measurements (di).

2. The device (10) as claimed in claim 1, wherein, The reference speed (v0) is the speed that enables the travel of a reference distance (d0) within a composite sampling period (Te') of the time-of-flight measurement, the reference distance being preferably equal to 0.5 m, and the composite sampling period being preferably equal to the basic sampling period (Te), which is equal to 96 ms.

3. The device (10) as claimed in any one of claims 1 and 2, wherein, The distance measuring device (3) includes multiple antennas (11, 12), and the device (10) for determining distance (d) also includes a cyclic device that is capable of cyclically using the antennas (11, 12) to generate the same number of basic distance prediction values ​​(dj) and determining a basic distance measurement value (di) equal to the minimum of these basic distance prediction values ​​(dj).

4. The device (10) as claimed in claim 3, wherein, The cyclic device uses these antennas (11, 12) cyclically according to the basic sampling period (Te), wherein the number of flight time measurements (n) and the number of basic distance measurements (di) are calculated based on a composite sampling period (Te'), which is equal to the basic sampling period (Te) multiplied by the number of antennas (11, 12) (p).

5. The device (10) as claimed in any one of claims 1 to 4, wherein, The speed measuring device includes a radar (4) mounted on the base station (1).

6. The device (10) as claimed in any one of claims 1 to 5, wherein, The speed measuring device includes a sensor (5) arranged on the moving entity (2) and a communication device (6) capable of transmitting the speed (v) to the base station (1).

7. The device (10) as claimed in any one of claims 1 to 6, wherein, The distance measuring device (3) includes a radio frequency transceiver (7) using ultra-wideband (UWB) modulation.

8. The device (10) as claimed in claim 7, wherein, The radar (4) is combined with the radio frequency transceiver (7), which is configured in radar mode.

9. The device (10) as claimed in claim 7 or 8, wherein, The communication device (6) is combined with the radio frequency transceiver (7), which is combined with the same radio frequency transceiver (8) arranged on the moving entity (2).

10. A method for determining the distance (d) between a base station (1) and a mobile entity (2), the base station (1) including a time-of-flight distance measurement device (3), the method comprising the steps of: - Determine the velocity (v) of the moving entity (2) relative to the base station (1), The method further includes the following steps: -The number of flight time measurements (n) is determined as the quotient of the reference speed (v0) and the speed (v) of the moving entity (2). - The distance measuring device (3) is instructed to perform a certain number (n) of flight time measurements in order to obtain the same number of basic distance measurements (di). - The distance (d) is determined by calculating the median of these basic distance measurements (di).

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