Keyless access system for a motor vehicle, and method for locating a signal generator of the access system

Abstract

A keyless access system for a motor vehicle, which includes a portable signal generator for access to one or more doors or flaps of the motor vehicle, wherein the signal generator transmits an enable signal to a receiver unit, mounted on the motor vehicle, by a short-range radio link. The receiver unit permits access to one or more doors or flaps if it is determined that the enable signal is valid and a distance criterion which represents a distance between the signal generator and the motor vehicle is satisfied. The distance criterion results from a comparison of a weighted reception field strength of the short-range radio link between the signal generator and the receiver unit with a threshold value.

Claims

1. A keyless access system for a motor vehicle, comprising: a portable signal generator for access to one or more doors or flaps of the motor vehicle, which signal generator transmits an enable signal to a receiver unit, mounted on the motor vehicle, by a short-range radio link, wherein the receiver unit permits access to one or more doors or flaps if it is determined that the enable signal is valid and a distance criterion which represents a distance between the signal generator and the motor vehicle is satisfied, wherein the distance criterion results from a comparison of a weighted reception field strength of the short-range radio link between the signal generator and the receiver unit with a threshold value, wherein the reception field strength is weighted with a distance value between the signal generator and the motor vehicle, and wherein the distance value is calculated from first position data of the signal generator and second position data of the motor vehicle, wherein the first and the second position data are based on transit time differences between signals from a plurality of satellites to a respective GNSS receiver.

2. The keyless access system as claimed in claim 1, wherein the reception field strength of a signal which is emitted by the signal generator is ascertained by the receiver unit.

3. The keyless access system as claimed in claim 2, wherein the weighted reception field strength is the measured reception field strength divided by the distance value.

4. The keyless access system as claimed in claim 2, wherein, if the measured reception field strength is a logarithmic representation of the field strength, the weighted reception field strength is the measured reception field strength minus the logarithm of the distance value.

5. The keyless access system as claimed in claim 1, wherein the signal generator comprises a GNSS receiver, by which the first position data and the second position data is determined, in particular at different times.

6. The keyless access system as claimed in claim 5, wherein the weighted reception field strength is the measured reception field strength divided by the distance value.

7. The keyless access system as claimed in claim 5, wherein, if the measured reception field strength is a logarithmic representation of the field strength, the weighted reception field strength is the measured reception field strength minus the logarithm of the distance value.

8. The keyless access system as claimed in claim 1, wherein the signal generator comprises a GNSS receiver, by which the first position data of the signal generator is determined, and the motor vehicle comprises a GNSS receiver, by which the second position data of the motor vehicle is determined.

9. The keyless access system as claimed in claim 8, wherein the weighted reception field strength is the measured reception field strength divided by the distance value.

10. The keyless access system as claimed in claim 8, wherein, if the measured reception field strength is a logarithmic representation of the field strength, the weighted reception field strength is the measured reception field strength minus the logarithm of the distance value.

11. The keyless access system as claimed in claim 1, wherein the weighted reception field strength is the measured reception field strength divided by the distance value.

12. The keyless access system as claimed in claim 1, wherein, if the measured reception field strength is a logarithmic representation of the field strength, the weighted reception field strength is the measured reception field strength minus the logarithm of the distance value.

13. The keyless access system as claimed in claim 1, wherein the distance criterion is a binary variable.

14. The keyless access system as claimed in claim 1, wherein the receiver unit and the signal generator comprise communication interfaces according to the Bluetooth Standard 802.15, wherein the communication between the receiver unit and the portable signal generator takes place via these communication interfaces.

15. A method for determining the location of a portable signal generator of a keyless access system for a motor vehicle, wherein the portable signal generator serves for the access to one or more doors or flaps of the motor vehicle, comprising: measuring a reception field strength of a signal, emitted by the portable signal generator, over a short-range radio link by a receiver unit mounted on the motor vehicle; weighing the measured reception field strength; acquiring a distance criterion from a comparison of the weighted reception field strength of the short-range radio link between the signal generator and the receiver unit with a threshold value, in which the reception field strength is weighted with a distance value between the signal generator and the motor vehicle, and in which the distance value is calculated from first position data of the signal generator and second position data of the motor vehicle, wherein the first and second position data are based on transit time differences between signals from a plurality of satellites to a respective GNSS receiver.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) An aspect of the invention is explained in greater detail below on the basis of an exemplary embodiment in the drawing. The FIGURE shows a schematic illustration of an exemplary embodiment of a keyless access system according to an aspect of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(2) The FIGURE shows a keyless access system 1 according to an aspect of the invention. The access system 1 serves to access one or more doors or flaps (not illustrated in more detail in the FIGURE) or to start a motor vehicle 10 (not illustrated in detail). Furthermore, the keyless access system 1 comprises a portable signal generator 20 which is present in the form of a mobile terminal 21. The mobile terminal 21 can be, for example, a mobile radio terminal such as e.g. a smart phone. The latter comprises, in a way which is typical for smartphones, for example a display 23 and an input means 24 in the form of one or more keypads. Furthermore, any other mobile electronic device can also be used as a mobile terminal 21 provided that the latter has the interfaces and properties described below.

(3) The mobile terminal 21 has a communication interface 26 which is designed to transmit data over a short range. The communication interface 26 can be embodied, for example, as a Bluetooth interface. Furthermore, the mobile radio terminal has a GNSS receiver 25, which can be used by the mobile terminal to carry out a position-determining process on the basis of transit time differences between the signals from a plurality of satellites. As is known to the person skilled in the art, and will therefore not be explained in more detail, the position-determining process requires differences in distance to be proportional to the time differences.

(4) Assuming that the mobile terminal 21 is a mobile radio terminal, the latter also comprises a further communication interface 27, e.g. on the basis of the known GSM or UMTS standard. However, since this communication interface 27 is not significant for the present invention, more details are not given on this or on further functions of the mobile radio terminal.

(5) The motor vehicle 10 (not illustrated in more detail) has a receiver unit 11 with a communication interface 12 for short-range communication (e.g. Bluetooth) as well as a computer unit 13 which is connected to the communication interface 12 and has the purpose of processing the signals received by the communication interface 12 as well as of making available signals which are to be emitted via the communication interface 12. The receiver unit 11 is, for example, a transceiver. In addition, the receiver unit has a means for determining the reception field strength 14 of a signal which is emitted by the mobile terminal 21. Furthermore, the vehicle 10 has an optional GNSS receiver.

(6) The communication between the communication interface 12 of the receiver unit 11 and the communication interface 26 of the mobile terminal 21 takes place via the communication path K1 via the short-range radio link, preferably Bluetooth.

(7) In order to determine the location of the mobile terminal 21, the RF field strength (RSSI) of the signal emitted by the mobile terminal 21 is measured by the means 14. In addition, a distance value, i.e. a distance between the mobile terminal 21 and the motor vehicle 10, is determined. This can be done by determining and setting off the positions of the respective GNSS receiver 15 of the motor vehicle 10 and of the respective GNSS receiver 25 of the mobile terminal 21 against one another. Since the position-determining process using a plurality of satellites is known from the prior art, it will not be explained in more detail here. The position which is ascertained by the mobile terminal 21 can be transmitted to the receiver unit 11 via the communication path K1 in order to determine the distance value.

(8) If the motor vehicle 10 does not have a GNSS receiver 15, the determination of the position of the motor vehicle 10 can also be performed using the mobile terminal 11. For this purpose, a position-determining process takes place, e.g. when the engine of the motor vehicle is switched off, wherein the position ascertained at this time is stored for later use. During this procedure, it is assumed that the mobile terminal 21 is located in the motor vehicle 10 at the time when the engine of the motor vehicle 20 switched off, and therefore corresponds to the position of the motor vehicle 10. At a later time, when the distance value between the motor vehicle 10 and the mobile terminal 21 is to be ascertained, the mobile terminal 21 determines its position and the position value is transmitted to the receiver unit 12 of the motor vehicle 10 via the communication path K1.

(9) In order to determine the location of the mobile terminal 21, the measured field strength RSSI is weighted with the distance value (i.e. the distance between the motor vehicle 10 and the mobile terminal 21). The weighting can occur, for example, as follows: RSSI.sub.weighted=RSSI/distance value. If the measured RF field strength RSSI is a logarithmic representation of the field strength, RSSI.sub.weighted=RSSI-log.sub.10(distance value) can be used as the weighted field strength.

(10) Subsequently, the weighted field strength RSSI.sub.weighted is used for qualitative determination of distance. For this purpose, for example comparison is made with a threshold value which has been defined previously, e.g. by means of tests. The result of this comparison is of merely binary nature, i.e. there is information available as to whether the determined position of the mobile terminal lies within a distance limiting value or not. Only in the former case can a signal which is transmitted to the motor vehicle by the mobile terminal bring about the execution of a specific function, e.g. the closing of a window or sunroof of the motor vehicle 10.

(11) As a result of the weighting of the measured RF field strength it is possible to use the functionalities which are known from conventional keyless access systems, wherein conventional keyless access systems are understood to be access systems which use LF frequencies within the scope of their communication.

(12) As a result of the described procedure for ascertaining the distance value, the accuracy of the GNSS measurement is also taken into account in the method. The ascertained position of the vehicle and the distance of the mobile terminal from the vehicle can also be used for further functions such as e.g. searching for a vehicle.

LIST OF REFERENCE SIGNS

(13) 1 Keyless access system 10 Motor vehicle 11 Receiver unit 12 Communication interface (e.g. Bluetooth) 13 Computer unit 14 Means for measuring the reception field strength 15 GNSS receiver 20 Portable signal generator 21 Transmitter unit (mobile radio terminal) 23 Display 24 Input means 25 GNSS receiver 26 Communication interface (e.g. Bluetooth) 27 Communication interface