Access control system with limited evaluation of code and distance information

• US 6,943,725 B2
• Filed: 03/05/2004
• Issued: 09/13/2005
• Est. Priority Date: 03/07/2003
• Status: Active Grant

• Current Assignee: Continental Automotive GmbH (Continental AG)
• Original Assignee: Siemens AG
• Inventors: Gila, Janos, Konrad, Wolfgang
• Primary Examiner(s): Sotomayor, John B.
• Application Number:
  US10/793,720
• Publication Number:
  US 20040189511A1
• Time in Patent Office: 557 Days
• Field of Search: 342 42- 51, 340/5.2, 340/5.7, 340/5.72, 340/825.36, 340/825.49
• US Class Current: 342/42
• CPC Class Codes: G01S 13/825 with exchange of information between interrogator and responder
• CPC Class Codes: G07C 2009/00555 comprising means to detect or avoid relay attacks
• CPC Class Codes: G07C 2009/00793 by Hertzian waves
• CPC Class Codes: G07C 2209/61 Signal comprising different frequencies, e.g. frequency hopping
• CPC Class Codes: G07C 2209/63 Comprising locating means for detecting the position of the data carrier, i.e. within the vehicle or within a certain distance from the vehicle
• CPC Class Codes: G07C 9/00309 operated with bidirectional data transmission between data carrier and locks

Abstract

An access control system for an object, particularly a motor vehicle, comprises at least one base station with a transceiver device that transmits a wideband modulated interrogation signal, at least one transponder that has a modulation device, in order to modulate an auxiliary carrier signal, the frequency of which is changed between an infinite number of frequency positions, onto an interrogation signal received at a distance from the base station and reflect it as a code-modulated response signal, and an evaluation device that is connected after the transceiver device and that evaluates the response signal in sidebands of the changed frequency positions, with respect code and distance.

Claims

1. An access control system for an object, particularly a vehicle, comprising:

At least one base station with a transceiver device that transmits a wideband modulated interrogation signal,

At least one transponder that has a modulation device, in order to modulate an auxiliary carrier signal, the frequency of which is re-keyed between a finite number of frequency positions, onto an interrogation signal received at a distance from the base station, and reflect it as a code-modulated response signal, and

An evaluation device that is connected downstream from the transceiver device and that evaluates the response signal in sidebands of the keyed frequency positions with regard to code and distance.

2. The access control system in accordance with claim 1, wherein the code signal is a binary data signal and the modulation device is a two-frequency keying device that changes the frequency of the auxiliary carrier signal between two frequency positions.

3. The access control system in accordance with claim 1, wherein the evaluation unit contains a Fourier transformation device for transforming the response signal.

4. The access control system in accordance with claim 3, wherein the Fourier transformation device is set up according to the fast (FFT) or discrete (DFT) Fourier transformation method, or in accordance with the Gö

rtzel signal processing method.

5. The access control system in accordance with claim 1, wherein the evaluation unit only generates an enable signal if the code information agrees with a stored set code information and the determined distance is less than a predeterminable distance threshold.

6. The access control system in accordance with claim 1, wherein the interrogation signal is a wideband modulated radar signal with a bandwidth greater than 60 MHz, with a center frequency in the 2.5 GHz, 5.8 GHz or 24 GHz range being particularly preferred.

7. The access control system in accordance with claim 1, wherein the transponder is formed as an active or passive transponder.

8. A method for operating an access control system for a vehicle that comprising the following steps:

transmitting a wideband modulated interrogation signal from at least one base station;

receiving the interrogation signal by at least one transponder located at a distance from the base station,

modulating the interrogation signal, in a modulation device, by a carrier signal, whose frequency is changed in the modulation device in relation to a code between a finite number of frequency positions, and

reflected the modulated interrogation signal as a code-modulated answer signal, and

evaluating, in at least one base station, the response signal in sidebands of the changed frequency positions in an evaluation unit with respect to code and distance.

9. The method in accordance with claim 8, wherein a two-frequency keying takes place in the modulation device and the code and distance are determined from the first and second frequency band of the response signal.

10. The method in accordance with claim 8, wherein the response signal in the frequency bands is evaluated by a Fourier transformation algorithm, particularly preferably by a fast (FFT) or discrete (DFT) Fourier transformation algorithm or according to the Gö

rtzel signal processing method.

11. The method in accordance with claim 8, wherein the evaluation unit generates an enable signal only if the evaluation of the sidebands shows that the code information agrees with the stored set code information and the determined distance is less than a predeterminable distance threshold.

12. The method in accordance with claim 8, wherein the interrogation signal is formed from a series of up-chirp ramps and down-chirp ramps rising and falling essentially in a monotone.

13. The method in accordance with claim 12, wherein the time duration of an up-chirp ramp and the time duration of a down-chirp ramp are selected to be of equal magnitude.

14. The method in accordance with claim 13, wherein the chosen time duration is greater than 1 μ

s and less than 100 milliseconds.

15. The method in accordance with claim 8, wherein the interrogation signal is transmitted intermittently until a response signal is received from a code transmitter.

16. The method in accordance with claim 8, wherein the interrogation signal is transmitted as a wideband modulated radar signal with a bandwidth of more than 60 MHz, with a center frequency in the 2.5 GHz, 5.8 GHz or 24 GHz range being particularly preferred.

17. The method in accordance with claim 8, wherein the code is divided into data packets and parts of the code are transmitted from the code transmitter to the base station depending on the spacing.

18. The method in accordance with claim 17, wherein the transmission of the code takes place at a data rate that is less in an area distant from the base station than in an area close to the base station.

19. The method in accordance with claim 17, wherein the code is transmitted encrypted.

20. The method in accordance with claim 17, wherein the transmission of the code is manually triggered by an actuating device on the code transmitter.