Method for identifying the position of a portable transponder, and an antitheft system

• US 20040207510A1
• Filed: 11/13/2002
• Published: 10/21/2004
• Est. Priority Date: 05/26/2000
• Status: Active Grant

• Current Assignee: Siemens AG
• Original Assignee: Siemens AG
• Inventors: Buchner, Reiner
• Granted Patent: US 7,034,656 B2
• Time in Patent Office: Days
• US Class Current: 340/5.61
• CPC Class Codes: B60R 25/24 using electronic identifiers containing a code not memorised by the user

Abstract

A method for the recognition of the proximity of a portable transponder (20) to a base station (2), comprises the steps of: the base station transmits a first test signal with a defined power, the transponder determines the field strength with which it received the first test signal, and transmits a response signal to the base station containing said field strength and the base station stores the same. The transponder transmits a second test signal with a defined power, the base station determines the field strength with which it receives the second test signal and determines, from a comparison of the two field strengths, whether the transponder is in the vicinity thereof.

Claims

1. A method for identifying a portable transponder as being located in the near area of a transmitting antenna of a base station, in which the base station sends a first test signal with a defined power level, the transponder determines the field strength with which it receives the first test signal and sends a response signal, which contains the field strength of the first test signal, to the base station, the base station stores the field strength with which the transponder has received the first test signal, the transponder sends a second test signal with a defined power level, the base station determines the field strength with which it receives the second test signal, and the two field strengths are compared in order to determine whether the transponder is located in the near area of the transmitting antenna of the base station.

2. The method as claimed in claim 1, in which the information contained in the response signal relating to the field strength of the first test signal is encrypted.

3. The method as claimed in claim 1, in which the transponder sends the response signal essentially at the same time as the second test signal.

4. The method as claimed in claim 2, in which the transponder sends the response signal essentially at the same time as the second test signal.

5. An antitheft system for a motor vehicle, containing a base station which is fixed to the vehicle and having a transmitting/receiving unit for wire-free communication with a transmitting/receiving unit of a portable transponder in which code information is stored, which can be sent from the transponder to the base station for authorization checking, with specific vehicle functions being enabled only after a positive authorization check, which base station and which transponder are designed such that the base station sends a first test signal with a predetermined power level, the transponder determines the field strength with which it receives the first test signal and sends a response signal with information about this field strength, the base station stores the received information about the field strength in a memory device, the transponder sends a second test signal with a predetermined power level, the base station determines the field strength with which the second test signal is received, compares the received field strength with the stored field strength and, in the event of any discrepancy which is greater than a predetermined level, assesses that the transponder is located outside the near area of the transmitting antenna of the base station.

6. A method for identifying a portable transponder as being located in the near area of a transmitting antenna of a base station, comprising the steps of:

transmitting a request signal to the portable transponder;

determining the field strength of the transmitted signal in the transponder;

transmitting a response signal to the base station;

transmitting the determined field strength to the base station;

determining the field strength of the response signal;

comparing the field strengths of the request signal and the response signal.

7. The method of claim 6, wherein the transmission of the response signal and the determined field strength of the request signal are combined to a single transmission.

8. The method of claim 6, wherein the determined field strength is transmitted together with a first response signal to the base station and wherein a second response signal is transmitted after a time delay.

9. The method of claim 6, wherein the base station stores the determined field strength of the request signal.

10. The method of claim 6, wherein the base station determines that the transponder is within the near area if the difference between the field strength of the request signal and the response signal are within a predefined range.

11. The method of claim 6, wherein the request signal comprises an identification number.

12. The method of claim 6, wherein the transmitted signals are data encrypted.

13. The method of claim 7, wherein the combined signals are data encrypted.