METHOD AND SYSTEM FOR LOCATING OBJECTS

• US 20140253296A1
• Filed: 07/31/2012
• Published: 09/11/2014
• Est. Priority Date: 08/04/2011
• Status: Active Grant

• Current Assignee: Technische Universitã¤T Wien
• Original Assignee: Technische Universitã¤T Wien
• Inventors: Arthaber, Holger
• Granted Patent: US 9,471,820 B2
• Time in Patent Office: Days
• US Class Current: 340/10.5
• CPC Class Codes: G01S 13/751 wherein the responder or reflector radiates a coded signal
• CPC Class Codes: G01S 13/825 with exchange of information between interrogator and responder
• CPC Class Codes: G01S 13/878 Combination of several spaced transmitters or receivers of known location for determining the position of a transponder or a reflector G01S13/874 takes precedence
• CPC Class Codes: G06K 7/10366 the interrogation device being adapted for miscellaneous applications

Abstract

The invention relates to a method for locating an RFID tag (1) using at least one RFID reading device (2). The invention is characterized in that the RFID reading device (2) transmits a query signal (3) which comprises a broadband signal (4); the RFID tag (1) modulates the query signal (3) with a code signal (5) by varying the antenna impedance of the RFID tag and reflects said signal as a reflected signal (6); the RFID reading device (2) receives the reflected signal (6) and obtains the code signal (5) and a scattered broadband signal (7) from the reflected signal; the RFID reading device (2) determines a travel time of the broadband signal (4) by comparing the broadband signal (4) with the scattered broadband signal (7); the RFID reading device (2) determines the distance between the RFID reading device (2) and the RFID tag (1) from the travel time difference.

Claims

1. A method for locating an RFID tag (1) using at least one RFID reading device (2), characterized in that

a. the RFID reading device (2) emits a query signal (3) comprising a broadband signal (4);

b. the RFID tag (1) modulates the query signal (3) with a code signal (5) and reflects it as a reflection signal (6);

c. the RFID reading device (2) receives the reflection signal (6) and obtains the code signal (5) and a scattered broadband signal (7) therefrom;

d. the RFID reading device (2) determines a propagation time of the broadband signal (4) by comparing the broadband signal (4) with the scattered broadband signal (7);

e. the RFID reading device (2) determines the distance between the RFID reading device (2) and the RFID tag (1) from the propagation time difference.

2. The method as claimed in claim 1, characterized in that the broadband signal (4) is in the form of a direct-sequence spread-spectrum signal, an OFDM signal or a chirp signal.

3. The method as claimed in claim 1 or 2, characterized in that the comparison in step d) is carried out as a correlation or in the form of a matching method.

4. The method as claimed in one of claims 1 to 3, characterized in that the code signal (5) is in the form of a digital signal which is free of mean values.

5. The method as claimed in claim 4, characterized in that the duration of a sub-bit of the code signal (5) is an integer multiple of the period duration of the broadband signal (4).

6. The method as claimed in one of claims 1 to 5, characterized in that the code signal (5) codes any desired data signal (8), in which case FM0 sequences, Miller sequences or other coding is/are used.

7. The method as claimed in one of claims 1 to 6, characterized in that, in step c), the scattered broadband signal (7) is multiplied by the sign of the code signal (5) in the respective time period and is added over one or more periods.

8. A method for determining the position of an RFID tag (1), in which case the position of one or more RFID reading devices (2) is known, characterized in that the distance between the RFID reading devices (2) and the RFID tag (1) is determined using a method as claimed in one of claims 1 to 7, and the position of the RFID tag (1) is calculated from the known positions of at least one of the RFID reading devices (2).

9. The method as claimed in one of claims 1 to 8, characterized in that data are transmitted between the RFID reading device (2) and the RFID tag (1) by means of modulated back-scattering or dedicated modulators.

10. The method as claimed in one of claims 1 to 9, characterized in that the carrier signal is in the form of a radio-frequency carrier signal and preferably has a frequency of 850 MHz to 950 MHz.

11. The method as claimed in one of claims 1 to 10, characterized in that the RFID tag (1) is a passive RFID tag according to EPC Class1 Gen2.

12. The method as claimed in one of claims 1 to 11, characterized in that the RFID reading device (2) additionally carries out an angle estimation in order to locate the RFID tag (1).

13. The method as claimed in one of claims 1 to 12, characterized in that subspace algorithms, in particular ESPRIT and/or MUSIC, are used on the RFID reading device (1) in step d) in order to improve the determination of the propagation time and/or in order to estimate the angle.

14. The method as claimed in one of claims 1 to 13, characterized in that the RFID tag carries out the modulation in step b) either by varying its antenna impedance or in the form of active modulation.

15. The method as claimed in one of claims 1 to 14, characterized in that the RFID tag emits a dedicated auxiliary signal for distance measurement.

16. A system for locating an RFID tag (1) using at least one RFID reading device (2), the RFID reading device (1) comprising a data processing unit (9) and at least one antenna (11), and the RFID tag (1) comprising at least one antenna (13) and a logic unit (14),

characterized in that

the RFID tag (1) is set up to reflect a query signal (3), modulated with a code signal (5), as a reflection signal (6),

the RFID reading device (2) is set up to emit a query signal (3) comprising a broadband signal (4) and to obtain the code signal (5) and a scattered broadband signal (7) from the reflection signal (6),

the data processing unit (9) is set up to determine a propagation time difference by comparing the broadband signal (4) with the scattered broadband signal (7) and to calculate the distance between the RFID reading device (2) and the RFID tag (1) therefrom.

17. The system as claimed in claim 16, characterized in that the system also comprises a data processing unit (15), which is connected or can be connected to the RFID reading devices (1), and a database (16), the positions of the RFID reading devices (1) being stored in the database and the data processing unit (15) being set up to calculate the position of the RFID tags (1) from the positions of the RFID reading devices (2) and the distances between the RFID reading devices (2) and the RFID tags (1).

18. The system as claimed in claim 16 or 17, characterized in that a plurality of antennas are provided on the RFID reading device in order to estimate the angle in one or two planes.

19. The system as claimed in one of claims 16 to 18, characterized in that the RFID tag is in the form of a passive, active or semi-active RFID tag.