Method and system for locating objects

• US 9,471,820 B2
• Filed: 07/31/2012
• Issued: 10/18/2016
• Est. Priority Date: 08/04/2011
• Status: Active Grant

• Current Assignee: Technische Universitã¤T Wien
• Original Assignee: Technische Universitã¤T Wien
• Inventors: Arthaber, Holger
• Primary Examiner(s): Syed, Nabil
• Application Number:
  US14/237,131
• Publication Number:
  US 20140253296A1
• Time in Patent Office: 1,540 Days
• US Class Current: 1/1
• 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

Method and systems for locating objects, in particular RFID tags, employ one or more RFID reading devices. The methods and/or systems make it possible to determine a distance between an RFID reading device and a deliberately selected RFID tag in a simple, robust manner. The RFID reading device determines a propagation time of a broadband signal by comparing the broadband signal with the scattered broadband signal. The RFID reading device determines a distance between the RFID reading device and the RFID tag from the propagation time difference.

Claims

1. A method for locating an RFID tag using at least one RFID reading device, the method comprising:

emitting a query signal comprising a broadband signal by the RFID reading device;

receiving by the RFID reading device a reflection signal from the RFID tag on which a code signal has been modulated by the RFID tag, and obtaining the code signal and a scattered broadband signal therefrom;

comparing the broadband signal with the scattered broadband signal by the RFID reading device to determine a propagation time of the broadband signal; and

determining a distance between the RFID reading device and the RFID tag from the propagation time difference by the RFID reading device,

wherein receiving the reflection signal from the RFID tag and obtaining the code signal and the scattered broadband signal therefrom includes multiplying the scattered broadband signal by a sign of the code signal in the respective time period and adding a resulting product of the multiplying over one or more periods.

2. The method as claimed in claim 1 wherein the broadband signal 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 wherein the comparing is carried out as a correlation or in the form of a matching method.

4. The method as claimed in claim 1, further comprising modulating the query signal with the code signal by the RFID tag and reflecting the modulate query signal as the reflection signal wherein the code signal is in the form of a digital signal which is free of mean values.

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

6. The method as claimed in claim 4 wherein the code signal codes any desired data signal, in which case at least one of FM0 sequences, Miller sequences are used.

7. A method for determining the position of an RFID tag, in which case the position of one or more RFID reading devices is known, the method comprising:

emitting a query signal comprising a broadband signal by the RFID reading device;

receiving by the RFID reading device a reflection signal from the RFID tag on which a code signal has been modulated by the RFID tag, and obtaining the code signal and a scattered broadband signal therefrom;

comparing the broadband signal with the scattered broadband signal by the RFID reading device to determine a propagation time of the broadband signal;

determining a distance between the RFID reading device and the RFID tag from the propagation time difference by the RFID reading device; and

calculating the position of the RFID tag from the known positions of at least one of the RFID reading devices,

wherein receiving the reflection signal from the RFID tag and obtaining the code signal and the scattered broadband signal therefrom includes multiplying the scattered broadband signal by a sign of the code signal in the respective time period and adding a resulting product of the multiplying over one or more periods.

8. The method as claimed in claim 7 wherein data is transmitted between the RFID reading device and the RFID tag by means of modulated back-scattering.

9. The method as claimed in claim 8 wherein the carrier signal is in the form of a radio-frequency carrier signal and has a frequency of 850 MHz to 950 MHz.

10. The method as claimed in claim 9 wherein the RFID tag is a passive RFID tag according to EPC Class1 Gen2.

11. The method as claimed in claim 10, further comprising performing an angle estimation by the RFID reading device in order to locate the RFID tag.

12. The method as claimed in claim 11 wherein comparing the broadband signal with the scattered broadband signal includes executing one or more subspace algorithms to improve the determination of the propagation time and/or in order to estimate the angle.

13. The method as claimed claim 7 further comprising modulating the query signal with the code signal by the RFID tag and reflecting the modulate query signal as the reflection signal by at least one of:

varying an antenna impedance.

14. The method as claimed in claim 13, further comprising emitting a dedicated auxiliary signal for distance measurement by the RFID tag.

15. A system for locating one or more RFID tags, the system comprising:

at least one RFID reading device, the at least one RFID reading device comprising a data processing unit and at least one antenna, and the one or more RFID tags each comprising at least one antenna and a logic unit, wherein the one or more RFID tags reflect one or more query signals, modulated with a code signal, as one or more reflection signals, the RFID reading device is set up to emit one or more query signals comprising a broadband signal and to obtain the code signal and a scattered broadband signal from the reflection signals,

the data processing unit of the at least one RFID reading device is set up to determine a propagation time difference by comparing the broadband signal with the scattered broadband signal and to calculate the distance between the RFID reading device and one or more RFID tags therefrom,

wherein the RFID reading device obtains the code signal and the scattered broadband signal from the reflection signals by, at least in part, multiplying the scattered broadband signal by a sign of the code signal in the respective time period and adding a resulting product of the multiplying over one or more periods.

16. The system as claimed in claim 15, further comprising a central data processing unit, which is connected or can be connected to the at least one RFID reading device, and a database, the positions of the at least one RFID reading device being stored in the database and the central data processing unit set up to calculate the position of the one or more RFID tags from the positions of the RFID reading devices and the calculated distances between the RFID reading devices and the one or more RFID tags.

17. The system as claimed in claim 15, wherein the RFID reading device includes a plurality of antennas in order to estimate an angle in one or two planes.

18. The system as claimed in claim 15 wherein the one or more RFID tags are in the form of a passive, active or semi-active RFID tags.