Method and apparatus for interference reduction in a positioning system

• US 6,788,251 B2
• Filed: 05/03/2001
• Issued: 09/07/2004
• Est. Priority Date: 05/03/2000
• Status: Expired due to Term

• Current Assignee: Stripe, Inc.
• Original Assignee: Thales Navigation Incorporated (MiTAC Holdings Corp.)
• Inventors: Lyusin, Sergey, Townsend, Todd V.
• Primary Examiner(s): PHAN, DAO LINDA
• Application Number:
  US09/848,768
• Publication Number:
  US 20040004570A1
• Time in Patent Office: 1,223 Days
• Field of Search: 342/145, 342/357.01, 342/357.02, 342/357.04, 342/384
• US Class Current: 342/384
• CPC Class Codes: G01S 19/05 providing aiding data
• CPC Class Codes: G01S 19/21 Interference related issues ; Issues related to cross-correlation, spoofing or other methods of denial of service
• CPC Class Codes: G01S 19/25 involving aiding data received from a cooperating element, e.g. assisted GPS
• CPC Class Codes: G01S 5/0045 Transmission from base station to mobile station G01S5/009 takes precedence

Abstract

Embodiments of the present invention relate to a method and apparatus for reducing interference in a positioning system. According to one or more embodiments of the present invention, the receiver in a conventional positioning system is configured to communicate with a terrestrial broadcast station. The terrestrial broadcast station transmits assistance signals to the receiver and may be another receiver. The assistance signals enable the receiver to locate very weak signals being transmitted from the satellites in the positioning system. In one embodiment, the assistance signals include Doppler frequencies for the satellites. In another embodiment, the assistance signals include Ephemeris data. In another embodiment, the assistance signals include almanac data. In other embodiments of the present invention, the assistance signal includes navigation bits demodulated from the carrier phase inversion signal of the satellite, time synchronization signals, and pseudo range differential corrections. A conventional correlation path is used to provide ghost satellite cancellation. When a signal is detected in the conventional path, it is inverted and subtracted from the assisted correlation path.

Claims

1. A positioning system comprising:

a first correlation path for detecting and correlating satellite position signals and providing an output when a signal is detected;

a second correlation path for detecting and correlating said satellite position signals;

a subtractor coupled to said first and second correlation paths for removing said output from an input of said second correlation path resulting in a presumed output signal that cancels out a presumed ghost signal.

2. The positioning system of claim 1 including an assistance signal coupled to said second correlation path.

3. The positioning system of claim 2 wherein said assistance signal includes one or more Doppler frequencies for said satellites.

4. The positioning system of claim 2 wherein said assistance signal includes one or more locations for said satellites.

5. The positioning system of claim 2 wherein said assistance signal includes a list of one or more satellites that are currently available.

6. The positioning system of claim 2 wherein said assistance signal includes one or more navigation bits in said signals from said satellites.

13. The method of claim 1, wherein said first correlation path presumes that the detected signal is a ghost signal.

14. The method of claim 13, wherein the detected signal is inverted and provided as said output to said subtractor.

7. A method for using a positioning system receiving signals from one or more satellites comprising the steps of:

detecting and correlating the signals in a first correlation path and providing an output when a signal is detected and correlated;

detecting and correlating the signals in a second correlation path having an input;

subtracting said output from said first correlation path from said input of said second correlation path resulting in a presumed output signal that cancels out a presumed ghost signal.

8. The method of claim 7 further including an assistance signal coupled to said second correlation path.

9. The method of claim 8 wherein said assistance signal includes one or more Doppler frequencies for said satellites.

10. The method of claim 8 wherein said assistance signal includes one or more locations for said satellites.

11. The method of claim 8 wherein said assistance signal includes a list of one or more satellites that are currently available.

12. The method of claim 8 wherein said assistance signal includes a list of one or more navigation bits in said signals from said satellites.

15. The method of claim 7, comprising said first correlation path presumes that the detected signal is a ghost signal.

16. The method of claim 7, comprising inverting the detected signal and providing said output in said subtracting step.

17. The method of claim 7, wherein the signal detected at the first correlation path is subtracted from a data sample stored in a memory unit, and this value is provided as said output in said subtracting step.

18. The method of claim 17, comprising estimating pseudoranges and signal strengths and subtracting this estimate from the data sample stored in memory.