Simulating Phase-Coherent GNSS Signals

• US 20110109506A1
• Filed: 09/23/2010
• Published: 05/12/2011
• Est. Priority Date: 09/24/2009
• Status: Abandoned Application

• Current Assignee: Apple Inc.
• Original Assignee: Coherent Navigation, Inc. (Apple Inc.)
• Inventors: Galusha, Bryan T., Ledvina, Brent M., Cohen, Clark E., Bencze, William J., Humphreys, Todd E.
• Application Number:
  US12/889,247
• Publication Number:
  US 20110109506A1
• Time in Patent Office: Days
• US Class Current: 342/357.68
• CPC Class Codes: G01S 19/215 issues related to spoofing

Abstract

A method and apparatus for simulating radio-frequency Global Navigation Satellite System (GNSS) signals that are carrier-phase and code-phase aligned with ambient GNSS signals at a user-specified location in the vicinity of the simulator. Such phase alignment allows the synthesized signals to be made to appear substantially the same as the authentic signals to a target receiver, allowing the target receiver to transition seamlessly between authentic and simulated signals. The method is embodied in a device, a phase-coherent GNSS signal simulator, which can be implemented on a digital signal processor for embedded applications.

Claims

1. A GNSS phase-coherent signal simulator comprising:

a GNSS signal receiver operable to receive one or more ambient radio-frequency GNSS signals;

a GNSS signal simulator operable to generate one or more simulated radio-frequency GNSS signals;

a timing oscillator coupled to both the GNSS signal receiver and the GNSS signal simulator; and

a control module operable to align both a carrier phase and a code phase of the one or more simulated GNSS signals respectively with a carrier phase and a code phase of the one or more ambient radio-frequency GNSS signals at a predetermined three-dimensional position offset and a predetermined velocity offset relative to a reference location on the GNSS phase-coherent signal simulator.

2. The GNSS phase-coherent signal simulator of claim 1, wherein at least one of the position offset and the velocity offset is substantially zero.

3. The GNSS phase-coherent signal simulator of claim 1, wherein the position offset and velocity offset are individually selectively variable.

4. The GNSS phase-coherent signal simulator of claim 1, wherein the position offset is less than about 10 km.

5. The GNSS phase-coherent signal simulator of claim 1, wherein the signal simulator is configured to compensate for at least one of a signal processing latency and an analog RF bias.

6. The GNSS phase-coherent signal simulator of claim 1, wherein the signal simulator is operable to align the simulated GNSS signal with the ambient GNSS signal within about one tenth of a carrier wavelength.

7. The GNSS phase-coherent signal simulator of claim 1, wherein the reference location comprises an input antenna location.

8. The GNSS phase-coherent signal simulator of claim 1, wherein position and velocity offset are selected to align the code and carrier phases along a trajectory.

9. A method of combining a plurality of GNSS signals, the method comprising:

receiving, at a GNSS signal receiver, one or more ambient radio-frequency GNSS signals;

generating, with a GNSS signal simulator, one or more simulated radio-frequency GNSS signals;

receiving, at both the GNSS signal receiver and the GNSS signal simulator, a common timing reference; and

aligning, via a control module, both a carrier phase and a code phase of the one or more simulated radio-frequency GNSS signals respectively with a carrier phase and a code phase of the one or more ambient radio-frequency GNSS signals at a predetermined three-dimensional position offset and a predetermined velocity offset relative to a reference location on the GNSS phase-coherent signal simulator.

10. The method of claim 9, wherein the aligning includes compensating for analog RF biases.

11. The method of claim 9, further comprising calibrating the GNSS signal simulator to account for signal processing latency.

12. The method of claim 9, wherein the velocity offset is selected for carrier phase and code phase alignment at a stationary point.

13. The method of claim 9, wherein the velocity offset is selected for continuous carrier phase and code phase alignment along a trajectory of a moving point.

14. The method of claim 9, wherein the simulated GNSS signal is aligned with the ambient GNSS signal within one tenth of a carrier wavelength.

15. The method of claim 9, further comprising estimating a Doppler frequency offset.

16. The method of claim 15, wherein the Doppler frequency offset is set to within about 1 Hz.

17. The method of claim 9, wherein the respective carrier and code phases are each aligned at a centimeter-level.

18. A method of phase aligning GNSS signals via a GNSS signal simulator, the method comprising:

receiving one or more ambient radio-frequency GNSS signals;

generating one or more simulated radio-frequency GNSS signals; and

aligning both a carrier phase and a code phase of the one or more simulated radio-frequency GNSS signals respectively with a carrier phase and a code phase of the one or more ambient radio-frequency GNSS signals at a predetermined three-dimensional position offset and a predetermined velocity offset relative to a reference location on the GNSS signal simulator.

19. The method of claim 18, further comprising providing a timing reference to a GNSS receiver and the GNSS simulator via an oscillator to facilitate phase alignment.