UTILIZING SBAS SIGNALS TO IMPROVE GNSS RECEIVER PERFORMANCE

• US 20100232351A1
• Filed: 03/11/2009
• Published: 09/16/2010
• Est. Priority Date: 03/11/2009
• Status: Active Grant

• Current Assignee: Qualcomm technologies international, ltd. (Qualcomm, Inc.)
• Original Assignee: CSR Technology Holdings Inc. (Qualcomm, Inc.)
• Inventors: Xie, Gang, CHANSARKAR, Mangesh, Zhang, Gengsheng
• Granted Patent: US 8,593,342 B2
• Time in Patent Office: Days
• US Class Current: 370/320
• CPC Class Codes: G01S 19/13 Receivers
• CPC Class Codes: G01S 19/25 involving aiding data received from a cooperating element, e.g. assisted GPS

Abstract

The present invention provides methods of improving GNSS receivers'"'"' satellite signal acquisition and TIFF performances by taking advantage of SBAS signals. Due to a SBAS satellite'"'"'s geostationary position and typically strong signal, the SBAS satellite signal can be acquired more quickly than a GPS satellite signal. Once a SBAS satellite signal is acquired the Doppler frequency search uncertainty may be reduced for remaining GNSS satellites which are to be acquired. Furthermore, a satellite search list may be optimized to search for satellites close to the line of sight (LOS) of the SBAS satellite for which a signal has been acquired, in receiver “warm” and “hot” start modes. Moreover, since a SBAS signal sub-frame is only one second long, which is shorter than six seconds for a GPS signal sub-frame, synchronization of the SBAS signal sub-frame may be achieved faster than for GPS signals. With aided time information, a receiver may compute the absolute time of week (TOW) from a sub-frame synchronized SBAS signal. Therefore, without necessarily waiting for TOW to be decoded from a GPS signal and with TOW extracted from a SBAS signal, a receiver can achieve better TTFF performance.

Claims

1. A method of reducing a satellite frequency search range in a satellite code division multiple access (CDMA) signal receiver, comprising:

searching for a geostationary satellite signal;

acquiring said geostationary satellite signal;

estimating receiver crystal oscillator frequency bias; and

calculating a frequency search range for subsequent satellite signals to be acquired.

2. A method as in claim 1, wherein said geostationary satellite signal is transmitted from a satellite-based augmentation system (SBAS) satellite.

3. A method as in claim 2, wherein said SBAS satellite is a wide area augmentation system (WAAS) satellite.

4. A method as in claim 1, wherein said CDMA signal receiver searches for said geostationary satellite signal before any other satellite signal.

5. A method as in claim 1, wherein said estimating includes ignoring Doppler frequency shift due to movement of said CDMA signal receiver relative to the geostationary satellite.

6. A method as in 1, wherein said frequency search range equals a Doppler frequency uncertainty caused by movement of said CDMA signal receiver relative to the geostationary satellite.

7. A method as in 1, wherein said calculating a frequency search range includes adding together only (1) a Doppler frequency uncertainty caused by movement of said CDMA signal receiver relative to the Earth'"'"'s surface, and (2) a Doppler frequency uncertainty caused by movement of the orbit of the geostationary satellite relative to the Earth'"'"'s surface.

8. A method of optimizing a satellite search list in a CDMA signal receiver, comprising:

acquiring a geostationary satellite signal;

calculating angles between the line of sight for the geostationary satellite and the line of sight for other satellites;

flagging satellites for which said angle is less than a threshold value; and

placing flagged satellites at the beginning of said satellite search list.

9. A method as in claim 8, wherein said geostationary satellite signal is transmitted from a satellite-based augmentation system (SBAS) satellite.

10. A method as in claim 8, wherein said other satellites include a SBAS satellite.

11. A method as in claim 8, further comprising placing the flagged satellites in an order corresponding to the size of the calculated angles, said order having the smallest of the calculated angles first.

12. A method as in claim 8, wherein said threshold value is 0.35 radians.

13. A method as in claim 8, wherein said other satellites are satellites not yet acquired by said CDMA signal receiver.

14. A method as in claim 8, wherein said other satellites include GPS satellites.

15. A method as in claim 8, wherein said other satellites include a second SBAS satellite.

16. A method in a GPS receiver of extracting GPS time from a satellite-based augmentation system (SBAS) satellite signal and aided time information, said method comprising:

acquiring said SBAS satellite signal;

identifying a repeating SBAS signal sub-frame preamble;

accepting said aided time information;

calculating one or more candidates for said GPS time; and

determining said GPS time from said one or more candidates.

17. A method as in claim 16, wherein said determining includes identifying the one of said one or more candidates that is within said uncertainty of said aided time.

18. A method as in claim 17, wherein said aided time information provides an aided time with an uncertainty of less than three seconds.

19. A method as in claim 16, wherein said determining includes:

acquiring multiple satellite signals;

generating a GPS position fix for each of said one or more candidates;

calculating pseudo-range residuals for each of said one or more candidates; and

choosing the one of said one or more candidates with the smallest residual.

20. A method as in claim 19, wherein said aided time information provides an aided time with an uncertainty and wherein there are multiple of said one or more candidates within said uncertainty.

21. A method as in claim 20, wherein said uncertainty is greater than three seconds.

22. A method as in claim 19, wherein said acquiring includes acquiring four satellite signals in addition to said SBAS satellite signal, said four satellite signals and said SBAS satellite signal being from five different satellites.

23. A method as in claim 22, wherein one of said four satellite signals is from a second SBAS satellite.

24. A method as in claim 19, wherein said acquiring includes acquiring three satellite signals in addition to said SBAS satellite signal, said three satellites signals and said SBAS satellite signal being from four different satellites, and wherein the altitude of said GPS receiver is known.

25. A method as in claim 24, wherein one of said three satellite signals is from a second SBAS satellite.

26. A method as in claim 19, further comprising checking the plausibility of each said GPS position fix for each of said one or more candidates, wherein said choosing includes choosing the one of said one or more candidates with the smallest residual and plausible GPS position fix.

27. A method as in claim 16, wherein said SBA signal is transmitted from a wide area augmentation system (WAAS) satellite.

28. A method as in claim 16, wherein said GPS time is time of week (TOW).

29. A method as in claim 16, wherein said aided time information is accepted from a cellular network.

30. A method as in claim 16, wherein said GPS receiver acquires said SBAS satellite signal before any other satellite signal.