Method and apparatus for weak data bit sync in a positioning system

• US 8,184,047 B1
• Filed: 11/24/2008
• Issued: 05/22/2012
• Est. Priority Date: 11/24/2008
• Status: Active Grant

• Current Assignee: Qualcomm technologies international, ltd. (Qualcomm, Inc.)
• Original Assignee: CSR Technology Holdings Inc. (Qualcomm, Inc.)
• Inventors: Lennen, Gary
• Primary Examiner(s): Tarcza, Thomas
• Assistant Examiner(s): McGue, Frank J
• Application Number:
  US12/276,987
• Time in Patent Office: 1,275 Days
• Field of Search: 342/357.12, 342/357.67
• US Class Current: 342/357.67
• CPC Class Codes: G01S 19/23 Testing, monitoring, correcting or calibrating of receiver elements
• CPC Class Codes: G01S 19/235 Calibration of receiver components
• CPC Class Codes: G01S 19/24 Acquisition or tracking or demodulation of signals transmitted by the system synchronisation aspects of direct sequence spread spectrum modulation H04B1/7073
• CPC Class Codes: G01S 19/258 relating to the satellite constellation, e.g. almanac, ephemeris data, lists of satellites in view

Abstract

The present invention is related to location positioning systems, and more particularly, to a method and apparatus of synchronizing to data bits in a positioning system signal. According to a first aspect, the present invention speeds up data bit sync by allowing high Pfa in the overall bit sync computation (e.g. 10⁻²) for coarse aided case. According to another aspect, the present invention combines and aligns signals from satellites for use in the bit sync computation (e.g. for improved sensitivity and speed).

Claims

1. A method for synchronizing to one or more signals in a positioning system, the method comprising:

accumulating respective first power values at a plurality of time offsets for a first one of the signals;

accumulating respective second power values at the plurality of time offsets for a second one of the signals;

time aligning the first and second signals;

combining the accumulated first and second power values at the plurality of time offsets after time alignment;

identifying a peak combined power value at one of the plurality of time offsets; and

determining whether the peak combined power value corresponds to successful synchronization.

2. A method according to claim 1, wherein the plurality of time offsets are twenty 1 msec intervals corresponding to a 20 msec data bit interval in a GPS signal.

3. A method according to claim 1, wherein the first and second power values correspond to combined I and Q values derived from the first and second signals, respectively.

4. A method according to claim 1, wherein the step of time aligning includes:

determining a difference in respective travel times of the first and second signals;

aligning the plurality of time offsets for the first and second signals based on the determined difference.

5. A method according to claim 1, wherein the step of time aligning includes:

obtaining an estimated position of respective transmitters of the first and second signals;

obtaining an estimated position of a common receiver of the first and second signals;

determining a difference in respective travel times of the first and second signals based on the obtained estimated positions;

aligning the plurality of time offsets for the first and second signals based on the determined difference.

6. A method according to claim 5, wherein the estimated positions are obtained from a network.

7. A method according to claim 5, wherein the respective transmitters are borne by respective satellite vehicles.

8. A method according to claim 1, further comprising:

identifying a signal quality of the one or more signals;

selecting the first and second signals from among the signals based on the identified signal quality before the combining step.

9. A device that performs the method of claim 1.

10. A method for synchronizing to one or more signals in a positioning system, the method comprising:

receiving estimated position information and an estimated time;

accumulating respective power values at a plurality of time offsets for two or more of the signals using the received estimated position information and the estimated time;

identifying a peak power value at one of the plurality of time offsets;

determining whether the peak power value corresponds to successful synchronization,

wherein a lower threshold of success is used if the received estimated position information and the estimated time satisfy a given criteria.

11. A method according to claim 10, wherein the plurality of time offsets are twenty 1 msec intervals corresponding to a 20 msec data bit interval in a GPS signal.

12. A method according to claim 10, wherein power values correspond to combined I and Q values derived from the signals.

13. A method according to claim 10, wherein the signals include first and second signals, the method further comprising:

determining a difference in respective travel times of the first and second signals from respective transmitters of the first and second signals to a common receiver of the first and second signals;

aligning the plurality of time offsets for the first and second signals based on the determined difference.

14. A method according to claim 10, wherein the signals include first and second signals, the method further comprising:

obtaining an estimated position of respective transmitters of the first and second signals from the estimated position information;

obtaining an estimated position of a common receiver of the first and second signals from the estimated position information;

determining a difference in respective travel times of the first and second signals based on the obtained estimated positions;

aligning the plurality of time offsets for the first and second signals based on the determined difference.

15. A method according to claim 14, wherein the estimated positions are obtained from a network.

16. A method according to claim 14, wherein the estimated positions are obtained from stored information that is retrieved in a hot start of the common receiver.

17. A device that performs the method of claim 10.

18. A method for synchronizing to one or more signals in a positioning system, the method comprising:

accumulating respective first power values at a plurality of time offsets for a first one of the signals;

identifying a first peak power value at one of the plurality of time offsets; and

determining whether the first peak power value corresponds to successful synchronization of the first signal;

accumulating respective second power values at the plurality of time offsets for a second one of the signals;

time aligning the first and second signals;

combining the accumulated first and second power values at the plurality of time offsets after time alignment;

identifying a peak combined power value at one of the plurality of time offsets; and

determining whether the peak combined power value corresponds to successful synchronization of the combined signals,

wherein a threshold for success of the combined signals is lower than a threshold for success of the first signal.

19. A method according to claim 18, wherein the plurality of time offsets are twenty 1 msec intervals corresponding to a 20 msec data bit interval in a GPS signal.

20. A method according to claim 18, wherein the first and second power values correspond to I and Q values derived from the first and second signals, respectively.

21. A method according to claim 18, wherein the step of time aligning includes:

determining a difference in respective travel times of the first and second signals from respective transmitters of the first and second signals to a common receiver of the first and second signals;

aligning the plurality of time offsets for the first and second signals based on the determined difference.

22. A method according to claim 18, wherein the step of time aligning includes:

obtaining an estimated position of respective transmitters of the first and second signals;

obtaining an estimated position of a common receiver of the first and second signals;

determining a difference in respective travel times of the first and second signals based on the obtained estimated positions;

aligning the plurality of time offsets for the first and second signals based on the determined difference.

23. A method according to claim 22, wherein the estimated positions are obtained from a network.

24. A device that performs the method of claim 18.

25. A method for synchronizing to one or more signals in a positioning system, the method comprising:

synchronizing to a common 20 msec data bit interval in the signals by identifying a combined peak power value at one of a plurality of aligned time offsets in two or more of the signals and comparing it to a low threshold of success; and

synchronizing to the 20 msec data bit interval in the signals by identifying a single peak power value at one of a plurality of single time offsets in a single one of the signals and comparing it to a higher threshold of success.

26. A device that performs the method of claim 25.