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

• US 8,970,431 B2
• Filed: 05/22/2012
• Issued: 03/03/2015
• Est. Priority Date: 11/24/2008
• Status: Active Grant

• Current Assignee: Qualcomm technologies international, ltd. (Qualcomm, Inc.)
• Original Assignee: Cambridge Silicon Radio Limited (Qualcomm, Inc.)
• Inventors: Lennen, Gary
• Primary Examiner(s): McGue, Frank J
• Application Number:
  US13/478,077
• Publication Number:
  US 20120299771A1
• Time in Patent Office: 1,015 Days
• Field of Search: 342/357.12, 342/357.62
• US Class Current: 342/357.62
• 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:

determining if sufficient a priori information on time or position associated with the signals is known;

setting a target probability of false alarm (Pfa) to a first value if the a priori information is determined to be not sufficient and setting the target Pfa to a second value that is less strict than the first value if the a priori information is determined to be sufficient;

setting thresholds for determining if data bit synchronization has been achieved in accordance with the target Pfa that has been set based on the determination of the a priori information; and

performing, by a positioning device having a receiver for receiving the signals, data bit synchronization using the signals and the thresholds that have been set in accordance with the target Pfa.

2. A method according to claim 1, wherein performing data bit synchronization includes:

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 based on the thresholds that have been set in accordance with the target Pfa.

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

4. A method according to claim 2, wherein the first and second power values correspond to combined I and Q values derived from the first and second signals, respectively.

5. A method according to claim 2, 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.

6. A method according to claim 2, 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.

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

8. A method according to claim 6, wherein the respective transmitters are borne by respective satellite vehicles.

9. A method according to claim 2, 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.

10. A method according to claim 1, wherein the step of determining if sufficient a priori information on time or position associated with the signals is known includes:

determining whether one or both of an unknown time offset between satellites associated with the signals and an unknown position of a receiver of the signals are within time and position uncertainty thresholds.

11. A method according to claim 10, wherein the time uncertainty threshold is half a modulo one millisecond uncertainty and the position uncertainty threshold is 150 km.

21. A method according to claim 2, wherein the first and second signals are respectively transmitted by first and second different transmitters in the positioning system.

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

receiving an estimated position information and an estimated time;

determining if the estimated position information and the estimated time are within respective position and time uncertainty ranges;

setting a target probability of false alarm (Pfa) to a first value if the estimated position information and the estimated time are determined to be not within the respective uncertainty ranges and setting the target Pfa to a second value that is less strict than the first value if the estimated position information and the estimated time are determined to be not within the respective uncertainty ranges;

setting thresholds for determining if data bit synchronization has been achieved in accordance with the target Pfa that has been set based on the determination of the estimated position information and the estimated time; and

performing, by a positioning device having a receiver for receiving the signals, data bit synchronization using the signals and the thresholds that have been set in accordance with the target Pfa.

13. A method according to claim 12, wherein performing data bit synchronization includes:

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; and

determining whether the peak power value corresponds to successful synchronization based on the thresholds that have been set in accordance with the target Pfa.

14. A method according to claim 13, wherein the plurality of time offsets are twenty 1 msec intervals corresponding to a 20 msec data bit interval in a GPS signal.

15. A method according to claim 13, wherein power values correspond to combined I and Q values derived from the signals.

16. A method according to claim 13, 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.

17. A method according to claim 13, 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.

18. A method according to claim 17, wherein the estimated positions are obtained from a network.

19. A method according to claim 17, wherein the estimated positions are obtained from stored information that is retrieved in a hot start of the common receiver.

20. A method according to claim 12, wherein the time uncertainty is half a modulo one millisecond uncertainty and the position uncertainty is 150 km.

22. A method according to claim 13, wherein the first and second signals are respectively transmitted by first and second different transmitters in the positioning system.