GPS synchronization for wireless communications stations

• US 20070161385A1
• Filed: 12/29/2005
• Published: 07/12/2007
• Est. Priority Date: 12/29/2005
• Status: Active Grant

• Current Assignee: Skyhook Holding, Inc. (Liberty Broadband Corp.)
• Original Assignee: TruePosition Incorporated
• Inventors: Anderson, Robert
• Granted Patent: US 7,593,738 B2
• Time in Patent Office: Days
• US Class Current: 455/502
• CPC Class Codes: G01S 19/03 Cooperating elements; Interaction or communication between different cooperating elements or between cooperating elements and receivers

Abstract

A method and system are specified to determine, provide, and exploit the precise time base relations between the distinct signal timings of the Global Positioning System (GPS) and a wireless communications system (WCS) for which the internal WCS downlink time base standards are not inherently synchronized to GPS timing. These downlink signal synchronization facilities are particularly beneficial for a wireless location system (WLS) and related methods and subsystems that provide mobile-station location determination through the exploitation of the time base synchronization information, e.g., to assist a GPS-equipped mobile station in determining its GPS-derived measurements with enhanced efficiency and accuracy.

Claims

1. A method for determining a GPS-synchronized timing representation for downlink signals transmitted from a base transceiver station (BTS) of a wireless communications system (WCS), comprising:

(a) receiving, at a measurement unit, a downlink signal transmitted by said BTS;

(b) evaluating said downlink signal to determine a time of arrival (TOA) at said measurement unit of a specified portion of said downlink signal; and

(c) determining an optimal time value for a GPS-based transmission time of an identifiable instant related to said measured TOA.

2. A method as recited in claim 1, wherein the step of receiving the downlink signal comprises receiving the downlink signal at a network of measurement units.

3. A method as recited in claim 1, further comprising communicating said optimal value to said WCS.

4. A method as recited in claim 1, further comprising communicating said optimal value to a mobile station (MS) served by said WCS.

5. A method as recited in claim 1, wherein said method is performed to support an augmenting service associated with said WCS serving a wireless mobile station (MS).

6. A method as recited in claim 5, further comprising communicating said optimal value to said augmenting service.

7. A method as recited in claim 1, wherein said identifiable instant comprises a communications data frame boundary.

8. A method as recited in claim 1, wherein said specified portion of said downlink signal comprises a communications data frame boundary.

9. A method as recited in claim 5, wherein said augmenting service comprises a wireless location service for determining the geographic location of the MS.

10. A computer readable medium comprising instructions for instructing a processor to perform a set of steps to determine a GPS-synchronized timing representation for downlink signals transmitted from a base transceiver station (BTS) of a wireless communications system (WCS), said set of steps comprising:

(a) receiving a downlink signal transmitted by said BTS;

(b) evaluating said downlink signal to determine a time of arrival (TOA) of a specified portion of said downlink signal; and

(c) determining an optimal time value for a GPS-based transmission time of an identifiable instant related to said measured TOA.

11. A computer readable medium as recited in claim 10, wherein the step of receiving the downlink signal comprises receiving the downlink signal at a measurement unit.

12. A computer readable medium as recited in claim 10, further comprising instructions for communicating said optimal value to said WCS.

13. A computer readable medium as recited in claim 10, further comprising instructions for communicating said optimal value to a mobile station (MS) served by said WCS.

14. A computer readable medium as recited in claim 10, wherein said set of steps are performed to support an augmenting service associated with said WCS serving a wireless mobile station (MS).

15. A computer readable medium as recited in claim 14, further comprising instructions for communicating said optimal value to said augmenting service.

16. A computer readable medium as recited in claim 10, wherein said identifiable instant comprises a communications data frame boundary.

17. A computer readable medium as recited in claim 10, wherein said specified portion of said downlink signal comprises a communications data frame boundary.

18. A computer readable medium as recited in claim 14, wherein said augmenting service comprises a wireless location service for determining the geographic location of the MS.

19. A wireless system, including a location measuring unit (LMU) and at least one base transceiver station (BTS) for communicating with at least one mobile station (MS), said LMU including a GPS receiver and a receiver for receiving downlink signals transmitted by said BTS, and a processor configured to control said LMU in performing a set of steps to determine a GPS-synchronized timing representation for downlink signals transmitted from said BTS, said set of steps comprising:

(a) receiving a downlink signal transmitted by said BTS;

(b) evaluating said downlink signal to determine a time of arrival (TOA) of a specified portion of said downlink signal; and

(c) determining an optimal time value for a GPS-based transmission time of an identifiable instant related to said measured TOA.

20. A wireless system as recited in claim 19, wherein the step of receiving the downlink signal comprises receiving the downlink signal at said LMU.

21. A wireless system as recited in claim 19, further comprising instructions for communicating said optimal value.

22. A wireless system as recited in claim 19, further comprising instructions for communicating said optimal value to a mobile station (MS).

23. A wireless system as recited in claim 19, wherein said set of steps are performed to support an augmenting service.

24. A wireless system as recited in claim 23, further comprising instructions for communicating said optimal value to said augmenting service.

25. A wireless system as recited in claim 23, wherein said augmenting service comprises a wireless location service for determining the geographic location of the MS.

26. A wireless system as recited in claim 19, wherein said identifiable instant comprises a communications data frame boundary.

27. A wireless system as recited in claim 19, wherein said specified portion of said downlink signal comprises a communications data frame boundary.

28. A signal processing method for use in processing a base transceiver station (BTS) downlink signal, comprising:

(a) acquiring a candidate time series from a received BTS downlink burst signal;

(b) correlating a frequency correction channel (FCCH) replica with a candidate broadcast control channel (BCCH) beacon signal to determine a nominal frame time alignment and time of arrival (TOA) for an FCCH burst signal;

(c) correlating a synchronization channel (SCH) extended training sequence to determine a time alignment and TOA for an SCH burst signal; and

(d) attempting to demodulate the SCH burst signal.

29. A signal processing method as recited in claim 28, further comprising:

(e) determining whether the SCH demodulation is acceptable and if so,

applying selected base station identity code (BSIC) and a frame number/reduced frame number (FN/RFN) to form a complete SCH replica;

correlating the SCH replica with the candidate BCCH signal to refine the TOA measurement for the SCH burst signal; and

integrating the SCH correlation with the associated FCCH correlation for the refined measurement of TOA.

30. A signal processing method as recited in claim 29, further comprising, as part of step (e), determining whether the correlation results are acceptable and if so propagating the measured GPS timebased TOA to an appropriate frame boundary, and forming a record of correlated BCCH carrier identification, BSIC, FN, and GPS-based TOA.

31. A signal processing method as recited in claim 28, further comprising:

(f) determining whether the SCH demodulation is acceptable and if not,

obtaining A-bis monitoring system (AMS)-derived possible partial/modulo frame and associated BSIC information for the candidate BCCH signal;

calibrating the AMS-derived timings to GPS-based times for possible partial/modulo frames, and using the candidate AMS-derived partial/modulo frame information to form the possible complete FNs with associated RFNs for the SCH;

applying selected BSIC and FN/RFN to form a complete SCH replica;

correlating the SCH replica with a candidate BCCH signal to refine the TOA measurement for the SCH burst signal;

integrating the SCH correlation with an associated FCCH correlation for a refined measurement of TOA.

32. A signal processing method as recited in claim 31, further comprising determining whether the correlation results are acceptable and, if so, propagating the measured GPS timebased TOA to an appropriate frame boundary, and forming a record of correlated BCCH carrier identification, BSIC, FN, and GPS-based TOA.