Autonomous data aided GPS signal acquisition method and system

• US 6,295,024 B1
• Filed: 02/19/1999
• Issued: 09/25/2001
• Est. Priority Date: 02/19/1999
• Status: Expired due to Term

• Current Assignee: CSR Technology Incorporated (Qualcomm, Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Durboraw, Issac N. III, King, Thomas M.
• Primary Examiner(s): PHAN, DAO LINDA
• Application Number:
  US09/253,318
• Time in Patent Office: 949 Days
• Field of Search: 342/357.06, 342/357.12, 342/352, 455/12.1, 701/213
• US Class Current: 342/357.64
• 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 19/30 code related G01S19/246 takes precedence

Abstract

A data-aided system and method of GPS signal acquisition from a plurality of broadcasted GPS signals includes receiving (401) the GPS signals and providing a digitized signal. Then, a first portion (407) of the digitized signal is correlated to a code replica and a real-time code phase delay is determined. A capture start time is determined (411) dependent on a Time Of Arrival (409) based on the determined real-time code phase delay. Next, a second portion of the digitized signal is captured into a memory (413) commencing coincident with the determined capture start time. Then the second portion of the digitized signal is extracted from the memory and correlated to the code replica (411) to determine an off-line code phase delay. A position fix is calculated (417) and includes the off-line code phase delay.

Claims

1. A method of GPS signal acquisition from a plurality of broadcasted GPS signals comprising the steps of:

receiving the plurality of broadcasted GPS signals and providing a digitized signal dependent thereon;

correlating a first portion of the digitized signal to a code replica and determining a real-time code phase delay;

determining a Time Of Arrival (TOA) of a deterministic portion of the digitized signal, dependent on the determined real-time code phase delay;

determining a capture start time dependent on the determined TOA;

capturing a second portion of the digitized signal into a memory commencing coincident with the determined capture start time; and

extracting the second portion of the digitized signal from the memory and correlating the extracted signal to the code replica and determining an off-line code phase delay dependent thereon.

2. A method in accordance with claim 1 wherein the step of correlating, associated with the step of extracting and correlating, occurs at a rate greater than the step of correlating a first portion of the digitized signal to a code replica.

3. A method in accordance with claim 1 further comprising a step of:

determining loss of correlation lock, and wherein the step of capturing a second portion of the digitized signal into a memory is executed when the loss of correlation lock is determined.

4. A method in accordance with claim 3 wherein the second portion of the digitized signal captured into memory comprises a plurality of trailing bits of a first GPS satellite broadcast message subframe, and a plurality of bits of a preamble of a second GPS satellite broadcast message subframe immediately following the first GPS satellite broadcast message subframe.

5. A method in accordance with claim 3 wherein the second portion of the digitized signal captured into memory comprises a hand-over word.

6. A method in accordance with claim 5 further comprising a step of determining a real-time Doppler shift dependent on the determined real-time code phase delay.

7. A method in accordance with claim 5 further comprising a step of determining a off-line Doppler shift dependent on the determined off-line code phase delay.

8. A method in accordance with claim 5 further comprising a step of computing a position fix dependent on the determined real-time code phase delay.

9. A method in accordance with claim 5 further comprising a step of computing a position fix dependent on the determined off-line code phase delay.

10. A method in accordance with claim 1 wherein the step of correlating a first portion of the digitized signal comprises a step of correlating a first portion of the digitized signal to a code replica and Doppler replica and determining code phase delays from at least two satellites comprising at least one real-time code phase delay, the method further comprising a step of:

computing a position fix dependent on at least three code phase delays comprising the determined off-line code phase delay.

11. A method of GPS signal acquisition from a plurality of broadcasted GPS signals comprising the steps of:

receiving the plurality of broadcasted GPS signals and providing a digitized signal dependent thereon;

correlating a first portion of the digitized signal to a code replica and determining a real-time code phase delay;

determining a Time Of Arrival (TOA) of a deterministic portion of the digitized signal, dependent on the determined real-time code phase delay;

determining a capture start time dependent on the determined TOA;

deriving a real-time code phase delay prediction dependent on the determined real-time code phase delay and Time Of Arrival (TOA) and identifying a reduced code replica search space dependent thereon;

capturing a second portion of the digitized signal into a memory commencing coincident with the determined capture start time; and

extracting the second portion of the digitized signal from the memory and, correlating the extracted signal to the reduced code replica search space and determining an off-line code phase delay dependent thereon.

12. A method in accordance with claim 11 wherein the step of correlating, associated with the step of extracting and correlating, occurs at a rate greater than the step of correlating the first portion of the digitized signal to a code replica.

13. A method in accordance with claim 11 further comprising a step of:

determining loss of correlation lock, and wherein the step of capturing a second portion of the digitized signal into a memory is executed when the loss of correlation lock is determined.

14. A method in accordance with claim 13 wherein the second portion of the digitized signal captured into memory comprises a plurality of trailing bits of a first GPS satellite broadcast message subframe, and a plurality of bits of a preamble of a second GPS satellite broadcast message subframe immediately following the first GPS satellite broadcast message subframe.

15. A method in accordance with claim 13 wherein the second portion of the digitized signal captured into memory comprises a hand-over word.

16. A method in accordance with claim 12 further comprising a step of determining a off-line Doppler shift dependent on the determined off-line code phase delay.

17. A method in accordance with claim 12 further comprising a step of computing a position fix dependent on the determined real-time code phase delay.

18. A method in accordance with claim 12 further comprising a step of computing a position fix dependent on the determined off-line code phase delay.

19. A method in accordance with claim 11 wherein the step of correlating a first portion of the digitized signal comprises a step of correlating a first portion of the digitized signal to a code replica and Doppler replica and determining code phase delays from at least two satellites comprising at least one real-time code phase delay, the method further comprising a step of:

computing a position fix dependent on at least three code phase delays comprising the determined off-line code phase delay.

20. A Global Positioning System (GPS) receiver comprising:

a GPS front-end for receiving a plurality of broadcasted GPS signals and providing a digitized signal dependent thereon;

a first correlator operatively couplable to the front-end for correlating a first portion of the digitized signal to a code replica and determining a real-time code phase delay, then determining a capture start time dependent on the determined real-time code phase delay; and

a memory operably coupled to the front-end for capturing a second portion of the digitized signal into a memory commencing coincident with the determined capture start time, and wherein the first correlator is operably couplable to the memory for extracting the second portion of the digitized signal from the memory and correlating the extracted signal to the code replica and determining an off-line code phase delay.

21. A receiver in accordance with claim 20 further comprising a clock source providing a clock signal to the first correlator, and wherein the determination of the real-time code phase delay is dependent on the clock signal.

22. A receiver in accordance with claim 21 wherein the clock source comprises a two-way communications receiver.

23. A receiver in accordance with claim 22 wherein the two-way communications receiver is one of a CDMA telephone, pager, and other radiotelephone device.

24. A receiver in accordance with claim 20 further comprising:

a second correlator operably coupled to the memory for extracting the second portion of the digitized signal from the memory and correlating the extracted signal to the code replica and determining an off-line code phase delay.

25. A method of GPS signal acquisition from a plurality of broadcasted GPS signals in a GPS receiver with a receiver front-end and a computational back-end, the method comprising the steps of:

powering on the GPS receiver front-end;

receiving the plurality of broadcasted GPS signals and providing a digitized signal dependent thereon;

correlating a first portion of the digitized signal to a code replica and Doppler replica and determining code phase delays from at least three satellites comprising at least one real-time code phase delay;

determining a first position fix dependent on each of the code phase delays and satellite broadcast ephemeris data extracted from the first portion of the digitized signal;

determining a local precise time dependent on the determined first position fix;

determining a satellite signal propagation time for at least one satellite of the at least three satellites;

determining a capture start time dependent on the determined local precise time and the satellite signal propagation time;

determining loss of correlation lock;

powering off the GPS receiver front-end for a period of time until the determined capture start time;

powering on the GPS receiver front-end and capturing a second portion of the digitized signal into memory commencing coincident with the determined capture start time;

powering off the GPS receiver front-end;

extracting the second portion of the digitized signal from the memory and correlating the extracted signal to the code replica, Doppler replica, and a predicted 50 BPS navigation data replica and determining an off-line code phase delay dependent thereon for each satellite signal contained in the second portion of the digitized signal in memory; and

computing a second position fix dependent on at least three code phase delays including the determined off-line code phase delay.

26. A method in accordance with claim 25 wherein the step of correlating, associated with the step of extracting and correlating, occurs at a rate greater than the step of correlating a first portion of the digitized signal to a code replica.

27. A method in accordance with claim 26 wherein the second portion of the digitized signal captured into memory comprises a plurality of trailing bits of a first GPS satellite broadcast message subframe, and a plurality of bits of a preamble of a second GPS satellite broadcast message subframe immediately following the first GPS satellite broadcast message subframe.

28. A method in accordance with claim 27 further comprising the steps of:

determining a real-time Doppler shift dependent on the at least one real-time code phase delay; and

computing a reduced code replica search space dependent on the at least one real-time code phase delay and the real-time Doppler shift, and a time difference between their determination and the determined capture start time.

29. A method in accordance with claim 28 wherein the step of

extracting the second portion of the digitized signal from the memory comprises a step of extracting the second portion of the digitized signal from the memory and correlating the extracted signal to the code replica, Doppler replica, and a predicted 50 BPS navigation data replica and determining an off-line code phase delay dependent thereon for each satellite signal contained in the second portion of the digitized signal in memory.

30. A method of GPS signal acquisition from a plurality of broadcasted GPS signals in a GPS receiver with a receiver front-end and a computational back-end, the method comprising the steps of:

receiving the plurality of broadcasted GPS signals and providing a digitized signal dependent thereon;

correlating a first portion of the digitized signal to a code replica and determining a real-time code phase delay;

determining a Time Of Arrival (TOA) of a deterministic portion of the digitized signal, dependent on the determined real-time code phase delay;

determining a capture start time dependent on the determined TOA;

capturing a second portion of the digitized signal into a memory;

powering off the GPS receiver front-end for a period of time until the determined capture start time;

extracting the second portion of the digitized signal from the memory and correlating the extracted signal to a code replica and determining a first off-line code phase delay estimate dependent thereon using a non-coherent integration method;

identifying a reduced code replica search space dependent on the first off-line code phase delay estimate;

powering on the GPS receiver front-end and capturing a third portion of the digitized signal into memory commencing coincident with the determined capture start time; and

extracting the third portion of the digitized signal from the memory and correlating the extracted signal to the reduced code replica search space and determining a second off-line code phase delay dependent thereon.

31. A method in accordance with claim 30 wherein the third portion of the digitized signal captured into memory comprises a plurality of trailing bits of a first GPS satellite broadcast message subframe, and a plurality of bits of a preamble of a second GPS satellite broadcast message subframe immediately following the first GPS satellite broadcast message subframe.

32. A method in accordance with claim 31 wherein the second portion of the digitized signal captured into memory comprises a hand-over word.

33. A method in accordance with claim 32 further comprising a step of computing a position fix dependent on the determined off-line code phase delay.

34. A method in accordance with claim 33 wherein the step of correlating a first portion of the digitized signal comprises a step of correlating a first portion of the digitized signal to a code replica and Doppler replica and determining code phase delays from at least two satellites comprising at least one real-time code phase delay, the method further comprising a step of:

computing a position fix dependent on at least three code phase delays comprising the determined off-line code phase delay.