Method and apparatus for performing signal correlation using historical correlation data

• US 20020172306A1
• Filed: 09/26/2001
• Published: 11/21/2002
• Est. Priority Date: 05/18/2001
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Global Locate Incorporated (Broadcom, Inc.)
• Inventors: Abraham, Charles, Diggelen, Frank van
• Granted Patent: US 6,819,707 B2
• Time in Patent Office: Days
• US Class Current: 375/343
• CPC Class Codes: G01S 19/23 Testing, monitoring, correcting or calibrating of receiver elements
• CPC Class Codes: G01S 19/29 carrier including Doppler, related G01S19/246 takes precedence
• CPC Class Codes: G01S 19/30 code related G01S19/246 takes precedence
• CPC Class Codes: G01S 19/37 Hardware or software details of the signal processing chain
• CPC Class Codes: G06F 17/15 Correlation function computation including computation of convolution operations arithmetic circuits for sum of products per se, e.g. multiply-accumulators G06F7/5443; digital filters, e.g. FIR, IIR, adaptive filters H03H17/00
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04B 1/70752 Partial correlation
• CPC Class Codes: H04B 1/7077 Multi-step acquisition, e.g. multi-dwell, coarse-fine or validation
• CPC Class Codes: H04B 2201/70715 with application-specific features

Abstract

A method and apparatus for computing a convolution between an input GPS signal and a reference code by generating the convolution result in real time without storing unprocessed signal samples. The apparatus comprises a vector multiplier running at high speed to achieve the same result as a vector multiplier sized to process an entire epoch. Additionally, historical correlation data is used to correct frequency and timing errors.

Claims

1. In a satellite positioning receiver, a method for estimating a receiver parameter comprising:

a) generating a correlation history comprising a sequence of correlation results for a signal received from at least one satellite; and

b) estimating at least one receiver parameter from the correlation history.

2. The method of claim 1 further comprising:

(c) using the at least one receiver parameter when performing further correlations.

3. The method of claim 2 wherein the further correlations are performed on signals from a different satellite than said signal received from at least one satellite.

4. The method of claim 1 wherein the at least one receiver parameter comprises a frequency of a receiver oscillator.

5. The method of claim 1 wherein the at least one receiver parameter comprises a receiver timing error.

6. The method of claim 5 wherein the receiver timing error is a modulo 20 millisecond estimate of an offset of a receiver clock with respect to a satellite reference time.

7. The method of claim 5 wherein the at least one receiver parameter further comprises a frequency of a receiver oscillator.

8. The method of claim 2 wherein the further correlations are performed using a standard correlation mode.

9. The method of claim 1 wherein generating a sequence of correlation results comprises:

(a1) dividing a pseudorandom reference code into a plurality of code segments;

(a2) selecting a code segment;

(a3) forming an inner product between said selected code segment and a set of digital signal samples to produce a partial correlation;

(a4) repeating steps (a1) and (a3) to produce a plurality of partial correlations; and

(a5) summing the plurality of partial correlations as each partial correlation is produced to form a plurality of correlations.

10. The method of claim 1 further comprising:

dividing the received signal into in-phase and quadrature components; and

separately performing steps a) and b) on the in-phase and quadrature components.

11. The method of claim 1 further comprising generating navigation data bits from the correlation history.

12. The method of claim 1 wherein step (b) comprises:

applying the correlation history to a sequential estimation algorithm to estimate at least one of signal frequency and bit timing.

14. The method of claim 13 further comprising:

(c) frequency correcting the correlation history;

(d) integrating the correlation history over a navigation bit period;

(e) computing a signal level for the signal within the navigation bit period;

(f) summing a plurality of successive signal level values to form an integrated signal level value as the signal level to be maximized.

15. The method of claim 13 wherein said signal level is at least one of signal power and signal magnitude.

16. The method of claim 14 wherein said signal level is at least one of signal power and signal magnitude.

17. The method of claim 13 further comprising:

searching over frequency to determine a maxima in signal level.

18. The method of claim 13 further comprising:

searching over bit timing to determine a maxima in signal level.

19. The method of claim 13 further comprising:

searching over frequency and bit timing to determine a maxima in signal level.

20. The method of claim 17 wherein searching comprises a downhill simplex method.

13. In a satellite positioning receiver, a method for estimating at least one receiver parameter from a correlation history comprising:

a) determining, in response to the correlation history, a plurality of estimates of signal level using a receiver frequency and bit timing hypothesis;

b) determining, in response to signal level estimates, estimates of at least one receiver parameter that provides a frequency and bit timing for the receiver that substantially maximizes signal level.

21. Apparatus for estimating at least one receiver parameter in a satellite positioning receiver comprising:

a) means for generating a correlation history comprising a sequence of correlation results from signals received from at least one satellite; and

b) means for estimating at least one receiver parameter from the correlation history.

22. The apparatus of claim 21 further comprising:

(c) a correlator for using the receiver parameter when performing further correlations.

23. The apparatus of claim 22 wherein the further correlations are performed on signals from a different satellite than said signal received from at least one satellite.

24. The apparatus of claim 21 wherein the at least one receiver parameter comprises a frequency of a receiver oscillator.

25. The apparatus of claim 21 wherein the at least one receiver parameter comprises a receiver timing error.

26. The apparatus of claim 25 wherein the receiver parameter further comprises a frequency of a receiver oscillator.

27. The apparatus of claim 25 wherein the receiver timing error is a modulo 20 millisecond estimate of an offset of a receiver clock with respect to a satellite reference time.

28. The apparatus of claim 21 wherein the means for generating a correlation history further comprises:

(a1) means for dividing a pseudorandom reference code into a plurality of code segments;

(a2) means for selecting a code segment;

(a3) means for forming an inner product between said selected code segment and a set of digital signal samples to produce a partial correlation;

(a4) means for repeatedly operating means (c1) and (c3) to produce a plurality of partial correlations; and

(a5) means for summing the plurality of partial correlations as each partial correlation is produced to form a plurality of correlations.

29. The apparatus of claim 21 further comprising:

means for dividing the received signal into in-phase and quadrature components; and

separately processing the in-phase and quadrature components.

30. The apparatus of claim 21 further comprising means for generating navigation data bits from the correlation history.

31. The apparatus of claim 21 further comprising:

means for determining an estimate relating to a signal level at a frequency and bit timing hypothesis.

32. A computer readable medium storing software that, when executed by a processor, causes a satellite positioning receiver to perform a method for estimating at least one receiver parameter from a correlation history comprising:

a) determining, in response to the correlation history, a plurality of estimates of signal level, using a receiver frequency and bit timing hypothesis;

b) determining, in response to the signal level estimates, estimates of at least one receiver parameter that provides a frequency and bit timing for the receiver that substantially maximizes signal level.

33. The method of claim 32 further comprising:

(c) frequency correcting the correlation history;

(d) integrating the correlation history over a navigation bit period;

(e) computing a signal level for the signal within the navigation bit period;

(f) summing a plurality of successive signal level values to form an integrated signal level value as the signal level to be maximized.

34. The method of claim 32 wherein said signal level is at least one of signal power and signal magnitude.

35. The method of claim 33 wherein said signal level is at least one of signal power and signal magnitude.

36. The method of claim 33 further comprising:

searching over frequency to determine a maxima in signal level.

37. The method of claim 33 further comprising:

searching over bit timing to determine a maxima in signal level.

38. The method of claim 32 further comprising:

searching over frequency and bit timing to determine a maxima in signal level.

39. The method of claim 38 wherein searching comprises a downhill simplex method.