Fast fourier transform with down sampling based navigational satellite signal tracking

• US 20070046536A1
• Filed: 08/31/2005
• Published: 03/01/2007
• Est. Priority Date: 08/31/2005
• Status: Active Grant

• Current Assignee: CSR Technology Holdings Inc. (Qualcomm, Inc.)
• Original Assignee: CSR Technology Holdings Inc. (Qualcomm, Inc.)
• Inventors: Wang, Chi-Shin, Jia, Zhike
• Granted Patent: US 8,466,836 B2
• Time in Patent Office: Days
• US Class Current: 342/357.630
• 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 19/246 involving long acquisition integration times, extended snapshots of signals or methods specifically directed towards weak signal acquisition
• CPC Class Codes: G01S 19/29 carrier including Doppler, related G01S19/246 takes precedence
• CPC Class Codes: G01S 19/35 Constructional details or hardware or software details of the signal processing chain
• CPC Class Codes: H04B 1/7085 using a code tracking loop, e.g. a delay-locked loop

Abstract

A method and device to track navigational satellite signals, are claimed. In this invention, a combination of down-sampling and frequency domain transformation are used to track the navigational satellite signals under dynamic environment. A Fast Fourier Transform (FFT) with long coherent integration has been employed to determine the varying frequency components with high resolution. By representing a number of correlation values with their average value, it is possible to represent a long sequence of input values by a smaller number of values and a relatively short length FFT can reveal the low frequency components that are present in the signal during tracking operation. A large reduction in the computational load may be achieved using this down-sampling method without compromising on the frequency resolution.

Claims

1. A method for tracking received signals in a global satellite navigation receiver, the method comprising:

collecting a sequence of correlation values derived from the received signals;

partitioning the collected sequence into N groups of consecutive correlation values, where N is a positive integer;

calculating from each of the N groups, a corresponding set of N values forming a down-sampled sequence;

converting the down-sampled sequence from time domain to frequency domain to produce a frequency domain sequence;

identifying a maximum power value in the frequency domain sequence;

calculating a frequency error between the received signals and a locally generated replica signal based on the identified maximum power value; and

adjusting a local replica carrier frequency by an amount equal to the frequency error.

2. The method of claim 1, wherein calculating the corresponding set of N values comprises averaging the consecutive correlation values in each of the N groups.

3. The method of claim 1, wherein calculating the corresponding set of N values comprises taking the root mean square of the consecutive correlation values in each of the N groups.

4. The method of claim 1, further comprising varying the value of N according to platform dynamics.

5. The method of claim 1, wherein the N values in the down-sampled sequence are assigned to temporal midpoints of the N groups.

6. The method of claim 1, wherein collecting the sequence of correlation values comprises selecting a total number of values to collect as a function of the receiver dynamics.

7. The method of claim 1, wherein adjusting the local replica carrier frequency comprises reducing a rate of adjustment to avoid spontaneous burst-like changes in the local replica carrier frequency due to signal noise.

8. The method of claim 1, further comprising fine-tuning the frequency error by interpolation.

9. The method of claim 1, further comprising employing a Frequency Lock Loop (FLL) to further improve the tracking performance.

10. The method of claim 9, wherein the frequency error obtained by FFT analysis is used as an input residual frequency to the Frequency Lock Loop (FLL).

11. The method of claim 1, wherein partitioning the collected sequence comprises aligning transitions between the groups with bit edge transitions.

12. The method of claim 1, comprising selecting a number of frequency bins as a function of receiver dynamics.

13. The method of claim 1, wherein converting the down-sampled sequence from time domain to frequency domain comprises using a maximum likelihood criterion based method to remove data modulation.

14. A global satellite navigation system receiver device comprising an RF front end for receiving signals from navigational satellites, a baseband section receiving IF signals from the RF front end, and a processor receiving I, Q correlation values from the baseband section, wherein the processor:

collects a sequence of the correlation values;

partitions the collected sequence into N groups of consecutive correlation values, where N is a positive integer;

calculates from each of the N groups, a corresponding set of N values forming a down-sampled sequence;

converts the down-sampled sequence from time domain to frequency domain to produce a frequency domain sequence;

identifies a maximum power value in the frequency domain sequence;

calculates a frequency error between the received signal and a locally generated signal based on the identified maximum power value; and

adjusts a local replica carrier frequency by an amount equal to the frequency error.

15. The device of claim 14, wherein calculating the corresponding set of N values comprises averaging the consecutive correlation values in each of the N groups.

16. The device of claim 14, wherein calculating the corresponding set of N values comprises taking the root mean square of the consecutive correlation values in each of the N groups.

17. The device of claim 14, further comprising varying the value of N according to platform dynamics.

18. The device of claim 14, wherein the N values in the down-sampled sequence are assigned to temporal midpoints of the N groups.

19. The device of claim 14, wherein collecting the sequence of correlation values comprises selecting a total number of values to collect as a function of the receiver dynamics.

20. The device of claim 14, wherein adjusting the local replica carrier frequency comprises reducing a rate of adjustment to avoid spontaneous burst-like changes in the local replica carrier frequency due to signal noise.

21. The device of claim 14, further comprising fine-tuning the frequency error by interpolation.

22. The device of claim 14, further comprising employing a Frequency Lock Loop (FLL) to further improve the tracking performance.

23. The device of claim 22, wherein the frequency error obtained by FFT analysis is used as an input residual frequency to the Frequency Lock Loop (FLL).

24. The device of claim 14, wherein partitioning the collected sequence comprises aligning transitions between the groups with bit edge transitions.

25. The device of claim 14, comprising selecting a number of frequency bins as a function of receiver dynamics.

26. The device of claim 14, wherein converting the down-sampled sequence from time domain to frequency domain comprises using a maximum likelihood criterion based method to remove data modulation.