Method and system for temporal autocorrelation filtering

• US 20040095990A1
• Filed: 11/18/2002
• Published: 05/20/2004
• Est. Priority Date: 11/18/2002
• Status: Active Grant

• Current Assignee: Google LLC (Alphabet Inc.)
• Original Assignee: Google Inc. (Alphabet Inc.)
• Inventors: Gossett, Carroll Philip, Gunter, Michial Allen
• Granted Patent: US 7,352,833 B2
• Time in Patent Office: Days
• US Class Current: 375/148
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04L 2025/03458 Lattice
• CPC Class Codes: H04L 2025/03471 Tapped delay lines H04L2025/03464 takes precedence
• CPC Class Codes: H04L 25/03038 with a non-recursive structure H04L25/03031 takes precedence

Abstract

An autocorrelation filter for use with a spread spectrum receiver. The autocorrelation filter can be used as a prefilter stage to reduce phase distortion present in a spread spectrum signal. The autocorrelation filter can be used to process the output from a lattice filter. The lattice filter is configured to remove magnitude distortion from the spread spectrum signal. The autocorrelation filter performs a series of correlations on the output of the lattice filter. The results of these correlations are integrated over a period of time to generate a running impulse response for characterizing and removing the phase distortion in the spread spectrum signal.

Claims

1. A spread spectrum receiver, comprising:

an antenna for receiving a spread spectrum signal;

a lattice filter coupled to the antenna, wherein the lattice filter is configured to remove magnitude distortion from the spread spectrum signal to produce a lattice filter output; and

an autocorrelation filter coupled to receive the lattice filter output, wherein the autocorrelation filter is configured to remove phase distortion from the lattice filter output.

2. The spread spectrum receiver of claim 1 further comprising:

an analog to digital converter coupled to the antenna for converting the spread spectrum signal to a digital signal and providing the digital signal to the lattice filter.

3. The spread spectrum receiver of claim 1 further comprising:

a correlation stage included in the autocorrelation filter to receive the lattice filter output and perform a set of time-shifted correlations on the lattice filter output.

4. The spread spectrum receiver of claim 3 further comprising:

an array of correlators included in the correlation stage, each of the correlators coupled to receive delayed versions of the lattice filter output and generate a respective correlation output.

5. The spread spectrum receiver of claim 3 further comprising:

an integration stage coupled to the correlation stage to integrate each output of the correlation stage.

6. The spread spectrum receiver of claim 5 wherein the integration stage includes a leaky integrator for integrating the output of the correlation stage.

7. The spread spectrum receiver of claim 5 further comprising:

an FIR filter using outputs of the integration stage as tap weights.

8. A spread spectrum receiver, comprising:

an antenna for receiving a spread spectrum signal; and

an autocorrelation filter coupled to the antenna, wherein the autocorrelation filter is configured to remove phase distortion from the spread spectrum signal received by the antenna.

9. The spread spectrum receiver of claim 8 further comprising:

an analog to digital converter coupled to the antenna for converting the spread spectrum signal to a digital signal and providing the digital signal to the autocorrelation filter.

10. The spread spectrum receiver of claim 8 further comprising:

a correlation stage included in the autocorrelation filter to receive the spread spectrum signal from the antenna and perform a set of time-shifted correlations on the spread spectrum signal.

11. The spread spectrum receiver of claim 10 further comprising:

an array of correlators included in the correlation stage, each of the correlators coupled to receive delayed versions of the spread spectrum signal received by the antenna and generate a respective correlation output.

12. The spread spectrum receiver of claim 10 further comprising:

an integration stage coupled to the correlation stage to integrate each output of the correlation stage.

13. The spread spectrum receiver of claim 12 wherein the integration stage includes a leaky integrator for integrating the output of the correlation stage.

14. The spread spectrum receiver of claim 12 further comprising:

an FIR filter using the outputs of the integration stage as tap weights.

15. An autocorrelation filter for removing phase distortion from a spread spectrum signal.

16. The autocorrelation filter of claim 15 wherein the autocorrelation filter is configured to function with a digitized spread spectrum signal.

17. The autocorrelation filter of claim 15 further comprising:

a correlation stage included in the autocorrelation filter to receive the spread spectrum signal and perform a correlation on the spread spectrum signal.

18. The autocorrelation filter of claim 17 further comprising:

an array of correlators included in the correlation stage, each of the correlators coupled to receive the spread spectrum signal and generate a respective correlation output.

19. The autocorrelation filter of claim 17 further comprising:

an integration stage coupled to the correlation stage for integrating the outputs of the correlation stage.

20. The autocorrelation filter of claim 19 wherein the integration stage includes a leaky integrator for integrating the outputs of the correlation stage.

21. The autocorrelation filter of claim 19 further comprising:

an FIR filter taking the outputs of the integration stage as tap weights to remove phase from the spread spectrum signal.

22. The autocorrelation filter of claim 17 further comprising:

an array of correlators included in the correlation stage, each of the correlators coupled to receive the spread spectrum signal and generate respective correlation outputs; and

a leaky integrator included in the integration stage, the leaky integrator coupled to receive the respective correlation outputs and integrate the respective correlation outputs over a time period.

23. The autocorrelation filter of claim 22 further comprising:

an FIR filter taking the outputs of the integration stage as tap weights to remove phase from the spread spectrum signal.

24. The autocorrelation filter of claim 15 wherein a spread spectrum signal is received from a lattice filter coupled to the autocorrelation filter.

25. A method for filtering out phase distortion from a spread spectrum receiver, comprising:

receiving a spread spectrum signal;

digitizing the spread spectrum signal;

removing magnitude distortion from the spread spectrum signal by using a lattice filter; and

removing phase distortion from the spread spectrum signal by using an autocorrelation filter.

26. The method of claim 25 further comprising:

performing an autocorrelation on an output of the lattice filter by using a correlation stage.

27. The method of claim 25 further comprising:

generating a plurality of correlation outputs by using an array of correlators, each of the correlators coupled to receive an output of the lattice filter.

28. The method of claim 27 further comprising:

integrating the plurality of correlation outputs by using an integration stage coupled to receive the plurality of correlation outputs.

29. The method of claim 28 wherein the integration stage includes a leaky integrator for integrating the plurality of correlation outputs over a period of time.

30. The method of claim 28 wherein the integrating of the plurality of correlation outputs over the period of time generates a running impulse response characterizing the phase distortion of the spread spectrum signal.

31. The method of claim 30 further comprising:

FIR filtering the spread spectrum signal using the running impulse response to remove phase distortion from the spread spectrum signal.

32. A method for filtering out phase distortion from a spread spectrum receiver, comprising:

receiving a spread spectrum signal;

digitizing the spread spectrum signal; and

removing phase distortion from the spread spectrum signal by using an autocorrelation filter.

33. The method of claim 32 further comprising:

performing an autocorrelation on a digitized spread spectrum signal by using a correlation stage.

34. The method of claim 32 further comprising:

generating a plurality of correlation outputs by using an array of correlators, each of the correlators coupled to receive a digitized spread spectrum signal.

35. The method of claim 34 further comprising:

integrating the plurality of correlation outputs by using an integration stage coupled to receive the plurality of correlation outputs.

36. The method of claim 35 wherein the integration stage includes a leaky integrator for integrating the plurality of correlation outputs over a period of time.

37. The method of claim 35 wherein the integrating of the plurality of correlation outputs over the period of time generates a running impulse response characterizing the phase distortion of the spread spectrum signal.

38. The method of claim 37 further comprising:

FIR filtering the spread spectrum signal using the running impulse response to remove phase distortion from the spread spectrum signal.

39. A method for generating a synchronization clock signal for a receiver, comprising:

partially removing phase with lag from a spread spectrum signal by using an autocorrelation filter;

generating a first correlation and a second correlation using respective correlators configured to receive the output of the autocorrelation filter;

comparing the first correlation and the second correlation using a comparator to locate a peak correlation and produce a corresponding comparator output;

controlling a voltage controlled oscillator by using the comparator output; and

producing the synchronization clock signal by using an output of the voltage controlled oscillator

40. The method of claim 39 further comprising:

locating the peak correlation by using the comparator to locate the first correlation on the less delayed side of the peak correlation and locate the second correlation on the more delayed side of the peak correlation.

41. The method of claim 40 further comprising:

generating a first delayed input for the first correlation and a second delayed input for the second correlation, the first delayed input and the second delayed input produced using a delay line.

42. The method of claim 39 further comprising:

centering the peak correlation between the first correlation and the second correlation by shifting a plurality of samples of the output of the autocorrelation filter.

43. The method of claim 42 further comprising:

shifting the samples by an integer amount to center the peak correlation between the first correlation and the second correlation.