METHODS AND SYSTEMS FOR ACQUIRING SIGNALS USING COHERENT MATCH FILTERING

• US 20080170645A1
• Filed: 01/12/2007
• Published: 07/17/2008
• Est. Priority Date: 01/12/2007
• Status: Active Grant

• Current Assignee: General Dynamics C4 Systems Incorporated (General Dynamics Corporation)
• Original Assignee: General Dynamics C4 Systems Incorporated (General Dynamics Corporation)
• Inventors: ARNESON, Steve Henry, KLEIDER, John Eric
• Granted Patent: US 7,907,679 B2
• Time in Patent Office: Days
• US Class Current: 375/343
• CPC Class Codes: H04L 2027/0067 Phase error detectors
• CPC Class Codes: H04L 2027/0095 in a preamble or similar structure
• CPC Class Codes: H04L 25/4902 Pulse width modulation; Pulse position modulation
• CPC Class Codes: H04L 27/2657 Carrier synchronisation
• CPC Class Codes: H04L 27/2662 Symbol synchronisation
• CPC Class Codes: H04L 27/2675 Pilot or known symbols

Abstract

Embodiments include methods and apparatus for verifying the detection of a correlation peak, which may represent an acquisition of a received acquisition code symbol sequence. The method includes determining a series of coherently-aligned peaks from a series of correlation peaks. Determining the plurality of coherently-aligned peaks includes correcting a frequency offset and a phase offset for each of the plurality of correlation peaks. A coherent match filter process is performed on the plurality of coherently-aligned peaks. A detection of the correlation peak may be verified when the match filter result exceeds a threshold.

Claims

1. A method for verifying a detection of a correlation peak representing an acquisition of a received acquisition code symbol sequence, the method comprising:

receiving the acquisition code symbol sequence, wherein the acquisition code symbol sequence includes a plurality of acquisition code symbols, and wherein an acquisition code symbol includes a subcode sequence having a plurality of subcodes;

performing a correlation of the plurality of subcodes to produce a plurality of correlation peaks;

correcting each peak of the plurality of correlation peaks in frequency, phase, and time to produce a plurality of coherently-aligned peaks;

performing a coherent match filter process on the plurality of coherently-aligned peaks to produce a match filter result; and

verifying the detection of the correlation peak when the match filter result exceeds a first threshold.

2. The method of claim 1 further comprising determining a frequency offset using a timing offset.

3. The method of claim 2 further comprising the steps of:

placing each peak of the plurality of correlation peaks in a common modulation state;

forming a phasor stack comprising a phasor stack entry for each peak of the plurality of correlation peaks; and

determining the frequency offset as a change in frequency over a change in time.

4. The method of claim 2 further comprising determining a phase offset as an offset remaining in the plurality of correlation peaks after correcting for the frequency offset.

5. The method of claim 1 wherein the step of performing the coherent match filter process further comprises determining an average of the plurality of coherently-aligned peaks.

6. The method of claim 5 wherein the step of performing the coherent match filter process further comprises determining a moving average.

7. The method of claim 1 further comprising the steps of:

performing a non-linear process on the plurality of coherently-aligned peaks to produce a non-linear process result;

comparing the non-linear process result to a second threshold; and

verifying the detection of the correlation peak when the match filter result exceeds the first threshold and the non-linear process result of the non-linear process exceeds the second threshold.

8. The method of claim 1 further comprising the step of adjusting a carrier frequency of a receiver receiving the acquisition code symbol sequence.

9. The method of claim 1 further comprising demodulating a payload when the detection of the correlation peak is verified.

10. A receiver configured to receive and detect an acquisition code symbol sequence from a received acquisition code symbol sequence having a plurality of subcodes, the receiver comprising:

a correlation calculator configured to produce a plurality of correlation peaks from a correlation of the received acquisition code symbol sequence and a stored version of the acquisition code symbol sequence;

a frequency offset calculator coupled to the correlation calculator and configured to determine a frequency offset from the plurality of correlation peaks;

a phase offset calculator coupled to the correlation calculator and configured to determine a phase offset from the plurality of correlation peaks;

a peak corrector coupled to the frequency offset calculator and the phase offset calculator, the peak corrector configured to produce a plurality of coherently-aligned peaks by adjusting the plurality of correlation peaks for frequency offset and phase offset; and

a coherent peak detector coupled to the peak corrector and configured to verify a detection of a correlation peak when the plurality of coherently-aligned peaks represents an acquisition of the acquisition code symbol sequence.

11. The receiver of claim 10 when the frequency offset calculator determines the frequency offset using a timing offset.

12. The receiver of claim 11 wherein the frequency offset calculator is further configured to:

place each peak of the plurality of correlation peaks in a common modulation state;

form a phasor stack comprising a phasor stack entry for each peak of the plurality of correlation peaks; and

determine the frequency offset as a change in frequency over a change in time.

13. The receiver of claim 11 wherein the phase offset calculator is further configured to determine a phase offset as an offset remaining in the plurality of correlation peaks after correcting for the frequency offset.

14. The receiver of claim 10 wherein the coherent peak detector is configured to perform a coherent match filter process on the plurality of coherently-aligned peaks.

15. The receiver of claim 14 wherein the coherent match filter process comprises averaging the plurality of coherently-aligned peaks to produce a match filter result, and comparing the match filter result to a first threshold.

16. The receiver of claim 15 wherein the coherent match filter process is performed using a moving average.

17. The receiver of claim 15 wherein the coherent peak detector is configured to:

perform a non-linear process on the plurality of coherently-aligned peaks to produce a non-linear process result;

compare the non-linear process result to a second threshold; and

verify the detection of a correlation peak when the match filter result exceeds the first threshold and the non-linear process result exceeds the second threshold.

18. The receiver of claim 10 further comprising an offset corrector configured to adjust a carrier frequency of the receiver.

19. The receiver of claim 10 further comprising a demodulator configured to demodulate a payload when the detection of the correlation peak is verified.

20. A method for acquiring an acquisition code symbol sequence comprising:

non-coherently detecting a correlation peak from a plurality of correlation peaks generated from an acquisition code symbol sequence;

correcting the plurality of correlation peaks for phase, frequency, and timing offsets to produce a plurality of corrected correlation peaks; and

coherently verifying a detection of the correlation peak from the plurality of corrected correlation peaks.