Carrier frequency detection for signal acquisition

• US 7,336,732 B1
• Filed: 07/28/2004
• Issued: 02/26/2008
• Est. Priority Date: 07/28/2004
• Status: Expired due to Fees

• Current Assignee: L-3 Communications Titan Corporation (L3Harris Technologies, Inc.)
• Original Assignee: L-3 Communications Titan Corporation (L3Harris Technologies, Inc.)
• Inventors: Wiss, John Robert
• Primary Examiner(s): Fan; Chieh M.
• Assistant Examiner(s): Fotakis; Aristocratis
• Application Number:
  US10/900,704
• Time in Patent Office: 1,308 Days
• Field of Search: 375/324, 375/316, 375/326, 375/261, 375/339, 375/329, 455/337, 455/23, 455/21, 329/304, 329/306, 329/307
• US Class Current: 375/326
• CPC Class Codes: H04L 2027/0034 using hypothesis testing
• CPC Class Codes: H04L 27/3818 using coherent demodulation, i.e. using one or more nominally phase synchronous carriers H04L27/227 and H04L27/389 take precedence

Abstract

A carrier frequency in a filtered received M-ary phase-shift keyed (MPSK) modulated signal having in-phase and quadrature components is detected by processing the filtered received signal to remove modulation components and thereby generate a test signal at the carrier frequency; processing the test signal to provide an amplitude spectrum of samples at different test frequencies; and processing the amplitude spectrum to detect the carrier frequency in accordance with the test frequency at which there is a test statistic of the highest magnitude. The magnitude of the test statistic is determined by processing a signal statistic in relation to a noise statistic. The signal statistic is the amplitude of the largest-amplitude sample. The filtered received signal is processed to provide approximate values of the modulus of the received signal and the phase of the received signal; and the approximate modulus and phase values are processed to generate the test signal.

Claims

1. A method of detecting a carrier frequency in a received modulated signal, comprising the steps of:

(a) filtering the received signal to pass the received signal in a band of frequencies including a carrier frequency at which the signal was received;

(b) processing the filtered received signal to remove modulation components and thereby generate a test signal at the carrier frequency;

(c) processing the test signal to provide an amplitude spectrum of samples at different test frequencies; and

(d) processing the amplitude spectrum to detect the carrier frequency in accordance with the test frequency at which there is a test statistic of the highest magnitude;

wherein step (d) comprises the steps of;

(e) determining the magnitude of the test statistic by processing a signal statistic in relation to a noise statistic, wherein the signal statistic is the amplitude of the largest-amplitude sample; and

(f) determining the noise statistic by averaging the amplitudes of samples outside of an exclusion region that includes the largest-amplitude sample, a number of samples immediately above the spectral position of largest-amplitude sample and a number of samples immediately below the spectral position of the largest-amplitude sample.

2. A method according to claim 1, wherein step (e) comprises the step of:

(g) determining the magnitude of the test statistic for an individual segment of the amplitude spectrum by subtracting from the signal statistic a multiple of the noise statistic and a detection parameter.

3. A method according to claim 2, wherein the detection parameter is a predetermined quantity divided by the number of samples that are averaged to determine the noise statistic.

4. A method according to claim 1, wherein step (d) comprises the steps of:

(g) segmenting the test signal into segments of limited bandwidth that are centered about different frequencies;

(h) processing a predetermined one of the limited-bandwidth segments that is centered about an assumed carrier frequency to determine whether the carrier frequency is within said one individual segment; and

(i) when it is determined that the carrier frequency is not in the predetermined one limited-bandwidth segment, processing at least one of the other said limited-bandwidth segments until it is determined that the carrier frequency is within the limited-bandwidth segment currently being processed.

5. A method according to claim 4, wherein the frequency bands of the limited-bandwidth segments overlap.

6. A method according to claim 4, in combination with the step of:

(j) when the carrier frequency is detected, providing a frequency control word for use in acquiring the received signal at the detected carrier frequency;

wherein step (j) comprises the steps of;

(k) temporarily providing a coarse frequency control word that is representative of the center frequency of the individual limited-bandwidth segment currently being processed; and

(l) composing the frequency control word by combining the currently provided coarse frequency control word with a fine frequency control word that is representative of a frequency-offset from the center frequency of the currently processed individual bandwidth segment to the test frequency at which the test statistic of the highest magnitude is detected.

7. A method according to claim 1, wherein step (d) comprises the steps of:

(g) segmenting the test signal into individual segments of limited-bandwidth that are centered about different frequencies; and

(h) processing the individual limited-bandwidth segments of the test signal in accordance with a Fast Fourier Transform to provide separate said amplitude spectra for respective said limited-bandwidth segments.

8. A method according to claim 7, wherein during step (d), steps (e) and (f) are performed for the individual limited-bandwidth segments.

9. A method of detecting a carrier frequency in a received modulated signal, comprising the steps of:

(a) filtering the received signal to pass the received signal in a band of frequencies including a carrier frequency at which the signal was received;

(b) processing the filtered received signal to remove modulation components and thereby generate a test signal at the carrier frequency;

(c) processing the test signal to provide an amplitude spectrum of samples at different test frequencies; and

(d) processing the amplitude spectrum to detect the carrier frequency in accordance with the test frequency at which there is a test statistic of the highest magnitude;

wherein step (d) comprises the steps of;

(e) segmenting the test signal into segments of limited bandwidth that are centered about different frequencies;

(f) processing a predetermined one of the limited-bandwidth segments that is centered about an assumed carrier frequency to determine whether the carrier frequency is within said one individual segment; and

(g) when it is determined that the carrier frequency is not in the predetermined one limited-bandwidth segment, processing at least one of the other said limited-bandwidth segments until it is determined that the carrier frequency is within the limited-bandwidth segment currently being processed;

in combination with the step of;

(h) when the carrier frequency is detected, providing a frequency control word for use in acquiring the received signal at the detected carrier frequency;

wherein step (h) comprises the steps of;

(i) temporarily providing a coarse frequency control word that is representative of the center frequency of the individual limited-bandwidth segment currently being processed; and

(j) composing the frequency control word by combining the currently provided coarse frequency control word with a fine frequency control word that is representative of a frequency-offset from the center frequency of the currently processed individual bandwidth segment to the test frequency at which the test statistic of the highest magnitude is detected.

10. A method according to claim 9, wherein the frequency bands of the limited-bandwidth segments overlap.

11. A method according to claim 9, wherein step (d) further comprises the step of:

(k) processing the individual limited-bandwidth segments of the test signal in accordance with a Fast Fourier Transform to provide separate said amplitude spectra for respective said limited-bandwidth segments.

12. A system for detecting a carrier frequency in a received modulated signal, comprising the steps of:

means for filtering the received signal to pass the received signal in a band of frequencies including a carrier frequency at which the signal was received;

means for processing the filtered received signal to remove modulation components and thereby generate a test signal at the carrier frequency;

means for processing the test signal to provide an amplitude spectrum of samples at different test frequencies; and

means for processing the amplitude spectrum to detect the carrier frequency in accordance with the test frequency at which there is a test statistic of the highest magnitude;

wherein the means for processing the amplitude spectrum include;

means for determining the magnitude of the test statistic by processing a signal statistic in relation to a noise statistic, wherein the signal statistic is the amplitude of the largest-amplitude sample; and

means for determining the noise statistic by averaging the amplitudes of samples outside of an exclusion region that includes the largest-amplitude sample, a number of samples immediately above the spectral position of largest-amplitude sample and a number of samples immediately below the spectral position of the largest-amplitude sample.

13. A system according to claim 12, wherein the means for determining the magnitude of the test statistic include:

means for determining the magnitude of the test statistic for an individual segment of the amplitude spectrum by subtracting from the signal statistic a multiple of the noise statistic and a detection parameter.

14. A system according to claim 13, wherein the detection parameter is a predetermined quantity divided by the number of samples that are averaged to determine the noise statistic.

15. A system according to claim 12, wherein the means for processing the amplitude spectrum include:

means for segmenting the test signal into segments of limited bandwidth that are centered about different frequencies;

means for processing a predetermined one of the limited-bandwidth segments that is centered about an assumed carrier frequency to determine whether the carrier frequency is within said one individual segment; and

means for processing at least one of the other said limited-bandwidth segments until it is determined that the carrier frequency is within the limited-bandwidth segment currently being processed, when it is determined that the carrier frequency is not in the predetermined one limited-bandwidth segment.

16. A system according to claim 15, wherein the frequency bands of the limited-bandwidth segments overlap.

17. A system according to claim 15, in combination with:

means for providing a frequency control word for use in acquiring the received signal at the detected carrier frequency when the carrier frequency is detected;

wherein the means for providing a frequency control word include;

means for temporarily providing a coarse frequency control word that is representative of the center frequency of the individual limited-bandwidth segment currently being processed; and

means for composing the frequency control word by combining the currently provided coarse frequency control word with a fine frequency control word that is representative of a frequency-offset from the center frequency of the currently processed individual bandwidth segment to the test frequency at which the test statistic of the highest magnitude is detected.

18. A system according to claim 12, wherein the means for processing the amplitude spectrum include:

means for segmenting the test signal into individual segments of limited-bandwidth that are centered about different frequencies; and

means for processing the individual limited-bandwidth segments of the test signal in accordance with a Fast Fourier Transform to provide separate said amplitude spectra for respective said limited-bandwidth segments.

19. A system according to claim 18, wherein the magnitude of the test statistic and the noise statistic are determined for the individual limited-bandwidth segments.

20. A system for detecting a carrier frequency in a received modulated signal, comprising the steps of:

means for filtering the received signal to pass the received signal in a band of frequencies including a carrier frequency at which the signal was received;

means for processing the filtered received signal to remove modulation components and thereby generate a test signal at the carrier frequency;

means for processing the test signal to provide an amplitude spectrum of samples at different test frequencies; and

means for processing the amplitude spectrum to detect the carrier frequency in accordance with the test frequency at which there is a test statistic of the highest magnitude;

wherein the means for processing the amplitude spectrum include;

means for segmenting the test signal into segments of limited bandwidth that are centered about different frequencies;

means for processing a predetermined one of the limited-bandwidth segments that is centered about an assumed carrier frequency to determine whether the carrier frequency is within said one individual segment; and

means for processing at least one of the other said limited-bandwidth segments until it is determined that the carrier frequency is within the limited-bandwidth segment being processed, when it is determined that the carrier frequency is not in the predetermined one limited-bandwidth segment;

in combination with means for providing a frequency control word for use in acquiring the received signal at the detected carrier frequency when the carrier frequency is detected;

wherein the means for providing the frequency control word include;

means for temporarily providing a coarse frequency control word that is representative of the center frequency of the individual limited-bandwidth segment currently being processed; and

means for composing the frequency control word by combining the currently provided coarse frequency control word with a fine frequency control word that is representative of a frequency-offset from the center frequency of the currently processed individual bandwidth segment to the test frequency at which the test statistic of the highest magnitude is detected.

21. A system according to claim 20, wherein the frequency bands of the limited-bandwidth segments overlap.

22. A system according to claim 20, wherein the means for processing the amplitude spectrum further include:

means for processing the individual limited-bandwidth segments of the test signal in accordance with a Fast Fourier Transform to provide separate said amplitude spectra for respective said limited-bandwidth segments.

23. A computer readable medium for use with a computer in a system for detecting a carrier frequency in a received modulated signal, said system comprising:

means for filtering the received signal to pass the received signal in a band of frequencies including a carrier frequency at which the signal was received;

means for processing the filtered received signal to remove modulation components and thereby generate a test signal at the carrier frequency;

processing the test signal to provide an amplitude spectrum of samples at different test frequencies; and

means for processing the amplitude spectrum to detect the carrier frequency in accordance with the test frequency at which there is a test statistic of the highest magnitude;

wherein the computer readable medium contains program instructions for;

(a) causing the computer to determine the magnitude of the test statistic by processing a signal statistic in relation to a noise statistic, wherein the signal statistic is the amplitude of the largest-amplitude sample; and

(b) causing the computer to determine the noise statistic by averaging the amplitudes of samples outside of an exclusion region that includes the largest-amplitude sample, a number of samples immediately above the spectral position of largest-amplitude sample and a number of samples immediately below the spectral position of the largest-amplitude sample.

24. A computer readable medium for use with a computer in a system for detecting a carrier frequency in a received modulated signal, said system comprising:

means for filtering the received signal to pass the received signal in a band of frequencies including a carrier frequency at which the signal was received;

means for processing the filtered received signal to remove modulation components and thereby generate a test signal at the carrier frequency;

processing the test signal to provide an amplitude spectrum of samples at different test frequencies;

means for processing the amplitude spectrum to detect the carrier frequency in accordance with the test frequency at which there is a test statistic of the highest magnitude; and

means for segmenting the test signal into segments of limited bandwidth that are centered about different frequencies;

wherein the computer readable medium contains program instructions for;

(a) causing the computer to process a predetermined one of the limited-bandwidth segments that is centered about an assumed carrier frequency to determine whether the carrier frequency is within said one individual segment; and

(b) when it is determined that the carrier frequency is not in the predetermined one limited-bandwidth segment, causing the computer to process at least one of the other said limited-bandwidth segments until it is determined that the carrier frequency is within the limited-bandwidth segment currently being processed;

(c) when the carrier frequency is detected, causing the computer to provide a frequency control word for use in acquiring the received signal at the detected carrier frequency;

(d) causing the computer to temporarily provide a coarse frequency control word that is representative of the center frequency of the individual limited-bandwidth segment currently being processed; and

(e) causing the computer to compose the frequency control word by combining the currently provided coarse frequency control word with a fine frequency control word that is representative of a frequency-offset from the center frequency of the currently processed individual bandwidth segment to the test frequency at which the test statistic of the highest magnitude is detected.