Method and computer program for identifying a transition in a phase-shift keying or frequency-shift keying signal

• US 20070153947A1
• Filed: 12/30/2005
• Published: 07/05/2007
• Est. Priority Date: 12/30/2005
• Status: Active Grant

• Current Assignee: L-3 Communications Corporation (L3Harris Technologies, Inc.)
• Original Assignee: L-3 Communications Integrated Systems LP (L3Harris Technologies, Inc.)
• Inventors: Ha, Stephen
• Granted Patent: US 7,590,209 B2
• Time in Patent Office: Days
• US Class Current: 375/355
• CPC Class Codes: H04L 27/144 with demodulation using spectral properties of the received signal, e.g. by using frequency selective- or frequency sensitive elements
• CPC Class Codes: H04L 27/1563 using transition or level detection
• CPC Class Codes: H04L 27/2337 using digital techniques to measure the time between zero-crossings

Abstract

The present invention is a method and computer program for identifying phase transitions in phase-shift keying signals and frequency transitions in frequency-shift keying signals. The method of the present invention is implemented via the computer program. With respect to phase-shift keying signals, the method broadly comprises the steps of: selecting a portion of the signal to analyze, wherein the signal comprises a plurality of data samples; applying a transform to the signal to obtain a frequency spectrum; determining a maximum frequency spectrum corresponding to a carrier frequency; determining a starting approximation value of a slope of the phase transition; calculating a bounded limit of slopes within which to search for the phase transition; selecting a plurality of lines, each having a slope within the bounded limit and an initial value, wherein each line passes through at least one of the data samples; calculating a sum for the data samples associated with each of the lines; and based on the sum for the data samples, identifying a line that corresponds to a location of the phase transition.

Claims

1. A method for identifying a transition in a signal comprising a plurality of data samples, the method comprising the steps of:

dividing the signal into a plurality of discrete segments;

determining a starting approximation value of a slope of the transition;

calculating a bounded limit of slopes within which to search for the transition;

selecting a plurality of lines, each having a slope within the bounded limit;

calculating a sum for the data samples associated with each of the lines; and

based on the sum for the data samples, identifying a line that corresponds to a location of the transition.

2. The method as claimed in claim 1, wherein the transition is a phase transition, and the signal is a phase-shift keying signal.

3. The method as claimed in claim 1, wherein the transition is a frequency transition, and the signal is a frequency-shift keying signal.

4. The method as claimed in claim 1, wherein the signal within the discrete segment comprises a non-transition portion of the signal and the transition.

5. The method as claimed in claim 1, wherein the starting approximation for the value of the slope of the transition is a slope perpendicular to the non-transition portion.

6. The method as claimed in claim 1, wherein the bounded limit is ±

20% of the slope perpendicular to the non-transition portion.

7. The method as claimed in claim 1, wherein the sum for the data samples is a weighted sum calculated via a statistical distribution.

8. A method for identifying at least one phase transition in a phase-shift keying signal comprising a plurality of data samples corresponding to phase values, the method comprising the steps of:

selecting a portion of the signal to analyze;

applying a transform to the signal to obtain a frequency spectrum;

determining a maximum frequency spectrum corresponding to a carrier frequency;

determining a starting approximation value of a slope of the phase transition;

calculating a bounded limit of slopes within which to search for the phase transition;

selecting a plurality of lines, each having a slope within the bounded limit and an initial value, wherein each line passes through at least one of the data samples;

calculating a sum for the data samples associated with each of the lines; and

based on the sum for the data samples, identifying a line that corresponds to a location of the phase transition.

9. The method as claimed in claim 8, wherein the portion of the signal to be analyzed is based on an independent variable, such that the signal is broken into a plurality of discrete segments.

10. The method as claimed in claim 9, wherein the independent variable is time.

11. The method as claimed in claim 9, wherein the independent variable is an amount of data contained within the signal.

12. The method as claimed in claim 8, wherein the transform is a Fast-Fourier Transform.

13. The method as claimed in claim 8, further comprising the step of mixing the carrier frequency so as to translate the carrier frequency to a low frequency.

14. The method as claimed in claim 8, wherein the starting approximation for the value of the slope of the phase transition is a slope perpendicular to the carrier frequency.

15. The method as claimed in claim 14, wherein the bounded limit for the slope is ±

20% of the slope perpendicular to the carrier frequency.

16. The method as claimed in claim 8, wherein the sum for the data samples is a weighted sum calculated via a statistical distribution.

17. The method as claimed in claim 16, wherein the line that corresponds to a location of the phase transition is the line with a maximum weighted sum amongst all the lines analyzed within the bounded limit.

18. The method as claimed in claim 16, wherein the line that corresponds to a location of the phase transitions is the line having a largest mean of the weighted sum.

19. The method as claimed in claim 8, wherein the method is applied to an unwrapped phase, such that the phase values of the carrier frequency are not limited to ±

π

.

20. The method as claimed in claim 8, wherein the carrier frequency corresponds to a non-transition portion and further wherein the carrier frequency is a first carrier frequency corresponding to a first non-transition portion before the phase transition.

21. The method as claimed in claim 20, further comprising the step of determining a second carrier frequency corresponding to a second non-transition portion after the phase transition.

22. The method as claimed in claim 21, further comprising the step of calculating a magnitude of a change in phase by determining a vertical distance of the phase transition lying between the first and second carrier frequencies.

23. The method as claimed in claim 8, further comprising the step of determining a baud of the signal by calculating a time interval between consecutive phase transitions, applying a clustering program to determine a minimum time interval, and calculating the inverse of the minimum time interval to obtain the baud.

24. A computer program for identifying at least one phase transition in a phase-shift keying signal comprising a plurality of data samples corresponding to phase values, the computer program stored on a computer-readable medium for operating a computing element, the computer program comprising:

a code segment operable to be executed by the computing element for selecting a portion of the signal to analyze;

a code segment operable to be executed by the computing element for applying a transform to the signal to obtain a frequency spectrum;

a code segment operable to be executed by the computing element for determining a maximum frequency spectrum corresponding to a carrier frequency;

a code segment operable to be executed by the computing element for determining a starting approximation value of a slope of the phase transition;

a code segment operable to be executed by the computing element for calculating a bounded limit of slopes within which to search for the phase transition;

a code segment operable to be executed by the computing element for selecting a plurality of lines, each having a slope within the bounded limit;

a code segment operable to be executed by the computing element for calculating a sum for the data samples associated with each of the lines; and

a code segment operable to be executed by the computing element for identifying a line that corresponds to a location of the phase transition based on the sum for the data samples.