FEATURELESS COHERENT CHAOTIC AMPLITUDE MODULATION

• US 20090310650A1
• Filed: 06/12/2008
• Published: 12/17/2009
• Est. Priority Date: 06/12/2008
• Status: Active Grant

• Current Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Original Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Inventors: Michaels, Alan J., Chester, David B.
• Granted Patent: US 8,068,571 B2
• Time in Patent Office: Days
• US Class Current: 375/146
• CPC Class Codes: H04J 13/0018 Chaotic
• CPC Class Codes: H04J 13/10 Code generation
• CPC Class Codes: H04L 25/4917 using multilevel codes
• CPC Class Codes: H04L 27/001 using chaotic signals for secret or secure communication H04L9/001

Abstract

Systems (400, 500, 600) and methods (300) for generating a chaotic amplitude modulated signal absent of cyclostationary features by preserving a constant variance. The methods involve: generating a PAM signal including pulse amplitude modulation having a periodically changing amplitude; generating a first part of a constant power envelope signal (FPCPES) by dividing the PAM signal by a square root of a magnitude of the PAM signal; generating a second part of the constant power envelope signal (SPCPES) having a magnitude equal to a square root of one minus the magnitude of the PAM signal; and generating first and second spreading sequences (FSS and SSS). The methods also involve combining the FPCPES with the FSS to generate a first product signal (FPS) and combining the SPCPES with the SSS to generate a second product signal (SPS). A constant power envelope signal is generated using the FPS and SPS.

Claims

1. A method for generating a chaotic amplitude modulated signal absent of cyclostationary features by preserving a constant variance, comprising the steps of:

generating a PAM signal including pulse amplitude modulation having a periodically changing amplitude;

generating a first part of a constant power envelope signal (FPCPES) by dividing said PAM signal by a square root of a magnitude of said PAM signal;

generating a second part of said constant power envelope signal (SPCPES) having a magnitude equal to a square root of one minus said magnitude of said PAM signal;

generating first and second spreading sequences formed as sequences of random values;

combining said FPCPES with said first spreading sequence to generate a first product signal;

combining said SPCPES with said second spreading sequence to generate a second product signal; and

generating a constant power envelope signal using said first and second product signals.

2. The method according to claim 1, further comprising the step of selecting each of said first and second spreading sequences to be orthogonal chaotic sequences.

3. The method according to claim 1, further comprising the step of generating said PAM signal using discrete time baseband modulation to form AM symbols.

4. The method according to claim 3, further comprising selecting said discrete time baseband modulation to comprise quadrature amplitude modulation (QAM).

5. The method according to claim 4, wherein each of said AM symbols is encoded as an in-phase component “

I” and

a quadrature component “

Q”

.

6. The method according to claim 1, further comprising the steps of:

transmitting said constant power envelope signal over a communication link to a receiver;

generating at the receiver a third spreading sequence which is identical to said first spreading sequence; and

correlating said constant power envelope signal with said third spreading sequence to recover said PAM signal.

7. The method according to claim 6, further comprising the steps of:

generating at said receiver a fourth spreading sequence which is identical to said second spreading sequence; and

correlating said constant power envelope signal with said fourth spreading sequence to recover said SPCPES.

8. A method for generating a coherent communication signal, comprising the steps of:

generating a first baseband pulse amplitude modulated signal;

generating a second baseband pulse amplitude modulated signal such that said first and second baseband pulse amplitude modulated signals generate output signals with variances that are compliments of each other;

generating first and second spreading sequences formed as sequences of random values;

combining said first baseband pulse amplitude modulated signal with said first spreading sequence to generate a first spread spectrum signal;

combining said second baseband pulse amplitude modulated signal with said second spreading sequence to generate a second spread spectrum signal; and

combining said first spread spectrum signal and said second spread spectrum signal to form a composite spread spectrum signal.

9. The method according to claim 8, further comprising the step of selecting each of said first and second spreading sequences to be chaotic sequences.

10. The method according to claim 8, further comprising the step of forming each of said first and second pulse amplitude modulated signals using quadrature amplitude modulation (QAM) to form QAM symbols.

11. The method according to claim 10, wherein each said QAM symbol of said first baseband pulse amplitude modulated signal is encoded as an in-phase component I and a quadrature component Q, and said second pulse amplitude modulated signal is encoded as I compliment, which is a compliment of I, and a Q compliment, which is a compliment of Q.

12. The method according to claim 8, further comprising the steps of:

transmitting said composite signal over a communications links to a receiver;

generating at said receiver a third spreading sequence which is identical to said first spreading sequence; and

correlating said composite spread spectrum signal with said spreading sequence to recover said first baseband pulse amplitude modulated signal.

13. The method according to claim 12, further comprising the steps of:

generating at said receiver a fourth spreading sequence which is identical to said spreading sequence; and

correlating said composite spread spectrum signal with said fourth spreading sequence to recover said second baseband pulse amplitude modulated signal.

14. The method according to claim 9, further comprising the steps of:

computing a plurality of first square root values by taking the square roots of each of a plurality of magnitude values of said first baseband pulse amplitude modulated signal; and

computing a plurality of second square root values by taking the square roots of each of a plurality of magnitude values of said second baseband pulse amplitude modulated signal.

15. The method according to claim 14, further comprising the steps of:

combining each square root value of said plurality of first square root values with a respective random number of said first spreading sequence to generate said first spread spectrum signal; and

combining each square root value of said plurality of second square root values with respective random numbers of said second spreading sequence to generate said second spread spectrum signal.

16. The method according to claim 8, wherein said second baseband pulse amplitude modulated signal has an amplitude which is a compliment of an amplitude of said first baseband pulse amplitude modulated signal and a phase which is the same as a phase of said first baseband pulse amplitude modulated signal.

17. The method according to claim 8, wherein said second baseband pulse amplitude modulated signal has an amplitude which is a compliment of an amplitude of said first baseband pulse amplitude modulated signal and a phase which is different from a phase of said first baseband pulse amplitude modulated signal.

18. A system, comprising:

a first generator configured for generating a PAM signal including pulse amplitude modulation having a periodically changing amplitude;

a second generator configured for generating a first part of a constant power envelope signal (FPCPES) by dividing said PAM signal by a square root of a magnitude of said PAM signal;

a third generator configured for generating a second part of said constant power envelope signal (SPCPES) having a magnitude equal to a square root of one minus said magnitude of said PAM signal;

a fourth generator configured for generating first and second spreading sequences formed as a sequence of random values;

a first combiner configured for combining said FPCPES with said first spreading sequence to generate a first product signal;

a second combiner configured for combining said SPCPES with said second spreading sequence to generate a second product signal; and

a fifth generator configured for generating a constant power envelope signal using said first and second product signals.

19. The system according to claim 18, wherein each of said first and second spreading sequences are orthogonal chaotic sequences.

20. The system according to claim 18, wherein said PAM signal is generated using discrete time baseband modulation to form AM symbols.

21. The system according to claim 20, wherein said discrete time baseband modulation is quadrature amplitude modulation (QAM).

22. The system according to claim 21, wherein each of said AM symbols is encoded as an in-phase component “

I” and

a quadrature component “

Q”

.

23. The system according to claim 18, further comprising a transmitter configured for transmitting said constant power envelope signal to a receiver over a communications link.

24. The system according to claim 23, wherein said receiver is configured for generating a third spreading sequence which is identical to said first spreading sequence and correlating said constant power envelope signal with said third spreading sequence to recover said PAM signal.

25. The system according to claim 23, wherein said receiver is configured for generating a fourth spreading sequence which is identical to said second spreading sequence and correlating said constant power envelope signal with said third spreading sequence to recover said SPCPES.