ADAPTIVE LINK COMMUNICATIONS USING ADAPTIVE CHAOTIC SPREAD WAVEFORM

• US 20110019719A1
• Filed: 07/22/2009
• Published: 01/27/2011
• Est. Priority Date: 07/22/2009
• Status: Active Grant

• Current Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Original Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Inventors: David, Chester B., Michaels, Alan J.
• Granted Patent: US 8,369,377 B2
• Time in Patent Office: Days
• US Class Current: 375/142
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04B 2201/70706 with means for reducing the peak-to-average power ratio
• CPC Class Codes: H04J 13/0018 Chaotic

Abstract

Systems (100) and methods (700) for providing a communications link with a power-limited communication transmitter (102) positioned remotely from an intended receiver system (104). The methods involve channel encoding a carrier signal with data provided at the power-limited communication transmitter to form an information signal. The methods also involve generating a chaotic spreading sequence based on a chaotic number sequence. The chaotic spreading sequence has a magnitude that is constant and a variable arbitrary phase angle comprising phase values which are uniformly distributed over a predetermined range of angles. A spread spectrum signal is formed by multiplying the information signal by the chaotic spreading sequence. The spread spectrum signal has an adjustable amplitude characteristic and a zero autocorrelation. The spread spectrum signal is transmitted from the power-limited communication transmitter to the intended receiver system.

Claims

1. A method for providing communications link with a power-limited communication transmitter positioned remotely from an intended receiver system, where said communication link is resistant to natural and artificial sources of interference, said method comprising:

channel encoding a carrier signal with data provided at said power-limited communication transmitter to form an information signal;

generating a chaotic spreading sequence based on a chaotic number sequence, said chaotic spreading sequence having a magnitude that is constant and a variable arbitrary phase angle comprising phase values which are uniformly distributed over a predetermined range of angles;

forming a spread spectrum signal by multiplying said information signal by said chaotic spreading sequence, said spread spectrum signal having an adaptable amplitude characteristic and a zero autocorrelation; and

transmitting said spread spectrum signal from said power-limited communication transmitter to said intended receiver system.

2. The method according to claim 1, wherein power-limited communication transmitter is configured to transmit information signals comprising data in a digital format.

3. The method according to claim 2, further comprising selectively modifying said chaotic spreading sequence to induce a pseudorandom or chaotic variation in said magnitude of said chaotic spreading sequence to increase a peak to average power ratio (PAPR) of said spread spectrum signal.

4. The method according to claim 3, further comprising modifying an average deviation of said magnitude of said chaotic spreading sequence to selectively control said PAPR of said spread spectrum signal.

5. The method according to claim 4, further comprising modifying said average deviation responsive to a measured signal to interference (S/I) ratio or an estimated S/I ratio.

6. The method according to claim 5, wherein said measured or estimated S/I ratio is determined at said intended receiver system, and communicated from said intended receiver system to said power-limited communication transmitter.

7. The method according to claim 1, further comprising selecting said phase values to have a plurality of uniform distributed phase values, where a number of phases is matched to subsequent signal processing to form a continuous distribution over said predetermined range of angles.

8. The method according to claim 1, wherein said phase values are chaotically varied for each spreading chip of said chaotic spreading sequence.

9. The method according to claim 1, wherein the spreading ratio of said chaotic spreading sequence is selectively varied in response to a measured signal to interference (S/I) ratio or an estimated S/I ratio.

10. The method according to claim 1, wherein said generating step comprises digitally generating a chaotic sequence.

11. The method according to claim 10, wherein said generating step further comprises

selecting a plurality of chaotic polynomial equations,

using residue number system (RNS) arithmetic operations to respectively determine a plurality of solutions for said plurality of chaotic polynomial equations, said plurality of solutions iteratively computed and expressed as RNS residue values, and

determining a chaotic series of digits in a weighted number system based on said plurality of RNS residue values.

12. The method according to claim 1, wherein said information signal, said chaotic spreading sequence and said spread spectrum signal are each digital signals comprised of an in-phase and a quadrature component.

13. The method according to claim 1, further comprising converting said spread spectrum signal from a digital signal to an analog RF spread spectrum signal prior to being transmitted from said power-limited communication transmitter.

14. The method according to claim 1, further comprising:

digitally generating, at said intended receiver system, a de-spreading sequence that is identical to said chaotic spreading sequence;

de-spreading said spread spectrum signal by using said de-spreading sequence to recover said information signal; and

channel decoding said information signal to recover said data.

15. The method according to claim 14, further comprising synchronizing said chaotic spreading sequence and said de-spreading sequence.

16. A method for providing communications link with a power-limited communication transmitter positioned remotely from an intended receiver system, where said communication link is resistant to natural and artificial sources of interference, said method comprising:

channel encoding, at said power-limited communication transmitter, a carrier signal with data using Phase Shift Keying (PSK) to form an information signal;

generating a chaotic spreading sequence based on a chaotic number sequence;

selecting said chaotic spreading sequence with a pseudo-randomly or chaotically variable magnitude, and a chaotically varying arbitrary phase angle including phase values which are band limited and distributed over a predetermined range of angles;

forming a spread spectrum signal by multiplying said information signal by said chaotic spreading sequence, said spread spectrum signal having a peak to average power ratio (PAPR);

selectively varying an average deviation of said magnitude of said chaotic spreading sequence to selectively control said PAPR; and

transmitting said spread spectrum signal from said power-limited communication transmitter to said intended receiver system.

17. The method according to claim 16, further comprising modifying said average deviation responsive to a measured signal to interference (S/I) ratio or an estimated S/I ratio.

18. The method according to claim 17, wherein said measured or estimated S/I ratio is determined at said intended receiver system, and communicated from said intended receiver system to said power-limited communication transmitter.

19. The method according to claim 16, wherein said average deviation is decreased as an S/I ratio decreases.

20. The method according to claim 16, further comprising reducing said average deviation to approximately zero in the presence of a maximum predetermined signal to interference level.

21. The method according to claim 16, further comprising dynamically selectively varying a gain of a high power amplifier used for amplifying said spread spectrum signal.

22. The method according to claim 21, further comprising increasing said gain as said PAPR is decreased.