Chaotic Spread Spectrum Communications System Receiver

• US 20090034727A1
• Filed: 08/01/2007
• Published: 02/05/2009
• Est. Priority Date: 08/01/2007
• 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 8,005,221 B2
• Time in Patent Office: Days
• US Class Current: 380/263
• CPC Class Codes: H04B 1/7075 with code phase acquisition
• CPC Class Codes: H04J 13/0018 Chaotic

Abstract

A method is provided for coherently demodulating a chaotic sequence spread spectrum signal at a receiver (104). The method includes receiving a chaotic sequence spread spectrum signal including a plurality of information symbols. The method also includes generating a first string of discrete time chaotic samples. The first string of discrete time chaotic samples is identical to a second string of discrete time chaotic samples generated at a transmitter. The method further includes processing the chaotic sequence spread spectrum signal at the receiver to identify a time offset and a frequency offset relative to the first string of discrete time chaotic samples. Each of the discrete time chaotic samples of the first string of discrete time chaotic samples has a shorter sample time interval than the duration of the information symbols.

Claims

1. A method for coherently demodulating a chaotic sequence spread spectrum signal at a receiver, comprising:

receiving a chaotic sequence spread spectrum signal including a plurality of information symbols at a receiver;

generating a first string of discrete time chaotic samples at said receiver by selecting a plurality of polynomial equations;

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

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

processing said chaotic sequence spread spectrum signal at said receiver to identify a time offset and a frequency offset relative to said first string of discrete time chaotic samples, each of said discrete time chaotic samples having a shorter sample time interval than a duration of said plurality of information symbols.

2. The method according to claim 1, wherein said first string of discrete time chaotic samples is identical to a second string of discrete time chaotic samples generated at a transmitter.

3. The method according to claim 2, further comprising utilizing an accurate time reference to minimize a timing difference uncertainty and a frequency difference uncertainty between said first string of discrete time chaotic samples and said second string of discrete time chaotic samples.

4. The method according to claim 1, further comprising correlating said chaotic sequence spread spectrum signal with said first string of discrete time chaotic samples to obtain correlation outputs.

5. The method according to claim 4, wherein said correlating step is performed at a symbol rate on symbol boundaries or at a symbol rate offset from symbol boundaries.

6. The method according to claim 4, further comprising processing said correlation outputs to produce a plurality of soft symbol decisions, to track a symbol timing, to track a plurality of timing offsets, to track a plurality of frequency offsets, to track a plurality of phase offsets, and to track a received signal strength.

7. The method according to claim 6, further comprising processing said plurality of soft symbol decisions to form hard symbol decisions.

8. The method according to claim 6, further comprising utilizing tracked timing offset information to adjust a timing of said receiver, to control a re-sampling of said chaotic sequence spread spectrum signal, or to control a re-sampling of said first string of discrete time chaotic samples.

9. The method according to claim 6, further comprising utilizing tracked frequency offset information to adjust a local oscillator so that a frequency of said local oscillator matches a frequency of said chaotic sequence spread spectrum signal.

10. The method according to claim 6, further comprising utilizing tracked phase offset information to correct a phase offset between said chaotic sequence spread spectrum signal and said first string of discrete time chaotic samples.

11. The method according to claim 6, further comprising utilizing tracked received signal strength information to adjust a gain for amplifying said chaotic sequence spread spectrum signal.

12. A chaotic spread spectrum communications system (CSSCS) receiver configured for coherently demodulating a chaotic sequence spread spectrum signal, comprising:

a receiving means configured for receiving a chaotic sequence spread spectrum signal including a plurality of information symbols;

a chaotic sequence generator configured for generating a first string of discrete time chaotic samples, said chaotic sequence generator comprising;

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

a mapping means configured for determining a series of digits in a weighted number system based on said plurality of RNS residue values;

a processing means configured for processing said chaotic sequence spread spectrum signal to identify a time offset and a frequency offset relative to said first string of discrete time chaotic samples, each of said discrete time chaotic samples having a shorter sample time interval than a duration of said plurality of information symbols.

13. The CSSCS receiver according to claim 12, wherein said first string of discrete time chaotic samples is identical to a second string of discrete time chaotic samples generated at a transmitter.

14. The CSSCS receiver according to claim 13, further comprising an accurate time reference configured for minimizing a timing difference uncertainty and a frequency difference uncertainty between said first string of discrete time chaotic samples and said second string of discrete time chaotic samples.

15. The CSSCS receiver according to claim 12, further comprising a correlator configured for correlating said chaotic sequence spread spectrum signal with said first string of discrete time chaotic samples to obtain correlation outputs.

16. The CSSCS receiver according to claim 15, wherein said correlator is further configured for correlating said chaotic sequence spread spectrum signal with said first string of discrete time chaotic samples at a symbol rate on symbol boundaries or at a symbol rate offset from symbol boundaries.

17. The CSSCS receiver according to claim 15, wherein said correlator is further configured for processing said correlation outputs to produce a plurality of soft symbol decisions.

18. The CSSCS receiver according to claim 17, further comprising a hard decision device configured for processing said plurality of soft symbol decisions to form hard symbol decisions.

19. The CSSCS receiver according to claim 15, further comprising a loop control circuit configured for tracking a symbol timing, tracking a plurality of timing offsets, tracking a plurality of frequency offsets, tracking a plurality of phase offsets, and tracking a received signal strength.

20. The CSSCS receiver according to claim 19, wherein said loop control circuit is further configured for adjusting a timing of said receiving means utilizing tracked timing offset information, controlling a re-sampling of said chaotic sequence spread spectrum signal, or controlling a re-sampling of said first string of discrete time chaotic samples.

21. The CSSCS receiver according to claim 19, wherein said loop control circuit is further configured for adjusting a local oscillator utilizing tracked frequency offset information so that a frequency of said local oscillator matches a frequency of said chaotic sequence spread spectrum signal.

22. The CSSCS receiver according to claim 19, wherein said loop control circuit is further configured for correcting a phase offset between said chaotic sequence spread spectrum signal and said first string of discrete time chaotic samples utilizing tracked phase offset information.

23. The CSSCS receiver according to claim 19, wherein said loop control circuit is further configured for adjusting a gain of an amplifier utilizing tracked received signal strength information.