SYMBOL DURATION DITHERING FOR SECURED CHAOTIC COMMUNICATIONS

• US 20100310072A1
• Filed: 06/08/2009
• Published: 12/09/2010
• Est. Priority Date: 06/08/2009
• 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 8,509,284 B2
• Time in Patent Office: Days
• US Class Current: 380/263
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04K 1/025 using an analogue chaotic signal

Abstract

A system for communicating a sequence of information symbols using a chaotic sequence spread spectrum signal. The system includes a transmitter (402) for transmitting a signal including the information symbols, the information symbols encoded into the signal using a first chaotic sequence of chips generated at the transmitter. The system also includes a receiver (404) configure to receive the signal and extract the information symbols from the signal, the information symbols extracted using a second chaotic sequence of chips generated at the receiver. In the system, the first and the second chaotic sequences are identical and synchronized in time and frequency, each of the sequence of symbols is associated with a randomly generated threshold symbol energy value, and the portion of chips in the first and the second chaotic sequences associated with each of the plurality of information symbols is selected based on the associated threshold symbol energy value.

Claims

1. A method for communicating a sequence of information symbols between a transmitter and a receiver using a chaotic sequence spread spectrum signal, the method comprising:

transmitting a signal comprising said sequence of information symbols, said information symbols encoded into said signal using a first chaotic sequence of chips generated at said transmitter; and

extracting said sequence of information symbols from said signal, said information symbols extracted using a second chaotic sequence of chips generated at said receiver,

wherein said first and said second chaotic sequences are identical and synchronized in time and frequency, wherein each of said sequence of symbols is associated with a randomly generated threshold symbol energy value, and wherein a portion of chips in said first and said second chaotic sequences associated with each of said plurality of information symbols is selected based on said associated threshold symbol energy value.

2. The method of claim 1, wherein said threshold symbol energy value is generated in said transmitter and said receiver using identical threshold generators using a linear function or a non-linear function.

3. The method of claim 2, wherein said threshold generator generates a pseudo random number sequence.

4. The method of claim 2, wherein said threshold generator generates a chaotic sequence.

5. The method of claim 1, wherein said transmitting further comprises:

modulating a carrier using a first portion of said first chaotic sequence of chips to transmit a current symbol from said sequence of information symbols;

calculating a total energy of said first portion;

comparing said total energy to said threshold symbol energy value associated with said current symbol; and

based on said comparing, ascertaining whether to select a next symbol from said sequence of information symbols.

6. The method of claim 5, said ascertaining further comprising:

if said total energy is greater than or equal to said threshold symbol energy value associated with said current symbol, selecting said next symbol, and repeating said modulating, said calculating, said comparing, and said ascertaining for a next portion of said first chaotic sequence of chips.

7. The method of claim 5, said ascertaining further comprising:

if said total energy for modulating is less than said threshold symbol energy value associated with said current symbol, repeating said modulating, said calculating, said comparing, and said ascertaining for a next portion of said first chaotic sequence of chips.

8. The method of claim 5, said calculating further comprising:

obtaining conjugate pair product values for each of said chips in said first portion; and

obtaining a sum of said conjugate pair product values.

9. The method of claim 1, wherein said extracting further comprises:

providing said threshold symbol energy for a current symbol of said sequence of said information symbols;

associating a current portion of said signal with said current symbol;

demodulating said current portion of signal using a first portion of said second chaotic sequence of chips;

calculating a total energy of said first portion of said second chaotic sequence;

comparing said total energy for demodulating to said threshold symbol energy value associated with said current symbol;

based on said comparison, ascertaining whether to associate a next portion of said signal with a next symbol of said sequence of information symbols;

10. The method of claim 9, said ascertaining during said receiving further comprising:

if said total energy is greater than or equal to said provided threshold symbol energy value provided for said current symbol, decoding said current symbol; and

providing said threshold symbol energy for a next symbol of said sequence of said information symbols;

associating a next portion of said signal with said next symbol; and

repeating said demodulating, said calculating, said comparing, and said ascertaining steps based on a next portion of said chaotic sequence of chips.

11. The method of claim 9, said ascertaining during said receiving further comprising:

if said total energy is less than said provided threshold symbol energy value, selecting a next portion of said transmitted carrier, and repeating said demodulating, said calculating, said comparing, and said ascertaining steps based on a next portion of said chaotic sequence of chips.

12. The method of claim 9, said calculating further comprising:

obtaining conjugate pair product values for each of said chips in said first portion of said second chaotic sequence; and

obtaining a sum of said conjugate pair product values.

13. A system for communicating a sequence of information symbols using a chaotic sequence spread spectrum signal, the system comprising:

a transmitter for transmitting a signal comprising said sequence of information symbols, said information symbols encoded into said signal using a first chaotic sequence of chips generated at said transmitter; and

a receiver configured to receive said signal and extract said sequence of information symbols from said signal, said information symbols extracted using a second chaotic sequence of chips generated at said receiver,

wherein said first and said second chaotic sequences are identical and synchronized in time and frequency, wherein each of said sequence of symbols is associated with a randomly generated threshold symbol energy value, and wherein a portion of chips in said first and said second chaotic sequences associated with each of said plurality of information symbols is selected based on said associated threshold symbol energy value.

14. The system of claim 13, wherein said transmitter and said receiver each have an identical threshold generator using a linear function or a non-linear function for generating said threshold symbol energy value.

15. The system of claim 14, wherein said threshold generator is configured for generating a pseudo-random number sequence.

16. The system of claim 14, wherein said threshold generator is configured for generating a chaotic sequence.

17. The system of claim 13, wherein said transmitter is further configured for:

modulating a carrier using a first portion of said first chaotic sequence of chips to transmit a current symbol from said sequence of information symbols;

calculating a total energy of said first portion;

comparing said total energy to said threshold symbol energy value associated with said current symbol; and

based on said comparing, ascertaining whether to select a next symbol from said sequence of information symbols.

18. The system of claim 17, wherein said transmitter is further configured during said ascertaining for:

if said total energy is greater than or equal to said threshold symbol energy value associated with said current symbol, selecting said next symbol, and repeating said modulating, said calculating, said comparing, and said ascertaining for a next portion of said first chaotic sequence of chips.

19. The system of claim 17, wherein said transmitter is further configured during said ascertaining for:

if said total energy for modulating is less than said threshold symbol energy value associated with said current symbol, repeating said modulating, said calculating, said comparing, and said ascertaining for a next portion of said first chaotic sequence of chips.

20. The system of claim 17, wherein said transmitter is further configured during said calculating for:

obtaining conjugate pair product values for each of said chips in said first portion; and

obtaining a sum of said conjugate pair product values.

21. The system of claim 13, wherein said receiver is further configured for:

providing said threshold symbol energy for a current symbol of said sequence of said information symbols;

associating a current portion of said signal with said current symbol;

demodulating said current portion of signal using a first portion of said second chaotic sequence of chips;

calculating a total energy of said first portion of said second chaotic sequence;

comparing said total energy for demodulating to said threshold symbol energy value associated with said current symbol;

based on said comparison, ascertaining whether to associate a next portion of said signal with a next symbol of said sequence of information symbols;

22. The system of claim 21, wherein said receiver is further configured during said ascertaining for:

if said total energy is greater than or equal to said provided threshold symbol energy value provided for said current symbol, decoding said current symbol; and

providing said threshold symbol energy for a next symbol of said sequence of said information symbols;

associating a next portion of said signal with said next symbol; and

repeating said demodulating, said calculating, said comparing, and said ascertaining steps based on a next portion of said chaotic sequence of chips.

23. The system of claim 21, wherein said receiver is further configured during said ascertaining for:

if said total energy is less than said provided threshold symbol energy value, selecting a next portion of said transmitted carrier, and repeating said demodulating, said calculating, said comparing, and said ascertaining steps based on a next portion of said chaotic sequence of chips.

24. The system of claim 21, wherein said receiver is further configured during said calculating for:

obtaining conjugate pair product values for each of said chips in said first portion of said second chaotic sequence; and

obtaining a sum of said conjugate pair product values.