SELECTIVE NOISE CANCELLATION OF A SPREAD SPECTRUM SIGNAL

• US 20090245327A1
• Filed: 03/26/2008
• Published: 10/01/2009
• Est. Priority Date: 03/26/2008
• Status: Active Grant

• Current Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Original Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Inventors: Michaels, Alan J.
• Granted Patent: US 8,040,937 B2
• Time in Patent Office: Days
• US Class Current: 375/130
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04J 13/0018 Chaotic
• CPC Class Codes: H04J 13/10 Code generation

Abstract

A method is provided for improving a signal-to-noise ratio in a received signal. The method involves receiving a spread spectrum signal (SSS) with a power level below a noise floor of a receiver. The SSS is generated by modulating a data signal using a spreading sequence (SS) comprised of a random number sequence (RNS). The SS can be generated using a chaos generator or any other deterministic means. The method also involves comparing a magnitude of each number of the RNS which was used to generate the SSS to an adaptable threshold value. The adaptable threshold value is selected based on a minimum magnitude of each number necessary to produce samples having a predetermined signal-to-noise ratio. Notably, samples of the received SSS are excluded from a receiver processing based on a result of the comparison. Similarly, each number of a random number sequence is excluded from the receiver processing based on the comparison.

Claims

1. A method for improving a signal-to-noise ratio in a received signal, comprising:

receiving a spread spectrum signal which has been generated by modulating a data signal using a spreading sequence comprised of a series of random numbers, said spreading sequence having a higher rate as compared to said data signal;

comparing a magnitude of each number comprising a coherent time synchronized copy of said series of random numbers which was used to generate said spread spectrum signal to an adaptable threshold value; and

selectively excluding samples of said received spread spectrum signal from a receiver processing step based on a result of said comparing step.

2. The method according to claim 1, further comprising excluding each said number of a random number sequence from said receiver processing step based on said comparing step.

3. The method according to claim 1, further comprising selecting said receiver processing step to include a correlation process.

4. The method according to claim 1, further comprising selecting said adaptable threshold based on a minimum magnitude of each said number necessary to produce samples having a predetermined signal-to-noise ratio.

5. The method according to claim 1, further comprising communicating each said random number of said series of random numbers and said respective sample of said spread spectrum signal to a correlator if said random number exceeds said adaptable threshold value.

6. The method according to claim 5, further comprising correlating said spread spectrum signal in said correlator with said random number sequence, absent of said samples and said numbers excluded as a result of said comparing step.

7. The method according to claim 1, further comprising selecting said subsequent processing step to include a de-spreading step configured for extracting said data signal from said spread spectrum signal.

8. The method according to claim 1, further comprising calibrating said spread spectrum signal to have a power level below a noise floor of a communications system receiver.

9. The method according to claim 1, further comprising generating said spreading sequence using an analog chaotic circuit or a digital pseudo-chaotic generator.

10. The method according to claim 1, further comprising generating a de-spreading sequence comprising said series of random numbers at a receiving device using a chaos generator or a digital pseudo-chaotic generator.

11. A machine-readable medium having stored thereon instructions, which when executed by a machine, cause the machine to perform the following operations comprising:

receiving a spread spectrum signal which has been generated by modulating a data signal using a spreading sequence comprised of a series of random numbers, said spreading sequence having a higher rate as compared to said data signal;

comparing a magnitude of each number comprising a coherent time synchronized copy of said series of random numbers which was used to generate said spread spectrum signal to an adaptable threshold value; and

selectively excluding samples of said received spread spectrum signal from a receiver processing operation based on a result of said comparing operation.

12. The machine-readable medium according to claim 11, further comprising instructions to cause the operation of excluding each said number of a random number sequence from said receiver processing operation based on said comparing operation.

13. The machine-readable medium according to claim 11, further comprising instructions to cause the operation of selecting said receiver processing operation to include a correlation process.

14. The machine-readable medium according to claim 11, further comprising instructions to cause the operation of communicating each said random number of said series of random numbers and said respective sample of said spread spectrum signal to a correlator if said random number exceeds said adaptable threshold value.

15. The machine-readable medium according to claim 14, further comprising instructions to cause the operation of correlating said spread spectrum signal in said correlator with said random number sequence, absent of said samples and said numbers excluded as a result of said comparing operation.

16. The machine-readable medium according to claim 11, further comprising instructions to cause the operation of selecting said subsequent processing operation to include a de-spreading operation configured for extracting said data signal from said spread spectrum signal.

17. The machine-readable medium according to claim 11, further comprising instructions to cause the operation of generating said spreading sequence using an analog chaotic or a digital pseudo chaotic generator.

18. The machine-readable medium according to claim 11, further comprising instructions to cause the operation of generating a de-spreading sequence comprising said series of random numbers at a receiving device using a chaos generator or a digital pseudo-chaotic generator.

19. A receiver of a communications system, comprising:

RF hardware configured for receiving a spread spectrum signal which has been generated by modulating a data signal using a spreading sequence comprised of a series of random numbers, said spreading sequence having a higher rate as compared to said data signal; and

a selective noise cancellation device configured for (a) comparing a magnitude of each number comprising a coherent synchronized replica of said series of random numbers which was used to generate said spread spectrum signal to an adaptable pre-defined threshold value, and (b) selectively excluding samples of said received spread spectrum signal from a receiver processing based on a result of said comparison.

20. The receiver according to claim 19, wherein said selective noise cancellation device is further configured for excluding each said number of a random number sequence from said receiver processing based on said comparison.

21. The receiver according to claim 19, wherein said receiver processing includes a correlation process.

22. The receiver according to claim 19, wherein said adaptable threshold is selected based on a minimum magnitude of each said number in the synchronized coherent replica of a spreading sequence necessary to produce samples having a predetermined signal-to-noise ratio.

23. The receiver according to claim 19, wherein said selective noise cancellation device is further configured for communicating each said random number of said series of random numbers and said respective sample of said spread spectrum signal to a correlator if said random number exceeds said adaptable threshold value.

24. The receiver according to claim 23, wherein said correlator is configured for correlating said spread spectrum signal with said random number sequence, absent of said samples and said numbers excluded as a result of said comparison.

25. The receiver according to claim 19, wherein said selective noise cancellation device is further configured for communicating each said random number of said series of random numbers and said respective sample of said spread spectrum signal to a de-spreader if said random number exceeds said adaptable threshold value.