Symbol estimation for chaotic spread spectrum signal

• US 8,406,352 B2
• Filed: 07/01/2009
• Issued: 03/26/2013
• Est. Priority Date: 07/01/2009
• Status: Active Grant

• Current Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Original Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Inventors: Michaels, Alan J., Chester, David B.
• Primary Examiner(s): Payne, David C.
• Assistant Examiner(s): Haider, Syed
• Application Number:
  US12/496,146
• Publication Number:
  US 20110002362A1
• Time in Patent Office: 1,364 Days
• Field of Search: 375/130, 375/138, 375/140, 375/141, 375/146, 375/147, 375/148, 375/149, 375/285, 375/296, 375/343, 375/346
• US Class Current: 375/343
• CPC Class Codes: H04L 27/001 using chaotic signals for secret or secure communication H04L9/001

Abstract

A communications system includes RF hardware (104) configured for receiving an input data signal includes a modulated carrier encoded with information symbols and modulated using a sequence of discrete time chaotic samples. The system also includes a chaotic sequence generator (340) configured for generating the sequence of discrete-time chaotic samples and a correlator (328). The correlator is configured for synchronizing the input data signal with the sequence of discrete-time chaotic samples and obtaining normalization factor values for each of the information symbols based on comparing a received symbol energy for the information symbols and a symbol energy of the discrete-time chaotic samples associated with the duration of transmission of the information symbols.

Claims

1. A method for improving symbol estimation in a received data signal, comprising:

receiving an input data signal at said receiver, said input data signal comprising at least one modulated carrier encoded with a sequence of information symbols, said modulated carrier modulated using a sequence of discrete time chaotic samples generated at a transmitter, each of said discrete time chaotic samples having a shorter sample time interval than a duration of transmission of each of said plurality of information symbols;

generating a replica of said sequence of discrete-time chaotic samples at said receiver;

synchronizing said input data signal in time with said replica of said sequence of discrete-time chaotic samples generated at said receiver;

correlating said input data signal with said replica to generate a de-spread data signal comprising a plurality of soft symbols;

obtaining at least one normalization factor value for each of said soft symbols based on a result obtained from comparing a received symbol energy for each of said plurality of information symbols and a symbol energy of said discrete-time chaotic samples associated with said duration of transmission for each of said plurality of symbols; and

using said normalization factor value to reduce an amplitude variance of said de-spread data signal so that a likelihood of incorrect hard symbol decisions due to non-stationary characteristics of a chaotic spreading sequence is reduced.

2. The method of claim 1, further comprising:

demodulating said input data signal using said sequence of discrete-time chaotic samples which has been synchronized with said input data signal; and

adjusting said demodulated signal associated with each of said plurality of information symbols based on said obtained normalization factor value.

5. The method of claim 1, wherein said input data signal comprises a plurality of modulated carriers combined at the transmitter, each of said plurality of modulated carriers associated with said normalization factor value.

6. The method of claim 1, wherein said generating further comprises:

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; and

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

3. A method for improving symbol estimation in a received data signal, comprising:

receiving an input data signal at said receiver, said input data signal comprising at least one modulated carrier encoded with a sequence of information symbols, said modulated carrier modulated using a sequence of discrete time chaotic samples generated at a transmitter, each of said discrete time chaotic samples having a shorter sample time interval than a duration of transmission of each of said plurality of information symbols;

generating said sequence of discrete-time chaotic samples at said receiver;

synchronizing said input data signal in time, phase, and frequency with said sequence of discrete-time chaotic samples generated at said receiver; and

obtaining one or more normalization factor values for each of said plurality of information symbols based on comparing a received symbol energy for each of said plurality of information symbols and a symbol energy of said discrete-time chaotic samples associated with said duration of transmission for each of said plurality of symbols;

wherein said obtaining further comprises;

for each of said plurality of information symbols, calculating a first sum of an energy provided by each discrete-time sample in said input data signal during said duration of transmission;

calculating a second sum of an energy provided by each of said discrete-time chaotic samples in said sequence generated at said receiver and synchronous with said duration of transmission; and

calculating said normalization factor based on said first sum and said second sum.

4. The method of claim 3, said obtaining further comprising:

for each of said plurality of information symbols, evaluating said first and said second sums for two or more previously received ones of said plurality of information symbols;

determining a gain adjustment value for each of said plurality of information symbols based on said evaluating;

adjusting said normalization factor with said gain adjustment value.

7. A non-transitory computer-readable storage medium, having stored therein a computer program for improving symbol estimation in a receiver, the computer program comprising a plurality of code sections, the code sections executable by a computer for causing the computer to perform the steps of:

digitizing an input data signal, said input data signal comprising a modulated carrier encoded with a sequence of information symbols, said carrier modulated using a sequence of discrete time chaotic samples generated at remote location, each of said discrete time chaotic samples having a shorter sample time interval than a duration of transmission of each of said plurality of information symbols;

generating a replica of said sequence of discrete-time chaotic samples;

synchronizing said digitized signal in time with said generated sequence of discrete-time chaotic samples generated;

correlating said input data signal with said replica to generate a de-spread data signal comprising a plurality of soft symbols;

obtaining at least one normalization factor value for each of said soft symbols based on a result obtained from comparing a received symbol energy for each of said plurality of information symbols and a symbol energy of said discrete-time chaotic samples associated with said duration of transmission for each of said plurality of symbols; and

using said normalization factor value to reduce an amplitude variance of said de-spread data signal so that a likelihood of incorrect hard symbol decisions due to non-stationary characteristics of a chaotic spreading sequence is reduced.

8. The computer-readable storage medium of claim 7, further comprising code sections for performing the steps of:

demodulating said digitized signal using said sequence of discrete-time chaotic samples which has been synchronized with said input data signal; and

adjusting said demodulated signal associated with each of said plurality of information symbols based on said obtained normalization factor value.

11. The computer-readable storage medium of claim 7, wherein said input data signal comprises a plurality of modulated carriers combined at the transmitter, each of said plurality of modulated carriers associated with said normalization factor value.

12. The computer-readable storage medium of claim 7, wherein said generating further comprises:

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; and

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

9. A non-transitory computer-readable storage medium, having stored therein a computer program for improving symbol estimation in a receiver, the computer program comprising a plurality of code sections, the code sections executable by a computer for causing the computer to perform the steps of:

digitizing an input data signal, said input data signal comprising a modulated carrier encoded with a sequence of information symbols, said carrier modulated using a sequence of discrete time chaotic samples generated at remote location, each of said discrete time chaotic samples having a shorter sample time interval than a duration of transmission of each of said plurality of information symbols;

generating said sequence of discrete-time chaotic samples;

synchronizing said digitized signal in time, phase, and frequency with said generated sequence of discrete-time chaotic samples generated;

obtaining one or more normalization factor values for each of said plurality of information symbols based on comparing a received symbol energy for each of said plurality of information symbols and a symbol energy of said discrete-time chaotic samples associated with said duration of transmission for each of said plurality of symbols;

for each of said plurality of information symbols, calculating a first sum of an energy provided by each discrete-time sample in said digitized signal during said duration of transmission;

calculating a second sum of an energy provided by each of said discrete-time chaotic samples in said generated sequence synchronous with said duration of transmission; and

calculating said normalization factor based on said first sum and said second sum.

10. The computer-readable storage medium of claim 9, said obtaining further comprising:

for each of said plurality of information symbols, evaluating said first and said second sums for two or more previously received ones of said plurality of information symbols in said digitized signal;

determining a gain adjustment value for each of said plurality of information symbols based on said evaluating;

adjusting said normalization factor with said gain adjustment value.

13. A communications system, comprising:

RF hardware configured to receive an input data signal, said input data signal comprising at least one modulated carrier encoded with a sequence of information symbols, said modulated carrier modulated using a sequence of discrete time chaotic samples generated at a transmitter, each of said discrete time chaotic samples having a shorter sample time interval than a duration of transmission of each of said plurality of information symbols;

a chaotic sequence generator configured to generate a replica of said sequence of discrete-time chaotic samples generated at said transmitter; and

a correlator configured to;

synchronize said input data signal in time with and said replica of said sequence of discrete-time chaotic samples;

correlating said input data signal with said replica to generate a de-spread data signal comprising a plurality of soft symbols;

obtaining at least one normalization factor value for each of said soft symbols based on a result obtained from comparing a received symbol energy for each of said plurality of information symbols and a symbol energy of said discrete-time chaotic samples associated with said duration of transmission for each of said plurality of symbols; and

using said normalization factor value to reduce an amplitude variance of said de-spread data signal so that a likelihood of incorrect hard symbol decisions due to non-stationary characteristics of a chaotic spreading sequence is reduced.

14. The system of claim 13, wherein said signal processing element is further configured for:

demodulating said input data signal using said sequence of discrete-time chaotic samples which has been synchronized with said input data signal; and

adjusting said demodulated signal associated with each of said plurality of information symbols based on said normalization factor value.

17. The method of claim 13, wherein said input data signal comprises a plurality of modulated carriers combined at the transmitter, each of said plurality of modulated carriers associated with said normalization factor value.

18. The system of claim 13, wherein said chaotic sequence generates said sequence of discrete-time chaotic samples 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; and

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

15. A communications system, comprising:

RF hardware configured for receiving a input data signal, said input data signal comprising at least one modulated carrier encoded with a sequence of information symbols, said modulated carrier modulated using a sequence of discrete time chaotic samples generated at a transmitter, each of said discrete time chaotic samples having a shorter sample time interval than a duration of transmission of each of said plurality of information symbols;

a chaotic sequence generator configured for generating a sequence of discrete-time chaotic samples identical to said sequence of discrete-time chaotic samples generated at said transmitter; and

a correlator configured for;

synchronizing said input data signal in time, phase, and frequency with and said identical sequence of discrete-time chaotic samples;

obtaining one or more normalization factor values for each of said plurality of information symbols based on comparing a received symbol energy for each of said plurality of information symbols and a symbol energy of said discrete-time chaotic samples associated with said duration of transmission for each of said plurality of symbols;

for each of said plurality of information symbols, calculating a first sum of an energy provided by each discrete-time sample in said input data signal during said duration of transmission;

calculating a second sum of an energy provided by each of said discrete-time chaotic samples in said sequence generated at said receiver and synchronous with said duration of transmission; and

calculating said normalization factor based on said first sum and said second sum.

16. The system of claim 15, wherein said correlator is further configured during said obtaining for:

for each of said plurality of information symbols, evaluating said first and said second sums for two or more previously received ones of said plurality of information symbols;

determining a gain adjustment value for each of said plurality of information symbols based on said evaluating;

adjusting said normalization factor with said gain adjustment value.