Method and apparatus for distributed polyphase spread spectrum communications

• US 20050281321A1
• Filed: 06/17/2004
• Published: 12/22/2005
• Est. Priority Date: 06/17/2004
• Status: Active Grant

• Current Assignee: General Dynamics C4 Systems Incorporated (General Dynamics Corporation)
• Original Assignee: General Dynamics C4 Systems Incorporated (General Dynamics Corporation)
• Inventors: Bergstrom, Chad Scott, Chuprun, Jeffery Scott, Arneson, Steve, Malone, Hugh Robert
• Granted Patent: US 7,327,777 B2
• Time in Patent Office: Days
• US Class Current: 375/144
• CPC Class Codes: H04B 1/7102 with transform to frequency domain

Abstract

Methods and apparatus are provided for distributed polyphase spread spectrum communication and non-contiguous spectrum underlay. The method includes polyphase channelizing a direct sequence spread spectrum (DSSS) signal, determining available spectrum in an observed frequency range having a noise floor based on detection of polyphase users below the noise floor, distributing the polyphase channelized signal among the available spectrum, and interference mitigation using a combination of standard signal detection and cyclostationary feature detection methods. The apparatus includes: a first processor adapted to polyphase channelize a code division multiple access (CDMA) spectrum and a digitized RF bandwidth containing a discontiguous polyphase waveform distribution; a second processor adapted to detect occupied bands, interferers and polyphase users in a spectrum and determine discontiguous frequency opportunities based on the detected interferers and polyphase users; and a third processor adapted to allocate the polyphase channelized CDMA spectrum among available spectrum based on the discontiguous frequency opportunities.

Claims

1. A method of communication comprising the steps of:

polyphase channelizing a signal;

determining available spectrum in an observed frequency range having a noise floor based on detection of polyphase users below the noise floor; and

distributing the polyphase channelized signal among the available spectrum.

2. A method of communication according to claim 1, wherein said signal is a direct sequence spread spectrum (DSSS) signal.

3. A method of communication according to claim 1, wherein said signal is a featureless waveform.

4. A method of communication according to claim 1, wherein said spectrum determining step comprises the steps of:

detecting at least one of occupied bands, interferers, and polyphase users in the observed frequency range using cyclostationary feature detection;

determining a total number of channels available within the observed frequency range based on detected occupied bands, interferers, and polyphase users; and

determining an aggregate bandwidth based on the total number of channels available within the observed frequency range.

5. A method of communication according to claim 1, wherein said channelizing step comprises the step of determining a number of channelized filters based on the total number of channels;

and wherein said distributing step comprises the step of distributing the channelized filters into available spectrum.

6. A method of communication according to claim 5, wherein said distributing step further comprises the steps of:

applying discontiguous polyphase channel sounding to the observed frequency range; and

mitigating wide band dispersion effects based on the channel sounding.

7. A method of communication according to claim 6, wherein said polyphase channel sounding step further comprises the steps of:

polyphase channelizing a discontiguous filtered impulse to produce impulse channels;

distributing the impulse channels according to an observed spectrum distribution to produce distributed impulse channels; and

transmitting the distributed impulse channels through a dispersive channel to produce a distorted discontiguous filtered impulse.

8. A method of communication according to claim 7, wherein said polyphase channel sounding step further comprises the steps of:

receiving the distorted discontiguous filtered impulse;

polyphase reconstructing the impulse channels to produce a distorted continuous filtered impulse; and

equalizing the channel using the distorted continuous filtered impulse.

9. A method of communication according to claim 1, wherein said distributing step comprises allocating the polyphase channelized signal among non-contiguous available spectrum.

10. A method of communication according to claim 1 further comprising the steps of:

up-converting the distributed polyphase channelized signal; and

transmitting the up-converted signal.

11. A method of communication according to claim 10, wherein said up-converted signal transmitting step comprises transmitting a discontiguous spectrum access control signal.

12. A method of communication according to claim 1 further comprising the steps of:

down-converting an analog radio frequency (RF) transmission having discontiguous polyphase waveform distribution of an original DSSS signal; and

digitizing the down-converted RF transmission.

13. A method of communication according to claim 12 further comprising the steps of:

polyphase channelizing the digitized RF transmission; and

mitigating interference from at least one of legacy signal interference and sub-band interferers.

14. A method of communication according to claim 13 further comprising the steps of:

receiving the discontiguous spectrum access control signal; and

adapting said polyphase channelizing step based on the control signal.

15. A method of communication according to claim 13 further comprising the steps of:

autonomously determining a transmitter channel allocation; and

adapting said polyphase channelizing step based on the determined channel allocation.

16. A method of communication according to claim 13, wherein said mitigating step comprises one of predicting interference using transversal filters, suppressing interfering spectral peaks by magnitude normalizing in frequency domain, adaptive inverse weighting in frequency domain, and decision directed feedback canceling.

17. A method of communication according to claim 16, wherein said decision directed feedback canceling comprises:

extracting interferer features using cyclostationary feature detection; and

coherent canceling of interferers based on the extracted interferer features.

18. A method of communication according to claim 17 further comprising the steps of:

re-assembling the polyphase channelized transmission into contiguous channels after said mitigating step; and

polyphase reconstructing the original DSSS signal from the re-assembled transmission.

19. A method of communication according to claim 17 further comprising the steps of:

re-assembling the polyphase channelized transmission into contiguous channels after said digitized RF transmission polyphase channelizing step; and

polyphase reconstructing the original DSSS signal from the re-assembled transmission.

20. A method of communication according to claim 19, wherein said polyphase reconstructing step comprises pre-conditioning data in the reassembled transmission to produce near-perfect reconstruction of the original DSSS signal

21. A method of communication according to claim 19, wherein said mitigating interference step follows said polyphase reconstructing step.

22. A spread spectrum radio comprising:

a signal processor configured to polyphase channelize a code division multiple access (CDMA) spectrum and a digitized RF bandwidth containing a discontiguous polyphase waveform distribution;

a signal detector configured to detect occupied bands, interferers and polyphase users in a spectrum and determine discontiguous frequency opportunities based on the detected interferers and polyphase users; and

a signal distributor configured to allocate the polyphase channelized CDMA spectrum among available spectrum based on the discontiguous frequency opportunities.

23. A method of communication according to claim 22 further comprising a control channel configured to produce spectrum access control signal.

24. A spread spectrum radio according to claim 22 further comprising an interference cancellation processor configured to perform one of interference prediction with inverse filtering of interference, spectral self-normalization to suppress interfering spectral peaks, adaptive inverse weighting in a frequency domain, and decision directed feedback cancellation.

25. A spread spectrum radio according to claim 22 further comprising:

a CDMA encoder configured to code and modulate a data packet or voice packet; and

a CDMA decoder configured to decode and demodulate a slotted CDMA signal.

26. A spread spectrum radio according to claim 22 further comprising:

an up-converter configured to convert the allocated spectrum from said signal distributor to a pre-determined frequency for transmission, said up-converter comprising;

at least one digital-to-analog converter (DAC);

at least one low pass filter connected to said at least one DAC; and

a balanced mixer connected to said at least one low pass filter; and

a down-converter configured to convert a full pre-determined bandwidth to a digitized RF bandwidth, said down-converter comprising;

a bandpass filter configured to removing extraneous signals;

a pair of quadrature mixers connected to said bandpass filter, said quadrature mixers configured to convert the filtered RF bandwidth to in-phase (I) and quadrature-phase (Q) baseband signals; and

at least one analog-to-digital converter (ADC) connected to said quadrature mixers.

27. A spread spectrum radio according to claim 26 further comprising:

an antenna; and

a transmit/receive switch configured to time-share said antenna between said up-converter and said down-converter.

28. A spread spectrum radio according to claim 22, wherein said signal processor comprises a processing unit adapted to perform a combination of standard and cyclostationary detection of non-occupied spectrum above and below a noise floor.

29. A spread spectrum radio according to claim 22, wherein said spread spectrum radio is a software programmable radio.

30. A spread spectrum radio according to claim 22, wherein said spread spectrum radio is a software defined radio.

31. A digital radio comprising:

a first processor configured to polyphase channelize a CDMA spectrum;

a second processor configured to determine available spectrum based on non-linear signal processing of an observed RF spectrum, said second processor detecting occupied bands, interferers, and polyphase users above and below a noise floor

a third processor configured to allocate the channelized spectrum from said first processor among the available spectrum;

a fourth processor configured to up-convert the allocated spectrum from said third processor to an RF transmit signal and down-convert RF received signals to digitized RF bandwidth; and

a fifth processor configured to polyphase channelize the digitized RF bandwidth from said fourth processor, cancel interference based on detected interferers from said second processor, and reconstruct an original CDMA spectrum.

32. A digital radio according to claim 31 further comprising:

a sixth processor configured to CDMA code and modulate packet data; and

a seventh processor configured to CDMA decode and demodulate the original CDMA spectrum from said fifth processor.