Method and apparatus for signal separation

• US 20050259724A1
• Filed: 05/24/2004
• Published: 11/24/2005
• Est. Priority Date: 05/24/2004
• 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, Maalouli, Ghassan Chehade
• Granted Patent: US 7,356,075 B2
• Time in Patent Office: Days
• US Class Current: 375/150
• CPC Class Codes: H04B 1/7075 with code phase acquisition
• CPC Class Codes: H04B 1/71 the interference being narrowband interference
• CPC Class Codes: H04B 2201/70715 with application-specific features

Abstract

Methods and apparatus are provided for spread spectrum communication having spectrum awareness and interference mitigation based on parameterizing an input signal having multiple mixed baseband signals. The method includes non-linearly transforming the input signal, removing carrier effects, removing higher order terms by passing the input signal through a low pass filter to produce a linear combination of data symbols and DC components, solving for the DC components, separating a plurality of mixed baseband signals from the input signal, and coordinate transforming each of the separated signals from polar coordinates to a Cartesian coordinates. A receiver is provided having: a non-linear transform operator receiving a digitized input signal and adapted to produce a linear combination of data symbols, DC components, and carrier effects; a low-pass filter connected to the non-linear transform for removing higher order terms; a separator unit for separating the plurality of mixed baseband signals; and, a coordinate transform for converting the separated signals from polar coordinates to Cartesian coordinates.

Claims

1. A method of parameterizing an input signal having a plurality of mixed baseband signals, the method comprising the steps of:

applying a non-linear transform to an input signal;

removing higher order terms of the input signal by passing the input signal through a low pass filter to produce a linear combination of data symbols and DC components;

determining the DC components;

separating a plurality of mixed baseband signals from the input signal; and

coordinate transforming each of the separated signals from polar coordinates to a Cartesian coordinates.

2. A method of parameterizing an input signal according to claim 1, wherein said non-linearly transforming step comprises the steps of:

passing an input signal through a conjugate delayed product multiplier having an iterative delay estimator; and

generating at least one of a complex output of the input signal and a real output of the input signal.

3. A method of parameterizing according to claim 1, wherein said DC component determining step is selected from performing a least squares operation, performing a null space projection, and performing a polynomial solution.

4. A method of parameterizing according to claim 1 further comprising extracting features from the separated signals using cyclostationary feature extraction.

5. A method of parameterizing according to claim 4, wherein said cyclostationary feature extraction is selected from performing a non-linear operation and performing a joint time-frequency autocorrelation.

6. A method of parameterizing according to claim 1 further comprising passing the coordinate transformed signal through a feature discriminator.

7. A method of recovering at least one baseband source signal from a plurality of mixed signals, the method comprising the steps of:

down-converting and digitizing a plurality of mixed signals in an RF bandwidth;

polyphase channelizing the digitized bandwidth;

re-assembling the channels into an original order of an original spectrum and polyphase reconstructing the original spectrum;

passing one of the polyphase channelized signal and the polyphase reconstructed signal through a non-linear transform and a low-pass filter;

determining DC components of each of the non-linear transformed signals;

separating a plurality of mixed baseband signals; and

coordinate transforming each of the separated signals from polar coordinates to Cartesian coordinates.

8. A method according to claim 7, wherein said separating step comprises performing:

x(t)=As(t)+u(t)
s(t)=[s₁(t),s₂(t)]^T
Q(ω

)=∥

x(t)−

As(t)∥

²
s′

(t)=(A^HA)<sup>−

1</sup>A^Hx(t)
Q(ω

)=∥

x(t)−

A(A^HA)<sup>−

1</sup>A^Hx(t)∥

²

where x(t) represents the output of the low pass filter in vector notation, u(t) represents the low pass version of noise related terms, Q(ω

) represents the cost function of a least squares approach, and s′

(t) minimizes Q(ω

).

9. A method according to claim 7, wherein said passing step comprises the steps of:

passing an input signal through a conjugate delayed product multiplier having an iterative delay estimator; and

generating at least one of a complex output of the input signal and a real output of the input signal;

wherein the input signal is selected from the polyphase channelized signal and the polyphase reconstructed signal.

10. A method according to claim 7, wherein said DC component determining step is selected from performing a least squares operator, performing a null space projection, and performing a polynomial solution.

11. A method according to claim 7 further comprising extracting features from the separated signals using cyclostationary feature extraction.

12. A method according to claim 11, wherein said cyclostationary feature extraction is selected from performing a non-linear transform operation and performing a joint time-frequency autocorrelation.

13. A method according to claim 7 further comprising passing the coordinate transformed signal through a feature discriminator.

14. A digital radio receiver comprising:

a channel transformer adapted to polyphase channelize a communications signal, re-assemble the channels into contiguous channels, and polyphase reconstruct the original transmission spectrum;

a non-linear transform operator receiving one of the polyphase channelized signal and the polyphase reconstructed signal from said channel transformer and adapted to produce a linear combination of data symbols, and DC components;

a low-pass filter connected to said non-linear transform operator for removing higher order terms;

a first signal separator connected to said low-pass filter and adapted to separate a plurality of mixed baseband signals; and

a coordinate transform operator connected to said first signal separator and adapted to transform the separated signals from polar coordinates to Cartesian coordinates.

15. A spread spectrum receiver according to claim 14 further comprising a second signal separator connected to said coordinate transform operator and adapted for less blind signal separation of the separated signals from said coordinate transform operator.

16. A spread spectrum receiver according to claim 15, wherein said second signal separator is adapted for cyclostationary feature detection selected from non-linear transform operation and joint time-frequency autocorrelation.

17. A spread spectrum receiver according to claim 15 further comprising a CDMA processor connected to said second signal separator for demodulating and decoding the less blind separated signals.

18. A spread spectrum receiver according to claim 14 further comprising:

a down-converter connected to said channel transformer for digitizing and down-converting a full RF band.

19. A spread spectrum receiver according to claim 14, wherein said non-linear transform operator comprises a conjugate delay product multiplier having an iterative delay estimator.

20. A spread spectrum receiver according to claim 14, wherein said first signal processor is adapted to perform one of a least squares operation, a null space projection, and a polynomial solution.