Separation of communication signals in an adaptive antenna array

• US 4,513,383 A
• Filed: 09/24/1981
• Issued: 04/23/1985
• Est. Priority Date: 09/24/1981
• Status: Expired due to Term

• Current Assignee: Rockwell International Corporation
• Original Assignee: Rockwell International Corporation
• Inventors: Hackett, Charles M. Jr.
• Primary Examiner(s): NOT, DEFINED
• Application Number:
  US06/305,296
• Time in Patent Office: 1,307 Days
• Field of Search: 364/516, 364/517, 364/570, 364/573, 364/581, 364/582, 343/5 DP, 343/5 NQ, 343/370, 343/372
• US Class Current: 702/190
• CPC Class Codes: H01Q 3/2617 Array of identical elements

Abstract

Method and apparatus are disclosed for separating radio frequency signals incident upon an array of antenna elements which has available from each of the elements an input signal capable of being processed by the method and apparatus. The processing includes combining the input signals according to a first set of complex weights, thereby providing a first output signal. The first set of weights is derived from the input signals and from the first output signal and converges to the eigenvector corresponding to the largest eigenvalue of the cross-correlation matrix of the complex envelopes of the input signals. The input signals are also combined according to a second set of complex weights to provide a second output signal. The second set of weights is derived from the input signals, from the second output signal and from the first set of weights. The second set of weights converges to the eigenvector corresponding to the second largest eigenvalue of said cross-correlation matrix. As a result of this processing, the first and second output signals respectively, correspond, in general, to the first and second most powerful signals incident on the array. Additional sets of weights can be developed to separate any additional signals.

Claims

1. A method for separating m radio frequency signals incident on an array n antenna elements, wherein there is, for each element, a time-varying signal from the element and a corresponding input signal capable of being processed by the method, which input signal is generated from the time-varying signal and can be representative of its complex envelope, said method comprising:

computing the weighted combination of the input signals for each set of weights in an ordered sequence of sets of weights, from a first set through an n-th set, with each of the resulting n computed combinations providing an output signal, designated with an index i as y_i, and associated with the i-th set of weights;

forming, for each one of the n output signals, a set of products of the one output signal and the complex conjugates of the input signals, and time smoothing each of said sets of products;

for each of the n sets of smoothed products, modifying the i-th set of smoothed products associated with the i-th output signal, in response to all of the sets of weights which precede the i-th set of weights in said sequence; and

for each of the n modified sets of smoothed products, normalizing the modified i-th set of smoothed products to provide the i-th set of weights, approaching that eigenvector of the cross-correlation matrix of the complex envelopes of said time-varying signals which corresponds to the -th largest eigenvalue of the matrix,

whereby each of said output signals corresponds predominately to a different one of said incident radio frequency signals for m less than or equal to n.

7. The method of claims 1 or 2, wherein the step of computing the weighted combination includes analog mixing said each set of weights and the input signals, and summing and band-pass filtering the results of the mixing at a sum frequency thereof.

8. The method of claims 1 or 2, wherein the steps of forming a set of products and time smoothing include analog mixing the input signals and said one output signal, and band-pass filtering the results of the mixing at a difference frequency thereof.

2. A method for separating m radiating signals incident on an array of n receiving elements, wherein there is, for each element, a time-varying signal derived from the element and a corresponding input signal capable of being processed by the method, which input signal is generated from the time-varying signal and can be representative of its complex envelope, said method comprising:

computing the weighted combination of the input signals for each set of weights in ordered sequence of sets of weights, from a first set through an n-th set, with each of the resulting n computed combinations providing an output signal, designated with an index i as y_i, and associated with the i-th set of weights;

forming, for each one of the n output signals, a set of products of the one output signal and the complex conjugates of the input signals, and time smoothing each of said sets of products;

for each of the n sets of smoothed products, modifying the i-th set of smoothed products associated with the i-th input signal, in response to all of the sets of weights which precede the i-th set of weights in said sequence; and

for each of the n modified sets of smoothed products, normalizing the modified i-th set of smoothed products to provide the i-th set of weights, approaching that eigenvector of the cross-correlation matrix of the complex envelopes of said time-varying signals which corresponds to the i-th largest eigenvalue of the matrix,

whereby each of said output signals corresponds predominantly to a different one of said incident signals for m less than or equal to n.

3. A method for separating m radio frequency signals incident on an array of n antenna elements, wherein there is, for each element, a time-varying signal derived from the element and a corresponding input signal capable of being processed by the method, which input signal is generated from the time-varying signal and can be representative of its complex envelope, said method comprising:

multiplying a vector, which has as components the input signals, by each weighting vector in an ordered sequence of weighting vectors, from a first through an n-th weighting vector, with each of the resulting n products providing an output signal, designated with an index i as y_i, and associated with the i-th weighting vector;

forming, for each one of the n output signals, the product of the one output signal and a vector having as components the complex conjugates of the input signals, and time smoothing each of the resulting n product vectors;

for each of the n smoothed product vectors, modifying the i-th smoothed product vector associated with the i-th output signal, in response to all of the weighting vectors which precede the i-th weighting vector in said sequence; and

for each of the n modified smoothed product vectors, normalizing the modified i-th smoothed product vector to provide the i-th weighting vector, approaching that eigenvector of the cross-correlation matrix of the complex envelopes of said time-varying signals which corresponds to the i-th eigenvalue of the matrix,

whereby each of said output signals corresponds predominantly to a different one of said incident signals for m less than or equal to n.

5. The method of claim 3 or 4, wherein the step of modifying includes, for each one of said weighting vectors which precedes the i-th weighting vector;

forming the inner product of said one preceding vector and said i-th smoothed product vector; and

multiplying the one preceding vector by said inner product and subtracting the result from the i-th smoothed product vector.

9. The method of claim 5, wherein the step of forming the inner product includes analog mixing of said one preceding vector and said i-th smoothed product vector, and summing and band-pass filtering the results of the mixing at a difference frequency thereof.

4. A method for separating m radiating signals incident on an array of n receiving elements, wherein there is, for each element, a time-varying signal derived from the element and a corresponding input signal capable of being processed by the method, which input signal is generated from the time-varying signal and can be representative of its complex envelope, said method comprising:

multiplying a vector, which has as components the input signals, by each weighting vector in an ordered sequence of weighting vectors, from a first through an n-th weighting vector, with each of the resulting n products providing an output signal, designated with an index i as y_i, and associated with the i-th weighting vector;

forming, for each one of the n output signals, the product of the one output signal and a vector having as components the complex conjugates of the input signals, and time smoothing each of the resulting n product vectors;

for each of the n smoothed product vectors, modifying the i-th smoothed product vector associated with the i-th output signal, in response to all of the weighting factors which precede the i-th weighting vector in said sequence; and

for each of the n modified smoothed product vectors, normalizing the modified i-th smoothed product vector to provide the i-th weighting vector, approaching that eigenvector of the cross-correlation matrix of the complex envelopes of said time-varying signals which corresponds to the i-th largest eigenvalue of the matrix,

whereby each of said output signals corresponds predominantly to a different one of said incident signals for m less than or equal to n.

6. The method of claim 4, wherein said input signals represent samples, as generated by a complex sampling operation, of the complex envelopes of the time-varying signals, and the steps of multiplying, forming, smoothing, modifying and normalizing are performed digitally and iteratively for a succession of said sample-representative input signals.

10. An apparatus for separating m radio frequency signals incident on an array of n antenna elements, wherein there is, for each element, a time-varying signal derived from the element and a corresponding input signal capable of being processed by the apparatus, which input signal is generated from the time-varying signal and can be representative of its complex envelope, said apparatus comprising:

means for computing the weighted combination of the input signals for each set of weights in an ordered sequence of sets of weights, from a first set through an n-th set, with each of the resulting n computed combinations providing an output signal, designated with an index i as y_i, and associated with the i-th set of weights;

means for forming, for each one of the n output signals, a set of products of the one output signal and the complex conjugates of the input signals, and time smoothing each of said sets of products;

means, for each of the n sets of smoothed products, for modifying the i-th set of smoothed products associated with the i-th output signal, in response to all of the sets of weigths which precede the i-th set of weights in said sequence; and

means, for each of the n modified sets of smoothed products, for normalizing the modified i-th set of smoothed products to provide the i-th set of weights, approaching that eigenvector of the cross-correlation matrix of the complex envelopes of said time-varying signals which corresponds to the i-th largest eigenvalue of the matrix,

whereby each of said output signals corresponds predominantly to a different one of said input signals for m less than or equal to n.

11. An apparatus for separating m radiating signals incident on an array of n receiving elements, wherein there is, for each element, a time-varying signal derived from the element and a corresponding input signal capable of being processed by the apparatus, which input signal is generated from the time-varying signal and can be representative of, its complex envelope, said apparatus comprising:

means for computing the weighted combination of the input signals for each set of weights in an ordered sequence of sets of weights, from a first set through an n-th set, with each of the resulting n computed combinations providing an output signal, designated with an index i as y_i, and associated with the i-th set of weights;

means for forming, for each one of the n output signals, a set of products of the one output signal and the complex conjugates of the input signals, and time smoothing each of said sets of products;

means, for each of the n sets of smoothed products, for modifying the i-th set of smoothed products associated with the i-th output signal, in response to all of the sets of weights which precede the i-th set of weights in said sequence; and

means, for each of the n modified sets of smoothed products, for normalizing the modified i-th set of smoothed products to provide the i-th set of weights, approaching that eigenvector of the cross-correlation matrix of the complex envelopes of said time-varying signals which corresponds to the i-th largest eigenvalue of the matrix,

whereby each of said output signals corresponds to a different one of said input signals for m less than or equal to n.