Adaptive beamforming method for smart antenna system

• US 20030128160A1
• Filed: 12/17/2002
• Published: 07/10/2003
• Est. Priority Date: 12/18/2001
• Status: Active Grant

• Current Assignee: LG Electronics, Inc. (LG Corporation)
• Original Assignee: LG Electronics, Inc. (LG Corporation)
• Inventors: Sim, Dong-Hi
• Granted Patent: US 6,771,219 B2
• Time in Patent Office: Days
• US Class Current: 342/382
• CPC Class Codes: G06F 2218/22 Source localisation; Inverse modelling
• CPC Class Codes: H01Q 3/2605 Array of radiating elements provided with a feedback control over the element weights, e.g. adaptive arrays

Abstract

An adaptive beamforming method for an antenna array is provided in which an array output is calculated based on a weight vector w, which is determined from an eigenvector corresponding to a maximum eigenvalueλ of a generalized eigenvalue problem consisting of autocovariance matrixes R_xx and R_yy of received signal vectors y and x, respectively. The present invention dramatically decreases the total computation requirements by omitting complex matrix operations from the weight vector calculation, thereby making it possible to reduce the weight vector calculation time so as to form the beam pattern for the array antenna system in real time.

Claims

1. A method for updating a weight vector for input signals from a plurality of antennas of a wireless communication system, comprising:

setting an initial weight vector for weighting the input signals;

separating desired signals from the input signals;

obtaining auto-covariance matrixes of the separated desired signals and the input signals, respectively;

computing an eigenvalue that maximizes a ratio of a vector that is a multiplication of the auto-covariance matrix of the separated desired signals and the initial weight vector over a vector that is a multiplication of the auto-covariance matrix of the input signals and the initial weight vector;

generating a new weight vector by adding a vector to the initial weight vector, wherein said added vector is proportional to the multiplication of the inverse of a diagonal matrix of the auto-covariance matrix of the input signals and a vector made from the multiplication of a vector of the separated desired signals and the initial weight vector and the inverse of the eigenvalue.

2. The method of claim 1, wherein said added vector is calculated by the steps of:

generating a first vector which is a multiplication of the Hermitian of a vector of the separated desired signals, the initial weight vector, and a vector of the separated desired signals added to the previous first vector multiplied by a forgetting factor;

generating a second vector which is a multiplication of the Hermitian of a vector of the input signals, the initial weight vector, and a vector of the input signals added to the previous first vector multiplied by a forgetting factor;

calculating said added vector by,

(1) dividing said first vector with said eigenvalue,

(2) subtracting said second vector from the divided first vector, and

(3) multiplying the result of step (2) by the inverse of a diagonal matrix of the auto-covariance matrix of the input signals.

3. The method of claim 2, wherein said forgetting factor is predetermined in a transmission interval and has a value from zero to one.

4. The method of claim 3, wherein said first vector is v(k), wherein:

5. The method of claim 4, wherein said added vector is o(k), said inverse of a diagonal matrix of the auto-covariance matrix of the input signals is [R_xx^D(k)]⁻

1 , and said eigenvalue is λ

(k), wherein;

6. The method of claim 1, wherein said desired signals are signals despread with a predetermined code from the input signals.

7. A method for updating the weight vector for input signals from a plurality of antennas of a wireless communication system, comprising:

setting an initial weight vector for weighting the input signals;

separating desired signals from the input signals;

obtaining auto-covariance matrixes of the separated desired signals and the input signals, respectively;

computing an eigenvalue that maximizes a ratio of a vector that is a multiplication of the auto-covariance matrix of the separated desired signals and the initial weight vector over a vector that is a multiplication of the auto-covariance matrix of the input signals and the initial weight vector;

generating a new weight vector by adding a vector to the initial weight vector, wherein said added vector is proportional to the multiplication of the inverse of a diagonal matrix of the auto-covariance matrix of the separated desired signals and a vector made from the multiplication of a vector of the input signals and the initial weight vector and the eigenvalue.

8. The method of claim 7, wherein said added vector is calculated by the steps of:

generating a first vector which is a multiplication of the Hermitian of a vector of the separated desired signals, the initial weight vector, and a vector of the separated desired signals added to the previous first vector multiplied by a forgetting factor;

generating second vector which is a multiplication of the Hermitian of a vector of the input signals, the initial weight vector, and a vector of the input signals added to the previous first vector multiplied by a forgetting factor;

calculating said added vector by,

(1) multiplying said second vector with said eigenvalue,

(2) subtracting said first vector from the multiplied first vector, and

(3) multiplying the result of step (2) by the inverse of a diagonal matrix of the auto-covariance matrix of the separated desired signals.

9. The method of claim 8, wherein said forgetting factor is predetermined in a transmission interval and has a value from zero to one.

10. The method of claim 9, wherein said second vector is γ

(k), wherein;

11. The method of claim 10, wherein said added vector is p(k), said inverse of a diagonal matrix of the auto-covariance matrix of the separated desired signals is [R_yy^D(k)]⁻

1, and said eigenvalue is λ

(k), wherein;

p(k)=[R_yy^D(k)]<sup>−

1</sup>[λ

(k)γ

(k)−

η

(k)]

12. The method of claim 7, wherein said desired signals are signals despread with a predetermined code from the Input signals.

13. A method for updating a maximum eigenvalue for generating a weight vector for weighting input signals from a plurality of antennas of a wireless communication system, comprising:

setting an initial weight vector for weighting the input signals;

separating desired signals from the input signals;

generating a first value by multiplying the Hermitian of a vector of the separated desired signals and the weight vector;

generating a second value by multiplying the Hermitian of a vector of the input signals;

computing a numerator of a new maximum eigenvalue by adding a square of said first value to a portion of a numerator of a previous maximum eigenvalue;

computing a denominator of the new maximum eigenvalue by adding a square of said second value to a portion of a denominator of the previous maximum eigenvalue; and

replacing the previous maximum eigenvalue with the new maximum eigenvalue having said numerator and denominator.

14. The method of claim 13, wherein said first value α

(k) is calculated in accordance with the following equation

α

(k)=y^H(k)w(k),

and wherein said second value β

(k) is calculated in accordance with the following equation

β

(k)=x^H(k)w(k).

15. The method of claim 14, wherein said numerator is calculated in accordance with the following equation

λ

_nom(k)=ƒ

λ

_nom(k−

1)+|α

(k)|² and,

said denominator is calculated in accordance with the following equation

λ

_den(k)=ƒ

λ

_den(k−

1)+|β

(k)|²

wherein ƒ

is a forgetting factor that is predetermined in a transmission interval and has a value from zero to one.

16. The method of claim 13, wherein said desired signals are signals despread with a predetermined code from the input signals.

17. An adaptive beam forming method for a communication receiver that inputs signals from an antenna array, comprising:

separating desired signals from the input signals;

calculating a maximum eigenvalue by defining it as a portion of a numerator and a portion of a denominator;

calculating a weight vector using said maximum eigenvalue, said desired signals, and said input signals; and

weighting signals from or to a plurality antennas in said antenna array with the weight vector.

18. The adaptive beamforming method of claim 17, wherein the maximum eigenvalue λ

(k) at a present snapshot is computed in accordance with following equation;

19. The adaptive beamforming method of claim 18, wherein α

(k) and β

(k) are obtained in accordance with the following equations;

α

(k)=y^H(k)w(k), and β

(k)=x^H(k)w(k),

where w is a weight vector, y(k) is a vector of the separated desired signals, x(k) is a vector of the input signals, and H is a Hermitian operator.

20. The adaptive beamforming method of claim 19, wherein the weight vector is updated in accordance with the following equation:

w(k+1)=w(k)+o(k)

where

21. The adaptive beamforming method of claim 20, wherein v(k) is obtained in accordance with the following equation:

22. The adaptive beamforming method of claim 21, wherein q(k) is obtained in accordance with the following equation:

23. The adaptive beamforming method of claim 19, wherein the weight vector w is updated in accordance with the following equation:

w(k+1)=w(k)+p(k),

where p(k)=[R_yy^D(k)]<sup>−

1</sup>[λ

(k)y(k)−

η

(k)].,

and where [R_yy^D(k)]<sup>−

1</sup> is an inverse of a diagonal matrix of the auto-covariance matrix of the separated desired signals.

24. The adaptive beamforming method of claim 23, wherein γ

(k) is obtained in accordance with the following equation;

25. The method of claim 17, wherein said desired signals are signals despread with a predetermined code from the input signals.

26. A method of obtaining a maximum eigenvalue for deriving a weight vector for weighting input signals from a plurality of antennas, comprising:

separating desired signals from the input signals;

setting an initial weight vector for weighting the input signals;

generating a first value based on a Hermitian of a vector of the separated desired signals;

generating a second value based on a Hermitian of a vector of the input signals; and

deriving the maximum eigenvalue from the first and second values.

27. The method of claim 26, further comprising deriving the weight vector using the separated desired signals, the input signals and the derived eigenvalue.

28. The method of claim 26, wherein the maximum eigenvalue is derived by:

adding a square of the first value to a portion of a numerator of a previous maximum eigenvalue to yield a new numerator;

adding a square of the second value to a portion of a denominator of the previous maximum eigenvalue to yield a new denominator; and

dividing the new numerator by the new denominator.

29. A method of updating a weight vector for weighting input signals from a plurality of antennas, comprising:

setting an initial weight vector for weighting the input signals;

separating desired signals from the input signals;

deriving an auto-covariance matrix of the separated desired signals;

deriving an auto-covariance matrix of the input signals;

deriving a maximum eigenvalue using the auto-covariance matrix of the separated desired signals, the auto-covariance matrix of the input signals and the initial weight vector; and

deriving a new weight vector by adding a vector to the initial weight vector, wherein the added vector is based on a vector of the separated signals, a vector of the input signals, the initial weight vector, the maximum eigenvalue, and one of the auto-covariance matrix of the input signals and the auto-covariance matrix of the separated desired signals.

30. The method of claim 29, wherein the added vector is proportional to the product of:

(1) the inverse of a diagonal matrix of the auto-covariance matrix of the input signals; and

(2) a vector derived from the product of a vector of the separated desired signals, the initial weight vector, and the inverse of the maximum eigenvalue.

31. The method of claim 29, wherein the added vector is proportional to the product of:

(1) the inverse of a diagonal matrix of the auto-covariance matrix of the separated desired signals; and

(2) a vector derived from the product of a vector of the input signals, the initial weight vector, and the inverse of the maximum eigenvalue.

32. The method of claim 29, wherein the maximum eigenvalue comprises an eigenvalue that maximizes a ratio of a first value to a second value, wherein the first value is defined by a vector that is the product of the auto-covariance matrix of the separated desired signals and the initial weight vector, and the second value is defined by a vector that is the product of the auto-covariance matrix of the input signals and the initial weight vector.

33. An adaptive beam forming method, comprising:

receiving input signals from a plurality of antennas;

separating desired signals from the input signals;

setting an initial weight vector for weighting the input signals;

generating a first value based on a Hermitian of a vector of the separated desired signals;

generating a second value based on a Hermitian of a vector of the input signals;

deriving a maximum eigenvalue from the first and second values;

deriving a weight vector using the separated desired signals, the input signals and the derived eigenvalue; and

applying the weight vector to the input signals or to signals being sent to the plurality of antennas.

34. The method of claim 33, wherein the maximum eigenvalue is derived by:

adding a square of the first value to a portion of a numerator of a previous maximum eigenvalue to yield a new numerator;

adding a square of the second value to a portion of a denominator of the previous maximum eigenvalue to yield a new denominator; and

dividing the new numerator by the new denominator.