Array beamforming with wide nulls

• US 6,970,722 B1
• Filed: 08/22/2002
• Issued: 11/29/2005
• Est. Priority Date: 08/22/2002
• Status: Expired due to Fees

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Lewis, Michael E.
• Primary Examiner(s): Tran, Pablo N.
• Application Number:
  US10/225,948
• Time in Patent Office: 1,195 Days
• Field of Search: 455/562.1, 455/501, 455269-2781, 455/280, 455/575.7, 455/101, 455/107, 455/108, 455/110, 455/13.3, 455 9- 10, 455/63.4, 455/65, 455 18- 25, 455/13.1, 342/372, 342/378, 342/380, 342/381, 342/383, 342/324, 370/342, 370/332
• US Class Current: 455/562.1
• CPC Class Codes: H01Q 3/42 using frequency-mixing H01Q3/2676 takes precedence

Abstract

A method and implementation of wireless communication are disclosed in which wireless signals are exchanged between at least one remote client and a directional antenna array associated with a wireless network, wherein the directional antenna array includes a plurality of antenna elements. A statistical matrix analysis is performed for each of the at least one client and the antenna array, in order to locate angles associated with directions of each client with respect to the antenna array. Values are determined for weighting factors for RF signals of each of the respective plurality of antenna elements, so as to create predetermined phase differences between the signals of the plurality of antenna elements. The predetermined phase differences are used to direct at least one null toward at least one source of interference, so as to avoid signal interference.

Claims

1. A method of wireless communication comprising:

exchanging wireless signals between at least one remote client and a directional antenna array associated with a wireless network, wherein the directional antenna array includes a plurality of antenna elements;

locating angles associated with directions of arrival for wireles signals from each client with respect to the antenna array;

determining values for weighting factors of wireless signals for each of the respective plurality of antenna elements, so as to create predetermined phase differences between the signals of the plurality of antenna elements, wherein the determining values for the weighting factors comprises sampling baseband signals from each antenna element, so as to obtain a representation of sampled signals from a particular client;

using the predetermined phase differences to direct at least one null toward at least one source of interference, so as to avoid signal interference;

wherein the sampled signals are used to buld up a covariance matrix R; and

wherein the sampled signals X have vector components x₀, x₁, x₂, . . . x_n that are expressed in matrix form such that X={x₀x₁x₂ . . . x_n}, and wherein the covariance matrix R is built up such that R=XX^H where R is the direct product of X, and X^H is the Hermitian matrix of X.

2. The method of claim 1 wherein the directional antenna array used for exchanging wireless signals with the at least one client has antenna elements distributed to form one of a one-dimensional linear array, a two-dimensional array and three-dimensional array.

3. The method of claim 1 wherein the antenna elements each include a modulator for applying the weighting factors to the outgoing RF signals from the respective antennas.

4. The method of claim 1 wherein the step of sampling is performed in at least one of the initial association of the client and during subsequent communications with the access point.

5. A method of wireless communication comprising:

exchanging wireless signals between at least one remote client and a directional antenna array associated with a wireless network, wherein the directional antenna array includes a plurality of antenna elements;

locating angles associated with directions of arrival for wireless signals from each client with respect to the antenna array;

determining values for weighting factors of wireless signals for each of the respective plurality of antenna elements, so as to create predetermined phase differences between the signals of the plurality of antenna elements, wherein the determining values for the weighting factors comprises sampling baseband signals from each antenna element, so as to obtain a representation of sampled signals from a particular client, wherein the sampled signals are used to build up a covariance matrix R;

performing an eigen-decomposition upon the covariance matrix for determining the dominant eigenvalues and the corresponding eigenvectors of the matrix upon building up the covariance matrix of sampled values from the client signal; and

using the predeternnined phase differences to direct at least one null toward at least one source of interference, so as to avoid signal interference;

wherein the sampled signals X have vector components x₀, x₁, x₂, . . . x_n that are expressed in matrix form such that X={x₀x₁x₂ . . . n_n}, and wherein the covariance matrix R is built up such that R=XX^H where R is the direct product of X, and X^H is the Hermitian matrix of X.

6. The method of claim 5 wherein the step eigen-decomposition is satisfied if the product of the covariance matrix R and the eigenvector is equal to the product of the scalar eigenvalue and the eigenvector such that R V_i=λ

_i V_i, where V_i is the eigenvector and λ

_i is the eigenvalues.

7. The method of claim 5 wherein, after the eigen-decomposition is performed, a recording step is performed of recording the dominant eigenvalue and its respective corresponding eigenvector into a table such that the eigenvectors are used as the weighting factors to produce the steering vector for forming the beam in the direction of the client.

8. The method of claim 7 further comprising a step of using the recorded weighting factors to steer the energy of the beam.

9. The method of claim 5 wherein the step of locating angles associated with directions of arrival comprises computing an array pattern for eigenvector weights and searching for a signal peak as a function of angle.

10. The method of claim 5 wherein the step of locating angles associated with directions of arrival comprises building a complimentary projection operator from the computed eigenvector, wherein an incident angle is then found corresponding to the maximum distance from a subspace defined by the dominant eigenvector and an array manifold defined by the separations of antenna elements in the antenna array.

11. The method of claim 10 wherein the array manifold a(φ

) is a vector used to generate a matrix A(φ

) such that A(φ

)=aa^H where A(φ

) is a matrix that is a function of the angle of incidence φ and

a^H is the Hermitian vector of a, where the dominant eigenvector of the array manifold matrix A defines the subspace.

12. The method of claim 11 wherein a projection operator P for A is found such that P=AA^H, which projects A onto a column space for the matrix A, and wherein the complimentary projection operator P is given as P′

=IP where I is the identity matrix for A, wherein the complementary projection operation P′

operates on the matrix A(φ

) so as to create a projection of A(φ

) in a direction perpendicular to the array manifold, so as to derive the incident angle of the client signal.

13. The method of claim 11 wherein the step of directing nulls comprises forming nulls by computing an integrated direct product of the array manifold over the angular range needed to control interference, such that:

$D={\int <br><br>}_{{\mathrm{\theta <br><br>}}_1}^{{\mathrm{\theta <br><br>}}_2}<br><br>{\mathrm{AA}}^H<br><br><br><br>d<br><br>\mathrm{\phi <br><br>}$

where θ and

θ

₂ represents the width of the null, further comprising a step of diagonalizing the matrix D and using the eigenvectors to form a complementary projection operator for the column space spanned of the original integrated matrix formed by the direct product of the array manifold, and comprising a further step of applying the complementary projection operator to the steering vector for the client to produce a new steering vector that produces a wide null in the array pattern of the desired position.

14. The method of claim 10 wherein the computed angle and the eigenvector corresponding to the dominant eigenvalue give a spatial signature for the client, and wherein a further step is provided of saving these values to form the steering vectors and determine which clients can access the channel at the same time.

15. The method of claim 14 further comprising a step of evaluating the spatial signatures to form nulls in the steering vectors, so that the nulls can be directed toward any nearby clients or other potentially interfering sources, wherein if two or more clients have adequate angular separation from the position of the antenna array as indicated by their spatial signatures, a step is performed of computing suitable array steering vectors for each client such that the computed steering vectors are used for both transmission and reception of messages from each respective client.