Complementary beamforming methods and apparatuses

• US 8,195,242 B2
• Filed: 04/12/2011
• Issued: 06/05/2012
• Est. Priority Date: 11/04/2002
• Status: Active Grant

• Current Assignee: XR Communications, LLC
• Original Assignee: XR Communications, LLC
• Inventors: Tarokh, Vahid, Choi, Yang-Seok, Alamouti, Siavash
• Primary Examiner(s): Afshar, Kamran
• Assistant Examiner(s): LAM, DUNG LE
• Application Number:
  US13/085,335
• Publication Number:
  US 20110299460A1
• Time in Patent Office: 420 Days
• Field of Search: 455/562.1, 455/575.7, 455/271, 342/351, 342/354, 342/67
• US Class Current: 455/562.1
• CPC Class Codes: H01Q 1/246 specially adapted for base stations
• CPC Class Codes: H01Q 3/26 varying the relative phase or relative amplitude of energisation between two or more active radiating elements; varying the distribution of energy across a radiating aperture H01Q3/12, H01Q3/22, H01Q3/24 take precedence
• CPC Class Codes: H04B 7/0617 for beam forming
• CPC Class Codes: H04W 52/42 in systems with time, space, frequency or polarisation diversity

Abstract

Improved methods and apparatuses are provided to address a potential “hidden beam problem” in wireless communication systems employing smart antennas. The improved methods and apparatuses utilize complementary beamforming (CBF) techniques, such as, for example, Subspace Complementary Beamforming (SCBF), Complementary Superposition Beamforming (CSBF) and/or Single Beam Complementary Beamforming (SBCBF) techniques.

Claims

1. A method comprising:

providing a smart antenna;

determining at least one signal operatively configured for subspace complementary beamforming (SCBF) in a wireless communication system;

generating the at least one signal such that the signal is operatively configured to cause said smart antenna to perform said SCBF and to transmit at least one complementary beam; and

determining the at least one signal using a Steering Matrix;

A=[α

(θ

₁) α

(θ

₂) . . . α

(θ

_k)], wherein α

(θ

_k) represents a steering vector of user k;

wherein;

if W=A*B, where B is a non-singular K-by-K matrix, then using a complementary beamforming matrix of

2. A method according to claim 1 wherein the step of determining the at least one signal comprises at least one of:

modifying a weight matrix to operatively support said SCBF;

expanding a size of the weight matrix to operatively support said SCBF.

3. A method according to claim 1, further comprising determining the at least one signal using a Downlink Beamforming Matrix:

W=UΛ

V^H.

4. A method according to claim 1, wherein it is assumed that 2K<

N,

W_a=(WA*)=U_aΛ

_aV_a^H, and

5. A method comprising:

providing a smart antenna;

determining at least one signal operatively configured for complementary superposition beamforming (CSBF) in a wireless communication system;

generating the at least one signal such that the signal is operatively configured to cause said smart antenna to perform said CSBF and to transmit at least one complementary beam, and

determining the at least one signal using a downlink beamforming matrix;

{tilde over (W)}=└

w₁ . . . w<sub>k−

1</sub> {tilde over (w)}_k w_k+1 . . . w_k┘

, where {tilde over (w)}_k=p₀w_k+W^cp and p is complex conjugate transpose of the l-th row of W^c,

6. A method comprising:

providing a smart antenna;

determining at least one signal operatively configured for complementary superposition beamforming (CSBF) in a wireless communication system;

generating the at least one signal such that the signal is operatively configured to cause said smart antenna to perform said CSBF and to transmit at least one complementary beam, and

determining the at least one signal using;

{tilde over (W)}=[w₁ w₂ . . . w_k W^cp]

wherein;

p is complex conjugate transpose of the l-th row of W^c,

W^c=√

{square root over (c₀[u_K+1,u_K+2, . . . , u_N])},

c₀ is a scalar, K=the number of users, N=the number of antennas and u_l is the l-th column vector of U.

7. A method according to claim 6 wherein said step of determining the at least one signal comprises using a null-generation technique that is configured to generate L nulls at angles θ

₁, θ

₂, . . . θ

_L at a beam.

8. A method according to claim 6 wherein said step of determining said at least one signal uses:

A=[α

(θ

₁) α

(θ

₂) . . . α

(θ

_L)].

9. A method according to claim 6 wherein said step of determining the at least one signal uses a vector:

w=(l−

P_s)w where P_s=A*(A^TA*)<sup>−

1</sup>A^T, and in scattering channel P_s=H*(H^TA*)<sup>−

1</sup>H^T.

10. A method according to claim 6 wherein said step of determining the at least one signal uses a null-widening technique that is configured to produce at least one null at a vicinity of selected angles.

11. A method according to claim 6 wherein said step of determining the at least one signal comprises selectively modifying a steering matrix to:

A=└

{tilde over (α

)}(θ

₁) {tilde over (α

)}(θ

₂) . . . {tilde over (α

)}(θ

_K)┘

, wherein {tilde over (α

)}(θ

_K)=└

α

(θ

_k−

Δ

θ

₁) α

(θ

_k) α

(θ

_k+Δ

θ

_r)┘

.

12. A method according to claim 6 wherein said step of determining the at least one signal comprises establishing at least two nulls such that a rank of A is less than N.

13. A method according to claim 6 wherein said step of determining the at least one signal uses adaptive control of a complementary beam level.

14. A method according to claim 6 wherein said step of determining the at least one signal, in a non-zero angular channel, comprises selectively reducing a complementary beam level.

15. A method according to claim 6 wherein said step of determining the at least one signal, for delay spread channels, comprises selectively reducing a complementary beam level.

16. A method according to claim 6 wherein said step of determining the at least one signal, in free space, comprises selectively increasing the complementary beam level.