Complementary beamforming methods and apparatuses

• US 7,099,698 B2
• Filed: 11/03/2003
• Issued: 08/29/2006
• Est. Priority Date: 11/04/2002
• Status: Active Grant

• Current Assignee: XR Communications, LLC
• Original Assignee: Vivato, Inc. (Vivato Networks, LLC)
• Inventors: Tarokh, Vahid, Choi, Yang-seok, Alamouti, Siavash
• Primary Examiner(s): Trinh, Sonny
• Assistant Examiner(s): LAM, DUNG LE
• Application Number:
  US10/700,991
• Publication Number:
  US 20040235529A1
• Time in Patent Office: 1,030 Days
• Field of Search: 455/562.1, 455/63.4, 455/575.7, 455/25
• 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 for use in a wireless communication system, the method comprising:

outputting at least one signal suitable for causing a smart antenna to transmit at least one complementary beam, said at least one signal being operatively configured to cause said smart antenna to perform single beam complementary beamforming (SBCBF);

causing said smart antenna to transmit said at least one complementary beam based on said at least one signal; and

configuring said at least one signal to cause said smart antenna to perform said SBCBF by transmitting energy at a detectable transmit power level in all smart antenna-supported directions while substantially preserving a shape of at least one main transmit beam having a transmit power level that is significantly greater than said detectable transmit power level, said SBCBF being operatively performed by said smart antenna that is operatively associated with a base station within a wireless communication system, said base station including a Butler matrix network configured to form said at least one main beam using said smart antenna, and further configured to provide at least one of post-combining SBCBF or pre-combining SBCBF.

2. The method as recited in claim 1, wherein outputting said at least one signal suitable for causing said smart antenna to transmit at least one complementary beam further includes:

using a zero-forcing beamformer to output said at least one signal.

3. The method as recited in claim 1, wherein outputting said at least one signal suitable for causing said smart antenna to transmit at least one complementary beam further includes:

using a maximum SINR beamformer to output said at least one signal.

4. The method as recited in claim 1, wherein outputting said at least one signal suitable for causing said smart antenna to transmit at least one complementary beam further includes:

outputting said signal based on at least a complementary beamforming matrix at time t given by;

$S^t=\left[{\left(A^H<br><br>A\right)}^{-1}<br><br>A^H/\sqrt{\mathrm{Tr}<br><br>\left({\left(A^H<br><br>A\right)}^{-1}\right)}+\frac{1}{\sqrt{k}}<br><br>\mathrm{\varepsilon <br><br>}<br><br><br><br>Z_t\right].$

5. The method as recited in claim 1, wherein outputting said at least one signal suitable for causing said smart antenna to transmit at least one complementary beam further includes:

outputting said signal based on at least matrices P₀, P₁, . . . , P<sub>m−

k</sub> having rows, respectively, U₀^H, U₁^H, . . . , U_m-k^H and wherein a fixed beamforming matrix is given by;

$S=\left[{\left(A^H<br><br>A\right)}^{-1}<br><br>A^H/\sqrt{\mathrm{Tr}<br><br>\left({\left(A^H<br><br>A\right)}^{-1}\right)}+\frac{1}{\sqrt{k}}<br><br>\mathrm{\varepsilon <br><br>}<br><br>\underset{i=1}{\overset{m-k}{\sum <br><br>}}<br><br><br><br>P_i\right].$

6. A method for use in a wireless communication system, the method comprising:

outputting at least one signal suitable for causing a smart antenna to transmit at least one complementary beam, said at least one signal being operatively configured to cause said smart antenna to perform subspace complementary beamforming (SCBF), and said at least one signal including N-K data streams operatively configured to cause said smart antenna to transmit energy in at least one side lobe;

determining said at least one signal by using a Downlink Beamforming Matrix;

W=UΛ

V^H;

 

determining said at least one signal by using a Steering Matrix;

A=[a(θ

₁) a(θ

₂) . . . a(θ

_K)], wherein a(θ

_k) represents a steering vector of user k;

and wherein;

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

$W^c=\sqrt{\frac{k_0<br><br>C_0}{N}}<br><br>\left[u_{K+1}<br><br><br><br>u_{K+2}<br><br><br><br>\mathrm{\cdots <br><br>}<br><br><br><br>u_N\right]$

 

wherein C₀=Nc₀ is the level of the main lobe, k₀ is the scaling factor and u₁ is the l-th column vector of U, otherwise using a complementary beamforming matrix of

$W^c=\sqrt{\frac{k_0<br><br>C_0}{N}}<br><br>\left[{\stackrel{\_}{u}}_{1<br><br>}<br><br>{\stackrel{\_}{u}}_2<br><br><br><br>\mathrm{\cdots <br><br>}<br><br><br><br>{\stackrel{\_}{u}}_{N-K}\right]$

 

wherein ū

₁ is the l-th left singular vector of the matrix

$\left(\underset{l=K+1}{\overset{N}{\sum <br><br>}}<br><br><br><br>{\tilde{u}}_l<br><br>{\tilde{u}}_l^H\right)<br><br>U<br><br><br><br>{\mathrm{\Lambda <br><br>}}^c=\stackrel{\_}{U}<br><br><br><br>\stackrel{\_}{\mathrm{\Lambda <br><br>}}<br><br><br><br>{\stackrel{\_}{V}}^H,$

 

and A*=Ũ

{tilde over (Λ

)}{tilde over (V)}^H is assumed, and in scattering channel H*=Ũ

{tilde over (Λ

)}{tilde over (V)}^H is assumed.

7. The method as recited in claim 6, further comprising:

determining said at least one signal by selectively modifying a weight matrix to operatively support said SCBF.

8. The method as recited in claim 6, further comprising:

determining said at least one signal by selectively expanding a size of a weight matrix to operatively support said SCBF.

9. The method as recited in claim 6, wherein it is assumed that 2K<

N,

$W_a=\lfloor <br><br>W<br><br><br><br>A^{*}\rfloor <br><br>=U_a<br><br>{\mathrm{\Lambda <br><br>}}_a<br><br>V_a^H,\mathrm{and}<br><br><br><br>W^c=\sqrt{\frac{k_0<br><br>C_0}{N}}<br><br>\left[u_{a,r+1}<br><br><br><br>u_{a,r+2}<br><br><br><br>\mathrm{\dots <br><br>}<br><br><br><br>u_{a,N}\right],$

and wherein r is rank of W_a.

10. A method for use in a wireless communication system, the method comprising:

outputting at least one signal suitable for causing a smart antenna to transmit at least one complementary beam, said at least one signal being operatively configured to cause said smart antenna to perform complementary superposition beamforming (CSBF); and

determining said at least one signal by 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,

$p_0=\frac{w_{k,l}^{*}}{<br><br>w_{k,l}<br><br>}$

 

is normalized complex conjugate of the l-th element of w_k.

11. The method as recited in claim 10, wherein W^c is associated with subspace complementary beamforming (SCBF).

12. The method as recited in claim 10, further comprising:

determining said at least one signal by using {tilde over (W)}=[w₁ w₂ . . . w_K W^cp].

13. The method as recited in claim 10, further comprising:

determining said at least one signal by using a null-generation technique that is configured to generate L nulls at angles θ

₁, θ

₂, . . . , θ

_L at a beam.

14. The method as recited in claim 10, further comprising:

determining said at least one signal by using A=[a(θ

₁) a(θ

₂) . . . a(θ

_L)].

15. The method as recited in claim 10, further comprising:

determining said at least one signal by projecting w onto orthogonal complement subspace of column space A*.

16. The method as recited in claim 10, further comprising:

determining said at least one signal by using a vector;

w=(I−

P_S)w where P_S=A*(A^TA*)<sup>−

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

1</sup>H^T.

17. The method as recited in claim 10, further comprising:

determining said at least one signal by using a null-widening technique that is configured to produce at least one null at a vicinity of selected angles.

18. The method as recited in claim 10, further comprising:

determining said at least one signal by selectively modifying a steering matrix to;

A=[ã

(θ

₁) {tilde over (a)}(θ

₂) . . . {tilde over (a)}(θ

_K)]

 

wherein ã

(θ

_k)=[a(θ

_k−

Δ

θ

₁) a(θ

_k) a(θ

_k+Δ

θ

_r)].

19. The method as recited in claim 10, further comprising:

determining said at least one signal by establishing at least two nulls such that a rank of A is less than N.

20. The method as recited in claim 10, further comprising:

determining said at least one signal by using adaptive control of a complementary beam level.

21. The method as recited in claim 10, further comprising:

determining said at least one signal by, in a non-zero angular channel, selectively reducing a complementary beam level.

22. The method as recited in claim 10, further comprising:

determining said at least one signal by, for delay spread channels, selectively reducing a complementary beam level.

23. The method as recited in claim 10, further comprising:

determining said at least one signal by, in free space, selectively increasing the complementary beam level.

24. A method for use in a wireless communication system, the method comprising:

outputting at least one signal suitable for causing a smart antenna to transmit at least one complementary beam, wherein said outputting includes selectively constructing a plurality of matrices Z₁, Z₁, . . . , Z_L, where L is a length of a downlink transmission period, such that said plurality of matrices satisfy at least one property selected from a group of properties comprising;

(a) for all 1≦

i≦

L, a matrix Z_i is a k×

m matrix whose rows are in a set {0, ±

U₀^H, ±

U₁^H, . . . , ±

U<sub>m−

k−

1</sub>^H};

(b) if L is even, then, Z₂=−

Z₁, Z₄=−

Z₃, . . . , Z_L=−

Z<sub>L−

1</sub>;

(c) if L is odd, then Z₂=−

Z₁, Z₄=−

Z₃, . . . , Z<sub>L−

1</sub>=−

Z<sub>L−

2</sub>, Z_L=0; and

(d) each element +U₀^H, −

U₀^H, +U₁^H, −

U₁^H, . . . , +U<sub>m−

k−

1</sub>^H, −

U<sub>m−

k−

1</sub>^H appear p times in a list of Lk rows of Z₁, Z₁, . . . , Z_L for some positive integer p.

25. The method as recited in claim 24, wherein rows of Z_2i−

1 are, respectively, U<sub>0⊕

i</sub>^H, U<sub>1⊕

i</sub>^H, . . . , U<sub>k−

1⊕

i</sub>^H and where i⊕

j denote (i+j)mod(m−

k) for i=1, 2, 3, . . . , [L/2] and wherein Z_2i=−

Z<sub>2i−

1</sub>.

26. The method as recited in claim 24, further comprising:

using as a beamforming matrix;

$S^t=\left[{\left(A^H<br><br>A\right)}^{-1}<br><br>A^H/\sqrt{\mathrm{Tr}<br><br>\left({\left(A^H<br><br>A\right)}^{-1}\right)}+\frac{1}{\sqrt{k}}<br><br>\mathrm{\varepsilon <br><br>}<br><br><br><br>Z_i\right]$

 

where ε

≧

0 is a fixed positive number.

27. The method as recited in claim 26, wherein said complementary beam is configured to cause a loss of at most 10 log₁₀(1+|ε

|²) in a received signal for an intended recipient.

28. The method as recited in claim 26, wherein said complementary beam is configured to direct a portion:

${<br><br>\mathrm{\varepsilon <br><br>}<br><br>}^2<br><br>\frac{\underset{j=1}{\overset{m}{\sum <br><br>}}<br><br><br><br>{<br><br>b_j<br><br>}^2}{m}$

of a resulting transmitted power to another recipient whose spatial signature is B=(b₁, b₂, . . . , b_m).

29. An apparatus for use in a wireless communication system, the apparatus comprising:

a smart antenna operatively coupled to receive at least one signal and configured to transmit at least one complementary beam based on said at least one signal; and

circuitry configured to output said at least one signal suitable for causing the smart antenna to transmit said at least one complementary beam, said at least one signal being operatively configured to cause said smart antenna to perform single beam complementary beamforming (SBCBF), said at least one signal being configured by said circuitry to cause said smart antenna to perform said SBCBF by transmitting energy at a detectable transmit power level in all smart antenna-supported directions while substantially preserving a shape of at least one main transmit beam having a transmit power level that is significantly greater than said detectable transmit power level, said smart antenna being operatively associated with a base station within the wireless communication system, said base station including at least a portion of said circuitry which includes a Butler matrix network configured to form said at least one main beam using said smart antenna, and said Butler matrix network being configured to provide at least one of post-combining SBCBF or pre-combining SBCBF.

30. The apparatus as recited in claim 29, wherein said circuitry employs a zero-forcing beamformer to output said at least one signal.

31. The apparatus as recited in claim 29, wherein said circuitry employs a maximum SINR beamformer to output said at least one signal.

32. The apparatus as recited in claim 29, wherein said circuitry is configured to output said signal based on at least a complementary beamforming matrix at time t given by:

$S^t=\left[{\left(A^H<br><br>A\right)}^{-1}<br><br>A^H/\sqrt{\mathrm{Tr}<br><br>\left({\left(A^H<br><br>A\right)}^{-1}\right)}+\frac{1}{\sqrt{k}}<br><br>\mathrm{\varepsilon <br><br>}<br><br><br><br>Z_t\right].$

33. The apparatus as recited in claim 29, wherein said circuitry is configured to output said signal based on at least matrices P₀, P₁, . . . , P_m−

k having rows, respectively, U₀^H, U₁^H, . . . , U<sub>m−

k</sub>^H and wherein a fixed beamforming matrix that is used is given by;

$S=\left[{\left(A^H<br><br>A\right)}^{-1}<br><br>A^H/\sqrt{\mathrm{Tr}<br><br>\left({\left(A^H<br><br>A\right)}^{-1}\right)}+\frac{1}{\sqrt{k}}<br><br>\mathrm{\varepsilon <br><br>}<br><br><br><br>\stackrel{m-k}{\underset{i=1}{\sum <br><br>}}<br><br>P_i\right].$

34. An apparatus for use in a wireless communication system, the apparatus comprising:

circuitry configured to output at least one signal suitable for causing a smart antenna to transmit at least one complementary beam, said at least one signal being operatively configured to cause said smart antenna to perform subspace complementary beamforming (SCBF), and said at least one signal including N−

K data streams operatively configured to cause said smart antenna to transmit energy in at least one side lobe;

wherein;

said circuitry is configured to determine said at least one signal by using a Downlink Beamforming Matrix;

W=UΛ

V^H;

said circuitry is configured to determine said at least one signal by using a Steering Matrix;

A=[a(θ

₁) a(θ

₂) . . . a(θ

_K)], wherein a(θ

_k) represents a steering vector of user k; and

wherein;

if W=A*B, where B is a non-singular K-by-K matrix, then said circuitry is configured to use a complementary beamforming matrix of

$W^c=\sqrt{\frac{k_0<br><br>C_0}{N}}<br><br>\left[u_{K+1}<br><br><br><br>u_{K+2}<br><br><br><br>\mathrm{\dots <br><br>}<br><br><br><br>u_N\right]$

 

wherein C₀=Nc₀ is the level of the main lobe, k₀ is the scaling factor and u_l is the l-th column vector of U,

otherwise said circuitry is configured to use a complementary beamforming matrix of

$W^c=\sqrt{\frac{k_0<br><br>C_0}{N}}<br><br>\left[{\stackrel{\_}{u}}_1<br><br><br><br>{\stackrel{\_}{u}}_2<br><br><br><br>\mathrm{\dots <br><br>}<br><br><br><br>{\stackrel{\_}{u}}_{N-K}\right]$

 

wherein ū

_l is the l-th left singular vector of the matrix

$\left(\underset{l=K+1}{\overset{N}{\sum <br><br>}}<br><br><br><br>{\tilde{u}}_l<br><br>{\tilde{u}}_l^H\right)<br><br>U<br><br><br><br>{\mathrm{\Lambda <br><br>}}^c=\stackrel{\_}{U}<br><br><br><br>\stackrel{\_}{\mathrm{\Lambda <br><br>}}<br><br><br><br>{\stackrel{\_}{V}}^H,$

 

and A*=Ũ

{tilde over (Λ

)}{tilde over (V)}^H is assumed, and in scattering channel H*=Ũ

{tilde over (Λ

)}{tilde over (V)}^H is assumed.

35. The apparatus as recited in claim 34, wherein said circuitry is configured to determine said at least one signal by selectively modifying a weight matrix to operatively support said SCBF.

36. The apparatus as recited in claim 34, wherein said circuitry is configured to determine said at least one signal by selectively expanding a size of a weight matrix to operatively support said SCBF.

37. The apparatus as recited in claim 36, wherein said circuitry is configured such that 2K<

N,

$W_a=\lfloor <br><br>\begin{array}{cc}W<br><br>& A^{*}\end{array}\rfloor <br><br>=U_a<br><br>{\mathrm{\Lambda <br><br>}}_a<br><br>V_a^H,\mathrm{and}<br><br>$ $W^c=\sqrt{\frac{k_0<br><br>C_0}{N}}<br><br>\left[\begin{array}{cccc}{u}_{a,r+1}& u_{a,r+2}& \mathrm{\cdots <br><br>}& u_{a,N}\end{array}\right],$

and wherein r is rank of W_a.

38. An apparatus for use in a wireless communication system, the apparatus comprising:

circuitry configured to output at least one signal suitable for causing a smart antenna to transmit at least one complementary beam, said circuitry being configured such that said at least one signal causes said smart antenna to perform complementary superposition beamforming (CSBF); and

wherein

said circuitry is configured to determine said at least one signal by 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,

$p_0=\frac{w_{k,l}^{*}}{<br><br>w_{k,l}<br><br>}$

 

is normalized complex conjugate of the l-th element of w_k.

39. The apparatus as recited in claim 38, wherein W^c is associated with subspace complementary beamforming (SCBF).

40. The apparatus as recited in claim 38, wherein said circuitry is configured to determine said at least one signal by using {tilde over (W)}=[w₁ w₂ . . . w_K W^cp].

41. The apparatus as recited in claim 38, wherein said circuitry is configured to determine said at least one signal by using a null-generation technique that is configured to generate L nulls at angles θ

₁,θ

₂, . . . , θ

_L at a beam.

42. The apparatus as recited in claim 38, wherein said circuitry is configured to determine said at least one signal by using A=[a(θ

₁) a(θ

₂) . . . a(θ

_L)].

43. The apparatus as recited in claim 38, wherein said circuitry is configured to determine said at least one signal by projecting w onto orthogonal complement subspace of column space A*.

44. The apparatus as recited in claim 38, wherein said circuitry is configured to determine said at least one signal by using a vector:

w=(I−

P_S)w where P_S=A*(A^TA*)<sup>−

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

1</sup>H^T.

45. The apparatus as recited in claim 38, wherein said circuitry is configured to determine said at least one signal by using a null-widening technique that is configured to produce at least one null at a vicinity of selected angles.

46. The apparatus as recited in claim 38, wherein said circuitry is configured to determine said at least one signal by selectively modifying a steering matrix to:

A=[{tilde over (a)}(θ

₁) {tilde over (a)}(θ

₂) . . . {tilde over (a)}(θ

_K)]

wherein ã

(θ

_k)=[a(θ

_k−

Δ

θ

₁) a(θ

_k) a(θ

_k+Δ

θ

_r)].

47. The apparatus as recited in claim 38, wherein said circuitry is configured to determine said at least one signal by establishing at least two nulls such that a rank of A is less than N.

48. The apparatus as recited in claim 38, wherein said circuitry is configured to determine said at least one signal by using adaptive control of a complementary beam level.

49. The apparatus as recited in claim 38, wherein said circuitry is configured to determine said at least one signal by, in a non-zero angular channel, selectively reducing a complementary beam level.

50. The apparatus as recited in claim 38, wherein said circuitry is configured to determine said at least one signal by, for delay spread channels, selectively reducing a complementary beam level.

51. The apparatus as recited in claim 38, wherein said circuitry is configured to determine said at least one signal by, in free space, selectively increasing the complementary beam level.

52. An apparatus for use in a wireless communication system, the apparatus comprising:

circuitry configured to output at least one signal suitable for causing a smart antenna to transmit at least one complementary beam, said circuitry being configured to construct a plurality of matrices Z₁, Z₁, . . . , Z_L, where L is a length of a downlink transmission period, such that said plurality of matrices satisfy at least one property selected from a group of properties comprising;

(a) for all 1≦

i≦

L, a matrix Z_i is a k×

m matrix whose rows are in a set {0, ±

U₀^H, ±

U₁^H, . . . , ±

U<sub>m−

k−

1</sub>^H};

(b) if L is even, then, Z₂=−

Z₁, Z₄=−

Z₃, . . . , Z_L=−

Z<sub>L−

1</sub>;

(c) if L is odd, then Z₂=−

Z₁, Z₄=−

Z₃, . . . , Z<sub>L−

1</sub>=−

Z<sub>L−

2</sub>, Z_L=0; and

(d) each element +U₀^H, −

U₀^H, +U₁^H, −

U₁^H, . . . , +U<sub>m−

k−

1</sub>^H, −

U<sub>m−

k−

1</sub>^H appear p times in a list of Lk rows of Z₁, Z₁, . . . , Z_L for some positive integer p.

53. The apparatus as recited in claim 52, wherein rows of Z_2i−

1 are, respectively, U<sub>0⊕

i</sub>^H, U<sub>1⊕

i</sub>^H, . . . , U<sub>k−

1⊕

i</sub>^H and where i⊕

j denote (i+j)mod(m−

k) for i=1, 2, 3, . . . , [L /2] and wherein Z_2i=−

Z<sub>2i−

1</sub>.

54. The apparatus as recited in claim 52, wherein said circuitry is configured to construct a beamforming matrix:

$S^t=\left[{\left(A^H<br><br>A\right)}^{-1}<br><br>A^H/\sqrt{\mathrm{Tr}<br><br>\left({\left(A^H<br><br>A\right)}^{-1}\right)}+\frac{1}{\sqrt{k}}<br><br>\mathrm{\varepsilon <br><br>}<br><br><br><br>Z_i\right]$

where ε

≧

0 is a fixed positive number.

55. The apparatus as recited in claim 54, wherein said complementary beam is configured to cause a loss of at most 10 log₁₀(1+|ε

|²) in a received signal for an intended recipient.

56. The apparatus as recited in claim 54, wherein said complementary beam is configured to direct a portion:

${<br><br>\mathrm{\varepsilon <br><br>}<br><br>}^2<br><br>\frac{\underset{j=1}{\stackrel{m}{\sum <br><br>}}<br><br>{<br><br>b_j<br><br>}^2}{m}$

of a resulting transmitted power to another recipient whose spatial signature is B=(b₁, b₂, . . . , b_m).