Codebook performance for non-linear arrays
View Patent ↗A method to improve codebook performance for non-linear arrays is described. The method includes determining a unitary matrix for a plurality of transmission antennas arranged in a given array type, the unitary matrix being determined based on a codebook, where the given array type is configured to steer beams in at least one of elevation and azimuth. The method also includes applying the determined unitary matrix to a signal to be transmitted across the plurality of transmission antennas. Apparatus and computer readable media are also described.
1. A method comprising:
determining, by a communication device, a unitary matrix for a plurality of transmission antennas arranged in a given array type, the unitary matrix being determined based on a plurality of entries of a codebook of the communication device and the given array type, where the given array type is configured to steer beams in at least one of elevation and azimuth;
applying, by the communication device, the determined unitary matrix to a signal precoded with a precoding vector from the codebook; and
transmitting, by the communication device, the signal across the plurality of transmission antennas.
2. The method of claim 1 , where the unitary matrix is also applied to a common reference symbol for the signal.
3. The method of claim 1 , wherein the unitary matrix is determined such that the power on transmit branches is approximately equal for codebook transmissions.
4. The method of claim 1 , wherein determining the unitary matrix comprises obtaining a pre-computed unitary matrix from a table look up.
5. The method of claim 1 , wherein the codebook is one of a rank 1 codebook and a multi-rank codebook.
6. The method of claim 1 , wherein the codebook is a uniform linear array codebook.
7. The method of claim 1 , wherein the given array type is a uniform circular array.
8. The method of claim 1 , where determining the unitary matrix comprises performing a gradient search.
9. The method of claim 1 , where the determined unitary matrix is a sparse matrix where each row only has one non-zero entry.
10. The method of claim 1 , where the determined unitary matrix maximizes one of: mean gain and minimum gain.
11. The method of claim 1 , where the determined unitary matrix, T, maximizes
∑
θ
∈
Ω
max
m
f
m
T
Ta
(
θ
)
2
,
where Ω is a set of angles of interest,
a(θ) is an array of manifold vectors, and
f is a vector from the codebook.
12. The method of claim 1 , where the determined unitary matrix, T, minimizes
∑
u
=
1
N
u
min
m
f
m
T
Te
u
2
,
where N u is the number of total users,
e u is a dominate eigenvector,
f is a vector from the codebook such that x(t)=f t s(t) where s(t) is the transmitted symbol at time t, and
x(t) is an original M×1 transmit signal on all antennas at time t.
13. The method of claim 1 , where the determined unitary matrix, T, minimizes
∑
θ
∈
Ω
Ta
UCA
(
θ
,
90
)
-
a
ULA
(
θ
)
2
,
where Ω is a set of angles of interest,
a UCA (θ) is an array of manifold vectors for a unitary circular array, and
a ULA (θ) is an array of manifold vectors for a unitary linear array.
14. An apparatus, comprising at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to perform at least the following:
to determine a unitary matrix for a plurality of transmission antennas arranged in a given array type, the unitary matrix being determined based on a plurality of entries of a codebook of the apparatus and the given array type, where the given array type is configured to steer beams in at least one of elevation and azimuth;
to apply the determined unitary matrix to a signal precoded with a precoding vector from the codebook; and
to transmit the signal across the plurality of transmission antennas.
15. The apparatus of claim 14 , wherein the unitary matrix is determined such that the power on transmit branches is approximately equal for codebook transmissions.
16. The apparatus of claim 14 , where, when determining the unitary matrix, the at least one memory and the computer program code are further configured to cause the apparatus to obtain a pre-computed unitary matrix from a table look up.
17. A non-transitory computer readable medium tangibly encoded with a computer program executable by a processor to perform actions comprising:
determining a unitary matrix for a plurality of transmission antennas arranged in a given array type, the unitary matrix being determined based on a plurality of entries of a codebook and the given array type, where the given array type is configured to steer beams in at least one of elevation and azimuth;
applying the determined unitary matrix to a signal precoded with a precoding vector from the codebook; and
transmitting the signal across the plurality of transmission antennas.
18. The computer readable medium of claim 17 , wherein the unitary matrix is determined such that the power on transmit branches is approximately equal for codebook transmissions.
19. An apparatus, comprising:
means for determining a unitary matrix for a plurality of transmission antennas arranged in a given array type, the unitary matrix being determined based on a plurality of entries of a codebook of the apparatus and the given array type, where the given array type is configured to steer beams in at least one of elevation and azimuth;
means for applying the determined unitary matrix to a signal precoded with a precoding vector from the codebook; and
means for transmitting the signal across the plurality of transmission antennas.
20. The apparatus of claim 19 , wherein the unitary matrix is determined such that the power on transmit branches is approximately equal for codebook transmissions.