Beamforming methods in closed-loop MIMO
View Patent ↗Methods and apparatus are disclosed for applying successive multi-rank beamforming strategies (e.g., successive precoding strategies) for the design of precoders over a set of parallel channels. Successive beamforming is applied to a narrow band channel model and is also applied for finer quantization of a single beamforming vector (e.g., recursive beamforming). A first embodiment provides the optimal approach with high complexity. An alternative embodiment provides successive beamforming for near optimal precoding selection with medium complexity. A low complexity method for precoder selection is also provided wherein a channel representative matrix for the set of parallel channels is determined and successive beamforming on the calculated channel representative is applied.
1. A method for transmission implemented in a wireless communication system using precoding, comprising:
precoding data using a precoding matrix based on a codebook of precoding matrices generated by picking one or more columns of a matrix with the following structure
A
(
v
1
,
v
2
,
v
3
,
…
)
=
[
v
1
,
HH
(
v
1
-
e
1
M
)
[
0
v
2
]
,
HH
(
v
1
-
e
1
M
)
[
0
HH
(
v
2
-
e
1
M
-
1
)
[
0
v
3
]
]
]
,
…
where e 1 N =[1,0, . . . ,0] T εC N (N=M, M−1, . . . ), C N being N-dimensional complex space, M is the number of transmit antennas, ν a denotes a column vector, HH(ν k −e 1 l ) is a rotation matrix that transforms vector ν k to the unit vector e 1 l and ν a is selected from a set ν a where V 1 ={ν i 1 εC M } i=1 N 1 , V 2 ={e 1 M−1 }, V 3 ={e 1 M−2 }, . . . .
2. The method of claim 1 , wherein
HH
(
w
)
=
{
I
-
2
ww
H
w
2
if
w
≠
0
I
if
w
=
0.
3. The method of claim 1 , wherein a scaled version of the precoding matrix is used.
4. The method of claim 1 , wherein the number of transmit antennas is 4.
5. The method of claim 1 , wherein the number of transmit antennas is 2.
6. The method of claim 1 , wherein the number of selected columns to from the precoding matrix is less than the number of transmit antennas.
7. The method of claim 1 , wherein all the columns are selected to form the precoding matrix.