Restricted codebooks and related signaling to perform beamforming
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 implemented in a mobile terminal used in a wireless communications system and configured to receive precoded data from a remote transmitter, comprising:
generating feedback information for transmission in order for the remote transmitter to select a precoding matrix from a codebook for M=4 transmit antennas having entries in the following form
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 , C N being N-dimensional complex space, v a denotes a column vector, HH(v k −e 1 l ) is a rotation matrix that transforms vector v k to the unit vector e 1 l and v a is selected from a set V a where V 1 =½{[1, 1, 1, 1] T , [1, −j, −1, j] T , [1, −1, 1, −1] T , [1, j, −1, −j] T , [1, f, −j, −g] T , [1, −g, j, f] T , [1, −f, −j, g] T , [1, g, j, −f] T , [1, 1, −1, −1] T , [1, −j, 1, −j] T , [1, −1, −1, 1] T , [1, j, 1, j] T , [1, 1, 1, −1] T , [1, 1, −1, 1] T , [1, −1, 1, 1] T , [1, −1, −1, −1] T }, f=(1−j)/√{square root over (2)}, g=(1+j)/√{square root over (2)}, j=√{square root over (−1)}, V 2 ={e 1 3 }, V 3 ={e 1 2 }, and V 4 ={e 1 1 }.
2. The method of claim 1 , wherein
HH
(
w
)
=
{
I
-
2
ww
H
w
2
if
w
≠
0
I
if
w
=
0
and is the house-holder transformation.
3. The method of claim 1 , wherein the precoding matrix is formed by picking columns from the matrix A(v 1 , v 2 , v 3 . . . ).
4. The method of claim 1 , wherein the precoding matrix is generated based on a vector codebook.
5. The method of claim 1 , wherein a transmission rank is determined by the remote transmitter.
6. The method of claim 1 , wherein a transmission rank is determined by the mobile terminal.
7. The method of claim 1 , wherein a scaled version of the precoding matrix is used.
8. The method of claim 3 , wherein the number of selected columns to form the precoding matrix is less than the number of transmit antennas.
9. The method of claim 3 , wherein all the columns are selected to form the precoding matrix.
10. The method of claim 1 , wherein the feedback information includes at least one of a rank, a channel quality index (CQI), and a precoding matrix index.