Quantized feedback strategies and signal generation
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 of transmission implemented in a mobile terminal, comprising:
generating precoding information in order for a remote transmitter to select a precoding matrix based on a codebook which has 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 the remote transmitter has M antennas, e 1 N =[1,0, . . . ,0] T εC N , C N being N-dimensional complex space, v a denotes a column vector, and HH(v k −e 1 l ) is a rotation matrix that transforms vector v k to the unit vector e 1 l ;
and providing the precoding information to the remote transmitter.
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 codebook entries are generated by selecting each vector v a from V a such that
V 1 ={v i 1 εC M } i=1 N 1 , V 2 ={v i 2 εC M−1 } i=1 N 2 , . . . , V M−1 ={v i M−1 εC 2 } i=1 N M−1 .
4. The method of claim 1 , wherein the precoding matrix is formed by picking one or more columns from the matrix A(v 1 , v 2 , v 3 , . . . ).
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 the precoding information includes at least one of a rank, a channel quality index (CQI), and a precoding matrix index.