Feedback generation in recursive multi-rank beamforming
View Patent ↗A quantized multi-rank beamforming scheme for multiple-antenna systems such as a multiple-input-multiple-output (MIMO) wireless downlink. User equipment (UE) estimates downlink channel and transmit power and determines rank and power allocations. A quantized beamforming matrix is then determined by the UE using successive beamforming. The UE also determines channel quality indices (CQI) which it feeds-back to the wireless downlink base station along with the index of the quantized beamforming matrix. The base station uses the CQI information to select a UE for scheduling of downlink transmission and the quantized beamforming matrix index received from the selected UE to beamform the downlink transmission to the UE. Base station overhead and is minimized while providing near-optimal performance given the constraints of a limited feed-back channel and computational complexity of the UE.
1. A method implemented in a mobile terminal, comprising:
generating feedback information for transmission in order for a remote transmitter to select a precoding matrix from a codebook comprising codebook entries V in the form
V
=
[
v
1
,
Φ
(
v
1
1
)
HH
(
v
1
Φ
(
v
1
1
)
-
e
1
M
)
[
0
v
2
]
,
Φ
(
v
1
1
)
HH
(
v
1
Φ
(
v
1
1
)
-
e
1
M
)
[
0
Φ
(
v
1
2
)
HH
(
v
2
Φ
(
v
1
2
)
-
e
1
M
-
1
)
[
0
v
3
]
]
]
,
…
where the remote transmitter has M=4 antennas, e 1 N =[1, 0, . . . , 0] T εC N (N=M, M−1, . . . ), C N being N-dimensional complex space, v a denotes a column vector, v b a denotes the b th element of the vector v a ,
Φ
(
v
b
a
)
=
v
b
a
v
b
a
,
HH
(
w
)
=
{
I
-
2
ww
H
w
2
if
w
≠
0
I
if
w
=
0
is the house-holder transformation of the vector w 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 }, where f=(1−j)/√{square root over (2)}, g=(1+j)/√{square root over (2)}, and j=√{square root over (−1)}, V 2 ={e 1 3 }, V 3 ={e 1 2 }, and V 4 ={e 1 1 };
and providing the feedback information to the remote transmitter.
2. The method of claim 1 , wherein precoding with the precoding matrix is performed over a chunk of OFDM tones.
3. The method of claim 1 , wherein the precoding matrix is formed by picking one or more columns of the matrix V.
4. The method of claim 3 , wherein the number of selected columns to form the precoding matrix is less than the number of transmit antennas.
5. The method of claim 3 , wherein all the columns are selected to form the precoding matrix.
6. The method of claim 1 , wherein a transmission rank is determined by the mobile terminal.
7. The method of claim 1 , wherein a transmission rank is determined by the remote transmitter.
8. The method of claim 1 , wherein the precoding matrix is generated based on a vector codebook.
9. The method of claim 1 , wherein a scaled version of the precoding matrix is used.
10. The method of claim 1 , wherein the feedback information includes at least one of a rank, a precoding matrix index, quantization power control, and a Signal to Interference and Noise Ratio (SINR).