Method of using a quantized beamforming matrix from multiple codebook entries for multiple-antenna systems
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 wireless communication system of performing multi-rank, quantized beamforming, comprising the step of:
precoding data using a quantized beamforming matrix that is selected 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
]
]
]
,
…
wherein a beamforming transmitter has M antennas and e 1 N =[1,0, . . . , 0] T εC N , 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
,
and
HH
(
w
)
=
{
I
-
2
ww
H
w
2
if
w
≠
0
I
if
w
=
0
is the house-holder transformation of the vector w.
2. 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 .
3. The method of claim 1 , wherein the multi-rank beamforming matrix is formed by picking columns of the matrix V.
4. The method of claim 3 , wherein the number of selected columns to form a precoder is less than the number of transmit antennas.
5. The method of claim 3 , wherein all the columns are selected to form a precoder.
6. The method of claim 1 , wherein the multi-rank beamforming matrix enables a transmission rank determined by a transmitter.
7. The method of claim 1 , wherein the multi-rank beamforming matrix enables a transmission rank determined by a receiver.
8. The method of claim 1 , wherein a scaled version of the precoder is used.
9. The method of claim 1 , wherein the number of transmit antennas is 4.
10. The method of claim 1 , wherein the number of transmit antennas is 2.