Beamforming in MIMO 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 base station of performing multi-rank, quantized beamforming, comprising:
precoding data using a precoding 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
]
]
]
,
…
where the base station has M 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 ={v i 1 εC M } i=1 N1 , V 2 ={e 1 M-1 }, V 3 ={e 1 M-2 }, . . . ; and
transmitting the precoded data to a mobile terminal,
wherein the precoding matrix is formed by picking one or more columns of the matrix V.
2. The method of claim 1 , wherein the precoding is performed over a chunk of OFDM tones.
3. The method of claim 1 , wherein the precoding matrix enables a transmission rank determined by the mobile terminal.
4. The method of claim 1 , wherein the precoding matrix enables a transmission rank determined by the base station.
5. The method of claim 1 , wherein the precoding matrix is generated based on a vector codebook.
6. The method of claim 1 , wherein a scaled version of the precoding matrix is used.
7. The method of claim 1 , wherein the number of transmit is 4.
8. The method of claim 1 , wherein the number of transmit antennas is 2.
9. The method of claim 1 , wherein the number of selected columns to form the precoding matrix is less than the number of transmit antennas.
10. The method of claim 1 , wherein all the columns are selected to form the precoding matrix.