Structured codebook and successive beamforming 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 of performing multi-rank, quantized beamforming comprising:
estimating a channel between a beamforming transmitter and a receiver at the receiver;
determining a beamforming rank based on the channel estimate;
determining a power allocation for each of a plurality of signal streams;
determining a quantized beamforming matrix;
providing an indication of the power allocation and quantized beamforming matrix to the beamforming transmitter; and
transmitting the plurality of signal streams from the beamforming transmitter to the receiver in accordance with the power allocation and quantized beamforming matrix,
wherein the beamforming transmitter has M antennas and the quantized beamforming matrix 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
)
[
Φ
(
v
1
2
)
HH
(
v
2
0
Φ
(
v
1
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,
v b a denotes the b th element of the vector v a ,
Φ
(
v
b
a
)
=
v
b
a
v
b
a
,
and
H
(
w
)
=
I
-
2
ww
T
w
2
.
2. The method of claim 1 , wherein the power allocation and quantized beamforming matrix are included in an augmented matrix having an index, the indication provided to the beamforming transmitter including said index.
3. The method of claim 1 , wherein the indication provided to the beamforming transmitter is provided over a limited bandwidth feedback channel from the receiver to the beamforming transmitter.
4. The method of claim 1 , including providing channel quality information from the receiver to the transmitter.
5. The method of claim 1 , wherein determining a beamforming rank includes determining a modified capacity measure of the channel.
6. The method of claim 1 , wherein the quantized beamforming matrix is determined using successive beamforming.
7. The method of claim 4 , comprising selecting which of a plurality of receivers to transmit to based on the channel quality information.
8. The method of claim 4 , comprising determining the channel quality information in accordance with a receiver type.
9. 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 .
10. A method of performing multi-rank, quantized beamforming comprising:
estimating a channel between a beamforming transmitter and a receiver at the receiver;
determining a beamforming rank based on the channel estimate;
determining a power allocation for each of a plurality of signal streams;
determining a quantized beamforming matrix;
providing an indication of the power allocation and quantized beamforming matrix to the beamforming transmitter; and
transmitting the plurality of signal streams from the beamforming transmitter to the receiver in accordance with the power allocation and quantized beamforming matrix,
wherein the quantized beamforming matrix is selected from a codebook that is optimized by using a p-metric defined as a distance between n-dimensional subspaces U and V as follows:
d
p
=
Arc
cos
(
det
(
I
+
pU
*
VV
*
U
(
1
+
p
)
n
)
1
2
)
,
where the value of p is selected in accordance with a desired signal-to-noise ratio.
11. The method of claim 10 , wherein the power allocation and quantized beamforming matrix are included in an augmented matrix having an index, the indication provided to the beamforming transmitter including said index.
12. The method of claim 10 , wherein the indication provided to the beamforming transmitter is provided over a limited bandwidth feedback channel from the receiver to the beamforming transmitter.
13. The method of claim 10 , including providing channel quality information from the receiver to the transmitter.
14. The method of claim 10 , wherein determining a beamforming rank includes determining a modified capacity measure of the channel.
15. The method of claim 10 , wherein the quantized beamforming matrix is determined using successive beamforming.
16. The method of claim 13 , comprising selecting which of a plurality of receivers to transmit to based on the channel quality information.
17. The method of claim 13 , comprising determining the channel quality information in accordance with a receiver type.