Method of precoding with a codebook for a wireless system
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 transmitter used in a wireless communications system, comprising:
precoding data using a precoding matrix selected from a codebook comprising matrices that are expressed as
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 transmitter 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 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 vector w; and
transmitting the precoded data to a receiver.
2. The method as in claim 1 , wherein the transmitter comprises a base station and the receiver comprises a user equipment (UE).
3. The method as in claim 1 , wherein the transmission is downlink transmission.
4. The method as in claim 1 , wherein v a is selected from a set V a where V 1 ={v i 1 εC M } i=1 N 1 , V 2 ={e 1 M-1 }, V 3 ={e 1 M-2 }, . . . .
5. The method as in claim 1 , wherein the number of transmit antennas is 2.
6. The method as in claim 1 , wherein the number of transmit antennas is 4.
7. The method as in claim 1 , wherein the precoding matrix is formed by selecting one or more columns of matrix V.
8. The method of claim 7 , wherein the number of selected columns to form the precoding matrix is less than the number of transmit antennas.
9. A method implemented in a receiver used in a wireless communications system, comprising:
receiving from a transmitter data precoded with a precoding matrix selected from a codebook comprising matrices that are expressed as
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 transmitter 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 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 vector w; and
decoding the precoded data.
10. The method as in claim 9 , wherein the transmitter comprises a base station and the receiver comprises a user equipment (UE).
11. The method as in claim 9 , wherein the reception is downlink reception.
12. The method as in claim 9 , wherein v a is selected from a set V a where V 1 ={v i 1 εC M } i=1 N 1 , V 2 ={e 1 M-1 }, V 3 ={e 1 M-2 }, . . . .
13. The method as in claim 9 , wherein the number of transmit antennas is 2.
14. The method as in claim 9 , wherein the number of transmit antennas is 4.
15. The method as in claim 9 , wherein the precoding matrix is formed by selecting one or more columns of matrix V.
16. The method of claim 15 , wherein the number of selected columns to form the precoding matrix is less than the number of transmit antennas.
17. A method implemented in a receiver used in a wireless communications system, comprising:
providing feedback information for transmission in order for a transmitter to select a precoding matrix from a codebook comprising matrices that are expressed as
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 transmitter 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 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 vector w; and
receiving precoded data from the transmitter.
18. The method as in claim 17 , wherein the transmitter comprises a base station and the receiver comprises a user equipment (UE).
19. The method as in claim 17 , wherein the transmission is downlink transmission.
20. The method as in claim 17 , wherein v a is selected from a set V a where V 1 ={v i 1 εC M } i=1 N 1 , V 2 ={e 1 M-1 }, V 3 ={e 1 M-2 }, . . . .
21. The method as in claim 17 , wherein the number of transmit antennas is 2.
22. The method as in claim 17 , wherein the number of transmit antennas is 4.
23. The method as in claim 17 , wherein the precoding matrix is formed by selecting one or more columns of matrix V.
24. The method of claim 23 , wherein the number of selected columns to form the precoding matrix is less than the number of transmit antennas.