Multi-user downlink linear MIMO precoding system
View Patent ↗Multi-user (MU-) MIMO systems with quantized feedback are designed to maximize the sum-rate via scheduling and linear precoding. To maximize throughput over the network, quantized CSIT is sent through a low-rate feedback link feedback from a plurality of users back to a base station. The base station then determines a subset of the plurality of users to transmit one or more signals to based on the received feedback and determines a preceding matrix based on the received feedback from the plurality of users wherein the precoding matrix maximizes a sum-rate throughput for the subset of the plurality of users. Additionally, based on the received feedback, the base station designs a quantization codebook. This codebook may be designed off-line and/or online. The codebook and/or precoding matrix are used to transmit signals to the users.
1. A method implemented in a base station used for a downlink multi-user (MU) multi-input multi-output (MIMO) system, comprising:
receiving an indication of a quantized vector from each of a plurality of user equipments;
determining the precoder;
precoding data streams for the plurality of user equipments; and
transmitting the precoded data to the plurality of user equipments,
wherein the precoded data is expressed by equation
x=Gu
where x is the precoded data, u denotes the data streams, G is a precoder comprising matrix [{circumflex over (v)} 1 , {circumflex over (v)} 2 , . . . , {circumflex over (v)} L ], and {circumflex over (v)} 1 , {circumflex over (v)} 2 , . . . , and {circumflex over (v)} L are indicated by the plurality of user equipments,
wherein the number of the data streams is equal to or greater than the number of the user equipments, and
wherein determining the precoder comprises:
(a) initializing initial precoder {tilde over (G)} (0) as
V
_
^
*
[
V
^
_
V
^
_
*
+
L
P
I
]
-
1
,
where {circumflex over (V)} =[{circumflex over (v)} 1 , {circumflex over (v)} 2 , . . . , {circumflex over (v)} L ] T , P is average power, L is the number of the data streams, and I is an identity matrix;
(b) determining k th precoder
G
(
k
)
=
P
G
~
(
k
)
tr
(
G
~
(
k
)
G
~
(
k
)
*
)
at a k th iteration;
(c) determining (k+1) th precoder {tilde over (G)} (k+1) as E εD └(H*ψ*AψH) −1 H*ψ*(I+γ)A┘| G (k) ,
where H is a channel matrix of transmission channels to the plurality of user equipments, E denotes the expectation operation, D is the set of channel over which the expectation is taken,
A
=
diag
(
1
A
1
,
1
A
2
,
…
1
A
L
)
,
H
=
[
H
1
T
H
2
T
…
H
L
T
]
T
,
ψ
=
diag
(
T
1
,
T
2
,
…
,
T
L
)
,
γ=diag(T 1 H 1 g 1 , T 2 H 2 g 2 , . . . T L H L g L ), g l is the l th column of the precoder G,
A
l
=
1
+
(
H
l
g
l
)
*
Ω
l
-
1
(
H
l
g
l
)
,
Ω
l
-
1
=
I
+
∑
i
=
1
,
i
≠
l
L
(
H
l
g
i
)
(
H
l
g
i
)
*
,
T
l
=
(
H
l
g
l
)
*
Ω
l
-
1
,
and
1
≤
l
≤
L
;
and
(d) performing (b) and (c) for a specific number of iteration, where the specific number of iteration ≧0.
2. A base station used for a downlink multi-user (MU) multi-input multi-output (MIMO) system, comprising:
a receiving unit to receive an indication of a quantized vector from each of a plurality of user equipments;
a control unit to determine the precoder;
a precoding unit to precode data streams for the plurality of user equipments; and
a transmission unit to transmit the precoded data to the plurality of user equipments,
wherein the precoded data is expressed by equation
x=Gu
where x is the precoded data, u denotes the data streams, G is a precoder comprising matrix [{circumflex over (v)} 1 , {circumflex over (v)} 2 , . . . , {circumflex over (v)} L ], and {circumflex over (v)} 1 , {circumflex over (v)} 2 , . . . , and {circumflex over (v)} L are indicated by the plurality of user equipments,
wherein the number of the data streams is equal to or greater than the number of the user equipments, and
wherein the control unit performs:
(a) initializing initial precoder
G
~
(
0
)
as
V
_
^
*
[
V
^
_
V
^
_
*
+
L
P
I
]
-
1
,
where {circumflex over (V)} =[{circumflex over (v)} 1 , {circumflex over (v)} 2 , . . . , {circumflex over (v)} L ] T , {circumflex over (v)} i being the quantized vector corresponding to the i th user equipment, P is average power, L is the number of the data streams, and I is an identity matrix;
(b) determining k th precoder
G
(
k
)
=
P
G
~
(
k
)
tr
(
G
~
(
k
)
G
~
(
k
)
*
)
at a k th iteration;
(c) determining (k+1) th precoder {tilde over (G)} (k+1) as E HεD └(H*ψ*AψH) −1 H*ψ*(I+γ)A┘| G (k) ,
where H is a channel matrix of transmission channels to the plurality of user equipments, E denotes the expectation operation, D is the set of channel over which the expectation is taken,
A
=
diag
(
1
A
1
,
1
A
2
,
…
1
A
L
)
,
H
=
[
H
1
T
H
2
T
…
H
L
T
]
T
,
ψ
=
diag
(
T
1
,
T
2
,
…
,
T
L
)
,
γ=diag(T 1 H 1 g 1 , T 2 H 2 g 2 , . . . T L H L g L ), g l is the l th column of the precoder G,
A
l
=
1
+
(
H
l
g
l
)
*
Ω
l
-
1
(
H
l
g
l
)
,
Ω
l
-
1
=
I
+
∑
i
=
1
,
i
≠
l
L
(
H
l
g
i
)
(
H
l
g
i
)
*
,
T
l
=
(
H
l
g
l
)
*
Ω
l
-
1
,
and
1
≤
l
≤
L
;
and
(d) performing (b) and (c) for a specific number of iteration, where the specific number of iteration ≧0.
3. A method implemented in a user equipment used for a downlink multi-user (MU) multi-input multi-output (MIMO) system, comprising:
transmitting an indication of a quantized vector to a base station; and
receiving data precoded with a precoder from the base station,
wherein the precoded data is precoded from data streams for a plurality of user equipments,
wherein the precoded data is expressed by equation
x=Gu
where x is the precoded data, u denotes the data streams, G is a precoder comprising matrix [{circumflex over (v)} 1 , {circumflex over (v)} 2 , . . . , {circumflex over (v)} L ], and {circumflex over (v)} 1 , {circumflex over (v)} 2 , . . . , and {circumflex over (v)} L are indicated by the plurality of user equipments,
wherein the number of the data streams is equal to or greater than the number of the user equipments, and
wherein the precoder is determined by:
(a) initializing initial precoder
G
~
(
0
)
as
V
_
^
*
[
V
^
_
V
^
_
*
+
L
P
I
]
-
1
,
where {circumflex over (V)} =[{circumflex over (v)} 1 , {circumflex over (v)} 2 , . . . , {circumflex over (v)} L ] T , P is average power, L is the number of the data streams, and I is an identity matrix;
(b) determining k th precoder
G
(
k
)
=
P
G
~
(
k
)
tr
(
G
~
(
k
)
G
~
(
k
)
*
)
at a k th iteration;
(c) determining (k+1 precoder {tilde over (G)} (k+1) as E HεD └(H*ψ*AψH) −1 H*ψ*(I+γ)A┘| G (k) ,
where H is a channel matrix of transmission channels to the plurality of user equipments, E denotes the expectation operation, D is the set of channel over which the expectation is taken,
A
=
diag
(
1
A
1
,
1
A
2
,
…
1
A
L
)
,
H
=
[
H
1
T
H
2
T
…
H
L
T
]
T
,
ψ
=
diag
(
T
1
,
T
2
,
…
,
T
L
)
,
γ=diag(T 1 H 1 g 1 , T 2 H 2 g 2 , . . . T L H L g L ), g l is the l th column of the precoder G,
A
l
=
1
+
(
H
l
g
l
)
*
Ω
l
-
1
(
H
l
g
l
)
,
Ω
l
-
1
=
I
+
∑
i
=
1
,
i
≠
l
L
(
H
l
g
i
)
(
H
l
g
i
)
*
,
T
l
=
(
H
l
g
l
)
*
Ω
l
-
1
,
and
1
≤
l
≤
L
;
and
(d) performing (b) and (c) for a specific number of iteration, where the specific number of iteration ≧0.