US 8,284,855 B2Granted

Multi-user downlink linear MIMO precoding system

AssigneeNEC Laboratories America, Inc.

InventorMohammad A. Khojastepour

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Abstract

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.

Claims3

Dependent claims

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 kth precoder
G
(
k
)
=
P
⁢
G
~
(
k
)
tr
⁡
(
G
~
(
k
)
⁢
G
~
(
k
)
*
)
at a kth iteration;
(c) determining (k+1)th precoder {tilde over (G)}(k+1) as EεD└(H*ψ*AψH)−1H*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(T1H1g1, T2H2g2, . . . TLHLgL), gl is the lth 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.

221 more elements

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 ith user equipment, P is average power, L is the number of the data streams, and I is an identity matrix;
(b) determining kth precoder
G
(
k
)
=
P
⁢
G
~
(
k
)
tr
⁡
(
G
~
(
k
)
⁢
G
~
(
k
)
*
)
at a kth iteration;
(c) determining (k+1)th precoder {tilde over (G)}(k+1) as EHεD└(H*ψ*AψH)−1H*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(T1H1g1, T2H2g2, . . . TLHLgL), gl is the lth 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.

230 more elements

Dependencies are inferred from the claim text.

Facts

Application: 13/273,880Filed 14 Oct 2011 · division
Priority: 20 Dec 2006
Published: US 2012/0033756 A19 Feb 2012
Granted: 9 Oct 2012
Term ends: Not estimatedThe source records don’t support an estimate.

Classification11 codes

H04W 72/23
Control channels or signalling for resource management: in the downlink direction of a wireless link, i.e. towards a terminal
H04B 7/0417
MIMO systems: feedback systems
H04B 7/0452
MIMO systems: multi-user MIMO systems
H04B 7/0626
Feedback content: channel coefficients, e.g. channel state information [CSI]

Family

Application60/870,930Us provisional application · filed 20 Dec 2006
Application12/002,874Parent of this division · filed 19 Dec 2007
US 2012/0033756 A1Pre-grant publication · published 9 Feb 2012
US 8,059,733 B2Parent of this division
US 2008/0159425 A1Published application
US 8,284,855 B2This patent

From the US filing history. Foreign family members aren’t listed.