Method and system for MU-MIMO communication
A method and system for data communication in a Multiple-Input and Multiple-Output (MIMO) system is provided. The method includes receiving, from a first UE, first channel information relating to a first subset of a plurality of antennae of the MIMO system and second channel information relating to a second subset of a plurality of antennae. The method further includes generating first and second sub-precoders according to the first and second channel information, respectively. A precoder is then generated according at least in part to the first sub-precoder and the second sub-precoder, and data is transmitted to the first UE using the precoder.
1. A method of data communication in a Multiple-Input and Multiple-Output (MIMO) system, the MIMO system including a base station comprising a plurality of antennae, and a plurality of user equipments (UEs), the method including:
receiving, from a first UE of the plurality of UEs, first channel information relating to a first subset of the plurality of antennae;
generating a first sub-precoder according to the first channel information;
receiving, from the first UE, second channel information relating to a second subset of the plurality of antennae;
generating a second sub-precoder according to the second channel information;
generating a precoder using at least the first sub-precoder and the second sub-precoder; and
transmitting data to the first UE using the precoder;
wherein the method further including:
determining one or more representative sub-channels for the first UE according to at least the first and second channel information; and generating a sub-precoder for each of the one or more representative sub-channels.
2. The method of claim 1 , wherein each of the first and second channel information comprises pre-coding matrix indicators (PMI).
3. The method of claim 1 , wherein the MIMO system comprises a Multi-user Multiple-Input and Multiple-Output (MU-MIMO) system.
4. The method of claim 1 , wherein the antennae are partitioned into a plurality of subsets, wherein the plurality of subsets includes the first subset and the second sub set.
5. The method of claim 1 , wherein the representative sub-channels are determined according to a rank indicator (RI) of the first UE.
6. The method of claim 1 , wherein the representative sub-channels Ĥ i are determined according to the following equation:
Ĥ i =Ĥ ( m *)ϵΩ RI , i= 1, . . . , N UE
where
m
*
=
argmax
m
tr
{
[
H
^
(
m
)
W
i
]
H
[
H
^
(
m
)
W
i
]
}
,
Ĥ(m)ϵΩ RI and Ω RI contains matrices Ĥ(m), m=1, . . . of size N RX ×μ TX when the rank of the first UE is equal to a number of receiver antennae of the first UE.
7. The method of claim 1 , wherein the representative sub-channels are determined by calculating correlation values for a plurality of sub-channels, and selecting the representative sub-channels based upon the correlation values.
8. The method of claim 1 , further comprising determining a sub-transmit-power of the first UE, and determining the sub-precoders associated with the first UE according to sub-transmit power.
9. The method of claim 1 , wherein the sub-precoders are generated using joint transmit and receive optimization according to at least the first and second channel information.
10. The method of claim 1 , wherein the sub-precoders F i(m) are generated iteratively over m according to the following equation:
F
i
(
m
+
1
)
=
[
∑
i
=
1
N
UF
H
i
H
G
i
(
m
)
H
G
i
(
m
)
H
i
+
υ
(
m
)
I
]
-
1
H
i
H
G
i
(
m
)
H
,
where G i(m) is a decoder of the i-th user, H(i) is a channel matrix, I is the identity matrix, and ν (m) is a Lagrangian multiplier.
11. The method of claim 10 , wherein the Lagrangian multiplier ν (m) is calculated by:
a) Computing λ n TX (m+1) as the singular values of the following decomposition:
U
(
m
+
1
)
Λ
(
m
+
1
)
U
(
m
+
1
)
=
∑
i
=
1
N
UE
H
i
H
G
i
(
m
+
1
)
H
G
i
(
m
+
1
)
H
i
;
b) Setting ν (m+1) =(ν max +ν min )/2;
c) Computing the following quantity
β
^
=
∑
n
TX
=
1
μ
TX
λ
n
TX
(
m
+
1
)
(
λ
n
TX
(
m
+
1
)
+
υ
(
m
+
1
)
)
2
d) determining if {circumflex over (β)}>β then set ν min =ν (m+1) otherwise set ν max =ν (m+1) ; and
e) Repeating steps b), c) and d) until |{circumflex over (β)}−β|<ϵ L .
12. The method of claim 1 , further comprising estimating a noise variance for the UE, and generating the sub-precoder according to the noise variance.
13. The method of claim 12 , wherein the noise variance σ i 2 is determined according to the following equation:
σ
i
2
=
P
/
N
UE
∑
l
=
1
L
i
SINR
il
/
L
i
,
i
=
1
,
…
,
N
UE
where L i is the number of code words used for the i-th UE, P is the transmit power, and SINR il is the signal-to-interference-plus-noise ratio.
14. The method of claim 1 , wherein generating the precoder comprises stacking the sub-precoders.
15. The method of claim 1 , wherein the plurality of antennae comprise a 4×4 array of antennae.
16. The method of claim 15 , wherein the 4×4 array of antennae is partitioned into 4 subsets of 4 antennae.
17. The method of claim 1 , further including:
receiving, from a second UE of the plurality of UEs, third channel information relating to the first subset of the plurality of antennae;
generating a third sub-precoder according to the third channel information;
receiving, from the second UE, fourth channel information relating to a second subset of the plurality of antennae;
generating a fourth sub-precoder according to the second channel information;
generating a second precoder according at least in part to the third sub-precoder and the fourth sub-precoder; and
transmitting second data to the second UE using the second precoder.
18. A non-transitory computer readable medium storing a control program for causing a computer to perform a process of controlling the base station of claim 1 .
19. A MIMO base station comprising a plurality of antennae, at least one memory storing instructions and a processor configured to execute the instructions to:
receive, from a first UE of the plurality of UEs, first channel information relating to a first subset of the plurality of antennae;
generate a first sub-precoder according to the first channel information;
receive, from the first UE, second channel information relating to a second subset of the plurality of antennae;
generate a second sub-precoder according to the second channel information;
generate a precoder according at least in part to the first sub-precoder and the second sub-precoder; and
transmit data to the first UE using the precoder;
wherein the processor further configured to execute the instructions to:
determines one or more representative sub-channels for the first UE according to at least the first and second channel information; and generating a sub-precoder for each of the one or more representative sub-channels.