Method and apparatus of detecting signal based on minimum mean square error in multiple input multiple output system
A receiver in a multiple-input multiple-output (MIMO) system is provided. The receiver includes a channel estimator estimating a channel based on a receiving signal, a minimum mean square error (MMSE) based reciprocal log likelihood ratio (R-LLR) calculator connected with the channel estimator and calculating an R-LLR based on the receiving signal and the estimated channel, and a channel decoder connected with the MMSE based R-LLR calculator and decoding the channel and the receiving signal based on the calculated R-LLR, wherein the R-LLR is calculated based on the reciprocity.
1. A receiver in a multiple-input multiple-output (MIMO) system, the receiver comprising:
a channel estimator configured for estimating a channel based on a receive signal;
a minimum mean square error (MMSE) based reciprocal log likelihood ratio (R-LLR) calculator, coupled to the channel estimator, and configured for calculating an R-LLR based on the receive signal and the estimated channel; and
a channel decoder, coupled to the MMSE based R-LLR calculator, and configured for decoding the channel and the receive signal based on the calculated R-LLR,
wherein the R-LLR is calculated based on reciprocity, and
wherein when SINR information for each stream is available or the SINRs for each stream are different, the MMSE based R-LLR calculator is configured for:
estimating the transmit symbol by calculating the MMSE solution based on the receive signal and the estimated channel;
performing slicing on the estimated transmit symbol;
testing whether the reciprocity of the sliced transmit symbol is established or not;
calculating an LLR based on the estimated transmit symbol and the sliced transmit symbol; and
calculating an R-LLR in which a priori term is added to the LLR, based on the calculated LLR and the establishment or not of the reciprocity.
2. The receiver of claim 1 , wherein the reciprocity is established at the time of satisfying the following Equation:
[
x
1
x
2
]
=
[
Q
(
h
1
H
||
h
1
||
2
(
y
-
h
2
x
2
)
)
Q
(
h
2
H
||
h
2
||
2
(
y
-
h
1
x
1
)
)
]
,
where H represents a gain matrix of the channel, y represents a vector of the receive signal, and xεΩ 2 represents a two-dimensional complex vector, Ω represents a set of complex constellation points, and function Q(•) represents a slicing function defined by the following Equation
Q
(
x
^
)
=
arg
min
x
∈
Ω
|
x
-
x
^
|
.
3. The receiver of claim 1 , wherein the R-LLR is calculated by the following Equation:
LLR
(
b
k
,
1
)
≈
ln
max
x
i
∈
S
k
+
p
(
x
~
1
,
MMSE
|
x
i
)
p
(
x
i
)
max
x
j
∈
S
k
-
p
(
x
~
1
,
MMSE
|
x
j
)
p
(
x
j
)
=
1
2
σ
1
2
(
|
x
~
1
,
MMSE
-
x
1
,
k
,
-
opt
|
2
-
|
x
~
1
,
MMSE
-
x
1
,
k
,
+
opt
|
2
)
+
ln
p
(
x
1
,
k
,
+
opt
)
p
(
x
1
,
k
,
-
opt
)
,
where b k, 1 represents the k-th bit of a first stream, S k + represents the symbol set of which the k-th bit is 1, S k − represents the symbol set of which the k-th bit is 0, {tilde over (x)} 1,MMSE represents an MMSE solution for the first stream, x i (i=1,2) represents a signal transmitted from an i-th transmit antenna, and σ 1 2 represents dispersion of circular symmetric Gaussian distribution representing a distribution of noise of the first stream
x
1
,
k
,
+
opt
=
arg
min
x
∈
S
k
+
|
x
~
1
,
MMSE
-
x
|
2
,
x
1
,
k
,
-
opt
=
arg
min
x
∈
S
k
-
|
x
~
1
,
MMSE
-
x
|
2
.
4. The receiver of claim 3 , wherein the priori term is calculated by the following Equation based on the establishment or not of the reciprocity
ln
p
(
x
1
,
k
,
+
opt
)
p
(
x
1
,
k
,
-
opt
)
=
{
ln
p
(
x
1
,
k
,
+
opt
|
x
^
MMSE
rcp
)
-
ln
1
-
p
(
x
i
,
k
,
+
opt
|
x
^
MMSE
rcp
)
|
Ω
|
-
1
,
if
x
^
MMSE
is
reciprocal
0
,
else
.
5. The receiver of claim 3 , wherein the priori term is calculated by the following Equation based on the establishment or not of the reciprocity
ln
p
(
x
i
,
k
,
+
opt
)
p
(
x
i
,
k
,
-
opt
)
≈
{
1
4
SNR
dB
,
if
reciprocal
0
,
else
.
6. A receiver in a multiple-input multiple-output (MIMO) system, the receiver comprising:
a channel estimator configured for estimating a channel based on a receive signal;
a minimum mean square error (MMSE) based reciprocal log likelihood ratio (R-LLR) calculator, coupled to the channel estimator, and configured for calculating an R-LLR based on the receive signal and the estimated channel; and
a channel decoder, coupled to the MMSE based R-LLR calculator, and configured for decoding the channel and the receive signal based on the calculated R-LLR;
wherein the R-LLR is calculated based on reciprocity, and
wherein when signal to interference noise ratio information (SINR) for each stream is not available or the SINRs for each stream are the same, the MMSE based R-LLR calculator is configured for:
estimating transmit symbols by calculating an MMSE solution based on the receive signal and the estimated channel;
performing slicing on the estimated transmit symbol; and
testing whether the reciprocity of the sliced transmit symbol is established or not.
7. The receiver of claim 6 , wherein when the reciprocity is established, the MMSE based R-LLR calculator is configured for calculating an LLR based on the estimated transmit symbol, the sliced transmit symbol, and the establishment or not of the reciprocity.
8. The receiver of claim 7 , wherein the MMSE solution is a most likelihood (ML) solution.
9. The receiver of claim 6 , wherein when the reciprocity is not established, the MMSE based R-LLR calculator is configured for determining an LLR of the transmit symbol as 0.
10. A method of detecting, using a computing device to perform operations, a signal in a multi-input multiple-output (MIMO) system, the method comprising:
estimating a channel based on a receive signal;
calculating a reciprocal log likelihood ratio (R-LLR) based on the receive signal and the estimated channel; and
decoding the channel and the receive signal based the calculated R-LLR, wherein the R-LLR is calculated based on reciprocity, and
wherein when the SINR information for each stream is available or the SINRs for each stream are different, the calculating of the R-LLR includes:
estimating the transmit symbol by calculating the MMSE solution based on the receive signal and the estimated channel;
performing slicing on the estimated transmit symbol;
testing whether the reciprocity of the sliced transmit symbol is established or not;
calculating an LLR based on the estimated transmit symbol and the sliced transmit symbol; and
calculating an R-LLR in which a priori term is added to the LLR, based on the calculated LLR and the establishment or not of the reciprocity.
11. The method of claim 10 , wherein the reciprocity is established at the time of satisfying the following Equation:
[
x
1
x
2
]
=
[
Q
(
h
1
H
||
h
1
||
2
(
y
-
h
2
x
2
)
)
Q
(
h
2
H
||
h
2
||
2
(
y
-
h
1
x
1
)
)
]
,
where H represents a gain matrix of the channel, y represents a vector of the receive signal, and xεΩ 2 represents a two-dimensional complex vector, Ω represents a set of complex constellation points, and function Q(•) represents a slicing function defined by the following Equation
Q
(
x
^
)
=
arg
min
x
∈
Ω
|
x
-
x
^
|
.
12. A method of detecting, using a computing device to perform operations, a signal in a multi-input multiple-output (MIMO) system, the method comprising:
estimating a channel based on a receive signal;
calculating a reciprocal log likelihood ratio (R-LLR) based on the receive signal and the estimated channel; and
decoding the channel and the receive signal based the calculated R-LLR, wherein the R-LLR is calculated based on reciprocity; and
wherein when signal to interference noise ratio information (SINR) for each stream is not available or the SINRs for each stream are the same, the calculating of the R-LLR includes:
estimating transmit symbols by calculating an MMSE solution based on the receive signal and the estimated channel;
performing slicing on the estimated transmit symbol; and
testing whether the reciprocity of the sliced transmit symbol is established or not.
13. The method of claim 12 , further comprising calculating an LLR based on the estimated transmit symbol, the sliced transmit symbol, and the establishment or not of the reciprocity, when the reciprocity is established.
14. The method of claim 12 , further comprising determining an LLR of the transmit symbol as 0, when the reciprocity is not established.