Apparatus and method for soft-decision demodulating in non-square quadrature amplitude modulation
Disclosed are an apparatus and a method for soft-decision demodulating in non-square quadrature amplitude modulation. The apparatus includes: a signal receiving unit receiving a quadrature amplitude modulation (QAM) modulated signal at an m modulation degree at a transmitting side; a soft-decision bit calculating unit determining a soft-decision bit value by calculating log likelihood ratios (LLRs) for m bits of the received QAM modulated signal; and a signal decoding unit restoring the received QAM modulated signal based on the determined soft-decision bit value, in which the soft-decision bit calculating unit defines a log likelihood ratio calculation equation by approximating soft-decision boundary points of constellation points for m bits of non-square QAM having odd bits, respectively.
1. An apparatus for soft-decision demodulating in non-square quadrature amplitude modulation, the apparatus comprising:
a signal receiving unit receiving a quadrature amplitude modulation (QAM) signal modulated using m states of modulation at a transmitting side;
a soft-decision bit calculating unit determining a soft-decision bit value by calculating log likelihood ratios (LLRs) for m bits of the received QAM modulated signal; and
a signal decoding unit restoring the received QAM modulated signal based on the determined soft-decision bit value,
wherein the soft-decision bit calculating unit defines a log likelihood ratio calculation equation by approximating soft-decision boundary points of constellation points for m bits of non-square QAM having odd bits, respectively, and
wherein the soft-decision bit calculating unit calculates a log likelihood ratio for a third bit by using an equation given below:
L
L
R
(
b
2
)
≅
{
y
Q
[
n
]
-
4
d
y
Q
[
n
]
>
y
I
[
n
]
y
I
[
n
]
-
4
d
,
elsewhere
where y I [n] represents an I channel value, y Q [n] represents a Q channel value, and d represents a distance value of a partition boundary when the bits b 2 =1 and b 2 =0.
2. The apparatus of claim 1 , wherein the soft-decision bit calculating unit calculates a log likelihood ratio for a first bit by using an I channel value.
3. The apparatus of claim 1 , wherein the soft-decision bit calculating unit calculates a log likelihood ratio for a second bit by using a Q channel value.
4. The apparatus of claim 1 , wherein the soft-decision bit calculating unit calculates a log likelihood ratio for a fourth bit by using an equation given below:
L
L
R
(
b
3
)
≅
{
max
(
y
I
[
n
]
-
2
d
,
-
y
Q
[
n
]
+
4
d
)
y
Q
[
n
]
>
3
d
,
y
Q
[
n
]
>
y
I
[
n
]
y
Q
[
n
]
-
2
d
,
elsewhere
where y I [n] represents the I channel value, y Q [n] represents the Q channel value, and d represents a distance value of a partition boundary when the bits b 3 =1 and b 3 =0.
5. The apparatus of claim 1 , wherein the soft-decision bit calculating unit calculates a log likelihood ratio for a fifth bit by using an equation given below:
L
L
R
(
b
4
)
≅
{
-
y
I
[
n
]
+
y
Q
[
n
]
y
I
[
n
]
>
4
d
,
y
Q
[
n
]
>
2
d
max
(
-
y
I
[
n
]
+
y
Q
[
n
]
-
2
d
,
y
Q
[
n
]
-
4
d
-
y
I
[
n
]
+
2
d
)
,
elsewhere
where y I [n] represents the I channel value, y Q [n] represents the Q channel value, and d represents a distance value of a partition boundary when the bits b 4 =1 and b 4 =0.
6. The apparatus of claim 1 , wherein the soft-decision bit calculating unit calculates a log likelihood ratio for an even numbered bit of a sixth bit or more by using an equation given below:
L
L
R
(
b
k
,
odd
)
=
{
-
(
y
Q
[
n
]
-
2
d
-
2
d
-
d
)
k
=
5
b
k
-
2
,
odd
-
d
/
2
k
-
5
2
,
k
>
5
where y I [n] represents an I channel value, y Q [n] represents a Q channel value, and d represents a distance value of a partition boundary when the bits b k =1 and b k =0.
7. The apparatus of claim 1 , wherein the soft-decision bit calculating unit calculates a log likelihood ratio for an odd numbered bit of a seventh bit or more by using an equation given below:
L
L
R
(
b
k
,
even
)
=
{
-
(
y
I
[
n
]
-
2
d
-
2
d
-
d
)
k
=
6
b
k
-
2
,
even
-
d
/
2
k
-
6
2
,
k
>
6
where y I [n] represents an I channel value, y Q [n] represents a Q channel value, and d represents a distance value of a partition boundary when the bits b k =1 and b k =0.
8. A method for soft-decision demodulating in non-square quadrature amplitude modulation, the method comprising:
receiving a quadrature amplitude modulation (QAM) signal modulated using m states of modulation at a transmitting side;
defining a log likelihood ratio calculation equation by approximating soft-decision boundary points of constellation points for m bits of non-square QAM having odd bits, respectively;
calculating log likelihood ratios (LLRs) for m bits of the received QAM modulated signal by using the defined log likelihood ratio calculation equation;
determining soft-decision bit values based on the calculated log likelihood ratios; and
restoring the received QAM modulated signal based on the determined soft-decision bit value,
wherein in the calculating of the log likelihood ratios (LLRs) for m bits, a log likelihood ratio for a third bit is calculated by using an equation given below:
L
L
R
(
b
2
)
=
{
y
Q
[
n
]
-
4
d
y
Q
[
n
]
>
y
I
[
n
]
y
I
[
n
]
-
4
d
,
elsewhere
where y I [n] represents an I channel value, y Q [n] represents a Q channel value, and d represents a distance value of a partition boundary when the bits b 2 =1 and b 2 =0.
9. The method of claim 8 , wherein in the calculating of the log likelihood ratios (LLRs) for m bits, a log likelihood ratio for a first bit is calculated by using an I channel value.
10. The method of claim 8 , wherein in the calculating of the log likelihood ratios (LLRs) for m bits, a log likelihood ratio for a second bit is calculated by using a Q channel value.
11. The method of claim 8 , wherein in the calculating of the log likelihood ratios (LLRs) for m bits, a log likelihood ratio for a fourth bit is calculated by using an equation given below:
L
L
R
(
b
3
)
≅
{
max
(
y
I
[
n
]
-
2
d
,
-
y
Q
[
n
]
+
4
d
)
y
Q
[
n
]
>
3
d
,
y
Q
[
n
]
>
y
I
[
n
]
y
Q
[
n
]
-
2
d
,
elsewhere
where y I [n] represents the I channel value, y Q [n] represents the Q channel value, and d represents a distance value of a partition boundary when the bits b 3 =1 and b 3 =0.
12. The method of claim 8 , wherein in the calculating of the log likelihood ratios (LLRs) for m bits, a log likelihood ratio for a fifth bit is calculated by using an equation given below:
L
L
R
(
b
4
)
≅
{
-
y
I
[
n
]
+
y
Q
[
n
]
y
I
[
n
]
>
4
d
,
y
Q
[
n
]
>
2
d
max
(
-
y
I
[
n
]
+
y
Q
[
n
]
-
2
d
,
y
Q
[
n
]
-
4
d
-
y
I
[
n
]
+
2
d
)
,
elsewhere
where y I [n] represents the I channel value, y Q [n] represents the Q channel value, and d represents a distance value of a partition boundary when the bits b 4 =1 and b 4 =0.
13. The method of claim 8 , wherein in the calculating of the log likelihood ratios (LLRs) form bits, a log likelihood ratio for an even numbered bit of a sixth bit or more is calculated by using an equation given below:
L
L
R
(
b
k
,
odd
)
=
{
-
(
y
Q
[
n
]
-
2
d
-
2
d
-
d
)
k
=
5
b
k
-
2
,
odd
-
d
/
2
k
-
5
2
,
k
>
5
where y I [n] represents the I channel value, y Q [n] represents the Q channel value, and d represents a distance value of a partition boundary when the bits b k =1 and b k =0.
14. The method of claim 8 , wherein in the calculating of the log likelihood ratios (LLRs) for m bits, a log likelihood ratio for an odd numbered bit of a seventh bit or more is calculated by using an equation given below:
L
L
R
(
b
k
,
even
)
=
{
-
(
y
I
[
n
]
-
2
d
-
2
d
-
d
)
k
=
6
b
k
-
2
,
even
-
d
/
2
k
-
6
2
,
k
>
6
where y I [n] represents the I channel value, y Q [n] represents the Q channel value, and d represents the distance value of a partition boundary when the bits b k =1 and b k =0.
15. An apparatus for soft-decision demodulating in non-square quadrature amplitude modulation, the apparatus comprising:
a signal receiving unit receiving a quadrature amplitude modulation (QAM) signal modulated using m states of modulation at a transmitting side;
a soft-decision bit calculating unit determining a soft-decision bit value by calculating log likelihood ratios (LLRs) for m bits of the received QAM modulated signal; and
a signal decoding unit restoring the received QAM modulated signal based on the determined soft-decision bit value,
wherein the soft-decision bit calculating unit defines a log likelihood ratio calculation equation by approximating soft-decision boundary points of constellation points for m bits of non-square QAM having odd bits, respectively, and
wherein the soft-decision bit calculating unit calculates a log likelihood ratio for a fourth bit by using an equation given below:
L
L
R
(
b
3
)
≅
{
max
(
y
I
[
n
]
-
2
d
,
-
y
Q
[
n
]
+
4
d
)
y
Q
[
n
]
>
3
d
,
y
Q
[
n
]
>
y
I
[
n
]
y
Q
[
n
]
-
2
d
,
elsewhere
where y I [n] represents the I channel value, y Q [n] represents the Q channel value, and d represents a distance value of a partition boundary when the bits b 3 =1 and b 3 =0.