Interleaving scheme for an LDPC coded QPSK/8PSK system
An approach is provided for interleaving low density parity check (LDPC) encoded bits in QPSK/8PSK modulation systems. By assigning the bits determining modulation symbols based on different bit degrees, one can efficiently find the desirable tradeoff between error performance and error floor provided by the LDPC codes in use.
1. A digital communications transmitter interleaving LDPC encoded bits in a QPSK modulation system based on a rule:
{
b
~
i
=
b
i
-
i
mod
256
+
(
i
mod
8
)
×
32
+
⌊
i
8
⌋
mod
32
b
~
i
+
1
=
b
(
i
+
1
)
-
(
i
+
1
)
mod
256
+
(
(
i
+
1
)
mod
8
)
×
32
+
⌊
i
+
1
8
⌋
mod
32
,
for
iε{i|0≦i≦N ldpc — bits −1, and imod2=0}iε{i|0≦i≦N ldpc — bits −1, and imod2=0}, where └x┘ is the floor function which returns the largest integer that is less than or equal to x, N ldpc — bits =15360 is the codeword length of the LDPC code in use.
2. A digital communications receiver employing an LDPC decoder for decoding interleaved LDPC encoded bits in a QPSK modulation mode based on a rule:
{
b
~
i
=
b
i
-
i
mod
256
+
(
i
mod
8
)
×
32
+
⌊
i
8
⌋
mod
32
b
~
i
+
1
=
b
(
i
+
1
)
-
(
i
+
1
)
mod
256
+
(
(
i
+
1
)
mod
8
)
×
32
+
⌊
i
+
1
8
⌋
mod
32
,
for iε{i|0≦i≦N ldpc — bits −1, and imod2=0}, where └x┘ is the floor function which returns the largest integer that is less than or equal to x, N ldpc — bits =15360 is the codeword length of the LDPC code in use.
3. A computer readable medium storing a computer program for performing a method specifying an interleaving scheme of LDPC encoded bits in a QPSK modulation system base on a rule:
{
b
~
i
=
b
i
-
i
mod
256
+
(
i
mod
8
)
×
32
+
⌊
i
8
⌋
mod
32
b
~
i
+
1
=
b
(
i
+
1
)
-
(
i
+
1
)
mod
256
+
(
(
i
+
1
)
mod
8
)
×
32
+
⌊
i
+
1
8
⌋
mod
32
,
for iε{i|0≦i≦N ldpc — bits −1, and imod2=0}, where └x┘ is the floor function which returns the largest integer that is less than or equal to x, N ldpc — bits =15360 is the codeword length of the LDPC code in use.
4. A digital communications transmitter interleaving LDPC encoded bits in a 8PSK modulation system based on a rule:
{
b
~
i
=
b
(
8
×
⌊
i
768
⌋
+
N
offset
+
i
3
mod
8
)
×
32
+
⌊
i
24
⌋
mod
32
b
~
i
+
1
=
b
(
8
×
⌊
i
768
⌋
+
N
offset
+
i
3
mod
8
+
160
)
×
32
+
⌊
i
24
⌋
mod
32
b
~
i
+
2
=
b
(
i
3
+
32
×
N
offset
+
10240
)
mod
N
idpc
_
bits
-
(
i
3
)
mod
256
+
(
i
3
mod
8
)
×
32
+
⌊
i
24
⌋
mod
32
for iε{i|0≦i≦N ldpc — bits −1, and imod3=0}, where └x┘ is the floor function which returns the largest integer that is less than or equal to x, N ldpc — bits =15360 is the codeword length of the LDPC code in use, and the offset values N Offset for different code rates are defined as:
Rate
N Offset
3/5
40
2/3
40
3/4
80
5/6
88
13/15
104
9/10
160.
5. A digital communications receiver employing an LDPC decoder for decoding interleaved LDPC encoded bits in a 8PSK modulation system based on a rule:
{
b
~
i
=
b
(
8
×
⌊
i
768
⌋
+
N
offset
+
i
3
mod
8
)
×
32
+
⌊
i
24
⌋
mod
32
b
~
i
+
1
=
b
(
8
×
⌊
i
768
⌋
+
N
offset
+
i
3
mod
8
+
160
)
×
32
+
⌊
i
24
⌋
mod
32
b
~
i
+
2
=
b
(
i
3
+
32
×
N
offset
+
10240
)
mod
N
idpc
_
bits
-
(
i
3
)
mod
256
+
(
i
3
mod
8
)
×
32
+
⌊
i
24
⌋
mod
32
for iε{i|0≦i≦N ldpc — bits −1, and imod3=0}, where └x┘ is the floor function which returns the largest integer that is less than or equal to x, N ldpc — bits =15360 is the codeword length of the LDPC code in use, and the offset values N Offset for different code rates are defined as:
Rate
N Offset
3/5
40
2/3
40
3/4
80
5/6
88
13/15
104
9/10
160.
6. A computer readable medium storing a computer program for performing a method specifying an interleaving scheme of LDPC encoded bits in an 8PSK modulation system base on a rule:
{
b
~
i
=
b
(
8
×
⌊
i
768
⌋
+
N
offset
+
i
3
mod
8
)
×
32
+
⌊
i
24
⌋
mod
32
b
~
i
+
1
=
b
(
8
×
⌊
i
768
⌋
+
N
offset
+
i
3
mod
8
+
160
)
×
32
+
⌊
i
24
⌋
mod
32
b
~
i
+
2
=
b
(
i
3
+
32
×
N
offset
+
10240
)
mod
N
idpc
_
bits
-
(
i
3
)
mod
256
+
(
i
3
mod
8
)
×
32
+
⌊
i
24
⌋
mod
32
for iε{i|0≦i≦N ldpc — bits −1, and imod3=0}, where └x┘ is the floor function which returns the largest integer that is less than or equal to x, N ldpc — bits =15360 is the codeword length of the LDPC code in use, and the offset values N Offset for different code rates are defined as:
Rate
N Offset
3/5
40
2/3
40
3/4
80
5/6
88
13/15
104
9/10
160.