Bit grouping for IEEE 802.16m CTC
Document Number:
IEEE C802.16m-09/0670
Date Submitted:
2009-03-09
Source:
Seunghyun Kang, Sukwoo Lee
LG Electronics
Re:
Email: {sh_kang, sugoo} @lge.com
IEEE 802.16m-09/0012, “Call for Contributions on Project 802.16m Amendment Working Document (AWD) Content”.
Target topic: “Channel Coding”
Venue:
IEEE Session #60, Vancouver, BC, Canada
Purpose:
To be discussed and adopted in the Amendment Working Document
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CTC Bit grouping method in IEEE 802.16e

16e bit grouping procedure



All of the encoded bits are demultiplexed into six subblocks denoted A,
B, Y1, Y2, W1, and W2.
The six subblocks are interleaved separately by using the same subblock
interleaver.
The output sequence of the bit grouping consists of the interleaved A
and B subblock sequence, followed by a bit-by-bit multiplexed
sequence of the interleaved Y1 and Y2 subblock sequences, followed by
a bit-by-bit multiplexed sequence of the interleaved W1 and W2
subblock sequences
CTC Bit grouping method in IEEE 802.16e

Block diagram
CTC Bit grouping method in IEEE 802.16e

Unevenly distributed bit reliabilities


In the case of using high order modulation(16QAM or 64QAM), the
codeword sequence is mapped onto 2 or 3 bit reliabilities depending on
the modulation order.
On the decoder point of view, the legacy bit grouping method unevenly
distributes the bit reliabilities of the systematic bits along whole
decoding trellis transitions.
Proposed Bit grouping method for IEEE 802.16m CTC

Simple modification of 16e bit grouping method

The interleaved sequence of the sub block B is circularly shifted to the
left once.
BShift (i )  B((i  1) mod N ), where i  0 ... N  1

The output sequence of the proposed bit grouping consists of the
interleaved A and BShift subblock sequence, followed by a bit-by-bit
multiplexed sequence of the interleaved Y1 and Y2 subblock sequences,
followed by a bit-by-bit multiplexed sequence of the interleaved W1 and
W2 subblock sequences.
Proposed Bit grouping method for 802.16m CTC

Block diagram
Proposed Bit grouping method for 802.16m CTC

Bit reliability comparison on the decoder point of view

Example with NEP=48 and 16QAM





For each subblock, the following table shows the bit reliability values of 24-bit subblock
sequence.
‘0’ represents low bit reliability and ‘1’ represents low bit reliability
A’ and B’ means the bit reliability values after CTC inner interleaving
‘Sum’ shows the sum of the bit reliability values for each decoding trellis transition.
As shown in the table, the proposed bit grouping method evenly distributes the bit
reliabilities along whole decoding trellis transitions
Bit Reliability
Subblocks
DEC
#1
DEC
#2
16e Bit grouping
Proposed Bit grouping
A
000011111111000000001111
000011111111000000001111
B
000011111111000000001111
111100000000111111110000
Sum
000022222222000000002222
111111111111111111111111
A’
001110100101011010001101
100100001111110000100111
B’
001110100101011010001101
011011110000001111011000
Sum
002220200202022020002202
111111111111111111111111
Simulation assumption

MCS table
MCS index
Modulation
Code rate
0
QPSK
31/256
1
QPSK
48/256
2
QPSK
71/256
3
QPSK
101/256
4
QPSK
135/256
5
QPSK
171/256
6
16QAM
102/256
7
16QAM
128/256
8
16QAM
155/256
9
16QAM
184/256
10
64QAM
135/256
11
64QAM
157/256
12
64QAM
181/256
13
64QAM
205/256
14
64QAM
225/256
15
64QAM
237/256
Simulation assumption
FEC block sizes NEP
Codeword size
Bit grouping methods
Decoding algorithm
MCS
Channel
960, 1000
 N EP / R 
 M M


, where M is modulation order and R is code rate.
Option-1
16e Bit grouping method [1]
Option-2
Bit grouping method from Huawei, Samsung and
MediaTek joint proposal [2]
Option-3
Proposed bit grouping method
Max-Log-MAP decoding with
- 8 decoding iterations
- Scaling factor: 0.75
10 MCS levels have been used.
- MCS indices of 6~15 in the MCS table
AWGN
Simulation result with NEP = 960
Simulation result with NEP = 960
Simulation result with NEP = 960
Simulation result with NEP = 1000
Simulation result with NEP = 1000
Simulation result with NEP = 1000
Simulation result with NEP = 1920
Simulation result with NEP = 1920
Simulation result with NEP = 1920
Conclusion

Comparing to Option-1 IEEE 802.16e Bit grouping method,
Performance
Complexity
(Additional
Blocks)

Option-2 [2]
Option-3: Proposed method
Case NEP=960,
-Better than Option-1
Case NEP=960,
- Better than Option-1
- Almost same as Option-2
Case NEP=1000,
- Almost same as Option-1
Case NEP=1000,
- Almost same as Option-1
Case NEP=1920,
- Better than Option-1
Case NEP=1920,
- Better than Option-1
- Almost same as Option-2
C-symbol permutation blocks for each
subblock
 Depending on modulation order,
different permutation patterns are used.
Only one circular shift block for the interleaved
B subblock sequence
According to above comparisons, we propose Option-3 bit grouping method
for IEEE 802.16m CTC.
Reference
[1] IEEE P802.16 Rev2/D9, “Draft IEEE Standard for Local and Metropolitan
Area Networks: Air Interface for Broadband Wireless Access,” Jan. 2009.
[2] IEEE C802.16m 09/0665, “Proposed Text of CTC Bit grouping for IEEE
802.16m Amendment” Mar.2009
Proposed Text
---------------------------------------- Text Start -------------------------------------15.13.1.x.x.x.x Bit grouping
After subblock interleaving, the interleaved sequence of the sub block B is
circularly shifted to the left once as follows.
BShift (i )  B((i  1) mod N ), where i  0 ... N  1
The output sequence of bit grouping shall consist of the interleaved A subblock
sequence and BShift subblock sequence followed by the bit-by-bit multiplexed
sequence of Y1 and Y2 sub blocks, followed by the bit-by-bit multiplexed sequence
of W1 and W2 subblock.
The bit-by-bit multiplexed sequence of interleaved Y1 and Y2 subblock sequences
shall consist of the first output bit from the Y1 subblock interleaver, the first output
bit from the Y2 subblock interleaver, the second output bit from the Y1 subblock
interleaver, the second output bit from the Y2 subblock interleaver, etc, The bit-bybit multiplexed sequence of interleaved W1 and W2 subblock sequences shall
consist of the first output bit from the W1 subblock interleaver, the first output bit
from the W2 subblock interleaver, the second output bit from the W1 subblock
interleaver, the second output bit from the W2 subblock interleaver, etc.
Figure xxx shows the interleaving and the bit grouping scheme.
Proposed Text
Figure xxx. Block diagram of the interleaving and bit grouping scheme
------------------------------------------ Text End-----------------------------------------