Proposed Randomization for 16m
Document Number: S80216m-09/1415r1
Date Submitted: 2009-07-10
Source:
Changlong Xu, Tom Harel, Huaning Niu, Jong-Kae Fwu, Yang-Seok Choi, Hujun Yin
Intel Corporation
Venue:
IEEE Session #62, San Francisco, US.
Re:
Base Contribution:
N/A
Purpose:
To be discussed and adopted by TGm for the 802.16m amendment.
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1
Outline
• Data randomization and subcarrier randomization in 16e
• Data randomization in current AWD text
• Proposed randomization
• Performance comparison
• Summary
2
1. Data randomizer and subcarrier
randomizer in 16e
Subcarrier
randomizer
Data to
transmit in
PHY burst
Randomizer
(8.4.9.1)
FEC
(8.4.9.2)
Bit-interleaver
(8.4.9.3)
Repetition
(8.4.9.5)
Modulation
(8.4.9.4)
Mapping to
OFDMA
subchannels
Figure 1 Channel coding process for regular and repetition coding transmission
3
1.1 Data randomizer
LSB
MSB
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
data out
data in
• Generator polynomial 1 + x14+x15
• Initial Vector [LSB] 0 1 1 0 1 1 1 0 0 0 1 0 1 0 1 [MSB] –Each FEC block
• Function Avoiding long runs of bit that are bad for modulator.
4
1.2 Subcarrier Randomizer
LSB
1
MSB
2
3
4
5
6
7
8
9 10 11
wk
•
•
Generator polynomial 1 + x9+ x11
Initial Vector - Each sub-frame
– b0 .. b4 5 LSB of IDcell
– b5,b6 the segment number + 1
– b7..b10 0b1111 for downlink; four least significant bits of the Frame
number in the uplink.
•
Function
– Randomize the interference between different cells
– Avoid exact repetition of QAM symbol. Repetition within an OFDM
symbol causes high PAPR and repetitive interference.
5
2. Data randomization in current AWD text
Subcarrier
randomizer
Work well?
Burst
CRC
encoder
Data
Randomizer
Burst
partition
FEC
block
CRC
encoder
FEC
encoder
Bit selection
&
Repetition
Collection
Modulation
Figure 2 Channel coding procedure in current AWD text
Problem:
Data Randomize is same as that in 16e. It is easy to consider the subcarrier
randomizer in 16e.
Reusing subcarrier randomizer in 16e do not work:
1.
Only 7-bit in initial vector for IDcell indicator. 10-bit IDcell is used in 16m.
2.
Different users in same cell has same initial vector may cause interference
each other for MU-MIMO case.
6
3. Proposed randomization
Move randomizer to the position before the modulation
Burst
CRC
encoder
Data
Randomizer
Burst
partition
FEC
block
CRC
encoder
FEC
encoder
Bit selection
&
Repetition
Collection
Modulation
• Low complexity (one randomizer instead of the two randomizer in
• Good performance
– Randomize the interference between adjacent cell
– Avoid exact repetition of QAM symbol
– Avoiding long runs of bit
7
Parameters for proposed randomization
LSB
1
Data in
MSB
2
3
4
5
6
. . .
18 19 20 21 22 23
Data out
•
Generator polynomial 1 + x18+x23
•
Initial Vector
b13 … b22 IDcell
b12
1 (avoid all zero initial state)
b0 … b11 STID
Reset the seed for each burst
8
4. Performance comparison
-Scenario
All zero’s
sequence for
padding
FEC
encoder
Modulation
Case 1: Without Randomization
All zero’s
sequence for
padding
Data
Randomizati
on
FEC
encoder
Modulation
IFFT
Case 2: Current AWD
All zero’s
sequence for
padding
Data
Randomizati
on
FEC
encoder
Modulation
Subcarrier
randomizat
ion
IFFT
Case 3: 16e solution
All zero’s
sequence for
padding
FEC
encoder
Proposed
randomizat
ion
Modulation
Case 4: Proposed solution
IFFT
9
4.1 CDF for average power of modulator
•
Assumption
–
–
–
–
1/3 CTC, 64QAM
All zero’s sequence source (padding)
2^14 symbols for randomizer in AWD
2^23/6 symbols for proposed randomizer
•
Results
–
–
Always maximum power without randomizer
Both of proposed randomizer and randomizer
in AWD can mitigate the high power of
modulator caused by long run of 0’s or 1’s 10
4.2 CDF for correlation of two adjacent cells
•
Assumption
–
–
–
–
First cell ID 0100000000
Second cell ID 0010000000
1024 IFFT
All zero’s sequence source
•
Results
– The correlation results of proposed
randomizer is less than 10% of 16e solution
– 16e Solution does not work
11
– The proposed randomizer works well
5. Summary
• Proposed a new randomizer instead of the original one in current
AWD
• Merit of the proposed randomizer
– Low complexity (one randomizer instead of the two randomizer in 16e)
– Good performance
• Randomize the interference between adjacent cell
• Avoid exact repetition of QAM symbol
• Avoiding long runs of bit
12