Correlated Scrambling Diversity Scheme for 802.16m E-MBS in SFN
Document Number:
IEEE S802.16m-08/893
Date Submitted:
2008-09-17
Source:
Hsien-Wen Chang, Ming-Hung Cheng, Chorng-Ren Sheu,
Ming-Chien Tseng, Chi-Fang (Richard) Li
ITRI
Kun-Yi Lin, Hsin-Piao Lin
NTUT
Shigeo Terabe, Tsuguhide Aoki
Toshiba Corporation
Yong Sun,
Toshiba Research Europe Limited
Venue:
80216m-08/033
Base Contribution:
IEEE C802.16m-08/893r1
Purpose:
Discussion and adoption for 802.16m SDD
Voice: +886-3-5915729
E-mail: [email protected]
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This document does not represent the agreed views of the IEEE 802.16 Working Group or any of its subgroups. It represents only the views of the
participants listed in the “Source(s)” field above. It is offered as a basis for discussion. It is not binding on the contributor(s), who reserve(s) the right to add,
amend or withdraw material contained herein.
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Copyright
2008 ITRI 工業技術研究院
Correlated Scrambling
Diversity Scheme for
802.16m E-MBS in SFN
Hsien-Wen Chang, Ming-Hung Cheng, Chorng-Ren Sheu,
Ming-Chien Tseng, Chi-Fang (Richard) Li
ITRI
Kun-Yi Lin, Hsin-Piao Lin
NTUT
Shigeo Terabe, Tsuguhide Aoki
Toshiba Corporation
Yong Sun,
Toshiba Research Europe Limited
Outline
• Background
• Proposed correlated scrambling diversity
scheme
• Simulation results
• Conclusion
Copyright 2008 ITRI 工業技術研究院
BACKGROUND
Copyright 2008 ITRI 工業技術研究院
SFN and cell edge problem
• 802.16m can be used as a
digital broadcast mechanism
through a Single Frequency
Network (SFN).
f
• At the cell edge between
transmitters in an SFN, a
e
receiver may receive the
same signal from two
transmitters almost
simultaneously.
Copyright 2008 ITRI 工業技術研究院
LOS path
Reflected path
g
c
a
h
b
i
d
j
Delay spread and channel response
Signal
Amp.
1st
path
2nd
path
1. large multipath
delay spread Dt
t
t
3rd
path
Channel
Response
0dB
nth
path
…
t … tn
delay
freq
coherent
bandwidth (over which the channel can
Dt
be considered "flat")
1st
2nd
path path
Signal
Amp.
2. small multipath
delay spread
(transmitter edge)
3rd
path
Channel
Response
0dB
nth
path
…
tt t … tn
delay
coherent
bandwidth
Dt
1st
path
Signal
Amp.
3. small multipath
delay spread and
inversed phase
rotation
Channel
Response
0dB
3rd
path
Threshold
value
t
t
Dt
freq
…
2nd
path
delay
coherent
bandwidth
freq
t
Copyright 2008 ITRI 工業技術研究院
6
OFDM and channel diversity
• Multi-carrier transmission
technique
• Channel coding together with
time interleaving technique
can correct the faded signal
parts by non-faded parts.
• It’s important to “create”
diversity for solving the
problem at cell edge.
Tx signal
spectrum
Channel
response
Rx signal
spectrum
Copyright 2008 ITRI 工業技術研究院
Frequency
PROPOSED CORRELATED
SCRAMBLING DIVERSITY
SCHEME
Copyright 2008 ITRI 工業技術研究院
Correlated scrambling diversity (CSD)
Phase of each sub-carrier is rotated by multiplying a scrambling
symbol which has unity gain (to keep signal power) and correlated
phase for contiguous sub-carriers.
ha
Transmitter A
p
p
p
p
p
p
p
p
p
p
p
p
p
p
p
p
p
p
p
p
an
ne
ta
The composite channel is sum of the
scrambled channels between the
receiver and each transmitter
t
lA
ha
Received Signal
Time
p
p
p
p
p
p
p
p
p
Independent to each other
p
p
p
p
Transmitter B
p
p
p
p
p
p
p
p
p
p
p
p
p
p
p
p
p
p
p
p
p
p
Copyright 2008 ITRI 工業技術研究院
p
p
p
p
p
Pattern Phase Response
Frequency
Time
p
p
p
p
p
C
p
p
p
hb
Composite Channel Response
p
p
Ch
Frequency
p
Pattern Phase Response
Frequency
Time
p
Freq.
n
han
el B
hb
tb
t
9
Apply CSD to the system
TX 1
Channel
Encoder
Bit
Interleaver
Modulator
OFDM
Multiplexer
Correlated
Scrambler
IFFT
RX
...
FFT
Symbol
Demapper
OFDM
Demultiplexer
TX M
Channel
Encoder
Bit
Interleaver
Modulator
OFDM
Multiplexer
Correlated
Scrambler
Tim
IFFT
Correlated Scrambler
Frequency
Scrambling Symbol
Generator
The scrambling symbols can
be correlated in frequency or
time domain, or both.
Copyright 2008 ITRI 工業技術研究院
Bit
Deinterleaving
e
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
Channel
Decoder
OFDM MUX
Symbol
10
CSD pattern generation example
e
Correlated Scrambler
Path
Generator
Doppler
Freq.
tim
Fourier
Transform
Scale &
Shift
τ
delay
With controllable Doppler
frequency, scrambling symbols
are correlated in time domain
in addition to frequency domain.
Frequency
Tim
e
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
Copyright 2008 ITRI 工業技術研究院
P
OFDM MUX
Symbol
SIMULATION RESULTS
Copyright 2008 ITRI 工業技術研究院
Simulation parameters
Parameter
Value
Channel bandwidth
10 MHz
Number of subcarriers
1,024
Subcarrier permutation
PUSC
Cyclic prefix
1/8
Modulation and Code rate
16-QAM 1/2
Channel coding
Convolutional turbo code (CTC)
FEC data block size
480 bits
Carrier frequency
2.5 GHz
Simulation time
3 sec
Number of cells
2
Channel model
ITU Vehicular A (VA) or single-path
Mobile station speed
30 km/hr
Channel estimation
Cluster based linear interpolation
Copyright 2008 ITRI 工業技術研究院
Simulation results: single-path
Coded BER v.s. SNR under 2 single-path channel
0
10
No diversity / Practical CE
/ Ideal CE
Proposed CSD / Practical CE
/ Ideal CE
-1
10
-2
Coded BER
10
-3
10
-4
Observation:
The proposed CSD scheme provides more
than 8 dB diversity gain to original system
for BER=10-3 considering single-path
channel.
10
-5
10
-6
10
5
10
15
20
SNR (dB)
Copyright 2008 ITRI 工業技術研究院
25
30
35
Simulation results: VA channel
Coded BER v.s. SNR under 2 VA channel
0
10
No diversity / Practical CE
/ Ideal CE
Proposed CSD / Practical CE
/ Ideal CE
-1
10
Observation:
For more realistic VA channel model,
proposed CSD scheme still exhibit 4
dB gain to original system for
BER=10-3.
-2
Coded BER
10
-3
10
-4
10
-5
10
-6
10
5
10
15
20
SNR (dB)
Copyright 2008 ITRI 工業技術研究院
25
30
35
CONCLUSION
Copyright 2008 ITRI 工業技術研究院
• In SFN, UE at cell edges experiencing flat
and/or slow fading cannot operate well.
• A novel correlated scrambling diversity
scheme is proposed to overcome this
problem.
• Through simulations the proposed scheme
has provided significant diversity gain
compared to the original system.
Copyright 2008 ITRI 工業技術研究院
Proposed text in SDD
15. Support for Enhanced Multicast Broadcast Service
15.x Correlated Scrambling Diversity Scheme
Correlated scrambling diversity (CSD) scheme can be considered for 802.16m systems. Each base
station generates its correlated scrambling pattern independently to others and applies it to the
transmitted signal as follows.
csd
X csd
m  Dm  X
j 
j 
j 
 is the
,e
,, e
where X  X , X ,, X  is the encoded signal to be transmitted, and Dcsd
m  e
j
scrambling pattern for m-th BS, e is the scrambling symbol for k-th subcarrier of m-th BS.
Scrambling patterns can be generated as follows. Let g be an Nx1 vector, and
T
1
2
m ,1
m, 2
m ,N
T
N
m ,k
 1 j a
 2  e , for n  1,
 j
1  e b , for n  1  d ,
gn  
 1  e j c , for n  1  2d ,
2
0, otherwise,

where g n denotes the n-th element of g, 2d is path delay of the pattern generator, and
random phase ranging between   .
Copyright 2008 ITRI 工業技術研究院
i , i  a, b, c
is a
Proposed text in SDD
Next, let G be the N-point DFT of g. Then, the phases of the scrambling symbols can be chosen as
Θ  1 , 2 ,, N 
T


 G  G min 
2
,
G MAX  G min
where |G|MAX and |G|min means the maximum and minimum value of , respectively.
N
The coherent bandwidth of the pattern, in terms of subcarrier spacing, is proportional to 2d , and
should be larger than frequency spacing between contiguous pilots for the ease of channel
estimation.
Copyright 2008 ITRI 工業技術研究院