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transcript
March 2007
Chang-Joo Kim, ETRI
Slide 1
doc.: IEEE 802.22-07-0114-00-0000
Submission
[Simulation results on 2 or 3 repetitions of preamble structure]
IEEE P802.22 Wireless RANs Date: 2007-03-12
Authors:
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Name Company Address Phone email Chang-Joo Kim ETRI Korea +82-42-860-1230 cjkim@etri.re.kr
Myung-Sun Song ETRI Korea +82-42-860-5046 mssong@etri.re.kr
Gwang-Zeen Ko ETRI Korea +82-42-860-4862 gogogo@etri.re.kr
Sung-Hyun Hwang ETRI Korea +82-42-860-1133 shwang@etri.re.kr
Jung-Sun Um ETRI Korea +82-42-860-4844 korses@etri.re.kr
March 2007
Chang-Joo Kim, ETRI
Slide 2
doc.: IEEE 802.22-07-0114-00-0000
Submission
Abstract
In this presentation, we will show the simulation results for initial synchronization regarding the number of repetitions within frame preamble. Through the simulation results, we can find that the preamble with 2 repetitions has good performances in preamble detection and carrier frequency offset estimation.
March 2007
Chang-Joo Kim, ETRI
Slide 3
doc.: IEEE 802.22-07-0114-00-0000
Submission
TDD Frame Structure
1-st Frame 2-nd Frame 3-rd Frame Last Frame
Superframe
10ms 10ms 10ms 10ms
SC
H
FC
H, D
S/U
S M
AP
DSDATA
USDATA
n-th Frame
10ms
FC
H, D
S/U
S M
AP
DSDATA
USDATA
Pilot Data
March 2007
Chang-Joo Kim, ETRI
Slide 4
doc.: IEEE 802.22-07-0114-00-0000
Submission
CR-OFDMA PHY Simulator
AWGN
FromMAC
ToMAC
Superframe&
FrameEncoder
RandomizerEncoderPuncturer
&Interleaver
MapperS/ PSubcarrierAllocator
Preamble&
PilotInsertor
IFFT
GuardInsertor
P/ S
Channel
Frequency& Timing
Offset
S/ PGuard
Remover
Synchronizer
FFT
ChannelEstimator
SubcarrierDeallocator P/ S
De-mapper
De-interleaver
&Depuncturer
DecoderDe-
randomizer
Superframe&
FrameDecoder
UncodedBit ER/ Block ER
Tester
CodedBit ER/ Block ER
Tester
SYMBOL-WISE SIGNAL PROCESSING BLOCK BIT-WISE SIGNAL PROCESSING BLOCK
CHANNEL
BLO
CK
March 2007
Chang-Joo Kim, ETRI
Slide 5
doc.: IEEE 802.22-07-0114-00-0000
Submission
Details of Synchronization Block
ADCDigitalFilter
FFOFSIFOPA
STOCompensation
STOFS
CPRemover
FFT FEQSubcarrierDeallocator
Demapper
( )*
| |
Z-NFFT/ 2
NGINFFT 2/
NW Find
MaxSTOFSFFOFS
( )*Z-7* TSYM
NP
tan-1( )
PreambleGenerator
( )*Z-v
( )*Z-2
Z-(v+2)
FFOPILOT
NPA Find
Max I FOPA
March 2007
Chang-Joo Kim, ETRI
Slide 6
doc.: IEEE 802.22-07-0114-00-0000
Submission
Algorithms of Initial Synchronization
• Timing synchronization– By using auto-correlation in time-domain between two received
samples apart from NFFT/2 or NFFT/3
• Fractional Frequency Offset Estimation– By calculating the phase at the point of optimum timing in time-
domain
• Integer Frequency Offset Estimation– By using cross-correlation with PN sequences of NFFT/2 or
NFFT/3 in frequency-domain
March 2007
Chang-Joo Kim, ETRI
Slide 7
doc.: IEEE 802.22-07-0114-00-0000
Submission
Timing Sync. using 2 Repetitions
• Auto-correlation of preamble with 2 repetitions
GI NFFT/ 2 NFFT/ 2
Auto-correlation
OFDMA symbol
March 2007
Chang-Joo Kim, ETRI
Slide 8
doc.: IEEE 802.22-07-0114-00-0000
Submission
Timing Sync. using 2 Repetitions (Cont’d)
• Auto-correlation result– Acquisition range: -GI/2 ~ +GI/2
AcquisitionRange
GI NFFT/ 2 NFFT/ 2 GI NFFT/ 2 NFFT/ 2
PreambleStart
March 2007
Chang-Joo Kim, ETRI
Slide 9
doc.: IEEE 802.22-07-0114-00-0000
Submission
Timing Sync. using 3 Repetitions
• Auto-correlation of preamble with 3 repetitions
GI NFFT/ 3
Auto-correlation
OFDMA symbol
NFFT/ 3 NFFT/ 3
March 2007
Chang-Joo Kim, ETRI
Slide 10
doc.: IEEE 802.22-07-0114-00-0000
Submission
Concerns on Timing Sync. using 3 Repetitions
• 2048 FFT size is not divided by 3, i.e. 2048/3=682.666=682+2/3
• Therefore, preamble has 3 repetitions with timing offset of 2/3 sub-carrier spacing by birth
• It means that there will be no perfect repetitions in the time domain
• It will disturb the robust initial synchronization
March 2007
Chang-Joo Kim, ETRI
Slide 11
doc.: IEEE 802.22-07-0114-00-0000
Submission
Concerns on Timing Sync. using 3 Repetitions (Cont’d)
• 3 repetitions with timing offset of 2/3 sub-carrier spacing
Start point of2nd
repetitions
2K FFT size
1 682683
13651366
2048
Start point of3rd
repetitions
Start point of1st
repetitions
March 2007
Chang-Joo Kim, ETRI
Slide 12
doc.: IEEE 802.22-07-0114-00-0000
Submission
Concerns on Timing Sync. using 3 Repetitions (Cont’d)
• 3 repetitions with timing offset of 2/3 sub-carrier spacing
0 10 20 30 40 50 60 70 80 90 100-0.03
-0.02
-0.01
0
0.01
0.02
0.03
Subcarrier index
Am
plitu
de (
in-p
hase
)
Overlapped preamble of 3 repetitions
First portion of preambleSecond portion of preambleThird portion of preamble
March 2007
Chang-Joo Kim, ETRI
Slide 13
doc.: IEEE 802.22-07-0114-00-0000
Submission
Phase Margin in FFO Estimation
)(ny
2/)()4/( jFFT enyNny
3/2)()3/( jFFT enyNny
jFFT enyNny )()2/(
23
4
March 2007
Chang-Joo Kim, ETRI
Slide 14
doc.: IEEE 802.22-07-0114-00-0000
Submission
Simulation Conditions
• WRAN channel B, C
• Normalized frequency offset: 5.5
• Symbol timing offset: 2560 samples
• 2K FFT, ¼ guard interval mode
• BPSK modulation
• Pilots in preamble are boosted to have equal power regardless of preamble structure
March 2007
Chang-Joo Kim, ETRI
Slide 15
doc.: IEEE 802.22-07-0114-00-0000
Submission
Simulation Results
• Preamble Missing Probability
• Mean-Squared Error of Symbol Timing Offset (STO)
• Mean-Squared Error of Fractional Frequency Offset (FFO)
• Mean-Squared Error of Carrier Frequency Offset (CFO, i.e. Fractional Frequency Offset and Integer Frequency Offset)
March 2007
Chang-Joo Kim, ETRI
Slide 16
doc.: IEEE 802.22-07-0114-00-0000
Submission
Correlation Result of Frame Sync
March 2007
Chang-Joo Kim, ETRI
Slide 17
doc.: IEEE 802.22-07-0114-00-0000
Submission
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
-10 -5 0 5 10
SNR (dB)
Mis
sin
g P
rob
abili
ty
2 Rep.(WRAN B)3 Rep.(WRAN B)2 Rep.(WRAN C)3 Rep.(WRAN C)
Missing Probabilityfor I EEE802.22 WRAN System- 2K FFT- Modulation: BPSK
Preamble Missing Probability
In the IEEE Std 802.11-1997 section 14.6.15.3, the detection is expected to be 90% accurate even in fairly good conditions
March 2007
Chang-Joo Kim, ETRI
Slide 18
doc.: IEEE 802.22-07-0114-00-0000
Submission
MSE of STO Estimate
1.0E- 01
1.0E+00
1.0E+01
1.0E+02
1.0E+03
1.0E+04
1.0E+05
1.0E+06
1.0E+07
1.0E+08
- 10 - 5 0 5 10 15 20 25 30 35
SNR (dB)
MS
E o
f S
TO
Est
imate
2 Rep.(AWGN)3 Rep.(AWGN)2 Rep.(WRAN B)3 Rep.(WRAN B)2 Rep.(WRAN C)3 Rep.(WRAN C)
MSE of STO Estimatefor IEEE802.22 WRAN System- 2K FFT- Modulation: BPSK
March 2007
Chang-Joo Kim, ETRI
Slide 19
doc.: IEEE 802.22-07-0114-00-0000
Submission
MSE of FFO Estimate
1.0E- 08
1.0E- 07
1.0E- 06
1.0E- 05
1.0E- 04
1.0E- 03
1.0E- 02
1.0E- 01
1.0E+00
- 10 - 5 0 5 10 15 20 25 30 35
SNR (dB)
MS
E o
f S
TO
Est
imate
2 Rep.(AWGN)3 Rep.(AWGN)2 Rep.(WRAN B)3 Rep.(WRAN B)2 Rep.(WRAN C)3 Rep.(WRAN C)
MSE of FFO Estimatefor IEEE802.22 WRAN System- 2K FFT- Modulation: BPSK
March 2007
Chang-Joo Kim, ETRI
Slide 20
doc.: IEEE 802.22-07-0114-00-0000
Submission
1.0E- 08
1.0E- 07
1.0E- 06
1.0E- 05
1.0E- 04
1.0E- 03
1.0E- 02
1.0E- 01
1.0E+00
1.0E+01
- 10 - 5 0 5 10 15 20 25 30 35
SNR (dB)
MS
E o
f S
TO
Est
imate
2 Rep.(AWGN)
3 Rep.(AWGN)
2 Rep.(WRAN B)3 Rep.(WRAN B)
2 Rep.(WRAN C)
3 Rep.(WRAN C)
MSE of CFO(FFO+IFO) Estimatefor IEEE802.22 WRAN System- 2K FFT- Modulation: BPSK
MSE of CFO (FFO+IFO) Estimate
In the IEEE Std 802.16-2004 section 8.4.14.1, CPE shall be synchronized to the BS with a tolerance of maximum 2% of sub-carrier spacing
March 2007
Chang-Joo Kim, ETRI
Slide 21
doc.: IEEE 802.22-07-0114-00-0000
Submission
Conclusions
No. of repetitionsItems
2 3 Note
SNR for 90% Preamble Detection
-5 dB -3 dBIn WRAN Channel
C
Estimation Range
in Time-Domain
-1.0 +1.01)
-1.5 +1.5
Normalized to sub-carrier spacing
SNR for 2% MSE
of CFO Estimate2 dB 7 dB
In WRAN Channel C, 2% of
subcarrier spacing
1) Because the integer frequency offset estimation is performed in frequency-domain, the estimation range in time-domain is meaningless.
March 2007
Chang-Joo Kim, ETRI
Slide 22
doc.: IEEE 802.22-07-0114-00-0000
Submission
Conclusions (Cont’d)
• Because integer frequency offset estimation is performed in frequency domain, the frequency offset estimation range in time-domain is meaningless
• Because 2 repetitions preamble has the largest phase margin (refer to slide 13), the accuracy (mean-squared error) of CFO estimation has the best performance.
• Because 3 repetitions preamble has the timing offset of 2/3 sub-carrier spacing by birth, all performances of initial synchronization are severely deteriorated