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:

Notice: This document has been prepared to assist IEEE 802.22. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein.

Release: The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.22.

Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures http://standards.ieee.org/guides/bylaws/sb-bylaws.pdf including the statement "IEEE standards may include the known use of patent(s), including patent applications, provided the IEEE receives assurance from the patent holder or applicant with respect to patents essential for compliance with both mandatory and optional portions of the standard." Early disclosure to the Working Group of patent information that might be relevant to the standard is essential to reduce the possibility for delays in the development process and increase the likelihood that the draft publication will be approved for publication. Please notify the Chair Carl R. Stevenson as early as possible, in written or electronic form, if patented technology (or technology under patent application) might be incorporated into a draft standard being developed within the IEEE 802.22 Working Group. If you have questions, contact the IEEE Patent Committee Administrator at patcom@iee.org.

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