August 2006

Sunghyun Hwang, ETRI

Slide 1

doc.: IEEE 802.22-06-0170-01-0000

Submission

[ETRI’s Simulation Results for OFDMA Parameters]

IEEE P802.22 Wireless RANs Date: 2006-09-18

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

Soon-Ik Jeon ETRI Korea +82-42-860-5947 sijeon@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

Bub-Joo Kang ETRI Korea +82-42-860-5446 kbj64370@etri.re.kr

Hyung-Rae Park ETRI Korea +82-2-300-0143 hrpark@mail.hangkong.ac.kr

Yun-Hee Kim ETRI Korea +82-31-201-3793 yheekim@khu.ac.kr

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.

August 2006

Sunghyun Hwang, ETRI

Slide 2

doc.: IEEE 802.22-06-0170-01-0000

Submission

Abstract

In this presentation, we show the simulation results for OFDMA parameters in various WRAN environments. First, we present the performances focusing on the timing synchronization and carrier frequency offset estimation using preamble only. Second, we present the performances on channel estimation for various preamble and pilot pattern. Lastly, we present the performances on tracking of frequency offset.

Based on our simulation results, we propose the modified preamble and pilot pattern.

August 2006

Sunghyun Hwang, ETRI

Slide 3

doc.: IEEE 802.22-06-0170-01-0000

Submission

Contents

• System parameters & OFDMA parameters (for 6MHz)

• Frame structure with preamble & pilot pattern

• Algorithms & operation procedure– Top block diagram of PHY simulator

– System model for synchronization

– Initial synchronization: Timing & CFO(IFO+FFO) estimation

– Channel estimation

– FFO tracking

• Simulation conditions

• Simulation results

• Conclusions

• Modified frame structure with preamble & pilot pattern

• Further works

August 2006

Sunghyun Hwang, ETRI

Slide 4

doc.: IEEE 802.22-06-0170-01-0000

Submission

System Parameters &OFDMA Parameters

August 2006

Sunghyun Hwang, ETRI

Slide 5

doc.: IEEE 802.22-06-0170-01-0000

Submission

System Parameters/Single Channel (6MHz)

Mode 1K 2K 4K 6K

FFT Size 1024 2048 4096 6144

Bandwidth(k = 1, 2, …, 6)

k MHz

Sampling Factor 8/7

No. of Used Subcarriers(including pilot, but not DC)

140 * k 280 * k 560 * k 840 * k

Sampling Frequency 48/7 MHz

Subcarrier Spacing 6.696 kHz(***) 3.348 kHz 1.674 kHz 1.116 kHz

Occupied Bandwidth 6.696 kHz*140*k 3.348 kHz*280*k 1.674 kHz*560*k 1.116 kHz*840*k

Bandwidth Efficiency(*) 93~94 %

FFT Time 149.33 us 298.66 us 597.33 us 896 us

Cyclic Prefix Time(**) 37.33 us 74.66 us 149.33 us 224 us

OFDMA Symbol Time 186.66 us 373.33 us 746.66 us 1120 us

(*) Bandwidth Efficiency = Subcarrier Spacing * (Number of Used Subcarriers + 1)/BW(**) It is assumed that cyclic prefix mode is 1/4.(***) Italics indicate an approximated value.

August 2006

Sunghyun Hwang, ETRI

Slide 6

doc.: IEEE 802.22-06-0170-01-0000

Submission

OFDMA Parameters (2K FFT Mode)

Parameter1 TV bands

6 7 8

Inter-carrier spacing, F (Hz) (*) 3348 3906 4464

FFT period, TFFT (s) (*) 298.66 256.00 224.00

Total no. of sub-carriers, NFFT 2048

No. of guard sub-carriers, NG (L, DC, R) 368 (184,1,183)

No. of used sub-carriers, NT = ND + NP 1680

No. of data sub-carriers, ND 1440

No. of pilot sub-carriers, NP 240

No. of sub-carriers per BIN 14 (12 datas + 2 pilots)

No. of BIN per subchannel 4

No. of sub-carriers per subchannel 56 (48 datas + 8 pilots)

Occupied bandwidth (MHz) (*) 5.628 6.566 7.504

Bandwidth Efficiency (%) (**) 93.8(*) Italics indicate an approximated value.(**) Bandwidth Efficiency = Subcarrier Spacing * (Number of Used Subcarriers + 1)/BW

August 2006

Sunghyun Hwang, ETRI

Slide 7

doc.: IEEE 802.22-06-0170-01-0000

Submission

Frame Structurewith Preamble & Pilot Pattern

August 2006

Sunghyun Hwang, ETRI

Slide 8

doc.: IEEE 802.22-06-0170-01-0000

Submission

Two Approaches of Frame Structure

• In our simulations, we consider two types of frame structure with preamble and pilot pattern.

• 1st Frame Structure– General frame structure

– With a preamble of one OFDMA symbol and the appropriate pilots

– The pilots are inserted in the header and data field.

• 2nd Frame Structure– Novel frame structure

– With a preamble of two OFDMA symbol and no pilots

– The header and data are purely transmitted without pilots.

August 2006

Sunghyun Hwang, ETRI

Slide 9

doc.: IEEE 802.22-06-0170-01-0000

Submission

TDD Frame Structure I

TDD Frame

Prea

mbl

e (1

OFD

MA s

ymbo

l)

Data with pilots

DL

Data with pilots

ULTTG RTG

FCH

, DL/

UL

MAP

wit

h pi

lots

Prea

mbl

e (1

OFD

MA s

ymbo

l, if

nece

ssar

y)

August 2006

Sunghyun Hwang, ETRI

Slide 10

doc.: IEEE 802.22-06-0170-01-0000

Submission

Preamble Pattern

• Two repetitions within one OFDMA symbol

• GI=1/4 (fixed)

• Preamble shall be modulated using BPSK modulation

• Used in channel estimation and synchronization

GI

NFFT/2 NFFT/2

NSYM

August 2006

Sunghyun Hwang, ETRI

Slide 11

doc.: IEEE 802.22-06-0170-01-0000

Submission

Preamble Pattern

• Preamble sequence

• PN sequence generator

– Initial states of PN sequence generator: 10001010100– Note that PN sequence has the order of 11 so that the period of

preamble sequence is 2047.• Total 840 chips are used for each preamble

otherwise

NmmkDkP usedm

T0

,4/0,2)21(2)(

otherwise

NmNmkDkP usedusedm

T0

2/4/,12)21(2)(

1)( 211 xxxg

August 2006

Sunghyun Hwang, ETRI

Slide 12

doc.: IEEE 802.22-06-0170-01-0000

Submission

Pilot Pattern of Frame Structure I

• Pilot Structure for Extendable Channel Estimation

• Available Pilot Pattern for Channel Estimation

Pilot

Data

frequency

time

RepetitionUnit

BIN

OFDMA Symbol

CopyCopy

CopyCopyCopyCopyCopyCopy

CopyCopyCopyCopy

August 2006

Sunghyun Hwang, ETRI

Slide 13

doc.: IEEE 802.22-06-0170-01-0000

Submission

TDD Frame Structure II

TDD Frame

Prea

mbl

e (2

OFD

MA s

ymbo

ls)

Pure Data without pilots

DL

Pure Data without pilots

ULTTG RTG

Pure

FCH

, DL/

UL

MAP

wit

hout

pilot

s

Prea

mbl

e (2

OFD

MA s

ymbo

ols,

if

nece

ssar

y)

August 2006

Sunghyun Hwang, ETRI

Slide 14

doc.: IEEE 802.22-06-0170-01-0000

Submission

Preamble Structure for Frame Structure II

• Modified Preamble Structure for Extendable Channel Estimation

• Available Pilot Pattern for Channel Estimation

frequency

time

OFDMA Symbol

Copy Copy Copy Copy Copy Copy CopyCopy Copy Copy Copy Copy Copy

Copy Copy Copy Copy Copy Copy CopyCopy Copy Copy Copy Copy Copy

Copy Copy Copy Copy Copy Copy CopyCopy Copy Copy Copy Copy Copy

Copy Copy Copy Copy Copy Copy CopyCopy Copy Copy Copy Copy Copy

Copy Copy Copy Copy Copy Copy CopyCopy Copy Copy Copy Copy Copy

Copy Copy Copy Copy Copy Copy CopyCopy Copy Copy Copy Copy Copy

Copy Copy Copy Copy Copy Copy CopyCopy Copy Copy Copy Copy Copy

Pilot Null DataNull Pilot Data

PureData

August 2006

Sunghyun Hwang, ETRI

Slide 15

doc.: IEEE 802.22-06-0170-01-0000

Submission

Decision Procedure of Preamble and Pilot Pattern

Yes No

Is it possible to achieve the sufficient performancesin initial synchronization using proposed preamble only?

Yes

Is it possible to achieve the sufficient performancesin tracking without pilots?

No

Reinforce the preamble!

Reinforce the preamble& Remove all pilots

Maintain (or slightly modify)the proposed preamble and pilots

Is it possible to achieve the sufficient performancesin channel estimation using proposed preamble only?

No

Use one preamble symbol& Remove all pilots

Yes

Is it possible to achieve the sufficient performancesin channel estimation using proposed preamble and pilots?

Yes No

Reinforce the preambleand(or) the pilots!

If we assume the phase noise model with PSD(0)=-100 dBc/Hz, the answer is ‘Yes’. However, if the phase noise effect becomes more severe, the answer may be ‘No’.

Frame Structrue II

Frame Structure I

August 2006

Sunghyun Hwang, ETRI

Slide 16

doc.: IEEE 802.22-06-0170-01-0000

Submission

Algorithms &Operation Procedure

August 2006

Sunghyun Hwang, ETRI

Slide 17

doc.: IEEE 802.22-06-0170-01-0000

Submission

Top Block Diagram of WRAN PHY Simulator

RandomizerEncoderPuncturer

&Interleaver

MapperSubcarrierAllocator

S/P

Preamble&

PilotInsertion

IFFT

GuardInsertion

P/S

AWGN

Channel

De-randomizer

DecoderDe-

interleaver&Depuncturer

De-mapper

SubcarrierDeallocator

P/SChannel

Estimation

FFT

GuardRemoval

S/P

Synchronization

FromMAC

ToMAC

Superframe&

FrameEncoder

Superframe&

FrameDecoder

Frequency&TimingOffset

)(kX i)(nxi

)(tx

)(ty

)(kYi

)(nyi

August 2006

Sunghyun Hwang, ETRI

Slide 18

doc.: IEEE 802.22-06-0170-01-0000

Submission

Signal Model for Synchronization

• Transmitted signal

• Received signal with carrier frequency offset (CFO)

• The time-sampled version of the received signal

• Demodulated symbol at the k-th subcarrier in the i-th OFDM symbol

spacing subcarrier theis /1 where,))(()()(1

0

))((2 TfTiTtpekXtxN

kGSYM

TiTtfkji

i

Gsym

offsetfrequency carrier theis ,,)()()()( 0

1

0

2 fwheretwethtxtyM

m

tfjmm

o

timesampling theiswhere,,)()(~)( 2S

nTfj Tnwenyny So

)()()()( )(2 0 kWkHkXeekY iiijTNiNfj

iSGSYM

August 2006

Sunghyun Hwang, ETRI

Slide 19

doc.: IEEE 802.22-06-0170-01-0000

Submission

Timing Synchronization

• With the Schmidl’s method– Autocorrelation method using the following

– The metric

– Timing

1

0

2

1

0

*

|)(|)(

)2/( ,)()()( where

D

n

D

n

ndydM

NDDndyndydP

)(max dTMtd

o

So NTfjenyN

ny )()2

(

)(

|)(|)(

dM

dPdTM

August 2006

Sunghyun Hwang, ETRI

Slide 20

doc.: IEEE 802.22-06-0170-01-0000

Submission

Timing Synchronization

• Enhanced timing metric – to resolve the timing ambiguity in the plateau

– to protect the timing outside the guard interval

2/

2/

)()(W

Ww

wdTMdNM

)(max dNMtd

o

August 2006

Sunghyun Hwang, ETRI

Slide 21

doc.: IEEE 802.22-06-0170-01-0000

Submission

CFO(FFO+IFO) Estimation

• When the timing is obtained, the received samples corresponding to the preamble are given by

• FFO estimates using Preamble in time-domain

))(Re(

))(Im(tan

1ˆ

0

01

tP

tPf

Tf

T o

1ˆ1

jNTfj y(n)ey(n)e)Ny(n So 2/

12/

0

212/

0

* |)(|)2/()((N

n

jN

no enyNnyny)tP

1ˆ1 f

August 2006

Sunghyun Hwang, ETRI

Slide 22

doc.: IEEE 802.22-06-0170-01-0000

Submission

CFO(FFO+IFO) Estimation

• Two components in the CFO

– Only the FFO can be estimated in the time domain

• Integral frequency offset (IFO) estimation– After compensating , the FFT output is given by

(IFO) offsetfrequency Integral :

(FFO) offsetfrequency Fractional

,1,...,1,0,...,1,

:11

2

i

f

fioTf

f

N

njj

i

o eenxy(n)

4

)( oji ekXkY )2()( FFT

August 2006

Sunghyun Hwang, ETRI

Slide 23

doc.: IEEE 802.22-06-0170-01-0000

Submission

CFO(FFO+IFO) Estimation

• IFO estimation– We can obtain the IFO using the correlation of the PN sequence

• Total CFO estimation range:

g

kY

gkPkYgkPkY

gF

c

c

Sk

TSk

T

,

|)(|

)2()()22()2(

)(2

**

|)(|maxˆ gFg

i

12ˆ12

August 2006

Sunghyun Hwang, ETRI

Slide 24

doc.: IEEE 802.22-06-0170-01-0000

Submission

CFO(FFO+IFO) Estimation Range

• Requirements on the CFO estimation– BS : 2 ppm

– CPE : 8 ppm

• Worst case scenario– BS - CPE : 10 ppm at the frequency of 862 MHz

– CFO estimation up to -8.62 kHz ~ 8.62 kHz

• Estimation with the proposed preamble– Estimation range in the time domain: -3.348 kHz ~ 3.348 kHz

– We should estimate IFO in (-2 ,2) (1 PN offset)

– Even though the proposed method can estimate the IFO up to 682, we set the estimation range as (-8, 8) at the receiver.

August 2006

Sunghyun Hwang, ETRI

Slide 25

doc.: IEEE 802.22-06-0170-01-0000

Submission

FFO Tracking Algorithms

• FFO estimation using GI in the time-domain

• FFO estimates using GI in the time-domain

)Re(

)Im(tan

2

1ˆ 1

f

Tf

T o 2

1ˆ2

1

22 jNTfj y(n)ey(n)eN)y(n So

1

0

221

0

* |)(|)()(GG N

n

jN

n

enyNnyny

5.0ˆ5.0 f

August 2006

Sunghyun Hwang, ETRI

Slide 26

doc.: IEEE 802.22-06-0170-01-0000

Submission

FFO Tracking Algorithms

• FFO estimation using Pilot in the frequency-domain

• FFO estimates using Pilot in the frequency-domain

where, RG is the ratio of GI size to FFT size

SSYM

SGSYM

TNfjii

iiijTNiNfj

i

ekYkkY

kWkHkXeekY0

0

21

)(2

)()(

)()()()(

symbolOFDMadjacenttheinpilotsbetweenspacingsubcarriertheisand

pilot,ththeofindextheiswhere,

)()()(1

0

221

01

* 0

k

n a

ekYkaYaY

n

N

n

TNfji

N

nnini

P

SSYM

P

)Re(

)Im(tan

)1(2

1ˆ 1

Gf R

4848.0ˆ4848.0 max, f

August 2006

Sunghyun Hwang, ETRI

Slide 27

doc.: IEEE 802.22-06-0170-01-0000

Submission

Channel Estimation

• Received Signal Vector

– Y: received signal vector in the frequency domain

– X: diagonal matrix containing data symbols

– W: AWGN

• At Pilot Positions

XP: diagonal matrix containing pilot symbols

HP: channel response at pilot positions

WXHY

PPPP WHXY

August 2006

Sunghyun Hwang, ETRI

Slide 28

doc.: IEEE 802.22-06-0170-01-0000

Submission

LMMSE Channel Estimation

• Linear minimum mean-squared error (LMMSE) estimation– Minimizes the mean-squared error between the channel response

and .

– High computational complexity but good performance.

• To reduce the complexity in LMMSE estimation, low-rank approximations or partitioned LMMSE may be used.

H H

August 2006

Sunghyun Hwang, ETRI

Slide 29

doc.: IEEE 802.22-06-0170-01-0000

Submission

LMMSE Channel Estimation• Wiener - Hopf Equation

– Assume that the estimator is constrained to be a linear function of .

– The problem is to find the matrix K that minimizes the mean-squared error between and the linear estimator .

– The necessary and sufficient condition for the mean-squared error to be minimized is for the estimation error to be orthogonal to each input sample, which is expressed by the Wiener-Hopf equation.

where is the noisey pilot estimates, is the variance of the channel noise Wp , and RPP is the autocovariance matrix of the noiseless pilots.

H

H PY

PKYH ˆ

PYYHYlmmseYYHYH

PP YRRHRRKYKYHEPPPPPP

11 ˆ0)(

IXRXYYER

XRHYER

nHPPPP

HPPYY

HPPH

HPHY

PP

P

2

ˆ

2np

August 2006

Sunghyun Hwang, ETRI

Slide 30

doc.: IEEE 802.22-06-0170-01-0000

Submission

LMMSE Channel Estimation• LMMSE(Linear Minimum Mean-Squared Error) Estimates

where,

– It also requires to know the covariance matrix of the channel and the average SNR.

lsPPPH

lsHPPnPPPH

PnHPPPP

HPPH

PYYHYlmmse

HISNR

RR

HXXRR

YIXRXXR

YRRHPPP

ˆ

ˆ

ˆ

1

ˆ

112ˆ

12ˆ

1

T

N

NPPls

P

P

X

Y

X

Y

X

YYXH

1

1

1

1

0

01 ...ˆ

22/1 kk XEXE 22

/ nkXESNR

August 2006

Sunghyun Hwang, ETRI

Slide 31

doc.: IEEE 802.22-06-0170-01-0000

Submission

Synchronization & Ch. Estimation Procedure

IFO estimation

PreambleTiming Synchronization

FFO estimation

FFO tracking

Channel Estimation

August 2006

Sunghyun Hwang, ETRI

Slide 32

doc.: IEEE 802.22-06-0170-01-0000

Submission

Simulation Conditions

August 2006

Sunghyun Hwang, ETRI

Slide 33

doc.: IEEE 802.22-06-0170-01-0000

Submission

Simulation Conditions

• Channel coding– 802.16e convolutional coding

– Code rate: 1/2, 2/3, 3/4, 5/6

• Modulation– Data: QPSK, 16QAM, 64QAM

– Preamble, Pilot: BPSK

– No boosting

• FFT size and GI ratio– FFT size: 2K(mandatory)

– GI ratio: 1/4

• Subchannelization– No. of used subcarriers for 2K: 1680 (30 subchannels x 56 subcarriers)

– Subchannel type: Diversity & AMC

August 2006

Sunghyun Hwang, ETRI

Slide 34

doc.: IEEE 802.22-06-0170-01-0000

Submission

Simulation Conditions

• Channel Modeling– AWGN

– Multipath profiles & Doppler: A, B, C, D• Approximation to nearest sampling point

• Jakes Rayleigh modeling method

Multipath Profile A B C D

RMS Delay Spread (us)

2.772 1.956 5.692 16.527(*)

(*) For WRAN profile D, we assume that the 6-th path has the excess delay of 60 us and relative power of -10 dB

August 2006

Sunghyun Hwang, ETRI

Slide 35

doc.: IEEE 802.22-06-0170-01-0000

Submission

Simulation Conditions

• Channel Modeling– Multipath profiles & Doppler

• Channel response of WRAN multipath profile

The span of 10 subcarriers

August 2006

Sunghyun Hwang, ETRI

Slide 36

doc.: IEEE 802.22-06-0170-01-0000

Submission

Simulation Conditions

• Channel Modeling– Carrier frequency offset (CFO) : 8.62 kHz

– Phase noise• Phase noise model in IEEE 802.11 TGn comparison criteria(doc. IEEE 802.11-03/814r31)

where, PSD(0)=-100 dBc/Hz, pole frequency fp=250 kHz, and zero frequency fz=7905.7 kHz

])/(1[

])/(1[)0()(

2

2

p

z

ff

ffPSDfPSD

(a) Ideal (b) PSD(0) = -100 dBc/Hz (c) PSD(0) = -65 dBc/Hz

Constellation [64QAM]

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5

InphaseQuad

ratu

re

Constellation [64QAM]

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5

Inphase

Quad

ratu

re

Constellation [64QAM]

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5

Inphase

Quad

ratu

re

August 2006

Sunghyun Hwang, ETRI

Slide 37

doc.: IEEE 802.22-06-0170-01-0000

Submission

Simulation Results1. Missing probability of preamble starting point2. MSE of CFO estimate (in acquisition)3. MSE of FFO estimate (in tracking)4. Uncoded BER of LMMSE estimation5. Performance comparison for calculation method of covariance matrix6. Performance comparison for frequency offset effect7. Uncoded BER performance using preamble alone8. Uncoded/Coded BER performance under ideal channel estimation

August 2006

Sunghyun Hwang, ETRI

Slide 38

doc.: IEEE 802.22-06-0170-01-0000

Submission

Missing Probability of Preamble Starting Point

• Window size W=64

• Missing probability is defined by the probability that the timing is obtained outside of the guard interval of the preamble.

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

-10 -5 0 5 10 15 20

SNR (dB)

Mis

sing

pro

babi

lity

WRAN profile A

WRAN profile B

WRAN profile D

Missing Probability

for IEEE802.22 WRAN System

- Multipath Fading

- 2K FFT

- Modulation: BPSK

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

August 2006

Sunghyun Hwang, ETRI

Slide 39

doc.: IEEE 802.22-06-0170-01-0000

Submission

MSE of FFO Estimate (Using Preamble)

• }|ˆ{| 2ffEMSE

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

1.E+01

-10 -5 0 5 10 15 20 25 30 35

SNR (dB)

MSE

WRAN profile A

WRAN profile B

WRAN profile D

MSE of FFO Estimate

for IEEE802.22 WRAN System

- Multipath Fading

- 2K FFT

- Modulation: BPSK

August 2006

Sunghyun Hwang, ETRI

Slide 40

doc.: IEEE 802.22-06-0170-01-0000

Submission

MSE of CFO Estimate (Using Preamble)

• }|ˆ{| 2 EMSE

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

1.E+01

-10 -5 0 5 10 15 20 25 30 35 40

SNR (dB)

MSE

WRAN profile A

WRAN profile B

WRAN profile D

MSE of CFO Estimate

for IEEE802.22 WRAN System

- Multipath Fading

- 2K FFT

- Modulation: BPSK

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

August 2006

Sunghyun Hwang, ETRI

Slide 41

doc.: IEEE 802.22-06-0170-01-0000

Submission

Assumptions for FFO Tracking Simulation• Residual frequency offset: 2% of subcarrier spacing

• 2 algorithms for FFO tracking– Using guard interval

– Using pilot

• Consider the phase noise model in IEEE 802.11 TGn comparison criteria

• 2K FFT size & GI ratio of 1/4

August 2006

Sunghyun Hwang, ETRI

Slide 42

doc.: IEEE 802.22-06-0170-01-0000

Submission

MSE of FFO Estimate (Using GI or Pilot)

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

1.E+01

-10 -5 0 5 10 15 20 25 30 35

SNR (dB)

MSE

WRAN profile A(GI)WRAN profile B(GI)WRAN profile C(GI)WRAN profile D(GI)WRAN profile A(PILOT)WRAN profile B(PILOT)WRAN profile C(PILOT)WRAN profile D(PILOT)

MSE of FFO Estimate

for IEEE802.22 WRAN System

- Multipath Fading

- 2K FFT

- CP Ratio: 1/4

- Modulation: QPSK

Using guard interval

Using pilot 2% ofsub-carrier spacing

August 2006

Sunghyun Hwang, ETRI

Slide 43

doc.: IEEE 802.22-06-0170-01-0000

Submission

Assumptions for Channel Estimation Simulation

• 3 Types of Partitioned LMMSE– LMMSE, 1 : Channel estimation using the pilot of each OFDM symbol– LMMSE, 3 : Channel estimation using the pilot of 3 OFDM symbols– LMMSE, 7 : Channel estimation using the pilot of 7 OFDM symbols

• Apply the partitioned LMMSE to reduce the complexity in LMMSE estimation (Subcarrier size = 56).

• Calculation method of covariance matrix– Method 1: Pre-calculation assuming exponential model– Method 2: Real-time calculation using actual measured model

• No channel coding employed• Initial frequency offset: 2KHz

– Assume that the CFO estimation using preamble is successful (< 2% of subcarrier spacing)

– Fine frequency offset tracking loop is ON

August 2006

Sunghyun Hwang, ETRI

Slide 44

doc.: IEEE 802.22-06-0170-01-0000

Submission

Uncoded BER Performance (Profile A, QPSK)

August 2006

Sunghyun Hwang, ETRI

Slide 45

doc.: IEEE 802.22-06-0170-01-0000

Submission

Uncoded BER Performance (Profile A, 64QAM)

August 2006

Sunghyun Hwang, ETRI

Slide 46

doc.: IEEE 802.22-06-0170-01-0000

Submission

Uncoded BER Performance (Profile C, QPSK)

August 2006

Sunghyun Hwang, ETRI

Slide 47

doc.: IEEE 802.22-06-0170-01-0000

Submission

Uncoded BER Performance (Profile C, 64QAM)

August 2006

Sunghyun Hwang, ETRI

Slide 48

doc.: IEEE 802.22-06-0170-01-0000

Submission

Uncoded BER Performance (Profile D, QPSK)

August 2006

Sunghyun Hwang, ETRI

Slide 49

doc.: IEEE 802.22-06-0170-01-0000

Submission

Uncoded BER Performance (Profile D, 64QAM)

August 2006

Sunghyun Hwang, ETRI

Slide 50

doc.: IEEE 802.22-06-0170-01-0000

Submission

Performance Comparison for Calculation Method of Covariance Matrix (Profile C, QPSK)

August 2006

Sunghyun Hwang, ETRI

Slide 51

doc.: IEEE 802.22-06-0170-01-0000

Submission

Performance Comparison for Calculation Method of Covariance Matrix (Profile D, QPSK)

August 2006

Sunghyun Hwang, ETRI

Slide 52

doc.: IEEE 802.22-06-0170-01-0000

Submission

Performance Comparisonfor Frequency Offset Effect (Profile A, QPSK)

August 2006

Sunghyun Hwang, ETRI

Slide 53

doc.: IEEE 802.22-06-0170-01-0000

Submission

Performance Comparisonfor Frequency Offset Effect (Profile A, 64QAM)

August 2006

Sunghyun Hwang, ETRI

Slide 54

doc.: IEEE 802.22-06-0170-01-0000

Submission

Uncoded BER PerformanceUsing Preamble Only (Profile A, QPSK)

August 2006

Sunghyun Hwang, ETRI

Slide 55

doc.: IEEE 802.22-06-0170-01-0000

Submission

Uncoded BER PerformanceUsing Preamble Only (Profile C, QPSK)

August 2006

Sunghyun Hwang, ETRI

Slide 56

doc.: IEEE 802.22-06-0170-01-0000

Submission

Uncoded BER PerformanceUsing Preamble Only (Profile D, QPSK)

August 2006

Sunghyun Hwang, ETRI

Slide 57

doc.: IEEE 802.22-06-0170-01-0000

Submission

Uncoded/Coded Bit Error Rate in AWGN

1.0E-07

1.0E-06

1.0E-05

1.0E-04

1.0E-03

1.0E-02

1.0E-01

1.0E+00

0 2 4 6 8 10 12 14 16

SNR(dB)

Bit

Erro

r Rat

e(Lo

g Sc

ale)

Text

Simulation

QPSK

16QAM

64QAM

Coded Bit ER Performances

for IEEE802.22 WRAN System

- AWGN Environments

- 2K FFT

- Convolutional Coding(16d)

- Code Rate: 1/2

- Encoded Block Size: 36 Bytes

Text: R. Van Nee et al., "OFDM for Wireless

Multimedia Communications," Artech House

Publishers, 2000.

1.0E-07

1.0E-06

1.0E-05

1.0E-04

1.0E-03

1.0E-02

1.0E-01

1.0E+00

0 5 10 15 20 25 30

SNR(dB)

Bit

Erro

r Rat

e(Lo

g Sc

ale)

Theory

Simulation

QPSK

16QAM

64QAM

Uncoded Bit ER Performances

for IEEE802.22 WRAN System

- AWGN Environments

- 2K FFT

August 2006

Sunghyun Hwang, ETRI

Slide 58

doc.: IEEE 802.22-06-0170-01-0000

Submission

Uncoded Error Rate in Fading Channel

1.0E-07

1.0E-06

1.0E-05

1.0E-04

1.0E-03

1.0E-02

1.0E-01

1.0E+00

0 5 10 15 20 25 30 35 40

SNR(dB)

Bit

Erro

r Rat

e(Lo

g Sc

ale)

Theory

WRAN profile A

WRAN profile D

Coded BER

in AWGN environments

Uncoded Bit ER Performances

for IEEE802.22 WRAN System

- Multipath Fading

- Ideal Channel Estimation

- 2K FFT

- Modulation: QPSK,16QAM,64QAM

QPSK 16QAM

64QAM

1.0E-02

1.0E-01

1.0E+00

0 5 10 15 20 25 30 35 40

SNR(dB)

Bit

Erro

r Rat

e(Lo

g Sc

ale)

WRAN profile A

WRAN profile D

Uncoded Block ER Performances

for IEEE802.22 WRAN System

- Multipath Fading

- Ideal Channel Estimation

- 2K FFT

- Modulation: QPSK,16QAM,64QAM

QPSK

64QAM16QAM

August 2006

Sunghyun Hwang, ETRI

Slide 59

doc.: IEEE 802.22-06-0170-01-0000

Submission

Conclusions

• From the simulations of initial synchronization– In the WRAN profile A, B, and C, we obtain 90% preamble

detection probability at -4 dB SNR.

– Even in the WRAN profile D, we obtain 90% preamble detection probability at -2 dB SNR

– In the WRAN profile A, B, and C, we can synchronize the CPE to the BS within 2 % of sub-carrier spacing at -2 dB SNR

– Even in the WRAN profile D, we can synchronize the CPE to the BS within 2 % of sub-carrier spacing at 4 dB SNR

August 2006

Sunghyun Hwang, ETRI

Slide 60

doc.: IEEE 802.22-06-0170-01-0000

Submission

Conclusions

• From the simulations of FFO tracking– The performance using guard interval is better than that using

pilot. Here, we assume the GI ratio of 1/4, i.e. 512 subcarriers for 2K FFT size.

– The performance difference is because the correlation size is different, the number of GI subcarriers is 512 and the number of pilot subcarriers is 240.

– Another reason is because the pilot in adjacent OFDM symbol has experienced the different channel distortion from the pilot in the previous OFDM symbol.

August 2006

Sunghyun Hwang, ETRI

Slide 61

doc.: IEEE 802.22-06-0170-01-0000

Submission

Conclusions• From the simulations of LMMSE channel estimation

– If 7 OFDM symbols are used in LMMSE estimation, there are the performance degradation of 0.2~0.5 dB and 2.0~2.5 dB compared to ideal channel estimation for profile A and profile D, respectively. If 1 or 3 OFDM symbols are used in LMMSE estimation, there are huge performance loss.

– Therefore, to prevent huge performance loss, it is necessary for pilot symbol to visit every subcarriers. It would be established using preamble or(and) pilot.

– Regarding the calculation method of covariance matrix, the real-time calculation using actual measured model has a much better performance than that of pre-calculation assuming exponential model. Even though the complexity is increasing, because the WRAN system is fixed, we can decrease the complexity by stopping the training of channel information after several frames.

– If we use the frequency offset tracking, the performance loss due to residual frequency offset is ignorable.

– The performance using two preamble alone (without pilots) is similar to the performance using 7 OFDMA symbols (with pilots).

August 2006

Sunghyun Hwang, ETRI

Slide 62

doc.: IEEE 802.22-06-0170-01-0000

Submission

Further Works• Regarding the phase noise effect

– We are now performing the simulations for coded BER considering various channel distortions, i.e. AWGN, multipath, doppler, frequency offset, timing offset, phase noise, etc.

– Based on the coded BER performance with modified preamble and pilot pattern, we will find out how much the performance loss is due to phase noise.

– We think that the effect of phase noise with PSD(0)=-100 dBc/Hz is ignorable. But in general the phase noise with PSD(0)=-65 to -60 dBc/Hz is assumed, in this case, we may not neglect the performance loss due to phase noise anymore.

– If the phase noise effect can be ignorable as TGn model, we can select the second novel frame structure. However, if the phase noise effect is significant, we should select the first general frame structure.

• Regarding the preamble and pilot pattern for Up Link– Actually this simulation is focused on the down link operation, however

as regards the up link, additionally we should consider the ranging function, the usage of symmetric channel property, the used algorithms in BS.