Doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 1 [ETRIs...
-
Upload
maria-hayes -
Category
Documents
-
view
215 -
download
1
Transcript of Doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 1 [ETRIs...
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 [email protected]
Myung-Sun Song ETRI Korea +82-42-860-5046 [email protected]
Soon-Ik Jeon ETRI Korea +82-42-860-5947 [email protected]
Gwang-Zeen Ko ETRI Korea +82-42-860-4862 [email protected]
Sung-Hyun Hwang ETRI Korea +82-42-860-1133 [email protected]
Jung-Sun Um ETRI Korea +82-42-860-4844 [email protected]
Bub-Joo Kang ETRI Korea +82-42-860-5446 [email protected]
Hyung-Rae Park ETRI Korea +82-2-300-0143 [email protected]
Yun-Hee Kim ETRI Korea +82-31-201-3793 [email protected]
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 [email protected].
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.