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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 1 [ETRIs Simulation Results for OFDMA Parameters] IEEE P802.22 Wireless RANs Date: 2006-09-18 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 IEEEs name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEEs 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 Chairhttp://standards.ieee.org/guides/bylaws/sb-bylaws.pdf Carl R. StevensonCarl 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.patcom@iee.org

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 2 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.

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 3 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

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 4 System Parameters & OFDMA Parameters

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 5 System Parameters/Single Channel (6MHz) Mode1K2K4K6K FFT Size1024204840966144 Bandwidth (k = 1, 2, …, 6) k MHz Sampling Factor8/7 No. of Used Subcarriers (including pilot, but not DC) 140 * k280 * k560 * k840 * k Sampling Frequency48/7 MHz Subcarrier Spacing6.696 kHz (***) 3.348 kHz1.674 kHz1.116 kHz Occupied Bandwidth6.696 kHz*140*k3.348 kHz*280*k1.674 kHz*560*k1.116 kHz*840*k Bandwidth Efficiency (*) 93~94 % FFT Time149.33 us298.66 us597.33 us896 us Cyclic Prefix Time (**) 37.33 us74.66 us149.33 us224 us OFDMA Symbol Time186.66 us373.33 us746.66 us1120 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.

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 6 OFDMA Parameters (2K FFT Mode) Parameter 1 TV bands 678 Inter-carrier spacing, F (Hz) (*) 334839064464 FFT period, T FFT ( s) (*) 298.66256.00224.00 Total no. of sub-carriers, N FFT 2048 No. of guard sub-carriers, N G (L, DC, R)368 (184,1,183) No. of used sub-carriers, N T = N D + N P 1680 No. of data sub-carriers, N D 1440 No. of pilot sub-carriers, N P 240 No. of sub-carriers per BIN14 (12 datas + 2 pilots) No. of BIN per subchannel4 No. of sub-carriers per subchannel56 (48 datas + 8 pilots) Occupied bandwidth (MHz) (*) 5.6286.5667.504 Bandwidth Efficiency (%) (**) 93.8 (*) Italics indicate an approximated value. (**) Bandwidth Efficiency = Subcarrier Spacing * (Number of Used Subcarriers + 1)/BW

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 7 Frame Structure with Preamble & Pilot Pattern

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 8 Two Approaches of Frame Structure In our simulations, we consider two types of frame structure with preamble and pilot pattern. 1 st 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. 2 nd Frame Structure –Novel frame structure –With a preamble of two OFDMA symbol and no pilots –The header and data are purely transmitted without pilots.

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 9 TDD Frame Structure I

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 10 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 N FFT /2 N SYM

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 11 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

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 12 Pilot Pattern of Frame Structure I Pilot Structure for Extendable Channel Estimation Available Pilot Pattern for Channel Estimation frequency time Repetition Unit BIN OFDMA Symbol

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 13 TDD Frame Structure II

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 14 Preamble Structure for Frame Structure II Modified Preamble Structure for Extendable Channel Estimation Available Pilot Pattern for Channel Estimation frequency time OFDMA Symbol Pure Data

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 15 Decision Procedure of Preamble and Pilot Pattern YesNo Is it possible to achieve the sufficient performances in initial synchronization using proposed preamble only? Yes Is it possible to achieve the sufficient performances in 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 performances in channel estimation using proposed preamble only? No Use one preamble symbol & Remove all pilots Yes Is it possible to achieve the sufficient performances in channel estimation using proposed preamble and pilots? YesNo Reinforce the preamble and(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 IIFrame Structure I

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 16 Algorithms & Operation Procedure

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 17 Top Block Diagram of WRAN PHY Simulator

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 18 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

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 19 Timing Synchronization With the Schmidls method –Autocorrelation method using the following –The metric –Timing

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 20 Timing Synchronization Enhanced timing metric –to resolve the timing ambiguity in the plateau –to protect the timing outside the guard interval

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 21 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

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 22 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 FFT

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 23 CFO(FFO+IFO) Estimation IFO estimation –We can obtain the IFO using the correlation of the PN sequence Total CFO estimation range:

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 24 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.

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 25 FFO Tracking Algorithms FFO estimation using GI in the time-domain FFO estimates using GI in the time-domain

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 26 FFO Tracking Algorithms FFO estimation using Pilot in the frequency-domain FFO estimates using Pilot in the frequency-domain where, R G is the ratio of GI size to FFT size

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 27 Channel Estimation Received Signal Vector – Y: received signal vector in the frequency domain – X: diagonal matrix containing data symbols – W: AWGN At Pilot Positions X P : diagonal matrix containing pilot symbols H P : channel response at pilot positions

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 28 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.

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 29 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 W p, and R PP is the autocovariance matrix of the noiseless pilots.

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 30 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.

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 31 Synchronization & Ch. Estimation Procedure IFO estimation Preamble Timing Synchronization FFO estimation FFO tracking Channel Estimation

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 32 Simulation Conditions

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 33 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

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 34 Simulation Conditions Channel Modeling –AWGN –Multipath profiles & Doppler: A, B, C, D Approximation to nearest sampling point Jakes Rayleigh modeling method Multipath ProfileABCD RMS Delay Spread (us) 2.7721.9565.69216.527 (*) (*) For WRAN profile D, we assume that the 6-th path has the excess delay of 60 us and relative power of -10 dB

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 35 Simulation Conditions Channel Modeling –Multipath profiles & Doppler Channel response of WRAN multipath profile The span of 10 subcarriers

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 36 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 f p =250 kHz, and zero frequency f z =7905.7 kHz (a) Ideal (b) PSD(0) = -100 dBc/Hz (c) PSD(0) = -65 dBc/Hz

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 37 Simulation Results 1. Missing probability of preamble starting point 2. MSE of CFO estimate (in acquisition) 3. MSE of FFO estimate (in tracking) 4. Uncoded BER of LMMSE estimation 5. Performance comparison for calculation method of covariance matrix 6. Performance comparison for frequency offset effect 7. Uncoded BER performance using preamble alone 8. Uncoded/Coded BER performance under ideal channel estimation

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 38 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. 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

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 39 MSE of FFO Estimate (Using Preamble)

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 40 MSE of CFO Estimate (Using Preamble) 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

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 41 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

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 42 MSE of FFO Estimate (Using GI or Pilot) 2% of sub-carrier spacing

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 43 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

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 44 Uncoded BER Performance (Profile A, QPSK)

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 45 Uncoded BER Performance (Profile A, 64QAM)

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 46 Uncoded BER Performance (Profile C, QPSK)

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 47 Uncoded BER Performance (Profile C, 64QAM)

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 48 Uncoded BER Performance (Profile D, QPSK)

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 49 Uncoded BER Performance (Profile D, 64QAM)

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 50 Performance Comparison for Calculation Method of Covariance Matrix (Profile C, QPSK)

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 51 Performance Comparison for Calculation Method of Covariance Matrix (Profile D, QPSK)

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 52 Performance Comparison for Frequency Offset Effect (Profile A, QPSK)

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 53 Performance Comparison for Frequency Offset Effect (Profile A, 64QAM)

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 54 Uncoded BER Performance Using Preamble Only (Profile A, QPSK)

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 55 Uncoded BER Performance Using Preamble Only (Profile C, QPSK)

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 56 Uncoded BER Performance Using Preamble Only (Profile D, QPSK)

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 57 Uncoded/Coded Bit Error Rate in AWGN

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 58 Uncoded Error Rate in Fading Channel

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 59 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

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 60 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.

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 61 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).

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doc.: IEEE 802.22-06-0170-01-0000 Submission August 2006 Sunghyun Hwang, ETRISlide 62 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.

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