Transcript of Overview of MB-OFDM UWB Baseband jmwu@ee.nthu.edu.tw UWB Base-band Time/Freq. Synchronization for...
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- Overview of MB-OFDM UWB Baseband jmwu@ee.nthu.edu.tw UWB
Base-band Time/Freq. Synchronization for SFO Reporter : :
2007/01/05
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Overview of MB-OFDM UWB Baseband jmwu@ee.nthu.edu.tw 2 Outline
MB-OFDM UWB Introduction Tx / Rx Block Diagram Synchronization of
SFO Time-domain effect SFO analysis Freq-domain effect Simulation
Result Future Work
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Overview of MB-OFDM UWB Baseband jmwu@ee.nthu.edu.tw 3 MB-OFDM UWB
Spectrum: 14 sub-bands 5 band groups
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Overview of MB-OFDM UWB Baseband jmwu@ee.nthu.edu.tw 4 MB-OFDM UWB
Data Rate (Mb/s) Modulat ion Coding Rate FDSTDSCoded Bits/ 6
Symbols Info Bits/ 6 Symbols 53.3QPSK1/3YES 300100 80QPSK1/2YES
300150 106.7QPSK1/3NOYES600200 160QPSK1/2NOYES600300
200QPSK5/8NOYES600375 320DCM1/2NO 1200600 400DCM5/8NO 1200750
480DCM3/4NO 1200900
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Overview of MB-OFDM UWB Baseband jmwu@ee.nthu.edu.tw 5
Timing-related parameters ParameterDescription Value Sampling
frequency528 MHz Total number of data subcarriers ( FFT size ) 128
Number of data subcarriers 100 Number of pilot subcarriers 12
Number of guard subcarriers 10 Total number of subcarriers used 122
Subcarrier frequency spacing4.125MHz IFFT and FFT period242.42ns
Number of samples in zero-padded suffix 37 Zero-padded suffix
duration in time70.08ns Symbol interval312.5ns Symbol rate3.2MHz
Total number of samples per symbol165
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Overview of MB-OFDM UWB Baseband jmwu@ee.nthu.edu.tw 6 Info. Data
rate (Mbps)53.380106.7160200320400480 Mod./ ConstellationOFDM /
QPSK or DCM FFT Size128 Coding Rate1/31/21/31/25/81/25/83/4
Conjugate Symmetric Input to IFFT (FDS) Yes No Time Spreading
Factor22222111 Overall Spreading Gain44222111 Data Tones100 Info.
Length242.42 nsec Zero-padded Prefix70.08 nsec Symbol Length312.5
nsec Channel Bit Rate640 Mbps Multi-path Tolerance70.08 nsec (The
version 4/2005 post at MBOA web page) System Parameters
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Overview of MB-OFDM UWB Baseband jmwu@ee.nthu.edu.tw 7 PA Data
Source P D+P Channel encoder Inter- leaver Signal Mapping Generate
Training Symbol Add Guard Tone 128-point IFFT Insert Preamble Pulse
Shaping PAPR Clipping DAC Time-Freq Code MB-OFDM UWB Tx Insert
Guard Interval
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Overview of MB-OFDM UWB Baseband jmwu@ee.nthu.edu.tw 8 MB-OFDM UWB
Rx LPF Symbol Window Control Packet Detection Symbol Timing
Estimation + Freq. Hopping Signal ADC Coarse carrier phase
Estimation Remove Guard Interval N-point FFT Channel Estimation
Channel Equalization Pilot Tracking Estimation Sampling Clock Sync
P/S Signal De- mapping De- Inter- leaver Channel Decoder LNA N P D
N D P D Decoded Information Bits Phase Offset Estimation Coarse
carrier phase compensation s/p
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Overview of MB-OFDM UWB Baseband jmwu@ee.nthu.edu.tw 9 Sampling
Freq. Offset (SFO) SFO is caused by sampling instant mismatch
between DAC and ADC. DAC ADC channel 2T3TT4T TT 2T 3T
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Overview of MB-OFDM UWB Baseband jmwu@ee.nthu.edu.tw 10 SFO Effects
Simulation (Time Domain)
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Overview of MB-OFDM UWB Baseband jmwu@ee.nthu.edu.tw 11 Sampling
Freq. Offset (SFO) (cont.) Effect in Time Domain OFDM Symbol Window
Drift FFT window This leads to irreducible ISI ! Need to add/drop 1
sample after every 151 OFDM symbols !
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Overview of MB-OFDM UWB Baseband jmwu@ee.nthu.edu.tw 12 SFO
analysis
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Overview of MB-OFDM UWB Baseband jmwu@ee.nthu.edu.tw 13 SFO
analysis (cont)
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Overview of MB-OFDM UWB Baseband jmwu@ee.nthu.edu.tw 14 SFO
analysis (cont)
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Overview of MB-OFDM UWB Baseband jmwu@ee.nthu.edu.tw 15 SFO
analysis (cont)
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Overview of MB-OFDM UWB Baseband jmwu@ee.nthu.edu.tw 16 Residual
Carrier Freq. Offset (RCFO) RCFO is caused by non-exact carrier
freq. offset (CFO) correction before FFT. Packet Detection CFO
Correction Coarse CFO Estimator Symbol Timing Estimator Remove CP
FFT Data Preamble
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Overview of MB-OFDM UWB Baseband jmwu@ee.nthu.edu.tw 17 Sampling
Freq. Offset (SFO) (cont.) Effect in Freq. Domain Sub-carrier
Symbol Rotation The rotated phase is the function of time and
different between sub-carriers ! So the receiver has to track and
compensate SFO and RCFO continuously in time ! Phase Rotation
pilot
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Overview of MB-OFDM UWB Baseband jmwu@ee.nthu.edu.tw 18 SFO Effects
Simulation (Frequency Domain) Timing offset in time domain
resulting in phase rotation in the freq domain
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Overview of MB-OFDM UWB Baseband jmwu@ee.nthu.edu.tw 19 General
Method Use Pilots to estimate SFO Symmetrically distributed around
middle subcarrier Use the knowledge of the linear relationship
between phase rotation of negative (C 1 ) and positive (C 2 ) set.
Received pilot subcarriers Calculate the rotation of the pilot from
this symbol to the previous
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Overview of MB-OFDM UWB Baseband jmwu@ee.nthu.edu.tw 20 General
Method (cont) Take the cumulative phase of for the two sets C 1 and
C 2 SFO estimation is given by
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Overview of MB-OFDM UWB Baseband jmwu@ee.nthu.edu.tw 21 Our
Proposed Method Estimation Method We use Least-Square (LS)
algorithm to estimate the SFO and RCFO
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Overview of MB-OFDM UWB Baseband jmwu@ee.nthu.edu.tw 22 LS
estimation No probabilistic assumptions about data, only a signal
model is assumed Data Model Least Squares error Signal model s[n]
Perturbation Noise Model inaccuracies x[n] Signal model s[n] x[n]
Error=[n]
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Overview of MB-OFDM UWB Baseband jmwu@ee.nthu.edu.tw 23 LS
estimation (cont) LS error criterion The value of that minimizes
J() is the LSE. If the signal s is linear, we can use matrix
notation:
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Overview of MB-OFDM UWB Baseband jmwu@ee.nthu.edu.tw 24 LS
estimation (cont) To find the minimum LS error, setting the
gradient equal to error :
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Overview of MB-OFDM UWB Baseband jmwu@ee.nthu.edu.tw 25 Proposed
Method (cont.) Enhance the BER performance by Using LS algorithm
!
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Overview of MB-OFDM UWB Baseband jmwu@ee.nthu.edu.tw 26 Simulation
of using LS algorithm to estimate the slope and intercept
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Overview of MB-OFDM UWB Baseband jmwu@ee.nthu.edu.tw 27 SFO
Simulation (without other noise)
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Overview of MB-OFDM UWB Baseband jmwu@ee.nthu.edu.tw 28 SFO
Simulation (with AWGN & CFO)
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Overview of MB-OFDM UWB Baseband jmwu@ee.nthu.edu.tw 29 Sampling
Frequency Offset Recovery FFT Add/Drop ADC Channel Equalizer Pilot
extraction SFO estimator 2 l : symbol indexk : subcarrier index SFO
Compensation Digital approach in Baseband
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Overview of MB-OFDM UWB Baseband jmwu@ee.nthu.edu.tw 30 Future Work
Continue completing all the simulation Make sure the sync. part
will work successfully : Combine with other parts in Rx-end
Consider the multi-path effect Chip implementation Design the
micro-architecture and write RTL code Verify the system by FPGA
board Tapeout
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Overview of MB-OFDM UWB Baseband jmwu@ee.nthu.edu.tw 31 Thanks for
your attention