Overview of MB-OFDM UWB Baseband UWB Base-band Time/Freq. Synchronization for SFO Reporter : 黃彥欽 指導教授 : 吳仁銘 博士 2007/01/05 通訊工程研究所 國立清華大學

Proprietary of NTHU Communication SOC Lab, 2006 Overview of MB-OFDM UWB Baseband 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

Proprietary of NTHU Communication SOC Lab, 2006 Overview of MB-OFDM UWB Baseband 3 MB-OFDM UWB Spectrum: –14 sub-bands –5 band groups

Proprietary of NTHU Communication SOC Lab, 2006 Overview of MB-OFDM UWB Baseband 4 MB-OFDM UWB Data Rate (Mb/s) Modulat ion Coding Rate FDSTDSCoded Bits/ 6 Symbols Info Bits/ 6 Symbols 53.3QPSK1/3YES QPSK1/2YES QPSK1/3NOYES QPSK1/2NOYES QPSK5/8NOYES DCM1/2NO DCM5/8NO DCM3/4NO

Proprietary of NTHU Communication SOC Lab, 2006 Overview of MB-OFDM UWB Baseband 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

Proprietary of NTHU Communication SOC Lab, 2006 Overview of MB-OFDM UWB Baseband 6 Info. Data rate (Mbps) 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 Factor Overall Spreading Gain Data Tones100 Info. Length 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

Proprietary of NTHU Communication SOC Lab, 2006 Overview of MB-OFDM UWB Baseband 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

Proprietary of NTHU Communication SOC Lab, 2006 Overview of MB-OFDM UWB Baseband 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

Proprietary of NTHU Communication SOC Lab, 2006 Overview of MB-OFDM UWB Baseband 9 Sampling Freq. Offset (SFO) SFO is caused by sampling instant mismatch between DAC and ADC. DAC ADC channel 2T3TT4T T’T’ 2T ’ 3T ’

Proprietary of NTHU Communication SOC Lab, 2006 Overview of MB-OFDM UWB Baseband 10 SFO Effects Simulation (Time Domain)

Proprietary of NTHU Communication SOC Lab, 2006 Overview of MB-OFDM UWB Baseband 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 !

Proprietary of NTHU Communication SOC Lab, 2006 Overview of MB-OFDM UWB Baseband 12 SFO analysis

Proprietary of NTHU Communication SOC Lab, 2006 Overview of MB-OFDM UWB Baseband 13 SFO analysis (cont)

Proprietary of NTHU Communication SOC Lab, 2006 Overview of MB-OFDM UWB Baseband 14 SFO analysis (cont)

Proprietary of NTHU Communication SOC Lab, 2006 Overview of MB-OFDM UWB Baseband 15 SFO analysis (cont)

Proprietary of NTHU Communication SOC Lab, 2006 Overview of MB-OFDM UWB Baseband 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

Proprietary of NTHU Communication SOC Lab, 2006 Overview of MB-OFDM UWB Baseband 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

Proprietary of NTHU Communication SOC Lab, 2006 Overview of MB-OFDM UWB Baseband 18 SFO Effects Simulation (Frequency Domain) Timing offset in time domain resulting in phase rotation in the freq domain

Proprietary of NTHU Communication SOC Lab, 2006 Overview of MB-OFDM UWB Baseband 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

Proprietary of NTHU Communication SOC Lab, 2006 Overview of MB-OFDM UWB Baseband 20 General Method (cont) Take the cumulative phase of for the two sets C 1 and C 2 SFO estimation is given by

Proprietary of NTHU Communication SOC Lab, 2006 Overview of MB-OFDM UWB Baseband 21 Our Proposed Method Estimation Method –We use Least-Square (LS) algorithm to estimate the SFO and RCFO

Proprietary of NTHU Communication SOC Lab, 2006 Overview of MB-OFDM UWB Baseband 22 LS estimation No probabilistic assumptions about data, only a signal model is assumed Data Model ： Least Squares error Signal model θ s[n] Perturbation Noise Model inaccuracies x[n] Signal model θ s[n] x[n] Error=ε[n] Σ

Proprietary of NTHU Communication SOC Lab, 2006 Overview of MB-OFDM UWB Baseband 23 LS estimation (cont) LS error criterion –The value of θthat minimizes J(θ) is the LSE. If the signal s is linear, we can use matrix notation:

Proprietary of NTHU Communication SOC Lab, 2006 Overview of MB-OFDM UWB Baseband 24 LS estimation (cont) To find the minimum LS error, setting the gradient equal to error :

Proprietary of NTHU Communication SOC Lab, 2006 Overview of MB-OFDM UWB Baseband 25 Proposed Method (cont.) Enhance the BER performance by Using LS algorithm !

Proprietary of NTHU Communication SOC Lab, 2006 Overview of MB-OFDM UWB Baseband 26 Simulation of using LS algorithm to estimate the slope and intercept

Proprietary of NTHU Communication SOC Lab, 2006 Overview of MB-OFDM UWB Baseband 27 SFO Simulation (without other noise)

Proprietary of NTHU Communication SOC Lab, 2006 Overview of MB-OFDM UWB Baseband 28 SFO Simulation (with AWGN & CFO)

Proprietary of NTHU Communication SOC Lab, 2006 Overview of MB-OFDM UWB Baseband 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

Proprietary of NTHU Communication SOC Lab, 2006 Overview of MB-OFDM UWB Baseband 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

Proprietary of NTHU Communication SOC Lab, 2006 Overview of MB-OFDM UWB Baseband 31 Thanks for your attention…