overview of mb-ofdm uwb baseband [email protected] uwb base-band time/freq. synchronization for...

Overview of MB-OFDM UWB Baseband [email protected] UWB Base-band Time/Freq. Synchronization for SFO Reporter : : 2007/01/05

Proprietary of NTHU Communication SOC Lab, Copyright @ 2006 Overview of MB-OFDM UWB Baseband [email protected] 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, Copyright @ 2006 Overview of MB-OFDM UWB Baseband [email protected] 3 MB-OFDM UWB Spectrum: 14 sub-bands 5 band groups

Proprietary of NTHU Communication SOC Lab, Copyright @ 2006 Overview of MB-OFDM UWB Baseband [email protected] 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

Proprietary of NTHU Communication SOC Lab, Copyright @ 2006 Overview of MB-OFDM UWB Baseband [email protected] 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, Copyright @ 2006 Overview of MB-OFDM UWB Baseband [email protected] 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

Proprietary of NTHU Communication SOC Lab, Copyright @ 2006 Overview of MB-OFDM UWB Baseband [email protected] 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, Copyright @ 2006 Overview of MB-OFDM UWB Baseband [email protected] 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, Copyright @ 2006 Overview of MB-OFDM UWB Baseband [email protected] 9 Sampling Freq. Offset (SFO) SFO is caused by sampling instant mismatch between DAC and ADC. DAC ADC channel 2T3TT4T TT 2T 3T

Proprietary of NTHU Communication SOC Lab, Copyright @ 2006 Overview of MB-OFDM UWB Baseband [email protected] 10 SFO Effects Simulation (Time Domain)

Proprietary of NTHU Communication SOC Lab, Copyright @ 2006 Overview of MB-OFDM UWB Baseband [email protected] 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, Copyright @ 2006 Overview of MB-OFDM UWB Baseband [email protected] 12 SFO analysis

Proprietary of NTHU Communication SOC Lab, Copyright @ 2006 Overview of MB-OFDM UWB Baseband [email protected] 13 SFO analysis (cont)

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

Proprietary of NTHU Communication SOC Lab, Copyright @ 2006 Overview of MB-OFDM UWB Baseband [email protected] 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]

Proprietary of NTHU Communication SOC Lab, Copyright @ 2006 Overview of MB-OFDM UWB Baseband [email protected] 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:

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

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

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

Proprietary of NTHU Communication SOC Lab, Copyright @ 2006 Overview of MB-OFDM UWB Baseband [email protected] 27 SFO Simulation (without other noise)

Proprietary of NTHU Communication SOC Lab, Copyright @ 2006 Overview of MB-OFDM UWB Baseband [email protected] 28 SFO Simulation (with AWGN & CFO)

Proprietary of NTHU Communication SOC Lab, Copyright @ 2006 Overview of MB-OFDM UWB Baseband [email protected] 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, Copyright @ 2006 Overview of MB-OFDM UWB Baseband [email protected] 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, Copyright @ 2006 Overview of MB-OFDM UWB Baseband [email protected] 31 Thanks for your attention

overview of mb-ofdm uwb baseband [email protected] uwb base-band time/freq. synchronization for...

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