Symbol Timing Estimation in Multiband Ofdm Based Uwb System

5.1 INTRODUCTION Multi-band orthogonal frequency division multiplexing (MB-OFDM) based transmission for ultra-wideband (UWB) is commercially successful for high speed Wireless Personal Area Networks (WPAN). It offers enhanced coexistence with traditional and protected radio services by dynamical turn on/off of subcarriers. The distinct feature of MB-OFDM is the use of Zero Padding (ZP) instead of Cyclic Prefix (CP). In a CP based OFDM, there exists a correlation between CP and OFDM signal. This manifests in the form of ripples in the Power Spectral Density (PSD) of the transmitted signal and hence results in additional power back-off. It has been reported that the use of ZP has reduced the ripples in PSD to zero (Batra et al 2003). In MB-OFDM, the availability of varying channel responses across different sub bands provide diversity gain. However, MB-OFDM system is highly sensitive to timing synchronization errors causing Inter Carrier Interference (ICI) as in OFDM systems. Symbol timing estimation in MB-OFDM based UWB is difficult due to the presence of strongest path at delayed instant. Hence signal processing algorithm to estimate and correct the timing has to be developed.