Ultra-Wideband Multi-Band OFDM Systems: Timing Synchronization and Frequency Offset Estimation

In digital communications systems, receiver synchronization (in terms of timing and carrier frequency offset estimation) is fundamental before accurate channel estimation can follow. Timing errors can cause intersymbol interferences (ISI) that destroy OFDM subcarriers' orthogonality and degrade system performance [Athaudage, 2002; Speth et al., 1997]. On the other hand, frequency offset (FO) may arise from random Doppler frequency shifts, carrier frequency mismatch between transmitter and receiver oscillators and sampling frequency errors. The FO causes severe reduction in signal amplitude and introduces intercarrier interferences (ICI) which cause severe bit error rate (BER) degradation [Moose, 1994]. It is hence critical to accurately estimate the timing and FO for reliable communications. For ultra-wideband (UWB) multi-band OFDM systems, the proposed algorithm, First significant multipath detection via Threshold comparison of Adjacent samples (FTA), focuses on detecting the first significant multipath component (MPC) by comparing the difference between two adjacent energy samples of a proposed metric against a pre-defined threshold. Each energy sample is obtained from summing received multipath components' energies. A simplified FO estimator is obtained from the proposed metric by averaging the phase differences between each corresponding subcarrier of the two identical adjacent training symbols. Using timing information, the maximum likelihood (ML) FO estimator and its theoretical Cramer Rao Bound (CRB) for the MB-OFDM UWB system are derived for comparison with FTA.