Abstract
Orthogonal frequency-division multiplexing (OFDM) is an effective transmission technique to cope with many impairments, such as cochannel interference, serve multipath fading and impulsive parasitic noise. However, a high accuracy in synchronization is required in an OFDM system. The synchronous detection of linear modulated carrier signals requires accurate symbol timing and carrier frequency references. In most cases, it is desired to estimate these parameters directly from measurements on the received data signal. Several different estimation strategies have evolvedfrom ingenious invention and experimentation, such as phase-lock loop (PLL), Costas loop, maximum-likelihood estimators, and stochastic approximation.In this thesis, a low complexity recursive algorithm for joint estimation of symbol timing and carrier frequency for OFDM systems, called recursive maximum-likelihood estimation (RMLE), has been derived based on the maximum-likelihood and stochastic approximation criterions. It utilizes the guard interval in OFDM signals and the frame synchronization and frequency offset estimation are considered simultaneously. The convergence of this algorithm has been justified, i.e., it is shown that both the bias and jitter of the estimation approach zero as the number of iterations becomes large.A fast version of this algorithm has been developed, which introduces a simplicity acquisition algorithm in preamble signal and applies RMLE during the tracking mode. The comparison of convergence rate will be represented by computer simulations.