Approximately Maximum Likelihood Synchronization in OFDM based Communication System

We consider approximately maximum likelihood (ML) synchronization in OFDM based communication system. For approximately ML estimation, we use both a preamble and cyclic prefix (CP) and modify the log likelihood function for ML estimation to find a closed form of ML estimator. The structure of a frame for an estimation of the time and frequency offset is equal to the schmidl's method which performs very well even at low signal to noise ratio (SNR). By the proposed scheme, the accuracy of the timing and frequency offset estimator is definitely improved and the timing metric has a peak only at the correct position whereas has a plateau due to CP in the conventional scheme. The performance of the proposed method is shown analytically in AWGN channel and by simulations in multipath channel.