Iterative ML estimation for frequency offset and time synchronization in OFDM systems

Orthogonal frequency division multiplexing (OFDM) technique has become attractive and important in both wireline and wireless communications. One of the well-known problems in OFDM systems is its vulnerability to frequency and time offset. This paper develops an iterative maximum-likelihood (ML) estimation algorithm for correction of both frequency and time offset in OFDM systems. Because of the complicated characteristics of log-likelihood function, not every chosen initial point for iteration procedure can always converge to the values resulting in acquisition of the global maximum of log-likelihood function. This implies that some of the selected initial points can only converge to the values which yield local maxima of log-likelihood function. According to the proposed iterative approaching algorithm, the global maximum of log-likelihood function can be definitely found to achieve both frequency and time synchronization. In addition, the seeking time for this global maximum in the iteration procedure can be reduced and evaluated.