Frequency Tracking by Method of Least Squares Combined With Channel Estimation for OFDM Over Mobile Wireless Channels

To track frequency offset and time-varying channel in Orthogonal Frequency Division Multiplexing (OFDM) systems over mobile wireless channels, a common technique is, based on one OFDM training block sample, to apply the Maximum-Likelihood (ML) algorithm to perform joint frequency tracking and channel estimation employing some adaptive iteration processes. The major drawback of such joint estimation techniques is the local extreme a problem arising from the highly nonlinear nature of the log-likelihood function. This makes the joint estimation process very difficult and complicated, and many a time the results are not very satisfactory if the algorithm is not well designed.