I. Introduction
ORTHOGONAL frequency division multiplexing (OFDM) [1], [2] has recently received considerable attention for its robustness against inter-symbol interference (ISI) and impulse noise, low implementation complexity and high spectral efficiency. One of the principal disadvantages of OFDM is its sensitivity to synchronization errors, represented by the so-called frequency and timing offsets. Frequency offset causes a reduction of desired signal amplitude in the output decision variable and introduces inter-carrier interference (ICI) due to the loss of orthogonality among sub-carriers. Timing offset results in the rotation of the OFDM sub-carrier constellation. As a result, an OFDM system cannot recover the transmitted signal without a near perfect synchronization, especially when high order of QAM modulation is implemented.