Compensation schemes for phase noise and residual frequency offset in OFDM systems

It is shown that a random phase noise Wiener process and a fixed but unknown residual (post-FFT) frequency offset, jointly perturbing an OFDM receiver, manifest themselves as a phase-rotation random variable which is common to all subcarriers, provided that their defining values (variance and fixed amount, respectively) are small, in which case the ICI (intercarrier interference) and the per-subcarrier amplitude distortion induced by them are both negligible. Assuming a known arbitrary channel profile, we propose and evaluate by simulations two decision-directed (i.e., non-pilot-based) compensation schemes, one intuitive and the other based on ML theory. The algorithms exhibit robustness despite the lack of pilots, whereas uncompensated performance degrades rapidly.