Phase-Impairment Effects and Compensation Algorithms for OFDM Systems

Phase-Impairment Effects and Compensation Algorithms for OFDM Systems The simultaneous perturbation of an orthogonal frequency-division multiplexing (OFDM) receiver by phase noise plus a residual frequency offset (due to synchronization errors) is modeled here as a combined phase impairment, whose effect is evaluated analytically for the case of a frequency-selective fading channel. A nonpilot-aided (decision-directed) scheme is proposed, which compensates for the common (over all the subcarriers) phase-impairment effect. By representing the resulting intercarrier interference as an uncorrelated, unequal-variance process in the frequency domain, maximum likelihood (ML), and approximate ML estimators of the complex-vector and phase-only type are derived and analytically evaluated. These schemes are also compared with other current methods based on individual phase tackers, one per subcarrier. Finally, two suggestions are introduced for increasing the robustness of the algorithms to tentative-decision errors. It is demonstrated through simulations that the analysis is accurate, and that the proposed schemes achieve error-rate performance close to that of ideal compensation.