Ml joint CFO and channel estimation in OFDM systems with timing ambiguity

This letter addresses the problem of joint estimation of carrier frequency offset (CFO) and channel for OFDM systems in the presence of timing ambiguity. Based on two signal models for quasi-synchronized OFDM systems, two joint CFO and channel estimators are derived from the Maximum Likelihood (ML) criterion. The first estimator obtained is a joint estimator for all unknown parameters, which needs a multi-dimensional search. The second estimator has a reduced complexity, but its performance slightly degrades compared with the first one. Through MSE analyses, we find that when the number of subcarriers is large, the two estimators are equivalent.