Optimal Joint CFO and Channel Estimation in Quasi-Synchronized OFDM Systems

This paper addresses the problem of joint estimation of carrier frequency offset (CFO) and frequency-selective channel in quasi-synchronized orthogonal frequency division multiplexing (OFDM) systems. Two equivalent signal models with embedded timing ambiguity are introduced first, and then two joint CFO and channel estimators are derived from the Maximum Likelihood (ML) criterion. The first estimator obtained is a joint estimator for timing, CFO and channel, which needs a two dimension search for parameter estimation. The second estimator has a reduced complexity, but its performance slightly degrades compared with the first estimator due to more unknown parameters required to be estimated. We analyze and compare the MSE performance of the two estimators and find that when the number of subcarriers is large, the two estimators are equivalent.