Approximate maximum likelihood estimation integer carrier frequency offset in OFDM systems

In orthogonal frequency division multiplexing (OFDM) systems, the carrier frequency offset can he normalized by the subcarrier bandwidth and then he divided into the integer and the fractional part. This paper focuses on the estimation of the integer carrier frequency offset and derives approximate maximum likelihood (ML) estimators in the presence and in the absence of pilot subcarriers. Simplified approximate ML estimators with reduced complexity are also proposed. The performance of the proposed estimators is compared with that of existing estimators, and it is shown by simulation that the proposed estimators outperform existing estimators.