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The ability of OFDM to mitigate channel frequency selectivity is impaired by its vulnerability to carrier frequency offset (CFO). In this paper, a new pilot-based carrier frequency offset estimation scheme for frequency selective slowly-varying channels is proposed. This scheme exploits the inherent redundancy introduced by the OFDM signaling and no additional training symbol is needed. The synchronization process is to minimize a LMS-like cost function, which essentially quantifies the variance of the pilot tones across several OFDM symbols. Moreover, a reduced-complexity estimator is also developed to reduce the implementation complexity. The CFO estimation range can span the whole OFDM signal bandwidth by nonuniformly distributing the embedded pilot tones in the frequency domain. Computer simulation results show that the performance of the proposed estimator can meet the requirement of typical OFDM communication systems.