MULTIPLE CFO ESTIMATION IN OFDM UNDERWATER COMMUNICATION SYSTEMS

When channel is severely frequency selective, Orthogonal Frequency Division Multiplexing (OFDM) is a suitable candidate for high rate communications. In multipath fading channels like harsh underwater channels, due to Inter Carrier Interference (ICI) and Carrier Frequency Offset (CFO) the performance of this technique is dramatically decreased. Therefore, these effects must be alleviated to overcome the performanee degradation. To do that, first the CFO's must be estimated. In this paper, we consider an underwater channel with three sets of paths and we assume that the paths in each set have similar Doppler scale factor. For minimum transmission power, Zero Padded OFDM (ZP-OFDM) is considered. We propose a new method based on MUltiple Signal Classification (MUSIC) technique that facilitates the estimation of multiple CFO's in Under Water Acoustic (UWA) channel and compare it with the derived Maximum Likelihood (ML) estimator algorithm. Simulation results show that the proposed method is robust against the received Signal to Noise Ratio (SNR) variations.