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 performance 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.