The OFDM Underwater Communication Frequency Equalization Based on LMS Algorithm and Pilot Sequence

An approach of channel frequency equalizer based on frequency domain least mean square (LMS) adaptive algorithm and block pilot is proposed recently. There have been tremendous demands for high speed data transmission in underwater acoustic communications. Orthogonal frequency division multiplexing (OFDM) has been introduced to high speed acoustic communications. Accurate channel equalizer is necessary for OFDM coherent detection of the underwater acoustic signals. We propose an approach using pilot training sequence to obtain the channel phase rotation in sent constellation by LS algorithm that initializes the channel information, then the frequency domain LMS adaptive equalizer is imposed to every subcarrier of the received training frequency domain OFDM symbol to obtain the information of impulse response. Frequency domain equalization is computationally efficient both in simulation and pool trial. Then the channel information is employed to equalize other OFDM symbols. Thus, this approach is very attractive for high speed implementation of an underwater acoustic OFDM receiver.