Doppler effect mitigation over mobile underwater acoustic OFDM system

Abstract

Orthogonal frequency division multiplexing (OFDM) has prevailed in high speed underwater acoustic(UWA) communications with obvious multipath effects. However, with the characteristic of being sensitive to the Doppler effect, the performance of an OFDM system is severely limited by the intercarrier interference (ICI) introduced by Doppler spread. In this paper, we build a hydroacoustic baseband defferentially encoded OFDM system and propose an effective approach to mitigate the Doppler effect for the system. After utilizing the Chirp-Z transform(CZT) to estimate a coarse common value of large scale Doppler factor a and null subcarriers for the estimation of residual Doppler am for each OFDM symbol, we use the method of polyphase filter resampling to compensate them. We also correct the phase rotation effect caused by timing sampling offset according to the residual Doppler estimation result. Simulation and experimental results show that while meeting the accuracy requirement of Doppler scaling factor estimation in mobile UWA communications, the proposed algorithm can be used to accurately and effectively estimate the Doppler scaling factor and requires lower computational complexity.