Doppler effect compensation for cyclic-prefix-free OFDM signals in fast-varying underwater acoustic channel

Abstract

We propose an OFDM receiver for underwater acoustic communications in fast-varying multipath channels. The OFDM signals are cyclic-prefix-free and the transmitted and pilot data are superimposed. The data symbols are encoded across subcarriers to exploit the frequency diversity. The receiver employs multiple stages for compensating the Doppler distortion. The first stage deals with an average compression factor and is implemented via time-varying re-sampling of the received signal. The second stage compensates for the non-uniform Doppler distortion of multipath components by exploiting a time-domain equalizer with local spline interpolation of equalizer weights. The third stage deals with the residual Doppler distortion and it is implemented using a frequency-domain Doppler equalizer. The receiver algorithm is verified using data from a sea experiment with data transmission at a distance of 40 km. The transducer motion resulted in a severe time-varying Doppler distortion of the received signal. The acoustic signal was received by a single hydrophone. The performance of the receiver is investigated for different parameter settings. In the sea experiment, the proposed receiver has allowed error-free detection at a data rate of 0.5 bits/s/Hz. © 2012 Acoustical Society of America.