Reliable Doppler-spread estimation using an evolutionary algorithm for underwater acoustic communications over channels with frequency-selective fading

There is a pressing need for reliable wideband underwater acoustic communication for enhanced performance of diver communications, underwater networks, control links to ROVs and data links to remote sensors and AUVs. The performance of such links is compromised by the doubly-spread acoustic channel, where multipath time-delay spread causes inter-symbol interference due to frequency-selective fading and Doppler-spread results in additional signal distortion and temporal variation of the channel characteristics. However, if the channel characteristics can be estimated accurately, especially the Doppler-spread, many of these problems can be resolved. Doppler-spread occurs because the Doppler velocity may be different on each path. The paper describes a method for improved-reliability Doppler spread estimation of channels that experience frequency-selective fading. The method uses a wideband sounding signal to overcome the frequency selective fading and the estimation of the Doppler spread is obtained from this complex waveform using multi-layered optimization based on evolutionary algorithms. The method has a wide dynamic range and can estimate the Doppler shift of weak multipath components in the presence of strong multipath components. The accuracy of the Doppler-spread estimate is not limited by the short duration of sounding signal and the method performs well even in the presence of significant noise.