Multipath-Doppler diversity of OFDM signals in an underwater acoustic channel

High-speed communications over the underwater acoustic channel are difficult due to time-varying multipath propagation and Doppler scattering. These phenomena, however, can be effectively used for joint multipath-Doppler diversity of received signals similarly to multipath diversity in a conventional RAKE receiver. We present a new signal processing technique for data transmission over fast fading underwater acoustic channel by using OFDM signals. This technique exploits multipath-Doppler diversity which is based on the channel model as a sum of macro-rays characterised by delays, Doppler parameters and transfer functions. Delay and Doppler estimation involves calculation of the cross-ambiguity function for a pilot signal; transfer function estimation exploits frequency domain B-spline approximation. Experimental results demonstrate high BER performance of the proposed algorithm for various propagation scenarios