Efficient estimation and compensation of Doppler shift for OFDM signals in underwater communications

A novel method of windowing for Doppler detection and compensation over an underwater acoustic (UWA) multipath channel employing orthogonal frequency division multiplex (OFDM) signaling is presented. This new method involves transmitting a preamble of upto three OFDM symbols, while at the receiver a windowing technique is applied to estimate the Doppler shift post FFT. This estimated shift is used to compensate the Doppler shift of further data symbols transmitted over the channel. Simulations have been performed over an UWA multipath channel in the presence of ambient ocean noise using the proposed method, with BER as a Quality of Service parameter, studied for different Doppler shifts. Significantly, the proposed approach avoids resampling as well as the need for buffering the whole data packet before demodulation and facilitates online receiver operation for an OFDM based UWA communication system. The proposed method is easily implemented with significantly reduced computational complexity.