Underwater communications in the presence of bubbles and Doppler shift

This paper analyzes the effect of bubble noise and Doppler shift in an underwater acoustic communication in addition to the influences by ambient noise and severe multipath propagation. Here Bubbles are assumed to be formed due to breaking of waves under strong winds. The bubble layer thus formed alters the speed of the sound in the field. The changed speed of the sound in the field, results in transmission loss during propagation and scattering of the signals. Existing Underwater Acoustic channel (UWA) models do not account for the combined effects. In this paper, first UWA multipath channel is modeled in the presence of ambient ocean noise and bubble noise. Subsequently a new method is proposed for Doppler shift compensation that avoids resampling as well as the need for preloading the whole data packet prior to demodulation and facilitates real time operation at receiver for an Orthogonal Frequency Division Multiplexing (OFDM) based UWA communication system. The proposed algorithm is simulated and verification is carried out by studying the Quality of Service parameter Bit Error Ratio (BER) for different Doppler shifts. The proposed method can be implemented with significantly reduced computational complexity.