Low frequency mobile communications in underwater networks

Abstract

We present a receiver for low frequency underwater acoustic communications addressing the Doppler shift that occurs during the transmission of frames at a very low data rate. The receiver handles constant or variable (linearly and nonlinearly) Doppler shift patterns. The waveform supported by the receiver is adapted to difficult underwater channel conditions, such as the ones present in long range under-ice Arctic communications. The bandwidth is extremely narrow (less than six Hz). Redundancy is very high (300%). Our main contributions are in an aspect of the receiver that handles arbitrary types of Doppler shifts. We use the idea of signal tracking function. It follows the progression of a carrier during the reception of a frame. Evaluation results are reported using our GNU Radio implementation.