Robust Communications for the Underwater Internet of Things

In recent years, the emergence of numerous applications and activities involving the underwater world have given rise to a new class of technologies that takes the name of Internet of Underwater Things (IoUT). Submarine activities such as remote control, pollution monitoring, data collection, disaster detection or even early warning and assisted navigation are just some of the main applications that require the use of underwater communication systems capable of providing connectivity between static and mobile nodes deployed at different depths. Generally, underwater communications employ audio signals which can propagate relatively far but are also significantly affected by Doppler distortions. In fact, physical properties of the water and spatial changes due to tides, currents and waves can cause channel variations or unwanted movements of the transmitter or receiver. A plethora of underwater communication techniques have been developed to address such challenging scenarios. In this thesis, we study how to correct Doppler effects in transmission employing JANUS, the first standard for underwater acoustic communication. In particular, we exploit the JANUS preamble, composed of an m-sequence of 32 pseudo-random symbols, to estimate and compensate for the Doppler shift caused by the relative motion of transceivers up to 5 m/s. The proposed method is validated using Watermark simulator and at-sea experiments. Then, we analyze the performance of S2C both in simulation and in-field experiments, based on our own S2C implementation. We undertake extensive simulation experiments, quantitatively measuring the impact of a variety of modulation parameters (such as the sweep duration and the number of coded symbols per sweep), and under different channel characteristics (depth, range, Doppler speed, etc.). Furthermore, we test the performances of the S2C modulation at sea, obtaining good results also in shallow waters.