This paper aims to enhance the reliability of underwater acoustic (UWA) communications by evaluating the effectiveness of various Forward Error Correction (FEC) codes. In the absence of standardized UWA physical layer simulators, we rely on in-situ data to assess the performance of six FEC codes: convolutional, turbo, Low-Density Parity Check (LDPC), Bose– Chaudhuri–Hocquenghem (BCH), Turbo Product Code (TPC), and polar. We examine two common payload sizes: 128-bit packets at a 1/5 encoding rate and 1024-bit packets at a 1/2 rate. Our comparative analysis leverages previously recorded single-carrier Phase-Shift Keying (PSK) signals, originally not intended for FEC evaluation. The signals were transmitted over various underwater links in a High North environment, including areas of sea surface ice floes, northwest of the Svalbard Islands. Using these signals, we formulate an optimal channel replay framework for FEC comparison through constellation dithering for M-ary PSK (M-PSK) modulation. This framework involves a Channel Estimate-Based-Decision Feedback Equalizer (CEB-DFE) with a varying number of input channels (hydrophones) at the receiver end. We focus on the Packet Error Rate (PER), maintaining consistent channel conditions for all codes under consideration. The polar code demonstrates the best performance by achieving the lowest PER for all tested packet lengths and varying number of hydrophones. Moreover, upgrading the equalizer with a turbo feature enables the polar code to achieve up to a 45% further reduction in PER in certain scenarios.

Monitoring ocean dynamics is extremely difficult due to its enormous physical dimensions and the wide range of spatio-temporal scales involved in its dynamical behaviour. It has been recently proposed that the most efficient way to monitor the ocean is through networks of small, intelligent and cheap robotic platforms. Drifting profiling floats and gliders were developed in this context. Floats move with the currents meanwhile they periodically sample the water column through controlled immersions. Conversely, gliders are underwater autonomous vehicles with controllable motion at sea. Both platforms are extensively employed in oceanography due to their high autonomy. A network called Argo of around 3000 profiling floats spreads out around the world's ocean. Glider networks are starting to settle down at smaller scale in different places. The advent of these networks and the still scarce resources for ocean sampling, create a demand for quantitative tools for optimizing their use. In this work, the problem of optimally merging networks of profiling floats and gliders is considered. Specifically, a genetic algorithm is employed to find optimal glider trajectories to get together an unevenly distributed network of floats the best quality of the sampled field. A measure of the quality of the oceanographic field (objective function to minimize) is defined in terms of the mean formal error obtained from an optimum interpolation scheme. Results show that the quality of the sampled field can be greatly improved by merging both networks if the resolution of glider observations is adequately selected. The spatial lag between glider observations is related to the geometry of the network of profiling floats and must be order of the grid spacing obtained from the mean data spacing of the network of floats.

Frequently, autonomous underwater vehicles (AUVs) must operate in turbulent ocean environments with complex spatio-temporal variability. Energetic flows, instabilities and currents can strongly perturb safety conditions and development of AUVs operations. A priori knowledge of this ocean variability would allow to adequately plan AUV missions, minimizing the possible negative effects of the environment on its operation. Unfortunately, present oceanographic technology is only capable to forecast large and slow components of the ocean variability, being fast and small scales of variability still unpredictable. This partial knowledge about future environmental conditions degrades AUV robustness, reducing its autonomy and safety. In this article, we propose a class of real-time algorithm to support AUVs navigation in strong turbulent ocean environments characterized by unpredictable small scale variability. The algorithm infers the two-dimensional structure of the current field in a limited region in front of the AUV, using the one-dimensional information obtained from an horizontal acoustic doppler current profiler (H-ADCP). Then, a planner locally optimizes the performance of the AUV in the inferred field. In this work reducing travelling time was of interest. The proposed procedure has been tested on simulated turbulent environments. Results indicate that, although sub-optimals, solutions provided by the algorithm required significantly less travelling time than straight line paths. An example where the proposed methodology increases AUV safety and autonomy is also provided

Autonomous Underwater Vehicles (AUVs) operate in ocean environments characterized by complex spatial variability which can jeopardize their missions. To avoid this, planning safety routes with minimum energy cost is of primary importance. This work explores the benefits, in terms of energy cost, of path planning in marine environments showing certain spatial variability. Extensive computations have been carried out to calculate, by means of an A* search procedure, optimal paths on ocean environments with different length scale of eddies and different current intensities. To get statistical confidence, different realizations of the eddy field and starting-ending points of the path have been considered for each environment. Unlike previous works, the more realistic and applied case of constant thrust power navigation is considered. Results indicate that substantial energy savings of planned paths compared to straight line trajectories are obtained when the current intensity of the eddy structures and the vehicle speed are comparable. Conversely, the straight line path between starting and ending points can be considered an optimum path when the current speed does not exceed half of the vehicle velocity. In both situations, benefits of path planning seem dependent of the spatial structure of the eddy field.