Abstract

Abstract
Autonomous Underwater Vehicles (AUVs) are widely used as a cost-effective mean to carry out underwater missions. During long-Term missions, AUVs may collect large amounts of data that usually needs to be sent to shore. An AUV may have to travel several kilometers before reaching an area of interest near the seafloor, thus surfacing is unpractical for most cases. Long-range underwater communications rely mostly on acoustic communications, which are characterized by very low bitrates, thus making the transfer of large amounts of data too slow. GROW is a novel solution for long-range, high bitrate underwater wireless communications between a survey unit (e.g., deep sea lander, AUV) and a central station at surface. GROW combines AUVs as data mules, short-range high bitrate wireless RF or optical communications, and long-range low bitrate acoustic communications for control.In this paper we present the Underwater Data Muling Protocol (UDMP), a communications protocol that enables the control and the scheduling of the Data Mule Units within the GROW framework. Experimental results obtained using an underwater testbed show that the use of UDMP and data mules can outperform acoustic communications, achieving equivalent throughput up to 150 times higher within the typical range of operation of the latter. © 2019 IEEE.

Abstract
The growth of the Blue Economy has been boosted by a set of traditional and new activities including maritime transportation, fisheries, environmental monitoring, deep sea mining, and inspection missions. These activities are urging for a cost-effective broadband communications solution capable of supporting both above and underwater missions at remote ocean areas, since many of them rely on an ever-increasing number of Autonomous Surface Vehicles (ASV), Autonomous Underwater Vehicles (AUV) and Remote Operated Vehicles (ROV), which need to transmit large amounts of data to shore. The BLUE-COM+ project has considered the usage of helium balloons to increase the antenna height, and overtake the earth curvature and achieve Fresnel zone clearance, combined with the use of sub-GHz frequency bands to enable long range communications. In this paper we present the results obtained in three sea trials. They show that the BLUECOM+ architecture is capable of supporting human and system activities at remote ocean areas by enabling Internet access beyond 50 km from shore, live video conference calls with the quality of experience available on land, and real-time data upload to the cloud by ASVs, AUVs and ROVs using standard access technologies with bitrates above 1 Mbit/s.

Abstract
In this paper we assess the influence of the conductivity of the medium on the radiation characteristics and input impedance of a loop antenna designed for underwater communications. The initial study is based on simulation of the antenna characteristics using FEKO electromagnetic (EM) software. Additionally, an equivalent circuit model of the antenna is also obtained and simulation of the input impedance on ADS software shows good agreement with the EM simulator. It is found that the radiation pattern, of the loop antenna changes significantly with the conductivity of the medium, from freshwater to seawater. The loop antennas were built with baluns and tested in freshwater, where the insertion loss between two identical antennas and the radiation pattern of one of them were also measured. The results show good agreement with the simulations.

Abstract
The radiation characteristics of a dipole antenna when immersed in both fresh and seawater are assessed through simulation and experimental work. Simulations show that the antenna's bandwidth and radiation pattern change with the properties of the medium where it is placed, namely the conductivity of the medium. Two dipoles antennas with current baluns were built and tested experimentally in freshwater. The tests included the measurement of the insertion loss between two identical dipole antennas and their radiation pattern. The results obtained show a good agreement between the simulation and experimental results.