Cost-Effective and Energy-Efficient Techniques for Underwater Acoustic Communication Modems

Finally, the modem developed has been tested experimentally in laboratory (aquatic environment) showing that can communicates at different data rates (100..1200 bps) compared to state-of-the-art research modems. The software used include LabVIEW, MATLAB, Simulink, and Multisim (to test the electronic circuit built) has been employed.Underwater wireless sensor networks (UWSNs) are widely used in many applications related to ecosystem monitoring, and many more fields. Due to the absorption of electromagnetic waves in water and line-of-sight communication of optical waves, acoustic waves are the most suitable medium of communication in underwater environments. Underwater acoustic modem (UAM) is responsible for the transmission and reception of acoustic signals in an aquatic channel. Commercial modems may communicate at longer distances with reliability, but they are expensive and less power efficient. Research modems are designed by using a digital-signal-processor (DSP is expensive) and field-programmable-gate-array (FPGA is high power consuming device). In addition to, the use of a microcontroller is also a common practice (which is less expensive) but provides limited computational power. Hence, there is a need for a cost-effective and energy-efficient UAM to be used in budget limited applications. In this thesis different objectives are proposed. First, to identify the limitations of state-of-the-art commercial and research UAMs through a comprehensive survey. The second contribution has been the design of a low-cost acoustic modem for short-range underwater communications by using a single board computer (Raspberry-Pi), and a microcontroller (Atmega328P). The modulator, demodulator and amplifiers are designed with discrete components to reduce the overall cost. The third contribution is to design a web based underwater acoustic communication testbed along with a simulation platform (with underwater channel and sound propagation models), for testing modems. The fourth contribution is to integrate in a single module two important modules present in UAMs: the PSK modulator and the power amplifier

Underwater Acoustic Modems

© 2016 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.Due to the growing interest using underwater acoustic networks, there are more and more research papers about underwater communications. These papers are mainly focused on deployments and studies about the constraints of the underwater medium. The underwater acoustic channel is highly variable and the signal transmission can change according to environmental factors such as the temperature, pressure or salinity of the water. For this reason, it is important to know how these devices are developed and the maximum distance and data transfer rates they can achieve. To this end, this paper presents an exhaustive study of existing underwater acoustic modems where their main features are highlighted. We also review the main features of their hardware. All presented proposals in the research literature are compared with commercial underwater acoustic modems. Finally, we analyze different programs and improvements of existing network simulators that are often used to simulate and estimate the behavior of underwater networks.This work was supported by the Ministerio de Ciencia e Innovacion through the Plan Nacional de I+D+i 2008-2011 within the Subprograma de Proyectos de Investigacion Fundamental under Project TEC2011-27516. The associate editor coordinating the review of this paper and approving it for publication was Dr. Lei Shu. (Corresponding author: Jaime Lloret.)Sendra, S.; Lloret, J.; Jimenez, JM.; Parra-Boronat, L. (2015). Underwater Acoustic Modems. IEEE Sensors Journal. 16(11):4063-4071. https://doi.org/10.1109/JSEN.2015.2434890S40634071161

Re-Evaluation of RF Electromagnetic Communication in Underwater Sensor Networks

Most underwater wireless networks use acoustic waves as the transmission medium nowadays, but the chances of getting much more out of acoustic modems are quite remote. Optical links are impractical for many underwater applications. Given modern operational requirements and digital communications technology, the time is now ripe for re-evaluating the role of electromagnetic signals in underwater environments. The research presented in this article is motivated by the limitations of current and established wireless underwater techniques, as well as the potential that electromagnetic waves can offer to underwater applications. A case study is presented that uses electromagnetic technology in a small-scale underwater wireless sensor network. The results demonstrate the likely effectiveness of the designated network

Data Muling for Broadband and Long Range Wireless Underwater Communications

During the past years, there has been an increasing interest in the exploration of underwater wireless communications. This interest has been related mainly to the need for establishing a reliable way of transferring large amounts of data gathered on remote locations in the ocean. This data comes from environmental exploration, oil and gas industries, or marine data from Autonomous Underwater Vehicles (AUVs). These activities require innovative solutions that can provide high bitrates at low costs. With this in mind, and given the current solutions - Optical, Acoustic, and Radio Frequency -, there is the need to create a solution that takes advantage of each technology and overcomes their limitations. In the case of optical communications, they can provide high bitrates, but requires line of sight, and depend significantly on water turbidity. Although acoustic solutions can provide a large range of operation, they have a low bandwidth due to the frequency of operation, and so they are not suitable for transferring high amounts of data. Finally, current radio frequency (RF) solutions allow high bit rates but are limited by the operation range due to the substantial attenuation of electromagnetic waves underwater. With this in mind, it is possible to say that currently, there is no solution for broadband long-range underwater communications. This dissertation aims to develop a solution that allows the increase of throughput and range of underwater wireless communications. To achieve this, a set of underwater data mules will be used. They will take advantage of the high bitrates of RF wireless communications and the long-range associated with acoustic solutions. With this dissertation, communication protocols designed for delay and disruption tolerant networks (DTNs) will be explored, and a protocol that will enable the scheduling of mules will be proposed and implemented, taking advantage of an out-of-band acoustic channel for controlling the mules, and the DTN for data transfer. The solution will be evaluated in a freshwater testbed