Spectrally Efficient Underwater Acoustic Communications
Spectrally Efficient Underwater Acoustic Communications

Author: Andreja Radošević

Publisher:

Published: 2012

Total Pages: 186

ISBN-13: 9781267433497

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In this dissertation, we consider design aspects of spectrally efficient underwater acoustic (UWA) communications. In particular, we first focus on statistical characterization and capacity evaluation of shallow water acoustic communications channels. Wideband single-carrier and multi-carrier probe signals are employed during the Kauai Acoustic Communications MURI 2008 (KAM08) and 2011 (KAM11) experiments, to measure the time-varying channel response, and to estimate its statistical properties and capacity that play an important role in the design of spectrally efficient communication systems. Besides the capacity analysis for unconstrained inputs, we determine new bounds on the achievable information rate for discrete-time Gaussian channels with inter-symbol interference and independent and uniformly distributed channel input symbols drawn from finite-order modulation alphabets. Specifically, we derived new bounds on the achievable rates for sparse channels with long memory. Furthermore, we explore design aspects of adaptive modulation based on orthogonal frequency division multiplexing (OFDM) for UWA communications, and study its performance using real-time at-sea experiments. Lastly, we investigate a channel estimation (CE) method for improving the spectral efficiency of UWA communications. Specifically, we determine the performance of a selective decision directed (DD) CE method for UWA OFDM-based communications.

High Spectral-Efficiency Signaling Schemes for Underwater Wireless Optical Communication Systems
High Spectral-Efficiency Signaling Schemes for Underwater Wireless Optical Communication Systems

Author: Taha Essalih

Publisher:

Published: 2021

Total Pages: 0

ISBN-13:

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Emerging maritime applications such as ecological monitoring, natural resource discovery, and port security have an inherent need for high data-rate underwater wireless links. Underwater wireless optical communications (UWOCs) are recognized as a cost-effective and energy-efficient alternative or complementary technology to acoustic and radiofrequency underwater communication systems. To extend the transmission range of UWOC systems, there has been a growing interest in employing silicon photo-multipliers (SiPMs) at the receiver, which ensure high sensitivity in addition to several implementation and operational advantages, as compared with photo-multiplier tubes, for instance.This thesis studies SiPM-based UWOC links and focuses on the appropriate signalling schemes that offer high spectral efficiency in order to overcome the bandwidth limitation of SiPMs and/or emitting devices. We consider, in particular, optical orthogonal frequency-division multiplexing (O-OFDM) schemes and investigate their advantages and limitations by taking into account the limited dynamic range of the transmitter and the receiver, as well as the constraint on the transmit electrical power. We start by studying the performance of the two popular schemes of DC-biased and asymmetrically-clipped O-OFDM (DCO- and ACO-OFDM), and show the advantage of the former in terms of link range flexibility. We further consider a few recently-proposed spectrally-enhanced schemes including the hybrid ACO and the layered ACO (HACO- and LACO-OFDM) and show the good compromise that they make between energy efficiency and operational range flexibility, at the cost of a higher computational complexity and a longer delay latency at the receiver.

In-Band Full-Duplex Underwater Acoustic Communications
In-Band Full-Duplex Underwater Acoustic Communications

Author: Zheng Guo

Publisher:

Published: 2021

Total Pages:

ISBN-13:

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In-band full-duplex (IBFD) communications is a promising technique for increased spectral efficiency. This dissertation investigates IBFD acoustic communications in the underwater environment. Four research thrusts are investigated. Due to the absence of near-field acoustic propagation models, these efforts are supported by extensive field tests in local rivers and lakes. Firstly, the near-field SI characteristics were analyzed at multiple acoustic frequencies. The SI cancellation performance deteriorated with the increased signal carrier frequency. Fast channel fluctuations were identified as the reason for the deterioration. The channel variation ratio (CVR) was proposed to quantify the intensity of channel fluctuations. Experimental and simulated results showed that CVRs were larger at higher acoustic frequencies, and large CVRs led to the deteriorated SI suppression. Secondly, the impact of channel fluctuations on the performance of the least-squares channel estimator was quantified. The channel estimation performance, measured by the channel estimation mean squared error (MSE) and the signal prediction error (SPE), was linked with the CVR by analytic expressions. Both the MSE and SPE had an error floor for time-varying impulse responses. It was confirmed that an optimum estimated channel length, achieving the minimum estimation error, existed for time-varying impulse responses. Next, multiple SI suppression methods, including physical separation, digital SI cancellation, directional transducers, and acoustic baffles, were investigated through field experiments. It was found that a 7-m physical separation provided a maximum SI reduction of 32.6 dB. The achieved digital SI cancellation decreased with the increased physical separation ranges. Marginal SI suppression was observed with directional transducers and acoustic baffles. Lastly, an iterative IBFD receiver was developed for IBFD acoustic communications. A control mechanism was used to regulate the digital SI cancellation. The SI cancellation control mechanism and the receiver performance were evaluated by the experimental measurements. A bit error rate (BER) in the order of 10^-2 was achieved at the range of 80 m for IBFD communications with the 28-kHz carrier frequency in a lake environment. With a lower carrier frequency of 10 kHz, a similar BER was demonstrated at the extended range of 100 m with a smaller receiving array.

OFDM for Underwater Acoustic Communications
OFDM for Underwater Acoustic Communications

Author: Sheng Zhou

Publisher: John Wiley & Sons

Published: 2014-03-21

Total Pages: 498

ISBN-13: 1118693817

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A blend of introductory material and advanced signal processing and communication techniques, of critical importance to underwater system and network development This book, which is the first to describe the processing techniques central to underwater OFDM, is arranged into four distinct sections: First, it describes the characteristics of underwater acoustic channels, and stresses the difference from wireless radio channels. Then it goes over the basics of OFDM and channel coding. The second part starts with an overview of the OFDM receiver, and develops various modules for the receiver design in systems with single or multiple transmitters. This is the main body of the book. Extensive experimental data sets are used to verify the receiver performance. In the third part, the authors discuss applications of the OFDM receiver in i) deep water channels, which may contain very long separated multipath clusters, ii) interference-rich environments, where an unintentional interference such as Sonar will be present, and iii) a network with multiple users where both non-cooperative and cooperative underwater communications are developed. Lastly, it describes the development of a positioning system with OFDM waveforms, and the progress on the OFDM modem development. Closely related industries include the development and manufacturing of autonomous underwater vehicles (AUVs) and scientific sensory equipment. AUVs and sensors in the future could integrate modems, based on the OFDM technology described in this book. Contents includes: Underwater acoustic channel characteristics/OFDM basics/Peak-to-average-ratio control/Detection and Doppler estimation (Doppler scale and CFO)/Channel estimation and noise estimation/A block-by-block progressive receiver and performance results/Extensions to multi-input multi-output OFDM/Receiver designs for multiple users/Cooperative underwater OFDM (Physical layer network coding and dynamic coded cooperation)/Localization with OFDM waveforms/Modem developments A valuable resource for Graduate and postgraduate students on electrical engineering or physics courses; electrical engineers, underwater acousticians, communications engineers

Underwater Communications
Underwater Communications

Author: Marco Lanzagorta

Publisher: Morgan & Claypool Publishers

Published: 2013

Total Pages: 132

ISBN-13: 160845844X

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Underwater vehicles and underwater moorings are increasing in tactical importance. As such, it is critical to have a robust and secure communication system connecting underwater vehicles on a long seaborne mission and a ground station. As a matter of fact, the deployment of efficient communication links with underwater vehicles is one of the greatest technological challenges presently confronted by the world's naval forces. To circumvent most of the limitations involved in the use of RF or acoustic channels for perfectly secure communications with underwater vehicles, it is worth considering the feasibility of an optical channel to facilitate a two-way satellite communication link secured via perfectly secure ciphers enabled by a quantum key distribution protocol. This book offers a concise review of underwater communications systems. Our approach is pedagogical, making a strong emphasis on the physics behind the attenuating properties of the oceanic environment and the propagation of electromagnetic signals in the ELF, VLF, and optical bands. We assume the reader is familiar with the basic principles of classical electrodynamics and optics. The system design, components, and noise analysis of an underwater optical communications device are discussed in detail. Furthermore, we offer simulations of the performance of the communication system for different types of ocean waters. Our final conclusion is that it appears to be feasible to design and build underwater communications using optical classical and quantum channels secured with quantum key distribution protocols.

Analysis and Design of Diversity Techniques for Terrestrial and Underwater Acoustic Communications
Analysis and Design of Diversity Techniques for Terrestrial and Underwater Acoustic Communications

Author: Homa Eghbali

Publisher:

Published: 2013

Total Pages: 151

ISBN-13:

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Since the early 1880's, wireless broadband communications have been growing at explosive rates. While the personal communication systems have almost exhausted the spectrum, higher and higher data rates are required to support the ever demanding wireless services. Recently, to improve the spectral efficiency, diversity gains, and interference and power management for wireless multimedia and internet services, by combining the signals at both ends and effectively creating multiple parallel spatial data pipes, the multiple-input multiple-output (MIMO) technology has become a convenient framework. Motivated by these practical concerns, this thesis addresses the analysis and design of diversity techniques for terrestrial and underwater acoustic communication channels, in two parts. Part I studies novel relay selection strategies and diversity techniques for single carrier frequency domain equalization (SC-FDE) multi-relay cooperative networks, considering maximum-likelihood (ML) and minimum mean-square error (MMSE) receivers. We further extend our analysis to two-way relaying (TWR) networks, while incorporating different power control techniques. Building on our results on the diversity and error performance of the single relay and TWR cooperative systems, we extend our analysis to design of MMSE-based optimum beamforming matrices at user and relay terminals in a multi-user, multi-antenna TWR cooperative system. We further present a joint user-relay antenna selection algorithm by applying the estimation of distribution algorithm (EDA). The final contribution of the first part of this thesis is to extend our analysis to large relay networks and address the prohibitive computational and implementation complexity cost of the exhaustive search algorithms for joint transceiver/relay beamforming matrix design in large amplify-and-forward (AF) MIMO TWR networks, while incorporating the orthogonal matching pursuit (OMP) algorithm. The second part of this thesis focuses on the performance of differentially encoded space-time and space-frequency block coding techniques for terrestrial and underwater communication channels.

Energy-Efficient Underwater Wireless Communications and Networking
Energy-Efficient Underwater Wireless Communications and Networking

Author: Goyal, Nitin

Publisher: IGI Global

Published: 2020-09-04

Total Pages: 339

ISBN-13: 1799836428

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Underwater wireless sensor networks (UWSN) are envisioned as an aquatic medium for a variety of applications including oceanographic data collection, disaster management or prevention, assisted navigation, attack protection, and pollution monitoring. Similar to terrestrial wireless sensor networks (WSN), UWSNs consist of sensor nodes that collect the information and pass it to a base station; however, researchers have to face many challenges in executing the network in an aquatic medium. Energy-Efficient Underwater Wireless Communications and Networking is a crucial reference source that covers existing and future possibilities of the area as well as the current challenges presented in the implementation of underwater sensor networks. While highlighting topics such as digital signal processing, underwater localization, and acoustic channel modeling, this publication is ideally designed for machine learning experts, IT specialists, government agencies, oceanic engineers, communication experts, researchers, academicians, students, and environmental agencies concerned with optimized data flow in communication network, securing assets, and mitigating security attacks.

Reinforcement Learning-Based Mobile Underwater Acoustic Communications
Reinforcement Learning-Based Mobile Underwater Acoustic Communications

Author: Qiang Fu

Publisher:

Published: 2022

Total Pages: 0

ISBN-13:

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Underwater acoustic communication technologies are becoming increasingly important due to the widespread adoption of autonomous unmanned vehicles (AUVs) in ocean data collection. The communication support provided by acoustic telemetry makes it possible for multiple AUVs to coordinate during underwater missions. Mobile underwater acoustic communications is still an active field of research. Various technical issues, such as reliable communications between two mobile nodes, multi-user communications, and joint optimization of navigation and communications are awaiting for satisfactory solutions. In this thesis, we develop solutions for several of these issues. The first effort considers an adaptive communication system based on time-reversed orthogonal frequency-division multiplexing methods for the underwater acoustic channels. In this adaptive system, the receiver sends truncated q-functions to the transmitter, which then performs mapping selection for the individual sub-carriers. Simulations demonstrate the advantages of the proposed adaptive system, achieving higher data rates and lower feedback costs. The second effort addresses the extended propagation delay in closed-loop adaptive communications for mobile platforms. An adaptive modulation strategy is developed based on reinforcement learning. Specifically, a Dyna-Q algorithm is presented to improve the communication throughput. Our simulations show that the Dyna-Q algorithm achieves a higher throughput and lower bit-error-rates than the direct feedback. The third effort provides a solution to the acoustic communication problem with multiple AUVs. We propose a virtual multiple-input/multiple-output (MIMO) strategy that selects transmitters from a subset of AUVs to form a virtual transmit array. A user selection algorithm is used to determine the active AUV subset for data transmissions. Adaptive modulation is combined to further improve throughput. The user selection and modulation choice are determined by the predicted data rates, thus increasing spectral efficiency of the uplink. In the last effort of this thesis, we address the trajectory optimization for underwater data muling with mobile nodes. In this scenario, multiple AUVs sample a mission area and autonomous surface vehicles (ASVs) visit underway AUVs to retrieve survey data. We propose a nearest-K reinforcement learning algorithm to optimize ASV travel tracks. The learning-based algorithm can simultaneously maximize fairness in data transmissions and minimize the travel distance of the surface nodes.

Digital Underwater Acoustic Communications
Digital Underwater Acoustic Communications

Author: Lufen Xu

Publisher: Academic Press

Published: 2016-09-16

Total Pages: 292

ISBN-13: 0128030291

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Digital Underwater Acoustic Communications focuses on describing the differences between underwater acoustic communication channels and radio channels, discusses loss of transmitted sound in underwater acoustic channels, describes digital underwater acoustic communication signal processing, and provides a comprehensive reference to digital underwater acoustic communication equipment. This book is designed to serve as a reference for postgraduate students and practicing engineers involved in the design and analysis of underwater acoustic communications systems as well as for engineers involved in underwater acoustic engineering. Introduces the basics of underwater acoustics, along with the advanced functionalities needed to achieve reliable communications in underwater environment Identifies challenges in underwater acoustic channels relative to radio channels, underwater acoustic propagation, and solutions Shows how multi-path structures can be thought of as time diversity signals Presents a new, robust signal processing system, and an advanced FH-SS system for multimedia underwater acoustic communications with moderate communication ranges (above 20km) and rates (above 600bps) Describes the APNFM system for underwater acoustic communication equipment (including both civil and military applications), to be employed in active sonar to improve its performance