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Our research focuses on the horizontal underwater acoustic communications. Towards the high rate objective, we address two key issues, namely channel estimation and symbol detection. To enhance channel estimation, we propose a cyclic approach (CA) for designing training sequences and an iterative adaptive approach (IAA) for estimating the channel. We also present a minimum mean-squared error (MMSE) based symbol detector, RELAX-BLAST, which combines vertical Bell Labs Layered Space-Time (V-BLAST) algorithm and the cyclic principle of RELAX. Towards the high reliability objective, we design robust MIMO transceivers that allow for very low-complexity receiver processing while achieving superb error performance even in turbulent sea. Our unique study on the correlation between the error performance and environmental data further confirms the robustness of our designs. We also performed theoretical capacity analysis as well as practical system designs of relay-aided (RA- )UAC to augment both the reliability and transmission range.
Our research focuses on the horizontal underwater acoustic communications. During this year, our research on multi-input multi-output underwater acoustic communications (MIMO-UAC) can be categorized into two thrusts: (1) Robust MIMO-UAC with Low-Complexity Receivers and (2) Enhanced Channel Estimation and Symbol Detection for High Speed MIMO-UAC. In terms of MIMO-UAC with low-complexity receivers, we have established a simple windowed least squares (LS) channel estimator, developed a differential MIMO scheme obviating channel estimation, and analyzed the effects of different doubly-selective channel models in UAC scenarios. For high-speed MIMO-UAC, we have focused on the channel estimation and symbol detection problems in MIMO-UAC. We have presented a cyclic approach approach for designing training sequences with good auto- and cross-correlation properties. Iterative adaptive approach (IAA) coupled with Bayesian information criterion and RELAX has been presented as an approach for estimating the channel impulse response. We also proposed a new detection method called RELAX-BLAST. Our proposed schemes are tested via both simulations and field data from the acoustic communications experiment (RACE'08) conducted by the Woods Hole Oceanographic Institution (WHOI).
A new receiver design using iterative block decision-feedback equalizer (BDFE) is proposed for high data rate single-carrier multiple-input, multiple-output (MIMO) underwater acoustic (UWA) communications. The adoption of BDFE enables a sequence-based log-likelihood ratio (LLR) calculation during iterative equalization, thus leading to better performance and faster convergence than existing low-complexity iterative equalization methods using symbol-based LLR evaluation. The proposed BDFE method is applied to overlapped blocks to reduce performance degradation at the tail of each block. The block size is flexibly selected depending on the practical channel condition. The proposed receiver scheme has been tested by extensive experimental data and proved to be robust to different transmission environments with consistently good detection performance. Data from collected during the SPACE08 experiment near Martha's Vineyard and the GOMEX08 experiment at the Gulf of Mexico, are both presented here.
This volume addresses the problem of designing efficient signalling and provides a link between the areas of communication theory and modem design for amplitude constrained linear optical intensity channel. It provides practical guidelines for the design of signalling sets for wireless optical intensity channels.
This is an unparalleled modern handbook reflecting the richly interdisciplinary nature of acoustics edited by an acknowledged master in the field. The handbook reviews the most important areas of the subject, with emphasis on current research. The authors of the various chapters are all experts in their fields. Each chapter is richly illustrated with figures and tables. The latest research and applications are incorporated throughout, including computer recognition and synthesis of speech, physiological acoustics, diagnostic imaging and therapeutic applications and acoustical oceanography. An accompanying CD-ROM contains audio and video files.
This open access State-of-the-Art Survey presents the main recent scientific outcomes in the area of reversible computation, focusing on those that have emerged during COST Action IC1405 "Reversible Computation - Extending Horizons of Computing", a European research network that operated from May 2015 to April 2019. Reversible computation is a new paradigm that extends the traditional forwards-only mode of computation with the ability to execute in reverse, so that computation can run backwards as easily and naturally as forwards. It aims to deliver novel computing devices and software, and to enhance existing systems by equipping them with reversibility. There are many potential applications of reversible computation, including languages and software tools for reliable and recovery-oriented distributed systems and revolutionary reversible logic gates and circuits, but they can only be realized and have lasting effect if conceptual and firm theoretical foundations are established first.
The continents of our planet have already been exploited to a great extent. Therefore man is turning his sight to the vast spaciousness of the ocean whose resources - mineral, biological, energetic, and others - are just beginning to be used. The ocean is being intensively studied. Our notions about the dynam ics of ocean waters and their role in forming the Earth's climate as well as about the structure of the ocean bottom have substantially changed during the last two decades. An outstanding part in this accelerated exploration of the ocean is played by ocean acoustics. Only sound waves can propagate in water over large distances. Practically all kinds of telemetry, communication, location, and re mote sensing of water masses and the ocean bottom use sound waves. Propa gating over thousands of kilometers in the ocean, they bring information on earthquakes, eruptions of volcanoes, and distant storms. Projects using acoustical tomography systems for exploration of the ocean are presently be ing developed. Each of these systems will allow us to determine the three-di mensional structure of water masses in regions as large as millions of square kilometers.