Download or read book Channel Equalization in Underwater Acoustic Communications Using Multiple Antennas written by Leili Baghaei Rad and published by . This book was released on 2006 with total page 178 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Combined Spatial Diversity and Time Equalization for Broadband Multiple Channel Underwater Acoustic Communications written by Violeta Skoro Kaskarovska and published by . This book was released on 2015 with total page 136 pages. Available in PDF, EPUB and Kindle. Book excerpt: High data rate acoustic communications become feasible with the use of communication systems that operate at high frequency. The high frequency acoustic transmission in shallow water endures severe distortion as a result of the extensive intersymbol interference and Doppler shift, caused by the time variable multipath nature of the channel. In this research a Single Input Multiple Output (SIMO) acoustic communication system is developed to improve the reliability of the high data rate communications at short range in the shallow water acoustic channel. The proposed SIMO communication system operates at very high frequency and combines spatial diversity and decision feedback equalizer in a multilevel adaptive configuration. The first configuration performs selective combining on the equalized signals from multiple receivers and generates quality feedback parameter for the next level of combining. The second configuration implements a form of turbo equalization to evaluate the individual receivers using the feedback parameters as decision symbols. The improved signals from individual receivers are used in the next iteration of selective combining. Multiple iterations are used to achieve optimal estimate of the received signal. The multilevel adaptive configuration is evaluated on experimental and simulated data using SIMO system with three, four and five receivers. The simulation channel model developed for this research is based on experimental channel and Rician fading channel model. The performance of the channel is evaluated in terms of Bit Error Rate (BER) and Signal-to-Noise-and-Interference Ratio (SNIR). Using experimental data with non-zero BER, multilevel adaptive spatial diversity can achieve BER of 0 % and SNIR gain of 3 dB. The simulation results show that the average BER and SNIR after multilevel combining improve dramatically compared to the single receiver, even in case of extremely high BER of individual received signals. The results demonstrate the ability of the proposed multilevel adaptive combining approach to significantly improve the performance of the shallow water acoustic channel, while preserving the same transmission power and channel bandwidth.

Download or read book Channel Equalization for Wireless Communications written by Gregory E. Bottomley and published by John Wiley & Sons. This book was released on 2012-01-03 with total page 192 pages. Available in PDF, EPUB and Kindle. Book excerpt: The most thorough, up-to-date reference on channel equalization—from basic concepts to complex modeling techniques In today's instant-access society, a high premium is placed on information that can be stored and communicated effectively. As a result, storage densities and communications rates are being pushed to capacity, causing information symbols to interfere with one another. To help unclog pathways for the clearer conveyance of information, this book offers in-depth discussion of the significant contributions and future adaptability of channel equalization and a set of approaches for solving the problem of intersymbol interference (ISI). Chapter explorations in Channel Equalization include: Channel equalization topics presented with incremental learning methodology—from the very fundamental concept to more advanced mathematical knowledge Coverage of technology used in second-, third- and fourth-generation cellular communication systems A set of homework problems that reinforce concepts discussed in the book Tutorial explanations of recent developments currently captured in IEEE technical journals Unlike existing digital communications books that devote cursory attention to channel equalization, this invaluable guide addresses a crucial need by focusing solely on the background, current state, and future direction of this increasingly important technology. A unique mix of basic concepts and complex frameworks for delivering digitized data make Channel Equalization a valuable reference for all practicing wireless communication engineers and students dealing with the pressing demands of the information age.

Download or read book OFDM for Underwater Acoustic Communications written by Sheng Zhou and published by John Wiley & Sons. This book was released on 2014-03-21 with total page 498 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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

Download or read book Analysis and Design of Diversity Techniques for Terrestrial and Underwater Acoustic Communications written by Homa Eghbali and published by . This book was released on 2013 with total page 151 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Frequency Domain Channel Estimation and Equalization for Single Carrier Underwater Acoustic Communications written by and published by . This book was released on 2007 with total page 7 pages. Available in PDF, EPUB and Kindle. Book excerpt: A new frequency-domain channel estimation and equalization (FDE) scheme is proposed for single carrier (SC) underwater acoustic communications. The proposed SC-FDE employs a small training signal block for initial channel estimation in the frequency domain and converts the estimated transfer function to a desired DFT (discrete Fourier transform) size for channel equalization of the data blocks. The frequency domain equalizer is designed using the linear minimum mean square error criterion. A new phase coherent detection scheme is also proposed and deployed to combat the phase drift due to the instantaneous Doppler in the underwater channels. The channel transfer functions and group-averaged phase drift are re-estimated adaptively in a decision-directed manner for each data block in a packet, which contains M blocks of QPSK data. The proposed SC-FDE method is applied to single input multiple output (SIMO) systems using the experimental data measured off the coast of Panama City, Florida, USA, June 2007. The uncoded bit error rate of the SIMO systems varies between 1.3% to 6.8 10( -5) when 4 tilde 8 receive hydrophones are utilized, and the source-receiver range is 5.06 km.

Download or read book Analysis of and Techniques for Adaptive Equalization for Underwater Acoustic Communication written by Ballard Justin Smith Blair and published by . This book was released on 2011 with total page 215 pages. Available in PDF, EPUB and Kindle. Book excerpt: Underwater wireless communication is quickly becoming a necessity for applications in ocean science, defense, and homeland security. Acoustics remains the only practical means of accomplishing long-range communication in the ocean. The acoustic communication channel is fraught with difficulties including limited available bandwidth, long delay-spread, time-variability, and Doppler spreading. These difficulties reduce the reliability of the communication system and make high data-rate communication challenging. Adaptive decision feedback equalization is a common method to compensate for distortions introduced by the underwater acoustic channel. Limited work has been done thus far to introduce the physics of the underwater channel into improving and better understanding the operation of a decision feedback equalizer. This thesis examines how to use physical models to improve the reliability and reduce the computational complexity of the decision feedback equalizer. The specific topics covered by this work are: how to handle channel estimation errors for the time varying channel, how to use angular constraints imposed by the environment into an array receiver, what happens when there is a mismatch between the true channel order and the estimated channel order, and why there is a performance difference between the direct adaptation and channel estimation based methods for computing the equalizer coefficients. For each of these topics, algorithms are provided that help create a more robust equalizer with lower computational complexity for the underwater channel.

Download or read book Novel Adaptive Signal Processing Techniques for Underwater Acoustic Communications written by and published by . This book was released on 2011 with total page 137 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Comparison of Channel Equalization Filtering Techniques in Underwater Acoustic Communications written by Ryan J. Kuchler and published by . This book was released on 2002-06-01 with total page 171 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this thesis, underwater acoustic communications signal processing techniques which are used to equalize the distortional effects associated with the ocean as a communications channel, are investigated for a shallow water ocean environment. The majority of current signal processing techniques employ a Finite Impulse Response (FIR) filter. Three equalization filters were investigated and presented as alternatives; they were the passive time-reversed filter, the inverse filter, and the Infinite Impulse Response (IIR) filter. The main advantage of the passive time-reversed filter and the inverse filter is simplicity of design. Bit error rates for the time-reversed filter were consistently around 10(exp -1) and those for the inverse filter were greater than 10(exp -1). However, inability of the passive time-reversed filter to completely eliminate multipath components and the ill-conditioned nature offline inverse filter made it difficult to achieve Probability of Error results below 10(exp -1). Research into the development of an array receiver using a time- reversed filter should improve calculated bit error rates. Simulations of the IIR filter were conducted with limited success. The main advantage of an IIR filter is that fewer parameters are required in the design of the filter. However, the potential for instability in the filter is a significant limitation. Probability of Error results were found to be on the order of those for current FIR filters at close ranges. Unfortunately, instability issues arose for receivers as range from the source increased. This research on the IIR filter is still in the embryonic stage whereas research using FIR filters is relatively highly developed. Further research is needed to address the issue of instability in IIR filters in order to make them effective signal processing technique employable in underwater acoustic communications.

Download or read book Multi carrier Communications Over Underwater Acoustic Channels written by Kai Tu and published by . This book was released on 2011 with total page 153 pages. Available in PDF, EPUB and Kindle. Book excerpt: Underwater acoustic communications face significant challenges unprecedented in radio terrestrial communications including long multipath delay spreads, strong Doppler effects, and stringent bandwidth requirements. Recently, multi-carrier communications based on orthogonal frequency division multiplexing (OFDM) have seen significant growth in underwater acoustic (UWA) communications, thanks to their well well-known robustness against severely time-dispersive channels. However, the performance of OFDM systems over UWA channels significantly deteriorates due to severe intercarrier interference (ICI) resulting from rapid time variations of the channel. With the motivation of developing enabling techniques for OFDM over UWA channels, the major contributions of this thesis include (1) two effective frequencydomain equalizers that provide general means to counteract the ICI; (2) a family of multiple-resampling receiver designs dealing with distortions caused by user and/or path specific Doppler scaling effects; (3) proposal of using orthogonal frequency division multiple access (OFDMA) as an effective multiple access scheme for UWA communications; (4) the capacity evaluation for single-resampling versus multiple-resampling receiver designs. All of the proposed receiver designs have been verified both through simulations and emulations based on data collected in real-life UWA communications experiments. Particularly, the frequency domain equalizers are shown to be effective with significantly reduced pilot overhead and offer robustness against Doppler and timing estimation errors. The multiple-resampling designs, where each branch is tasked with the Doppler distortion of different paths and/or users, overcome the disadvantages of the commonly-used single-resampling receivers and yield significant performance gains. Multiple-resampling receivers are also demonstrated to be necessary for UWA OFDMA systems. The unique design effectively mitigates interuser interference (IUI), opening up the possibility to exploit advanced user subcarrier assignment schemes. Finally, the benefits of the multiple-resampling receivers are further demonstrated through channel capacity evaluation results.

Download or read book Direct form Adaptive Equalization for Underwater Acoustic Communication written by Atulya Yellepeddi and published by . This book was released on 2012 with total page 143 pages. Available in PDF, EPUB and Kindle. Book excerpt: Adaptive equalization is an important aspect of communication systems in various environments. It is particularly important in underwater acoustic communication systems, as the channel has a long delay spread and is subject to the effects of time- varying multipath fading and Doppler spreading. The design of the adaptation algorithm has a profound influence on the performance of the system. In this thesis, we explore this aspect of the system. The emphasis of the work presented is on applying concepts from inference and decision theory and information theory to provide an approach to deriving and analyzing adaptation algorithms. Limited work has been done so far on rigorously devising adaptation algorithms to suit a particular situation, and the aim of this thesis is to concretize such efforts and possibly to provide a mathematical basis for expanding it to other applications. We derive an algorithm for the adaptation of the coefficients of an equalizer when the receiver has limited or no information about the transmitted symbols, which we term the Soft-Decision Directed Recursive Least Squares algorithm. We will demonstrate connections between the Expectation-Maximization (EM) algorithm and the Recursive Least Squares algorithm, and show how to derive a computationally efficient, purely recursive algorithm from the optimal EM algorithm. Then, we use our understanding of Markov processes to analyze the performance of the RLS algorithm in hard-decision directed mode, as well as of the Soft-Decision Directed RLS algorithm. We demonstrate scenarios in which the adaptation procedures fail catastrophically, and discuss why this happens. The lessons from the analysis guide us on the choice of models for the adaptation procedure. We then demonstrate how to use the algorithm derived in a practical system for underwater communication using turbo equalization. As the algorithm naturally incorporates soft information into the adaptation process, it becomes easy to fit it into a turbo equalization framework. We thus provide an instance of how to use the information of a turbo equalizer in an adaptation procedure, which has not been very well explored in the past. Experimental data is used to prove the value of the algorithm in a practical context.

Download or read book Harvesting Time frequency space Diversity with Coded Modulation for Underwater Acoustic Communications written by Konstantinos Pelekanakis and published by . This book was released on 2009 with total page 360 pages. Available in PDF, EPUB and Kindle. Book excerpt: (Cont.) Both systems are combined with specific space-time block codes (STBC) when two or three transmit antennas are used. Moreover, pilot-symbol-aided channel estimation is performed by using a robust 2-D Wiener filter, which copes with channel model mismatch by employing appropriate time and frequency correlation functions. The following result was obtained by testing the aforementioned systems using both simulated and experimental data from RACE '08: the BICM scheme performs better when the UWA channel exhibits limited spatial diversity. This result implies that coded modulation schemes emphasizing higher Hamming distances are preferred when there is no option for many receive/transmit hydrophones. The TCM scheme, on the other hand, becomes a better choice when the UWA channel demonstrates a high spatial diversity order. This result implies that coded modulation schemes emphasizing higher free Euclidean distances are preferred when multiple receive/transmit hydrophones are deployed.

Download or read book Iterative Equalization and Decoding Applied to Underwater Acoustic Communication written by James F. Sifferlen and published by . This book was released on 2008 with total page 134 pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation focuses on data communication over shallow, long-range underwater acoustic (UWA) channels, which are characterized by relatively long, time-varying impulse responses and acute sensitivity to Doppler effects. The latter is a result of the slow speed of sound in water, while the former is a consequence of the waveguide nature of shallow, long-range UWA channels. A succession of novel receiver algorithms are developed which recover digital information transmitted across such channels. The first considers the case of a single, fixed source transducer transmitting information to a single, fixed receive hydrophone. The second extends the first to allow nontrivial source motion, for instance, that of an autonomous undersea vehicle. The third extends the second to allow processing of data received on an array of hydrophones. The algorithms employ iterative detection. Iterative processing is creating a paradigm shift in digital communication, made possible by ever-increasing computational capabilities. There are two major components to the algorithms: an equalizer and a decoder. The main focus of this dissertation is the former which, because of the features of the UWA channel, and since the channel is not assumed known a priori at the receiver, entails adaptive resampling to correct for Doppler distortion, adaptive filtering to estimate the time-varying channel, and adaptive equalization to compensate for intersymbol interference produced by the long channel impulse responses. While decoding is performed using standard methods, its role is nonetheless crucial to the overall functioning of the algorithms. In fact, they rely on the iterative exchange of information between equalizer and decoder, and the improvement of that information with each iteration. Successful performance of the algorithms is demonstrated using data from at-sea experiments.

Download or read book OFDM for Underwater Acoustic Communications written by Sheng Zhou and published by John Wiley & Sons. This book was released on 2014-06-03 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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

Download or read book Coding for MIMO Communication Systems written by Tolga M. Duman and published by John Wiley & Sons. This book was released on 2008-03-11 with total page 366 pages. Available in PDF, EPUB and Kindle. Book excerpt: Coding for MIMO Communication Systems is a comprehensive introduction and overview to the various emerging coding techniques developed for MIMO communication systems. The basics of wireless communications and fundamental issues of MIMO channel capacity are introduced and the space-time block and trellis coding techniques are covered in detail. Other signaling schemes for MIMO channels are also considered, including spatial multiplexing, concatenated coding and iterative decoding for MIMO systems, and space-time coding for non-coherent MIMO channels. Practical issues including channel correlation, channel estimation and antenna selection are also explored, with problems at the end of each chapter to clarify many important topics. A comprehensive book on coding for MIMO techniques covering main strategies Theories and practical issues on MIMO communications are examined in detail Easy to follow and accessible for both beginners and experienced practitioners in the field References at the end of each chapter for further reading Can be used with ease as a research book, or a textbook on a graduate or advanced undergraduate level course This book is aimed at advanced undergraduate and postgraduate students, researchers and practitioners in industry, as well as individuals working for government, military, science and technology institutions who would like to learn more about coding for MIMO communication systems.

Download or read book Multicarrier Modulation for Underwater Acoustic Communications written by Baosheng Li and published by . This book was released on 2009 with total page 174 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Spatiotemporal Processing and Time reversal for Underwater Acoustic Communications written by Daniel Y. Wang and published by . This book was released on 2005 with total page 67 pages. Available in PDF, EPUB and Kindle. Book excerpt: High-rate underwater acoustic communication can be achieved using transmitter/receiver arrays. Underwater acoustic channels can be characterized as rapidly time-varying systems that suffer severe Inter Symbol Interferences (ISI) caused by multi-path propagation. Multi-channel combining and equalization, as well as time-reversal techniques have been used over these channels to reduce the effect of ISI. As an alternative, a spatiotemporal focusing technique had been proposed. This technique is similar to time-reversal but it explicitly takes into account elimination of ISI. To do so, the system relies on the knowledge of channel responses. In practice, however, only channel estimates are available. To assess the system performance for imperfectly estimated time-varying channels, a simulation analysis was conducted. Underwater acoustic channels were modeled using geometrical representations of a 3-path propagation model. Multi-path fading was incorporated using auto regressive models. Simulations were conducted with various estimator delay scenarios for both the spatiotemporal focusing and simple time-reversal. Results demonstrate performance dependence on the non-dimensional product of estimation delay and Doppler spread. In particular, it has been shown that when this product is low, the performance of spatiotemporal focusing remains superior to simple time- reversal.