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 Adaptive Channel Equalization in the Time Varying Underwater Acoustic Channel Performance Characterization and Robust Equalizers written by and published by . This book was released on 2004 with total page 23 pages. Available in PDF, EPUB and Kindle. Book excerpt: Channel-estimate-based equalizers are adaptive coherent equalizers for which observations of the received signal are used to estimate channel parameters and these estimates are used to calculate the equalizer filter weights. Traditional channel-estimate- based equalizers calculate filter weights assuming that the estimates of the channel parameters are perfect. This work presents a common framework for evaluating both the performance of channel-estimate- based equalizers when the channel estimates are perfect (i.e. the minimal achievable error of the equalizer) and the degradation in performance of these equalizers due to errors in the channel estimates (i.e. the excess error). For the three type of equalizers considered (DFE Linear MMSE and Passive Time Reversal) the expressions for minimal achievable error take the form of the results from classical estimation theory for estimation error achieved by MMSE and matched filter estimators. These expressions are interpreted to give insights into the characteristics of "good" and "bad" channels. For the case when the channel estimates are MMSE estimates of the channel-impulse response, the excess error is shown to be proportional to the 2-norm of the calculated feedforward filter weight vector of the equalizer. This result is analogous to the "white noise gain" result characterizing the sensitivity of adaptive array processors to mismatch. This result is used to evaluate the relative sensitivity of all three types of equalizers to environmental mismatch. The analytic predictions of equalizer performance are compared with observed performance using data from several field experiments in different underwater acoustic environments. The expressions for minimal achievable error and excess error give insights into potential methods of improving the robustness to channel mismatch of adaptive equalizers such as the DFE. Several of these methods are implemented and evaluated.

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 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 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 The Application of Tikhonov Regularised Inverse Filtering to Digital Communication Through Multi channel Acoustic Systems written by Pierre M. Dumuid and published by . This book was released on 2012 with total page 261 pages. Available in PDF, EPUB and Kindle. Book excerpt: Communication between underwater vessels such as submarines is difficult to achieve over long distances using radio waves because of their high rate of absorption by water. Using underwater acoustic wave propagation for digital communication has the potential to overcome this limitation. In the last 30 years, there have been numerous papers published on the design of communication systems for shallow underwater acoustic environments. Shallow underwater acoustic environments have been described as extremely difficult media in which to achieve high data rates. The major performance limitations arise from losses due to geometrical spreading and absorption, ambient noise, Doppler spread and reverberation from surface and seafloor reflections (multi-path), with the latter being the primary limitation. The reverberation from multi-path in particular has been found to be very problematic when using the general communication systems that have been developed for radio wave communication systems. In the early 1990s, the principal means of combating multi-path in the shallow underwater environment was to use non-coherent modulation techniques. Coherent of obtaining a phase-lock and also that the environment was subject to fading. Designs have since been presented that addressed both of these problems by using a complex receiver design that involved a joint update of the phase-lock loop and the taps of the decision feedback filter (DFE). In recent years a technique known as time-reversal has been investigated for use in underwater acoustic communication systems. A major benefit of using the time-reversal filter in underwater acoustic communication systems is that it can provide a fast and simple method to provide a receiver design of low complexity. A technique that can be related to time-reversal and possibly used in underwater acoustics is Tikhonov regularised inverse filtering. The Tikhonov regularised inverse filter is a fast method of obtaining a stable inverse filter design by calculating the filter in the frequency domain using the fast Fourier transform, and was originally developed for use in audio reproduction systems. Previous research has shown that the Tikhonov regularised inverse filter design outperformed time-reversal when using a Dirac impulse transmission within a simulated underwater environment. This thesis aims to extend the previous work by examining the implementation of Tikhonov regularised inverse filtering with communication signals. In addressing this goal, two topics have been examined: the influence of the sensitivities in the filter designs, and an examination of various design implementations for Tikhonov regularised inverse filtering and similar filtering techniques. The influence of transducer sensitivities on the Tikhonov regularised inverse filter: During the implementation of the Tikhonov regularised inverse filter it was observed that both the Tikhonov regularised inverse filter and the time-reversal filter were influenced by the sensitivity of the transducers to the acoustic signals, which is determined by the transducer design and the amplifying stages. Unlike single channel systems, setting the sensitivities of the transducers to their maximum value for multi-channel systems does not always maximise the coherence between the input and output of the entire system consisting of the inverse filter, the sensitivities and the electro-acoustic system where the channel is the electro-acoustic transfer function between the transmitter and receiver. The influence the sensitivities have on the performance of the multi-channel Tikhonov regularised inverse filters and the time-reversal filter was examined by performing a mathematical examination of the system. An algorithm was developed that adjusted gains to compensate for the decrease in performance that results from the poor sensitivities. To test the algorithm, a system with an inappropriate set of sensitivities was examined. The performance improvement of the communication system was examined using the generated gains to scale the signal. The algorithm was found to reduce the signal degradation and cross-talk. If the gains were used in the digital domain (after the analog to digital and before the digital to analog converters) then the quality of the signal was improved at the expense of the signal level. During this examination it was found that the time-reversal filter is equivalent to the Tikhonov regularised inverse filter with infinite regularisation. Variations of the Tikhonov regularised inverse filter and performance comparisons: In this thesis, various design structures for the implementation of the Tikhonov inverse filter were proposed and implemented in an experimental digital communication system that operated through an acoustic environment in air. It was shown that the Tikhonov inverse filter and related filter design structures could be classified or implemented according to three different classifications. The Tikhonov inverse filter was implemented according to each of these classifications and then compared against each other, as well as against two other filter designs discussed in the literature: time-reversal filtering, and the two-sided filter developed by Stojanovic [2005]. Due to the number of parameters that could be varied, it was difficult to identify the influence each parameter had on the results independently of the other parameters. A simulation was developed based on a model of the experiment to assist in identifying the influences of each parameter. The parameters examined included the number of transmitter elements, carrier frequency, data rate, and the value of the regularisation parameter. When the communication system consisted of a signal receiver, the Stojanovic two-sided filter generally outperformed the Tikhonov regularised inverse filter designs when communicating. However, at higher data rates, the Stojanovic two-sided filter required the addition of a regularisation parameter to allow it to continue to operate. However, given an appropriately selected regularisation parameter, the difference between the performance of the Tikhonov filter and the Stojanovic two-sided filter was minimal. When performing multi-channel communications, the full MIMO implementation of the Tikhonov regularised inverse filter design was shown to have the best performance. For the environment considered, the Tikhonov regularised inverse filter was the only design that was able to eliminate all symbol errors.

Download or read book Physically Constrained Maximum Likelihood PCML Mode Filtering and Its Application as a Pre processing Method for Underwater Acoustic Communication written by Joseph C. Papp and published by . This book was released on 2009 with total page 87 pages. Available in PDF, EPUB and Kindle. Book excerpt: (cont.) Data processing results are presented from the Shallow Water 2006 experiment, showing the reduced sensitivity of the PCML-MPDR filter to white noise compared with the reduced rank pseudoinverse filter. Lastly, a linear, decision-directed, RLS equalizer is used to combine the response of several modes and its performance is compared with an equalizer applied directly to the data received on each hydrophone.

Download or read book Sparse Channel Estimation and Tracking for Underwater Acoustic Communications written by Danqing Yin and published by . This book was released on 2016 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis focuses on estimation and tracking of underwater acoustic channels. A model of underwater acoustic channel suitable to study the channel estimation problem is constructed. The model is used together with a Bellhop acoustic wave propagation simulator to generate channels for various propagation environments, depths and distances, and we studied their sparseness and variation properties. Finally a number of estimation methods such as basis pursuit and approximate message passing are adapted to channel estimation problems and tested on a number of channels. Window-based and Kalman- filter based channel tracking is also studied. A detailed comparison of estimation and tracking methods is presented.

Download or read book OCEANS 2016 Shanghai written by and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Papers on ocean technology, exhibits from ocean equipment and service suppliers, student posters and student poster competition, tutorial on ocean technology, workshops and town hall meetings on policy and governmental process.

Download or read book Springer Handbook of Acoustics written by Thomas Rossing and published by Springer Science & Business Media. This book was released on 2007-06-21 with total page 1179 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Underwater Acoustic Sensor Networks written by Yang Xiao and published by CRC Press. This book was released on 2010-05-19 with total page 352 pages. Available in PDF, EPUB and Kindle. Book excerpt: A detailed review of underwater channel characteristics, Underwater Acoustic Sensor Networks investigates the fundamental aspects of underwater communication. Prominent researchers from around the world consider contemporary challenges in the development of underwater acoustic sensor networks (UW-ASNs) and introduce a cross-layer approach for effec

Download or read book Communications Signal Processing and Systems written by Qilian Liang and published by Springer. This book was released on 2018-06-07 with total page 2798 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book brings together papers presented at the 2017 International Conference on Communications, Signal Processing, and Systems (ICCSP 2017), which was held on July 14–17, 2017 in Harbin, China. Presenting the latest developments and discussing the interactions and links between these multidisciplinary fields, the book spans topics ranging from communications, signal processing and systems. It is aimed at undergraduate and graduate electrical engineering, computer science and mathematics students, researchers and engineers from academia and industry as well as government employees.

Download or read book Conference Proceedings written by and published by . This book was released on 1999 with total page 594 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Digital Underwater Acoustic Communications written by Lufen Xu and published by Academic Press. This book was released on 2016-09-16 with total page 292 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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

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 Cognitive Underwater Acoustic Networking Techniques written by Dimitri Sotnik and published by Springer Nature. This book was released on 2020-09-29 with total page 89 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book summarizes the latest research on cognitive network-layer methods and smart adaptive physical-layer methods in underwater networks. Underwater communication requires extendable and delay-tolerant underwater acoustic networks capable of supporting multiple frequency bands, data rates and transmission ranges. The book also discusses a suitable foreground communication stack for mixed mobile/static networks, a technology that requires adaptive physical layer waveforms and cognitive network strategies with underlying cooperative and non-cooperative robust processes. The goal is to arrive at a universally applicable standard in the area of Underwater Internet-of-Things [ISO/IEC 30140, 30142, 30143]. The book is the second spin-off of the research project RACUN, after the first RACUN-book "Underwater Acoustic Networking Techniques" (https://link.springer.com/book/10.1007%2F978-3-642-25224-2)