Underwater Acoustic Channel Estimation Using Multiple Sources and Receivers in Shallow Waters at Very-high Frequencies
Underwater Acoustic Channel Estimation Using Multiple Sources and Receivers in Shallow Waters at Very-high Frequencies

Author: Samar Kaddouri

Publisher:

Published: 2015

Total Pages: 120

ISBN-13:

DOWNLOAD EBOOK

The underwater channel poses numerous challenges for acoustic communication. Acoustic waves suffer long propagation delay, multipath, fading, and potentially high spatial and temporal variability. In addition, there is no typical underwater acoustic channel; every body of water exhibits quantiably different properties. Underwater acoustic modems are traditionally operated at low frequencies. However, the use of broadband, high frequency communication is a good alternative because of the lower background noise compared to low-frequencies, considerably larger bandwidth and better source transducer efficiency. One of the biggest problems in the underwater acoustic communications at high frequencies is time-selective fading, resulting in the Doppler spread. While many Doppler detection, estimation and compensation techniques can be found in literature, the applications are limited to systems operating at low frequencies contained within frequencies ranging from a few hundred Hertz to around 30 kHz. This dissertation proposes two robust channel estimation techniques for simultaneous transmissions using multiple sources and multiple receivers (MIMO) that closely follows the rapidly time-varying nature of the underwater channel. The first method is a trended least square (LS) estimation that combines the traditional LS method with an empirical modal decomposition (EMD) based trend extraction algorithm. This method allows separating the slow fading modes in the MIMO channels from the fast-fading ones and thus achieves a close tracking of the channel impulse response time fluctuations. This dissertation also outlines a time-varying underwater channel estimation method based on the channel sparsity characteristic. The sparsity of the underwater communication channel is exploited by using the MIMO P-iterative greedy orthogonal matching pursuit (MIMO-OMP) algorithm for the channel estimation. Both techniques are demonstrated in a fully controlled environment, using simulated and experimental data. To test the proposed channel estimation techniques, an acoustic model for a MIMO channel is developed using the method of images applied to a completely closed three-dimensional duct with a pressure release surface boundary and five rigid walls. The MIMO simulated channel provides the strength and delay of all echoes forming the channel. Both simulation and experimental results show a signicant improvement in the estimation of the channel impulse response, thus validating the two proposed algorithms.

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

DOWNLOAD EBOOK

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

Springer Handbook of Acoustics
Springer Handbook of Acoustics

Author: Thomas Rossing

Publisher: Springer Science & Business Media

Published: 2007-06-21

Total Pages: 1179

ISBN-13: 0387304460

DOWNLOAD EBOOK

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.

Compressed Sensing-based Channel Estimation and Prediction for Underwater Acoustic Communications
Compressed Sensing-based Channel Estimation and Prediction for Underwater Acoustic Communications

Author: Yi Zhang

Publisher:

Published: 2017

Total Pages:

ISBN-13:

DOWNLOAD EBOOK

This thesis develops approaches for estimating and predicting sparse shallow-water acoustic communication channels. The broadband shallow-water channel has three characterizations: a large dimension of channel impulse response caused by excessively long delay spread, fast temporal variability induced by scattering from the moving sea surface, and a sparse channel structure due to the resolvable paths. Traditional least square estimation techniques fail to utilize the sparse channel structure, and suffer from the limitations on the capability of estimating large-dimensional channels with rapid fluctuations. Compressed sensing also known as compressive sensing (CS), has been intensively studied recently. It has been applied in various areas such as imaging, radar, speech recognition, and data acquisition. Recently, applying CS to sparse channel estimation has been largely accepted. This thesis details the application of CS to sparse estimation of both time-invariant and time-varying shallow-water acoustic channels. Specifically, various reconstruction algorithms are used to find the sparse channel coefficients. However, a priori knowledge of channel sparsity is often not available in practice. The first part of the thesis proposes an improved greedy pursuit algorithm which iteratively identifies the sparse channel coefficients without requiring a priori knowledge of channel sparsity. Then, the proposed algorithm is employed to estimate both time-invariant and time-varying sparse channels. In addition, a comparative study of the state-of-the-art of various CS-based signal reconstruction algorithms is performed to gain better understanding of the mathematical insights. Furthermore, based on CS theory, different pilot placement choices will directly affect the performance of the channel estimation algorithm. The second part of the thesis investigates the pilot pattern design in sparse channel estimation. Unlike the equally spaced pilots for conventional channel estimation, randomly placed pilot tones are most used in existing CS-based channel estimation methods. In order to improve the efficiency of the optimal pilot pattern searching, a novel pilot pattern selection scheme is proposed based on the concatenated cyclic difference set. The performance of the proposed design is also compared with the existing search-based pilot placement methods. It should be noted that the proposed reconstruction algorithm and the pilot placement scheme are not restricted to underwater acoustic communication systems, but they can be applied so sparse channel estimation in other communication systems. Finally, an outdated channel estimation will lead to severe performance degradation when the channel varies rapidly. Hence, to predict future channel state information, an efficient sparse channel prediction scheme is proposed which does not require any statistical a priori knowledge of channels and noise. A receiver structure which combines a sparse channel estimator and a decision feedback based adaptive channel predictor is developed to further improve the prediction accuracy.Simulation results are shown to demonstrate the performance of the proposed algorithms and schemes. The study of this thesis contributes to a better understanding of the channel physical constraints on algorithm design and potential performance improvement.

Springer Handbook of Acoustics
Springer Handbook of Acoustics

Author: Thomas Rossing

Publisher: Springer

Published: 2015-01-15

Total Pages: 1280

ISBN-13: 1493907557

DOWNLOAD EBOOK

Acoustics, the science of sound, has developed into a broad interdisciplinary field encompassing the academic disciplines of physics, engineering, psychology, speech, audiology, music, architecture, physiology, neuroscience and others. Here is an unparalleled modern handbook reflecting this richly interdisciplinary nature edited by one of the acknowledged masters in the field, Thomas Rossing. Researchers and students benefit from the comprehensive contents spanning: animal acoustics including infrasound and ultrasound, environmental noise control, music and human speech and singing, physiological and psychological acoustics, architectural acoustics, physical and engineering acoustics, medical acoustics and ocean acoustics. The Springer Handbook of Acoustics reviews the most important areas of acoustics, 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, e.g. computer recognition and synthesis of speech, physiological acoustics, psychological acoustics, thermoacoustics, diagnostic imaging and therapeutic applications and acoustical oceanography. This new edition of the Handbook features over 11 revised and expanded chapters, new illustrations and two new chapters covering microphone arrays, acoustic metamaterials and acoustic emission. These improvements will make the handbook even more useful as a reference and a guide for researchers and students in every branch of acoustics. Praise for the first edition: "This treatise is a successful attempt to cover in one book the diverse field of acoustics, which ranges from physics to music and from formal mathematics to technological applications. ... It is this reviewer's opinion that a handbook like Rossing's, which covers the whole field of acoustics, serves a real purpose because it not only gives one a chance to see how one's specialty is covered but it also permits one to make a quick survey of other acoustical areas." (Leo Beranek, American Journal of Physics, Vol. 77 (12), December, 2009) "The Springer Handbook of Acoustics falls into that exceptional list. ...every physics department should have a copy available." (John L. Hubisz, The Physics Teacher, Vol. 48, March, 2010) "This handbook is an excellent addition to the acoustics literature. ... The handbook nicely covers both basics and advances in several areas of acoustics. Several chapters provide good mathematical depth, making the handbook useful as a research and technical resource. ...Overall, a very useful educational and research resource. Summing Up: Recommended. Upper-division undergraduates through professionals." (M. G. Prasad, CHOICE, Vol. 45 (5), January, 2008) "This book covers a wide range of topics and the inclusion of musical acoustics, computer and electronic music appeal to me (singer, song-writer, performer and recording studio co-owner). This handbook is probably well suited for an undergraduate-level introduction to an acoustics course. ... The wide range of topics, inclusion of music-related chapters, eye-pleasing presentations and other useful features make this a very good book to have on your shelf." (Tim Casey, International Journal of Acoustics and Vibration, Vol. 13 (1), 2008) "The Springer Handbook of Acoustics comprises 28 chapters written by 33 authors. The Handbook of Acoustics is useful as a source book for anyone who needs or wants to become familiar with the jargon and issues related to a specific subfield of acoustics ... ." (Robert I. Odom, Siam Review, Vol. 50 (3), 2008) The Springer Handbook of Acoustics reviews the most important areas of acoustics, 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, e.g. computer recognition and synthesis of speech, physiological acoustics, psychological acoustics, thermoacoustics, diagnostic imaging and therapeutic applications and acoustical oceanography. This new edition of the Handbook features over 13 revised and expanded chapters, new illustrations and 3 new chapters covering microphone arrays, acoustic metamaterials and acoustic emission. These improvements will make the handbook even more useful as a reference and a guide for researchers and students in every branch of acoustics.

Adaptive Feature Representation to Improve, Interpret and Accelerate Channel Estimation and Prediction for Shallow Water Acoustic Environments
Adaptive Feature Representation to Improve, Interpret and Accelerate Channel Estimation and Prediction for Shallow Water Acoustic Environments

Author: Ryan A. McCarthy (PhD)

Publisher:

Published: 2021

Total Pages: 0

ISBN-13:

DOWNLOAD EBOOK

In my doctoral dissertation I investigate new approaches to real-time channel estimation of underwater acoustic communications that complement existing estimation techniques. Modified sparse optimization algorithms have been used to improve channel estimation with some success. This work aims to improve these algorithms by applying pattern recognition through adaptive signal processing and machine learning to accelerate estimation time. Specifically, it investigates a model-agnostic geometric feature morphology based on braid theory to interpret diverse channel phenomena. The computational goal is to detect, separate and interpret multipath features in the channel delay spread across time, frequency, and varying degrees of channel sparsity. The main contribution of the thesis is development of braids feature representations and related channel tracking and learning algorithms to track salient bands of multipath activity. We develop robust signal processing and braided feature engineering approaches that evolve dynamically to the fluctuating channel multipath activity. To test the hypothesis that braids can track and adapt to diverse activity developing within the channel, simulated shallow water environments created through the well-known BELLHOP model and data from the SPACE08 field experiment are examined. Several simulated shallow water environments are examined with additive white Gaussian noise and varying degrees of activity to evaluate the performance of braiding and machine learning for shallow water acoustic channel estimation and interpretation. Performance is evaluated through visual confirmation and ground truths are provided by BELLHOP's outputs (e.g. eigenrays, arrivals, etc.). Results show that braids can evolve to capture dynamically changing multipath scattering activity in the shallow water acoustic channel. Furthermore, we demonstrate that leveraging braid feature representations with acoustic physics propagation models can successfully predict the number of reflectors in active channel multipath. We also demonstrate the significance of braid manifold representation in improving the computational speed for channel estimation. On average, this technique has improved estimation speed by ~.02 seconds as compared to the existing estimation techniques. These results suggest that braids can be used for useful pattern recognition to bridge the gap between purely statistical data analysis and physics-driven interpretation of the ocean acoustics that create the multipath channel delay spread. Beyond underwater acoustics, these feature learning techniques are broadly applicable to any paradigms where spectral features may evolve and intersect.

Advanced Signal Processing Techniques for Underwater Acoustic Communication Networks
Advanced Signal Processing Techniques for Underwater Acoustic Communication Networks

Author: Chunshan Liu

Publisher:

Published: 2011

Total Pages:

ISBN-13:

DOWNLOAD EBOOK

In this thesis, we develop and investigate novel signal processing techniques for underwater acoustic communication networks. Underwater acoustic channels differ from radio communication channels in the lower speed of signal propagation, richer and often sparse multipath arrivals, and more severe Doppler effect. Therefore, many signal processing techniques developed for radio communications may not work equivalently well for underwater acoustic channels. To investigate signal processing techniques in underwater acoustics, efficient simulation of signal transmission is required. Specifically, there is requirement for accurate simulation of doubly-selective underwater channels for different acoustic environments. In this thesis, a low-complexity channel simulator has been developed for scenarios with moving transmitter/receiver. The simulator is based on efficient generation of time-varying channel impulse response obtained using interpolation over a set of waymark impulse responses for a relatively small number of sampling points on the transmitter/receiver trajectory. The waymark impulse responses are generated using an acoustic field computation method, which is the most computationally expensive part of the simulator. To reduce the trajectory sampling rate, and thus, to reduce the complexity of the field computation, an approach for adjusting the time-varying multipath delays has been developed. For setting the trajectory sampling interval, a simple rule has been proposed, based on the waveguide invariant theory. To further reduce the simulator complexity, local spline interpolation is exploited. The developed simulator has been verified by comparing the simulated data with data from real ocean experiments. In particular, applying simulated data to an OFDM modem shows similar performance with that obtained from the data of a deep water experiment. In communication networks, knowledge of positions of communication nodes is important for improving the system performance. A multi-source localization technique has been proposed based on the matched field (MF) processing. The technique locates the nodes by solving a set of basis pursuit de-noising (BPDN) problems corresponding to a set of source frequencies. An efficient technique combining the homotopy approach and coordinate descent search has been developed to solve the BPDN problem. Further reduction in the complexity has been achieved by applying a position grid refinement method. Verified using simulated data generated by the proposed simulator and data from real experiment, the proposed technique outperforms other MF techniques in resolving sources positioned closely to each other, tolerance to noise and capability of locating multiple sources. To provide reliable localization based on MF techniques, accurate knowledge of the underwater acoustic environment is essential. However, such knowledge is not always available. Estimating uncertain environmental parameters can be achieved using MF inversion techniques. This requires solving a global optimization problem. Several global optimization algorithms have been investigated and an algorithm combining the simulated annealing and downhill simplex method has been applied for estimating the sound speed profile in a deep water scenario. Accurate MF localization results have been demonstrated when using the estimated sound speed profile. A very important task of communication receivers is accurate channel estimation. The knowledge of node positions and the environment can be exploited for enhancing the channel estimation accuracy and reducing the estimation complexity. This knowledge can be used to define the structure of the channel impulse response, such as the multipath spread and the sparsity. A channel estimator exploiting the channel sparsity estimated from the node positions has been proposed and investigated. The sparse taps of the channel impulse response are identified by solving a BPDN problem. The estimator employs an iterative tap-by-tap processing and uses local splines to interpolate the time-varying tap coefficients. This allows reduction in the complexity and memory requirement, whereas providing a high estimation accuracy.

Frequency-Domain Channel Estimation and Equalization for Single Carrier Underwater Acoustic Communications
Frequency-Domain Channel Estimation and Equalization for Single Carrier Underwater Acoustic Communications

Author:

Publisher:

Published: 2007

Total Pages: 7

ISBN-13:

DOWNLOAD EBOOK

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.

Underwater Acoustic Channel Modeling
Underwater Acoustic Channel Modeling

Author: Bo Zhang

Publisher:

Published: 2011

Total Pages: 68

ISBN-13:

DOWNLOAD EBOOK

In recent years, interests in Underwater Acoustic (UWA) communications have exponentially grown due to many emerging commercial and military applications such as ocean pollution monitoring, off-shore oil exploration and data telemetry, oceanic environment sensing and surveillance, underwater wireless sensor networking, submarine communications, and so on. The UWA channels have specific properties which differ from radio channels, which make it a big challenge to apply current radio wireless systems to it directly. There are three main characters attached in UWA channels: low speed of sound that varies with medium conditions; attenuation that increases with both transmission range and frequency; time-varying multipath propagation that depends on boundary conditions. The wireless communication systems build on UWA channels would suffers from limited bandwidth, long multipath delays, large Doppler shift and spread which means low data rate, sever inter symbol interference (ISI) and complex equalization. The design and analysis of underwater acoustic communication systems rely on the fundamental characterization of underwater acoustic signal propagation. Several channel models have been developed to investigate channel properties in different environment set ups. Currently, there are no standardized models for acoustic channel fading. There are two kinds of models developed so far for different purposes: deterministic models and statistical models. While the former one focuses on the reflections when boundary conditions are fixed, the latter one concentrates on overall channel's statistical probability distributions with changing boundaries. Statistical models raise too much debate and the assumptions of the models with various statistical distributions remain to be further tested. On the other hand, many deterministic models have been tested and implemented as appropriate tools to investigate the reflection and refraction behavior of underwater acoustic signal propagation. In this thesis, we aim to study the power delay profile of underwater acoustic communication channels for given specific system configuration. Specifically, we investigated the multipath channel impulse responses of underwater acoustic channels by considering firstly a deterministic ray/beam tracing model and then a statistically random environment. We simulated an underwater acoustic channel model on MATLAB based on geometry of transceiver and surrounding environment and wave propagation equations. The amplitude and delays of the multipath channel impulse responses were compared and analyzed for underwater acoustic channels with various transceiver configurations such as range, depth, frequency, random water surface and bottom. Simulation results show that the depth location of underwater transceivers does not affect much the delay profile of the multipath received signals, however, it does change the power distribution of the multipath signals as the closer the transceiver to the boundaries, the less power received. Regarding various ranges between the transmitter and receiver, it is interesting to observe that the power delay profile of the multipath signals vary randomly, and the number of delay paths is uncorrelated to the ranges. Regarding underwater acoustic communication with different frequencies, while the delay profile of multipath signals remains stable with the same system geometry, the attenuation of multipath signals decreases as the frequency of acoustic signals increases. Moreover, the boundary conditions (water surface and/or bottom) of underwater acoustic channel affect the power delay profile of multipath signals significantly. In both fixed boundary and randomly varying boundary (e.g. water surface waves), the power delay profile of multipath signals exhibits a random pattern, which raises significant challenge in channel estimation in underwater acoustic communication. Our findings are helpful to the design of high-rate underwater acoustic communication systems. Our ultimate goal is to apply the MIMO-OFDM concept in underwater communication scenario in order to increase the date rate of underwater acoustic communication systems, in which channel estimation, channel multipath mitigation, signal processing, and data detection, need to be redesigned properly to take into account the unique characteristics of underwater acoustic channels.

Underwater Acoustic Channel
Underwater Acoustic Channel

Author: Junying Hui

Publisher: Springer Nature

Published: 2022-05-19

Total Pages: 243

ISBN-13: 9811907749

DOWNLOAD EBOOK

This book introduces sonar system and acoustic channel model, average energy channel, coherent multipath channel, the theoretical basis for the stochastic time-varying space-variant channel, slowly time-varying coherent multipath channel, and reverberation channel. Based on the basic theory of underwater acoustic channels and the various characteristics of the marine acoustic environment factor, this textbook aims to help students understand the impact of the marine acoustic channel on the sonar system. It helps students to grasp underwater acoustic signal processing principles and obtain the ability to solve practical problems in underwater acoustic channel engineering. Finally, it aims at laying a foundation for the further sonar system design. This textbook is recommended for graduate or undergraduate students in the field of sonar signal processing, underwater acoustic engineering, as well as some related subjects of marine technology.