Statistical Characterization of a Class of Underwater Acoustic Communication Channels
Statistical Characterization of a Class of Underwater Acoustic Communication Channels

Author: Parastoo Qarabaqi

Publisher:

Published: 2014

Total Pages: 91

ISBN-13:

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Acoustic channel models provide a tool for predicting the performance of underwater communication systems prior to deployment, and are thus essential for system design. In this dissertation, we offer a statistical channel model, which incorporates physical laws of acoustic propagation (frequency-dependent attenuation, bottom-surface reflections) as well as the effects of inevitable random local displacements. We focus on random displacements on two scales: small-scale effects, that involve distances on the order of a few wavelengths, and large-scale effects, that involve many wavelengths. Small-scale effects include scattering and motion-induced Doppler shifting, and are responsible for fast variations of the instantaneous channel response; while large-scale effects describe the location uncertainty and changing environmental conditions, and affect the locally-averaged received power. We model each propagation path by a large-scale gain and micro-multipath components that cumulatively result in a complex Gaussian distortion. Random surface motion and transducer displacement introduce additional variation whose temporal correlation is described by Bessel-type functions. The total power, or the gain contained in the channel, averaged over small-scale, is modeled as log-normally distributed. The models are validated using real data obtained from four experiments. Specifically, experimental data are used to assess the distribution and the auto-correlation functions of the large-scale transmission loss and the short-term path gains. While the former indicates a log-normal distribution with an exponentially decaying auto-correlation, the latter indicates a conditional Ricean distribution with Bessel-type auto-correlation. Based on the proposed model, we design a channel simulator which we employ to generate a time-varying channel whose statistical characteristics match with those of a real underwater channel. The simulated channel is applied to convey an OFDM signal to coherent and differentially coherent detectors, and the MSE performance of the experimental and simulated systems are shown to be similar. Finally, we investigate the feasibility of adaptive power control using an experimental data set as well as theoretically. Based on the observed time-correlation properties of the large-scale channel gain, linear power prediction is employed and achievable power savings are obtained analytically (assuming a log-normal gain distribution) and experimentally. The results indicate that substantial power savings are possible over extended periods of time.

Characterization of Active Underwater Acoustic Channels. Part I.A New Formulation for Scattering by Random Media and Interfaces
Characterization of Active Underwater Acoustic Channels. Part I.A New Formulation for Scattering by Random Media and Interfaces

Author:

Publisher:

Published: 1974

Total Pages: 128

ISBN-13:

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A general approach to scattering phenomena is developed and applied specifically to underwater acoustic scattering situations involving the medium and its interfaces. The fundamental elements of the method are the development of the available scattering elements into a hierarchy of independent scatter processes, based on the scatterers activated, at any given instant. This, with the governing class of Langevin equation (e.g., forms of the (scalar) wave equation here) permits a corresponding development, in linear superposition, of the received, scattered field x sub m as a hierarchy of independent processes, x sub m(k), k=0,1,2., representing different scales of inhomogeneity which may be present in the medium, or upon its interfaces. First- and second-order moments (covariances and generalized spectra) are obtained in canonical form, representing global properties of the channel and the local properties of the medium itself. A number of probability densities are also obtained in important limiting cases, e.g. various (conditional) normal p.d.f.'s. Part I concludes with some remarks on an experimental program, designed to test and quantify various aspects of the general model, both for studies of the medium itself (and its associated interfaces), and for the broad class of statistical communication applications, such as detection, extraction, classification, communications per se, as well as signal and aperture design problems

Characterization and Modeling of Underwater Acoustic Communications Channels for Frequency-Shift-Keying Signals
Characterization and Modeling of Underwater Acoustic Communications Channels for Frequency-Shift-Keying Signals

Author:

Publisher:

Published: 2006

Total Pages: 7

ISBN-13:

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In a fading channel, bit error rate for frequency-shift- keying signals is determined predominantly by the envelope amplitude fading statistics of the signal. The narrowband envelope amplitude distributions are measured from the TREX04 data (as a function of frequency) using M-sequence signals centered at 17 kHz with a 5 kHz bandwidth. The results do not fit the Rayleigh, Rician, Nakagami m-distributions. In contrast, we find that the data are fitted well by a K-distribution. We also analyze the data in terms of long-term and short-term statistics. The long-term and short-term fading statistics are well fitted by the lognormal distribution and Rayleigh distribution respectively, choosing the average time scale to be ~0.2 sec. The joint probability distribution function of a lognormal and the Rayleigh distribution is approximately the K-distribution.

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.

Underwater Acoustic Channel Modeling
Underwater Acoustic Channel Modeling

Author: Bo Zhang

Publisher:

Published: 2011

Total Pages: 68

ISBN-13:

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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.

Modelling, Simulation and Data Analysis in Acoustical Problems
Modelling, Simulation and Data Analysis in Acoustical Problems

Author: Claudio Guarnaccia

Publisher: MDPI

Published: 2020-06-23

Total Pages: 584

ISBN-13: 3039282840

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Modelling and simulation in acoustics is currently gaining importance. In fact, with the development and improvement of innovative computational techniques and with the growing need for predictive models, an impressive boost has been observed in several research and application areas, such as noise control, indoor acoustics, and industrial applications. This led us to the proposal of a special issue about “Modelling, Simulation and Data Analysis in Acoustical Problems”, as we believe in the importance of these topics in modern acoustics’ studies. In total, 81 papers were submitted and 33 of them were published, with an acceptance rate of 37.5%. According to the number of papers submitted, it can be affirmed that this is a trending topic in the scientific and academic community and this special issue will try to provide a future reference for the research that will be developed in coming years.

Analysis of Acoustic Communication Channel Characterization Data in the Surf Zone
Analysis of Acoustic Communication Channel Characterization Data in the Surf Zone

Author: James Willard Partan

Publisher:

Published: 2000

Total Pages: 130

ISBN-13:

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A channel characterization experiment for the underwater acoustic communication channel was carried out at Scripps Pier in May 1999. The experiment investigated acoustic transmission in very shallow water and breaking waves. In analyzing the data, several questions arose. The majority of the acoustic channel probe data was corrupted by crosstalk in the receiver array cable. This thesis investigates methods to correct for the effects of the crosstalk, to attempt to recover the channel probe data. In selected regions, the crosstalk could be removed quite effectively using a linear least-squares method to estimate the crosstalk coefficients. The bulk of the data could not be corrected, however, primarily due to crosstalk from a receiver channel which was not recorded, and hence could not be well estimated. A second question addressed by this thesis is concerned with acoustic propagation in shallow water under bubble clouds. The breaking waves injected air deep into the water column. The resulting bubble clouds heavily attenuated acoustic signals, effectively causing total dropouts of the acoustic communication channel. Due to buoyancy, the bubbles gradually rise, and the communication channel clears. The channel clearing was significantly slower than predicted by geometric ray acoustic propagation models, however. Proposed explanations included secondary, unobserved, breaking events causing additional bubble injection; delayed rising of bubbles due to turbulent currents; or failure of the geometric ray model due to suppression by bubble clouds of acoustic signals which are not along the geometric ray paths. This thesis investigated the final hypothesis, modeling the acoustic propagation in Scripps Pier environment, using the full wave equation modeling package OASES. It was determined that the attenuation of the propagating acoustic signal is not accurately predicted by the bubble-induced attenuation along the geometric ray path.

Online Learning of the Spatial-Temporal Channel Variation in Underwater Acoustic Communication Networks
Online Learning of the Spatial-Temporal Channel Variation in Underwater Acoustic Communication Networks

Author:

Publisher:

Published: 2019

Total Pages:

ISBN-13:

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Abstract : Influenced by environmental conditions, underwater acoustic (UWA) communication channels exhibit spatial and temporal variations, posing significant challenges for UWA networking and applications. This dissertation develops statistical signal processing approaches to model and predict variations of the channel and relevant environmental factors. Firstly, extensive field experiments are conducted in the Great Lakes region. Three types of the freshwater river/lake acoustic channels are characterized in the aspects of statistical channel variations and sound propagation loss, including stationary, mobile and under-ice acoustic channels. Statistical data analysis shows that relative to oceanic channels, freshwater river/lake channels have larger temporal coherence, higher correlation among densely distributed channel paths, and less sound absorption loss. Moreover, variations of the under-ice channels are less severe than those in open water in terms of multipath structure and Doppler effect. Based on the observed channel characteristics, insights on acoustic transceiver design are provided, and the following two works are developed. online modeling and prediction of slowly-varying channel parameters are investigated, by exploiting their inherent temporal correlation and correlation with water environment. The temporal evolution of the channel statistics is modeled as the summation of a time-varying environmental process, and a Markov latent process representing unknown or unmeasurable physical mechanisms. An algorithm is developed to recursively estimate the unknown model parameters and predict the channel parameter of interest. The above model and the recursive algorithm are further extended to the channel that exhibits periodic dynamics. The proposed models and algorithms are evaluated via extensive simulations and data sets from two shallow-water experiments. The experimental results reveal that the average channel-gain-to-noise-power ratio, the fast fading statistics, and the average delay spread can be well predicted. The inhomogeneity of the sound speed distribution is challenging for Autonomous underwater vehicles (AUVs) communications and acoustic signaling-based AUV localization due to the refraction effect. Based on the time-of-flight (TOF) measurements among the AUVs, a distributed and cooperative algorithm is developed for joint sound speed estimation and AUV tracking. The joint probability distribution of the time-of-flight (TOF) measurements, the sound speed parameters and the AUV locations are represented by a factor graph, based on which a Gaussian message passing algorithm is proposed after the linearization of nonlinear measurement models. Simulation results show that the AUV locations and the sound speed parameters can be tracked with satisfying accuracy. Moreover, significant localization improvement can be achieved when the sound speed stratification effect is taken into consideration.

Characterization of Active Underwater Acoustic Channels. Part II. Scattering in an Isovelocity Ocean
Characterization of Active Underwater Acoustic Channels. Part II. Scattering in an Isovelocity Ocean

Author:

Publisher:

Published: 1974

Total Pages: 254

ISBN-13:

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The general approach to scattering phenomena developed here is now applied specifically to underwater acoustic scattering problems in an isovelocity medium, for the present without absorption and inhomogeneous properties other than the various possible scattering mechanisms themselves. Among the principal new results are (1) the explicit inclusion of doppler, which is shown to produce a nonstationary frequency-modulation of the injected signal; (2) the presence and effects of two orders of inhomogeneities in the second-order media statistics, e.g., poisson, or specular point scatterers (k=1) and continuous scattering elements (k=2); (3) the coherence properties and spectrum of the specular component (k=0); (4) necessary and sufficient conditions for the applicability of the poisson model alone (and of the earlier poisson models cited in the literature); (5) conditions that the medium be a WSSUS medium; (6) for weak scattering interactions, the wave number spectra of surfaces and volumes, including the interaction of surface displacement and motion; (7) various experimental programs for the measurement and underwater remote sensing of the medium; (8) an extensive development of wave surface statistics, particularly point and directional covariances, spectra, and wave number spectra for a variety of sea surface models, including the author's recent model; (9) strong-scattering results; and (10) channel characterizations by means of the local bicovariance and cospreading functions, with specific examples