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Oceanic Engineering, IEEE Journal of

Issue 4 • Date Oct. 2013

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Displaying Results 1 - 22 of 22
  • Table of contents

    Page(s): C1 - C4
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  • IEEE Journal of Oceanic Engineering publication information

    Page(s): C2
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  • Editorial Remembering Stan Ehrlich: 1925–2013

    Page(s): 601 - 602
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  • UComms: A Conference and Workshop on Underwater Communications, Channel Modeling, and Validation

    Page(s): 603 - 613
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  • Propagation and Scattering Effects in Underwater Acoustic Communication Channels

    Page(s): 614 - 631
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (4111 KB) |  | HTML iconHTML  

    Systematic measurements were performed to characterize shallow-water acoustic propagation channels for applications in the field of underwater communications. The survey was conducted in northern Europe and covers the continental shelf, Norwegian fjords, a sheltered bay, a channel, and the Baltic Sea. The measurements were performed in various frequency bands between 2 and 32 kHz. The outcome of the study is a variety of channels that differ in many ways, defying any attempt to define a typical acoustic communication channel. Miscellaneous forward propagation effects are presented, which are relevant to channel models for the design of modulation schemes, network protocols, and simulation environments. View full abstract»

    Open Access
  • The Suspension of Large Bubbles Near the Sea Surface by Turbulence and Their Role in Absorbing Forward-Scattered Sound

    Page(s): 632 - 641
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    There is anecdotal evidence that under conditions of moderate to high wind speeds (8-15 m ·s- 1), clouds of bubbles entrained in the near-surface layer by breaking waves can create a benign underwater communications channel through the resonant absorption of forward-scattered sound, reducing reverberation times and the occurrence of high-intensity, Doppler-shifted arrivals. Current models for the effects of bubbles on surface-interacting sound show two effects: refraction of low-frequency sound due to reductions in sound speed near the surface and resonant absorption at higher frequencies. These models include uncertainty in the numbers and sizes of the largest bubbles present in the near-surface layer, and their dependence on wind speed. This uncertainty makes quantitative prediction of bubble effects in the underwater acoustic communications band of workhorse frequencies (10-30 kHz) difficult. The model calculations presented here show that resonant absorption associated with the largest bubbles is strongly frequency and wind-speed dependent. The frequency dependence can be explained by the concept of a bubble escape radius; this being the radius of a bubble for which turbulent fluid velocity fluctuations and bubble terminal velocity in the upper ocean boundary layer balance. Bubbles smaller than the escape radius tend to remain trapped by fluid turbulence while larger bubbles are lost to the surface through buoyant degassing. Calculation of the escape radius provides a means of estimating the lowest frequency at which resonant absorption can be expected for a given wind speed. Initial estimates suggest that resonant absorption at 10 kHz begins at 10-m wind speeds of around 8 ms -1, and significant surface bounce losses at frequencies lower than this are expected in the range of wind speeds 13-20 m·s- 1. View full abstract»

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  • Simulation of an Underwater Acoustic Communication Channel Characterized by Wind-Generated Surface Waves and Bubbles

    Page(s): 642 - 654
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3637 KB) |  | HTML iconHTML  

    Sea-surface scattering by wind-generated waves and bubbles is regarded to be the main nonplatform related cause of the time variability of shallow acoustic communication channels. Simulations for predicting the quality of acoustic communication links in such channels thus require adequate modeling of these dynamic sea-surface effects. For frequencies in the range of 1-4 kHz , there is an important effect of bubbles on sea-surface reflection loss due to refraction, which can be modeled with a modified sound-speed profile (SSP) accounting for the bubble void fraction in the surface layer. The bubble cloud then acts as an acoustic lens, enhancing the rough-surface scattering by the resulting upward refraction. It is shown here that, for frequencies in the considered range of 4-8 kHz, bubble extinction, including both the effects of bubble scattering and absorption, provides a significant additional contribution to the surface loss. Model-based channel simulations are performed by applying a ray tracer, together with a toolbox for generation of rough sea-surface evolutions. This practical simulation framework is demonstrated to provide realistic results for both stationary and mobile communication nodes by capturing specific features observed in experiments, such as time variability, fading reverberation tails, and wind-speed dependence of the Doppler power spectrum. View full abstract»

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  • Ray/Beam Tracing for Modeling the Effects of Ocean and Platform Dynamics

    Page(s): 655 - 665
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1985 KB) |  | HTML iconHTML  

    In recent years, there have been notable technical advances in modulation schemes for underwater acoustic communications, and inexpensive commercial modems are now readily available. This has generated a renewed interest in modeling the effects of the underwater sound channel on the transmission of a known time series. The previously developed Virtual Timeseries Experiment (VirTEX) algorithm addressed the need for such models. It utilizes a sequence of ray-tracing computations on temporal snapshots of the environment. This approach can handle practical environments with arbitrary source, receiver, or sea-surface motion. While VirTEX can model the transmission of a known time series to any desired accuracy, its utility is offset by the computational resources required. In this paper, we present two new algorithms for modeling the propagation of a known time series in a restricted class of time-varying environments. The first algorithm can address steady motion of the source and/or receiver. The second algorithm can address a moving sea surface that satisfies some simple constraints. While more restrictive and less accurate than VirTEX, these new algorithms are significantly faster and more efficient. This makes them much more attractive for applications involving the modeling of extensive “what-if” scenarios. The algorithms can be implemented in software by postprocessing of the output from popular ray-tracing computer programs. View full abstract»

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  • A Single-Carrier Turbo-Coded System for Underwater Communications

    Page(s): 666 - 677
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    In the last several years, the Swedish Defence Research Agency (FOI, Stockholm, Sweden) has been engaged in developing a system for underwater (UW) acoustic communications for both point-to-point (P2P) and network applications. The basis of the system is a single-carrier (SC) scheme with recursive equalization on the receiver side. In this paper, we will give a motivation for our choice of SC by discussing some aspects of modulation and coding for UW communication systems from an information-theoretic point of view. The system is able to take advantage of the diversity offered by the multipath and/or by multiple receivers. Due to the great variations in the UW channel, reliable prediction of communication performance in terms of achievable range and data rate is nontrivial. This has motivated the development of a simulation tool called COMLAB, based on combining the communication system with hybrid ray-trace plane-wave time-domain modeling of sound propagation. The simulation tool is designed to account for environmental effects with significant influence on communication performance, including surface and bottom reflections, transmission loss, ambient noise, and ray-path-dependent Doppler shifts caused by moving source, receivers, or surface waves. Short descriptions of the communication system and the simulation tool are given. A comparison of the predicted performance with experiments made at the UAN'11 trials in the Trondheim fjord (Norway) is presented. View full abstract»

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  • Ultrawideband Underwater Acoustic Communication Channels

    Page(s): 678 - 688
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    Traditional channel models for communications research are designed for narrowband systems. Underwater acoustic communication systems use a bandwidth that is not small compared with the center frequency of the signal and qualify as ultrawideband (UWB) in a relative sense. In this paper, measurements and analysis of acoustic propagation effects demonstrate the shortcomings of narrowband channel models. These effects are frequency-dependent fluctuation rates and frequency-dependent attenuation, where the frequency dependence of the attenuation differs between paths. This frequency selectivity of the medium violates the assumption of uncorrelated taps and requires a UWB channel model. It is also shown that correlative channel sounders preserve wideband properties, which renders them suitable for UWB channel simulation based on the principle of direct replay. View full abstract»

    Open Access
  • Validation of Replay-Based Underwater Acoustic Communication Channel Simulation

    Page(s): 689 - 700
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    This paper discusses validation methods for underwater acoustic communication channel simulators, and validates direct and stochastic replay of underwater acoustic communication channels as implemented in a channel simulator called Mime. Direct replay filters an input signal directly with a measured time-varying impulse response, whereas stochastic replay filters an input signal with a synthetic impulse response consistent with the scattering function of the measured channel. The validation uses data from two sea experiments and a diverse selection of communication schemes. Good agreement is found between bit error rates and packet error rates of in situ transmissions and simulated transmissions. Long-term error statistics of in situ signaling are also reproduced in simulation when a single channel measurement is used to configure the simulator. In all except one comparison, the packet error rate in simulation is within 20% of the packet error rate measured on location. The implication is that this type of channel simulator can be employed to test new modulation schemes in a realistic fashion without going to sea, except for the initial data collection. View full abstract»

    Open Access
  • Statistical Characterization and Computationally Efficient Modeling of a Class of Underwater Acoustic Communication Channels

    Page(s): 701 - 717
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    Underwater acoustic channel models provide a tool for predicting the performance of communication systems before deployment, and are thus essential for system design. In this paper, 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. Specifically, we focus on random displacements on two scales: those that involve distances on the order of a few wavelengths, to which we refer as small-scale effects, and those that involve many wavelengths, to which we refer as large-scale effects. 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 micromultipath components that cumulatively result in a complex Gaussian distortion. Time- and frequency-correlation properties of the path coefficients are assessed analytically, leading to a computationally efficient model for numerical channel simulation. Random motion of the surface and transmitter/receiver displacements introduce additional variation whose temporal correlation is described by Bessel-type functions. The total energy, 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 autocorrelation 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 autocorrelation, the latter indicates a conditional Ricean distribution with Bessel-type autocorrelation. View full abstract»

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  • Sparse Underwater Acoustic Channel Parameter Estimation Using a Wideband Receiver Array

    Page(s): 718 - 729
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2711 KB) |  | HTML iconHTML  

    This paper considers a channel parameter estimation problem using a wideband multichannel receiver array. We estimate the sparse underwater acoustic communication channel parameters, such as time-delay, incidence angle, Doppler frequency, and complex amplitude of impinging multipath components. Multichannel signals from a receiver array are modeled to obtain additional sparsity in the incidence angle and the angle-delay-Doppler-spread function is defined to parameterize the channel. To estimate the principal entries of the angle-delay-Doppler-spread function, we propose a modified version of the orthogonal matching pursuit (OMP) algorithm to utilize a redundant dictionary. We introduce a space-alternating scheme which divides the entire parameter search space into smaller subsets to avoid handling large parameter search space. The performance of the proposed method is evaluated using two experimental data: one from large-scale water tank with the capability of generating surface gravity wave and the other from shallow sea water which shows sparse channel structure. Our results demonstrate that the proposed method accurately estimates the time-varying multipath channel parameters with lower residual error than the OMP. View full abstract»

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  • Temporal Response of the Underwater Optical Channel for High-Bandwidth Wireless Laser Communications

    Page(s): 730 - 742
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    This paper describes a high-sensitivity, high-dynamic range experimental method for measuring the frequency response of the underwater optical channel in the forward direction for the purpose of wireless optical communications. Historically, there have been few experimental measurements of the frequency response of the underwater channel, particularly with regard to wireless communication systems. In this work, the frequency response is measured out to 1 GHz over a wide range of water clarities (approximately 1-20 attenuation lengths). Both spatial and temporal dispersions are measured as a function of pointing angle between the transmitter and the receiver. We also investigate the impact of scattering function and receiver field of view. The impact of these results to the link designer is also presented. View full abstract»

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  • An End-to-End Signal Strength Model for Underwater Optical Communications

    Page(s): 743 - 757
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    In this paper, we present a generic model of signal strength in underwater optical communications. The model includes light sources, detectors, amplifier and detector circuitry, optics, as well as a simple extinction model of the water channel. The end-to-end model provides insights into optimization approaches for underwater optical modems and enables relative pose estimation between underwater optical transmitters and receivers. We instantiate our model to the AquaOptical model by determining its parameters and verifying the model prediction in a suite of pool experiments. View full abstract»

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  • Linking Acoustic Communications and Network Performance: Integration and Experimentation of an Underwater Acoustic Network

    Page(s): 758 - 771
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    Underwater acoustic networks (UANs) are an emerging technology for a number of oceanic applications, ranging from oceanographic data collection to surveillance applications. However, their reliable usage in the field is still an open research problem, due to the challenges posed by the oceanic environment. The UAN project, a European-Union-funded initiative, moved along these lines, and it was one of the first cases of successful deployment of a mobile underwater sensor network integrated within a wide-area network, which included above water and underwater sensors. This contribution, together with a description of the underwater network, aims at evaluating the communication performance, and correlating the variation of the acoustic channel to the behavior of the entire network stack. Results are given based on the data collected during the UAN11 (May 2011, Trondheim Fjord area, Norway) sea trial. During the experimental activities, the network was in operation for five continuous days and was composed of up to four Fixed NOdes (FNOs), two autonomous underwater vehicles (AUVs), and one mobile node mounted on the supporting research vessel. Results from the experimentation at sea are reported in terms of channel impulse response (CIR) and signal-to-interference-plus-noise ratio (SINR) as measured by the acoustic modems during the sea tests. The performance of the upper network levels is measured in terms of round trip time (RTT) and probability of packet loss (PL). The analysis shows how the communication performance was dominated by variations in signal-to-noise ratio, and how this impacted the behavior of the whole network. Qualitative explanation of communication performance variations can be accounted, at least in the UAN11 experiment, by standard computation of the CIR and transmission loss estimate. View full abstract»

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  • Impact of Time-Varying Underwater Acoustic Channels on the Performance of Routing Protocols

    Page(s): 772 - 784
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    The recent development of underwater acoustic modems has enabled multihop networking capabilities that can be used in important military and civilian applications. For this reason, routing protocols for underwater acoustic networks (UANs) have recently been proposed and evaluated. However, the interactions between channel dynamics and networking performance are not well understood. In this paper, we investigate and quantify the effect of the time-varying (TV) link quality on routing protocols in static UANs. In order to do so, we simulate the considered routing protocols in several network scenarios, obtained by changing the network density, the number of packet retransmissions, the packet length, the modulation type, and the power level with both TV and time-invariant (TI) channel conditions. Results confirm that, when evaluating the performance of routing protocols, it is important to understand the TV behavior of the channel quality over intervals of time sufficiently long to accommodate multihop communications. Finally, we also present experimental results, confirming the outcome of the simulations. The experiments have been conducted in collaboration with the NATO Centre for Maritime Research and Experimentation (CMRE) during the CommsNet12 sea trial. View full abstract»

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  • Statistical Bit Error Trace Modeling of Acoustic Communication Links Using Decision Feedback Equalization

    Page(s): 785 - 795
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    Underwater network simulation and performance analysis require accurate packet error models. The packet error probability depends on the packet length and the temporal distribution of bit errors. We analyze error traces from decision-feedback-equalized single-carrier acoustic communication links from several shallow-water experiments and show that clustering of bit errors occurs at several timescales. We propose a two-part statistical error model consisting of a generalized Pareto fractal renewal parent process that drives Bernoulli daughter processes with generalized extreme value distributed lifetimes. We present an algorithm to simulate communication errors using this error process model and show that the simulated packet loss probability accurately matches experimental observations. View full abstract»

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  • A State Observation Technique for Highly Compressed Source Coding of Autonomous Underwater Vehicle Position

    Page(s): 796 - 808
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    In this paper, a novel technique is presented for using state observers in conjunction with an entropy source encoder to enable highly compressed telemetry of autonomous underwater vehicle (AUV) position vectors. In this work, both the sending vehicle and receiving vehicle or human operator are equipped with a shared real-time simulation of the sender's state based on the prior transmitted positions. Thus, only the innovation between the sender's actual state and the shared state need be sent over the link, such as a very low throughput acoustic modem. The distribution of this innovation can be modeled a priori or assembled adaptively. This distribution is then paired with an arithmetic entropy encoder, producing a very low cost representation of the vehicle's position vector. This system was analyzed on experimental data from the GLINT10 and AGAVE07 expeditions involving two different classes of AUVs performing a diverse number of maneuvers, and implemented on a fielded vehicle in the MBAT12 experiment. Using an adaptive probability distribution in combination with either of two state observer models, greater than 90% compression, relative to a 32-b integer baseline, was achieved. View full abstract»

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  • Erratum to “Validation of Replay-Based Underwater Acoustic Communication Channel Simulation” [R. Otnes, P. A. van Walree, T. Jenserud, IEEE J. Ocean. Eng., DOI: 10.1109/JOE.2013.2262743]

    Page(s): 809
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    In the first row of Table I of the above-named article, the following reference numbers should be fixed: reference [12] should be [13], reference [13] should be [14], reference [11] should be [12], and reference [20] should be [21]. The corrected version of Table I is included here. View full abstract»

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  • 2013 Index IEEE Journal of Oceanic Engineering Vol. 38

    Page(s): 810 - 820
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  • IEEE Oceanic Engineering Society Information

    Page(s): C3
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Aims & Scope

The IEEE Journal of Oceanic Engineering (ISSN 0364-9059) is published quarterly by the IEEE Oceanic Engineering Society (IEEE OES). The scope of the Journal is the field of interest of the IEEE OES, which encompasses all aspects of science, engineering, and technology that address research, development, and operations pertaining to all bodies of water. This includes the creation of new capabilities and technologies from concept design through prototypes, testing, and operational systems to sense, explore, understand, develop, use, and responsibly manage natural resources.

Full Aims & Scope

Meet Our Editors

Editor-in-Chief
N. Ross Chapman
School of Earth & Ocean Sciences
University of Victoria
3800 Finnerty Road
Victoria, BC V8P 5C2 Canada
chapman@uvic.ca