Special Issue "Underwater Acoustics, Communications and Information Processing"

A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Acoustics and Vibrations".

Deadline for manuscript submissions: closed (30 November 2017).

Special Issue Editors

Prof. Dr. Kiseon Kim
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Guest Editor
MT-IT Collaborations Center, Gwangju Institute of Science and Technology (GIST), Gwangju 500-712, Korea
Special Issues and Collections in MDPI journals
Prof. Georgy Shevlyakov
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Guest Editor
Peter the Great St. Petersburg Polytechnic University, St. Petersburg, 195251, Russia
Interests: robust detection and estimation; robust signal processing under hostile environment; robust communications system analysis
Special Issues and Collections in MDPI journals
Prof. Dr. Jea Soo Kim
E-Mail
Guest Editor
Department of Convergence Study on the Ocean Science and Technology, Korea Maritime and Ocean University, Busan 606-791, Korea
Interests: underwater acoustics; acoustics propagation modeling; acoustics system analysis and design; SONAR systems
Prof. Dr. M. Soufian
E-Mail
Guest Editor
Industrial Automation, SEBE, Edinburgh Napier University, Edinburgh, Scotland EH11 4BN, UK
Interests: e-Systems; ICT-based Interdisciplinary engineering; AI; IoT; applications of intelligence for engineering systems
Prof. Dr. Lyubov Statsenko
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Guest Editor
Department of the Infocommunication Technology and Communication Systems, Far Eastern Federal University, Sukhanova Street, 8, Vladivostok 690091, Russia
Interests: applied mathematics for underwater acoustics; underwater communications; hydrophysics for communication engineering

Special Issue Information

Dear Colleagues,

Information and communication technologies (ICT) have brought various useful tools and services, enabling another Internet-based industrial revolution over the last few decades. However, oceans or underwater spaces are not enjoying the benefits of the ICT conveniences, mainly due to the complicate underwater physiology and poorly propagating electromagnetics. Subsequently, underwater acoustics and medium channels have been widely investigated including the limited bandwidth, extended multi-path, refractive properties of the medium, severe fading, rapid time-variation and large Doppler shifts. Further information processing and communication techniques over the underwater acoustic channel are under successful adopting and upgrading towards practical ocean tools, from the originally developed for terrestrial channels.

Underwater acoustics for oceanology and fishery compose a well-defined scientific area physically and theoretically for the underwater information and communications, while the digital communication engineering complements practical devices, systems and networks for the interdisciplinary underwater communications. Fully utilizing emerging and state-of-art tools from both the underwater acoustic sciences and communication engineering, we are expecting a quantum jump of various development and interdisciplinary underwater engineering, covering, for example, shallow water channel characterization, high-speed underwater communication system, underwater physiological property monitoring, underwater surveillance network, and many more applications for the daily ocean life equipped with Internet-of-things.

This Special Issue is aimed at providing the underwater acoustics community with scientific tools, novel information processing algorithms and methods, underwater applications of acoustics in oceanology and fishery. Manuscripts are solicited to address a wide range of topics on principles and applications of underwater acoustics, including, but not limited to, the following:

  • Underwater channel modeling and data processing

  • Robust detection/estimation and ranging/localization against underwater channels

  • High-speed underwater communication systems and networks

  • Ocean Internet-of-things and applications

  • Underwater and ocean physiological property monitoring  

  • Underwater tracking and surveillance networks  

  • Underwater acoustics in ocean ad coastal applications

Prof. Dr. Kiseon Kim
Prof. Georgy Shevlyakov  
Prof. Jea Soo Kim
Prof. M. Soufian
Prof. Lyubov Statsenko  
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Applied Sciences is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Underwater Acoustics

  • Acoustic Communications

  • Robust Detection

  • ICT-based Interdisplinary Engineering

  • Acoustic System and Networks

  • Ocean IoT

  • Underwater Information Processing

Published Papers (17 papers)

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Editorial

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Open AccessEditorial
Editorial for Special Issue: Underwater Acoustics, Communications, and Information Processing
Appl. Sci. 2019, 9(22), 4873; https://doi.org/10.3390/app9224873 - 14 Nov 2019
Abstract
Information and communication technologies (ICT) have brought forth various useful tools and services, enabling another Internet-based industrial revolution over the last few decades [...] Full article
(This article belongs to the Special Issue Underwater Acoustics, Communications and Information Processing)

Research

Jump to: Editorial

Open AccessArticle
Experimental Estimation of the Constant Envelope FM-OFDM Method Usage in Underwater Acoustic Communication Systems
Appl. Sci. 2018, 8(3), 402; https://doi.org/10.3390/app8030402 - 09 Mar 2018
Cited by 2
Abstract
Nowadays, more and more complex methods of signal modulating and processing are actively used for organizing underwater acoustic communication with and between submerged mobile vehicles due to harsh underwater conditions. In this research, the method that is based on multi-frequency signals forming (OFDM) [...] Read more.
Nowadays, more and more complex methods of signal modulating and processing are actively used for organizing underwater acoustic communication with and between submerged mobile vehicles due to harsh underwater conditions. In this research, the method that is based on multi-frequency signals forming (OFDM) with the constant envelope is applied to the problem. It is based on multi-frequency FM-OFDM signals forming with Quadrature Phase Shift Keying (QPSK) modulated subcarriers and FM spectrum spreading coefficients of 1, 2, 4, and 10. The proposed solution was modeled in a software simulator, which implements a noisy underwater acoustic multipath channel, changing the bit error rate (BER) from 0.15 to 10−3. In addition, it was tested during the full-scale data transmission experiments at 25 km distance using a low frequency (400 Hz) underwater acoustic apparatus under conditions of strong impulse noises and quasi-non-stationary channel. The results of in-situ experiments were similar to the ones that were obtained during the simulation. Full article
(This article belongs to the Special Issue Underwater Acoustics, Communications and Information Processing)
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Open AccessArticle
Numerical Investigation into Effects of Viscous Flux Vectors on Hydrofoil Cavitation Flow and Its Radiated Flow Noise
Appl. Sci. 2018, 8(2), 289; https://doi.org/10.3390/app8020289 - 15 Feb 2018
Cited by 4
Abstract
In this study, cavitation flow around a hydrofoil and its radiated hydro-acoustic fields were numerically investigated, with an emphasis on the effects of viscous flux vectors. The full three-dimensional unsteady compressible Reynolds-averaged Navier–Stokes equations were numerically solved. The mass transfer model was adopted [...] Read more.
In this study, cavitation flow around a hydrofoil and its radiated hydro-acoustic fields were numerically investigated, with an emphasis on the effects of viscous flux vectors. The full three-dimensional unsteady compressible Reynolds-averaged Navier–Stokes equations were numerically solved. The mass transfer model was adopted to model phase changes between liquid water and vapor. To resolve the numerical instability problem arising from the rapid changes in local density and speed of sound of the mixture, the preconditioning and dual-time stepping methods were employed. The filter-based turbulent model was applied to resolve the unstable cavitation flow field more accurately. In splitting the viscous terms, three approaches for dealing with viscous flux vectors were considered: the so-called viscous lagging, full viscous, and thin-layer models. Radiated hydro-acoustic waves were predicted by applying the Ffowcs Williams and Hawkings equations. The effects of the viscous flux vectors on the predicted flow fields and its radiated noise were then examined by comparing the hydro-dynamic forces, velocity distribution, volume fraction, far-field sound directivities, and sound spectrum of the three approaches. The results revealed that the thin-layer model can provide predictions as accurate as the full viscous model, but required less computational time. Full article
(This article belongs to the Special Issue Underwater Acoustics, Communications and Information Processing)
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Open AccessArticle
Target Localization in Underwater Acoustic Sensor Networks Using RSS Measurements
Appl. Sci. 2018, 8(2), 225; https://doi.org/10.3390/app8020225 - 01 Feb 2018
Cited by 11
Abstract
This paper addresses the target localization problems based on received signal strength (RSS) measurements in underwater acoustic wireless sensor network (UWSN). Firstly, the problems based on the maximum likelihood (ML) criterion for estimating target localization in cases of both known and unknown transmit [...] Read more.
This paper addresses the target localization problems based on received signal strength (RSS) measurements in underwater acoustic wireless sensor network (UWSN). Firstly, the problems based on the maximum likelihood (ML) criterion for estimating target localization in cases of both known and unknown transmit power are respectively derived, and fast implementation algorithms are proposed by transforming the non-convex problems into a generalized trust region subproblem (GTRS) frameworks. A three-step procedure is also provided to enhance the estimation accuracy in the unknown target transmit power case. Furthermore, the Cramer–Rao lower bounds (CRLBs) in both cases are derived. Computer simulation results show the superior performance of the proposed methods in the underwater environment. Full article
(This article belongs to the Special Issue Underwater Acoustics, Communications and Information Processing)
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Open AccessArticle
A New Resource Allocation Protocol for the Backhaul of Underwater Cellular Wireless Networks
Appl. Sci. 2018, 8(2), 178; https://doi.org/10.3390/app8020178 - 25 Jan 2018
Cited by 1
Abstract
In this paper, an underwater base station initiating (UBSI) resource allocation is proposed for underwater cellular wireless networks (UCWNs), which is a new approach to determine the backhaul capacity of underwater base stations (UBSs). This backhaul is a communication link from a UBS [...] Read more.
In this paper, an underwater base station initiating (UBSI) resource allocation is proposed for underwater cellular wireless networks (UCWNs), which is a new approach to determine the backhaul capacity of underwater base stations (UBSs). This backhaul is a communication link from a UBS to a UBS controller (UBSC). Contrary to conventional resource allocation protocols, a UBS initiates to re-determine its backhaul capacity for itself according to its queue status; it releases a portion of its backhaul capacity in the case of experiencing resource under-utilization, and also requests additional backhaul capacity to the UBSC if packet drops are caused due to queue-overflow. This protocol can be appropriate and efficient to the underwater backhaul link where the transmission rate is quite low and the latency is unneglectable. In order to investigate the applicability of the UBSI resource allocation protocol to the UCWN, its performance is extensively analyzed via system level simulations. In our analysis, considered performance measures include average packet drop rate, average resource utilization, average message overhead, and the reserved capacity of the UBSC. In particular, the simulation results show that our proposed protocol not only utilizes most of the given backhaul capacity (more than 90 percent of resource utilization on the average), but also reduces controlling message overheads induced by resource allocation (less than 2 controlling messages on the average). It is expected that the simulation results and analysis in this paper can be used as operating guidelines to apply our new resource allocation protocol for the UCWN. Full article
(This article belongs to the Special Issue Underwater Acoustics, Communications and Information Processing)
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Open AccessArticle
Chaos-Based Underwater Communication With Arbitrary Transducers and Bandwidth
Appl. Sci. 2018, 8(2), 162; https://doi.org/10.3390/app8020162 - 24 Jan 2018
Cited by 11
Abstract
In this work, an enhanced differential chaos shift keying (DCSK), based on a first order hybrid chaotic system, is being proposed for a high reliability underwater acoustic communication system. It can be integrated into systems that use standard existing transducers. We show that [...] Read more.
In this work, an enhanced differential chaos shift keying (DCSK), based on a first order hybrid chaotic system, is being proposed for a high reliability underwater acoustic communication system. It can be integrated into systems that use standard existing transducers. We show that a coherent operation between the received signal and the time reversal of the basis function in a first order hybrid chaotic system maximizes the signal to noise ratio at the receiver. Concurrently, DCSK configuration is used to resist the distortion caused by the complex underwater acoustic channel. Our simulation results show that the proposed method has lower bit error rate (BER). In addition, it shows higher communication reliability over underwater acoustic channel as compared to the conventional DCSK using logistic map and its variant forms such as Correlation Delay Shift Keying (CDSK), Phase-Separate DCSK (PS-DCSK), High Efficiency DCSK (HE-DCSK), and Reference Modulated DCSK (RM-DCSK). Full article
(This article belongs to the Special Issue Underwater Acoustics, Communications and Information Processing)
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Open AccessArticle
An Experimental Study of the Special Aspects of Scalar-Vector Sound Field Spatial Structures in the Shallow Sea Area
Appl. Sci. 2018, 8(2), 157; https://doi.org/10.3390/app8020157 - 24 Jan 2018
Cited by 1
Abstract
This paper discusses the results of an experimental study of the spatial structure of a scalar-vector sound field formed during towing of a low-frequency acoustic source on the continental shelf of the Sea of Japan. Methodologically, the experiment was carried out by towing [...] Read more.
This paper discusses the results of an experimental study of the spatial structure of a scalar-vector sound field formed during towing of a low-frequency acoustic source on the continental shelf of the Sea of Japan. Methodologically, the experiment was carried out by towing the acoustic source emitting a 134 Hz tone signal at a depth of 20 m on various acoustic paths at distances of up to 10 km from the combined receiving system, which consisted of a sound pressure receiver and three orthogonal sound pressure gradient components. Particular attention was paid to the investigation of the interference structure of scalar and vector fields in controlled hydrological conditions. The quantitative characteristics and features of the formation of signal interference at several depths along the tracks are discussed. The most interesting are the unique results of comparing horizontal and vertical field components, which make it possible to identify the presence of vortex structures in the acoustic source field on several tracks. The possibility of practical application of current research results is analyzed. Full article
(This article belongs to the Special Issue Underwater Acoustics, Communications and Information Processing)
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Open AccessArticle
Variability of Hydroacoustic Noise Probability Density Function at the Output of Automatic Gain Control System
Appl. Sci. 2018, 8(1), 142; https://doi.org/10.3390/app8010142 - 20 Jan 2018
Cited by 2
Abstract
This research presents results of the estimation of temporal variability of the hydroacoustic noise probability density function (PDF) in shallow waters within the frequency band of 0.03–3.3 kHz; the studies were conducted near the Primorsky Aquarium on Russky Island, Vladivostok, Russia. Signals were [...] Read more.
This research presents results of the estimation of temporal variability of the hydroacoustic noise probability density function (PDF) in shallow waters within the frequency band of 0.03–3.3 kHz; the studies were conducted near the Primorsky Aquarium on Russky Island, Vladivostok, Russia. Signals were received via unidirectional hydrophone and automatic gain control of the received signals. The hydrophone was attached to a drifting buoy via an elastic suspension; the received signals were transmitted by cable to a boat drifting with the buoy. The results of the comparison of the sea noise probability density function (PDF) estimates at the output of a system with automatic gain control (AGC) with similar results for a white Gaussian noise in the same frequency band are described. Full article
(This article belongs to the Special Issue Underwater Acoustics, Communications and Information Processing)
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Open AccessArticle
Underwater Cylindrical Object Detection Using the Spectral Features of Active Sonar Signals with Logistic Regression Models
Appl. Sci. 2018, 8(1), 116; https://doi.org/10.3390/app8010116 - 15 Jan 2018
Cited by 3
Abstract
The issue of detecting objects bottoming on the sea floor is significant in various fields including civilian and military areas. The objective of this study is to investigate the logistic regression model to discriminate the target from the clutter and to verify the [...] Read more.
The issue of detecting objects bottoming on the sea floor is significant in various fields including civilian and military areas. The objective of this study is to investigate the logistic regression model to discriminate the target from the clutter and to verify the possibility of applying the model trained by the simulated data generated by the mathematical model to the real experimental data because it is not easy to obtain sufficient data in the underwater field. In the first stage of this study, when the clutter signal energy is so strong that the detection of a target is difficult, the logistic regression model is employed to distinguish the strong clutter signal and the target signal. Previous studies have found that if the clutter energy is larger, false detection occurs even for the various existing detection schemes. For this reason, the discrete Fourier transform (DFT) magnitude spectrum of acoustic signals received by active sonar is applied to train the model to distinguish whether the received signal contains a target signal or not. The goodness of fit of the model is verified in terms of receiver operation characteristic (ROC), area under ROC curve (AUC), and classification table. The detection performance of the proposed model is evaluated in terms of detection rate according to target to clutter ratio (TCR). Furthermore, the real experimental data are employed to test the proposed approach. When using the experimental data to test the model, the logistic regression model is trained by the simulated data that are generated based on the mathematical model for the backscattering of the cylindrical object. The mathematical model is developed according to the size of the cylinder used in the experiment. Since the information on the experimental environment including the sound speed, the sediment type and such is not available, once simulated data are generated under various conditions, valid simulated data are selected using 70% of the experiment cylinder data. The selected simulated data are used to train the model. Randomly selected experiment cylinder data, which are 70% of the total experimental cylinder data, and the rock measurement data are used to test the model. This process is repeatedly carried out 1000 times. The results show that the proposed method is effective under the circumstance where experimental data are not sufficient and a mathematical model is available for a target. Full article
(This article belongs to the Special Issue Underwater Acoustics, Communications and Information Processing)
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Open AccessArticle
Virtual Source Array-Based Multiple Time-Reversal Focusing
Appl. Sci. 2018, 8(1), 99; https://doi.org/10.3390/app8010099 - 11 Jan 2018
Cited by 2
Abstract
Time reversal (TR) is the process of generating a spatio-temporal focus at a probe source (PS) location by transmitting a time-reversed version of a received signal. While TR focusing requires the PS for a coherent acoustic focus at its origin, the requirement of [...] Read more.
Time reversal (TR) is the process of generating a spatio-temporal focus at a probe source (PS) location by transmitting a time-reversed version of a received signal. While TR focusing requires the PS for a coherent acoustic focus at its origin, the requirement of the PS has been partially relaxed by the introduction of the concept of a virtual source array (VSA) (J. Acoust. Soc. Am. 2009, 125, 3828–3834). A VSA can serve as a remote platform or lens and redirect a focused field to a selected location beyond the VSA for which the field is assumed as a homogeneous medium with constant sound speed. The objective of this study is to extend VSA-based single TR focusing to simultaneous multiple focusing. This is achieved using the optimization theory by employing the multiple constraints method derived from a constraint matrix, which consists of appropriately synchronized transfer functions. Through numerical simulations, it is found that simultaneous multiple focusing can be achieved with distortionless response at selected multiple locations, and its performance degrades in the presence of sound speed mismatch. For achieving robust multiple focusing in the mismatch environment, singular value decomposition is applied to obtain the weight vector (i.e., backpropagation vector) that best approximates the column vectors of the constraint matrix. Numerical simulation results show that VSA-based multiple TR focusing using SVD is not a method to simultaneously focus on multiple locations, but a method of constructing a field which robustly passes through multiple locations in sound speed mismatch environment. Full article
(This article belongs to the Special Issue Underwater Acoustics, Communications and Information Processing)
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Open AccessArticle
Study on the Structure of an Efficient Receiver for Covert Underwater Communication Using Direct Sequence Spread Spectrum
Appl. Sci. 2018, 8(1), 58; https://doi.org/10.3390/app8010058 - 03 Jan 2018
Cited by 5
Abstract
This paper proposes an underwater communication receive model based on the spread spectrum technique in order to provide the characteristic of a low probability of interception. To do this, turbo equalization techniques employing Bahl-Cocke-Jelinek-Raviv (BCJR) decoding to improve performance through repetition are applied [...] Read more.
This paper proposes an underwater communication receive model based on the spread spectrum technique in order to provide the characteristic of a low probability of interception. To do this, turbo equalization techniques employing Bahl-Cocke-Jelinek-Raviv (BCJR) decoding to improve performance through repetition are applied to offer excellent performance even at a low signal to noise ratio (SNR) of transmitted signals due to the spread spectrum technique. A turbo equalization model based on RAKE which increase signal power by summing the received signal through the multipath is proposed to compensate distorted data due to multipath channel and the performance improvements were proven by applying the threshold and weighted coefficient in the RAKE receiver model. The model was applied to covert underwater communication in a multi-sensor environment, and the efficiency of the proposed method was proven through underwater experiments. Full article
(This article belongs to the Special Issue Underwater Acoustics, Communications and Information Processing)
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Open AccessArticle
A Novel Approach for the Estimation of Doubly Spread Acoustic Channels Based on Wavelet Transform
Appl. Sci. 2018, 8(1), 38; https://doi.org/10.3390/app8010038 - 01 Jan 2018
Cited by 2
Abstract
In this paper, the estimation of doubly spread underwater acoustic (UWA) channels is investigated. The UWA channels are characterized by severe delay spread and significant Doppler effects, and can be well modeled as a multi-scale multi-lag (MSML) channel. Furthermore, exploiting the sparsity of [...] Read more.
In this paper, the estimation of doubly spread underwater acoustic (UWA) channels is investigated. The UWA channels are characterized by severe delay spread and significant Doppler effects, and can be well modeled as a multi-scale multi-lag (MSML) channel. Furthermore, exploiting the sparsity of UWA channels, MSML channel estimation can be transformed into the estimation of parameter sets (amplitude, Doppler scale factor, time delay). Based on this, the orthogonal matching pursuit (OMP) algorithm has been widely used. However, the estimation accuracy of OMP depends on the size of the dictionary, which is related with both delay spread and Doppler spread. Thus it requires high computational complexity. This paper proposes a new method, called wavelet transform (WT) based algorithm, for the UWA channel estimation. Different from OMP algorithm which needs to search in both time domain and Doppler domain, WT-based algorithm only needs to search in time domain by using the Doppler invariant characteristic of hyperbolic frequency modulation (HFM) signal. The performance of the proposed algorithm is evaluated by computer simulations based on BELLHOP. The simulation results show that WT-based algorithm performs slightly better than OMP algorithm in low signal to noise ratio (SNR) while can greatly reduce computational complexity. Full article
(This article belongs to the Special Issue Underwater Acoustics, Communications and Information Processing)
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Open AccessArticle
PHD and CPHD Algorithms Based on a Novel Detection Probability Applied in an Active Sonar Tracking System
Appl. Sci. 2018, 8(1), 36; https://doi.org/10.3390/app8010036 - 27 Dec 2017
Cited by 3
Abstract
Underwater multi-targets tracking has always been a difficult problem in active sonar tracking systems. In order to estimate the parameters of time-varying multi-targets moving in underwater environments, based on the Bayesian filtering framework, the Random Finite Set (RFS) is introduced to multi-targets tracking, [...] Read more.
Underwater multi-targets tracking has always been a difficult problem in active sonar tracking systems. In order to estimate the parameters of time-varying multi-targets moving in underwater environments, based on the Bayesian filtering framework, the Random Finite Set (RFS) is introduced to multi-targets tracking, which not only avoids the problem of data association in multi-targets tracking, but also realizes the estimation of the target number and their states simultaneously. Usually, the conventional Probability Hypothesis Density (PHD) and Cardinalized Probability Hypothesis Density (CPHD) algorithms assume that the detection probability is known as a priori, which is not suitable in many applications. Some methods have been proposed to estimate the detection probability, but most assume that it is constant both in time and surveillance region. In this paper, we model the detection probability through the active sonar equation. When fixed the false detection probability, we can get the analytic expression for the detection probability, which is related to target position. In addition, this novel detection probability is used in PHD and CPHD algorithms and applied to underwater active sonar tracking systems. Also, we use the adaptive ellipse gate strategy to reduce the computational load in PHD and CPHD algorithms. Under the linear Gaussian assumption, the proposed detection probability is illustrated in both Gaussian Mixture Probability Hypothesis Density (GM-PHD) and Gaussian Mixture Cardinalized Probability Hypothesis Density (GM-CPHD), respectively. Simulation results show that the proposed Pd-GM-PHD and Pd-GM-CPHD algorithms are more realistic and accuratein underwater active sonar tracking systems. Full article
(This article belongs to the Special Issue Underwater Acoustics, Communications and Information Processing)
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Open AccessArticle
Message Collision Avoidance Protocols for Detecting Stray Nodes in a Scuba Diving Group Using Ultrasonic Multi-Hop Message Communication
Appl. Sci. 2018, 8(1), 24; https://doi.org/10.3390/app8010024 - 25 Dec 2017
Cited by 1
Abstract
Recent years have seen a growing interest in underwater communication and some progress has been made in this area. However, underwater communication is still immature compared with terrestrial communication. A prime reason for this is that the underwater environment is intrinsically not suitable [...] Read more.
Recent years have seen a growing interest in underwater communication and some progress has been made in this area. However, underwater communication is still immature compared with terrestrial communication. A prime reason for this is that the underwater environment is intrinsically not suitable for propagation of electric waves. Instead, ultrasonic waves are mainly used for underwater communication. Since ultrasonic waves cannot provide sufficient communication speed or capacity, they cannot use existing network technologies, which assume use of radio waves. In particular, communication in shallow water is still an uncharted territory. Few communication technologies are employed in environments where people enjoy scuba diving. This paper addresses problems faced by recreational scuba divers. It proposes constructing an ad hoc mesh-shaped network between divers within a group and use ultrasonic waves as transmission media in order to enable the detection of a stray diver. It also proposes a communication protocol in which messages are relayed in multiple hops, and a message collision avoidance method, which is intended to reduce the rate of packet loss caused by message propagation delay. We have implemented the proposed methods in a network simulator, and compared them with an existing communication method that has no message collision avoidance function, in terms of the packet loss rate, the stray driver detection rate, and the rate of the ability to communicate in multiple hops. Full article
(This article belongs to the Special Issue Underwater Acoustics, Communications and Information Processing)
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Open AccessArticle
Estimate of Passive Time Reversal Communication Performance in Shallow Water
Appl. Sci. 2018, 8(1), 23; https://doi.org/10.3390/app8010023 - 25 Dec 2017
Cited by 3
Abstract
Time reversal processes have been used to improve communication performance in the severe underwater communication environment characterized by significant multipath channels by reducing inter-symbol interference and increasing signal-to-noise ratio. In general, the performance of the time reversal is strongly related to the behavior [...] Read more.
Time reversal processes have been used to improve communication performance in the severe underwater communication environment characterized by significant multipath channels by reducing inter-symbol interference and increasing signal-to-noise ratio. In general, the performance of the time reversal is strongly related to the behavior of the q -function, which is estimated by a sum of the autocorrelation of the channel impulse response for each channel in the receiver array. The q -function depends on the complexity of the communication channel, the number of channel elements and their spacing. A q -function with a high side-lobe level and a main-lobe width wider than the symbol duration creates a residual ISI (inter-symbol interference), which makes communication difficult even after time reversal is applied. In this paper, we propose a new parameter, E q , to describe the performance of time reversal communication. E q is an estimate of how much of the q -function lies within one symbol duration. The values of E q were estimated using communication data acquired at two different sites: one in which the sound speed ratio of sediment to water was less than unity and one where the ratio was higher than unity. Finally, the parameter E q was compared to the bit error rate and the output signal-to-noise ratio obtained after the time reversal operation. The results show that these parameters are strongly correlated to the parameter E q . Full article
(This article belongs to the Special Issue Underwater Acoustics, Communications and Information Processing)
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Open AccessArticle
Cognitive Routing in Software-Defined Underwater Acoustic Networks
Appl. Sci. 2017, 7(12), 1312; https://doi.org/10.3390/app7121312 - 17 Dec 2017
Cited by 7
Abstract
There are two different types of primary users (natural acoustic and artificial acoustic), and there is a long propagation delay for acoustic links in underwater cognitive acoustic networks (UCANs). Thus, the selection of a stable route is one of the key design factors [...] Read more.
There are two different types of primary users (natural acoustic and artificial acoustic), and there is a long propagation delay for acoustic links in underwater cognitive acoustic networks (UCANs). Thus, the selection of a stable route is one of the key design factors for improving overall network stability, thereby reducing end-to-end delay. Software-defined networking (SDN) is a novel approach that improves network intelligence. To this end, we propose a novel SDN-based routing protocol for UCANs in order to find a stable route between source and destination. A main controller is placed in a surface buoy that is responsible for the global view of the network, whereas local controllers are placed in different autonomous underwater vehicles (AUVs) that are responsible for a localized view of the network. The AUVs have fixed trajectories, and sensor nodes within transmission range of the AUVs serve as gateways to relay the gathered information to the controllers. This is an SDN-based underwater communications scheme whereby two nodes can only communicate when they have a consensus about a common idle channel. To evaluate our proposed scheme, we perform extensive simulations and improve network performance in terms of end-to-end delay, delivery ratio, and overhead. Full article
(This article belongs to the Special Issue Underwater Acoustics, Communications and Information Processing)
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Open AccessArticle
A Novel Fractional Fourier Transform-Based ASK-OFDM System for Underwater Acoustic Communications
Appl. Sci. 2017, 7(12), 1286; https://doi.org/10.3390/app7121286 - 11 Dec 2017
Cited by 5
Abstract
A key research area in wireless transmission is underwater communications. It has a vital role in applications such as underwater sensor networks (UWSNs) and disaster detection. The underwater channel is very unique as compared to other alternatives of transmission channels. It is characterized [...] Read more.
A key research area in wireless transmission is underwater communications. It has a vital role in applications such as underwater sensor networks (UWSNs) and disaster detection. The underwater channel is very unique as compared to other alternatives of transmission channels. It is characterized by path loss, multipath fading, Doppler spread and ambient noise. Thus, the bit error rate (BER) is increased to a large extent when compared to its counterpart of cellular communications. Acoustic signals are the current best solution for underwater communications. The use of electromagnetic or optical waves obviously entails a much higher data rate. However, they suffer from high attenuation, absorption or scattering. This paper proposes a novel fractional fast Fourier transform (FrFT)—orthogonal frequency division multiplexing (FrFT-OFDM) system for underwater acoustic (UWA) communication—which employs the amplitude shift keying (ASK) modulation technique (FrFT-ASK-OFDM). Specifically, ASK achieves a better bandwidth efficiency as compared to other commonly used modulation techniques, such as quadrature amplitude modulation (QAM) and phase shift keying (PSK). In particular, the system proposed in this article can achieve a very promising BER performance, and can reach higher data rates when compared to other systems proposed in the literature. The BER performance of the proposed system is evaluated numerically, and is compared to the corresponding M-ary QAM system in the UWA channel for the same channel conditions. Moreover, the performance of the proposed system is compared to the conventional fast Fourier transform (FFT)-OFDM (FFT-OFDM) system in the absence and presence of the effect of carrier frequency offset (CFO). Numerical results show that the proposed system outperforms the conventional FFT-based systems for UWA channels, even in channels dominated by CFO. Moreover, the spectral efficiency and data rate of the proposed system are approximately double the values of the corresponding conventional OFDM systems for the same parameters. Full article
(This article belongs to the Special Issue Underwater Acoustics, Communications and Information Processing)
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