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Journal ArticleDOI

Underwater acoustic communication channels: Propagation models and statistical characterization

TL;DR: There are no standardized models for the acoustic channel fading, and experimental measurements are often made to assess the statistical properties of the channel in particular deployment sites, but the channel capacity depends on the distance, and may be extremely limited.
Abstract: Acoustic propagation is characterized by three major factors: attenuation that increases with signal frequency, time-varying multipath propagation, and low speed of sound (1500 m/s). The background noise, although often characterized as Gaussian, is not white, but has a decaying power spectral density. The channel capacity depends on the distance, and may be extremely limited. Because acoustic propagation is best supported at low frequencies, although the total available bandwidth may be low, an acoustic communication system is inherently wideband in the sense that the bandwidth is not negligible with respect to its center frequency. The channel can have a sparse impulse response, where each physical path acts as a time-varying low-pass filter, and motion introduces additional Doppler spreading and shifting. Surface waves, internal turbulence, fluctuations in the sound speed, and other small-scale phenomena contribute to random signal variations. At this time, there are no standardized models for the acoustic channel fading, and experimental measurements are often made to assess the statistical properties of the channel in particular deployment sites.

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Citations
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Journal ArticleDOI
TL;DR: It is pointed out that a popular assumption - that multipath channels are sparse in their equivalent baseband representation - has pitfalls and there are over-complete dictionaries that lead to much sparser channel representations and better estimation performance.
Abstract: Compressive sensing is a topic that has recently gained much attention in the applied mathematics and signal processing communities. It has been applied in various areas, such as imaging, radar, speech recognition, and data acquisition. In communications, compressive sensing is largely accepted for sparse channel estimation and its variants. In this article we highlight the fundamental concepts of compressive sensing and give an overview of its application to pilot aided channel estimation. We point out that a popular assumption - that multipath channels are sparse in their equivalent baseband representation - has pitfalls. There are over-complete dictionaries that lead to much sparser channel representations and better estimation performance. As a concrete example, we detail the application of compressive sensing to multicarrier underwater acoustic communications, where the channel features sparse arrivals, each characterized by its distinct delay and Doppler scale factor. To work with practical systems, several modifications need to be made to the compressive sensing framework as the channel estimation error varies with how detailed the channel is modeled, and how data and pilot symbols are mixed in the signal design.

553 citations

Journal ArticleDOI
21 Mar 2018
TL;DR: This work presents the design, fabrication, control, and oceanic testing of a soft robot fish that can swim in three dimensions to continuously record the aquatic life it is following or engaging and exhibits a lifelike undulating tail motion enabled by a soft robotic actuator design.
Abstract: Closeup exploration of underwater life requires new forms of interaction, using biomimetic creatures that are capable of agile swimming maneuvers, equipped with cameras, and supported by remote human operation. Current robotic prototypes do not provide adequate platforms for studying marine life in their natural habitats. This work presents the design, fabrication, control, and oceanic testing of a soft robotic fish that can swim in three dimensions to continuously record the aquatic life it is following or engaging. Using a miniaturized acoustic communication module, a diver can direct the fish by sending commands such as speed, turning angle, and dynamic vertical diving. This work builds on previous generations of robotic fish that were restricted to one plane in shallow water and lacked remote control. Experimental results gathered from tests along coral reefs in the Pacific Ocean show that the robotic fish can successfully navigate around aquatic life at depths ranging from 0 to 18 meters. Furthermore, our robotic fish exhibits a lifelike undulating tail motion enabled by a soft robotic actuator design that can potentially facilitate a more natural integration into the ocean environment. We believe that our study advances beyond what is currently achievable using traditional thruster-based and tethered autonomous underwater vehicles, demonstrating methods that can be used in the future for studying the interactions of aquatic life and ocean dynamics.

469 citations


Cites methods from "Underwater acoustic communication c..."

  • ...Communication frequencies were chosen by considering typical ranges of human hearing, frequency-dependent attenuation in underwater channels [56], Doppler effects, SoFi’s motor noise, the microcontroller’s sampling capabilities, parameters of the receiver’s detection algorithm, expected sources of environmental noise such as wind and waves [92, 93], and marine life....

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  • ...We therefore used acoustic communications, which have been widely adopted for underwater applications [55, 56, 57]....

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Journal ArticleDOI
TL;DR: A comprehensive survey of various UASN architectures and a large number of localization techniques is presented, followed by a discussion on the performance of the localization techniques and open research issues.
Abstract: The widespread adoption of the Wireless Sensor Networks (WSNs) in various applications in the terrestrial environment and the rapid advancement of the WSN technology have motivated the development of Underwater Acoustic Sensor Networks (UASNs). UASNs and terrestrial WSNs have several common properties while there are several challenges particular to UASNs that are mostly due to acoustic communications, and inherent mobility. These challenges call for novel architectures and protocols to ensure successful operation of the UASN. Localization is one of the fundamental tasks for UASNs which is required for data tagging, node tracking, target detection, and it can be used for improving the performance of medium access and network protocols. Recently, various UASN architectures and a large number of localization techniques have been proposed. In this paper, we present a comprehensive survey of these architectures and localization methods. To familiarize the reader with the UASNs and localization concepts, we start our paper by providing background information on localization, state-of-the-art oceanographic systems, and the challenges of underwater communications. We then present our detailed survey, followed by a discussion on the performance of the localization techniques and open research issues.

396 citations


Cites background from "Underwater acoustic communication c..."

  • ...Time-variability is mainly due to the surface waves where the place of the reflection point changes with the waves [35]....

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Journal ArticleDOI
TL;DR: This work considers detection based on deep learning, and shows it is possible to train detectors that perform well without any knowledge of the underlying channel models, and demonstrates that the bit error rate performance of the proposed SBRNN detector is better than that of a Viterbi detector with imperfect CSI.
Abstract: We consider detection based on deep learning, and show it is possible to train detectors that perform well without any knowledge of the underlying channel models Moreover, when the channel model is known, we demonstrate that it is possible to train detectors that do not require channel state information (CSI) In particular, a technique we call a sliding bidirectional recurrent neural network (SBRNN) is proposed for detection where, after training, the detector estimates the data in real time as the signal stream arrives at the receiver We evaluate this algorithm, as well as other neural network (NN) architectures, using the Poisson channel model, which is applicable to both optical and molecular communication systems In addition, we also evaluate the performance of this detection method applied to data sent over a molecular communication platform, where the channel model is difficult to model analytically We show that SBRNN is computationally efficient, and can perform detection under various channel conditions without knowing the underlying channel model We also demonstrate that the bit error rate performance of the proposed SBRNN detector is better than that of a Viterbi detector with imperfect CSI as well as that of other NN detectors that have been previously proposed Finally, we show that the SBRNN can perform well in rapidly changing channels, where the coherence time is on the order of a single symbol duration

305 citations


Cites background from "Underwater acoustic communication c..."

  • ...Some examples of the latter are underwater communication using acoustic signals [1] as well as molecular communication, which relies on chemical signals to interconnect tiny devices with sub-millimeter dimensions in environments such as inside the human body [2]–[5]....

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Proceedings ArticleDOI
01 Oct 2009
TL;DR: A network simulator based on NS-2, Aqua-Sim, which effectively simulates the attenuation of underwater acoustic channels and the collision behaviors in long delay acoustic networks and provides a rich set of basic and advanced protocols.
Abstract: In this paper, we present a network simulator, Aqua-Sim, for underwater sensor networks. Aqua-Sim is based on NS-2, one of the most widely used network simulators, and it follows object-oriented design style and all network entities are implemented as classes. Aqua-Sim effectively simulates the attenuation of underwater acoustic channels and the collision behaviors in long delay acoustic networks. Moreover, Aqua-Sim supports three-dimensional network deployment and provides a rich set of basic and advanced protocols. Through several case studies, we show that Aqua-Sim can "reproduce" the real world with high fidelity and flexibility.

292 citations

References
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Journal ArticleDOI
TL;DR: This work takes an information-theoretic approach and defines the bandwidth corresponding to optimal signal energy allocation -- one that maximizes the channel capacity subject to the constraint that the transmission power is finite.
Abstract: Path loss of an underwater acoustic communication channel depends not only on the transmission distance, but also on the signal frequency. As a result, the useful bandwidth depends on the transmission distance, a feature that distinguishes an underwater acoustic system from a terrestrial radio one. This fact influences the design of an acoustic network: a greater information throughput is available if messages are relayed over multiple short hops instead of being transmitted directly over one long hop. We asses the bandwidth dependency on the distance using an analytical method that takes into account physical models of acoustic propagation loss and ambient noise. A simple, single-path time-invariant model is considered as a first step. To assess the fundamental bandwidth limitation, we take an information-theoretic approach and define the bandwidth corresponding to optimal signal energy allocation -- one that maximizes the channel capacity subject to the constraint that the transmission power is finite. Numerical evaluation quantifies the bandwidth and the channel capacity, as well as the transmission power needed to achieve a pre-specified SNR threshold, as functions of distance. These results lead to closed-form approximations, which may become useful tools in the design and analysis of acoustic networks.

904 citations


"Underwater acoustic communication c..." refers background in this paper

  • ...…the bandwidth and power needed to achieve a prespecified SNR over some distance can be approximated as B(l) = b ⋅ l –β , P(l) = p ⋅ l ψ , where the coefficients b, p and the exponents β ∈ (0, 1), ψ ≥ 1 depend on the target SNR, the parameters of the acoustic path loss, and the ambient noise [2]....

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Book
01 Jan 1982
TL;DR: The ocean as an acoustical medium ray theory of the sound field in the ocean reflection of sound from the surface and bottom of the ocean plane was proposed in this article, where sound propagation in the random ocean scattering and absorption of sound by gas bubbles in water.
Abstract: The ocean as an acoustical medium ray theory of the sound field in the ocean reflection of sound from the surface and bottom of the ocean plane waves reflection of sound from the surface and bottom of the ocean point source propagation of sound in shallow water underwater sound channel (USC) range-dependent waveguide antiwave guide sound propagation scattering of sound at rough surfaces sound propagation in the random ocean scattering and absorption of sound by gas bubbles in water.

739 citations


"Underwater acoustic communication c..." refers background or methods in this paper

  • ...The absorption coefficient a(f) can be obtained using an empirical formula [ 1 ]....

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  • ...IEEE Communications Magazine • January 2009 85 spectral density of ambient noise for several values of wind speed (wind drives the surface waves) and several levels of distant shipping activity (which is modeled on a scale from 0 to 1). The power spectral density of ambient noise decays at a rate of approximately 18 dB/decade, as shown by the straight dashed line in Fig. 2 [ 1 ]....

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BookDOI
01 Jan 2003

737 citations

Proceedings ArticleDOI
18 Sep 2005
TL;DR: The micro-modem is a compact, low-power, underwater acoustic communications and navigation subsystem which has the capability to perform low-rate frequency-hopping frequency-shift keying, variable rate phase-coherent keying and two different types of long base line navigation, narrow-band and broadband.
Abstract: The micro-modem is a compact, low-power, underwater acoustic communications and navigation subsystem. It has the capability to perform low-rate frequency-hopping frequency-shift keying (FH-FSK), variable rate phase-coherent keying (PSK), and two different types of long base line navigation, narrow-band and broadband. The system can be configured to transmit in four different bands from 3 to 30 kHz, with a larger board required for the lowest frequency. The user interface is based on the NMEA standard, which is a serial port specification. The modem also includes a simple built-in networking capability which supports up to 16 units in a polled or random-access mode and has an acknowledgement capability which supports guaranteed delivery transactions. The paper contains a detailed system description and results from several tests are also presented

548 citations

Book
07 May 1997
TL;DR: This revision, with 100 additional pages, completely updates the material in the first edition and includes new models based on current research and includes problems and solutions in every chapter, making the book more useful in teaching.
Abstract: Senior level/graduate level text/reference presenting state-of-the- art numerical techniques to solve the wave equation in heterogeneous fluid-solid media. Numerical models have become standard research tools in acoustic laboratories, and thus computational acoustics is becoming an increasingly important branch of ocean acoustic science. The first edition of this successful book, written by the recognized leaders of the field, was the first to present a comprehensive and modern introduction to computational ocean acoustics accessible to students. This revision, with 100 additional pages, completely updates the material in the first edition and includes new models based on current research. It includes problems and solutions in every chapter, making the book more useful in teaching (the first edition had a separate solutions manual). The book is intended for graduate and advanced undergraduate students of acoustics, geology and geophysics, applied mathematics, ocean engineering or as a reference in computational methods courses, as well as professionals in these fields, particularly those working in government (especially Navy) and industry labs engaged in the development or use of propagating models.

523 citations