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 as Gaussian, not white, but has a decaying power spectral density. channel capacity depends on the distance, may be extremely limited. Because acoustic best supported at frequencies, total available bandwidth low, an communication system inherently wideband in sense...

With the advances in acoustic modem technology that enabled high-rate reliable communications, current research focuses on communication between various remote instruments within a network environment. Underwater (UWA) networks are generally formed by acoustically connected ocean-bottom sensors, autonomous underwater vehicles, and surface station, which provides link to an on-shore control center. While many applications require long-term monitoring of deployment area, battery-powered nodes...

Path loss of an underwater acoustic communication channel depends not only on the transmission distance, but also signal frequency. As a result, useful bandwidth feature that distinguishes system from terrestrial radio one. This fact influences design network: greater information throughput is available if messages are relayed over multiple short hops instead being transmitted directly one long hop. We asses dependency distance using analytical method takes into account physical models...

Underwater acoustic (UWA) channels are wideband in nature due to the small ratio of carrier frequency signal bandwidth, which introduces frequency-dependent Doppler shifts. In this paper, we treat channel as having a common scaling factor on all propagation paths, and propose two-step approach mitigating effect: 1) nonuniform compensation via resampling that converts "wideband" problem into "narrowband" 2) high-resolution uniform residual Doppler. We focus zero-padded orthogonal...

This paper examines the main approaches and challenges in design implementation of underwater wireless sensor networks. We summarize key applications phenomena related to acoustic propagation, discuss how they affect operation communication systems networking protocols at various layers. also provide an overview communications hardware, testbeds simulation tools available research community.

In recent years, underwater acoustic (UWA) communications have received much attention as their applications begun to shift from military toward commercial. Digital through UWA channels differ substantially those in other media, such radio channels, due severe signal degradations caused by multipath propagation and high temporal spatial variability of the channel conditions. The design communication systems has until recently relied on use noncoherent modulation techniques. However, achieve...

High-speed phase coherent communications in the ocean channel are made difficult by combined effects of large Doppler fluctuations and extended, time-varying multipath. In order to account for these effects, we consider a receiver which performs optimal synchronization equalization jointly. Since intersymbol interference some underwater acoustic channels spans several tens symbol intervals, making maximum-likelihood unacceptably complex, use suboptimal, but low complexity, decision feedback...

The past 30 years have seen a growing interest in underwater acoustic communications because of its applications marine research, oceanography, commercial operations, the offshore oil industry and defense. Continued research over has resulted improved performance robustness as compared to initial communication systems. In this paper, we aim provide an overview key developments point-to-point techniques well networking protocols since beginning decade. We also insight into some open problems...

Underwater acoustic channel models provide a tool for predicting the performance of communication systems before deployment, and are thus essential system design. In this paper, we offer statistical model which incorporates physical laws propagation (frequency-dependent attenuation, bottom/surface reflections), as well effects inevitable random local displacements. Specifically, focus on displacements two scales: those that involve distances order few wavelengths, to refer small-scale...

Long propagation delays and low bit rates of underwater acoustic networks make these systems fundamentally different from the packet radio networks. As a consequence, many network protocols designed for channels are either not applicable, or have extremely efficiency over channels. These facts necessitate dedicated design an network. A medium access control (MAC) protocol suitable is proposed analyzed. The based on channel discipline called floor acquisition multiple (FAMA) which combines...

A theoretically optimal multichannel receiver for intersymbol interference communication channels is derived, and its suboptimal versions with linear decision feedback equalizer are presented. practical based on any of these structures encounters difficulties in the underwater acoustic which extended time-varying multipath accompanied by phase instabilities. that overcomes problems jointly performing adaptive mean-squared error diversity combining, carrier-phase synchronization equalization...

Path loss of an underwater acoustic communication channel depends not only on the transmission distance, but also signal frequency. As a result, useful bandwidth feature that distinguishes system from terrestrial radio one. This fact influences design network: greater information throughput is available if messages are relayed over multiple short hops instead being transmitted directly one long hop.We asses dependency distance using analytical method takes into account physical models...

Multiple-input-multiple-output (MIMO) techniques have been actively pursued recently in underwater acoustic communications to increase the data rate over bandwidth-limited channels. In this communication, we present a MIMO system design, where spatial multiplexing is applied with orthogonal-frequency-division-multiplexing (OFDM) signals. The proposed receiver works on block-by-block basis, null subcarriers are used for Doppler compensation, pilot channel estimation, and detector consisting...

An adaptive algorithm is proposed for OFDM signal detection on Doppler-distorted, time-varying multipath channels. The focus of the approach low complexity post-FFT processing. receiver performs MMSE combining signals received across an array, using channel estimation. Non-uniform Doppler compensation subbands performed a single adaptively estimated parameter representing rate. Algorithm performance demonstrated experimental data, transmitted through shallow water over distance 2.5 km. QPSK...

Multi-hop transmission is considered for large coverage areas in bandwidth-limited underwater acoustic networks. In this paper, we present a scalable routing technique based on location information, and optimized minimum energy per bit consumption. The proposed Focused Beam Routing (FBR) protocol suitable networks containing both static mobile nodes, which are not necessarily synchronized to global clock. A source node must be aware of its own the final destination, but those other nodes.

In this paper, we explore design aspects of adaptive modulation based on orthogonal frequency-division multiplexing (OFDM) for underwater acoustic (UWA) communications, and study its performance using real-time at-sea experiments. Our criterion is to maximize the system throughput under a target average bit error rate (BER). We consider two different schemes level adaptivity: in first scheme, only levels are adjusted while power allocated uniformly across subcarriers, whereas second both...

This paper proposes a channel access protocol for ad-hoc underwater acoustic networks which are characterized by long propagation delays and unequal transmit/receive power requirements. The saves transmission energy avoiding collisions while maximizing throughput. It is based on minimizing the duration of hand-shake taking advantage receiver's tolerance to interference when two nodes closer than maximal range. Nodes do not need be synchronized, can move, half-duplex, use same power. achieves...

Acoustic propagation is characterized by three major factors: attenuation that depends on the signal frequency, multipath propagation, and low speed of sound (1500 m/s). The channel has a sparse impulse response, where each physical path acts as time-varying low-pass filter, motion introduces additional Doppler spreading shifting. Because best supported at frequencies, acoustic communication systems are inherently wideband. way in which these facts influence design processing methods...

We examine the problem of utilizing an autonomous underwater vehicle (AUV) to collect data from sensor network. The sensors in network are equipped with acoustic modems that provide noisy, range-limited communication. AUV must plan a path maximizes information collected while minimizing travel time or fuel expenditure. propose planning methods extend algorithms for variants Traveling Salesperson Problem (TSP). While executing path, can improve performance by communicating multiple nodes at...

The past three decades have seen a growing interest in underwater acoustic communications. Continued research over the years has resulted improved performance and robustness as compared to initial communication systems. Research expanded from pointtopoint communications include networks well. A series of review papers provide an excellent history development field until end last decade. In this paper, we aim overview key developments, both theoretical applied, two decades. We also hope...

A phase synchronization method, which provides non-uniform frequency offset compensation needed for wideband OFDM, is coupled with low-complexity channel estimation in the time domain. Sparsing of impulse response leads to an improved performance, while adaptive supports decision-directed operation and yields low overhead. System performance demonstrated using experimental data transmitted over a 1 km shallow water 19 kHz - 31 band.

Inspired by the theory of compressed sensing and employing random channel access, we propose a distributed energy-efficient sensor network scheme denoted Random Access Compressed Sensing (RACS). The proposed is suitable for long-term deployment large underwater networks, in which saving energy bandwidth crucial importance. During each frame, randomly chosen subset nodes participate process, then share using access. Due to nature packets may collide at fusion center. To account packet loss...

This paper focuses on statistical characterization and capacity evaluation of shallow water acoustic communications channels. Wideband single-carrier multi-carrier probe signals are employed to measure the time-varying channel response, estimate its properties that play an important role in design bandwidth-efficient power-efficient communication systems. To assess underwater channel, we first probability density functions model signal fading. Rician fading is found provide a good match for...

In this paper, we focus on orthogonal frequency-division multiplexing (OFDM) receiver designs for underwater acoustic (UWA) channels with user- and/or path-specific Doppler scaling distortions. The scenario is motivated by the cooperative communications framework, where distributed transmitter/receiver pairs may experience significantly different distortions, as well single-user scenarios, distinct factors exist among propagation paths. conventional approach of front-end resampling that...