Underwater Link Research Articles

Design of a Hybrid Transceiver Through P-Spice Simulation for Establishing Underwater Optical Wireless Communication Link

In this work, using PSpice Simulator we try to implement an underwater optical wireless communication link and to determine at which wavelength the attenuation is minimum for the given transmission medium characteristics. Because in coastal waters, both inherent and apparent optical properties are influenced by a wide array of physical, biological and chemical processes leading to optical variability. Hence, appropriate channel modeling will be performed. The main challenge for the development of efficient underwater wireless sensor networking solutions posed by the underwater environment is the requirement of different wavelengths of light for different ocean conditions. To overcome this drawback, a hybrid transceiver is designed in such way that the transmitter will transmit a particular wavelength optical signal in order to have least BER depending on the characteristics of the underwater optical channel.

16 Gb/s PAM4 UWOC system based on 488-nm LD with light injection and optoelectronic feedback techniques.

A 16 Gb/s four-level pulse amplitude modulation (PAM4) underwater wireless optical communication (UWOC) system based on 488-nm laser diode (LD) with light injection and optoelectronic feedback techniques is proposed and successfully demonstrated. Experimental results show that such a 1.8-GHz 488-nm blue light LD with light injection and optoelectronic feedback techniques is enough forceful for a 16 Gb/s PAM4 signal underwater link. To the authors' knowledge, this study is the first to successfully adopt a 488-nm LD transmitter with light injection and optoelectronic feedback techniques in a PAM4 UWOC system. By adopting a 488-nm LD transmitter with light injection and optoelectronic feedback techniques, good bit error rate performance (offline processed by Matlab) and clear eye diagrams (measured in real-time) are achieved over a 10-m underwater link. The proposed system has the potential to play a vital role in the future UWOC infrastructure by effectively providing high transmission rate (16 Gb/s) and long underwater transmission distance (10 m).

Semiconductor optical amplifiers for underwater optical wireless communications

Underwater optical wireless communications (UOWC) systems have recently received significant attention as an attractive solution for both research and commercial use because of their ability to provide high bandwidth communications over relatively short transmission spans along with their low operational cost. However, high absorption and scattering of optical transmission in the water limit the achievable range of underwater optical wireless links to only few metres. In this study, in an effort to increase the range and reliability of underwater optical wireless links, the authors propose to utilise semiconductor optical amplifiers at the receiver and discuss in a quantitative fashion the performance enhancements that can be achieved. After developing the required analytical framework, extensive numerical results are further provided to demonstrate the performance of the proposed scheme for different operating conditions. Specifically, assuming intensity modulation and direct detection schemes with on–off keying modulation, they evaluate the bit error rate of the proposed system configuration for different water types, link distances and forward error correction schemes. Performance evaluation results reveal that the use of optical amplification can significantly improve the quality of UWOC links.

Scalable Nodes Deployment Algorithm for the Monitoring of Underwater Pipeline

Underwater Wireless Linear Sensor Networks (UW-LSNs) possess unique features as compared to the terrestrial sensor networks for pipeline monitoring. Other than long propagation delays for long range underwater pipelines and high error probability, homogeneous node deployment also makes it harder to detect and locate the pipeline leakage efficiently. Determining the exact leakage position with minimum delay stays a major issue where pipelines length is extremely long and expensive to deploy many underwater sensors. In order to tackle the problem of large scale pipeline monitoring and unreliable underwater link quality, many algorithms have been proposed and even some of them provided good solutions for these issues but the scalable nodes deployments still need focus and prime attention. In order to handle the problem of nodes deployment, we therefore propose a dynamic nodes deployment algorithm where every node in the network is assigned location in a quick and efficient way without needing any localization scheme. It provides an option to handle the heterogeneous types of nodes, distribute topology and mechanism in which new nodes are easily added to the network without affecting the existing network performance. The proposed distributed topology algorithm divides the pipeline length into segments and sub-segments in order to manage the higher delay issue. Normally nodes are randomly deployed for the long range underwater pipeline inspection yet it requires some proper dynamic nodes deployment algorithm assigning unique position to each node

Underwater Channel Characterization to Design Wireless Sensor Network by Bellhop

Acoustic underwater link due to low attenuation is employed for underwater sensor network (UWSN). Due to water changing physical properties and different environmental conditions, the sound propagation for every underwater channel are different. So, the most important parameters to design reliable UWSN are: the shadow zone determination, optimum nodes placement, high signal to noise ratio and more power efficiency of nodes. This paper simulates underwater channel for 7 KHz carrier frequency, with measured physical water properties and remote sensing data. Based on defined scenario, the research determines optimum nodes placement and link budget analysis based on bottom to surface acoustic link. The paper utilizes Bellhop acoustic toolbox as a simulator, GeoMapApp program to collects bathymetry data and Aviso+ database to determine wind speed on sea surface. As a result the paper based on simulation of sound propagation in channel and transmission loss determination in depth and range, finds the optimum nodes positions and link budget calculation to prove the results.

Image-Processing-Based Transceiver Design for Acoustic PPM Underwater Links

Underwater pulse position modulation (PPM) transmission uses acoustic pulses since they allow communication, remote control of underwater vehicles, and positioning estimation; the last one when more than one detector is present by using only one technology, that is, the same transmission module. On the other hand, PPM pulses are difficult to detect since they carry information on signal delays, assuring that reliable information delivery both in shallow- and deep-sea channels may be considered a timely challenge due to strong multipath and other interference sources/causes giving rise to signal fluctuation and high noise level. This paper proposes a transceiver architecture characterized by a signal analyzer and an adaptive detection based on the channel features. The signal analysis is based on the Wigner–Ville transform (WVT) that converts a 1-D signal into an image. Edge detection procedures performed on the obtained image so as to discover the interference features and understand the main characteristics of multipath with their adverse effects on detection of pulse position information have been taken into account. Based on this, maximal ratio combining (MRC) and equal gain combining (EGC) for RAKE reception and truncated channel equalization have been considered. Numerical results showing the ability of the proposed transceiver to detect pulses in the presence of multipath and interference generated by external acoustic sources have been carried out also by taking into account the estimation error effects and by comparing the actual performance with ideal cases. Finally, field tests corroborate the reliability of the proposed approach.

Performance Evaluation of Short Range Underwater Optical Wireless Communications for Different Ocean Water Types

This paper has presented our interesting in wireless underwater communications for different ocean water types. Recent interest in ocean exploration has brought about a desire for developing wireless communication techniques in this challenging environment. Due to its high attenuation in water, a radio frequency (RF) carrier is not the optimum choice. Acoustic techniques have made tremendous progress in establishing wireless underwater links, but they are ultimately limited in bandwidth. In traditional communication systems, constructing a link budget is often relatively straight forward. In the case of underwater optical systems the variations in the optical properties of ocean water lead to interesting problems when considering the feasibility and reliability of underwater optical links. The main focus of this paper is to construct an underwater link budget which includes the effects of scattering and absorption of realistic ocean water. As well as we have developed the underwater optical wireless communication systems to have shorter ranges, that can provide higher bandwidth (up to several hundred Mbit/s) communications by the assistant of exciting high brightness blue LED sources, and laser diodes suggest that high speed optical links can be viable for short range application. The received signal power, signal to noise ratio, bit error rate, transmitted signal bandwidth, and transmission bit rates are the major interesting parameters for different ocean water mediums as a criteria of the best signal transmission characteristics of short wireless optical communications over wide range of the affecting parameters.

Under Water Optical Wireless Communications Technology for Short and Very Short Ranges

This paper has presented our interest in wireless underwater optical communications. Recent interest in ocean exploration has brought about a desire for developing wireless communication techniques in this challenging environment. Due to its high attenuation in water, a radio frequency (RF) carrier is not the optimum choice. Acoustic techniques have made tremendous progress in establishing wireless underwater links, but they are ultimately limited in bandwidth. In traditional communication systems, constructing a link budget is often relatively straight forward. In the case of underwater optical systems the variations in the optical properties of sea water lead to interesting problems when considering the feasibility and reliability of underwater optical links. The main focus of this paper is to construct an underwater link budget which includes the effects of scattering and absorption of realistic sea water. As well as we have developed the underwater optical wireless communication systems to have shorter ranges, that can provide higher bandwidth (up to several hundred Mbit/sec) communications by the assistant of exciting high brightness blue LED sources, and laser diodes suggest that high speed optical links can be viable for short range application.

Approximated Generalized Torques by the Hydrodynamic Forces Acting on Legs of an Underwater Walking Robot

In this paper, we present the concept and main mission of the Crabster, an underwater walking robot. The main focus is on the modeling of drag and lift forces on the legs of the robot, which comprise the main difference in dynamic characteristics between on-land and underwater robots. Drag and lift forces acting on the underwater link are described as a function of the relative velocity of the link with respect to the fluid using the strip theory. Using the translational velocity of the link as the rotational velocity of the joint, we describe the drag force as a function of joint variables. Generalized drag torque is successfully derived from the drag force as a function of generalized variables and its first derivative, even though the arm has a roll joint and twist angles between the joints. To verify the proposed model, we conducted drag torque simulations using a simple Selective Compliant Articulated Robot Arm.

Performance Evaluation of Acoustic Underwater Data Broadcasting Exploiting the Bandwidth-Distance Relationship

Despite being a fundamental networking primitive, data broadcasting has so far received little attention in the context of underwater networks. This paper proposes an adaptive push system for data broadcasting in underwater acoustic wireless networks with locality of client demands. The proposed system exploits the characteristic relationship between the bandwidth of an underwater acoustic link and the transmitter-receiver distance in order to improve performance in environments with locality of client demands. Simulation results show superior performance of the proposed approach in the underwater environment compared to existing systems.

Fatigue life evaluation of a through-girder steel railway bridge

Over the recent years, the Marmaray project has come into realization in Istanbul in order to connect the two continents, Europe and Asia, by providing an underwater link for the first time. Some existing steel railway bridges will also be used for the proposed railway infrastructure. The purpose of this study is to identify the factors affecting the remaining effective service life of such a bridge, and possible fatigue life extension. Firstly, the whole structure was inspected visually for any existing damage due to highway traffic passing underneath. Detailed field measurements and in-depth analytical studies were conducted to determine the axle loads and bridge responses under current operating conditions. A statistical description of typical train cars was developed. Using the computer model which was refined by field measurements, the bridge was re-assessed according to expected train traffic for the future. The results were then used to determine the remaining life of the steel railway bridge. In order to improve the fatigue life, a strengthening scheme to extend the service life has been proposed for a typical bridge component.

Mote-based underwater sensor networks: opportunities, challenges, and guidelines

Most underwater networks rely on expensive specialized hardware for acoustic communication and modulation. This has impeded wide scale deployments of underwater sensor networks and has forced researchers to use simulations to investigate these systems. To address these issues, this paper examines a system that integrates off-the-shelf acoustic hardware built-in to sensor modules with software modems for establishing underwater acoustic links. Because the hardware in our system is readily available, we have conducted several rounds of field experiments to evaluate it. Building on our recent field experiments in a river, canal, pond, and swimming pool, this paper outlines the technical and logistical challenges for deploying software-driven underwater sensor networks. The design choices include methods for signal modulation at the sender, and symbol synchronization, signal filtering, and signal demodulation at the receiver. We also discuss higher layer communication protocol issues, with a focus on cross-layer optimization, as well as practical solutions to logistical deployment challenges, such as waterproofing and casing, calibration, and fouling. The design guidelines in this paper lay the groundwork for further development of software-driven of underwater sensor networks.

RZ-DPSK field trial over 13 100 km of installed non-slope-matched submarine fibers

This work presents the first field trial using the return-to-zero differential-phase-shift-keying (RZ-DPSK) modulation format. A 96/spl times/10-Gb/s RZ-DPSK field trial was conducted over a 13 100-km optical undersea path by double passing the installed 6550-km underwater link which was deployed with non-slope-matched submarine fibers. All channels performed with more than a 3-dB forward-error correction margin, including channels that accumulated over /spl plusmn/13 000ps/nm of dispersion. It is also shown that the RZ-DPSK format has similar residual dispersion and channel power tolerance for both slope-matched and non-slope-matched fibers. Furthermore, it is demonstrated that the chirped RZ-DPSK format could further improve system performance by 1-2 dB.

Acoustic telemetry system for underwater control

Underwater acoustic communication in the multipath environment encountered in shallow water is restricted mostly by signal fading. It degrades the signal detection and time synchronization required for reliable acoustic communication. An approach to time synchronization and to the frequency diversity method is presented. A communication algorithm for obtaining a reliable acoustic underwater link, and offering an easy-to-implement decoding scheme is introduced, and system realization is described. >

Technology 1991: transportation

Significant developments during 1990 are discussed. In particular, western European nations launched a project to unify and upgrade their air traffic systems in three stages from 1990 through 2005. The crash of an Indian Airlines Airbus A-320 was attributed to pilot error, a consequence of inadequate training. A new commercial aircraft, the MD-11 entered the market, while developments in rail technology, notably an underwater link up between France and the UK, made some gains.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>