OEC

UNDERWATER WIRELESS COMMUNICATION

Underwater wireless communication is the wireless communication in which acoustic signals (waves) carry digital information through an underwater channel. Electromagnetic waves are not used as they propagate over short distances. Over the past decades, heavy cables were used to establish a high speed communication between remote end and the surface. To overcome such difficulties, underwater wireless communication has come into existence.INTRODUCTIONWired underwater is not feasible in all situations as shown below-:Temporary experimentsBreaking of wiresSignificant cost of deploymentExperiment over long distances. To cope up with above situations, we require underwater wireless communication.

NECESSITY OF UNDERWATER WIRELESS COMMUNICATIONPath loss: Due to attenuation and geometric spreading.Noise: Man-made noise and ambient noise(due to hydrodynamics)Multi-path propagationHigh propagation delayDoppler frequency spread.

FACTORS INFLUENCING ACOUSTIC COMMUNICATION4 Sensor Interface: Must develop common interface with different sensors (chemical, optical, etc.) and communication elements (transducer) .Wide (constantly changing) variety of sensors, sampling strategies Communication Interface:- Amplifiers, Transducers- Signal modulationHardware:Software Defined Acoustic Modem (SDAM)Reconfigurable hardware known to provide, flexible, high performance implementations for DSP applications

HARDWARE PLATFORM INTERFACESEmploy advanced modulation scheme and channel equalization for improved signal to noise ratio.Employ high performance error detection and correction coding scheme which reduces bit error rate to less than 10-7Parts of an acoustic modem:DSP Board AFE(Analog Front End) BoardDC/DC Converter

ACOUSTIC MODEM

When no data is being transmitted, the modem stays in sleep mode, it periodically wakes up to receive possible data being transmitted by far end modem. This results in low power consumption. Similarly when the data is to be transmitted , the modem receives data from its link in sleep mode and then switches to transmit mode and transmit the data.DATA TRANSMISSION IN MODEM

ADVANCED MODEMS AVAILABLE

Group of sensors and vehicles deployed underwater and networked via acoustic links, performing collaborative tasks.EquipmentAutonomous Underwater Vehicles (AUVs)Underwater sensors (UW-ASN)

UNDERWATER ACOUSTIC SENSOR NETWORKS (UW-ASN)

Autonomous Underwater Vehicles (AUVs)It is a robot which travels underwater without requiring input from an operator.

Applications Of AUVUntil relatively recently, AUVs have been used for a limited number of tasks dictated by the technology available. With the development of more advanced processing capabilities and high yield power supplies, AUVs are now being used for more and more tasks with roles and missions constantly evolving.

CommercialThe oil and gas industry uses AUVs to make detailed maps of the seafloor before they start building sub sea infrastructure; pipelines and sub sea completions can be installed in the most cost effective manner with minimum disruption to the environment. The AUV allows survey companies to conduct precise surveys of areas where traditional bathymetric surveys would be less effective or too costly. Also, post-lay pipe surveys are now possible.

Seismic monitoring. Pollution monitoring Ocean currents monitoring Equipment monitoring and control Autonomous Underwater Vehicles (AUV) Remotely operated vehicle(ROV) Acoustic navigation technology for multiple AUVs. Solar Powered AUVs

APPLICATIONS

Battery power is limited and usually batteries can not be recharged easily.The available bandwidth is severely limited.Underwater sensors are prone to failures because of fouling, corrosion, etc.Highly affected by environmental and natural factors such as heterogeneities of the water column, variations of sound velocity versus depth, temperature and salinity, multiple and random sea reflections and significant scattering by fish, bubble clouds and plankton.

LIMITATIONSDespite much development in this area of the underwater wireless communication, there is still an immense scope so more research as major part of the ocean bottom yet remains unexploded. The main objective is to overcome the present limitations and implement advanced technology for oceanographic research and cope up with the environmental effects on the noise performance of acoustic systems to compete with the future challenges like effective transmission of audio and video signals etc.CONCLUSIONwww.ieee.org/organizations/pubs/newsletters/oes/html/spring06/underwater.html www.link-quest.com/html/oceans2000.pdf/www.gleonrcn.org/pgm-download_media.php?name=Aquanode.pps www.cs.virginia.edu/sigbed/archives/akyildiz.pdf

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