UNDER WATER COMMUNICATION
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12-01-2011, 04:44 PM





.pdf   underwatercommunication.pdf (Size: 641.97 KB / Downloads: 851)

DR.AIT,Bangalore

INTRODUCTION

The future tactical ocean environment will be increasingly complicated. In addition to traditional communication links there will be a proliferation of unmanned vehicles in space, in the air, on the surface, and underwater. Above the air/water interface wireless radio frequency communications will continue to provide the majority of communication channels.Underwater, where radio waves do not propagate, acoustic methods will continue to be used.However, while there have been substantial advances in acoustic underwater communications, acoustics will be hard pressed to provide sufficient bandwidth to multiple platforms at the same time. Acoustic methods will also continue to have difficulty penetrating the water/air interface. This suggests that high bandwidth, short range underwater optical communications have high potential to augment acoustic communication methods.

The variations in the optical properties of ocean water lead to interesting problems when considering the feasibility and reliability of underwater optical links. Radio waves do not propagate underwater, however with the proliferation of unmanned autonomous vehicles the need to communicate large amounts of data is quickly increasing. Making physical connections underwater to transfer data is often impractical operationally or technically hard to do. Traditionally most underwater communication systems have been acoustic and relatively low bandwidth. However, the development of high brightness blue/green LED sources, and laser diodes suggest that high speed optical links can be viable for short range applications. Underwater systems also have severe power, and size constraints compared to land or air based systems. Underwater vehicles also encounter a wide range of optical environments. In shallow water the effects of absorption by organic matter and scattering by inorganic particulates can be severe compared to deep ocean water. Where the system operates in the water column can also have strong influence. Near the sea floor, ocean currents and silt can play a factor, while in the middle of the water column the medium may be considered more homogeneous, but with its optical properties varying as a function of depth. Near the surface, sunlight can provide a strong background signal that needs to be filtered, and the amount of wave action can have significant effects.In this thesis the use of free space optical links will be investigated for underwater applications. With the use of MathCAD, optical link budgets for three different scenarios are considered:

• A blue/green LED based, bottom moored buoy system operating in relatively shallow water.
• A blue/green laser based system operating in deep clear ocean water with unlimited power and size constraints.

• A power and size constrained, diode laser system suitable for small unmanned underwater vehicle operation.

Inputs into the link budget include: light source type, wavelength, optical power, beam divergence, ocean water optical parameters based on depth, geographic location and time of day, and photodetector type. As a point of comparison, the relative merits of these systems are compared to a conventional acoustic communications links.

A secondary focus of the thesis was to construct light emitting diode based links. The choice of using LEDs instead of Lasers was largely economic, however in the underwater environment can be very challenging optically and many of the advantages that lasers have in terms of beam quality can be rapidly degraded by scattering and turbulence.

Free Space Optics Concepts

Free-space optics (FSO) is a line-of-sight (LOS) link that utilizes the use of lasers or light emitting diodes, LEDs, to make optical connections that can send/receive data nformation, voice, and video through free space. FSO also has attractive characteristics of dense spatial reuse, low power usage per transmitted bit, and relatively high bandwidth. FSO is license-free and offers easy to deploy, fast, high bandwidth connections. Moreover, the optical spectrum is not regulated by the FCC allowing the use of large amounts of unlicensed bandwidth. Due to the large investment in traditional fiber based optical communications networks, LED’s, lasers, photodetectors are available today cheaply and in large volumes. A free space link requires a light source, modulation/demodulation device, and transmitting and receiving telescopes. For moving targets, the transmitter and receiver are placed on gimbal system with feedback controls1 . Instead of propagating through silica glass, as with optical fiber, the light travels through free space.

The main disadvantage of FSO networks is that the transmission medium is uncontrolled. The effects of atmospheric distortions, scintillation, weather and attenuation can only be minimized or compensated by the transmitter/receiver hardware. Free-space optics above and below water have similar issues that need to be accommodated when building a system.


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.ppt   oil-milica-oct06.ppt (Size: 2.98 MB / Downloads: 287)
Underwater Communications
Massachusetts Institute of Technology
Future systems / requirements
Today: point-to-point acoustic links
Future: autonomous networks for ocean observation
Examples of future networks:
ad hoc deployable sensor networks
autonomous fleets of cooperating AUVs
Overview
Channel characteristics
Signal processing: bandwidth-efficient underwater acoustic communications
Example: application to oil field monitoring
Future research
Communication channel / summary
Physical constraints of acoustic propagation:
limited, range-dependent bandwidth
time-varying multipath
low speed of sound (1500 m/s)
Real-time underwater video?
Experiment:
Woods Hole, 2002
6 bits/symbol (64 QAM)
150 kbps in 25 kHz bandwidth
Open problems and future research
Channel characteristics: Attenuation and noise
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30-01-2012, 10:23 AM


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07-03-2012, 04:49 PM

UNDER WATER COMMUNICATION


.pdf   Underwater_Communications.pdf (Size: 5.58 MB / Downloads: 155)

FEATURES
Advanced Digital Signal Processing results in a large number of selectable functions and frequencies with superior voice quality.
AN/UQC compatible default settings: In default mode, the system is compatible with AN/UQC series systems (carrier frequency 8.087 kHz, USB, 200 watt output power). TIPE default frequencies are also selected.
TIPE (Transponder, Interrogator and Pinger/Echo Sounder) Modes provide automatic ranging, tracking pinger, and when used with a vertically oriented transducer, depth below the surface or altitude above the bottom. It also operates on operator selected frequencies between 5 - 45* kHz.
AN/WQC Mode: In WQC Mode the system can communicate with the AN/WQC system and provide automatic ranging against an ARD-8000.
If used with an external power amplifier, the system is capable of the same output acoustic source levels as the AN/WQC.


OPERATOR INTERFACE
All operator controls are located on the front panel. The front panel has adjustable backlighting, except for Power On/Off, speaker Volume, Squelch and TIPE Transmission Rate, all system operator controls are membrane switches. Frequently used functions have dedicated controls, while less frequently used functions are selected by numeric code entries on the keypad. This makes operation simple while allowing flexibility and a virtually unlimited number of functions. Functions selected and parameter values are displayed on red LEDs. The frequency and Range displays are also used for display of warning messages and for results of initiated tests.



VOICE & CW COMMUNICATION

Voice and Continuous Wave (CW) communication is the Model 5400 UWT’s primary application. Communication can be established between any two points (surface ships, submarines, fixed installations, or any combination of these) in the same body of water at ranges to 20,000 yards. Operating frequencies are selectable.
Broad frequency range, adjustable output power, and selectable USB/LSB modulation, allows the Model 5400 UWT to provide discrete communication when multiple telephones are used in the same operating area as well as communication with diver carried underwater telephones.


TELEMETRY
The Model 5400 UWT’s transceiver and transducer(s) can be used to transmit and receive data from peripheral equipment via a connector located on the telephone’s back panel.
Typical applications are interrogation of coded transponders, and Identification Friend or Foe (IFF).
Frequency coverage is 5 to 45* kHz in 1 Hz increments.
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Underwater Communications



.ppt   oil-milica-oct06_2.ppt (Size: 2.97 MB / Downloads: 145)

Communication channel

Physical constraints of acoustic propagation:
limited, range-dependent bandwidth
time-varying multipath
low speed of sound (1500 m/s)


Signal processing for high rate acoustic communciations


Bandwidth-efficient modulation (PSK, QAM)
phase-coherent detection:
synchronization
equalziation
multichannel combining

Current achievements


Point-to-point (2/4/8PSK;8/16/64QAM)
medium range (1 km-10 km ~ 10 kbps)
long range (10 km – 100 km ~1 kbps)
basin scale (3000 km ~ 10 bps)
vertical (3 km~15kbps, 10 m~150 kbps)

Mobile communications
AUV to AUV at 5 kbps

Multi-user communications
five users, each at 1.4 kbps in 5 kHz band



Open problems and future research


Fundamental questions:
Statistical channel modeling
Network capacity

Research areas:
Data compression
Signal processing for communications:
adaptive modulation / coding
channel estimation / prediction
multiple in/out channels (tx/rx arrays)
multi-user communications
communications in hostile environment
Communication networks:
network layout / resource allocation and reuse
network architecture / cross layer optimization
network protocols: all layers



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25-05-2012, 01:52 PM

Underwater Communication


.ppt   Underwater Communication.ppt (Size: 1.04 MB / Downloads: 23)

Introduction

Underwater communication is a technique of sending and receiving message below water
Typical frequency: 1 Hz to 1 MHz
Hydroacoustics

Traditional approach for ocean-bottom monitoring

Uses sensors to record data
Disadvantages:
Real time monitoring is not possible.
No interaction b/w onshore control systems and the monitoring instruments.
failures or misconfigurations may occur
Limited storage capacity

Challenges

Battery Power is limited
Limited available bandwidth
Channel characteristics
UW sensors are prone to failures because of fouling, corrosion, etc
Mobility

Applications of Underwater Communication

Seismic monitoring.
Pollution monitoring
Ocean currents monitoring
Equipment monitoring and control
Autonomous Underwater Vehicles (AUV)








The ocean can be as deep as 10 km
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to get information about the topic "underwater communication" full report ppt and related topic refer the link bellow

topicideashow-to-underwater-wireless-communication-full-report

topicideashow-to-under-water-communication

topicideashow-to-under-water-communication?pid=73728#pid73728

topicideashow-to-underwater-wireless-communication-using-high-speed-acoustic-modems
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Underwater Communication



.ppt   Under water communication 1.ppt (Size: 1.04 MB / Downloads: 26)

Introduction

Underwater communication is a technique of sending and receiving message below water

Typical frequency: 1 Hz to 1 MHz
Hydroacoustics


Traditional approach for ocean-bottom monitoring


Uses sensors to record data
Disadvantages:
Real time monitoring is not possible.
No interaction b/w onshore control systems and the monitoring instruments.
failures or misconfigurations may occur
Limited storage capacity


Challenges


Battery Power is limited
Limited available bandwidth
Channel characteristics

UW sensors are prone to failures because of fouling, corrosion, etc
Mobility
The ocean can be as deep as 10 km



Applications of Underwater Communication


Seismic monitoring.
Pollution monitoring
Ocean currents monitoring
Equipment monitoring and control
Autonomous Underwater Vehicles (AUV)




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