Optical Free Space Communication
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#1
22-09-2008, 10:04 AM


Introduction
With the improvements in semiconductors optical free space communication has become n attractive alternative to existing signal conducts as fibre or wireless (RF). It offers high data rates and is much less expensive than underground fibre. But there are a few restrictions, which may mean it remains an alternative. Many engineers are familiar with one of two successful existing technologies for data communication: (1) Guided wave (e.g. fibre optics) and (2) wireless free space communication (e.g. RF). Fibre optics offers extremely high bandwidths for high data rate, while RF communications offers the advantage of wireless connectivity and the ability to broadcast over a wide area. Optical free space communication fits into the 2nd group, but has some properties of the 1st. Many aspects are related to fibre optics with the difference, that the media is air and not fibers. Therefore are the required devices similar to those used with fibers.

The advantages of such a system are the following:
_ No need for digging up the roads
_ No radio frequency licenses are required
_ Bandwidth is equal or superior to fibre systems and much better than RF
_ Doesn't cause interference with existing electromagnetic equipment because interference on narrow band point-to-point connections is rather unlikely.

But there are as well some limitations:
_ Absorption (caused primarily by the water vapor and carbon dioxide)
_ Scattering (depends of the used wavelength and the number and size of scattering elements in the air e.g. fog)
_ Shimmer (due to a combination of factors, including atmospheric turbulence, air density, light refraction, cloud cover, and wind which cause a similar disturbance when a laser beam is transmitted through the atmosphere)
_ Moving building (although we are not aware of the movement, buildings often sway from side to side even settle into the ground causing offset to the laser beam and making the receiver laser receive less power)

Applications

Free space applications
Due to its properties optical free space communications is suited very well for providing high bandwidth to point-to-point connections. The attenuation characteristics of free space make inter-satellite connections a promising application for optical free space communication. Systems of this kind are already being deployed as a communications media in a number of key applications around the world.

Terrestrial applications
For terrestrial applications emerged a solution to the .last mile problem.. This consists in the fact that needs for bandwidth cannot be satisfied because the next fibre backbone is too far away. Laser links between the backbone and the user can provide quickly a high bandwidth much more cost effective than with other technologies. Due to the atmospheric effects on the propagation of light only short distance links can be established assuring a comparable bit error rate to fibre networks. With optical free space communication devices it's as well possible to replace lower speed wired lines between computer networks with fibre-like delay-free high bandwidth. It turned out as well that optical free space communication can be used to interconnect LAN's in campus or industrial environments in a reasonable way or to deploy temporary internet connection while the fibre installation can be done. Another application is to use laser links to bypass a broken data connection.

Military applications
There are not many information about military applications available. However there have been successful experiments to track moving objects with a laser beam as well for communication purposes using so called spatial light modulators.
Use Search at http://topicideas.net/search.php wisely To Get Information About Project Topic and Seminar ideas with report/source code along pdf and ppt presenaion
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#2
03-04-2010, 10:24 AM

please read topicideashow-to-freespace-optics-full-report and topicideashow-to-optical-satellite-communication-seminar and presentation-report and topicideashow-to-future-satellite-communication--5509 and topicideashow-to-optical-satellite-communication-download-full-report-and-abstract for getting Laser Communication Systems or Free Space Laser Communications or future satellite communication seminar and presentation informations
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#3
07-02-2012, 12:13 PM

FREE SPACE OPTICAL COMMUNICATION

.ppt   free_space_opticshjk.ppt (Size: 201.5 KB / Downloads: 56)

WIRELESS CONNECTION
1. DISTRIBUTE DATA EVERYONE ,SECURITY IS JUDGED BY THE WEP
2. LICENCE REQ. TO PLANNING & COORDINATION
3. SUSCEPTIBLE TO RAIN ,LINK LENGTH
4. PP MICROWAVE PROVIDE HIGHER CAPACITY
Eg. LMDS
FIBER OPTIC BASED SOLUTION
1.FIBER OPTICS ARE TWO TYPE
A) SINGLE MODE [UPTO 60KM]


B)MULTI MODE [UPTO 2KM]
2)FIBER OPTICS ARE
SECURE
PROVIDE SPEED IN TERABYTE
PROTECTED FROM TAPPING
IMPOSIBLE TO DETECT LIGHT PULSE
FREE SPACE OPTICS
1)NO CABLES REQUIRED
2)TRANSMITTED IN ATMOSPHERE
3)REQUIRE LINE OF SITE AVAILABILITY


ADVANTAGES
FSO LASER BEAM CANNOT BE DETECTED WITH RF METER OR SPECTRUM ANALYSER
LOS PATH CANNOT BE INTERCEPTED EASILY
DATA CAN BE TRANSMITTED OVER AN ENCRYPTED CONNECTION
FREEDOM FROM LICENSING AND REGULATION
POSSBLE TO MOUNT INSIDE THE BUILDING


.ATMOSPHERE CHALLENGE
1.FOG
IT AFFECT ON NEAR INFRARED WAVELENGTH
AND HAVE SAME EFFECT AS RAINFALL HAVE ON THE RF
.PHYSICAL OBSTRUCTIONS
1.THESE CAN BE REMOVED BY WIDELY SPACED
REDUNDANT TRANSMITTERS AND LARGE RECEIVE OPTICS


.SCINTILLATION
THESE CAN BE REMOVED BY AUTOMATIC GAIN CONTROL CHAR.,TUNED RECEIVED
FILTERING,CLOCK RECOVERY PHASE LOCK
LOOP TIME CONSTANT
.SOLAR INTERFERENCE
IT CAN BE COMBATED BY
1.LONG PASS OPTICAL FILTER WINDO
2. OPTICAL NARROWBAND FILTERING







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15-02-2012, 12:47 PM

to get information about the topic optical communication in space full report ,ppt and related topic refer the link bellow

topicideashow-to-optical-communications-in-space--3821

topicideashow-to-optical-space-communication-or-free-space-optical-communication-fso

topicideashow-to-optical-free-space-communication

topicideashow-to-underwater-optical-communication

topicideashow-to-optical-satellite-communication-seminar and presentation-report
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#5
18-05-2012, 03:48 PM

Free-space Optical Communications



.pdf   free space comunication.pdf (Size: 448.56 KB / Downloads: 57)

Introduction

Free-space optical communication (FSO) systems (in
space and inside the atmosphere) have developed in response
to a growing need for high-speed and tap-proof communication
systems. Links involving satellites, deep-space probes,
ground stations, unmanned aerial vehicles (UAVs), high altitude
platforms (HAPs), aircraft, and other nomadic communication
partners are of practical interest. Moreover, all
links can be used in both military and civilian contexts. FSO
is the next frontier for net-centric connectivity, as bandwidth,
spectrum and security issues favor its adoption as an adjunct
to radio frequency (RF) communications [1].


Discussion of Selected Modulation Schemes

The optical carrier can be modulated in its frequency,
amplitude, phase, and polarization. The most commonly
used schemes because of their relatively simple implementation
are amplitude modulation with direct detection and
phase modulation in combination with a (self-)homodyne or
heterodyne receiver.



The Optical Link Equation

The overall system performance of a link is quantified
using a link margin derived from the link equation. The optical
link equation is analogous to the link equation for any
radio frequency (RF) communication link. Starting with the
transmit power the designer identifies all link degradations
and gains to determine the received signal level. The received
signal level is then compared with the sensitivity of
the receiver, thus giving the link margin.

Channel Without Atmospheric Disturbance

In this section optical links unaffected by the atmosphere
are discussed. In the basic free-space channel the optical
field generated at the transmitter propagates only with
an associated beam spreading loss. For this system the performance
can be determined directly from the power flow.
The signal power received PRx [W] depends on the transmit
power PTx [W], transmit antenna gain GTx, receive antenna
gain GRx, the range loss Gr, and system-dependent losses
Asystem;lin.
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