Iaetsd design and implementation of low cost maritime

DESIGN AND IMPLEMENTATION OF LOW COST MARITIME
BOUNDARY IDENTIFICATION SYSTEM USING FIBER OPTIC
TECHNOLOGY
R.Sathya1
, R.Iswarya2
, V.Revathi3
, R.Sathiyapriya4
Associate Professor / IT1
, M.Tech IT First Year 2
,
Ganathipathy Tulsi Jain College of Engineering and Technology, Vellore.
ABSTRACT
Everywhere on this planet hair-thin
optical fibers carry vast quantities of information
from place to place. There are many desirable
properties of optical fibers for carrying this
information. They have enormous information-
carrying capacity, low cost and possess
immunity from many disturbances that can
afflict electrical wires and wireless
communication link. Optical fibers have
become a widely used aid to navigation
worldwide and its useful tool for map-making,
land surveying, commerce, scientific uses,
tracking, surveillance and hobbies such as
geocaching and way marking. None of the
present optical fibers systems satisfy the
requirements for the safety of civilian navigation
in the sea as the maritime boundary of a country
cannot be marked.
This paper deals on the versatility and the
usefulness of optical fibers in the sea. The main
objective of the paper is to help the fishermen
not to navigate beyond other country’s border. If
a fisherman navigates beyond the country’s
border, an alarm is generated indicating that the
fisherman has crossed the border. Additionally,
a laser transmitter interface will send a message
to base station located on the shore indicating
that a vessel has crossed the border. Thus guards
in the shore can assist and provide additional
help to those fishermen if needed. Keeping in
mind about lives of Indian fishermen, this device
has been created to help them not to move
beyond Indian. On the whole, it is an attempt to
build a suitable device for the fishermen at a
reasonably low cost.
Keywords: Fiber Optic, Laser, FDDI
networks, SONET
1. INTRODUCTION
The Tamil Nadu factor in India-Sri
Lanka relations that had been quiet for long has
come to the fore in the form of the fishermen
issue. Frequent incidents of fishermen from
Tamil Nadu getting shot in the Sri Lankan’s
maritime boundary have enraged all citizen of
the state. From Tamil Nadu about 18,000 boats
of different kinds conduct fishing along the
India-Sri Lanka maritime border. Ever since
violence broke out in Sri Lanka two decades
ago, fishing activity has not been peaceful.
Tamil Nadu fishermen are arrested, or shot, by
the Sri Lankan Navy. From the fishermen's point
of view, straying takes place inadvertently, due
to sheer ignorance about maritime boundaries.
At times, the drift is because of engine
failure or strong currents. At the same time
however, quite a few Indian fishermen engage in
free floating to exploit marine resources in Sri
Lankan waters, knowing full well, the risks
involved in crossing the International Maritime
Boundary Line (IMBL). Growing markets for
marine resources has forced Tamil Nadu
fishermen to take risks. Laser is increasingly
being used for a wide range of applications. It
provides reliable positioning, navigation, and
timing services to worldwide users on a
continuous basis in all weather, day and night,
anywhere on or near the Earth. None of the
present optical systems satisfy the requirements
for the safety of civilian navigation in the sea as
the maritime boundary of a country cannot be
marked.
This paper add on the versatility and the
usefulness of an optical cable in the sea. The
main objective of the paper is to help the
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International Association of Engineering and Technology for Skill Development
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fishermen not to navigate beyond other
country’s border. If a fisherman navigates
beyond the country’s border, an alarm is
generated indicating that the fisherman has
nearing the border. With this alarm, the
fisherman can be caution and come back inside
the country’s border. Additionally, a message
transmitter is interfaced with the device to send
a message to base station located on the shore
indicating that a vessel has crossed the border.
Thus guards in the shore can assist and provide
additional help to those fishermen if needed.
2. EXISTING SYSTEM
At present, there are few existing
systems which help to identify the current
position of the boats/ships using GPS system
and view them in an electronic map. GPS
provides the fastest and most accurate method
for mariners to navigate, measure speed, and
determine location. This enables increased levels
of safety and efficiency for mariners worldwide
and accurate position, speed and heading are
needed to ensure the vessel reach its destination
safely. The accurate position information
becomes even more critical as the vessel departs
from or arrives in port. GPS receiver which
receives signals from the satellite and gives the
current position of the boat. With already known
details of the latitude and longitude of the
maritime boundary, the microcontroller
calculates the current position and stored
boundary positions and indicates the fisherman
that he has crossed the boundary by an alarm
system.
Fig1. Block diagram of Existing System
3. PROPOSED SYSTEM
The proposed system is used to detect
the maritime boundary of the country where the
long time dispute between Sri Lanka and India
still exists. This mainly happens when fisherman
crosses maritime border of neighboring country
as he is not aware of the limits in sea. .
A laser emits light in a very narrow
beam– much like a searchlight. Laser light is
very spectrally pure -- it is of a very pure, well-
defined color -- and is very bright. These
properties make a laser ideal for shining light
from place to place over long distances, and it
was soon proposed that this provided new
opportunities to expand the usefulness of optical
communication links Every compact disk player
contains a low-cost, semiconductor laser, whose
beam illuminates the pattern of information
encoded into the surface of the CD and allows
its rapid re-translation into music or computer
data.. The most widely used type of laser is the
semiconductor laser, which has much in its
technology in common with the semiconductor
devices that we use in modern electronic
devices.
The principal difference between these
two semiconductor technologies is that
conventional electronic semiconductors are
almost exclusively based on the element silicon,
whereas semiconductors used in lasers (and
related so-called optoelectronic devices) are
based primarily on mixed semiconductors made
up from gallium (Ga) and arsenic (As) , and
often aluminum (Al) as well. It is semiconductor
lasers made up from GaAs / GaAlAs that
provide the light for optical communication
along optical fibers. This phenomenon causes
light to reflect, rather than refract, when it
attempts to cross the boundary from one
transparent optical medium to another of lower
optical density, at a sufficiently large angle. He
did this by showing light being guided along a
stream of water flowing from a container. His
simple demonstration proves that in the right
circumstances light need not travel in straight
lines.
4. DISTANCE CALCULATION
The distance the vessel has travelled can
be calculated from the starting point of the
vessel. This allows the fisherman to know how
GPS
Reciever
LCD Display
MicroController Alarm
generator
GSM Module
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much distance he has travelled from the shore.
This calculation can be done on basis of the
Harversine formula.
R=earth’s radius(mean radius=6,371km)
diff_lat=lat2−lat1
diff_long=long2−long1
a=sin²(diff_lat/2)+cos(lat1).cos(lat2).sin²(diff_lo
ng/2)
c=2.atan2((a)^(½),(1-a)^(½))
distance = R*c
Buzzer
Buzzer is used to indicate that the vessel has
crossed the border. Buzzer is connected to NPN
transistor. The ground connection is given to
buzzer. The 5V is connected to transistor. Under
normal conditions, i.e., when vessel is inside
country’s border, current flows through emitter.
And hence, buzzer is not activated. When vessel
crosses border, circuit is closed and current
flows to buzzer. Thus alarm is generated.
TOTAL INTERNAL REFLECTION:
When a ray of light passes from one
transparent medium to another, i.e. at the surface
of a pool of water, it generally bends at the
boundary. This phenomenon is well known: a
stick poked into water appears to bend. The
bending of the ray at the boundary is described
by Snell’s law, a simple relationship between the
sines of the angles that the ray makes on the two
sides of the boundary. Mathematically, Snell’s
law can be written
as:n1sin 1=n2sin 2where 1 is the angle of
the ray on one side of the boundary, as shown in
Fig.(2), and 2 is the angle on the other side.
The quantities n1 and n2 are the refractive
indices of the media on opposite sides of the
boundary.
Fig.2 Internal Reflection
The refractive index of each medium is a
number that characterizes the optical density of
the medium relative to a vacuum. It is a number
that describes how much more slowly light
travels in the medium relative to its velocity in a
vacuum. If n2 is less than n1 this equation
restricts the angles at which a ray of light can get
across the boundary.
If light is passing from medium 1 to medium 2
and the angle 1 is greater than the critical
angle, then the light can not refract across the
boundary (because 1 can not be greater than
90o
). The critical angle is the angle whose sine
is n2/n1. When a ray of light strikes a boundary
at an angle greater than the critical angle it
reflects, and does not cross. Although many
devices that we use in real life use this
phenomenon, and although many natural optical
phenomena depend on its occurrence, we may
not be aware of it. A simple example can be
given, which involves what a swimmer sees who
is underwater and attempting to look upwards
through the surface.
Fig.3. Swimmer’s point of view
Optical fibers use total internal reflection to keep
a light ray trapped within the denser glass of the
center of a composite cylindrical glass fiber,
the core. It is as if light rays are guided down the
core of the fiber in a zigzag path by a succession
of total internal reflections at the boundary
between the core glass and the less dense glass
surrounding it – the cladding.
4.1 Maritime Boundary between India and
Sri Lanka:
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Fig. 4,. Graphical
A KEY TECHNOLOGICAL DEVELOPMENT
- EXTREMELY TRANSPARENT GLASS
Conventional window glass, whether it
be soda-lime glass or borosilicate (Pyrex), is not
really very transparent. It only appears so
because we usually use it in thin sheets –
typically a few millimeters thick. If you examine
a piece of such sheet glass by viewing it from
the narrow edge it is easily seen that the glass
has a deep green or brown color when viewed in
thicknesses of several centimeters. Even so,
glass not much more transparent than this was
used, as early as 1957, to make fiber imaging
bundles. In these structures, which were
primarily developed for medical imaging, a large
number of optical fibers are bonded together to
make an aligned bundle. An optical image
projected onto one end of the bundle is relayed
along the bundle, and appears at the far end,
where it can be viewed. For viewing distances of
a few tens of centimeters, the amount of
transmitted light reaching the far end of
conventional glass was sufficiently large to
allow these imaging bundles to be used for
looking into confined spaces, Attenuation (dB)=
10 log(P1/P2).
In the example above the attenuation of
the fiber is 1000 dB per km (1000 dB/km).
Clearly, a fiber with so much attenuation is
useless for long distance light transmission. In
the early 60s it was quickly realized that unless
more transparent glass could be developed, it
was merely a dream to contemplate the use of
glass fibers to carry information optically over
long distances.
Kao and Hockham’s work spurred the efforts of
others and in 1970 scientists Donald Keck,
Robert Maurer, and Peter Schultz at Corning
Glass achieved the attenuation figure of 20
dB/km. By 1975 this figure was down to 4
dB/km. Attenuation in state-of-the-art fibers has
declined steadily since then, reaching 0.5 dB/km
in 1976 and 0.2 dB/km in 1979. This last figure
can be put into perspective by pointing out that
for a fiber 10km long with an attenuation of 0.2
dB/km, about 63% of the light reaches the far
end of the fiber. Imagine still being able to see
quite clearly through a window 10 km thick!
The development of fibers possessing such low
attenuation has provided optical communication
systems with the information carrying channel
that they need. It can not be stressed too strongly
how the efforts of glass scientists have made
possible the information technology age.
Reductions in attenuation of modern fibers have
been accomplished by developing optical fiber
fabrication techniques that eliminate impurities,
particularly hydroxyl ions when the lowest
attenuations are required. It should be
acknowledged that the lowest attenuation levels
have not been achieved for visible light but at
two wavelengths in the near-infrared part of the
spectrum, near 1.3 micrometers ( m) and
1.55 m. Fig.(5) shows the variation of
attenuation with wavelength of a typical modern
fiber . The attenuation in the near-infrared is
close to the minimum achievable values, which
are determined by fundamental physical
phenomena in the glass, which are not
determined by impurities.
Fig. 5
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5. ABSORPTION IN OPTICAL FIBERS
Residual absorption in low loss modern optical
fibers comes from several sources: residual
ultraviolet absorption, residual infrared
absorption, and Rayleigh scattering. Hydroxyl
ions (OH-
) absorb light near 2.73 m, with
weaker absorptions at 1.39, 0.95 and 0.72 m.
The hydroxyl content must be kept below 1 part
per million (ppm) in order that the attenuation at
0.9 m be less than 1 dB/km. Even if the water
content of the fiber is minimized, residual
absorption remains from the infrared absorption
of the fundamental vibrations of the bonds that
make up the glass, which occur at 7.3 m for
boron-oxygen bonds, 8.0 m for phosphorous-
oxygen bonds, 9.0 m for silicon-oxygen
bonds, and 11.0 m for germanium-oxygen
bonds.
These absorptions influence the
attenuation of the fiber even at shorter
wavelengths. The remaining significant,
unavoidable attenuation mechanism in the fiber
is Rayleigh scattering -- the natural tendency for
any atom or module to reradiate in all directions
a part of the electromagnetic radiation incident
on it. The magnitude of this scattering increases
dramatically at shorter wavelengths, and is
enhanced by the random structural character of
glass. Indeed it is this phenomenon that causes
the sky to appear blue: the shorter wavelengths
in sunlight (the blue light) scatter more strongly
than other colors. Microscopic variations in
material density in a glass fiber lead to
concomitant variations in refractive index that
enhance Rayleigh scattering. This loss can be
minimized by drawing the fiber during
production so as to minimize compositional
variations.
6. WHY ARE OPTICAL FIBERS SO GOOD
FOR COMMUNICATIONS?
The information-carrying capacity of an optical
fiber is far greater than it is for its competitors:
wires, coaxial cables, and microwave links. In
addition, optical fibers are inexpensive to
produce, do not conduct electricity (which
makes them immune to disturbance by lightning
storms, and other electromagnetic signals –
except nuclear radiation), do not corrode, and
are of small size. The primary reason that optical
fibers have very much larger information-
carrying capacity than other media, is that they
carry light: this might seem a trivially obvious
observation but it has fundamental significance.
The frequency of the light beams that travel
along optical fibers is in the vicinity of two
hundred trillion cycles per second (Hz).
Compare this with the frequency of the latest
generation of personal communication service
(PCS) cellular wireless systems – approximately
two billion cycles per second (2 GHz). Consider
the frequencies that must be transmitted for
voice communications, which cover the range
(bandwidth) from about 50Hz to 20,000Hz
(20kHz). Indeed, since there is very little need to
include the high frequencies for understandable
voice communications, the actual bandwidth
needed is really only about 4 kHz. It is possible,
in principle, to carry about 50 billion voice
conversations on a single laser beam in an
optical fiber. This capacity results from the very
simple calculation:
2.1014
Hz/4.103
Hz=50.109
.
The entire population of the Earth could be on
the phone on a single fiber at the same time! The
corresponding capacity of a PCS link is about
500,000 simultaneous voice channels. In
practice, it has not proven possible to achieve
these maximum capacities, although in current
links the optical fiber wins by a huge margin.
7. DIGITAL ENCODING OF
INFORMATION
Many years ago all information was transferred
in an analog format, which meant that the
message was transmitted essentially as an exact
copy of the original. The best example comes
from early telephones. When a person spoke on
the telephone, a microphone in the handset
converted the sound waves from the voice into
an electrical signal (varying electrical voltage or
current), which mimicked the variations in air
pressure produced by the persons’s voice. This
analog signal was sent along electrical wires to
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its destination, where the electrical signal drove
a small loudspeaker and recreated the sound of
the caller’s voice. The principal problem in this
scheme was that the electrical signal became
distorted in its passage from caller to listener.
Consider a short duration record of a voice. This
could be a time-varying voltage of the form
shown schematically in Fig.(5). At each instant
of time, the magnitude of the voltage has a
specific value, which can be represented as V(t).
This voltage can on an arbitrary scale be
represented by a normal decimal number,
say N(t). If we convert the number Ninto the
binary system then it will be written as a series
of "ones" and "zeros," called bits. For example,
if N=59, then we can
write:59=32+16+8+2+1,which can be seen to
be59=25
+24
+23
+21
+20
.So, the binary
representation of 59 is 111011. Note that the
"ones" show up where the appropriate power of
2 is needed to build up the number. This binary
number could be represented by the binary
voltage signal shown in Fig.(6).
Fig.6
If we take the values of V(t) at equally spaced
time intervals, and represent each value of the
voltage by its binary voltage signal, then we can
create a continuous binary representation of the
original analog signal. This is called analog to
digital conversion (A/D). To make this binary
representation an accurate record of the original
signal there must be sufficient samples of the
analog voltage taken, and each must be encoded
by sufficient binary bits.. In addition, samples
should be taken at twice the maximum
frequency it is desired to include in the
representation of the signal. So, for example,
speech digitized at 8 bits (28
=256) to include
frequencies up to 4kHz would produce a bit rate
of 64,000 bits per second (b/s).
(64,000=8X4,000X2.) Music digitized at 16 bits
to include frequencies up to 20kHz would need a
bit rate of 640,000 bits per second.
It is worthwhile considering for a moment the
number of bits of digital data associated with the
transmission (or storage) of various kinds of
information. A compact disc (CD) with one hour
of music typically contains about 680 Megabits
(Mbs) of digital data . A computer CD ROM
contains a similar quantity of data. Video
requires somewhat larger numbers of bits per
hour, because both the picture and
accompanying sound must be stored. However,
clever techniques for compressing the imagery
can reduce the quantity. The latest generation of
digital video discs carry 4.7 Gb of data per side.
Double sided, double layered DVDs can carry
four times as much data – more than 17 Gb of
data. A single-sided, single-layered disc, stores
133 minutes of film (with accompanying audio),
so the average rate of data transfer during
viewing is about 0.6 Mb /s.
For real time video transmissions the rate of data
transfer required is higher, in the range from 3 to
5 Mb/s. To download a 2 hour long DVD movie
over a link within 10 seconds requires a data
transfer rate of around 0.5 Gb/s. You can’t get
such data rates through your phone line!
However, if optical fiber is installed directly to
your home this changes your access to
information directly. Fiber-to-the-home, as it is
called, is not yet here because of the cost
involved – estimated to be around $1,000 per
household. The telephone and cable companies
have not identified a current demand for digital
communication services that needs the data rates
provided in this way. The technology to do it is
here, but not the will for the capital investment
required.
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8. REPEATERS AND DISPERSION
This process was traditionally carried out with
a repeater. This is a device incorporating a light
detector, processing electronics, and a new laser.
An incoming stream of optical pulses,
corresponding to the transmitted information in
binary code, is detected and becomes an
equivalent stream of electrical pulses. These
electrical pulses are amplified, reshaped
electronically to restore their original shape, and
are then used to drive the new laser to re-
transmit the information along the next stretch of
fiber.
In this way, a stream of optical pulses can be
transmitted over great distances, such as under
the Atlantic Ocean, by spacing a series of
repeaters along the fiber cable. Typically
repeaters are spaced every 45-70 km.
Consequently, a long fiber cable must
incorporate conventional electrical wires to
provide the power to drive the repeaters.
One great advantage of a system with repeaters
is that it has the ability to restore their original
shape to propagating light pulses. There is a
natural tendency for an optical pulse traveling
along an optical fiber to change its shape. This
results from a phenomenon called dispersion.
short optical pulse always contains a range of
wavelengths. Although this might not be
obvious, an analogy can be made. A pure
musical tone, in its ideal form gives a sound
wave that undulates at a distinct frequency, for
example middle C is 523.25 Hz.
If the pulses were able to spread to a width of
1ns they would overlap, and their distinct
identity in the pulses stream would be lost. If
these pulses are detected at a repeater before
they have spread too much, their original 0.5ns
width can be restored, and the pulses will not
continue to broaden in traveling great distance
along a fiber. This is the clear advantage of a
fiber system with repeaters. However, there is a
disadvantage to repeaters: they can not
distinguish pulses at one wavelength from pulses
at another wavelength..
9. ERBIUM DOPED FIBER AMPLIFIERS
(EDFAs)
In 1987 David Payne and his co-workers at the
University of Southampton in England reported
the operation of the first practical optical
amplifier suitable for lightwave communication
systems. The EDFA uses an optical fiber with
the rare- earth ion erbium added as an impurity.
If optical energy is fed into a section of such a
fiber, which uses an auxiliary laser (called the
pump laser), than a stream of optical pulses will
pass through the amplifier and each pulse in the
stream will be amplified (boosted in size). This
amplification process occurs for a relatively
broad wavelength range near 1.55 m
The development of low loss, low
overall dispersion, single-mode fibers, with
EDFAs to allow long distance transmission, may
serve to satisfy the world's insatiable appetite for
ever-increasing data rates. This is graphically
illustrated by Fig.(7), which shows how the data
rates of communication channels have grown
since the early days of the telegraph. This figure
was drawn in 1995, and is already out of date.
The projected capacity of a single fiber
communication channel of 1012
bits per second
(1 Terabit/s), which the figure above suggests
will happen around 2,005, is already here.
Worldwide Internet traffic is about 1 Terabit per
second, and could therefore, in principle, be
carried on a single optical fiber. A typical optical
fiber cable containing 8 distinct fibers will carry
8 Terabits per second, or 20 million Terabits per
month.
Fig 7.
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10. OPTICAL COMMUNICATION
NETWORKS
Fiber optic links have been extensively installed
worldwide. Most long distance (trunk) lines use
single-mode fiber and increasingly high data
rates. A current standard is the 2.488 Gbit/s
maximum data rate of SONET (synchronous
optical network). A typical SONET optical fiber
link will carry 32,000 simultaneous two-way
voice or data channels on one pair of fibers.
SONET is designed to interface with and replace
existing communication networks that operate at
various data rates. The lowest level SONET
signal is called the Synchronous Transport
Signal Level 1 (STS-1), which has a data rate of
51.84 Mbit/s. Higher data rates are achieved by
multiplexing N of these data streams up to a
maximum of N=48. SONET uses single-mode
fiber and different types of light source
depending on the ranges involved. Short reach
links (up to 2 km) use light emitting
diodes(LEDs) or multimode lasers operating at
1.31 m; intermediate reach links (up to 15
km) use 50 W single- or multi-mode laser
transmitters operating at 1.31 m or 1.55 m.
Long reach links (up to 40 km) use 500 W
laser transmitters at 1.31 m or 1.55 m. For
local area networks (LANs) that use LED
sources and multimode fiber the Ethernet
standard (3 Mbit/s) is widely used, although
when higher data rates are required the Fiber
Distributed Data Interface (FDDI) standard is
common.
TRANS-OCEAN OPTICAL FIBER
CABLES
The longest fiber links are those that span the
world's oceans, including several across the
Atlantic from North America to Europe and
several from the United States to Japan. Many
additional long distance fiber links exist: by
1995 there were nine across the Atlantic, four
from the United States to Japan, one from Japan
to China, with additional links for Australia,
Korea, India, South and Central America, South
Africa, and New Zealand . The transatlantic
cable laid in 1988 (TAT-8) contains eight fibers
and can carry 40,000 telephone calls at one time:
each pair of fibers carries 560Mb/s. The next
generation of cables (TAT-9 and TAT-10),
which came into service in 1992, carry double
this number of calls. TAT-11 has the same
capacity as TAT-9 and TAT-10. It stretches
7,162 km from Manahawkin, New Jersey to a
location 600 miles from both Ireland and France
where it splits and continues to Swansea, in the
U,K, and St. Hilaire in France.
The newest trans-Atlantic cable TAT-12/13 is
the first such cable to use EDFAs rather than the
old-style repeaters. This cable forms a ring of
undersea segments connecting together cable
stations in Green Hill, Rhode Island; Lands End,
England; Penmarch, France; and Shirley, New
York. It is 12,400 km long. The segment from
Green Hill to Lands End is 5,913 km long. One
segment of the cable 3,759 km long was
installed by STC Submarine Systems. There are
133 EDFAs spaced 45 km on the remaining
segment 2,154 km long installed by AT&T
Submarine Systems. Each of the cable segments
contains two fiber pairs, one used for regular
service, and the other for emergency restoration
service. The capacity of each fiber pair is
2.5Gb/s, so the overall capacity of the system is
10 Gb/s. The two main cables are laid several
hundreds of kilometers apart on the ocean floor,
and are routed to avoid hazardous areas, surface
and deep-sea current, seismic activity, military
activity, and fishing.
Tyco Submarine Systems (TSSL) announced
that a doubling of capacity of TAT-12/13 would
be achieved by July 1998 by upgrading it to 2-
wavelength WDM operation. An extension to a
third wavelength, which would increase capacity
to 30 Gb/s, is being considered for July, 1999.
It could carry 7.7 million telephone calls at the
same time. About 80% of the cable capacity will
be allocated to Internet and multimedia traffic. If
one considers that the lowest typical price for a
Trans-Atlantic telephone call is 10 cents per
minute, and probably averages in reality about
$1.00 per minute, then the cable pays for its
installation costs in about 24 hours!. Because
carriers can charge more for high speed
connections the system (if fully utilized)
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probably makes back its installation costs in
about 12 hours! The two cables are laid 740 km
apart. This cable was a joint venture of
Cable&Wireless and WorldCom.
OPTICAL FIBER NETWORK
ARCHITECTURES
three popular topologies of optical networks.
In these arrangements of transmitters and
receivers, each transmitter/receiver pair on the
network, which is called anode or subscriber can
communicate with every other. The construction
of such networks relies on the use of various
passive optical components for their
implementation. The most important of these is
the fiber coupler, that either splits or combines
optical signals. This is a four-port device. In the
simplest sense such a device is fabricated by
fusing together two single mode fibers so that
their cores come close together, allowing light to
leak from one core to the other. Depending on
the splitting ratio between the ports the device
can be described as either a tap or splitter.
if light enters port 1 it is split on output between
ports 3 and 4. Port 2 functions in the same way,
although usually one of ports 1 or 2 will be
unused if it is desired to act as a Y (or T) coupler.
If the intensities leaving ports 3 and 4,
respectively, on injection of light at port 1 are
equal the coupler is referred to as a 3 dB coupler
or splitter, on the other hand if 99% of the input
power passes from port 1 to port 3, with only 1%
leaving at port 4 the device is described as a 20
dB coupler or tap.
LINE-OF-SIGHT OPTICAL LINKS
Line-of-sight optical links, which involve the
free space propagation of the encoded light
signal from source to receiver, have only
limited, short range application in ground-based
situations. Turbulence, scattering, and
absorption by the atmosphere introduce
amplitude and phase noise into the transmitted
signal and cause significant signal amplitude
decay over moderate distances. However,
ground-to-satellite, satellite-to-satellite, and
deep-space communication links represent
important application areas for line-of-sight
optical communicationsThe most challenging
application of such a link is in deep-space
communications. In explorations of the outer
planets in programs such as Pioneer and
Voyager, data is relayed to and from the space
craft with microwaves. Because the transmission
distances are so long, high transmitter powers
are required, which presents a problem for the
space craft end of the system, which must rely
on solar power. If a short wavelength laser is
used as the transmitter on the spacecraft, a
substantial reduction in transmitted power is
possible because a more directional beam is
possible.
11. CONCLUSIONS AND FUTURE
ENHANCEMENT
It is a useful device for safer navigation,
especially for fishermen. Since Sri Lanka and
India have got lots ofproblems regarding the
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ISBN : 978 - 1505606395
42

maritime boundary of the country, this device is
made to identify the maritime boundary and to
provide assistance if needed. The main
advantage of this paper is compact and low cost.
Our paper can be extended to advance future
components and PIC microcontroller, so that it
can be widened to largeapplications with more
accurate results. The design of the device can be
made even smaller than proposed by modifying
the design specifications. Efficiency can be
improved by implementing more accurate laser.
REFERENCE:
[1] HARVERSINE FORMULA:
http://en.wikipedia.org/wiki/Harversine_formula
[2] Shwu-Jing Chang “Vessel identification and
monitoring systems for maritime security”. This
paper appeared in: Security Technology, 2003.
Proceedings, IEEE 37th Annual 2003
International Carnahan Conference, 14-16 Oct.
2003.
[3] GPS-based vessel position monitoring and
display system. This paper appears in:
Aerospace and Electronic Systems Magazine,
IEEE Publication Date: Jul 1990.
[4] Practical aspects of Embedded System
Design using Microcontrollers by Jivan S.Parab,
Santhosh A.Shinde, Vinod G.Shelake, Rajanish
K.Kamat, Gourish M.Naik.
www.iaetsd.in
ISBN : 978 - 1505606395
43

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