Fiber-Optic Telecommunication & Better ICT in Bangladesh

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Offline mukul Hossain

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Fiber-Optic Telecommunication & Better ICT in Bangladesh
« on: June 19, 2013, 08:36:58 AM »

I. INTRODUCTION
It is said that the transistor has done
for man’s brain in this Information
Age what the steam engine did for his
brawn in the Industrial Age. Hence, it
comes as little surprise that we are
faced with the technological ability to
communicate conveniently with
anyone, anywhere and at any time in
many different ways - voice, data,
facsimile, e-mail, image and video -
and all this at an affordable cost
judging by the mushrooming number
of “internet cafes” at every corner.
Thus modern society has effectively
been reduced to a global village and
information exchange has experienced
an enormous explosion. However, it is
also said that the biggest hurdle to the
full deployment of this technology is
posed by the world’s fragmented telecommunications
networks – especially
in developing countries.
In Bangladesh the bulk of
international telecommunication
traffic still relies on the geo-stationary
satellite and terrestrial microwave link
system operated by the Bangladesh
Telegraph and Telephone Board
(BTTB). Unfortunately, Bangladesh
is well known for its monsoon rains
and the annual floods. As shown in
Figure 1, the flatness combined with
the large number of rivers in
Bangladesh makes it particularly
prone to becoming water logged
during the rainy seasons.
Despite system allowances for a large
rain fade margin in this region, the
handling capacity of the satellite links
is reduced – especially under adverse
conditions. Also, floods (or any other
water surface) can cause signal
interference due to multi-path
propagation as it travels through the
microwave radio links. However,
these are only the minor problems for
the country’s telecommunication
system. The major natural disasters
such as cyclones, high winds and tidal
waves originating from the Bay of
Bengal that cause substantial physical
damage to the towers and other
equipment are by far the most
significant problems. The 1991
cyclones knocked over the microwave
tower in Chittagong thereby
effectively severing the country’s
international link.
Thus, while appraising the country’s
telecommunications system requirements,
optical fiber technology makes
a compelling case as a solution to
Bangladesh’s pressing needs. Short
distance optical fiber links to handle
dense traffic in intra-city
communication started being used in
the mid 80’s in the digital telephone
networks. With a view to establishing
a fully optical ISDN system to link the
capital with other major cities, the
government has implemented several
major inter-city fiber links.
II. AN OVERVIEW OF SATELLITE &
MICROWAVE TECHNOLOGY
Since the introduction of modulated
microwaves in the 1920’s for
communication between two distant
points, this technology has gone
through a tremendous amount of
development. However, these links
were limited to distances within the
‘line of sight’ (roughly 30 kilometers).
Thus, the need for orbiting satellites to
relay information over long distances
was realized; pilot concepts evolved in
the early 1950’s and were followed by
the successful deployment of
communication satellites a decade
later.
Today satellites of all shapes and
capabilities have been launched to
serve almost all the countries of the
World. Most communication satellites
are in geo-stationary orbits (some
35,800 km above the Earth’s surface)
and are able to ‘see’ nearly one half of
the Earth from this vantage point. To
provide continuous coverage to any
point on Earth, only three satellites in
such an orbit are sufficient.
However, signals are weakened about
a hundred times after traveling these
large distances. A more pertinent
problem, is the delay and echo often
experienced in long distance phone
calls that use these satellites. The
accommodation of ever increasing
traffic requires the usage of higher
frequency bands for satellite
communications. Some of the
fundamental limitations on the
performance of satellite
communication systems at frequencies
greater than 10 GHz result from a
strong interaction of radio waves with
rain and ice in the lower atmosphere.
Thus, system reliability demands
detailed knowledge of these
interactions. Rain attenuation
dominates the power margin for
systems operating above 10 GHz;
hence multiple sites are required to
meet high availability objectives.
Also, in satellite communication
systems the capacity per beam is
strongly affected by rain. For
example, to provide the same quality
of transmission during a rainy period,
the capacity may have to be halved.
Finally, a substantial number of
terrestrial relays (microwave radio
links that operate only within ‘line of
sight’ distances) are required to
transmit the information to the
telecommunication network exchange
that may be up to a few hundred
kilometers away from the satellite
ground station.
III. OPTICAL FIBER TECHNOLOGY
Faced with the aforementioned
fundamental shortfalls of a satellitebased
system, real interest in optical
communication was aroused with the
invention of the laser in early 1960's.
Proposals for using optical fibers to
avoid degradation of the optical signal
while propagating through the
atmosphere were made almost
simultaneously in 1966 [2]. Early
systems exhibited high attenuation
(1000 dB/km). Today, less than 40
years on, attenuation of less than 0.2
dB/km is easily achieved for a carrier
wavelength of 1.55µm. Unlike some
of its predecessors, fiber optics
technology has many unrivaled
advantages, some of which are listed
below:
1. Enormous potential bandwidth: the
optical carrier frequency in the range
1013 to 1014Hz offers the potential for
a fiber information carrying capacity
that is many orders of magnitude in
excess of that obtained using copper
cable or wideband radio systems. This
enables fibers to simultaneously carry
voice, data, image and video signals.
2. Small size and weight: an optical
fiber is often no wider than the
diameter of a human hair; thus even
after applying protective layers, they
are far smaller and much lighter than
corresponding copper cables. This is a
tremendous boon to alleviating duct
congestion in cities.
3. Immunity to interference and cross
talk: they form a dielectric and are
therefore free from electromagnetic
interference.
4. Signal security: as light from a fiber
does not radiate significantly, a
transmitted optical signal cannot be
obtained non-invasively, thus ensuring
a high degree of signal security.
5. Low transmission loss: this enables
extremely wide repeater spacings (70
to 100km) in long-haul communication
links.
6. System reliability and ease of
maintenance: due to the low loss
property, system reliability is
generally enhanced in comparison to
conventional electrical conductor
systems. Furthermore, reliability of
optical components have predicted