28-04-2011, 10:21 AM
Presented by:
CH.RAGHAVENI
S.GHOUSIA SULTANA
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ABSTRACT: -
Earthquakes and Tsunamis strike without warning. The resulting damage can be minimized and lives can be saved if the people living in the earth quake-prone area are already prepared to survive the strike. This requires a warning before the strong ground motion from the earthquake arrives. Such a warning system is possible because the energy wave released at the epicenter travels slower (at 3.5 to 8km/s) than light, which is the principle behind developing this application.
The warning signal from the earthquake or tsunami epicenter can be transmitted to different places using the satellite communication network, fiber-optics network, pager service, cellphone service or a combination of these. The satellite based wireless network such as ISS is idle if system has to cover a large continent like ASIA.
The credential part of the paper lies in the applications part where the applications of ISS as an alert system for “EARTHQUAKE and TSUNAMI” like natural disasters with which the casualties can be reduced drastically. For EARTHQUAKE, TSUNAMI-prone countries like Indonesia, Japan seismic alert system using the ISS network spread throughout the earth is proposed here.
This paper unleashes the system facts such as the network architecture and coverage, satellite constellation, Frequency plan and modulation of ISS system and its operation along with its advantages and applications. Last but not least, the innovative application of ISS as TSUNAMI, EARTHQUAKE alert system is explained in brief.
PROLOGUE: -Iridium is a satellite based wireless personal communications network designed to permit a wide range of mobile telephone services includingvoice,data,networking, facsimile, geolocation, fax capabilities and paging. With this system caller can call to any person, anywhere at any time in the world.
IRIDIUM SYSTEM ARCHITECTURE:
The iridium uses GSM-based telephony architecture to provide a digitally switched telephone network and global roaming feature is designed in to the system.
1) Operation: The 66-vehicle LEO inter-linked satellite constellation can track the location of a subscriber’s telephone handset, determine the best routing through a network of ground-based gateways and inter-satellite links, establish the best path for the telephone call, Initiate all the necessary connections, and terminate the call upon completion. The unique feature of iridium satellite system is its cross-links.
Its main intention is to provide the best service in the telephone world, allowing telecommunication anywhere, any time, and any place Each satellite is cross-linked to four other satellites; two satellites in the same orbital plane and two in an adjacent plane To relay digital information around the globe. Feeder page link antennas relay information to the terrestrial gateways and the system control segment located at earth stations
IRIDIUM SATELLITE CONSTELLATION:
3) The Iridium constellation consists of 66 operational satellites and 14 spares orbiting in a constellation of six polar planes. Each plane has 11 mission satellites performing as nodes in the telephony network. The 14 additional satellites orbit as spares ready to replace any unserviceable satellite. This constellation ensures that every region on the globe is covered by at least one satellite at all times.
Iridium uses 66 operational satellites configured at a mean elevation of 420 miles above earth in six nearly polar orbital times of 100 min 28 sec. The first and last planes rotate in opposite directions, creating a virtual beam. The co-rotating planes are separated by 31.6 degrees and the beam planes are 22 degrees apart.
Each satellite is equipped with 3 L-band antennas forming a honeycomb pattern that consists of 48 individual spot beams with a total of 1628 cells aimed directly below the satellite. As the satellite moves in its orbit, the footprints move across earth’s surface and subscriber signals are switched from one beam to the next or from one satellite to the next in a handoff process. Each cell has 174 full duplex voice channels for a total of 283,272 channels worldwide.
IRIDIUM SATELLITE NETWORK COVERAGE:
IRIDIUM SYSTEM SPOT BEAM FOOTPRINT PATTERN
4) Each satellite is equipped with 3 L-band antennas forming a honeycomb pattern that consists of 48 individual spot beams, with a total of 1628 cells aimed directly below the satellite as shown in above figure each of the spot beam approximately measuring around 30miles or 50k.m.
FREQUENCY PLAN AND MODULATION: -
All ka-band up-links and cross-links are packetized TDM/FDMA using quadrature phase shift keying and FEC1/2 rate convolutional coding with viterbi decoding.
L-band subscriber to satellite voice links=1.616GHZ TO 1.6265GHZ
Ka-band gateway downlinks=19.4 GHZ to 19.6GHZ.
Ka-band gateway up-links=29.1GHZ to 29.3GHZ
Ka-band inter-satellite cross-links =23.18GHZ to 23.38GHZ
Comparison between iridium and traditional satellite systems: -
Using satellite cross links is the unique key to the iridium system and the primary differentiation between iridium and the traditional satellite bent pipe system where all transmissions follow a path from earth to satellite to earth.
Iridium is the first mobile satellite to incorporate sophisticated, onboard digital processing on each satellite.
Entire global coverage by a single wireless network system.
Only provider of truly global voice and data solutions.
With this system the subscriber will never listen a message called ”OUT OF COVERAGE AREA”
