SATELLITE COMMUNICATION SYSTEMS OVERVIEW
Satellite communicating enables two Stations on the Earth to pass on through wireless broadcast which are located far off from each other. The two Stationss use orbiter as a relay station for their communicating. One of the Earth station will convey to the orbiter.
This is called as Uplink. The orbiter Transponder will change over the signal and sends it down to the other Earth station. This is called a Downlink. The satellite communicating is advantageous over tellurian communicating because of the immense coverage country and high bandwidth capablenesss. The disadvantages of satellite communicating are big extension hold, communicating cost and gradual addition in usage of bandwidth. The basic factors to be considered in satellite communicating are ; lift angle is the angle of the Earth surface to the halfway line of the orbiter transmittal beam. This angle gives considerable effects on orbiters coverage country.
Ideally, lift angle should be 0 grades, so that the transmittal beam will make the skyline seeable to the orbiter in all waies. However, there is a minimal lift angle of Earth Stationss because of the environmental factors like objects barricading the transmittal, atmospheric fading, and earth electrical background noise. Coverage angle is the step of the part of the Earth surface seeable to a orbiter taking the minimal lift angle into history. [ 1 ] It is denoted as,R/ ( R+h ) = cos (& A ; beta ;+& A ; theta ;) /cos (& A ; theta ;)Here ‘R ‘ is earth radius ( 6370 Km ) , ‘h ‘ is satellite orbit tallness, ‘ & amp ; Beta ; ‘ is coverage angle and ‘ ? ‘ is the minimal lift angle. There are damages like free infinite loss, atmospheric fading caused by rain and fog will make considerable effects during transmittal. [ 1 ]There are different type of orbiter services viz. , Fixed Satellite Services ( FSS ) to offers point to indicate communicating. Broadcast Satellite Services ( BSS ) to supply satellite telecasting and wireless.
Mobile orbiter Services ( MSS ) will supply telephone. There are figure of orbiters revolving in different orbits. [ 1 ]The types of orbiter orbits are ( GEO ) geostationary Earth orbit, Medium Earth orbit ( MEO ) , Low Earth orbit ( LEO ) Molniya and tundra orbit.GEO orbiters are in orbit 35,863 kilometer above the Earth ‘s surface along the equator.
Objects in Geostationary orbit revolve around the Earth at the same velocity so as the Earth rotates. This means GEO orbiters remain in the same place relation to the surface of Earth. This orbiter has big coverage country which about one 4th of the Earth ‘s surface. It has 24 hr uninterrupted position of the peculiar parts of the Earth, so it is used for broadcast medium and multipoint applications. These GEO orbiters have trouble in airing in near polar region.LEO orbiters are much closer to the Earth than GEO orbiters, runing from 500 to 1,500 kilometers above the surface.
LEO orbiters do n’t remain in fixed place relation to the surface, and are merely seeable for 15 to 20 proceedingss each base on balls. So a web of LEO orbiters is necessary for LEO orbiters to be utile. A LEO orbiter ‘s propinquity to earth compared to a GEO orbiter gives it a better signal strength and less clip hold, which is better for point to indicate communicating. A LEO orbiter ‘s smaller country of coverage is less of a waste of bandwidth. Atmospheric retarding force affects LEO orbiters, doing gradual orbital impairment. A MEO orbiter is in orbit someplace between 8,000 kilometers and 18,000 kilometers above the Earth ‘s surface.
MEO orbiters are similar to LEO orbiters in functionality.MEO orbiters are seeable for much longer periods of clip than LEO orbiters, normally between 2 to 8 hours.MEO orbiters have a larger coverage country than LEO orbiters. Tundra and Molniya Orbit Satellites are used by Russia for decennaries. Molniya Orbit is an egg-shaped orbit. The orbiter remains in a about fixed place relation to Earth for eight hours. A series of three Molniya orbiters can move like a GEO orbiter.
It is utile for operations in near Polar Regions. [ 1 ] International Telecommunication Union ( ITU ) has done the frequence allotment and planning for all orbiter services. To ease efficient frequence planning, the whole universe is divided into three parts. [ 1 ] They are,Region 1: Europe, Africa, MongoliaRegion 2: Gronland, South and North AmericaRegion 3: Australia, Asia, South west PacificFrequency set are allocated within these parts to supply assorted orbiter services. Some of the orbiter services are Broadcasting Satellite Services, Mobile orbiter services, fixed orbiter services, Navigational and meteorological orbiter services. [ 1 ]Different types of orbiters use assorted frequence sets.
They are given in the tabular array below,
|FREQUNCY BAND||OPERATING Frequency( GHz )||TYPES OF SATELLITE SERVICE USES|
|S- Band||2-4||Multiple sclerosis|
|Ku-Band||12.5-18||FSS and BSS|
|K-Band||18-26.5||FSS and BSS|
|Ka-band||26.5- 40||Degree fahrenheit|
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