Satellite Communication Systems Overview

air Communication Systems OverviewSATELLITE COMMUNICATION SYSTEMS OVERVIEW beam communication enables two Stations on the primer coat to communicate through radio broadcast which be located far away from to each one new(prenominal). The two stations use artificial transmit as a relay station for their communication. One of the state station will transmit to the satellite. This is called as Uplink. The satellite Transponder will convert the signal and sends it down to the other earth station. This is called a Downlink. The satellite communication is advantageous over terrestrial communication because of the huge insurance coverage ara and high bandwidth capabilities. The disadvantages of satellite communication be large propagation delay, communication cost and piecemeal increase in use of bandwidth. The basic factors to be considered in satellite communication be visor angle is the angle of the earth surface to the center line of the satellite transmission diaphysis. T his angle gives broad effects on satellites coverage domain. Ideally, elevation angle should be 0 degrees, so that the transmission beam will reach the horizon visible to the satellite in all directions. However, there is a minimal elevation angle of earth stations because of the environmental factors like objects blocking the transmission, atmospheric attenuation, and earth galvanising background noise. Coverage angle is the measure of the portion of the earth surface visible to a satellite taking the minimum elevation angle into account. 1 It is denoted as,R/(R+h) = cos ( + )/cos ()Here R is earth radius (6370 Km), h is satellite orbit height, is coverage angle and ? is the minimum elevation angle. There are impairments like free space loss, atmospheric attenuation caused by rain and fog will gain considerable effects during transmission. 1There are different type of satellite services namely, Fixed Satellite Services (FSS) to offers point to point communication. Broadcast S atellite Services (BSS) to provide satellite television and radio. active satellite Services (MSS) will provide telephony. There are number of satellites orbiting in different orbits. 1The types of satellite orbits are (GEO) geostationary earth orbit, Medium earth orbit (MEO), Low earth orbit ( social lion) Molniya and tundra orbit.GEO satellites are in orbit 35,863 km above the earths surface along the equator. Objects in Geostationary orbit wheel around the earth at the same speed so as the earth rotates. This means GEO satellites stay on in the same position relative to the surface of earth. This satellite has large coverage area which well-nigh one fourth of the earths surface. It has 24 hour continuous view of the particular regions of the earth, so it is used for transmit and multipoint applications. These GEO satellites have difficulty in broadcasting in near polar region.king of beasts satellites are much close-hauled to the earth than GEO satellites, ranging from 500 t o 1,500 km above the surface.LEO satellites dont stay in fixed position relative to the surface, and are only visible for 15 to 20 minutes each pass. So a network of LEO satellites is necessary for LEO satellites to be useful. A LEO satellites proximity to earth compared to a GEO satellite gives it a better signal strength and less clipping delay, which is better for point to point communication. A LEO satellites smaller area of coverage is less of a waste of bandwidth. Atmospheric drag affects LEO satellites, cause gradual orbital deterioration. A MEO satellite is in orbit somewhere between 8,000 km and 18,000 km above the earths surface.MEO satellites are similar to LEO satellites in functionality.MEO satellites are visible for much longer periods of time than LEO satellites, usually between 2 to 8 hours.MEO satellites have a larger coverage area than LEO satellites. Tundra and Molniya Orbit Satellites are used by Russia for decades. Molniya Orbit is an elliptical orbit. The sat ellite remains in a nearly fixed position relative to earth for eight hours. A series of terce Molniya satellites can act like a GEO satellite. It is useful for operations in near Polar Regions. 1 world-wide Telecommunication Union (ITU) has done the frequency allocation and planning for all satellite services. To facilitate cost-effective frequency planning, the whole world is divided into three regions. 1 They are,Region 1 Europe, Africa, MongoliaRegion 2 Greenland, southeasterly and North AmericaRegion 3 Australia, Asia, South west pacificFrequency band are allocated within these regions to provide non-homogeneous satellite services. Some of the satellite services are Broadcasting Satellite Services, Mobile satellite services, fixed satellite services, Navigational and meteorological satellite services. 1Different types of satellites use various frequency bands. They are given in the table below,FREQUNCY BANDOPERATING FREQUENCY(GHz)TYPES OF SATELLITE swear out USESL-Band1-2 MSSS- Band2-4MSSC-Band4-8FSSX-Band8-12.5FSSKu-Band12.5-18FSS and BSSK-Band18-26.5FSS and BSSKa-band26.5- 40FSSReferencescourses.missouristate.edu/HuiLiu/csc690/slides/Satellite.ppt (http//search.missouristate.edu/advanced/courses.aspx)