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Lecture Wireless and mobile computing – Chapter 26: Satellite communications

The following will be discussed in this chapter: Parabolic reflective antenna, antenna gain, signal loss in satellite communication, noise types, refraction, fading, diffraction and scattering, fast and slow fading, flat and selective fading, diversity techniques. | Satellite Communications Lecture 26 Overview Requirement of Satellite Communication Satellite UpLink and DownLink Types of Satellites Satellite Foot Print (Coverage Area) Satellite Transmission Bands UpLink and DownLink Frequencies Signal Propagation Delay Transponder Effect of Rain on Satellite Communication Microwave Communication (Why) Satellite System Elements Losses Capacity Allocation Strategies Why Satellite Communication? The Earth is a sphere & the microwave frequencies travel in straight line but to connect two regions very far away on the two side of the sphere, the link requires lot of repeaters because of Earth’s curvature. A single satellite can do the magic linking the continents with one repeater. Motivation to use Satellites Communication Satellite A Communication Satellite can be looked upon as a large microwave repeater It contains several transponders which listens to some portion of spectrum, amplifies the incoming signal and broadcasts it in another frequency to avoid interference with incoming signals. Satellite It is a repeater which receives signal from Earth at one frequency, amplify it & transmit it back to Earth at other frequency. EARTH STATION There are two earth station in a simple Satellite communication link. One transmits the signal to satellite called transmitting Earth station. The other receives the signal from satellite called receiving Earth Station. UPLINK & DOWN LINK The communication link from Transmitting earth station to satellite is called Up-link. The communication link from satellite To receiving earth station is called Down-link. Altitudes of Orbits Above the Earth There are 3 common types of satellite based on altitude, i.e. GEO, MEO & LEO Orbit Altitude Missions possibles Low-Earth orbit LEO 250 to 1,500 km Earth observation, meteorology, telecommunications (constellations) Medium-Earth orbit MEO 10,000 to 30,000 km Telecommunications (constellations), positioning, science . | Satellite Communications Lecture 26 Overview Requirement of Satellite Communication Satellite UpLink and DownLink Types of Satellites Satellite Foot Print (Coverage Area) Satellite Transmission Bands UpLink and DownLink Frequencies Signal Propagation Delay Transponder Effect of Rain on Satellite Communication Microwave Communication (Why) Satellite System Elements Losses Capacity Allocation Strategies Why Satellite Communication? The Earth is a sphere & the microwave frequencies travel in straight line but to connect two regions very far away on the two side of the sphere, the link requires lot of repeaters because of Earth’s curvature. A single satellite can do the magic linking the continents with one repeater. Motivation to use Satellites Communication Satellite A Communication Satellite can be looked upon as a large microwave repeater It contains several transponders which listens to some portion of spectrum, amplifies the incoming signal and broadcasts it in another .