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View File - University of Engineering and Technology, Taxila

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FIGURE 1.2Communication between two earth stations via a satellite.1.3 CHARACTERISTIC FEATURES OFCOMMUNICATION SATELLITESSatellite communication circuits have several characteristic features. Theseinclude1. Circuits that traverse essentially the same radi<strong>of</strong>requency (RF)pathlength regardless <strong>of</strong> the terrestrial distance between the terminals.2. Circuits positioned in geosynchronous orbits may suffer a transmissiondelay, t d , <strong>of</strong> about 119 ms between an earth terminal <strong>and</strong> thesatellite, resulting in a user-to-user delay <strong>of</strong> 238 ms <strong>and</strong> an echodelay <strong>of</strong> 476 ms.For completeness, transmission delay is calculated usingt d ¼ h 0ð1:1Þcwhere h 0 is the altitude above the subsatellite point on the earthterminal <strong>and</strong> c is the speed <strong>of</strong> light (c ¼ 3 10 8 m=sec).For example, consider a geostationary satellite whose altitude h 0above the subsatellite point on the equator is 35,784 km. This givesa one-way transmission delay <strong>of</strong> 119 msec, or a roundtrip transmissiondelay <strong>of</strong> 238 msec. It should be noted that an earth terminal notlocated at the subsatellite point would have greater transmissiondelays.Copyright © 2002 by Marcel Dekker, Inc. All Rights Reserved.

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