Introduction to Satellite Communications

Abstract

Introduction to Satellite CommunicationsA communications satellite is an orbiting artificial earth satellite that receives a communications signal from a transmitting ground station, amplifies and possibly processes it, then transmits it back to the earth for reception by one or more receiving ground stations. Communications information neither originates nor terminates at the satellite itself. The satellite is an active transmission relay, similar in function to relay towers used in terrestrial microwave communications.The commercial satellite communications industry has its beginnings in the mid-1960s, and in less than 50 years has progressed from an alternative exotic technology to a mainstream transmission technology, which is pervasive in all elements of the global telecommunications infrastructure. Today's communications satellites offer extensive capabilities in applications involving data, voice, and video, with services provided to fixed, broadcast, mobile, personal communications, and private networks users.Satellite communications are now an accepted fact of everyday life, as evidenced by the antennas or 'dishes' that dot city and country horizons, or the nearly instantaneous global news coverage that is taken for granted, particularly in times of international crises.The communications satellite is a critical element in the overall telecommunications infrastructure, as represented by Figure 1.1, which highlights, by the shaded area, the communications satellite component as related to the transmission of information. Electronic information in the form of voice, data, video, imaging, etc., is generated in a user environment on or near the earth's surface. The information's first node is often a terrestrial interface, which then directs the information to a satellite uplink, which generates an RF (radio frequency) radiowave that propagates through the air link to an orbiting satellite (or satellites). The information bearing radiowave is amplified and possibly processed at the satellite, then reformatted and transmitted back to a receiving ground station through a second RF radiowave propagating through the air link. Mobile users, indicated by the vehicle and handheld phone on the figure, generally bypass the terrestrial interface only for direct mobile-to-mobile communications.