 of a much lower level. On satellite systems operating below 10 GHz, very little link margin is required; there is essentially no fading, as experienced with LOS microwave. The discussion here only deals with geostationary orbit (GEO) communication satellites. Satellite communications presents another method of extending the digital network (Chapter 6). These digital trunks may be used as any other digital trunks for telephony, data, the Internet, facsimile, and video. However, fiber optics has become a strong com- petitor of satellite communications. Only very small aperture terminal (VSAT) systems are showing any real growth in the GEO arena. A new type of communication satellite is being fielded. This is the LEO class of satellites, which we discuss in Chapter 15. Three-fourths of the satellite transponders over North America are used to provide entertainment services such as direct broadcast television and cable system head-end feeds, as well as for private broadcaster connectivity. 9.3.2 The Satellite Most of the commercial communication satellites that are presently employed are RF repeaters. A typical RF repeater used in a communication satellite is illustrated in Figure 9.17. The tendency is to call these types of satellite bent pipe as opposed to processing satellites. A processing satellite, as a minimum, demodulates and regenerates the received digital signal. It may also decode and recode (FEC) 10 a digital bit stream. It also may have some bulk switching capability, switching to crosslinks connecting to other satellites. Theoretically, three GEO satellites placed correctly in equatorial orbit could provide connectivity from one earth station to any other located anywhere on the surface of the earth (see Figure 9.18). However, high latitude service is marginal and it is nil north of 80°N and south of 80°S. 9.3.3 Three Basic Technical Problems As the reader can appreciate, satellite communication is nothing more than LOS micro- wave using one (or two)¹ located at great distances from the terminal earth