lecture 1: satellite communications 1_EEC 284 Lecture 2.pdf
- 1. Overview of Satellite Systems
- 5. Satellite in communication systems • The satellites form an essential part of telecommunications systems worldwide, carrying large amounts of data and telephone traffic in addition to television signals. • Satellite system advantages: • Very large areas of the earth are visible from a satellite. • The satellite can form the star point of a communication network. • The satellite can link many users who may be widely separated geographically. • The same feature enables satellites to provide communications links to remote communities in sparsely populated areas that are difficult to access by other means. • Satellites are also used for remote sensing, examples being the detection of water pollution • The monitoring and reporting of weather conditions. • Some of these remote sensing satellites also form a vital link in search and rescue operations for downed aircraft and the like.
- 6. The satellite system cost • The satellite system cost: • To give some idea of cost, the construction and launch cost of the Canadian Anik-E1 satellite (in 1994 Canadian dollars) was $281.2 million, and that of the Anik-E2, $290.5 million. The combined launch insurance for both satellites was $95.5 million. • A feature of any satellite system is that the cost is distance insensitive, meaning that it costs about the same to provide a satellite communications link over a short distance as it does over a large distance. • Thus a satellite communications system is economical only where the system is in continuous use and the costs can be reasonably spread over a large number of users.
- 7. The satellite system cost • Three different types of applications are briefly described in this chapter: 1. The largest international system, Intelsat. 2. The domestic satellite system in the United States, Domsat. 3. U.S. National Oceanographic and Atmospheric Administration (NOAA) series of polar orbiting satellites used for environmental monitoring and search and rescue.
- 8. Frequency Allocations for Satellite Services • Some of the services provided by satellites are: • Fixed satellite service (FSS) : Connect between different communication companies. The signals may be telephone or video signals. • Broadcasting satellite service (BSS), Direct broadcast satellite (DBS), or Direct-to-home (DTH) : Connect the audio or video signals directly to the end user (homes) • Mobile satellite services: include land mobile, maritime mobile, and aeronautical mobile. • Navigational satellite services: include global positioning systems (GPS). • Meteorological satellite services: weather monitoring and often provide a search and rescue service.
- 9. Frequency Allocations for Satellite Services • L-band: Mobile satellite services, navigation and weather satellite. The required low power and low gain antennas. • C-band: FSS from 4 to 6 for downlink, and from 6 to 8 for uplink example 6/4 GHz (6GHz for uplink and 4GHz for down link) . Not used for DBS, because of the required very large antenna. • Ku-band: used for both DBS, FSS. Use downlink in the range of 12 to 14 GHz.
- 11. International Telecommunications Satellite (InTelSat) • The organization was created in 1964 and currently has over 140 member countries and more than 40 investing entities. • In July 2001 INTELSAT became a private company and in May 2002 the company began providing end-to-end solutions through a network of teleports, leased fiber, and points of presence (PoPs) around the globe. • Starting with the Early Bird satellite in 1965, a succession of satellites has been launched at intervals of a few years. Figure 1.1 illustrates the evolution of some of the INTELSAT satellites. As the figure shows, the capacity, in terms of number of voice channels, increased dramatically with each succeeding launch, as well as the design lifetime.
- 13. International Telecommunications Satellite (InTelSat) • These satellites are in geostationary orbit, meaning that they appear to be stationary in relation to the earth. • At this point it may be noted that geostationary satellites orbit in the earth’s equatorial plane and their position is specified by their longitude. • INTELSAT covers three main regions: • Atlantic Ocean Region (AOR) • Indian Ocean Region (IOR), • Pacific Ocean Region (POR) and what is termed Intelsat America’s Region.
- 14. International Telecommunications Satellite (InTelSat) • For the ocean regions the satellites are positioned in geostationary orbit above the particular ocean, where they provide a transoceanic telecommunications route. For example, INTELSAT satellite 905 is positioned at 335.5 ° east longitude. The footprints for the C-band antennas are shown in Fig. 1.2a,