Presentation on theme: "Satellites offer a number of features not readily available with other means of communications. Because very large areas of the earth are visible from."— Presentation transcript:
Satellites offer a number of features not readily available with other means of communications. Because very large areas of the earth are visible from satellite, the satellite can form the star point of a communications net linking together many users simultaneously, users who may be widely separated geographically. The same feature enables satellites to provide communication links to remote communities. 1
This is especially valuable for communities in sparsely populated areas that are difficult of access by other means. Of course, satellite signals ignore political boundaries as well as geographical ones, which may or may not be a desirable feature. Satellites are also used for remote sensing, examples being the detection of water pollution and 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. 2
3 Radio communication by satellite is an outcome of research for increasing radio communication range and capabilities. Satellite Communication combines the missile and microwave technologies The space era started in 1957 with the launching of the first artificial satellite (sputnik). SYNCOM was the first Geostationary satellite, launched in 1963.
1956 First Trans-Atlantic Telephone Cable: TAT Sputnik: Russia launches the first earth satellite st Successful DELTA Launch Vehicle 1961 Formal start of TELSTAR, RELAY, and SYNCOM Programs 1962 TELSTAR and RELAY launched 1963 SYNCOM launched 1964 INTELSAT formed 1965 COMSAT's EARLY BIRD: 1969 INTELSAT-III series provides global coverage 1972 ANIK: 1st Domestic Communications Satellite (Canada) 1974 WESTAR: 1st U.S. Domestic Communications Satellite 1975 INTELSAT-IVA: 1st use of dual-polarization 1975 RCA SATCOM: 1st operational body-stabilized comm. satellite 1976 MARISAT: 1st mobile communications satellite 1976 PALAPA: 3rd country (Indonesia) to launch domestic comm. satellite 1979 INMARSAT formed TAT-8: 1st Fiber-Optic Trans-Atlantic telephone HISTORY OF SATELLITES
Frequency Allocations for Satellite Services R1: Europe, Africa, what was formerly the Soviet Union, and Mongolia R2:North and South America and Greenland R3:Asia,Australia, and the south-west Pacific Frequency and band designations are listed in table1.1 5
Satellite Bands C Band - 4/6 GHz 7 Uplink frequencies: GHz Downlink frequencies: GHz First choice for satellites because it was also used for terrestrial microwave. Equipment and expertise were available. Interference with terrestrial microwave Used for video delivery, VSAT, news gathering, telephony Band is saturated
Satellite Bands Ku Band - 12/14 GHz 8 Uplink frequencies: GHz Downlink frequencies: GHz Up/downlink frequencies differ for US and Europe. Smaller/cheaper earth stations used than for C Band. Rain produces attenuation problems so more powerful transmitters are needed. Used for video delivery, VSAT, news gathering, telephony, direct-to-home video/audio, internet access, voice, video, data Band will become saturated.
9 Some Other Bands L Band GHz –Voice/low speed data to mobile terminals. S Band GHz –Cellular telephony, data, paging Ka Band18-31 GHz –Internet access, voice, video, data, videoconferencing –Very powerful transmitters to deal with attenuation
It is clearly seen that there is a successive increase in the size and capacity of the satellites, the latest in the series, Intelsat VI, being capable of providing 80,000 voice channels. The design lifetime for recently launched satellites ranges from 10 to 15 years (ThaiCom will last about 14 years). The international regions served by Intelsat are divided into the Atlantic Ocean Region (AOR), the Pacific Ocean Region (POR) and Indian Ocean Region (IOR). For each region, satellites are positioned in geostationary orbit above the particular ocean. 11
U.S. Domsats Domsat is an abbreviation for domestic satellite. Domsats are used to provide various telecommunications services such as voice, data, and video transmissions, within a country. 12
Satellite Uses 13 Used for television (both network and DSB), long-distance telephone, and private business networks. Particularly suitable for creating networks where cabling is not practical. –Low subscriber densities –Mobile stations
Satellite Limitations 14 Limited bandwidth, even with dish antennas directionality is limited. –Satellites cannot be placed close to each other unless they are processing the same signals. Long propagation delays due to distance. –Distracting for voice communications. –Data communications requires special protocols.