Satellite Communications

In 1945, Arthur C. Clarke, then an officer with the Royal Air Force, proposed the use of Geosynchronous Earth Orbit spacecraft operating at an altitude of 22,300 miles or 35,680 kilometers . A decade later, John Pierce, working at Bell Laboratories, examined the use of satellite repeaters for carrying international phone calls.

The first trans-Atlantic telephone cable (TAT-1) was designed to carry 36 simultaneous phone calls for nearly $50 million. On October 4, 1957, the Soviet Union launched Sputnik, marking the beginning of the modern space age. The National Aeronautical and Space Administration (NASA) was consequently formed in 1958.

However, it was the Army Ballistic Missile Agency that actually launched the first American satellite, “Explorer”, on January 31,1958. AT&T launched its first Medium Earth Orbit (MEO) spacecraft, Telstar 1 in 1963. In the same year, the U.S. drafted the Communications Satellite Act forming COMSAT with an initial funding of $200 million.

Later on, COMSAT became the U.S. signatory to the newly formed Intelsat, an international communication satellite cooperative comprised initially of 11 member countries. In 1965, Intelsat launched EARLY BIRD (Intelsat 1) followed by Soviet Union, USA, UK, Italy, Canada and France. Over the next 25 years, Intelsat grew to over 140 member countries and expanded their fleet of satellites to nearly 20 in-orbit spacecraft.

Intelsat became responsible for carrying approximately 90% of international telephone traffic and virtually all international television programming. Beginning in 1972 Canada launched ANIK-1, domestic satellite operators began operating primarily to service the television entertainment industries followed by the United States, Indonesia and Japan in the 1970’s; India, Australia, Brazil, Mexico, Israel, China, Sweden, and Luxembourg in the 1980’s; Argentina, Pakistan, Chile, Thailand, Korea, Malaysia, and Portugal in the 1990’s.

In 1984, PanAmSat became the world’s first private satellite operator, generating a privatization of Intelsat and Eutelsat, the two largest satellite consortia. Today the satellite industry is dominated by private operators offering global coverage, represented by PanAmSat, Loral Skynet via the Loral Global Alliance, and SES Global formed by GE Americom and SES/Astra.

During the past forty years, satellite communications systems have been developed not only for commercial uses, but also for military applications. These include, Air Force Satellite communications (AFSATCOM) at Ultra High Frequencies (UHF), Defense Satellite Communication Systems (DSCS) at Super High Frequencies (SHF) and Military Strategic and Tactical Relay (MILSTAR) Satellite System at Extremely High Frequencies (EHF).

Historically, the first satellite network accessing Internet called SATNET was initiated in mid 1975. The network was sponsored by the Advanced Research Projects Agency (ARPA), the Defense Communications Agency, the British Post Office and the Norwegian telecommunications Administrations.

The network consists of four ground stations (two in the Washington, D.C. area at Etam and Clarksburg; one in Goonhilly, England; and one in Tanum, Sweden) interconnected by a simplex, 64 Kbps Intelsat IV-A SPADE channel. The ground station sites are equipped with satellite
message processors, called Satellite IMPs (SIMPs) which are extensions of the ARPANET IMPs and which implement channel access and network access protocols.

Gateway computers, implemented with PDP-11 hardware, connect SATNET and ARPANET to permit internetwork communications. One of the goals of the SATNET experiments was to test the feasibility and extensibility of different channel access schemes and to gain experience with the implementation, operation and performance evaluation of packet satellite networks.

New generation satellite networks are being developed with main requirement of supporting Internet access and multimedia services and applications. These satellite networks are classified as satellite connectivity networks for global coverage and satellite access networks for regional coverage. The broadband satellite networks, the TCP/IP enhancements, the QoS models, and the design problems which form the main focus of this chapter, are discussed in the following sections.