10-2  Satellite Communications

Satellite communications began in 1976 with the launch by COMSAT of the MARISAT satellites to provide communications to ships at sea.  The International Maritime Satellite Organization（INMARSAT）was subsequently formed in 1979，and that organization now provides mobile satellite communications services to aircraft and land-based terminals. A number of national mobile satellite communications systems also serve the United States，Canada，Australia，and Japan with many more planned.

The spectacular growth of terrestrial mobile communications systems has provided a catalyst for efforts to provide global mobile communications through the use of mobile satellite communications systems in low-，medium-，and geostationary-Earth orbit.[1]

Until now，second-generation terrestrial and satellite mobile communications systems have existed as two independent environments. However，these environments are beginning to combine to form a third-generation global mobile communications system in which terrestrial and satellite systems have complementary instead of independent roles and form a single universal integrated system.

A Brief History of Satellite Communications

In an article in Wireless World in 1945，Arthur C. Clarke proposed the idea of placing satellites in geostationary orbit around Earth such that three equally spaced satellites could provide worldwide coverage. However，it was not until 1957 that the Soviet Union launched the first satellite Sputnik 1，which was followed in early 1958 by the U. S. Army’s Explorer 1．Both Sputnik and Explorer transmitted telemetry information.

The first communications satellite，the Signal Communicating Orbit Repeater Experiment（SCORE)，was launched in 1958 by the U. S. Air Force. SCORE was a delayed-repeater satellite，which received signals from Earth at 150 MHz and stored them on tape for later retransmission. A further experimental communication satellite，Echo 1，was launched on August 12，1960 and placed into inclined orbit at about 1500 km above Earth. Echo 1 was an aluminized plastic balloon with a diameter of 30 m and a weight of 75.3 kg. Echo 1 successfully demonstrated the first two-way voice communications by satellite.

On October 4，1960，the U. S. Department of Defense launched Courier into an elliptical orbit between 956 and 1240 km，with a period of 107 min. Although Courier lasted only 17 days, it was used for real-time voice, data, and facsimile transmission. The satellite also had five tape recorders onboard；four were used for delayed repetition of digital information，and the other for delayed repetition of analog messages.

Direct-repeated satellite transmission began with the launch of TelstarⅠon July 10，1962. Telstar Ⅰwas an 87-cm，80-kg sphere placed in low-Earth orbit between 960 and 6140 km，with an orbital period of 158 min. Telstar Ⅰwas the first satellite to be able to transmit and receive simultaneously and was used for experimental telephone，image，and television transmission.  However, on February 21, 1963, TelstarⅠsuffered damage caused by the newly discovered Van Allen belts.

Telstar Ⅱ was made more radiation resistant and was launched on May 7，1963．Telstar Ⅱ was a straight repeater with a 6.5-GHz uplink and a 4.1-GHz downlink. The satellite power amplifier used a specially developed 2- W traveling wave tube. Along with its other capabilities, the broadband amplifier was able to relay color TV transmissions. The first successful trans-Atlantic transmission of video was accomplished with Telstar Ⅱ, which also incorporated radiation measurements and experiments that exposed semiconductor components to space radiation.

The first satellites placed in geostationary orbit were the synchronous communication（SYNCOM）satellites launched by NASA in 1963. SYNCOM Ⅰ failed on injection into orbit. However, SYNCOM Ⅱ was successfully launched on July 26，1964 and provided telephone, teletype, and facsimile transmission. SYNCOM Ⅲ was launched on August 19，1964 and transmitted TV pictures from the Tokyo Olympics. The International Telecommunications by Satellite（INTELSAT）consortium was founded in July 1964 with the charter to design, construct, establish, and maintain the operation of a global commercial communications system on a nondiscriminatory basis. The INTELSAT Ⅰnetwork started with the launch on April 6, 1965, of INTELSAT Ⅰ, also called Early Bird. On June 28, 1965, INTELSAT Ⅰ began providing 240 commercial international telephone channels as well as TV transmission between the United States and Europe.

In 1979，INMARSAT established a third global system. In 1995, the INMARSAT name was changed to the International Mobile Satellite Organization to reflect the fact that the organization had evolved to become the only provider of global mobile satellite communications at sea，in the air，and on the land.

Early telecommunication satellites were mainly used for long-distance continental and intercontinental broadband, narrowband, and TV transmission. With the advent of broadband optical fiber transmission, satellite services shifted focus to TV distribution, and to point-to-multipoint and very small aperture terminal（VSAT）applications. Satellite transmission is currently undergoing further significant growth with the introduction of mobile satellite systems for personal communications and fixed satellite systems for broadband data transmission.

Types of Telecommunications Satellite Services

Because satellite communications cover the whole range of voice, data, and video transmission,  telecommunication satellite services are normally classified into three types：

Fixed satellite service（FSS）networks are mainly intended for long-distance operation of telecommunications networks. FSS satellites are employed to relay signals between large，complex, and expensive Earth stations, which are connected to the terrestrial telecommunications network.

Direct-broadcast satellite service（DBS）networks transmit broadcast and TV signals from a large central Earth station，via a satellite to receive-only Earth stations. DBS receive stations either are distribution heads for cable TV or are located in homes for direct-to-home transmission.

Mobile satellite services（MSS）networks are relayed via satellite between large fixed Earth stations and small mobile terminals fitted to a ship, an aircraft, or a vehicle. Increasingly, MSS networks are formed to relay communications to portable handheld terminals.

In 1996，the ITU defined the Global Mobile Personal Communications by Satellite (GMPCS) as comprising the following systems：

Geostationary Earth Orbit（GEO）MSS are for voice and low-speed data mobile personal communications services.

Non-GEO（NGEO）MSS are for narrowband mobile personal communications services excluding voice -- because these are invariably based on low-Earth orbit（LEO）satellites，they are also called Little-LEO．

NGEO MSS for narrowband mobile personal communications include voice, operating in LEO,  medium-Earth  orbit（MEO），or highly elliptical orbit（HEO）- also called Big- LEO．

GEO and NGEO FSS offer fixed and transportable multimedia broadband services -- also called Super- LEO.

WORDS AND PHRASES

satellite 卫星

geostationary-Earth 与地球同步的

catalyst 催化剂

telemetry 遥感勘测,自动测量记录传导

aluminize 以铝覆盖,以铝处理

terrestrial 陆地

simultaneously 同时地

teletype  电传打字机,电报交换机,打字电报通讯

consortium  财团, 联营企业

very small aperture terminal甚小孔径终端

diameter 直径

facsimile 传真

NOTES

[1] The spectacular growth of terrestrial mobile communications systems has provided a catalyst for efforts to provide global mobile communications through the use of mobile satellite communications systems in low-，medium-，and geostationary-Earth orbit.

通过在近地、中端和地球同步轨道的移动卫星通信系统，陆地移动通信系统的壮大发展催生了全球移动通信诞生。

[2] However，these environments are beginning to combine to form a third-generation global mobile communications system in which terrestrial and satellite systems have complementary instead of independent roles and form a single universal integrated system.

然而，这些环境条件正结合形成一个第三代全球移动通信系统，陆地系统将和卫星系统优势互补形成一个独一的整体集成系统，而不是自成一家。

[3] With the advent of broadband optical fiber transmission, satellite services shifted focus to TV distribution, and to point-to-multipoint and very small aperture terminal（VSAT）applications.

随着光纤宽带传输的到来，卫星服务的焦点转向电视传播、点到多点和极小孔径终端（甚小孔径终端）的应用。

卫星在轨处理能力增强，推动了未来无线网络功能和协议栈星上部署的快速发展，有利于降低业务时延，提高服务质量。本报告结合未来6G星地融合网络发展趋势，探讨卫星边缘计算对于网络架构和网络功能的影响，并基于星地协同计算框架，讨论星地多维资源调度相关的技术发展趋势和关键问题。