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Lý thuyết mạng không dây P7

The first reference to satellite communication systems was made in the mid-1940s by Arthur Clarke [1]. In this paper, Clarke described a number of fundamental issues relating to the building of a satellite network that entirely covers the earth including issues related to spectrum use, the power needed to run the network and the way of bringing the satellites to orbit. Clarke also introduced the concept of geostationary satellites, which – as explained later – orbit the earth in a radius that allows them to appear stationary from the earth’s surface | Wireless Networks. P. Nicopolitidis M. S. Obaidat G. I. Papadimitriou and A. S. Pomportsis Copyright 2003 John Wiley Sons Ltd. ISBN 0-470-84529-5 7 Satellite Networks 7.1 Introduction 7.1.1 Historical Overview The first reference to satellite communication systems was made in the mid-1940s by Arthur Clarke 1 . In this paper Clarke described a number of fundamental issues relating to the building of a satellite network that entirely covers the earth including issues related to spectrum use the power needed to run the network and the way of bringing the satellites to orbit. Clarke also introduced the concept of geostationary satellites which - as explained later - orbit the earth in a radius that allows them to appear stationary from the earth s surface. These ideas seemed to be too ambitious at the time of the publication due to the fact that technology was not advanced enough to allow for reliable transceivers and easy deployment of satellites. Nevertheless after no more than 40 years satellites have emerged to be a significant industry. This is mainly due to a the introduction of transistors which enabled the construction of small and reliable devices and b the advancements made in rocket technology which now allows for easier and less costly deployment of satellites as well as easier access by the astronauts for maintenance purposes. The evolution of satellite technology did not occur over a small time period but rather followed an evolutionary path. Satellite technology was enabled by the advances in radio telemetry and rocketry technology during World War II and the cold war era. The first attempts to establish communications via objects orbiting the earth commenced in 1956 by the US Navy. The orbiting object that was used was the natural satellite of Earth the moon. This project used 26-m antennae in two base stations in Washington and Hawaii which exchanged messages by bouncing signals off the moon s surface. Two years later the ECHO project offered single .