Basics of satellite communications
This chapter introduces satellite communication technology from a non-specialist point of view. The basic principles will be introduced along with a list of generic functions that satellite technology can perform (broadcast, unicast, bi-directional, multicasting). The chapter traces a broad history of satellite technology and discusses the developments currently taking place, covering broadcast type functions and additional applications and services.
It will further introduce general trends within the overall ICT sector that have an influence on the evolution of satellite technology. Although some issues and topics may not seem directly related to the use of satellites in an educational context, it is important to understand the fundamentals of the technology. This chapter is not the easiest part of the report and the reader may consider skipping to the following chapter which discusses the practical applications and return to this chapter at a later stage. Both chapters are self contained and can be read independently of the rest of the report. Introduction
A satellite is an object that orbits or revolves around another object. For example, the Moon is a satellite of Earth, and Earth is a satellite of the Sun. In this document, we will examine human-made satellites that orbit Earth. They are highly specialized wireless receiver/transmitters that are launched by a rocket and placed in orbit around the Earth. There are hundreds of satellites currently in operation. Satellite communication is one particular example of wireless communication systems. Similar and maybe more familiar examples of wireless systems are radio and television broadcasting and mobile and cordless telephones. Systems of this type rely on a network of ground-based transmitters and receivers. They are commonly referred to as 'terrestrial' systems as opposed to satellite systems. Satellite communication systems differ from terrestrial systems in that the transmitter is not based on the ground but in the sky: the transmitter here consists of a ground-based part called the uplink, and the satellite-based part that 'reflects' the signals towards the receivers. This part is called the transponder. Purpose
Satellites come in many shapes and sizes and have many uses. The first artificial satellite, called Sputnik, was launched by the Soviet Union in 1957 and was the size of a basketball. Its purpose was simply to transmit a Morse code signal repeatedly. In contrast, modern satellites can receive and transmit hundreds of signals at the same time, from simple digital data to complex television programmes. They are used for many purposes such as television broadcasting, amateur radio communications, Internet communications, weather forecasting and Global Positioning Systems (GPS). Communications satellites
Communications satellites act as relay stations in space. One could imagine them as very long, invisible poles that relay high frequency radio waves. They are used to bounce messages from one part of the world to another. The messages can be telephone calls, TV pictures or Internet connections. Certain communications satellites are, for example, used for broadcasting: they send radio and TV signals to homes. Nowadays, there are more than 100 such satellites orbiting Earth, transmitting thousands of different TV (and radio) programmes all over the world. Other applications: remote-sensing satellites
Military, government, weather, environment, scientific, positioning Remote-sensing satellites study the surface of the Earth. From a relatively low height (480 km) up, these satellites use powerful cameras to scan the planet. The satellite then transmits valuable data on the global environment to researchers, governments, and businesses including those working in map making, farming, fishing, mining and many other industries. Instruments on remote-sensing satellites gather data about features such as the Earth's plant cover,...
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