Introduction

Satellite communication systems have enabled efficient global coverage by facilitating communication between user terminals on earth using artificial satellites placed in space. Huge effort has gone behind the implementation and advancement of this technology. The unique advantages offered by this system have resulted in making them an integral part of today's wireless era with applications ranging from weather forecasting to radio broadcasting and from military applications to personal location tracking. Milestones in the development of satellite communications are tabulated in Table 12.1.

Artificial satellites are launched and placed in space such that they revolve round the earth in a fixed designated path and in a particular orientation. Earth stations are installed and any station which falls in the coverage of the satellite can communicate with it using two separate frequencies for either-way communication. Figure 12.1 shows two satellites in space communicating with earth stations present in their coverage. The path and orientation of a satellite in space may vary due to many external forces. Stabilization methods are employed to get over this challenge. In the following sections, the basics of satellite communication will be discussed with a focus on topics like frequency allocation, satellite and earth station components, orbital elements, variants of satellites, laws governing satellite motion, stabilization techniques and factors causing adverse effects on performance. The chapter concludes by explaining the working principle behind the Global Positioning System.