Satellite Communication Systems - Design Principles

Modulation

In chapter four we learnt the basics of radio link design. The design goal was to achieve a specified carrier to noise ratio at the demodulator input. It was mentioned that the carrier to noise ratio is related to the demodulated signal quality by a modulation dependent factor - without in any way attempting to quantify the factor or explain the modulation process.

In this chapter the topic of modulation is discussed. Modulation is the process of imparting baseband information to a carrier. Baseband signals are the basic information-carrying signals, such as output from a voice coder or a video camera. The subject of modulation has received extensive coverage in the literature (e.g. Taub and Schilling, 1986; Schwartz, 1987) and is a subject in its own right. Here we briefly review at a system level only those aspects of modulation relevant to satellite communications. The basic characteristics of various types of modulation used in satellite communication systems are covered.