Satellite Communication Systems - Design Principles


Chapter five covered various modulation schemes quantifying the relationship between carrier to noise ratio at the input of a demodulator and the baseband signal quality. In many satellite communication applications the desired carrier to noise ratio is not achievable. For instance a VSAT terminal may not have adequate RF sensitivity or the signal received in a mobile terminal may fluctuate. In such applications a technique known as coding is often used. Coding is the technique of protecting message signals from signal impairments, by adding redundancy to the message signal.

In this chapter we discuss coding as applied in satellite communications. The subject of coding has received extensive coverage in the literature. The treatment here is at a system level and briefly reviews only aspects relevant to satellite communications. There are many interpretations of coding. As discussed here, coding refers to the process of providing protection to the message signals against corruption of RF signal by incorporating redundant bits to the baseband digital signals.

A brief introduction of information theory is included in the first part of the chapter to develop an appreciation of the fundamental communication capacity limitations of a channel The understanding of basics of information theory can broaden the outlook of a perceptive student. This is followed by a discussion of basic principles of coding schemes commonly used in satellite communication systems.