- 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.