OVERVIEW

In this chapter we consider the principles and performance characteristics of digital modulation techniques that are frequently employed. Before dealing with bandwidth-efficient modulation techniques, we shall review the principles of the simplest baseband signal processing and modulation methods. This introductory material is the foundation for the understanding of more complex, higher-state M-ary systems.

The performance of pulse amplitude modulated (PAM) baseband and of coherent phase shift keyed (PSK) systems in an additive white gaussian noise (AWGN) environment is considered in depth here. In this chapter it is assumed that the channel does not contain any non-linearities such as those caused by travelingwave tube (TWT) amplifiers or by power-efficient solid-state non-linear amplifiers. The non-linear effects of these microwave amplifiers on the performance of digitally modulated systems, such as AM to AM or AM to PM conversion, are presented in later chapters. A linear AWGN channel is a somewhat simplistic theoretical model for a microwave system. However, for deeply faded channels this model can represent real conditions if employed carefully. It is simple, mathematically tractable, and permits system comparison.

In addition to PAM baseband and PSK modulated systems, a number of other modulation techniques are in use in digital microwave systems. Correlative coding, also known as generalized duobinary or partial response, amplitude phase keying (APK), digital vestigial-sideband suppressed carrier (VSB-SC), quadrature digital AM (QAM), and pulse amplitude modulated FM are among these modulation techniques. Here the probability of error, P(e), performance of these systems in an...