Wireless Communications

4Digital Modulation

Abstract

Digital modulation, in nature, involves mapping a set of discrete symbols into a set of waveforms for efficient transmission. For wireless communication, a convenient way to implement digital modulation is to use information symbols to modulate the amplitude, phase, or frequency of a sinusoidal carrier. Each set of the modulated signals can be viewed as continuous-time waveforms in the functional space or as signal points in the Euclidean space. This duality in signal representation offers insight into the nature of different digital modulation schemes and provides flexibility in their performance analysis. Besides their geometrical implications, different modulation schemes have their physical significance in terms of spectral efficiency, power efficiency, and reliability in signal detection. In this chapter, we focus on typical modulation schemes such as MPSK, square -QAM, coherent and noncoherent MFSK, and differential MPSK, with an emphasis on revealing their physical/geometrical nature and demonstrating the ideas, formulation, and methodology used in their performance analysis.

4.1 Introduction

Digital transmission over wireless channels, such as cellular, microwave radio, and satellite links, requires carrier modulation for a number of reasons. First, as a very precious resource, the frequency spectrum is regulated by the governments and international ...