Modulation and Demodulation

This chapter discusses common types of modulation and their variants. It explores the spectral effects of modulation and explains why certain types of modulation are used in differing situations. The chapter also explains, using mathematical notation, the operation of modulators and demodulators. It provides block diagrams of modulators and demodulators, both analog and digital, and derives the mathematical expressions for their form where appropriate. The chapter then discusses notion of phase lock and the phase‐locked loop (PLL) and Costas loops. It demonstrates the operation of multibit digital modulation using quadrature amplitude modulation (QAM) and quadrature phase shift keying (QPSK). The chapter helps the reader to understand the use of advanced modulation techniques, such as orthogonal frequency division multiplexing (OFDM), for increased digital bit rate; and spread‐spectrum (SS) techniques: direct‐sequence SS and frequency‐hopping SS.