Elements of Digital Modulation

This chapter discusses the requirements for digital modulation: narrow bandwidth of the modulated signal, low bit error rate, and easy implementation of the modulation/ demodulation circuits. It describes briefly some general topics of digital modulation and demodulation. Amplitude shift keying (ASK) and quadrature amplitude modulation (QAM) fall into the category of linear modulation. Linear modulation by definition can be generated by multiplying the baseband modulating signal(s) by a carrier signal. The chapter also discusses the power spectral density of digitally modulated signals. The methods of demodulation are classified into coherent or synchronous detection and noncoherent detection, depending on whether a carrier signal is or is not used, respectively. Computer simulation experiments can be a powerful method for evaluating and designing digital modulation/demodulation systems, as well as other parts of a digital communication system. Operation of the experimental system is simulated by software programs on a computer.