ABSTRACT
This chapter describes the major components of a conventional digital telecommunications system and recalls that the primary source of errors is the analog channel. It explains why a realistic channel model must include at least Additive White Gaussian Noise (AWGN) and band-limiting. The chapter reviews the notion of Bit Error Rate as a way of comparing digital modulation schemes. In digital communications, the digital information has to be transmitted over a band-pass analog channel. Because digital information cannot be directly transmitted over an analog channel, first it has to be mapped to analog sample functions having finite length. Based on the noisy and distorted received sample functions the receiver must recognize the digital information transmitted. The chapter provides a clear exposition of the important issues in both conventional and chaotic modulation/demodulation techniques. Although symbol synchronization has to be solved in every digital communications system, it belongs to the decision circuit and not to the demodulation process.
