# 1 Background Material

## Introduction to Chapter 1

#### Before we can make sense of the issues important in the design of a digital communications link, it is essential to have a good grounding in the relationship between the shape of a digital waveform in the time domain, and its corresponding spectral content in the frequency domain. #### Many of the modulation processes to be described in this book become intuitive when working with the sine and cosine terms that make up the modulating signals. In contrast, in the time domain we have to deal with the more complex issues of correlation and convolution. To this end, the first two sections of this chapter present the basics of Fourier series and trigonometrical relationships, as a starting point or refresher course for the reader as required. #### The chapter also provides a broad-brush overview of network and protocol aspects of data communications. This brief summary cannot do justice to the subject, which in some respects commands the lion's share of a digital communications system. The focus of this book however is on the modem part of the link, where we are concerned with getting the data bits (1s and 0s) which appear at the network interface over the channel in the most efficient (as regards cost, power, bandwidth, time) and error free manner. It is here, at the physical interface layer, that many of the biggest design challenges occur. #### The final section of the chapter provides a summary of terms and ideas used throughout the book, so that jargon does not defeat the reader at the first hurdle.

####