A Simple Approach to Digital Signal Processing

6

Encoding of Waveforms – Increasing the Channel Bandwidth

Communications form a large part of modern life. Massive amounts of data are carried via telephone networks, TV channels and private and military data networks. The provision of data-carrying capacity is expensive and using it as efficiently as possible is paramount.

In this chapter we shall look at the different methods by which we encode speech and video signals so that we can transmit them over physical media. Unfortunately, in order to keep this chapter to a reasonable length we shall not be able to look at any forms of error management. Further reading of more in-depth textbooks, for example, Jayant and Noll [1984], will provide information on this topic.

This chapter is divided roughly into three parts. The first section covers the different forms of waveform encoding that can be used to reduce the bandwidth of either speech, image or data signals for transmission. The second section looks at vocoding schemes where the periodic nature of speech is used to design innovative encoding techniques. Finally, we shall look at encoding schemes that are specific to systems that combine image and speech signals, for example, videophones and other multimedia applications. Some of the coding methods mentioned are still under discussion by their respective standards committees at the time of writing this book.

ANALOG WAVEFORM CODING

In our new digital world of DSPs we still come across some old-fashioned analog waveform encoding ...