ABSTRACT
Whenever we try to make accurate measurements we discover that the quantities we are obseiVing appear to fluctuate randomly by a small amount. This limits our ability to make quick, accurate measurements and ensures that the amount of information we can collect or communicate is always finite. These random fluctuations are called Noise. They arise because the real world behaves in a quantised or 'lumpy' fashion. A common question when designing or using information systems is, 'Can we do any better?' In some cases it's possible to improve a system by choosing a better design or using it in a different way. In other cases we're up against fundamental limits set by unavoidable noise effects. To decide whether it is worth trying to build a better system we need to understand how noise arises and behaves. Here we will concentrate on electronic examples. However, you should bear in mind that similar results arise when we consider information carried in other ways (e.g. by photons in optonics systems).
