文档介绍：10/27/04 10:19 AM Page
Source: STANDARD HANDBOOK OF ELECTRONIC ENGINEERING
CHAPTER
NOISE AND INTERFERENCE
Geoffrey C. Orsak, H. Vincent Poor, John B. Thomas
GENERAL
In a general sense, noise and interference are used to describe any unwanted or undesirable signals -
munication channels and systems. Since in many cases these signals are random or unpredictable, some study
of random processes is a useful prelude to any consideration of noise and interference.
RANDOM PROCESSES
A random process X(t) is often defined as an indexed family of random variables where the index or parame-
ter t belongs to some set T; that is, t ⑀ T.
The set T is called the parameter set or index set of the process. It may be finite or infinite, denumerable
or nondenumerable; it may be an interval or set of intervals on the real line, or it may be the whole real
line −∞< t < ∞. In most applied problems, the index t will represent time, and the underlying intuitive notion
will be a random variable developing in time. However, other parameters such as position and temperature may
also enter in a natural manner.
There are at least two ways to view an arbitrary random process: (1) as a set of random variables: this view-
point follows from the definition. For each value of t, the random process reduces to a random variable; and
(2) as a s