Editing Bandwidth (signal processing) (section)

== Overview ==

Bandwidth is a key concept in many [[telecommunications]] applications. In [[radio]] communications, for example, bandwidth is the frequency range occupied by a modulated [[carrier signal]]. An [[FM radio]] receiver's [[tuner (radio)|tuner]] spans a limited range of frequencies.  A government agency (such as the [[Federal Communications Commission]] in the United States) may apportion the regionally available bandwidth to [[broadcast license]] holders so that their [[signal (electronics)|signals]] do not mutually interfere. In this context, bandwidth is also known as [[channel spacing]].

For other applications, there are other definitions. One definition of bandwidth, for a system, could be the range of frequencies over which the system produces a specified level of performance.  A less strict and more practically useful definition will refer to the frequencies beyond which performance is degraded. In the case of [[frequency response]], degradation could, for example, mean more than 3&nbsp;[[decibel|dB]] below the maximum value or it could mean below a certain absolute value. As with any definition of the ''width'' of a function, many definitions are suitable for different purposes.

In the context of, for example, the [[sampling theorem]] and [[Nyquist rate|Nyquist sampling rate]], bandwidth typically refers to [[baseband]] bandwidth. In the context of [[Nyquist rate|Nyquist symbol rate]] or [[Shannon-Hartley]] [[channel capacity]] for communication systems it refers to [[passband]] bandwidth.

The '''{{vanchor|Rayleigh bandwidth}}''' of a simple radar pulse is defined as the inverse of its duration.  For example, a one-microsecond pulse has a Rayleigh bandwidth of one megahertz.<ref>Jeffrey A. Nanzer, ''Microwave and Millimeter-wave Remote Sensing for Security Applications'', pp. 268-269, Artech House, 2012 {{ISBN|1608071723}}.</ref>

The '''{{vanchor|essential bandwidth}}''' is defined as the portion of a [[signal spectrum]] in the frequency domain which contains most of the energy of the signal.<ref>{{cite book|last=Sundararajan|first=D.|title=A Practical Approach to Signals and Systems|url=https://books.google.com/books?id=1Oo55lFE6UoC&pg=PA109|date=4 March 2009|publisher=John Wiley & Sons|isbn=978-0-470-82354-5|page=109}}</ref>