Editing Carrier system (section)

{{more footnotes|date=January 2013}}

A '''carrier system''' is a [[transmission system]] that [[transmission (telecommunications)|transmits]] information, such as the voice signals of a [[telephone call]] and the video signals of [[television]], by modulation of one or multiple [[carrier signal]]s above the principal voice frequency or data rate.<ref name=weco>Western Electric (1969) ''Fundamentals of Telephone Communication Systems'', p.16.2</ref>

Carrier systems typically transmit multiple channels of communication simultaneously over the [[shared medium]] using various forms of [[multiplexing]]. Prominent multiplexing methods of the [[carrier signal]] are [[time-division multiplexing]] (TDM) and [[frequency-division multiplexing]] (FDM). A [[cable television system]] is an example of frequency-division multiplexing. Many television programs are carried simultaneously on the same [[coaxial cable]] by sending each at a different frequency. Multiple layers of multiplexing may ultimately be performed upon a given input [[signal]]. For example, in the [[public switched telephone network]], many telephone calls are sent over shared trunk lines by time-division multiplexing. For long-distance calls several of these channels may be sent over a [[communications satellite]] link by frequency-division multiplexing. At a given receiving [[node (networking)|node]], specific channels may be demultiplexed individually.