Editing Single-frequency network (section)

{{short description|Broadcast network}}
{{other uses|SFN (disambiguation)}}
A '''single-frequency network''' or '''SFN''' is a [[broadcast network]] where several [[transmitter]]s simultaneously send the same signal over the same [[frequency]] channel.

[[File:SFN model.svg|thumb|upright|'''Single Frequency Network model'''<br />Top:Multi Frequency Network<br />Bottom:Single Frequency Network]]
Analog [[amplitude modulation|AM]] and [[Frequency modulation|FM]] radio broadcast networks as well as digital broadcast networks can operate in this manner. SFNs are not generally compatible with [[analog television]] transmission, since the SFN results in [[ghosting (television)|ghosting]] due to echoes of the same signal.

A simplified form of SFN can be achieved by a low power co-channel [[Repeater#Radio repeater|repeater]], booster or [[broadcast translator]], which is utilized as a gap filler transmitter.

The aim of SFNs is efficient utilization of the [[radio spectrum]], allowing a higher number of radio and TV programs in comparison to traditional [[multi-frequency network]] (MFN) transmission. An SFN may also increase the coverage area and decrease the outage probability in comparison to an MFN, since the total received signal strength may increase to positions midway between the transmitters.

SFN schemes are somewhat analogous to what in non-[[Broadcasting|broadcast]] wireless communication, for example [[cellular network]]s and wireless computer networks, is called transmitter [[macrodiversity]], [[CDMA]] [[soft handoff]] and [[Dynamic Single Frequency Network]]s (DSFN).

SFN transmission can be considered as creating a severe form of [[multipath propagation]]. The radio receiver receives several echoes of the same signal, and the constructive or destructive [[Interference (wave propagation)|interference]] among these echoes (also known as '''self-interference''') may result in [[fading]]. This is problematic especially in [[wideband]] communication and high-data rate digital communications, since the fading in that case is frequency-selective (as opposed to flat fading), and since the time spreading of the echoes may result in [[intersymbol interference]] (ISI). Fading and ISI can be avoided by means of [[diversity scheme]]s and [[Equalization (communications)|equalization filter]]s.

Transmitters, which are part of a SFN, should not be used for navigation via [[direction finding]] as the direction of signal minima or signal maxima can differ from the direction to the transmitter.