View source for Engineering:Signal-to-interference ratio

{{Short description|Ratio of useful signal versus co-channel interference received}}
The '''signal-to-interference ratio''' ('''SIR''' or '''''S/I'''''), also known as the '''carrier-to-interference ratio''' ('''CIR''' or '''''C/I'''''), is the quotient between the average received modulated carrier power ''S'' or ''C'' and the average received [[Physics:Co-channel interference|co-channel interference]] power ''I'', i.e. [[Crosstalk|crosstalk]], from other transmitters than the useful signal.<ref>{{Cite book |last=Schwartz |first=Mischa |url=https://books.google.com/books?id=rAiyyKM9ppoC |title=Mobile Wireless Communications |date=2005 |publisher=Cambridge University Press |isbn=978-0-521-84347-8 |pages=63–64 |language=en}}</ref><ref>{{Cite web |title=Signal to Interference Ratio - an overview {{!}} ScienceDirect Topics |url=https://www.sciencedirect.com/topics/computer-science/signal-to-interference-ratio |access-date=2023-01-11 |website=www.sciencedirect.com}}</ref> 

The CIR resembles the [[Engineering:Carrier-to-noise ratio|carrier-to-noise ratio]] (CNR or ''C/N''), which is the [[Physics:Signal-to-noise ratio|signal-to-noise ratio]] (SNR or ''S/N'') of a modulated signal before demodulation. A distinction is that interfering radio transmitters contributing to ''I'' may be controlled by [[Physics:Radio resource management|radio resource management]], while ''N'' involves noise power from other sources, typically [[Additive white Gaussian noise|additive white Gaussian noise]] (AWGN).

==Carrier-to-noise-and-interference ratio (CNIR)==
The CIR ratio is studied in interference limited systems, i.e. where ''I'' dominates over ''N'', typically in cellular radio systems and broadcasting systems where frequency channels are reused in view to achieve high level of area coverage. The ''C/N'' is studied in noise limited systems. If both situations can occur, the carrier-to-noise-and-interference ratio (CNIR or ''C/(N+I)'') may be studied. 

==See also==
* [[Engineering:Carrier-to-noise ratio|Carrier-to-noise ratio]] (CNR or ''C''/''N'')
* Carrier-to-receiver noise density ''C/''N''<sub>0</sub>
* [[Physics:Co-channel interference|Co-channel interference]] (CCI)
* [[Crosstalk]]
* [[Physics:Signal-to-noise ratio|Signal-to-noise ratio]] (SNR or ''S''/''N'')
* [[Engineering:SINAD|SINAD]] (ratio of signal-plus-noise-plus-distortion to noise-plus-distortion)

== References ==
{{Reflist}}{{Noise}}

[[Category:Engineering ratios]]
[[Category:Radio frequency propagation]]
[[Category:Interference]]
[[Category:Television terminology]]



{{Sourceattribution|Signal-to-interference ratio}}