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 co-channel interference power I, i.e. crosstalk, from other transmitters than the useful signal.{{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}}{{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}}

The CIR resembles the carrier-to-noise ratio (CNR or C/N), which is the 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 radio resource management, while N involves noise power from other sources, typically additive white Gaussian noise (AWGN).