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 Co-channel interference or CCI is crosstalk from two different radio transmitters using the same channel. Co-channel interference can be caused by many factors from weather conditions to administrative and design issues. Co-channel interferen ...

power ''I'', i.e.

crosstalk In electronics, crosstalk is any phenomenon by which a signal transmitted on one circuit or channel of a transmission system creates an undesired effect in another circuit or channel. Crosstalk is usually caused by undesired capacitive, i ...

, from other transmitters than the useful signal. The CIR resembles the

carrier-to-noise ratio In telecommunications, the carrier-to-noise ratio, often written CNR or ''C/N'', is the signal-to-noise ratio (SNR) of a modulated signal. The term is used to distinguish the CNR of the radio frequency passband signal from the SNR of an analog b ...

(CNR or ''C/N''), which is the

signal-to-noise ratio Signal-to-noise ratio (SNR or S/N) is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. SNR is defined as the ratio of signal power to the noise power, often expressed in de ...

(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 Radio resource management (RRM) is the system level management of co-channel interference, radio resources, and other radio transmission characteristics in wireless communication systems, for example cellular networks, wireless local area networks, ...

, while ''N'' involves noise power from other sources, typically

additive white gaussian noise Additive white Gaussian noise (AWGN) is a basic noise model used in information theory to mimic the effect of many random processes that occur in nature. The modifiers denote specific characteristics: * ''Additive'' because it is added to any nois ...

(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.

Carrier-to-noise-and-interference ratio (CNIR)

See also