Carrier to Interference Ratio (CIR) is a characteristic value from mobile radio technology that stands for the effectiveness of the radio signal and depends on the number of active subscribers in a radio cell.
The CIR ratio is determined from the level ratio of the carrier frequency (CW) to the interference (I) and is specified in decibels (dB). Carrier signals are adversely affected in quality by adjacent interference, noise and other background signals.
The carrier to interference ratio is directly dependent on the number of active subscribers in a radio cell. As the number of subscribers increases, interference increases and the carrier-to-interference ratio deteriorates. If the CIR ratio for UMTS is 0 dB for one subscriber, it is about -15 dB for 50 subscribers and -20 dB for 100 subscribers.