Outage Probability Estimation for Licensed Systems in the Presence of Cognitive Radio Interference

Cognitive radios (CRs) improve spectral efficiency by transmitting unlicensed signals over licensed frequency bands. A key requirement for CRs is to limit the interference to the licensed system. However, the variability in the radio channel caused by fading and shadowing makes this task more difficult. In this paper the performance of the licensed system has been analysed by calculating the probability of outage of the licensed receiver (LR). A Poisson field of CRs is considered such that the CRs are distributed uniformly around the LR. A circular exclusion zone of radius R has been defined with the LR at the center so that CRs are permitted to transmit only if they are outside this zone. For the first time, expressions for outage probabilities have been developed for different values of R, taking into account the variability in the radio channel. Rayleigh, lognormal and Suzuki channels have been analysed. The effects of channel characteristics on the outage probability have been investigated. Results show the extent to which increasing R improves the performance of the licensed system significantly.