Co-Channel Interference

For cellular radio systems the radio link performance is usually limited by interference rather than noise and, therefore, the probability of co-channel interference (CCI), is of primary concern. The definition of the probability of CCI depends on the the assumptions made about the radio receiver and propagation environment. At higher velocities, the radio receiver can usually average over the fast envelope variations by using coding and interleaving techniques. In this case, the transmission quality will be acceptable provided that the average received carrier-to-interference ratio, Λ, exceeds a receiver threshold Λ_th. The receiver threshold Λ_th is determined by the performance of the radio link in the presence of envelope fading. Once Λ_th has been determined, the variations in Λ due to path loss and shadowing will determine the probability of CCI. At lower velocities, the radio receiver cannot average over the fast envelope variations due to the delay constraints imposed by voice traffic. In this case, the transmission quality will be acceptable provided that the instantaneous received carrier-to-interference ratio, λ, exceeds another receiver threshold λ_th1. Once λ_th has been specified, variations in λ due to path loss, shadowing, and envelope fading, will determine the probability of CCI.