Cochannel interference modelling and performance analysis of microcell systems for wireless personal communications

Cochannel interference in microcell radio systems with frequency-selective fading is investigated. Two microcell cochannel interference models, the Rician/Rayleigh model and the Rician/Rayleigh-plus-lognormal model, are presented. In the first model, the desired signal within a microcell experiences Rician fading while interfering signals from cochannel cells are subject to Rayleigh fading. In the second model, the cochannel interfering signals are subject to superimposed Rayleigh fading and lognormal shadowing. Frequency-selective multipath fading is considered in both models. The probability density function of the power ratio between the desired signal and composite interferers is derived. In evaluating the composite interference, both coherent and noncoherent interference addition are considered. Using the probability density function of the signal-to-interference ratio, expressions of the system outage probability are derived. Microcell systems are compared with medium/large-cell systems in terms of the outage probability. It is shown that the former outperform the latter. The effect of frequency-selective multipath fading and that of shadowing on the outage probability are observed. The issue of cochannel reuse distance is studied and the relation between the outage probability and the reuse distance is examined. An “irreducible outage probability” due to frequency-selective multipath fading is observed.