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

Abstract

Cochannel interference in microcell radio systems with frequency-selective fading is investigated in this paper. 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.Dans cet article, nous analysons l'interférence entre les canaux des systèmes microcellulaires en présence d'évanouissements sélectifs en fréquence. Deux modélisations de l'interférence entre canaux sont proposées: la première utilise le modèle de Rice/Rayleigh et la seconde utilise le modèle de Rice/Rayleigh incluant l'affaiblissement Log-Normal. Dans le premier modèle, le signal utile à l'intérieur d'une cellule donnée est soumis à des affaiblissements de type Rice tandis que les signaux interférents provenant des autres canaux sont soumis à des affaiblissements de Rayleigh. Dans le second modèle, les signaux interférents provenant des autres canaux sont soumis à la fois à des affaiblissements de Rayleigh et à des phénomènes d'ombrage de type Log-Normal. Pour ces deux modèles, nous considérons également des évanouissements sélectifs en fréquence introduits par les phénomènes de multi-trajets. Une expression de la fonction de densité de probabilité du rapport de la puissance du signal utile à la puissance des signaux interférents est également donnée. Lors de l'évaluation du signal interfèrent composite, nous avons considéré à la fois des interférences additives cohérentes et noncohérentes. À partir de la fonction de densité de probabilité du rapport Signal à Interférents, nous dérivons des expressions de la probabilité de coupure. Cette dernière est ensuite utilisée pour comparer les performances des systèmes microcellulaires avec celles des systèmes cellulaires moyens/grands. Nous montrons que le premier système donne de meilleures performances que le second. Les effets des évanouissements s...

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