Investigations into Cochannel Interference in Microcellular Mobile Radio Systems

A microcell interference model termed the Nakagami m,/m, is introduced in this paper. The desired signal as well as the cochannel interferers are assumed to have Nakagami statistics but with different amounts of fading. A special case of this model is obtained when the desired signal has Nakagami statistics while the cochannel interferers are subject to Rayleigh fading. The probability density function of the signal-to-interference ratio in the Nakagami m,/m, model is derived. This model is also compared with a Rician/Rayleigh microcellular model. The Nakagami m,/m, model is chosen to investigate the microcellular systems because Nakagami distributions fit experimental data better than either Rayleigh or Rician distributions in many cases. Expressions for the outage probabilities in microcell systems are derived. Numerical results show that, compared to medium/large cell systems, the microcellular systems have a lower outage probability. The impact of diversity on the microcellular system is also studied. Both signal-to-noise plus interference ratio selection diversity and signal-plus-interference selection diversity are investigated and an improvement to the outage probability due to diversity is observed.