New techniques for the calculation of the average SIR and the outage probability of the uplink of CDMA systems

New techniques for the calculation of the average signal-to-interference ratio (SIR) and the outage probability of the uplink of a single cell CDMA based mobile communications system are introduced. We show the differences between the often employed lower bound on the average SIR and the exact value of the average SIR. These differences are significant if the variance of the SIR gets higher which will affect the outage probability. A high signal-to-noise ratio, a low voice activity factor and a high grade of imperfection of the power control system cause a higher variance of the SIR. These effect is emphasized especially if there is a few number of subscribers. Usually, in the literature the capacity of such CDMA based mobile systems is often calculated by employing a lower bound on the average SIR. Generally, our basic approach shows that this is not possible.