A Simple Analysis of CDMA Soft Handoff Gain and its Effect on the Cell’s Coverage Area

This paper presents an analysis of soft handoff and its effect on the coverage area of a CDMA system. The analysis is based on the determination of outage probabilities around the system’s coverage area, incorporating in part the effects of CDMA reverse link power control and soft handoff gains. We obtain the probability of service at the edge of the cell and hence the area reliability of the CDMA system. We also examine the dependence of the service probability and the area reliability on the soft handoff area and the required fade margin. A CDMA network planning tool based on the soft handoff analyses has been used to calculate the average outage probability (area reliability) on a site-by-site basis. It is observed that the outage probability is underestimated if the analysis is entirely conditioned on soft handoff. It is shown that the soft handoff gain is dependent on the percentage of median area in handoff and on the probability of handoff. The soft handoff gain over hard handoff is around 4 dB for about 40% – 50% median area in soft handoff.