Network Simulations for IS-95 CDMA Systems

Abstract

A simulation methodology on the network planning aspects of TIA/EIA IS-95 CDMA system is presented. The forward and reverse link network performance under various cell site layouts, traffic loads and system parameter settings can be assessed using this simulation model. Effects due to reverse power control, forward power allocation, soft and softer handoff, mobile traffic distribution, and target Eb/Nt are incorporated. The effect of correlated lognormal shadowing can be applied to the radio coverage plots. From the simulation results, it is shown that soft handoff provides significant diversity gains on both forward and reverse links under lognormal shadowing. The reverse capacity loading and forward power allocation statistics of a given base station can be accurately estimated. The forward link radio coverage can be assessed from the available pilot Ec/Io plot, the soft/softer handoff state plot, and the required forward traffic power allocation plot. The reverse link radio coverage can be assessed from the required mobile transmit power plot. All these plots can be generated with and without Monte Carlo shadowing runs. If shadowing is included a specified reliability target can be set for the plots. It is found that the radio coverage is normally reverse link limited due to the lower maximum mobile transmit power. However, poor pilot Ec/Io coverage may exist in the forward link when many base stations have competing signal strengths. The forward traffic channel coverage is generally acceptable in the soft handoff region due to diversity, but may exhibit large fluctuations in regions right before soft handoff, especially for high speed mobiles. The ability to perform fast handoff state update and fast traffic power allocation is important in mitigating these fluctuations. The optimal handoff threshold should be set considering all the following factors. The threshold should be set lower in maintaining the same coverage for a higher load. As long as the coverage objective is achieved for the anticipated load, the threshold should be set higher to reduce the soft handoff probability which incurs equipment overheads. The threshold should also be set low enough to mitigate unstable forward traffic coverage right before handoff as well as providing enough reverse link soft handoff gains so that reverse capacity and coverage can be improved.