Link quality in SIR based power control for UMTS CDMA systems

This paper examines the related issues of capacity, coverage and power control in a multi-cell WCDMA network. The network capacity in this case is based on required link quality thresholds. If all users achieve the required link SIR targets for a given percentage of all power control time slots, the network is deemed not to have exceeded its capacity. When this is 50%, the analysis reverts to the conventional mean SIR target performance. For network operators however a substantially higher link quality requirement is likely. In this case, 95% is considered. This means all users must achieve a SIR of greater than or equal to the target value for 95% of the time. The analysis is based on extended models used for IS-95 systems which relies on Gaussian assumptions of interference. This approach gives an insight into the effects of varying traffic types, different allowances for SIR targets and mixed traffic. This paper presents analysis which allows the minimum required power control to be determined based on network load and traffic mix. It also presents analysis which allows the impact of mobile by mobile power control to be examined.