Multiple access interference model in a TD-CDMA system for capacity evaluation and throughput optimization

The aim of this study is to evaluate the performance of UTRA-TDD at a system level by taking into account a tight model of the quality of service (QoS) at a link level. CDMA system capacity evaluation is usually made by assuming the spreading sequences to be random like and the interference distribution to be Gaussian. Therefore, the QoS is related to an equivalent SIR incorporating a mean orthogonality factor between users. In a downlink UTRA-TDD context, these assumptions are not appropriate. Realistic interference distribution is investigated. Two types of receivers are considered: a RAKE receiver and a multi-user detector. A tight analysis of the impact of the interference on the link quality is carried out using exact analytical evaluation, approximate calculus and link level simulations. Simplified QoS metrics are proposed and discussed. These results modeling the link level behavior can be used as inputs for a system level in order to evaluate a power control algorithm or resource allocation strategy.