Effect of multicode interference on the downlink capacity of a UMTS TDD CDMA cellular system

The impact of multicode transmission on the capacity of a UMTS TDD CDMA system is investigated. The interference incurred by using such a transmission technique is often overlooked, resulting in optimistic performance evaluations. The multicode interference contribution is expressed in closed-form. This multicode contribution can be integrated to existing capacity studies without great restructuring needs. The performance degradation is assessed by using a multi-cell multi-service system-level simulation tool that evaluates the capacity of the system with and without multicode interference. The simulation tool parameters are based on principles and assumptions of 3GPP. The main results of this study show that a network with high-rate users in a vehicular environment can suffer from a substantial performance degradation due to multicode transmission, especially if the orthogonality between channelization codes cannot be maintained.