Capacity and performance issues in UMTS FDD WCDMA system for the support of mixed heterogeneous services are investigated. The focus is on the downlink with traffic corresponding to UMTS quality of service (QoS) classes. After an initial capacity evaluation on a single service basis, the work is directed to assess the system performance in mixed services. The study aims at discerning the mutual interactions that exist among the services and evaluating the relationships between system performance and service characteristics. The emphasis is on how system performance and service behavior are inter-related in mixed traffic configurations and thus get an insight into resource control. The results are collected in terms of percentage of satisfied users, user blocking, probability of outage, throughput and delay. The analysis indicates that high data rate users are the most demanding and care must be taken at resource allocation to achieve QoS targets.