Analytic Modelling of the WCDMA Downlink Capacity in Multi-Service Environments

The Universal Mobile Telecommunication System (UMTS) operates with Wideband Code Division Multiple Access (WCDMA) over the air interface. In the literature, the CDMA uplink, e.g. as implemented by the IS-95 standard, receives most attention due to its limiting influence on the overall network capacity in voice only environments. But with the growing demand of the mobile user for multimedia content, the 3G systems like UMTS provide service classes specifically designed for asymmetric traffic such as video streams. This makes the WCDMA downlink (forward link) the potential bottleneck for the network capacity. Another distinction of WCDMA to IS-95 is the introduction of fast power control mechanisms on the downlink. In this paper, we propose an analytic algorithm to approximate the WCDMA downlink cell capacity in a multi-service environment. It is based on a recursion formula and includes the effects of soft blocking and imperfect power control. Due to its design, the algorithm is time and memory efficient and is well suited for the use in network planning tools for e.g. capacity planning or dimensioning issues.