F. Granelli et al. (Eds.): MOBILIGHT 2009, LNICST 13, pp. 1–14, 2009. © ICST Institute for Computer Sciences, Social-Informatics and Telecommunication Engineering 2009 Thorough Analysis of Downlink Capacity in a WCDMA Cell Ioannis B. Daskalopoulos, Vassilios G. Vassilakis, and Michael D. Logothetis WCL, Dept. of Electrical & Computer Engineering, University of Patras, Patras, Greece {idaskalopou,vasilak,m-logo}@wcl.ee.upatras.gr Abstract. In WCDMA networks, the Call Blocking Probability (CBP) assess- ment is necessary for proper cell capacity determination, in respect of traffic load in erlangs, and network dimensioning. This paper focuses on the downlink capacity estimation, through CBP calculation in a WCDMA cell. To this end, we study an analytical model for the WCDMA cell by taking into consideration the effects of the following: the multi-service environment, the soft blocking, the imperfect power control and multipath propagation. In this model, the maximum transmission power of a base station in the downlink is considered as the shared system resource. To analyze the system, we follow the methodology proposed by Mäder & Staehle, and describe the WCDMA cell by a Markov chain, where each system state represents a certain number of resources occu- pied by mobile users. We solve the Markov chain and provide an efficient re- current formula for the system occupancy distribution, as well as the so-called local blocking probabilities. Based on them, we calculate the CBP of different service-classes accommodated in the cell, versus the total offered traffic load. We evaluate the analytical model through simulation. The results show that the accuracy of the model is very satisfactory. The main contribution of this paper is the improved determination of several parameters involved in the downlink capacity estimation, in comparison to the calculations that appear in the work of Mäder & Staehle. In addition, we show the effect of the intra-cell interference (due to orthogonality factor) on the erlang capacity of the cell. Keywords: WCDMA, downlink capacity, soft blocking, Markov chain, call blocking probability. 1 Introduction Each cell covering a geographical area of a mobile cellular network is controlled by a Base Station (BS) which is named NodeB in Wideband Code Division Multiple Ac- cess (WCDMA) networks. Most of Third Generation (3G) networks operate with WCDMA over the air interface. The system bandwidth in WCDMA is 5MHz with 3.84 Mcps system chiprate [1]. WCDMA networks support applications with different QoS requirements and rates, while offering wide range of voice and data services. Second Generation (2G) systems were designed for symmetric traffic such as voice and SMS. The 3G systems have introduced services, such as multimedia, internet and video stream, which have asymmetric traffic. Given that the offered-traffic load is