Ubiquitous Computing and Communication Journal 4 MODELING AND DIMENSIONING OF THE IUB INTERFACE IN THE UMTS NETWORK M. Stasiak, J. Wiewióra, P. Zwierzykowski Poznan University of Technology, Chair of Communication and Computer Networks ul. Polanka 3, 60965 Poznan, Poland e-mail: pzwierz@et.put.poznan.pl ABSTRACT The article presents a new analytical method for blocking probability determination in the interface of the UMTS network. In our consideration we use a modified model of full-availability group with multi-rate traffic. The proposed scheme is applicable for cost-effective IuB resource management in 3G mobile networks and can be easily applied to network capacity calculations. Keywords: modeling, dimensioning, UMTS, IuB interface 1 INTRODUCTION Universal Mobile Telecommunications System (UMTS) using the WCDMA radio interface is one of the standards proposed for third generation cellular technologies (3G). According to the 3rd Generation Partnership Project (3GPP) recommendations, 3G systems should include services with circuit switching and packet switching, transmit data at a speed of up to 7,2 Mbit/s, and ensure access to multimedia services [1]. The dimensioning process for the UMTS system should make it possible to determine such a capacity of individual elements of the system that will secure - with the assumed load of the system - a pre-defined level of Grade of Service (GoS). With dimensioning the UMTS system, the most characteristic constraints are: radio interface and the IuB interface. When the radio interface is a constraint, then, in order to increase the capacity, access technology should be changed or subsequent branches of the system should be added (another NodeB). If, however, the constraint on the capacity of the system results from the capacity of the IuB interface, then a decision to add other stations (nodes) can be financially unfounded, having its roots in incomplete or incorrect analysis of the system. This means that in any analysis of the system, a model that corresponds to the IuB interface should be routinely included. Because of the possibility of resource allocation for different traffic classes, the capacity determination of the WCDMA radio interface is much more complex than in the case of GSM systems. The capacity of the WCDMA interface is limited by the increase in interference, which is caused by the users serviced by other cells of the system who make use of the same frequency channel as well as by the users making use of the adjacent radio channels and by the multipath propagation occurring in the radio channel. To ensure an appropriate level of service in UMTS it is thus necessary to limit interference by decreasing the number of active users or the allocated resources employed to service them. Several papers have been devoted to traffic modelling in cellular systems with the WCDMA radio interface [2-14,21]. To date, however, no IuB models that take the dynamic resource allocation for different services into account have been considered by any author simultaneously. 1 This article presents a blocking probability determination method for a cellular system with the IuB interface and a dynamic resource allocation scheme. The article has been divided into five sections. Section 2 discusses basic dependencies describing the IuB interface in the UMTS network. Section 3 presents an analytical model applied for a blocking probability determination for static and dynamic resource allocation for different traffic classes. The following section includes the results obtained in the study of the system. The final section sums up the discussion. 2 ARCHITECTURE OF THE UMTS NETWORK Let us consider the structure of the UMTS network presented in Fig. 1. The presented network consists of three functional blocks designated respectively: UE (User Equipment), UTRAN (UMTS Terrestrial Radio Access Network) and CN (Core Network). The following notation has been adopted in Fig. 1: RNC is the Radio Network Controller, Uu is the radio interface and IuB is the interface connecting Node B and RNC. 1 This article is the extended version of the paper published on CSNDSP 2008 [20].