Stochastic modeling and analysis of 3g mobile communication systems

Abstract

Third-generation (3G) mobile communication systems are currently one of the key communication technologies in research and development due to the high market demand for advanced wireless communication. The current evolution is primarily characterized by a transition from circuit-switched voice-oriented networks to integrated multi-service all IP networks. To effectively design complex mobile communication systems, the design process should be accompanied by stochastic modeling and quantitative evaluation of different design alternatives. The most popular language for model specification used in industrial projects is the Unified Modeling Language (UML). Although conceived as a general-purpose modeling language, the current version of the UML does not contain building blocks for introducing stochastic timing into UML diagrams. The first part of this thesis presents new results for numerical quantitative analysis of discreteevent stochastic systems specified in Petri net notation or as UML diagrams. An efficient algorithm for the state space generation out of an UML state diagram or activity diagram that allows quantitative analysis by means of the underlying stochastic process is presented. Furthermore, this thesis considers new methodological results for the effective numerical analysis of finite-state generalized semi-Markov processes with exponential and deterministic events by an embedded general state space Markov chain (GSSMC). Key contributions constitute (i) the observation that elements of the transition kernel of the GSSMC can always be computed by appropriate summation of transient state probabilities of continuous-time Markov chains and (ii) the derivation of conditions under which kernel elements are constant. To provide automated tool support, the presented algorithms are included in the software package DSPNexpress-NG available for download on the Web. The support of multimedia services over wireless channels presents a number of technical challenges. One of the major challenges is to effectively utilize the scarce radio bandwidth in the access network by adaptive control of system parameters. The second part of this thesis is devoted to this topic. A Markov model representing the sharing of radio channels by circuitswitched connections and packet-switched sessions under a dynamic channel allocation scheme is evaluated. Closing the loop between network operation and network control, a framework for the adaptive quality of service management for 3G mobile networks is introduced. Building on this framework, a novel call admission control and bandwidth reservation scheme for the optimization of quality of service for mobile subscribers is presented. The performance of the solutions proposed in this thesis is investigated experimentally based on numerical quantitative analysis and discrete-event simulation.