stochastic modeling and analysis of 3g mobile communication systems

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 discrete-event 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 circuit-switched 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

Performance modeling tools with applications

This paper deals with the role of performance modeling tools. It introduces 3 major tool development centers and shows how a given tool can be applied to investigate the performance of a finite-source retrial queueing system

List of requirements on formalisms and selection of appropriate tools

This deliverable reports on the activities for the set-up of the modelling environments for the evaluation activities of WP5. To this objective, it reports on the identified modelling peculiarities of the electric power infrastructure and the information infrastructures and of their interdependencies, recalls the tools that have been considered and concentrates on the tools that are, and will be, used in the project: DrawNET, DEEM and EPSys which have been developed before and during the project by the partners, and M\uf6bius and PRISM, developed respectively at the University of Illinois at Urbana Champaign and at the University of Birmingham (and recently at the University of Oxford)

A probabilistic extension of UML statecharts: specification and verification

This paper is the extended technical report that corresponds to a published paper [14]. This paper introduces means to specify system randomness within UML statecharts, and to verify probabilistic temporal properties over such enhanced statecharts which we call probabilistic UML statecharts. To achieve this, we develop a general recipe to extend a statechart semantics with discrete probability distributions, resulting in Markov decision processes as semantic models. We apply this recipe to the requirements-level UML semantics of [8]. Properties of interest for probabilistic statecharts are expressed in PCTL, a probabilistic variant of CTL for processes that exhibit both non-determinism and probabilities. Verification is performed using the model checker Prism. A model checking example shows the feasibility of the suggested approach

Methodologies synthesis

This deliverable deals with the modelling and analysis of interdependencies between critical infrastructures, focussing attention on two interdependent infrastructures studied in the context of CRUTIAL: the electric power infrastructure and the information infrastructures supporting management, control and maintenance functionality. The main objectives are: 1) investigate the main challenges to be addressed for the analysis and modelling of interdependencies, 2) review the modelling methodologies and tools that can be used to address these challenges and support the evaluation of the impact of interdependencies on the dependability and resilience of the service delivered to the users, and 3) present the preliminary directions investigated so far by the CRUTIAL consortium for describing and modelling interdependencies