Scientific publications

In this chapter we present an overview of decomposition-based analysis techniques for large open queueing networks. We present a general decompositionbased solution framework, without referring to any particular model class, and propose a general fixed-point iterative solution method for it. We concretize this framework bydescribing the well-known QNA method,as proposedby Whitt in the early 1980s, in that context, before describing our FiFiQueues approach.

A good mobility model is an essential prerequisite for performance evaluation of protocols for wireless networks with node mobility. Sensor nodes in a Wireless Body Area Network (WBAN) exhibit high mobility. The WBAN topology may completely change because of posture changes and movement evenwithin a certain typeof posture.

In this paper we address the problem of sink placement for Gossip-based Wireless Sensor Networks (GWSN). Sink placement plays an important role in planning and deployment of sensor networks. It is an efficient means to improve performance and achieve design objectives. Sink deployment requires an optimization strategy to search a space of possible placement options, and a performance evaluation method to assess the quality of different sink placements.

We consider the problem of constructing critical paths from incomplete information. In general, a directed acyclic graph of tasks with their execution times (i.e., a task graph) is necessary to extract critical paths. We assume, however, that only the set of tasks, and their start and end times are known, e.

Wireless sensor networks are typically operating in a dynamic context where events, such as moving sensor nodes and changing external interference, constantly impact the qualityof-service of the network. We present a distributed feedback control mechanism that actively balances multiple conflicting network-wide quality metrics, such as power consumption and end-to-end packet latency, for a heterogeneous wireless sensor network operating in a dynamic context.

Scenario-aware dataflow graphs (SADFs) efficiently model dynamic applications. The throughput of an application is an important metric to determine the performance of the system. For example, the number of frames per second output by a video decoder should always stay above a threshold that determines the quality of the system.

Practical experience reveals the characteristic properties of Wireless Body Area Networks (WBANs), signifying the need for a well-designed communication protocol. High mobility, stringent resource constraints, and low and time-variant quality of wireless links are some of the challenging issues in WBANs.

Adaptation of the network architecture through ondemand data forwarding is an efficient mechanism to provide robustness against long outages in WBANs. We developed an experimental testbed that provides online observation of the network behavior for different data propagation approaches in WBANs. The demonstration shows how different approaches deal with special challenges in WBANs such as low quality of wirelesslinks, topology variations due to posture changes, and mobility.

This paper describes the use of a formal method to support component-based development in the healthcare domain. The method is based on a commercial tool suite which combines formal modeling, compositional model checking, and code generation. The main approach of the tool suite will be explained and demonstrated from a user point of view.

In this paper, we report on our research to improve the creation, implementation, and evolution of interoperability standards. Our approach was to systematically investigate a particular evolving interoperability standard, i.e., Teletext, to obtain relevant and beneficial insights that might generalize to other standards.