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.

Evolvability, the ability to respond effectively to change, represents a major challenge to today's high-end embedded systems, such as those developed in the medical domain by Philips Healthcare. These systems are typically developed by multi-disciplinary teams, located around the world, and are in constant need of upgrading to provide new advanced features, to deal with obsolescence, and to exploit emerging enabling technologies.

The performance and dependability of critical infrastructures, such as water-treatment facilities is essential. In this paper we use various performance and dependability measures to analyze a simplified model of a water treatment facility. Building on the existing architectural framework Arcade a model is derived in XML format and then automatically mapped to the model checker PRISM Using the stochastic model checking capabilities that PRISM offers, we compare different repair strategies, with respect to their costs, system reliability, availability and survivability.

Wireless sensor networks (WSNs) are developing into a promising solution for many applications, for example in healthcare. In many scenarios, there is some form of node mobility. The medium access control (MAC) mechanisms should support the expected kind of mobility in the network. Mobility is particularly complicating for contention free MAC protocols like TDMA-based protocols, because they dedicate unique slotsto every node in a neighborhood.

The use of mobile devices is often limited by the battery lifetime. Some devices have the option to connect an extra battery, or to use smart battery-packs with multiple cells to extend the lifetime. In these cases, scheduling the batteries or battery cells over the load to exploit the recovery properties of the batteries helps to extend the overall systems lifetime.

Modern multi-processor systems need to provide guaranteed services to their users. A communication assist (CA) helps in achieving tight timing guarantees. In this paper, we present a CAfor a tile-based MP-SoC. Our CA has smaller memory requirements and a lower latency than existing CAs. The CAhas been implemented in hardware.

Media processing systems often have limited resources and strict performance requirements. An implementation must meet those design constraints while minimizing resource usage and energy consumption. Design-space exploration techniques help system designers to pinpoint bottlenecks in a system for a given configuration.

The concept of Reference Architectures is novel in the business world. However, many architects active in the creation of complex systems frequently use the term Reference Architecture. Yet, these experienced architects do not collectively have a consistent notion of what constitutes a Reference Architecture, what is the value of maintaining the Reference Architecture, what is the best approach to visualizing a Reference Architecture, what is the most appropriate level of abstraction, and how should an architect make use of the Reference Architecture in their work? This paper examines current Reference Architectures and the driving forces behind development of them to come to a collective conclusion on what a Reference Architecture should truly be.