Simon Tschirner

Model-based validation of QoS properties of biomedical sensor networks

A Biomedical Sensor Network (BSN) is a small-size sensor network for medical applications, that may contain tens of sensor nodes. In this paper, we present a formal model for BSNs using timed automata, where the sensor nodes communicate using the Chipcon CC2420 transceiver (developed by Texas Instruments) according to the IEEE 802.15.4 standard. Based on the model, we have used UPPAAL to validate and tune the temporal configuration parameters of a BSN in order to meet desired QoS requirements on network connectivity, packet delivery ratio and end-to-end delay. The network studied allows dynamic reconfigurations of the network topology due to the temporally switching of sensor nodes to power-down mode for energy-saving or their physical movements. Both the simulator and model-checker of UPPAAL are used to analyze the average-case and worst-case behaviors. To enhance the scalability of the tool, we have implemented a (new text-based) version of the UPPAAL simulator optimized for exploring symbolic traces of automata containing large data structures such as matrices. Our experiments show that even though the main feature of the tool is model checking, it is also a promising and competitive tool for efficient simulation and parameter tuning. The simulator scales well; it can easily handle up to 50 nodes in our experiments. The model checker installed on a notebook can also deal with networks with 5 up to 16 nodes within minutes depending on the properties checked; these are BSNs of reasonable size for medical applications. Finally, to study the accuracy of our model and analysis results, we compare simulation results by UPPAAL for two medical scenarios with traditional simulation techniques using OMNeT++, one of the most used simulation tools for wireless sensor networks. The comparison shows that our analysis results coincide with the simulation results by OMNeT++ in most cases although there are some differences caused the simplified wireless channel model in UPPAAL.

Credo Methodology

Credo offers tools and techniques to model and analyze highly reconfigurable distributed systems. In this paper, we present an integrated methodology to use the Credo tool suite. In this methodology, we advertise the use of top-down design, component-based modeling and compositional analysis to address the complexity of highly reconfigurable distributed systems. As a running example, we model a peer-to-peer file-sharing system and show how and when to apply the different modeling and analysis techniques of Credo.

Solutions to the problem of inconsistent plans in railway traffic operation

Abstract The demands on modern railway traffic systems are high. Higher efficiency is required, meaning better utilisation of infrastructure capacity and reduced energy consumption. Timeliness has a high priority and safety has to be unconditional. The operation of railway traffic includes many actors in different roles and separate organisations. Our studies of train traffic control have shown that improved collaboration between the actors and advanced control systems are needed to meet the high demands. Instead, many actors are following their own plans based on their own goals and insufficient information. This paper explores the concept of a real-time traffic plan (RTTP) to coordinate collaboration between the different actors, and demonstrates how it can be implemented in systems for train traffic control and driver information. We present the traffic control system STEG and the driver advisory system CATO. Both systems are in use, allowing re-planning and sharing of such an RTTP. Based on these systems, we discuss general and specific design solutions, in accordance with human factors and explain a way of introducing automation that supports the traffic controllers without interfering with their planning. With these systems, we are able to show that a more holistic approach to train traffic control, based on an RTTP, is technically feasible and that sharing this plan with the train drivers substantially improves qualities in train traffic control.

Recognizing Complexity: Visualization for Skilled Professionals in Complex Work Situations

In our research, we study IT-systems for highly skilled professionals in complex and dynamic work situations. Such situations can be found in e.g. health care, process and traffic control and in administration. The demands on the operators/users are often very high concerning quality performance, efficiency, timeliness, safety, communication and cooperation. Our experience shows that human operators can overview, interpret and in real time use an almost unlimited amount of information, if it is relevant to the situation and visualized according to human capabilities. The solution to the visualization problem is therefore not to avoid or hide complexity, but to cope with it, to accept that the complexity must be there. The challenge is to develop systems for visualization and support, which can be used efficiently in relation to the complexity of the work task. We believe in recognizing complexity. First, we describe the scientific foundation of such an approach. Second, we give a detailed example of a complex visualization problem, emphasizing the demanding cognitive operations the operators have to conduct. Finally, we describe the solutions, the visualizations and interactions that make it possible to support the cognitively demanding task, taking care of the complexity without losing the rich amount of information necessary for the operators in different situations, but without adding unnecessary complexity in terms of complicated handling of the user interface and the information systems. Some of these visualizations now run in real systems and have been evaluated, and we end up by suggesting recommendations for successful visualizations in complex work tasks.

Improved railway service by shared traffic information

Many different actors have to collaborate in order to guarantee efficient railway traffic that is safe, on time, comfortable, eco-friendly and economic. Appropriate planning is necessary: The transport company has to provide rolling stock and personnel, the traffic controllers have to solve perturbations proficiently, and the train drivers have to drive in a way, as far as the traffic plan allows, that saves energy and reduces wearing on rolling stock and infrastructure. In order to find a globally optimal solution, all actors need optimal access to information on the current traffic situation. In reality, the situation in European railway traffic is far from optimal: The traffic controllers have limited or delayed knowledge about perturbations and disruptions occurring at tracks, trains, or platforms, while train drivers often have limited or outdated information about the actual traffic plan and the surrounding traffic situation. Information exchange can only happen via telephone. There is a clear need for systems allowing efficient information exchange. We have developed a completely new strategy for train traffic control that focuses on continuous re-planning. This strategy is implemented and evaluated in Sweden. The new system allows sharing the updated traffic plan automatically and it is even connected to a driver advisory system. Combined, these systems clearly improve information exchange between train drivers and traffic controllers. Both systems are designed according to the identified needs of professional traffic controllers and train drivers. This paper presents the problem of insufficient information exchange and our findings in form of design concepts for systems supporting collaboration between train drivers and traffic control.

Authority and level of automation : Lessons to be learned in design of in-vehicle assistance systems

Motor vehicles and drivers’ relationship with them will change significantly in the next decades. Still, most driving tasks are likely to involve humans behind the wheel, emphasizing the design of in-vehicle assistance systems. A framework for distribution of control between human beings and technology is presented, as well as a model to be used in analysis, design, development, and deployment of decision support systems. The framework and the model are applied in a project aiming for design of in-vehicle systems for future long-haul vehicles. The empirical investigations conducted support the design-as-hypotheses approach. The search for improvements of design concepts and levels of automation leads to a shift away from abstract ideas of autonomous cars to empirical issues such as how to support the driver. The need to discuss authority in relation to levels of automation is recognized, emphasizing the fact that human-machine interaction takes place on two distinct levels.

The credo methodology

This paper is an extended version of the Credo Methodology [16]. Credo offers tools and techniques to model and analyze highly reconfigurable distributed systems. In a previous version we presented an integrated methodology to use the Credo tool suite. Following a compositional, component-based approach to model and analyze distributed systems, we presented a separation of the system into components and the network. A high-level, abstract representation of the dataflow level on the network was given in terms of behavioral interface automata and a detailed model of the components in terms of Creol models. Here we extend the methodology with a detailed model of the network connecting these components. The Vereofy tool set is used to model and analyze the dataflow of the network in detail. The behavioral automata connect the detailed model of the network and the detailed model of the components. We apply the extended methodology to our running example, a peer-to-peer file-sharing system.