Jörg Hähner

TinyCubus: a flexible and adaptive framework sensor networks

With the proliferation of sensor networks and sensor network applications, the overall complexity of such systems is continuously increasing. Sensor networks are now heterogeneous in terms of their hardware characteristics and application requirements even within a single network. In addition, the requirements of currently supported applications are expected to change over time. All of this makes developing, deploying and optimizing sensor network applications an extremely difficult task. In this paper, we present the architecture of TinyCubus, a flexible and adaptive cross-layer framework for TinyOS-based sensor networks that aims at providing the necessary infrastructure to cope with the complexity of such systems. TinyCubus consists of a data management framework that selects and adapts both system and data management components, a cross-layer framework that enables optimizations through cross-layer interactions, and a configuration engine that installs components dynamically. Furthermore, we show the feasibility of our architecture by describing and evaluating a code distribution algorithm that uses application knowledge about the sensor topology in order to optimize its behavior.

A meta-model and framework for user mobility in mobile networks

Mobility patterns play an important role for performance evaluations of mobile networks. To simulate user movement, existing simulation tools provide only a few simple mobility models (e.g., random movement) suitable for particular scenarios. To evaluate a new scenario, an appropriate model needs to be created, but this requires extra work that distracts the researcher from his/her main task. In general, three key elements determine the mobility of users: the spatial environment, the user trip sequences, and the user movement dynamics (e.g., speed). In this paper, we introduce a meta-model that integrates these three elements in an easy-to-use framework, allowing a flexible modeling of user mobility in custom scenarios. The framework is available for download as a stand-alone trace generator and may be used together with any simulation or emulation tool for mobile networks to evaluate a specific scenario.

Requirements of Peer-to-Peer-based Massively Multiplayer Online Gaming

Massively multiplayer online games have become increasingly popular. However, their operation is costly, as game servers must be maintained. To reduce these costs, we aim at providing a communication engine to develop massively multiplayer online games based on a peer-to-peer system. In this paper we analyze the requirements of such a system and present an overview of our current work.

Observation and Control of Organic Systems

Organic Computing (OC) assumes that current trends and recent developments in computing, like growing interconnectedness and increasing computational power, pose new challenges to designers and users. In order to tackle the upcoming demands, OC has the vision to make systems more life-like (organic) by endowing them with abilities such as self-organisation, self-configuration, self-repair, or adaptation. Distributing computational intelligence by introducing concepts like self-organisation relieves the designer from exactly specifying the low-level system behaviour in all possible situations. In addition, the user has the possibility to define a few high-level goals, rather than having to manipulate many low-level parameters.

Organic traffic light control for urban road networks

In recent years, autonomic and organic computing have become areas of active research in the informatics community. Both initiatives aim at handling the growing complexity in technical systems by focusing on adaptation and self-optimisation capabilities. A promising application for organic concepts is the control of road traffic signals in urban areas. This article presents an organic approach to traffic light control in urban areas that exhibits adaptation and learning capabilities, allowing traffic lights to autonomously react on changing traffic conditions. A coordination mechanism for neighbouring traffic lights is presented that relies solely on locally available traffic data and communication among neighbouring intersections, resulting in a distributed and self-organising traffic system for urban areas. The organic systems efficiency is demonstrated in a simulation-based evaluation.

Spatial Partitioning in Self-Organizing Smart Camera Systems

We propose a decentralized, self-organizing system architecture for wireless networked smart cameras (SCs) with pan, tilt, and zoom abilities. Each SC communicates with its neighbors and independently calculates the optimal position for its field of view. Thereby, SCs autonomously organize themselves and spatially partition the area they observe. This is achieved by a decentralized algorithm that makes way for self-organization in SC systems. The system quickly adapts to new situations caused by joining and failing nodes. Simulations with hundreds of cameras show that scalability and reliability are achieved. We analyze the performance of different camera densities and show that optimal surveillance coverage is achieved in a short time (20 s) while maintaining low communication traffic using a simulated 350-node outdoor SC system.

Towards Trust in Desktop Grid Systems

The Organic Computing (OC) Initiative deals with technical systems, that consist of a large number of distributed and highly interconnected subsystems. In such systems, it is impossible for a designer to foresee all possible system configurations and to plan an appropriate system behaviour completely at design time. The aim is to endow such technical systems with the so-called self-X properties, such as self-organisation, self-configuration or self-healing. In such dynamic systems, trust is an important prerequisite to enable the usage of Organic Computing systems and algorithms in market-ready products in the future. The OC-Trust project aims at introducing trust mechanisms to improve and assure the interoperability of subsystems. In this paper, we deal with aspects of organic systems regarding trustworthiness on the subsystem level (agents) in a desktop grid system. We develop an agent-based simulation of a desktop grid to show, that the introduction of trust concepts improves the systems performance, in such that they speed up the processes on the agent level. Specifically, we investigate a bottom-up self-organised development of trust structures that create coalition groups of agents that work more efficiently than standard algorithms. Here, an agent can determine individually to what extent it belongs to a Trusted Community.

Organic traffic control

Urban road networks are an infrastructural key factor for modern cities. To facilitate an efficient transportation of people and goods, it is crucial to optimise the networks’ signalisation and to route drivers quickly to their destination. As road networks are widespread and their traffic demands are dynamically changing, adaptive and self-organising (and therefore organic) control systems are required. This article demonstrates the potential benefits of organic traffic control: It presents an Observer/Controller that optimises an intersection’s signalisation and introduces a self-organising coordination mechanism that allows for the traffic-responsive creation of progressive signal systems (or green waves). All presented mechanisms advance the state of the art and help to reduce the negative environmental and economical impact of traffic.

Efficiency and Robustness Using Trusted Communities in a Trusted Desktop Grid

Bringing forward trust from social systems to system-to-system level can lead to efficiency and robustness improvements in self-organising complex systems. In this paper, we show how trust can enhance the matchmaking and robustness regarding malicious nodes in a Desktop Grid and Volunteer Computing System (DGVCS). We give the agent a suited degree of autonomy to continuously adapt to their environment in both worker and submitter role. In this paper, we introduce adaptivity in submitter and worker role for our trust-adaptive agents. The evaluation shows that using trust based adaptivity algorithms in a DGVCS leads to efficiency improvements and robustness regarding malicious nodes.

A protocol for data dissemination in frequently partitioned mobile ad hoc networks

Distribution of data in mobile ad hoc networks is challenged when the mobility of nodes leads to frequent topology changes. Existing approaches so far address either the network partitioning problem or are capable of handling large amounts of data, but not both at the same time. In this paper, a novel approach is presented which is based on a negotiation scheme enhanced by an adaptive repetition strategy. Different strategies for the selection of repeated data are presented and evaluated. Simulation results show a reduction of data transfer volume compared to hyper-flooding by 30% to 40% even in the presence of frequent network partitions.