Christoph Weyer

Prediction accuracy of link-quality estimators

The accuracy of link-quality estimators (LQE) is missioncritical in many application scenarios in wireless sensor networks (WSN), since the link-quality metric is used for routing decisions or neighborhood formation. Link-quality estimation must offer validity for different timescales. Existing LQEs describe and approximate the current quality in a single value only. This method leads to a limited accuracy and expressiveness about the presumed future behavior of a link. The LQE developed in this paper incorporates four quality metrics that give a holistic assessment of the link and its dynamic behavior; therefore, this research is an important step to achieving a higher prediction accuracy including knowledge about the short- and long-term behavior.

Scheduling Transmission of Bulk Data in Sensor Networks Using a Dynamic TDMA Protocol

Sensor networks are increasingly used in applications where sensors periodically measure data with high rates. The reliable transport of high volumes of sampled data through a multi-hop network with limited resources requires sophisticated protocols. This paper presents a novel protocol for this task that uses minimal energy, provides high throughput, and requires only small amounts of additional buffer. The protocol is based on a dynamic TDMA scheme and is robust against omission failures.

Long-term Reliable Data Gathering Using Wireless Sensor Networks

This paper presents the design of a long-term reliable data gathering service for many-to-one communication in wireless sensor networks: all nodes send periodically delay- tolerant data to a single node. The service operates reliably despite strict resource constraints, poor link qualities, and frequent disconnects. This paper presents a novel protocol for gathering periodically measured data including a solution for the wear-leveling problem of the EEPROM. Furthermore, theoretical limits of this approach based on available bandwidth and local memory are provided. Finally, preliminary results of an implementation of the service are presented. In particular, a detailed analysis of the energy consumption during the different phases of this experiment is provided.

Randomized self-stabilizing algorithms for wireless sensor networks

Wireless sensor networks (WSNs) pose challenges not pre- sent in classical distributed systems: resource limitations, high failure rates, and ad hoc deployment. The lossy nature of wireless communication can lead to situations, where nodes lose synchrony and programs reach arbitrary states. Traditional approaches to fault tolerance like replication or global resets are not feasible. In this work, the concept of self-stabilization is applied to WSNs. The majority of self-stabilizing algorithms found in the literature is based on models not suitable for WSNs: shared memory model, central daemon scheduler, unique processor identifiers, and atomicity. This paper proposes problem-independent transformations for algorithms that stabilize under the central daemon scheduler such that they meet the demands of a WSN. The transformed algorithms use randomization and are probabilistically self-stabilizing. This work allows to utilize many known self-stabilizing algorithms in WSNs. The proposed transformations are evaluated using simulations and a real WSN.

Automated CORBA-based application management

Enterprises are more and more dependent on business processes which are based on distributed computer applications. Business processes are adapted frequently to the changing enterprise needs. In order to support such requirements, middlewarebased distributed multi-tier application architectures have been developed. Managing such complex distributed environments with respect to availability, performance etc. is a complicated task. The integration of traditional systems and network management disciplines together with application management is a first step towards necessary solutions. This paper describes an architecture and the current project status of a flexible management environment primarily used for configuration, event and performance management of distributed applications. The CORBA middleware is used for integrating the management objects, relying on gateways for incorporating traditional environments, like SNMP. CORBA services are used to build higher-level management functions, e.g. for representing the information model or for distributing events. Thus, delegated management functionality and flexibility in configuring management applications is achieved. For automating standard management procedures, which is considered critical for the future acceptance of distributed systems, an automata-based approach has been selected. The overall approach is currently applied for the management of CORBA applications.

Application specific vs. standard Web service interfaces for the vertical integration of fieldbus systems

The paper compares two approaches for developing Web service interfaces for the vertical integration of TTP/A fieldbus systems. High-level abstractions are provided by application specific interfaces, generated from metadata describing fieldbus systems. In contrast standardised interfaces such as OPC XML DA only allow lower levels of abstractions. But these enable accessing the fieldbus system from a broad range of standard clients, while high-level abstractions reflecting the application programmers view on the system facilitate the development of more specific clients and workflows.

A Dynamic Topology Control Algorithm for Wireless Sensor Networks

Topology control algorithms TCAs are used in wireless sensor networks to reduce interference by carefully choosing communication links. Since the quality of the wireless channel is subject to fluctuations over time TCAs must repeatedly recompute the topology. TCAs ensure quick adjustment to new or deteriorating links while preventing precipitant changes due to transient faults. This paper contributes a novel dynamic TCA that provides a compromise between agility and stability, and constructs connected topologies for low latency routing. Furthermore, it enforces memory restrictions and is of high practical relevance for real sensor network hardware.

TDMA-Schemes for Tree-Routing in Data Intensive Wireless Sensor Networks

A particular class of data intensive wireless sensor networks are those networks where sensors periodically measure data with high rates. The focus of this work is on the efficient transport of high volumes of sampled data through a multi-hop network with limited resources using a routing tree. This paper analyzes TDMA schemes for this purpose with respect to buffer usage and energy consumption. In particular, it is shown, that classical TDMA schemes are not optimal for tree-routing in data-intensive sensor networks.

SelfWISE: A Framework for Developing Self-Stabilizing Algorithms

This paper introduces SelfWISE, a framework for enabling wireless sensor networks to be programmed in a self-stabilizing manner. The framework eases the formal specification of algorithms by abstracting from low-level details such as wireless channel and hardware-specific characteristics, SelfWISE consists of a language for expressing self-stabilizing algorithms; a runtime environment for simulating algorithms in wireless sensor networks, and supporting tools. The hereby applied transformation of formally described algorithms into the simulation environment preserves the self-stabilizing properties. Development, evaluation, and debugging of self-stabilizing algorithms is considerably facilitated by utilizing SelfWISE.

Performance of energy-efficient TDMA schemes in data-gathering scenarios with periodic sources

Energy-efficient transportation of periodical sensor readings towards a single sink in wireless sensor networks is a challenging task. In general, two data-gathering strategies exist: on-demand and bulk data forwarding. For both strategies, cross-layer techniques are a promising approach, where TDMA is tailored to the underlying routing tree. Therefore, different TDMA schemes are compared regarding achievable throughput, packet delay, and energy-efficiency for various sampling rates and scenarios. Existing schemes perform well in dedicated topologies only. The new and simple TDMA scheme presented in this paper outperforms its predecessors in all scenarios under consideration. These findings are substantiated by both theoretical analysis and extensive simulation.