Jochen H. Schiller

Connecting Wireless Sensornets with TCP/IP Networks

Wireless sensor networks are based on the collaborative efforts of many small wireless sensor nodes, which collectively are able to form networks through which sensor information can be gathered. Such networks usually cannot operate in complete isolation, but must be connected to an external network through which monitoring and controlling entities can reach the sensornet. As TCP/IP, the Internet protocol suite, has become the de-facto standard for large-scale networking, it is interesting to be able to connect sensornets to TCP/IP networks. In this paper, we discuss three different ways to connect sensor networks with TCP/IP networks: proxy architectures, DTN overlays, and TCP/IP for sensor networks. We conclude that the methods are in some senses orthogonal and that combinations are possible, but that TCP/IP for sensor networks currently has a number of issues that require further research before TCP/IP can be a viable protocol family for sensor networking.

Utilizing solar power in wireless sensor networks

Sensor networks are designed especially for deployment in adverse and non-accessible areas without a fixed infrastructure. Therefore, energy conservation plays a crucial role for these networks. We propose to utilize solar power in wireless sensor networks, establishing a topology where, changing over time, some nodes can receive and transmit packets without consuming the limited battery resources. We propose and evaluate two protocols that perform solar-aware routing. The presented simulation results show that both protocols provide significant energy savings when utilizing solar power. The paper shows that incorporating the solar status of nodes in the routing decision is feasible and results in reduced overall battery consumption.

CrossTalk: cross-layer decision support based on global knowledge

The dynamic nature of ad hoc networks makes system design a challenging task. Mobile ad hoc networks suffer from severe performance problems due to the shared, interference-prone, and unreliable medium. Routes can be unstable due to mobility and energy can be a limiting factor for typical devices such as PDAs, mobile phones, and sensor nodes. In such environments cross-layer architectures are a promising new approach, as they can adapt protocol behavior to changing networking conditions. This article introduces CrossTalk, a cross-layer architecture that aims at achieving global objectives with local behavior. It further compares CrossTalk with other cross-layer architectures proposed. Finally, it analyzes the quality of the information provided by the architecture and presents a reference application to demonstrate the effectiveness of the general approach.

Performance considerations for mobile web services

Web services are an emerging technology that provides a flexible platform for web interaction. We evaluate Web service performance of handheld resource-constrained clients using different wireless technologies. Due to the usage of XML, message sizes in Web services are larger than in traditional web technologies and therefore, compression of Web service messages is attractive. As shown in our experiments, this especially holds for mobile clients with poor connectivity and high communication costs. However, compression requires CPU time at both the server and the clients. We present measurement results of a simple dynamic scheme that provides benefits by compressing responses only when the required server resources are available.

ScatterWeb - Low Power Sensor Nodes and Energy Aware Routing

ScatterWeb, a distributed, heterogeneous platform for the ad-hoc deployment of sensor networks offers hardware together with open, fully documented software for the deployment of embedded sensor networks. Already low power by design, the sensor nodes offer additional energy conservation mechanisms and support energy efficient routing, such as, e.g., solar-aware routing. In order to enable a battery-free operation, the nodes implement permanent power sensing and start the transmission if and only if the energy stored in a capacitor is sufficient for the complete transmission plus the reception of an acknowledgement. Energy-aware routing takes the current incoming power of environmental energy sources into account. Depending on the current power generated by, e.g., solar cells, traffic is always forwarded by the nodes having sufficient power. Together with additional power saving, auto-configuration, and remote reprogramming techniques, these mechanisms enable ScatterWeb nodes to survive many years in real-life scenarios without any on-site maintenance.

Autonomous Gas-Sensitive Microdrone: Wind Vector Estimation and Gas Distribution Mapping

This article presents the development and validation of an autonomous, gas sensitive microdrone that is capable of estimating the wind vector in real time using only the onboard control unit of the microdrone and performing gas distribution mapping (DM). Two different sampling approaches are suggested to address this problem. On the one hand, a predefined trajectory is used to explore the target area with the microdrone in a real-world gas DM experiment. As an alternative sampling approach, we introduce an adaptive strategy that suggests next sampling points based on an artificial potential field (APF). Initial results in real-world experiments demonstrate the capability of the proposed adaptive sampling strategy for gas DM and its use for gas source localization.

Gas source localization with a micro-drone using bio-inspired and particle filter-based algorithms

Gas source localization (GSL) with mobile robots is a challenging task due to the unpredictable nature of gas dispersion, the limitations of the currents sensing technologies, and the mobility constraints of ground-based robots. This work proposes an integral solution for the GSL task, including source declaration. We present a novel pseudo-gradient-based plume tracking algorithm and a particle filter-based source declaration approach, and apply it on a gas-sensitive micro-drone. We compare the performance of the proposed system in simulations and real-world experiments against two commonly used tracking algorithms adapted for aerial exploration missions.

A system for distributed event detection in wireless sensor networks

Event detection is a major issue for applications of wireless sensor networks. In order to detect an event, a sensor network has to identify which application-specific incident has occurred based on the raw data gathered by individual sensor nodes. In this context, an event may be anything from a malfunction of monitored machinery to an intrusion into a restricted area. The goal is to provide high-accuracy event detection at minimal energy cost in order to maximize network lifetime. In this paper, we present a system for collaborative event detection directly on the sensor nodes. The system does not require a base station for centralized coordination or processing, and is fully trainable to recognize different classes of application-specific events. Communication overhead is reduced to a minimum by processing raw data directly on the sensor nodes and only reporting which events have been detected. The detection accuracy is evaluated using a 100-node sensor network deployed as a wireless alarm system on the fence of a real-world construction site.

FACTS – A Rule-based Middleware Architecture for Wireless Sensor Networks

Introducing a middleware layer into wireless sensor networks is a widely accepted solution to facilitate application programming and to allow network organization. In this paper we introduce FACTS, a highly flexible middleware architecture able to provide support for a wide range of different applications. Instead of developing middleware and application apart from one another, we seek to combine them at programming level. Our rule-based language, tailored to this concept and the domain of networked sensors, enables high-level software development. The objective is to combine advantages of event-centric processing and rule-based execution while preserving low resource usage

Fence monitoring: experimental evaluation of a use case for wireless sensor networks

In-network data processing and event detection on resource-constrained devices are widely regarded as distinctive and novel features of wireless sensor networks. The vision is that through cooperation of many sensor nodes the accuracy of event detection can be greatly improved. On the practical side however, little real-world experience exists in how far these goals can be achieved. In this paper, we present the results of a small deployment of sensor nodes attached to a fence with the goal of collaboratively detecting and reporting security relevant incidents, such as a person climbing over the fence. Based on experimental data we discuss in detail the process of innetwork event detection both from the conceptual side and by evaluating the results obtained. Reusing the same traces in a simulated network, we also look into the impact of multi-hop event reporting.