Carsten Buschmann

Neighborhood-Based Topology Recognition in Sensor Networks

We consider a crucial aspect of self-organization of a sensor network consisting of a large set of simple sensor nodes with no location hardware and only very limited communication range. After having been distributed randomly in a given two-dimensional region, the nodes are required to develop a sense for the environment, based on a limited amount of local communication. We describe algorithmic approaches for determining the structure of boundary nodes of the region, and the topology of the region. We also develop methods for determining the outside boundary, the distance to the closest boundary for each point, the Voronoi diagram of the different boundaries, and the geometric thickness of the network. Our methods rely on a number of natural assumptions that are present in densely distributed sets of nodes, and make use of a combination of stochastics, topology, and geometry. Evaluation requires only a limited number of simple local computations.

SpyGlass: a wireless sensor network visualizer

In this paper we present a modular and extensible visualization framework for wireless sensor networks. These networks have typically no means of visualizing their internal state, sensor readings or computational results. Visualization is therefore a key issue to develop and operate these networks. Data emitted by individual sensor nodes is collected by gateway software running on a machine in the sensor network. It is then passed on via TCP/IP to the visualization software on a potentially remote machine. Visualization plug-ins can register to different data types, and visualize the information using a flexible multi-layer mechanism that renders the information on a canvas. Developers can easily adapt existing or develop new custom tailored plug-ins for their specific visualization needs and applications.

Compressing SOAP Messages by using Pushdown Automata

In environments with limited network bandwidth or resource-constrained computing devices the high amount of protocol overhead caused by SOAP is disadvantageous. Therefore, recent research work concentrated on more compact, binary representations of XML data. However, due to the special characteristics of SOAP communication most of these approaches are not applicable in the field of Web services. First, we give a detailed overview of the latest developments in the field of XML data compression. Then we will introduce a new approach for compressing SOAP data which utilizes information on the structure of the data from an XML schema or WSDL document to generate a single custom pushdown automaton. This cannot only be used as a highly efficient validating parser but also as a compressor: its transitions are tagged with short binary identifiers which replace XML tags during compression. This approach leads to extremely compact data representations as well as low memory and CPU utilization

Enhanced transport bindings for efficient SOAP messaging

Within the past years the Web service technology emerged into more and more fields of application. In some cases the classical approach of using HTTP as a transport binding for SOAP seems no longer adequate. As a full scale application protocol HTTP causes a high amount of protocol overhead and is too inflexible for many Web Service scenarios. In this paper we initially give an in-depth review of existing transport bindings with a strong focus on data rate efficiency. Then we introduce an advanced UDP binding called PURE that significantly reduces the protocol overhead and enables interesting additional features such as point-to-multipoint communication via IP multicast and broadcast.

MarathonNet: adding value to large scale sport events - a connectivity analysis

The project MarathonNet develops wireless sensor networks for monitoring runners during marathon events. The application requires a high degree of connectivity in order to provide actual data for runners and spectators. Depending on the distribution of the runners on the track, the communication range and the number of base stations network partitions might occur that reduce connectivity. To investigate these dependencies in detail we conducted various simulations on connectivity. In this paper we first introduce the application scenario and discuss the impact of the different parameters and their interrelations. We then present the simulation results and discuss their consequences for the application design.

Minimal transmission power as distance estimation for precise localization in sensor networks

Positioning sensor nodes requires distance information to reference points. Due to resource limitations in sensor networks, distance determination in low-cost sensor nodes without additional hardware is difficult. Known techniques such as distance estimation based on received signal strength (RSSI) are mostly inaccurate or have limitations. We propose a new method to measure the distance between a transmitting node and a receiving node using the minimal transmission power. The determined distance is more precise than RSSI, has a low variance and is therefore particularly suitable for positioning. Finally, we implemented a demonstrator application using weighted centroid localization to show the practical implementation.

Radio propagation-aware distance estimation based on neighborhood comparison

Distance estimation is important for localization and a multitude of other tasks in wireless sensor networks.We propose a new scheme for distance estimation based on the comparison of neighborhood lists. It is inspired by the observation that distant nodes have fewer neighbors in common than close ones. Other than many distance estimation schemes, it relies neither on special hardware nor on unreliable measurements of physical wireless communication properties like RSSI. Additionally the approach benefits from message exchange by other protocols and requires a single additional message exchange for distance estimation. We will show that the approach is universally applicable and works with arbitrary radio hardware. We discuss related work and present the new approach in detail including its mathematical foundations. We demonstrate the performance of our approach by presenting various simulation results.

Estimating Distances Using Neighborhood Intersection

Information about distances to other nodes in wireless sensor networks has proven advantageous not only for location discovery but is also helpful for context aware applications in general. In this paper we present a novel approach to distance estimation that does neither depend on special hardware nor on unreliable measurements of physical wireless communication properties. Instead, it is inspired by the observation that distant nodes have fewer neighbors in common than close ones and calculates distances from intersection cardinalities of sets of adjacent nodes. We discuss related work and present the new approach in detail including its mathematical foundations. A simulative performance analysis comprising different scenarios shows that our scheme yields competitive results.

Bandwidth and Latency Considerations for Efficient SOAP Messaging

Although Web service technology is being used in more and more distributed systems, its areas of application are inherently limited by high latencies and high amounts of protocol overhead. For messaging in environments with user interaction, like Web platforms for business or multimedia applications, the response time of the whole system needs to be kept in tight boundaries. In other scenarios including mobile communication and battery-powered devices, bandwidth-efficient communication is imperative. In this paper, we address both of these issues. First we conduct a detailed latency analysis of different transport mechanisms for SOAP and then we thoroughly investigate their protocol overhead. For both aspects we present a theoretical analysis as well as experimental measurement results. We then will introduce a new transport binding called PURE that significantly reduces the protocol overhead while featuring low latency. Furthermore it enables interesting additional features such as point-to-multipoint communication via IP multicast and broadcast.

Integrating a Decentralized Web Service Discovery System into the Internet Infrastructure

A weak point of web services is the lack of suitable technologies for implementing service registries. Universal description, discovery and integration (UDDI), as a centralized approach, conflicts with the distributed nature of service-oriented architectures and did not prevail in practice. Hence, in this paper we propose an architecture for discovering and locating web services using the domain name system (DNS). After a detailed survey on current technologies for finding services we present a novel service discovery scheme that is easy to implement and scalable at the same time. Each service provider runs one or more discovery proxies in its Internet domain and sets DNS records pointing to them. Then, local services can register at these proxies. Service users from the local network as well as from the Internet can now locate these proxies using the DNS and query them for available services in this domain. Thus, the local proxies are linked together by the DNS forming one coherent global service directory.