Marcel Busse

TECA: a topology and energy control algorithm for wireless sensor networks

In order to prolong a sensors operational lifetime, a main challenge in the field of sensor networks is energy efficiency. Since much energy is spent for the radio communication, many approaches exist that put sensor nodes into a sleep mode with the communication radio turned off. We propose a new Topology and Energy Control Algorithm called TECA that uses a very simple clustering approach and connects these clusters in a very energy-efficient way. Using the concept of virtual links, passive nodes decide in a distributed way if they should join the topology and stay active or rather go into a low-powered sleep mode. Compared to other approaches, TECA establishes a well-connected topology and is able to save more energy. By means of simulations, we show that TECA outperforms the two other approaches in terms of operational lifetime, packet delivery, and network connectivity.

Lightweight QoS-support for networked mobile gaming

In this paper, we present an approach to provide Quality of Service (QoS) for networked mobile gaming. In order to examine the QoS requirements of mobile games, we ported a simple real-time game called GAV (GPL Arcade Volleyball) to a PDA and performed several traffic measurements over both GPRS and UMTS networks. We show that due to high end-to-end delay and delay jitter, real-time games are not supported by GPRS. While UMTS improves both delay and jitter, it still does not match the requirements of real-time games. The key reason for this problem is that overprovisioning, as it is used to allow real-time games in the Internet, is very expensive in mobile networks. At the same time, QoS classes for mobile networks are not tailored to real-time games. In order to reduce delay and jitter for this application class, while still accounting for the very bursty nature of real-time game flows, we propose to use a combination of statistical multiplexing and QoS guarantees. The general idea is to aggregate multiple game flows and perform reservation for that aggregate. As a theoretical background, we use a queuing system based model. Through simulation of a sample network with the traffic data generated by GAV, we validate our assumptions and demonstrate the performance and characteristics of our approach.

Energy-efficient forwarding schemes for wireless sensor networks

Energy-efficient forwarding becomes important if resources and battery lifetime are limited such as in wireless sensor networks. Although widely used, simple hop-based forwarding along a path from one node towards a sink can be very inefficient in terms of delivery rate as well as energy efficiency, especially in lossy environments. We will show that just minimizing the expected number of transmissions within the network is not always the most efficient forwarding strategy. Using a realistic link loss model, we derive two new forwarding schemes named single-link and multi-link energy-efficient forwarding that trade off delivery rate and energy costs best by maximizing energy efficiency. Multi-link forwarding further benefits from addressing multiple receivers during packet forwarding, instead of a single one. By mathematical analyses, extensive simulations, and experimental evaluations we contrast the performance of our approaches against a comprehensive framework of other forwarding strategies

Real-time service provisioning for mobile and wireless networks

As mobile devices and wireless networks are becoming ubiquitous, the interest of users to deploy real-time applications, e.g. online gaming or Voice-over-IP in such environments is also increasing. Due to the difference between traditional and wireless networks, in particular in terms of available bandwidth and network structure, the concepts used for supporting real-time applications in both networks are different. This paper gives an overview of the key technical challenges that are fundamental and need to be solved in order to easily support real-time applications in wireless and mobile environments. In a first step, issues related to service provisioning in mobile networks are discussed. This is followed by a look at the Quality of Service supported by wireless networks and possible techniques for improving it. Finally, concepts for securing the communication between the users of real-time applications in wireless and mobile networks are presented. For each of these issues, we provide a detailed analysis and an overview of the state-of-the-art. Moreover, we illustrate the main points using distributed online games as an example.

Multi perspective panoramic imaging

Panoramic images have only been feasible if all contributing image patches share a common center of projection. Then, they can be consolidated into a single image using perspective transforms. In contrast to that, we propose a novel non-linear warping scheme which allows the merging of multi-perspective images, thus taking advantage of scattered cameras. Therefore, a polygonal cut is defined in two source images to be merged. Usually, the layout of the cuts does not allow a user to stitch both images together naively. Thus, two convex combinations of a warped and a canonic coordinate system are applied so that both source images fit together at the cutting edge while the inevitable distortion decreases towards the borders of the image to obtain a natural appearance.

Huginn: a 3D visualizer for wireless ns-2 traces

Discrete-event network simulation is a major tool for the research and development of mobile ad-hoc networks (MANETs). These simulations are used for debugging, teaching, understanding, and performance-evaluating MANET protocols. For the first three tasks, visualization of the processes occurring in the simulated network is crucial for verification and credibility of the generated results. Working with the popular network simulator ns-2, we have not yet found a visualization toolkit capable of reading native ns-2 trace files and providing means to change the evaluated parameters without changing the visualization software. Thus, we developed Huginn, a software providing an intuitive way to visualize simulation properties and to determine how they should be displayed without the need of programming. In addition, Huginn has a 3D interface allowing an improved exploitation of the (human) users perceptual system. It helps to handle the significant cognitive load associated with the mental reconstruction of simulated network processes. Besides presenting the software interface and architecture, we describe algorithmic solutions that might be of a more general interest for similar problems.

Scriptable sensor network based home-automation

Today, proprietary home automation targets very specific applications which operate mostly on a cable based infrastructure. In contrast to that, our implementation builds a wireless ad-hoc multi-hop network based on the ESB sensor node platform from the FU-Berlin. The nodes gather sensor readings in a home and transmit them to a central automation server. There, the readings are matched against a list of script statements. In case of a match, a specific action is performed. In this work we will show how the user can implement complex home automation applications optimized for his specific needs by defining very simple script statements. An important property of the system is also that the control of all home appliances is done by means of IR communication and Ethernet enabled multiple plugs. This way, the cooperation between manufacturers is no necessity in order to connect devices to the home automation network.

Energy-efficient forwarding in wireless sensor networks

For maximizing the energy efficiency in a wireless network, we propose two forwarding schemes termed single-link and multi-link energy-efficient forwarding that tradeoff delivery ratios against energy costs. Multi-link forwarding improves the network performance substantially by addressing multiple receivers at once during the packet forwarding process. If the first forwarding node does not receive a packet correctly, other nodes may act as backup nodes and perform the forwarding instead. By means of mathematical analyses, we derive how the energy efficiency of a forwarding path can be computed and how a forwarding tree is established. Routing cycles are explicitly taken into account and prevented by means of sequence numbers. Simulations and real-world experiments provide a comparison to other reference strategies, showing a superior performance of our forwarding scheme in terms of energy efficiency.

Energy-Efficient Data Dissemination for Wireless Sensor Networks

In order to disseminate a large amount of data through a sensor network, it is common to split the data into small-sized chunk packets. If the data is additionally encoded by a forward error correction (FEC) code, missed chunks can be recovered. Fountain codes are a special kind of FEC code which have the property that the sender provides the data in a virtually endless stream by combining original chunks at random. No matter which chunks get lost, each receiver only needs any k chunks from the stream. In broadcast scenarios, fountains have the additional advantage that only little redundancy is required, even if several receivers have missed different chunks. We will show the benefit of Fountain codes in wireless sensor networks in comparison to raw transmissions and other FEC codes. To support the actual data dissemination, we propose two generic distributed protocols: an acknowledgement-based and a request-based protocol. The evaluation is carried out in a real testbed consisting of 20 sensor nodes

Energy-Efficient Aggregation Forwarding for Wireless Sensor Networks

Based on an energy efficiency metric that is defined by the fraction of end-to-end delivery ratio and required energy, we propose a new distributed algorithm for the case of correlated data. In contrast to related work, our metric considers energy savings due to aggregation a priori and achieves a superior performance. However, a problem that arises from the ability to aggregate and to change energy cost during the construction of a forwarding tree is that routing cycles may occur because information used may be out-dated. By employing different types of sequence numbers, our strategy is able to prevent such cycles, accounting for the distributed nature of sensor networks.