Christian Bettstetter

Professor, University of Klagenfurt, Networked and Embedded Systems

 

Research Portfolio

[Jump down to research activities]
 

Christian Bettstetter and his research group work on the design, modeling, and analysis of future networked communication systems, with focus on mobile and wireless networking (see figure below). Research expertise covers

  • distributed algorithms and protocols;
  • network theory;
  • modeling, simulation, and performance analysis; and
  • network and protocol architectures.

One goal is to design technology that will enable new applications going beyond classical applications of communication and computer networks, such as infrastructure-less wireless networks and networked embedded systems with applications, e.g., in disaster management and automotive safety. Such systems require a different architectural thinking than usual telecommunication networks. We believe that four paradigms are especially important, and they are currently in the core of our activities:

  • self-organization in communication and computer networks;
  • multihop communications (ad hoc networking, relaying);
  • exploiting cooperation between network devices; and
  • exploiting the inherent mobility of devices.

Of interest are also interdisciplinary and theoretical aspects of self-organization and networked systems in general.

Research portfolio

The research methodology is theoretical, simulation-based, and experimental. Methods range from protocol engineering and system simulation over prototyping on real hardware platforms to a set of mathematical methods (mainly stochastic processes, random graph theory, and complex networks). Research is at the intersection of electrical engineering and information technology, informatics, and applied mathematics.

The group cooperates with researchers from Orange Labs, DOCOMO Euro-Labs, Soongsil University, University of Porto, TU Munich, the University of Passau, and the Max Planck Institute for Dynamics and Self-Organization. Funding is obtained from major international companies as well as national and European funding agencies. In particular, the group is part of the Erasmus-Mundus doctoral school ICE and the ESF-funded research network MiNEMA.

Research Activities

 

Current research topics and projects of Bettstetter and his team are the following:

Furthermore, the group participates in the following research programs and clusters:

Completed research activities include the following:

  • Ad hoc networking with adaptive antennas
    At DOCOMO Euro-Labs, 2004-2005, with TU Munich
  • Distributed medium access control with QoS support in multihop networks
    At DOCOMO Euro-Labs, 2003-2005, with TU Berlin
  • IP-based protocols for multihop radio access networks
    At DOCOMO Euro-Labs, 2003-2004
  • Mobility modeling, connectivity, and adaptive clustering in ad hoc networks
    At TU Munich, 2000-2003, funded by DFG
  • IP-based communication protocols in a car environment
    At TU Munich, 1999, with and funded by BMW
  • Turbo decoding with tail-biting trellises
    At University of Notre Dame and TU Munich, 1998

Self-Organizing Synchronization in Wireless Systems

Since Aug 2005
 

Slot synchronization is an essential building block in wireless communications and networking. It enables time coordination between devices - a feature that is needed on various layers of the protocol stack. In slotted communication systems, time is divided into periods of fixed duration ("slots"). Slot synchronization is accomplished if nodes throughout the network agree on a common start of a slot. Classical means of providing a slot structure in a wireless system involves centralized control. In cellular networks, for instance, in each cell, the base station broadcasts a reference signal ("beacon") on a dedicated synchronization channel. All mobile devices within the cell synchronize to the base station. The base stations are typically mutually synchronized using the Global Positioning System. In infrastructureless ad hoc wireless networks, the state-of-the-art approach is to select a "master device" among a set of devices, whose task is to coordinate the time slots in its surrounding. Such centralized algorithms have some drawbacks, for instance, the need for re-selection of the master device if it switches off or moves away.

The overall objective of research in this area is to design and assess a solution for slot synchronization for wireless communications that is completely distributed, i.e., it does not rely on any centralized master devices, neither a predetermined master device nor an elected master device. We believe that particularly in ubiquitous computing scenarios, where large number of tiny wireless devices are interconnected to meshed networks, such a distributed algorithm is preferable.

Our approach has been inspired by a phenomenon of self-organization occurring in nature: the synchronous flashing of fireflies. The idea is adapt and enhance a mathematical model for this phenomenon (Mirollo and Strogatz) to make it work in wireless communications. A simple one-to-one transfer of the model is however infeasible, due to the characteristics of radio communications.

Our research addresses the following issues:

  • Synchronization with realistic assumptions of wireless communications (e.g., use of packets instead of pulses and consideration of delays)
  • Synchronization in multihop network topologies
  • Seamless emergence of synchronization
  • Robustness of self-organizing synchronization against erronous behaviour by faulty or misbehaving nodes
  • Implementation of an overall solution on a wireless hardware platform and technology integration

The work has been done in cooperation with DOCOMO Euro-Labs (Germany), Lakeside Labs (Austria), and the Max Planck Institute for Dynamics and Self-Organization (Germany). The work will be funded as a disseration fellowship project by the Austrian Research Promotion Agency (FFG) from 2010 to 2013.

Selected publications:

Patents and patent applications:

Cooperative Relaying in Wireless Networks

Since Sep 2006
 

Cooperative relaying is a new wireless communication technique promising significant gains in throughput and energy-efficiency of mobile systems. It exploits the broadcast nature of the wireless medium and benefits from a new, distributed form of spatial diversity that mitigates the negative effects of signal fading and interference.

The basic building block of this emerging area is the "relay channel": A source node S transmits a signal to a destination D; a third node R overhears this transmission and relays the signal to D; finally, the destination D combines the two received signals to improve decoding. It was shown that the maximum achievable throughput of this channel can be increased compared to direct S-D transmission and non-cooperative S-R-D relaying. Alternatively, less power is needed to achieve the same throughput.

Although better understanding of cooperative relaying has been achieved during the past years, most research efforts have focused on information-theoretic and physical-layer aspects, not accounting for higher-layer protocols and networking issues. The goal of our research activities is thus to investigate the benefits and tradeoffs of cooperative relaying from a networking perspective and to develop and assess algorithms and protocols above the physical layer that will facilitate its use.

More specifically, Bettstetter's team works in the following areas:

  • Distributed protocols for relay selection
  • Medium access issues in cooperative relaying
  • Network capacity of cooperative relay networks
  • Overall system and protocol architecture
  • Implementation and measurements on a wireless hardware platform

If successful, these activities will provide building blocks and a new understanding for the design of cooperative wireless networks, with the expectation of large performance improvements over current approaches. Results can be applied in the context of self-organizing multihop networks and relay-enhanced cellular systems.

The research projects in this area have been performed in cooperation with Orange Labs (France) and Lakeside Labs (Austria), who both have provided a major part of the funding.

Selected publications:

Patents and patent applications:

  • Apparatus and method for cooperative relaying in wireless systems using an extended channel reservation
  • Cooperative relay scheme having backward compatibility

Flooding in Random and Complex Networks

Since 2007
 

Flooding is a fundamental technique for information dissemination in several networking scenarios, such as link state advertisements in wireless multihop networks and query propagation in peer-to-peer networks. In its most simple form, flooding leads to many redundant and unnecessary transmissions. An optimization goal is to minimize the number of transmissions while still achieving "global outreach" of the sent message. In other words, all nodes in the network should receive the message to be disseminated, using as few overall transmissions as possible. Finding an optimum scheme for flooding a message with minimum overhead in a given network is known to be NP-complete. To tackle this problem, different types of approximation algorithms (both deterministic and probabilistic algorithms) were proposed.

We study various flooding algorithms in different kinds of networks. The major goal is to take a more formal, mathematical approach than previous work, employing methods from graph theory and stochastic processes to draw conclusions for the design and parameterization of flooding algorithms. Networks under investigation include Erdös Rényi random graphs, geometric random graphs, and small world networks. Algorithms under investigation include probabilistic flooding, multipoint relaying, and flooding based on network coding. First, in probabilistic flooding, a node forwards a new incoming message with a given probability. Second, multipoint relaying is a deterministic flooding scheme that approximates a connected dominating set within a two-hop neighborhood of each node, thus forming a backbone of forwarding nodes. Third, we also study new flooding proposals making use of network coding, i.e., they allow nodes to mix multiple messages through algebraic operations.

The work is done in cooperation with the the University of Porto (João Barros) and is partly funded by a scholarship from the Portuguese Science and Technology Fund (FCT).

Results are as follows:

Communication in Sparse Mobile Networks

Since Sep 2006
 

The mobility of nodes is usually being experienced as a challenge and handicap in wireless systems. In the physical layer, it inflicts frequency displacements. In higher layers, it demands for protocols for routing and localization to cope with the dynamic positions of the nodes. Recently, however, researchers have found instances in which mobility can yield benefits. Therefore, the notion of "exploiting mobility" gained increasing interest in the literature, especially in the areas of mobile ad hoc networks and delay-tolerant applications. Mobility can yield benefits in particular if the network topology is sparsely connected, i.e., it consists of several isolated network clusters so that paths between nodes are only available over time.

The main goal our work in this area is to design and evaluate algorithms and protocols for information delivery that exploit the inherent mobility of nodes in sparse wireless networks. Work packages include:

  • Modeling and mathematical analysis of sparse network topologies, in particular with inhomogeneous spatial node distributions;
  • Impact analysis of node mobility on sparse network topologies; and
  • Design and assessment of algorithms for information propagation in sparse networks.
The work has been partly funded by Soongsil University (Seoul, Korea).

Publications include the following:

Collaborative Microdrones

Since Jan 2009
 

Microdrones are small-scale unmanned aerial vehicles carrying payloads such as cameras and sensors. Conventional microdrones can be regarded as an autonomous isolated system that flies in the air, senses the environment, and communicates with the ground station. It is typically manually controlled by a human operator using a remote control or using predefined routes. Such systems are used today for aerial imaging, police and fire rescue operations, and military missions. Despite these advances, the use of a single microdrone has severe drawbacks, demanding for a system in which several microdrones fly in formations and cooperate to achieve a certain mission.

The Lakeside Labs project cDrones aims at advancing the current state-of-the-art in the domain of cooperating, wireless networked microdrones. The project develop algorithms, concepts, and methods for three key technological areas:

  • networked flight formation;
  • mission planning; and
  • control, and sensor data interpretation.
Although the developed technology should be of general applicability, the project focuses on networked microdrones for fire rescue scenarios.

The project is a joint activity of four research groups at the University of Klagenfurt, one group at TU Graz, and another group at the University of Central Florida. It is funded within the research platform Lakeside Labs. A demo video can be found on the right side. Detailed information is available from the project Website.

Publications: