University of Bonn

Computer Science Department IV

Communication Systems


Dr. rer. nat. Michael Gerharz

Contact:

Dr. Michael Gerharz
 
E-mail: gerharz@cs.uni-bonn.de
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Research Interests:


Projects

Performance Engineering [2004- ]

Performance Engineering is a wholistic approach towards product design keeping performance issues to the front throughout the development cycle. As an industry-wide standard design language, the Unified Modeling Language (UML) provides means for annotating models with performance measures using the newly established UML RT-Profile.

From those annotated system models, a performance model may be generated which is then used to analyse the system in order to identify performance bottlenecks in as early a development stage as possible. Common performance models used for this purpose include queueing networks, petri nets, or event-driven simulation, depending on the level of detail requested and available. Additionally, measurements using prototype implementations provide further insight that complements the analytical estimates gained from the earlier development steps.

Diploma Theses

  • Felix Leder, Performance evaluation of current mobile phone architectures with respect to multimedia applications
  • Lukas Pustina, Performance evaluation of UML system architectures with queueing networks in early stages of development
  • Heiko Pfeffer

Praktikum

  • Daniel Panteleit, Performance enginnering durch simulative Leistungsbewertung unter Benutzung von UML State Charts
  • Andreas Klein und Jörg Runkel, Performance engineering am Beispiel einer VoIP-Implementation

Route Discovery Strategies in Mobile Ad Hoc Networks [2002- ]

Beyond 3G telecommunication networks, mobile ad hoc networks lead the way to truely ubiquituous communication by providing a self-configuring, easy to use, and cheap networking structure independent of any fixed infrastructure. While the basic challenge of multihop routing has seen IETF RFCs such as the Ad-hoc On-Demand Routing Protocol (AODV) evolve, more advanced questions like routing stability still lack satisfying answers.

As part of the BMBF funded IPonAir project, metrics for identifying stable links in highly mobile ad hoc networks have been developed. The metrics are based on a thorough statistical evaluation of link lifetimes in mobile ad hoc networks and provide on-line estimation of link failure risks. Using a generalisation of Dijkstra's well-known shortest paths algorithm, these metrics are able to discover stable communication paths using standard on-demand routing protocols such as AODV or DSR. Moreover, this generalised route discovery strategy may also be used to discover QoS-routes using arbitrary maximisable routing metrics.

A loosely related topic is the challenge of finding optimal network topologies. Unlike wired networks, the communication range of a wireless device is not fixed. Rather, transmission power adaptation may be used to actively form the network topology. We have developed an efficient distributed topology control algorithm based on cooperative transmission power adjustment.

Diploma Theses

  • Nicholas Dille, Design and Simulative Evaluation of Route Discovery Schemes based on the Observation of Link Lifetimes
  • Frank Meyer, Entwurf und Bewertung von adaptiven Verfahren zur Verbesserung der Pfadhaltbarkeit in Ad-hoc-Routingprotokollen
  • Christian Vogt, Design and Evaluation of Routing Concepts for Quality of Service in Mobile Ad-hoc Networks
  • Rainer Meller, Design und Evaluierung von Konzepten zur dynamischen Regelung der Sendeleistung in drahtlosen Ad-Hoc Netzen

Praktikum

  • Florian Purnhagen, ”Reality Check” of Route Discovery Strategies in Mobile Ad Hoc Networks based upon Link Lifetime Observations
  • Holger Nelson, Vergleich von zwei Verfahren zur Bereitstellung von QoS in mobilen Ad-Hoc-Netzwerken
  • Alexander Honnef,  Signalstärkebasierte Pfadauswahl in AODV
  • Nicholas Dille, Ein LinkState-Routing-Protokoll für den Netzwerksimulator NS2
  • Klaus Lutterjohann, Vergleich von zwei Routing-Protokollen für mobile Ad-hoc Netze

Ad hoc Network Emulation using Packet Filters [2003-2004]

To support our work in the IPonAir project, we have developed an ad hoc network emulation tool called AdhocEmu. Using this emulator, it is possible to experience the effects of our protocols on the realtime performance of multimedia applications in an ad hoc environment.

The emulator is complemented by BonnMotion, a JAVA based movement generation and analysis tool. BonnMotion may be used to generate scenarios based upon a range of well-known mobility models and analyse the  communicational characteristics of those scenarios.

On the right hand side, you can see a visualisation of a typical ad hoc scenario. Our visualisation tool provides information on communication routes, transmission as well as interference ranges, and several statistical data.

Praktikum

  • Tobias Blechmann und Tobias Honecker, Entwicklung eines Paketfilters zur Emulation von Paketfehlern
  • Jan Ellenbeck und Ehsan Darroudi, Erweiterung und Kopplung einer Netzwerk-Visualisierungs- und Emulationsumgebung
  • Lukas Pustina, Prototypische Implementierung eines Sprachübertragungsdienstes über Bluetooth auf einem Symbian-Mobiltelefon
Visualisation of an ad hoc network


Wireless Local Connectivity (Wilco) [2001-2002]

Under certain circumstances, Wireless LAN (IEEE 802.11) can provide a cheap alternative to cellular networks based on GSM/UMTS. However, unlike commercial cellular networks, IEEE 802.11 in its original version offers best-effort service only. In order to provide improved service quality with IEEE 802.11-based networks as well, several extensions are required including mobility management, base station selection, and admission control to restrict the access to the network.

Praktikum

  • Christian Vogt, Wireless Local Connectivity (Wilco) - Mobility Management
  • Sherif Moustafa, Wireless Local Connectivity (Wilco) - Base Station Selection
  • Maxim Lobko und Tomasz Lipinski, Wireless Local Connectivity (Wilco) - Admission Control

List of Publications:

  • Lukas Pustina, Michael Gerharz, Peter Martini, Volker Deichmann, Simon Schwarzer
    Performance Aware Design of Communication Systems
    31st Annual IEEE Conference on Local Computer Networks (LCN), Tampa (FL), USA, November 2006
  • Nils Aschenbruck, Michael Gerharz, Matthias Frank, Peter Martini
    Modelling Voice Communication in Disaster Area Scenarios
    31st Annual IEEE Conference on Local Computer Networks (LCN), Tampa (FL), USA, November 2006
  • Oliver Stanze, Michael Gerharz, Martina Zitterbart et al.
    Routing and Self-organization in IP based wireless access networks
    it - Information Technology Journal, Themenheft "IP basierte mobile Netze", Vol. 48, No. 5, October 2006
  • Michael Gerharz
    Stabile Kommunikation in dynamischen Ad-hoc-Netzen
    Dissertation Rheinische Friedrich-Wilhelms-Universität Bonn, GCA-Verlag, ISBN 3-89863-220-2, July 2006
  • Edmund Coersmeier, Andreas Bauer, Martin Kosakowski, Nadine Pfuhl, Boris Spahl, Daniel Tolksdorf, Yuhuan Xu, Michael Gerharz, Wolfgang Hansmann, Felix Leder
    Evaluation Architecture For Digital Radio Mondiale Multimedia Applications
    Proc. of the IASTED International Conference on Communication Systems and Applications (CSA 2005), Banff, Canada, July 2005
  • Michael Gerharz, Christian de Waal, Peter Martini, Paul James
    A Cooperative Nearest Neighbour Topology Control Algorithm for Wireless Ad Hoc Networks
    Telecommunication Systems, Vol. 28, No. 3-4, pp. 317-331, March 2005
    [ Abstract and full article ]
  • Michael Gerharz, Christian de Waal, Peter Martini
    How To Discover Optimal Routes In Wireless Multihop Networks
    Proc. of the 6th IFIP IEEE International Conference on Mobile and Wireless Communication Networks (MWCN), Paris, France, October 2004
  • Patrick Peschlow, Michael Gerharz, Christian de Waal, Peter Martini
    An Efficient Transport Capacity Estimation Method for Wireless Multihop Network Topologies
    Proc. of the 34th Annual Conference of the Gesellschaft für Informatik (2nd German Workshop on Mobile Ad-hoc Networks), Vol. 1, pp. 90-94, Ulm, Germany, September 2004
    [ Abstract and full paper ]
  • Michael Gerharz, Christian de Waal, Matthias Frank, Peter Martini
    Influence Of Transmission Power Control On The Transport Capacity of Wireless Multihop Networks
    Proc. of the 15th IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC), Barcelona, Spain, September 2004
    [ Abstract and full paper ]
  • Christian Vogt, Michael Gerharz, Christian de Waal
    Corridor Routing in Mobile Ad-hoc Networks
    Proc. of the 3rd Annual Mediterranean Ad Hoc Networking Workshop (Med-Hoc-Net), Bodrum, Turkey, June 2004
  • Michael Gerharz
    Adaptive Stability Threshold Selection for Mobile Wireless Networks
    Technical Report, April 2004
  • Martina Zitterbart, Kilian Weniger, Olvier Stanze, Michael Gerharz et al.
    IPonAir - Drahtloses Internet der nächsten Generation
    PIK Themenheft "Mobile Ad-hoc-Netzwerke", Dezember 2003
  • Michael Gerharz, Christian de Waal, Peter Martini, Paul James
    A Cooperative Nearest Neighbour Topology Control Algorithm for Wireless Ad Hoc Networks
    Proc. of the 12th International Conference on Computer Communications and Networks (ICCCN), Dallas, Texas, October 2003
    [ Abstract and full paper ]
  • Michael Gerharz, Christian de Waal, Peter Martini, Paul James
    Strategies for Finding Stable Paths in Mobile Wireless Ad Hoc Networks
    Proc. of the 28th Annual IEEE Conference on Local Computer Networks (LCN), Königswinter/Bonn, Germany, October 2003
    [ Abstract and full paper ]
  • Michael Gerharz, Christian de Waal, Matthias Frank, Paul James
    A Practical View on Quality-of-Service Support in Wireless Ad Hoc Networks
    Proc. of the 3rd IEEE Workshop on Applications and Services in Wireless Networks (ASWN), Berne, Switzerland, July 2003
    [ Abstract and full paper ]
  • Michael Gerharz, Christian Vogt, Christian de Waal
    Current Approaches Towards Improved Quality-of-Service Provision in Mobile Ad-hoc Networks
    Technical Report, March 2003
    [ Full Paper]
  • Michael Gerharz, Christian de Waal, Matthias Frank, Peter Martini
    Link Stability in Mobile Wireless Ad Hoc Networks
    Proc. of the 27th Annual IEEE Conference on Local Computer Networks (LCN), Tampa, Florida, November 2002
    [ Abstract and full paper ]

Professional Experience

  • Tutorial on TCP/IP and Quality-of-Service in the Internet at T-Mobile, Bonn
  • Tutorial on Ad-hoc-Networking at Nokia Research Center, Bochum
    focus on routing, Quality-of-Service, and stability aspects
  • Program Commitee IEEE Wireless Local Networks Workshops 2004 & 2005
  • Reviewer for the IEEE Communications Letters and the ACM/Kluwer Wireless Networks Journal

Teaching

SS04

  • Exercises to "Mobile Communications" (lecture by Prof. Dr. Martini and Dr. Frank)
  • Praktikum "Route Discovery Strategies in Mobile Ad Hoc Networks"

WS03/04

  • Lecture and Exercises to "Mobile Communications" (lecture for the international Master Programme of B-IT in cooperation with Prof. Dr. Martini and colleagues)
  • Praktikum "Route Discovery Strategies in Mobile Ad Hoc Networks"
  • Praktikum "Ad hoc Network Emulation using Packet Filters"

SS03

  • Proseminar "Internetprotokolle/Mobilfunkprotokolle"
  • Praktikum "Route Discovery Strategies in Mobile Ad Hoc Networks"
  • Seminar "Rechnernetze"

WS02/03

  • Proseminar "Internetprotokolle/Mobilfunkprotokolle"
  • Praktikum "Route Discovery Strategies in Mobile Ad Hoc Networks"
  • Praktikum "Ad hoc Network Emulation using Packet Filters"

SS02

  • Exercises to "Mobile Communications" (lecture by Prof. Dr. Martini and Dr. Frank)
  • Praktikum "Route Discovery Strategies in Mobile Ad Hoc Networks"
  • Seminar "Rechnernetze"

WS01/02

  • Praktikum "Wireless Local Connectivity (Wilco)"
  • Seminar "Rechnernetze"

SS01

  • Exercises to "Mobile Communications" (lecture by Prof. Dr. Martini and Dr. Frank)

University of Bonn / Computer Science / Department IV