Publications of Wolfgang Effelsberg

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Artikel

Konferenz Beitrag

Forschungs Papier

  • Marcel Busse, Thomas Haenselmann und Wolfgang Effelsberg. , Technical Reports. 2006 The Impact of Forward Error Correction on Wireless Sensor Network Performance Mannheim, . 06-005
    In networks there are basically two methods to tackle the problem of erroneous packets: Automatic Repeat Requests (ARQ) and Forward Error Correction (FEC). While ARQ means packet retransmissions, FEC uses additional bits to detect and correct distorted data. However, extensive field test of our sensor nodes have shown that FEC can take effect only as long as both sender and receiver are bit-wise synchronized. Otherwise, all following bits are misinterpreted which results in an uncorrectable number of errors. We will thus introduce a new resync scheme which is particularly tailored for many sensor network platforms using UARTs in conjunction with radio transmission. We can show that only using an appropriate resync mechanism exploits the full potential of FEC.
  • Marcel Busse, Thomas Haenselmann und Wolfgang Effelsberg. , Technical Reports. 2006 The Impact of Resync on Wireless Sensor Network Performance Mannheim, . 06-004
    Many of todays sensor nodes exhibit special transmission errors. These errors are due to some common hardware components being used, particularly the so-called UART (serial communication) circuits that interconnects radio transceivers and the CPUs. UARTs generate start-, data- and stop-bits. As long as the state machine at the sender and the receiver is synchronized, even single bit errors can often be corrected by Forward Error Correction (FEC). However, once one or several bits are missed, the state machine at the receiver side will get out of sync so that data bits are misinterpreted as start- or stop-bits and vice versa, rendering the entire remaining communication useless. In this paper, we will devise a periodic resync scheme that enables the receiver to catch up on a data stream even in case of skipped bits. In noisy environments as well as for weak senders, we can improve the overall data throughput significantly.
  • Daniel Görgen, Matthias Transier, Peter Sturm und Wolfgang Effelsberg. Univ., . 2006 Distributed Script - A Mobile Application for Multi-hop Ad-hoc Networks Mannheim, .
    This work introduces an application based on mo- bile end-user devices in a university environment. It is intended to help students to create a lecture script in a shared and distributed manner. The application makes intensive use of the broadcast property of the wireless network, tries to reduce network load by sending small pieces of information piggybacked on beacon messages, configures the communication mechanisms to its needs, and uses the device location to assign context to geographic regions in a self-organizing manner. Furthermore, the application is used to investigate the applicability of nearly stateless position- based multi-hop communication to this kind of scenario.
  • Thomas King, Thomas Butter, Matthias Brantner, Stephan Kopf, Thomas Haenselmann, Alexander Biskop, Andreas Färber und Wolfgang Effelsberg. , Technical Reports. 2006 Distribution of Fingerprints for 802.11-based Positioning Systems Mannheim, . 06-019
    While indoor positioning systems based on 802.11 and fingerprinting work pretty well, it is unknown how to distribute a large amount of fingerprint data to mobile devices. Even worse, many mobile devices are restricted in terms of memory. In this demo proposal, we present two distribution approaches for fingerprints that fill this gap: the Strongest Access Point (SAP) and the Intersection of Access Points (IAP) algorithms. These approaches utilize the 802.11 infrastructure to download only a subset of the complete fingerprint data to a mobile device. The subset covers the area close to the actual position of the mobile device in such a way that position estimates can be computed. For the MDM~2007 demo session, we offer to demonstrate how these distribution approaches for fingerprint data work. The demo will include live indoor positioning of visitors using mobile devices while concurrently displaying the distribution of fingerprint data.
  • Thomas King, Thomas Haenselmann, Stephan Kopf und Wolfgang Effelsberg. , Technical Reports. 2006 Overhearing the Wireless Interface for 802.11-based Positioning Systems Mannheim, . 06-018
    Not only the proliferation of 802.11, but also the capability to determine the position of mobile devices make 802.11 highly appealing for many application areas. Typically, a mobile device that wants to know its position regularly performs active or passive scans to obtain the signal strength measurements of neighboring access points. Active and passive scanning are survey techniques originally intended to be performed once in a while to learn about the presence and signal reception quality of access points within communication range. Based on this survey the best suitable access point is selected as the gateway to the wired network. However, so far, no investigations are known to have been launched into how regular scanning affects concurrent data transmissions from an end-user point of view. In this paper, we explore how common data communication is affected while actively or passively scanning at the same time. We found that with an active scanning interval of less than 2 seconds the network conditions such as throughput and round trip delay are insufficient for interactive applications. The same is true for passive scanning if a scanning interval of less than 7 seconds is chosen. Furthermore, we present a novel scan scheme called Monitor Sniffing to reduce client service disruptions. Monitor Sniffing exploits the fact that 802.11 operates on overlapping channels by overhearing the wireless interface. We have implemented our Monitor Sniffing algorithm using commodity 802.11g hardware, and we demonstrate that it is faster than active and passive scanning and does not disturb concurrent data communication. Finally, our approach only requires software modifications on the client side, making the adoption process quite easy.
  • Thomas King, Stephan Kopf, Thomas Haenselmann, Christian Lubberger und Wolfgang Effelsberg. , Technical Reports. 2006 COMPASS: A Probabilistic Indoor Positioning System Based on 802.11 and Digital Compasses Mannheim, . 06-012
    Positioning systems are one of the key elements required by context-aware application and location-based services. This paper presents the design, implementation and anaylsis of a positioning system called COMPASS which is based on 802.11 compliant network infrastructure and digital compasses. On the mobile device, COMPASS samples the signal strength values of different access points in communication range and utilizes the orientation of the user to preselect a subset of the training data. The remaining training data is used by a probabilistic position determination algorithm to determine the position of the user. While prior systems show only limited accuracy due to blocking effects caused by human bodies, we apply digital compasses to detect the orientations of the users so that we can handle these blocking effects. After a short period of training our approach achieves an average error distance of less than 1.65~meters in our experimental environment of 312 square meters.
  • Sascha Schnaufer, Holger Füßler, Matthias Transier und Wolfgang Effelsberg. , . 2006 Unicast Ad-Hoc Routing in Vehicular City Scenarios , .
    Within Vehicular Ad-Hoc Networking (VANET), i.e., networking between radio-equipped vehicles, unicast packet forwarding can be separated into the one-dimensional highway case and the two-dimensional city case. In this report, we survey the routing methods developed in the FleetNet and Network-on-Wheels projects plus a novel combination of two wellknown methods called PBR-DV or Position-Based Routing with Distance-Vector recovery. On the quest for a city-capable candidate routing algorithm as a possible standard, we discuss the usability and performance of the protocols in city scenarios. Finally, we conclude proposing PBR-DV as a candidate protocol for small-hop-count unicast VANET scenarios.
  • Marc Torrent-Moreno, Felix Schmidt-Eisenlohr, Holger Füßler und Wolfgang Effelsberg. , Technical report. 2006 Packet Forwarding in VANETs, the Complete Set of Results Karlsruhe ; Mannheim, . 2006-2
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