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Employing IEEE 802.11k Neighborhood Reports to Reduce Scanning Times during a Handover


Existing legacy 802.11 systems experience an unacceptable long interruption of the link layer connection during handover. This is due to the time spent in the required scanning phase.

Protocol mechanisms which are currently developed in the 802.11 standardization body provide means to exchange information regarding the existance of neighboring accesspoints and their location. In combination with the mobile users trajectory, this information can be used to:

  • reduce the time spent in scanning as this procedure may be limited to those frequecies on which neighboring access points are well known to operate on
  • reduce the total number of hanodvers and thus the time spent for handover as mobile termininals may select the access point as a next communication parter which is known to be located along the mobile's trajectory.

This project aims to quantifiy the performance improvement regarding the scanning behavior which can be achieved using upcoming standardized protocol mechanisms by means of simulation.

In order to fascilita the project's work, the 802.11 simulation model in OPNET was enhanced within a previous project. In now includes

  • Transmission of location information by the access point in the advertised beacons or pilot frames.
  • Alternative algorithms to decide to which access point a mobile should connect during a handover, i.e.
    • first access point found during the scanning process
    • access point with the strongest RSSI (radio-signal-srength-indicator)
    • access point which is the closes to the estimated mobile's trajectory
  • Experience in C/C++ programming
  • TKN lectures and exercises course on communication networks

Within this project, the students are required to

  • enhance the existing simulation model with the functionality to broadcast or explicitly request neighborhood reports either from the access point or the mobile client,
  • develop and implement alternative handover / scanning approaches which employ the knowledge provided by neighborhod reports (i.e. limit the scanning process to those frequencies where neighbors are known to operate on). The improved scanning behavior is subject to a performance evaluation.

In both cases, the sudents will be guided by supervisors who are actively participating in the ongoing IEEE 802.11 standardization process.

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Contact Marc Emmelmann <>


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