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Publications by Type: Undergrad Theses (Bachelor, Diplom, and Master Theses) and Study Projects

Quantitative Analysis of Physical Layer and Link Layer Measurements in WiFi Networks
Citation key S-QAPLLLMWN-11
Author Schulz-Zander, Julius
Year 2011
Address Berlin, Germany
Month September
School Technische Universit├Ąt Berlin
Abstract In this thesis, we present a measurement study on the quantification of lost transmission opportunities in IEEE 802.11 networks, which is an increasingly more important problem due to a higher number of IEEE 802.11-based deployments. Lost transmission opportunities can arise from both unwanted traffic and link impairments. We perform passive measurements to gain information about unwanted traffic which lead to a reduction of available airtime and active measurements to gain information on link impairments which lead to packet loss or unfairness. In both cases, we follow a cross layer approach, since measuring lost transmission opportunities depends on information from two layers: (1) the physical (PHY) layer which provides signal quality and transmission statistics and (2) the medium access-control (MAC) layer which provides IEEE 802.11 protocol specific information, and throughput and loss statistics. We examine unwanted traffic to understand the impact on the environment and to support the development of mitigating mechanisms. To measure link impairments, we adapt an active measurement approach [17], which is, to the very best of our knowledge, the only approach that is able to estimate the majority of the reasons behind packet loss. We present our measurement methodology on how to collect network wide measurements with off-the shelf WiFi hardware. All measurements are performed in a typical office environment located on the 16th floor in the TEL building at the Technische Universit├Ąt Berlin. Using our measurement framework, we collect several network wide measurements that contain, for example, the hardware states of the WiFi card, link statistics and packet traces, and store everything on a central server. Using these measurements, we show that both active and passive cross-layer measurements are valuable in measuring lost transmission opportunities, and that this cannot be done purely on just a single layer. From passive measurements, we show that a significant overhead of IEEE 802.11 control and management traffic exist, reducing the wireless network capacity. In addition, we show that, with active measurements by using the link impairment estimator from [17] a close estimation of the root-cause of loss due to link impairments is possible.
Bibtex Type of Publication Diplomarbeit
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