| dc.description.abstract | With billions of WiFi devices now in use, and growing, combined with the rising
popularity of high-bandwidth applications, such as streaming video, demands on
WiFi networks continue to rise. To increase performance for end users the
802.11n WiFi standard introduces several new features that increase Physical
Layer Data Rates (PLDRs). However, the rates are less robust (i.e., more prone
error). Optimizing throughput in an 802.11n network requires choosing the
combination of features that results in the greatest balance between PLDRs and
error rates, which is highly dependent on the environmental conditions. While
the faster PLDRs are an important factor in the throughput gains afforded by
802.11n, it is only when they are used in combination with the new MAC layer
features, namely Frame Aggregation (FA) and Block Acknowledgements (BAs), that
802.11n achieves significant gains when compared to the older 802.11g standard.
FA allows multiple frames to be combined into a large frame so that they can be
transmitted and acknowledged as one aggregated packet, which results in the
channel being used more efficiently.
Unfortunately, it is challenging to experimentally evaluate and compare the
performance of WiFi networks using different combinations of 802.11n features.
WiFi networks operate in 2.4 and 5 GHz bands, which are shared by WiFi devices,
included in computers, cell phones and tablets; as well as Bluetooth devices,
wireless keyboards/mice, cordless phones, microwave ovens and many others.
Competition for the shared medium can negatively impact throughput by increasing
transmission delays or error rates. This makes it difficult to perform
repeatable experiments that are representative of the conditions in which WiFi
devices are typically used. Therefore, we need new methodologies for
understanding and evaluating how to best use these new 802.11n features.
An existing trace-based simulation framework, called T-RATE, has been shown to
be an accurate alternative to experimentally evaluating throughput in 802.11g
networks. We propose T-SIMn, an extension of the T-RATE framework that includes
support for the newer 802.11n WiFi standard. In particular, we implement a new
802.11n network simulator, which we call SIMn. Furthermore, we develop a new
implementation of the trace collection phase that incorporates FA. We
demonstrate that SIMn accurately simulates throughput for one, two and
three-antenna PLDRs in 802.11n with FA. We also show that SIMn accurately
simulates delay due to WiFi and non-WiFi interference, as well as error due to
path loss in mobile scenarios. Finally, we evaluate the T-SIMn framework
(including trace collection) by collecting traces using an iPhone. The iPhone is
representative of a wide variety of one antenna devices. We find that our
framework can be used to accurately simulate these scenarios and we demonstrate
the fidelity of SIMn by uncovering problems with our initial evaluation
methodology. We expect that the T-SIMn framework will be suitable for easily and
fairly evaluating rate adaptation, frame aggregation and channel bandwidth
adaptation algorithms for 802.11n networks, which are challenging to evaluate
experimentally. | en |
