Isolating Physical PER for Smart Rate Selection in 802.11

Current rate control (selection) algorithms in IEEE 802.11 are not based on accurate measurements of packet errors caused at the physical layer. Instead, algorithms act on measurements which, either implicitly or explicitly, mix physical errors with those arising from contention. In this paper we first illustrate how contention can adversely affect the performance of these algorithms, and point out the potential benefits of an ability to isolate physical packet error rate. We introduce and compare two variants of a single core idea enabling the isolation and accurate measurement of physical packet error, based on exploiting existing features of the MAC standard in a novel way. One is based on the RTS/CTS mechanism, and the other on packet fragmentation. Using proof of concept experimental results from a wireless testbed, we show these mechanisms can be used to improve the performance of two existing algorithms, SampleRate and AMRR, both for individual stations and for the system as a whole, and show how incremental deployment is unproblematic. We discuss how the methodology can be integrated in a modular way into rate control algorithms with acceptable overhead.