Title: Antenna selection performance in 802.11 networks
Description: In this thesis we explore the use of antenna selection as a new avenue of performance improvement in mobile wireless ad hoc networks. We built an Unmanned Aerial Vehicle (UAV) testbed using commodity dual-antenna 802.11 hardware and performed field experiments to answer the questions of (1) how links perform between various types and orientations of antennas, (2) whether there exist independent outages that could be avoided using antenna selection, and (3) whether antenna selection can react quickly enough to changing channel conditions to realize a net gain in performance. To answer these questions, we evaluate antenna selection in four major steps, which we present as our contributions. (1) We recorded packet loss and signal strength data for constant bit rate (CBR) streams sent over 4 UAV antennas and received by 5 ground antennas, giving measurements of 20 parallel channels. (2) We built a trace-based multi-antenna channel emulator that, driven by the pre-recorded packet traces, allows us to evaluate production software in the lab. (3) Using the channel emulator, we evaluated the performance of an antenna selection implementation in 60 2x2 systems (systems with 2 transmit and 2 receive antennas) constructible from the 20 antenna pairs measured in step 1. We found that 2x2 systems running antenna selection nearly always beat the best of the 4 individual antenna combinations, with the largest average packet loss improvement of 69%. (4)

We measured the performance of the antenna selection implementation of step 3 in a 2x2 UAV field experiment, where the UAV carried 2 transmit and a ground node 2 receive antennas. We found that antenna selection lead to improved performance, albeit at a relatively low confidence due to a small number of flights. However, we were able to make a qualitative observation that selection generally chose the logical antenna combination based on our knowledge of antenna patterns and orientations. Based on these findings, we conclude that antenna selection is an effective performance improvement technique in environments with high mobility and rate of node orientation change. We expect that selection will be useful in such environments even when combined with more advanced multi-antenna techniques such as MEMO communications.