Thesis Defense - Neufeld

Omnidirectional antennas in conjunction with 802.11 wireless networks afford relatively poor scalability in typical community networking scenarios. Even with relatively few stations in a given area, available bandwidth per client quickly drops to that of analog modems over telephone lines. One approach for improving scalability and performance in these networks is to use electronically steerable directional antennas. However, these antennas introduce an entirely new set of problems associated with their use, in particular the introduction of a large number of hidden terminals arising from the use of narrow transmission profiles. These problems have generally been attacked by directly modifying the 802.11 MAC layer, typically in a way which breaks backward compatibility with existing hardware.

In this work I propose and evaluate techniques for addressing the problems which occur when using directional antennas while still maintaining interoperability with existing equipment. A subset of these techniques may even be utilized without modifying the 802.11 MAC protocol, permitting the use of a wide variety of inexpensive "off the shelf" equipment. These techniques are effective at both reducing the number of hidden terminals introduced by directional gain patterns as well as mitigating the negative effects caused by them.