Application-oriented link adaptation for IEEE 802.11

Abstract

The thesis addresses the ever-persistent problem of quality guarantees in wireless data networks. The quality guarantees are especially important for real-time streaming applications. While in fixed links most of the quality issues could be, and are still resolved by over-provisioning, in the world of wireless communications things get complicated. The main reason for wireless links being a bottleneck in terms of both achievable throughput and packet loss and delay guarantees, is the resource limitation that will always be there. Our work showed that while there is no magic solution that can resolve all link quality-related problems in wireless networks, a lot could be done to mitigate them. The first, and the most important, is to make the radio as adaptive to the changes of the link conditions as possible. This can be done through our advanced hybrid rate-control algorithm. The algorithm combines a stable throughput-based solution with a rapid link-quality feedback supplement into a novel controller that has both swift response and stable performance. The second solution, which is dependant on the first one, is the propagation of link status-related information from the link layer to the application. The latter can use this feedback to change its data stream properties to match those of the underlying wireless link. This behaviour proves most useful in cases when the radio cannot compensate for a deterioration of the radio connection such as a significant drop of the signal strength due to obstruction, or too many users competing to use the same medium.