Yongqiang Liu

LeapFrog: Fast, Timely WiFi Handoff

Widely used wireless LAN infrastructure often deploys multiple access points to cover a large area. A user terminal needs to handoff between these access points as the user moves. Unfortunately, the IEEE 802.11 standard introduces large latency during the handoff process (> 300ms), which greatly affects the performance of mobile applications. Worse yet, it only attempts a handoff when wireless signal quality degrades to a point where current connectivity is threatened. From the application point of view, a desirable WiFi handoff scheme should have sufficiently low handoff latency to support even the most demanding realtime applications, make timely handoff decisions to always connect the terminal to the access point of the best signal quality and/or the lowest load, not incur significant extra power consumption at the terminal, and facilitate easy deployment and be backwards compatible with the 802.11 standard. Very few existing proposals have all these properties. This paper presents the design, implementation, and experimental evaluation of a scheme called LeapFrog that, with efficient, proactive WiFi channel probing, achieves all the four properties.