Practical schemes for smooth MAC layer handoff in 802.11 wireless networks

The limited service range of the access points demands mobile wireless stations to handoff frequently between different cells in the IEEE 802.11 infrastructure networks. However, the handoff scheme used in the current 802.11 infrastructure networks is far from graceful. In this paper, we propose a smooth MAC layer handoff scheme and a greedy smooth MAC layer handoff scheme. Our schemes scan channels in a smooth manner so that the handoff can have less impact on upper layer applications. In order to limit the frequency of channel scanning, an adaptive mechanism is used to dynamically adjust the threshold triggering the channel scanning operations. We have implemented our handoff schemes using commodity 802.11 devices and extensive experiments have been conducted to evaluate the performance. The experimental results demonstrate that our schemes reduce packet delay and loss during handoff. Our handoff schemes are implemented in the client side only and do not require changes to access points. Therefore, our schemes can be deployed in the existing 802.11 networks