Modeling and optimizing IEEE 802.11 DCF for long-distance links

Abstract

Most rural areas in developing countries are isolated due to the lack of appropriate low-cost communication technologies. Previous experiences have shown that IEEE 802.11 can be used for the deployment of large static mesh networks with only minor changes to the MAC layer that enable WiFi transceivers to work properly even for very long distances (up to 100 Km in point to point links, and almost 40 Km in point to multipoint setups). However, the impact of distance on performance of such long links has not been deeply analysed. In addition, previous analytical models of IEEE 802.11 DCF can not be applied because they implicitly assume that the propagation time can be neglected. This paper formally studies the impact of the distance on the behaviour of IEEE 802.11 DCF, and presents an analytical model of IEEE 802.11 DCF that accounts for distances correctly. The model is validated with simulations and within a controlled experimental framework, based on wireless channel emulation. Finally, we propose adjustments for ACKTimeout, CTSTimeout, SlotTime, and CWmin parameters that improve significantly the performance of DCF over long distances.