MOAR: a multi-channel opportunistic auto-rate media access protocol for ad hoc networks

The IEEE 802.11 wireless media standard supports multiple frequency channels as well as multiple data rates at the physical (PHY) layer. In this paper, we introduce the multi-channel opportunistic auto rate (MOAR), an enhanced MAC protocol for multi-channel and multi-rate IEEE 802.11 enabled wireless ad hoc networks to opportunistically exploit the presence of frequency diversity (in the form of multiple frequency channels). The key mechanism of MOAR is that if the signal to noise ratio on the current channel is not favorable, mobile nodes can opportunistically skip to better quality frequency channels enabling data transmission at a higher rate. As channel separation for IEEE 802.11 is greater than the coherence bandwidth, different channels experience independent fading and hence there is a high probability that the skipping nodes will find better channel conditions on one of the other frequency channels. Each skip comes at the cost of resources spent in channel measurement since channel quality of different channels is not known a priori. Consequently, we devise an optimal skipping rule for MOAR which maps the channel conditions at the PHY layer to a MAC rule which allows each node to determine its optimum number of skips based on average channel conditions. Finally, we perform an extensive set of ns-2 simulations to evaluate the performance of MOAR and the impact of such factors as location distribution, channel conditions and error in channel measurements on the throughput gains offered by MOAR.