Time-varying channel conditions, due to multipath fading, present a unique challenge for wireless network design. In this paper, we take a cross-layer approach to study frequency-agile medium access control design for ad hoc networks. Specifically, building on the IEEE 802.11 standard, we propose an opportunistic multi-channel MAC protocol (OMC-MAC), with three key features: 1) by exploiting the channel variations across multiple channels, OMC-MAC achieves selection diversity gain in an opportunistic and distributed manner; 2) the size of the contention window is adjusted adaptively based on the estimate of the number of competing stations, which is obtained via using a sequential Monte Carlo technique; and 3) OMC-MAC achieves "resource pooling" and thus improves the stability of the network. Analysis results reveal that OMC-MAC in wireless LANs achieves significant throughput gain, even under heavy traffic conditions. Extensive simulation studies show that OMC-MAC can achieve efficient channel utilization for each added channel, compared with the standard 802.11 MAC protocol and other multichannel protocols such as DCA and MMAC. Finally, we show via examples that the sequential Monte Carlo method is effective for the adaptation of the contention window size
['Dong Zheng', 'Junshan Zhang']
Protocol design and throughput analysis of frequency-agile multi-channel medium access control