802 . 11 a Modeling and MAC Enhancements for High Speed Rate Adaptive Networks

In this study, we model the IEEE 802.11a protocol in our network simulator, QualNet. By implementing and modeling characteristics of the physical 802.11a layer, we aim to understand the underlying OFDM modem and its interactions with the 802.11 PHY and MAC layers. With an accurate 802.11a model in place, we propose a solution to improve the efficiency of the 802.11a MAC layer. It is widely known that as physical radio bit rate increases, current wireless distributed medium access control techniques suffer from throughput inefficiency. This drawback is of increasing importance as typical ad hoc networks are now often equipped with high-speed auto rate adjusting radios. Through an in-depth understanding of 802.11a OFDM training and synchronization sequences, we propose a protocol to alleviate MAC and PHY inefficiencies. We show that physical layer preamble and medium access control mechanisms account for significant unnecessary overhead. After justifying our enhancements, simulation results in MANETs show that our scheme improves overall throughput significantly. Our future direction would be to integrate an OFDM simulator into QualNet to more accurately simulate the physical modem and to model the time varying and frequency selected shifting characteristics of the wireless channel in additions to the channel models currently in placed.