Cross-Layer Exploitation of MAC Layer Diversity in Wireless Networks

The conventional function of the medium access control (MAC) layer in wireless networks is interference management. We show how the MAC can also be used to mitigate the effect of fading. We begin by providing experimental data to demonstrate that multipath fading effects are seen at the MAC layer. These effects appear at timescales on the same order of the IEEE 802.11 protocol and therefore, interact negatively with the RTS-CTS-DATA-ACK handshake. We identify two types of MAC diversities to jointly combat fading and interference, called multi-receiver diversity and multi-channel diversity respectively, through canonical scenarios. In order to harness these MAC layer diversities, we propose a simple dynamic-binding multi-channel MAC (DB-MCMAC) protocol that is backward compatiable with IEEE 802.11. DB-MCMAC exploits MAC diversities by opportunistically acquiring the floor for the best receiver on each channel, and dynamically binding data transmissions after the floor has been acquired. We employ a simple continuous time Markov chain model to analyze the expected performance of the DB-MCMAC protocol. A comprehensive performance evaluation of DB-MCMAC using ns-2 shows that it can successfully harness multi-receiver and multi-channel fading and interference diversities to provide considerable improvements over a baseline multi-channel MAC in several situations.