Performance Evaluation of New MAC Mechanisms for IEEE 802.11n

The medium access control (MAC) layer can be seen as the main bottleneck for the IEEE 802.11-based wireless networks. The famous overhead occurred at the MAC layer prevents the wireless local area networks (WLANs) from reaching the intended performance, which drag along a problem in the upcoming very high-speed WLANs where the physical layer rate may exceed 216 Mbps. To mitigate the overhead problem, we investigate in this paper a new MAC layer scheme; named aggregation with fragment retransmission (AFR). In this scheme, multiple packets are aggregated and transmitted in a single large frame reducing the access overheads and hence increasing the data rate. In addition, we investigate the performance added value when each large frame is fragmented so in the case of erroneous data frame, only the inaccurate fragments are to be retransmitted reducing the error control overheads and this decreases the frame error rate without requiring more overhead. This aggregation with retransmission of only erroneous fragments improves the global performance of the network. We evaluate the performance of AFR scheme considering the existing IEEE 802.11b standard and the future IEEE 802.1 In one. Simulation results show that AFR improves the performances of the MAC protocol compared to the utilisation of 802.11 distributed coordination function (DCF) which is the fundamental function to access the wireless medium in IEEE 802.11 networks.