Throughput improvement of IEEE 802.11 using adaptive slot size

摘要

Although recent IEEE 802.11 wireless LAN standards (such as 802.11n/ac) support physical layer (PHY) transmission speed more than 10 times that of 802.11g, the user level throughput has not seen a proportionate increase. The primary reason for this anomaly are the various overheads of channel access, preamble and acknowledgements. In this paper, we present a MAC protocol that enables the access point (AP) in an infrastructure based 802.11 WLAN system to dynamically reduce the slot time used in the protocol thereby reducing the channel access overhead. A major component of slot time is the clear channel assessment (CCA) time, which is the time taken by a node to determine if the wireless medium is idle or busy. A key fact we exploit is that any node requires less time for CCA if the SNR of all nodes in the network at this node are high. Our protocol first determines the worst-case pair-wise SNR of all nodes in the WLAN by polling nodes by leveraging the PCF mode of 802.11 and then determines the optimal CCA and slot time. We present a theoretical analysis to determine the optimal CCA time given SNR and evaluate our protocol using the Qualnet Simulator.