Nonsaturation throughput analysis of IEEE 802 11b distributed coordination function under the imperfect channel conditions

Abstract

Wireless Local Area Networks (WLANs) are gaining popularity at an unprecedented rate, at home, at work, and in public hot spot locations. The heart of the current 802.11 WLANs mechanism is the Distributed Coordination Function (DCF). The Binary Exponential Back off (BEB) algorithm in the IEEE 802.11 Medium Access Control (MAC) protocol does not work well when the wireless channel is not favourable for packet transmission. To cope with the varying channel conditions, the IEEE 802.11b standard defines multiple transmission rates. In the recent past, many algorithms have been proposed to enhance the performance of the 802.11 DCF under ideal channel conditions. This thesis presents the analytical model for both single rate and multi-rate 802.11 wirelesses LAN. A new back off algorithm called Back off Algorithm-Same Stage (BA-SS) is proposed in this thesis. This algorithm reduces the channel idle time and improves the performance of IEEE 802.11 DCF under non-ideal channel conditions. Another back off algorithm proposed in this thesis is Back off Algorithm-Reservation Stage (BA-RS). The numerical results show that the BA-RS algorithm outperforms as compared with BA-SS algorithm and BEB algorithm. Based on the concept of treating packet collision and transmission error in different manner, these proposed algorithms provide better performance than BEB algorithm. The IEEE 802.11b standard defines four transmission rates (1,2,5.5, and 11Mbps) to mitigate the effect of the channel conditions. The analytical model of single rate transmission is extended for multi-rate environment. By treating packet collision and transmission error in a different manner, the aggregate throughput of the 802.11b network is improved in the multi-rate environment. The analysis result shows that the performance of this algorithm is better than that of Auto Rate Fallback (ARF) algorithm which is most widely employed in the WLAN devices available in the market. newline