Mitigating 802.11 Mac Anomaly Using SNR To Control Backoff Contention Window

Abstract

The standard 802.11 presents a MAC anomaly when the same Access Point operates stations with different data rates. Analysis shows that the degradation is higher for the station with a high data rate that operates with good signal to noise ratio (SNR). Consequently, the station with low SNR has higher throughput then stations with high SNR. To evaluate the anomaly an experimental test was created to obtain the WLAN behavior with wireless host transmitting with low SNR together with hosts with high SNR. The anomaly was evaluated experimentally utilizing two architectures: Fat and Thin. The anomaly was detected in the Fat architecture and was not detected in the Thin architecture. This paper presents a strategy to justify the result obtained with Thin architecture, using SNR to control the contention window and consequently mitigate the anomaly. Simulations using Network Simulator (NS) are presented to demonstrate the anomaly and to evaluate the mitigation anomaly strategy. The strategy configures the wireless stations with low SNR to work with large contention windows and wireless stations with high SNR with small contention windows. With this strategy the station with high SNR obtains higher throughput than the station with low SNR.