Research On Link Adaptation Technology Based On IEEE 802.11 Block ACK Mechanism

As the requirements for wireless network performance gradually increased,the most important protocol in WLAN-IEEE 802.11 not only in the physical layer has been to improve the transmission rate,but also in the MAC layer continuously improved the transmission efficiency.The frame aggregation and Block ACK mechanism were proposed by IEEE working group in 802.11n,which greatly reduce the transmission access cost.In the latest 802.11ac,the A-MPDU in frame aggregation is already the standard transmission mode of data frame.In the face of the changes in MAC layer,the previous link adaptation mechanism may no longer apply to the new standard,so the research of these mechanisms under the new standard has a great significance.In this paper,we mainly study the rate adaptation algorithm and the adaptive frame aggregation mechanism.The troditional rate adaptation algorithm under the way of statistic in the MAC layer is generally based on the common ACK mechanism,and therefore can not be well applied to the new frame aggregation and the Block ACK mechanism.In this paper,we firstly analyze the ARF algorithm under the Block ACK mechanism.Then for the problems that arise,a weight-based method under the Block ACK mechanism is proposed,which can more accurately describe the current channel condition by giving each MPDU a more appropriate weight.The new algorithm E-WFD is simulated by NS-3.The results show that the new algorithm outperforms the previous algorithms in multiple channel environments.In addition,we derive and analyze the relationship between system performance andsubframe length under the frame aggregation mechanism.Then we propose a new adaptive frame aggregation method with weight analysis.According to the real-time feedback of the channel,the new algorithm can adaptively adjust the threshold of the frame length and dynamically combine the fragment mechanism and the two-level frame aggregation with the threshold.Simulation results in NS-3 show that the new method can improve the performance significantly.