Research On Key Technologies Of IEEE 802.11n MAC Layer

IEEE 802.1 In standard had been proposed to meet the requirements of high speed and high throughput, the highest rate in the PHY layer can even reach up to 600Mbps. However, with the increasing of rate, the throughput performance is limited by high MAC overhead. To improve the efficiency of MAC layer, IEEE 802.1 In proposes the frame aggregation and Block ACK mechanism. The rate adaptation mechanism can also leverages throughput. So the analysis of these mechanisms has important significance.Firstly, this paper analyzes the frame aggregation and Block ACK mechanism that proposed by 802.1 In by an improved mathematical analysis model. The model analyzes the saturation throughput under Block ACK and frame aggregation mechanism considering the anomalous slot, backoff freezing mechanism and the bit error rate of channel. And we also analyze the two-level frame aggregation. Then we analyze the relationship between the throughput and the A-MPDU, A-MSDU, channel access mechanism using the results of the model in Matlab. The simulation results show that the RTS/CTS access model performs better than the basic access model in Block ACK mechanism. We prove that frame aggregation and Block ACK mechanism can improve the MAC efficiency and the RTS/CTS access model is more suitable to Block ACK mechanism.Then we study the rate adaptation algorithms under the Block ACK mechanism with RTS/CTS access model. Now many popular rate adaptation algorithms are based on the ACK mechanism, which have not good performance under Block ACK mechanism due to the Block ACK mechanism has longer time scale of reacting channel than the ACK mechanism and the number of one-time statistical MPDU changes. We find that ARF algorithm has some problems when it is applied on the Block ACK mechanism:1) it increases or decreases the rate by multiple times after receiving the BA frame; 2) it does not handle the BA frame timeout reasonable. To solve these problems, the paper proposes a B-ARF algorithm based on the Block ACK mechanism and analyzes the performance of it under the slow channel and fast channel by NS-3 simulator. The simulation results prove that B-ARF algorithm has better performance than the other algorithms in each case.