The Ieee 802.11n The Mac Frame Aggregation Technology Research And Improvement

With the rapid development of communication technology, the demand for network communication is also constantly increasing, the development of personal data communication tends to be more and more wireless. Although the transmission rate of WLAN continue to increase and the cost is also constantly decline, the direction of further development is still faster speed WLAN because of the ever-increasing high bandwidth applications.Next-generation WLAN technology IEEE 802.11n whose goal is high throughput performancet is the amendments made to IEEE 802.11 standards. 802.11n defines a high transmission rate physical specification, and proposes frame aggregation mechanisms and Block Ack mechanisms to slove the problem of insufficient transmission capacity of MAC layer. This thesis studied and improved the frame aggregation mechanism which proposed by 802.11n standard.Frame aggregation mechanisms optimized the structure of data frame and saved the overhead of MAC layer.However, due to relatively large length of the aggregate frame, the use of frame aggregation mechanism will also increase the probability of data frame retransmissions and system burden under the non-ideal wireless channel. For this problem, Choosing saturation throughput for the parameter, this thesis used two methods of modeling and simulation to analyse the WLAN system performance which used A-MSDU and A-MPDU mechainsm. First, for the purpose of improving the saturation throughput of 802.11n system in non-ideal channel, the thesis proposed a algorithms which can adjust the length and number of aggregate frame dynamically according to the bit error rate of wireless channel. This algorithm balances the advantage of saving additional cost and the disadvantage of increasing retransmission probability when use frame aggregation mechanisms. The algorithm also optimizes system performance. Second, after analysing the fragmentation mechanism and aggregation mechanism in depth, the thesis proposed fragmentation-aggregation mechanism which combined the advantages of these two mechanisms. As to the impact fragment length on system performance in non-ideal channel, the thesis proposed a fragmentation algorithm. This algorithm make the system can maintain a stable and efficient performance faced with different channel bit error rate.