Research On Dynamic Aggregation Threshold And Aggregation Proportion Of Frame Aggregation Mechanism In WLAN

Wireless Local Area Network(WLAN), characterized by convenient deployment and low cost, has been widely used in families、companies and so many public places. As the mainstream standard of WLAN, IEEE 802.11 has a continuous improvement and update, which results in the better stability and higher transmission rate. Frame aggregation mecha-nism, proposed in IEEE 802.11n, is one of the methods to improve the efficiency of the MAC. IEEE 802.11ac adds no new mode in aggregated frame and specifies that all aggre-gated frame are only transmitted in A-MPDU. However, both 802.11n and 802.11ac do not explain how to use frame aggregation mechanism. In frame aggregation mechanism, the ag-gregation threshold is a method that decide when to stop the frame aggregation, which is a key factor that affect the thoughput and delay. It’s significant to adjust aggregation threshold dynamically to make good use of frame aggregation mechanism according to channel envi-ronment and payload.The main work of this thesis is carried out from following parts. Firstly, this thesis analyzes the existing algorithm in aggregation threshold. Based on the paper about the effect of aggregate subframe length on the system performance under non-ideal channel conditions, we proposed an improved dynamic aggregation thresholding algorithm. The algorithm does not consider the priority of different QoS, the algorithm adjusts aggregation threshold according to the current channel conditions periodiy to improve the throughput and channel utilization. It is validated by simulation that the proposed dynamic aggregation algorithm has a better performance in throughput and delay than using a fixed threshold algorithm. Secondly, in multi-services scenarios, since different services have different time delay requirements as well as payloads, we proposed an algorithm which can dynamically allocate the proportion of different QoS frame in an aggregated frame. The algorithm consider delay of services and the buffer queue data packet length as weigjt factors, which decides the proportion of different QoS frame in an aggregated frame. It is proved by simulation that the proposed algorithm meets the requirements of different QoS for delay. Then the influence of different weight factor on the performance of the system is compared.This thesis contains four chapters. Chapter 1 introduces the background of this thesis, the improvement of 802.11, current research status of aggregation frame, the main work of this thesis and arrangement. Chapter 2 introduces related mechanisms of MAC layer, especially TXOP, Block ACK, frame aggregation and amendment of MAC in 802.11ac. Chapter3 proposed an improved dynamic aggregation threshold algorithm based on frame length threshold and time threshold. Chapter 4 proposed an algorithm which can dynamically allocate the proportion of different QoS frame in a aggregated frame. Finally, conclusion and prospect wrap up this thesis.