Advanced MAC Mechanisms In WLAN With AP Dense Deployment

With the development of the Internet, Wireless Local Network( WLAN) has been widely used in our daily life. WLAN medium access control(MAC) protocol determines the mode of nodes shareing channel and fundamentally affects the performance of the whole network. IEEE 802.11 standard is current widely used specification in the WLAN network. IEEE 802.11 MAC as a core part of the wireless local area network has many notable advantages when used in single-rate sparse networks. However, with the development of WLAN networks, this access mechanism is no longer suitable for AP densely deployed networks, so it is imperative to explore advanced MAC access mechanisms. In this thesis, we depthly analyse the problems existing in AP densely deployed networks and propose improved MAC access mechanisms. Our research work is focused on the following two issues:(1) 802.11 DCF MAC mechanism was initially designed for single rate networks.This mechanism provides every node the same channel access opportunities and ensures that every node fairly occupies channel. Currently multi-rate networks are still using802.11 DCF as the basic access mechanism, resulting in that low rate node persistently occupies channel, and thus cannot fully take advantages of high-speed transmission.The throughput of all the nodes in the network are driven down to the throughput of the low rate node, which is the wildly known as “performance anomaly problem in multi-rate network ". Aiming at solving this problem, we first use TBR access mechanism to analysis this problem, then we provide an advanced MAC optimization mechanism called CCDa P to ensure the node’s Throughput Proportional Fairness in multi-rate networks, by using modeling and analysis. NS-2 simulations show that, the proposed access mechanism can ensures all nodes throughput Proportional fairness and improves the overall network throughput. In particular, even the length of packets in the multi-rate WLAN are not equal, the mechanism still guarantees node’s fairness.(2) Given a thorough analysis to the hidden/exposed terminal problems in AP densely deployed networks, and propose an advanced MAC mechanism-- SACA. This mechanism analyses the relationship between the received signal strength and successfully sending ratio, then establishes a diagram, which is called RSS_SR diagram.Nodes in the network according to the diagram choose a proper time to transmit. NS-2network simulations show that this mechinism not only reduces packets loss caused by hidden/exposed terminal, but also improves the overall performance of the network.