Research, Based On The Ieee802.11 Wlan Qos Mechanisms

IEEE 802.11 WLAN is one of the widest wireless protocols with the fastest developing speed at present. With its constant revision and perfection, its transmission rate is higher and higher. IEEE802.11a adopts OFDM modulation technology, its highest transmission rate is 54Mbps. Now IEEE802.11 n working group has already been established, which adopts MIMO-OFDM technology, plant to increase the transmission rate from 54Mbps to 108Mbps, and up to 320Mbps, becoming another break-through after 802.11b, 802.11a, 802.11g. WLAN has such the high transmission rate that it can meet multimedia demand absolutely. It is very important for a commercial wireless network to support proper quality of service(QoS). The expert prophesies, the degree of support that the wireless LAN requires to QoS is whether it can obtain the key to success in the wireless field of future.The paper mainly carries on research to QoS of IEEE802.11 WLAN. Firstly , the paper introduces the operation principle and shortcoming to support QoS of DCF and PCF MAC access mechanism. Next , the paper introduces 802. 11 MAC enhanced mechanism 802.11e. Because of the actual condition and research condition, the paper mainly carries on research to contention-based channel access mechanism ( EDCF ) and analyses EDCF theoretically by Markov model . QoS support in EDCF is realized with the introduction of traffic categories, and EDCF provides differentiated distributed access to wireless medium for eight priorities of stations. the dataflow with higher prior will be distributed smaller IFS and CW, in order to guarantee the high PRI data accessing channel first and obtaining the bandwidth of greater transmission, thus the applications requiring delay, packet-loss are satisfied. But there are some problems, such asthroughput, high load condition collision causing the channel utilization to drop, QoS of network will be seriously influenced. The paper makes further research to QoS of WLAN MAC sublayer, and puts forward several enhanced scheme of QoS. To CFB mechanism , paper proposes one group ACK mechanism and analysed theoretically, at the same time proposes using FEC/ARQ mechanism for the wireless network in order to improve network quality. A adaptive mechanism CBRA to "chain reaction" existing in wireless network is proposed to reduce data packet collision and improve the channel utilization ratio.The idea is to dynamically to adjust PF based on the age of a real-time packet in transmission queue and the lifetime of the packet to change CW and improve quality of service of network. These methods are carried on function proved and performance investigated by NS-2. 26 simulator tool. The paper analyses their performance in detail and draws the conclusion through the throughput simulation curve. Finally, the paper analyses end-to-end QoS mechanism based on IP network .