Research And Improvement For QoS Of WLAN

The WLAN technology has been adopted widely in computer and communications networks. Compared with the traditional Ethernet, WLAN has some predominant advantages in terms of mobility, constructivity, maintainability, anti-jamming and security, which makes it easier access to portable devices and LANS and more efficient to transmit image information ,voice message and email. With the rise of time-delay sensitivity business (e.g. video) and the limitation of network bandwidth resources, the requirement of taking assurance of QoS into application is brought on exigently. The channel-access technology in the MAC layer is the crucial link for the assurance of QoS technology. So it is important to research the access technology in the WLAN MAC layer.IEEE 802.11x protocols are the mainstream protocols in WLAN technologies which mainly prescribe the access technologies in the MAC layer. Primarily, this paper will make a research on the access technologies in the MAC layer and do an analysis on the realization mechanisms of the PCF and DCF that is deeply analyzed based on Markov chain model proposed by Bianchi and then make a discussion and conclusion about the cons and pros of QoS mechanisms based on IEEE 802.11. Next, this paper will make a detailed introduction on access mechanisms in the MAC layer as well as QoS mechanisms based on IEEE 802.11e and do an analysis on the realization difference between IEEE 802.11 and IEEE 802.11e using QoS mechanisms and then draw a conclusion about advantages of EDCA over DCF. Finally, in conformity to the Markov chain model this paper will make an analysis on relationships among EDCA throughput, time delay, the numbers of STA and the value of CW, and hereby according to dynamic setup and value of network status present an improved scheme ---DEDCA scheme, which is validated that it is better than EDCA by comparing the throughout and time delay with the emulating of these two schemes using NS2 tool.