Research Of Quality Of Multimedia Services Scheme In IEEE 802.11e Based Ad Hoc Networks

Wireless Local Network (WLAN), as a kind of broadband wireless network, is playing a more and more important role in many occasions for their mobility, flexibility, easy extension and low cost. There are many standards about the WLAN and the IEEE 802.11 serial are the most widely used standards in WLAN. The services of WLAN have been extended from traditional data service to real time multimedia services. A number of amendments to the base 802.11 standard have been approved by the IEEE and implemented by manufacturers since 1997. IEEE 802.11e, especially, which has increased a lot of new QoS related contents and made redescription about the meaning-changing contents, has been issued at year 2005 to support QoS in WLAN.IEEE 802.11 standard adopted CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) mechanism in MAC layer. Each station is scheduled to access the wireless medium through the contention window control algorithm, which is named as binary exponential back-off algorithm. Although amended the Quantity of Service part, IEEE 802.11e, which has achieved QoS enhancements by access category and transmit opportunity, has the same back off mechanism as 802.11. Research shows that, by using this mechanism, WLAN achieve much lower throughput comparing with physical rate. The main research achievements of this paper are as follows:Analyzed the characteristics and theory of 802.11 and 802.11e;Analyzed the problem of binary exponential back off algorithm of 802.11 series media access control mechanism;SA-MILD (Self-Adaptive Multiplicative Increase Linear Decrease), which is based on MILD (Multiplicative Increase Linear Decrease) and very easy to implement, is presented. Also studied the performance of this algorithm theoretically;The simulation results show that, comparing with the traditional binary exponential back off algorithm of MAC, SA-MILD obtains lower delay, higher throughput and effectiveness.