Analyse & Research Of Quality Of Service In IEEE802.11

As the development of wireless networks (WLAN), it brings much more convenience to us. Besides, Quality of Service (QoS) demand emerges due to the popularity of multimedia traffic. However, the WLAN can't provide QoS Guarantees for the shortcoming of channel access mechanism. Therefore, it is quite worthwhile to do researches about how to provide QoS in WLAN. IEEE802.11e, is published by IEEE802.11 committee on Nov. 2005, and provides guidance to implement QoS Guarantees in WLAN at medium access control (MAC) layer.Firstly, after discussing the limitation of the IEEE 802.11 MAC on QoS, the thesis gives a comprehensive study of the IEEE802.11e. The main QoS facility of IEEE802.11e is Hybrid Coordination Function (HCF) mechanism. The HCF uses both a contention-based channel access mechanism, called the Enhanced Distributed Channel Access (EDCA) mechanism, and a controlled channel access mechanism, referred to as the HCF Channel Access (HCCA) mechanism.Secondly, the thesis researches the characteristics of EDCA parameters, and describes the defects of CW in providing QoS. So the thesis proposes a dynamic scheme which adjusts the CW. After each successful transmission, in order to increase the goodput, the scheme combines the network conditions and traffic requirements to dynamically adjust the CW by taking into account average collision rate and applying the principle of token bucket algorithm; after each collision, in order to decrease delay of higher priority traffic, the scheme considers both the age time of frame and network conditions. Then, the thesis implements the scheme in Network Simulator (NS). Results show that the proposed scheme gets a good performance in goodput and delay, especially at high traffic load conditions.Finally, the thesis proposes a simple but effective scheme to provide delay guarantee for transmitting VBR in HCF. After discussing the characteristics of EDCA and VBR, it is suitable to transmit VBR under EDCA. This scheme provides delay guarantee for VBR by both using HCCA and EDCA. The simulator results validates the scheme can decrease delay for VBR.