Abstract:
The MAC layer of the IEEE 802.11 standard defines Distributed Channel Function (DCF), that provides simple and effective medium access mechanism. However with the increasing demand in multimedia applications and higher data rates, DCF can not provide QoS requirements since 802.11 standard does not meet the need of Quality of Service (QoS) in high data rate multimedia applications like VoIP and IPTV. For this reason, necessary extensions are made to improve data rates and MAC control schemes according to the dynamically changing needs. To provide QoS for the multimedia applications, IEEE de ned a new MAC mechanism, 802.11e Enhanced Distributed Channel Access (EDCA). With new access categories that enable prioritization between different traffic classes. Such prioritization provides QoS for multimedia applications by increasing the probability of higher priority class packets accessing the medium. The purpose of this thesis is to design an adaptive optimization system in EDCA mechanism in order to provide better QoS for multimedia applications from both delay and throughput perspectives. To achieve this goal, analytical model of the DCF mechanism, already de ned in the literature, is improved for the EDCA mechanism. Based on the back-off procedure in EDCA, that is represented using a Markov model, the estimates of throughput and delay are obtained by determining the probabilities in the Markov model. In order to validate the estimated throughput and delay, real time simulations in OPNET are carried out and the correlation between analytical results and simulation results are included in the thesis. Based on the validated analytical model, a new algorithm is proposed in order to maximize throughput while decreasing delay and minimizing collision probability for a higher access category.
