Dynamic dual adaptation of EDCA mode for QoS support in IEEE 802.11 wireless AD HOC networks
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In this study we focus on Quality of Service QoS support for wireless ad-hoc networks. First we present overview of MAC sublayer and a contention based channel access scheme EDCA defined in IEEE 802.11e for QoS support in IEEE 802.11 ad-hoc networks and other enhanced algorithms that have been proposed for support of QoS in wireless ad-hoc networks. Next we present three enhancements of EDCA with dynamic adaptation algorithms called Dynamic Algorithm for tuning of Contention Window (DACW), Dynamic Dual Adaptation of EDCA (DDAE) and Dynamic Dual Adaptation of EDCA with Adaptive Fair (DDAE-AF) that enables each station to tune its Contention Window (CWi) and Arbitration Interframe Space (AIFSi) at run time based on the channel load and traffic status. We simulated our dynamic adaptation algorithms using ns-2 network simulator and compared the performance of our dynamic adaptation algorithms with basic EDCA and other dynamic adaptations such as AEDCF, AF-EDCA and DCWmin . The results of the simulation demonstrates that DACW outperforms DDAE, AEDCF, DCWmin and EDCA in terms of mean audio-delay, jitter, on the other hand DDAE improves the throughput and medium utilization. The mean audio delay in DACW is 33% lower than in DCWmin. The overall gain on goodput of DDAE is about 8% higher than that of DACW and 12% higher than AEDCF. For low contention, channel usage for DDAE is about 70% higher than that of DACW, DCWmin, AEDCF and EDCA. Simulation of Dynamic Dual Adaptation of EDCA with Adaptive Fair (DDAE-AF) provides better results in terms of collisions rate, medium utilization and throughput when the number of nodes are more than 20 nodes compared to AFEDCA, AEDCA, EDCA, DCWmin, DACW and DDAE.