AEDCF: Enhanced Service Differentiation for IEEE 802.11 Wireless Ad-Hoc Networks
Résumé
This report proposes an adaptive service differentiation scheme for QoS enhancement in IEEE 802.11 wireless ad hoc networks. Our approach, called Adaptive Enhanced Distributed Coordination Function (AEDCF), is derived from the new EDCF introduced in the upcoming IEEE 802.11e standard. One of the main problems of EDCF is the static reset of the Contention Window (CW) which decreases significantly the throughput performance and increases the collision rate specially at high load conditions. Our scheme aims to share the transmission channel efficiently while providing different priorities to access the wireless medium. Relative priorities are provisioned by adjusting the size of the Contention Window (CW) of each traffic class taking into account both applications requirements and network conditions. We have implemented AEDCF in the NS-2 network simulator. Several simulation scenarios have been used to evaluate its performance and to determine the optimal value of certain parameters. We analyse through simulations the efficiency of the slow and adaptive decrease of the CW after each successful transmission and compare it with the classic scheme proposed in the standard. Results show that AEDCF outperforms the basic EDCF, especially at high load conditions- . Indeed, our scheme increases the medium utilization ratio and reduces for more than 50 rate. While achieving delay differentiation, low jitter is also maintained, and the overall goodput obtained is up to 20 Moreover, the complexity of AEDCF remains similar to the EDCF scheme, enabling the design of cheap implementations.