Enhance the Performance of EDCA Protocol by Adapting Contention Window

Abstract

The real-time application is the main challenge that faces the wireless network. It must achieve the quality of service (QOS) requirements to success. IEEE802.11 standards use Enhanced Distributed Channel Access (EDCA) protocol and Distributed Coordinate Function (DCF) protocol in its Media Access Control (MAC) layer. EDCA protocol is used to overcome the drawback of supporting QOS in DCF protocol. The mechanism of EDCA protocol is based on dividing the data to four queues; voice, video, best effort and background. The queues have different priorities to access the medium. The voice queue has the highest priority and its data will serve firstly. Using the default parameter values for EDCA protocol will lead to increasing the collisions in the wireless network and decreasing the capacity. In this paper, the limitation of supporting QOS in EDCA protocol was presented by using OPNET simulation and mathematical model. The new mathematical model was designed by using Markov chain mechanism to evaluate the performance of the EDCA protocol under saturation and non-saturation conditions, aimed to separate between uplink and downlink throughput with different data types. Moreover, the new algorithm was proposed to enhance the capacity of the EDCA protocol and increase the number of the active voice users. Through our algorithm, the throughput was increased by 27.72% and the EDCA can support 14 voice users rather than 11 in the default EDCA protocol. The evaluation of our new algorithm was verified by using OPNET simulation and mathematical model.