Using Markov Chain Model to Evaluate the Performance of EDCA Protocol Under Saturation and Non-Saturation Conditions

Abstract

Nowadays, there is a significant increment of internet usage in public locations such as airports, restaurants and bus stations. Ease of extension and low costs make wireless networks more suitable than wire networks in these public locations. Providing quality of service (QOS) is the main challenge that wireless networks face. IEEE802.11e is developed to support QOS for real time applications. It uses the Enhanced Distributed Channel Access (EDCA) protocol rather than the Distributed Coordination Function (DCF). EDCA protocol uses four queues in its MAC layer. These queues have different priorities and serve different types of data (video, voice, best effort and background). On the other hand, DCF protocol has only one queue for all types of data. In this paper, a new Markov chain model is proposed for the EDCA protocol, which works in saturation and non-saturation conditions. The Markov chain model covers the difference between the station and the access point (AP). Also, it presents how the AP is considered as the bottleneck of the network, and it hinders the wireless network to serve more voice users with supporting QOS. The throughput of stations and AP are calculated for different data types. In addition to that, an adjusting contention window mechanism is proposed to enhance the capacity of wireless networks to support more voice users.