Introducing Finer Prioritization in EDCA using Random AIFSN

The recently adopted WLAN standard IEEE 802.11e provides quality of service (QoS) differentiation by grouping the traffic into different access categories (ACs) with different priorities. It defines different arbitration inter-frame space number (AIFSN) on a per-category basis to ensure that each category has different probability of accessing the channel. Within an AC, random back-off mechanism is used to spread the traffic. However, when there are a large number of QoS stations (QSTAs) within an AC, the probability of two or more stations choosing the identical back-off values is increased leading to increased packet collisions. In this paper, we propose the use of randomized AIFSN. The random AIFSN method can be exploited to introduce finer priority values within an AC. Each AC is assigned an AIFSN interval and a probability distribution function (PDF) defined over that interval. The simulation results indicate that the proposed method leads to reduced probability for collisions and higher throughput. We also present some testbed results to verify the improvement using random AIFSN method.