Contention Window Optimization for Distributed Coordination Function (DCF) to Improve Quality of Service at MAC Layer

Abstract

With emergence of new multimedia and real-time applications demanding high throughput and reduced delay, the existing wireless local networks (WLANs) characterized by mobile stations with a low bandwidth and high rate error are not able to provide these QoS (Quality of Service) requirements.

After collisions during competitive access to the channel, packets must be retransmitted. These retransmissions consume enough bandwidth and increase the end-to-end delay for these packets. To address this, our solution tries to propose a new incrementing way for contention window (CW) with more realistic values in DCF (Distributed Coordination Function) at MAC layer. In order, to provide an opportunity for each station which needs to use a given channel, a way to access it after a small number of attempts called “Ret” (i.e. avoid the problem of starvation), we proposed to use “Ret” value in a new way to calculate CW values.

To show the performance of the proposed solution, simulations were conducted under Network Simulator (NS2) to measure the traffic control and packet loss ratio under various constraints (mobility, density, etc...).