MILD based sliding contention window mechanism for QoS in Wireless LANs

Multimedia applications and real time communications like audio, voice, and video over IEEE 802.11 WLANs requires quality of service (QoS). IEEE 802.11 does not have an in-built QoS supported MAC protocol. Existing work provides service differentiation based on contention window separation (CWS) or variation of the waiting time using Inter Frame Space (IFS). In CWS, the higher priority traffic receives a CW that results in a smaller Backoff Interval (BI) whereas lower priority receives a CW that results in longer BI. Nafaa et al. used Sliding Contention Window (SCW) with Linear-Increase Linear-Decrease (LILD) mechanism as the backoff algorithm. LILD does not provide strict service differentiation in case of high network congestion and suffers from fairness problem. In order to ensure firm service differentiation while maintaining maximum bandwidth utilization and provide fairness, this paper proposes a new MAC protocol for WLANs that uses SCW scheme for each network flow with Multiplicative-Increase Linear-Decrease (MILD) mechanism as the backoff algorithm. The simulation results show that SCW with MILD scheme provide strict service differentiation, increased throughput, decreased delay and better fairness in high network population and high congestion.