QoS-Based Adaptive Contention/Reservation Medium Access Control Protocols for Wireless Local Area Networks

In the conventional IEEE 802.11 medium access control protocol, the distributed coordination function is designed for the wireless stations (WSs) to perform channel contention within the wireless local area networks (WLANs). Research work has been conducted to modify the random backoff mechanism in order to alleviate the packet collision problem while the WSs are contending for channel access. However, most of the existing work can only provide limited throughput enhancement under specific number of WSs within the network. In this paper, an adaptive reservation-assisted collision resolution (ARCR) protocol is proposed to both improve packet collision and reduce the backoff delays from the random access scheme. With its adaptable reservation period, the contention-based channel access can be adaptively transformed into a reservation-based system if there are pending packets required to be transmitted between the WSs and the access point. Moreover, in order to support quality-of-service requirements, the enhanced-ARCR (E-ARCR) protocol is further proposed to provide adaptation for multiple prioritized traffic in the WLAN. Analytical models are derived for both proposed schemes to evaluate their throughput performance. It can be observed from both analytical and simulation results that the proposed protocols outperform existing schemes with enhanced channel utilization and network throughput.