QoS guarantee and provisioning at the contention-based wireless MAC layer in the IEEE 802.11e wireless LANs

This article investigates and provides novel solutions for a new research avenue to support QoS in contention-based distributed WLANs. Although QoS is easier to manage in centrally controlled and reservation-based MAC protocols, they are hardly implemented in today's products due to several reasons, such as their higher complexity and their inefficiency for normal data transmissions, lack of robustness, and the strong assumption of global synchronizations. Additionally, end users like contention-based protocols because they plug and play. Almost all end-user networks need a MAC layer, and the IEEE 802.11 WLAN and Ethernet have become widely deployed since these contention-based MAC protocols are simple, robust, and allow fast installation with minimal management and maintenance costs. There is a clear need to support QoS guarantees and provisioning at the contention-based MAC layer. QoS guarantee and bandwidth allocation schemes have been well studied for mobile cellular networks, in which bandwidth is deterministic in terms of number of channels by frequency division, time division, or code division. On the other hand, bandwidth allocation in contention-based distributed WLANs is extremely challenging due to the contention constraint, the packet-based network, and, most important, an unknown number of stations competing for access to the only channel available. As a consequence, both guaranteeing QoS and efficiently allocating bandwidth are challenging issues.