Adaptive Tuning of MIMO-Enabled 802.11e WLANs with Network Utility Maximization

The IEEE 802.11-based wireless local area networks (WLANs) are widely used for high-speed wireless data access. With the recent 802.11e quality-of-service (QoS) extension, realtime applications such as voice over IP and video streaming are finding their way to be running over WLANs. The recent 802.11n proposal aims to provide higher throughput support for bandwidth-intensive multimedia applications. It uses the multiple-input-multiple-output (MIMO) technology at the physical layer to increase the transmission rate. MIMO introduces several new features at the physical layer such as the spatial diversity and spatial multiplexing gains. These new characteristics at the wireless physical layer require corresponding adaptation at higher layers to achieve a better performance. This paper proposes a joint adaptation of the MIMO physical layer and the 802.11e MAC layer through the formulation of a network utility maximization problem. The MIMO configuration at the physical layer and the contention window sizes for different access categories' traffic at the MAC layer are jointly optimized. Simulations are carried out in the ns-2 simulator to show the effectiveness of the proposed method.