Maximizing QoS by cooperative vertical and horizontal handoff for tightly coupled WiMAX/WLAN overlay networks

In the past few years, the deployment of WLAN proliferated throughout the world due to easy installation, low cost and higher bandwidth. The latest IEEE 802.11 standard (802.11n) offers the maximum data rate of about 600 Mbps which makes it an accepted benchmark for deploying WLANs. One of the disadvantages in WLAN is its small coverage which is not suitable for mobiles with high velocity. The alternate network technology for WLAN with almost equal bandwidth and QoS support with wider coverage area is WiMAX, which is one of the rapidly growing technologies across the world. Hence, the integration of WiMAX and WLAN is considered to be a sound approach in 4G. In this paper, we present handoff and integration related issues in WiMAX/WLAN overlay networks, numerical methods for calculating network conditions of both WiMAX and WLAN networks and impact on 802.11n clients by legacy 802.11a/b/g clients. Also, we propose QoS based proactive handoff algorithms for WiMAX/WLAN overlay networks which performs both vertical and horizontal handoffs based on the network condition, acceptable packet delay, required bandwidth and client type. Simulation results demonstrate that the proposed handoff algorithm enhances the QoS significantly.