QOS Oriented Vertical Handoff for Wimax/Wlan in Overlay Network

Vertical Handoff (VHO) scheme is designed based on the interworking architecture of WLAN/WIMAX which aims to provide always the best Quality of Service (Qos) for users. The performance of applications and network conditions are considered in the handoff process. The handoff procedures are normally initiated when the stations move across the border of WLANs. As a result, both the fixed station and the mobile stations within overlapped areas cannot benefit from VHOs. VHO could be initiated by two factors: mobility when a station moves out of the coverage of its connected WLAN and QoS when the connected network cannot satisfy the requirements. The whole handoff process is achieved by Vertical Handoff Manager (VHOM), which works on the Medium Access Control (MAC) layers of WiMAX and WLAN. VHOM uses the VHO decision algorithm to control smooth handoff between the WIMAX and WLAN. Moreover, evaluation algorithms to estimate the conditions of both WIMAX and WLAN networks in terms of available bandwidth and throughput. A simulation has demonstrated that schemes can keep stations always being connected. KeywordsWIMAX, WLAN, vertical handoff.