Abstract
As mobile communication evolves into 3G beyond, the interworking of multiple heterogeneous networks serves as the major effort for taking the best advantage of different technologies available in supporting various emerging services, such as VoIP, Video on Demand (VoD), and IP Television (IPTV), etc. Vertical handoff is one of the key mechanisms in achieving Always Best Connected (ABC) for the mobile users by leveraging the benefits of deploying different types of networks for provisioning seamless handoff/roaming services in presence of user mobility. This paper aims to introduce a novel cooperative two-step vertical handoff scheme for the integration of 3G Wireless Wide-Area Networks (WWAN) and the IEEE 802.11 Wireless Local-Area Networks (WLANs). The proposed scheme is based on the cooperation based access point (AP) and mobile station (MS), where the AP manipulates the sensed signal strength to determine whether a pre-handoff action should be initiated. To improve the accuracy of user mobility prediction, a Markov model that incorporates with a novel parameter training process is developed at the AP for acquiring the hotspot geographic arrangement, such as the location of aisles, walls, and entrances/exits, etc., which is considered as the major factor of determining the user mobility patterns in an indoor hotspot. We will justify feasibility and discuss the operation complexity of the proposed cooperative vertical handoff. Moreover, error propagation due to inaccurate signal strength measurement is studied through Maximum Likelihood estimation. Finally, we will clearly demonstrate the merits gained by using the proposed two-step vertical handoff mechanism through extensive simulation, where the derived analytical models are verified.
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