Access Network Selection and Optimized Handovers in Heterogeneous Wireless Networks
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In recent years there has been rapid growth in deployment and usage of real-time network applications such as Voice-over-IP, video calls/video conferencing, live network seminars, and networked gaming. The increase in the popularity of such real-time applications requires that more attention is focused on Quality of Service (QoS) parameters such as delay, jitter and packet loss in access networks. At the same time, wireless technologies have become increasingly popular in a wide array of consumer devices such as laptop computers, Personal Digital Assistants (PDAs), and smart cellular phones with built-in 3GPP, Wi-Fi and WiMAX interfaces. For real-time applications to be successful over a variety of wireless networks, simple, robust and effective QoS mechanisms suited for a variety of heterogeneous wireless networks must be devised. Implementing the QoS mechanisms across multiple neighboring networks aids seamless handover by ensuring that a user application will be treated in the same way, both before and after handover. To provide a good user experience during a handover it is pivotal to guarantee both service continuity and service quality, both of which rely not just on the type of network, but also on how those networks are managed and even how different services should be charged for as well as settlement across several providers. QoS is also influenced by the types of applications a mobile terminal (MT) is running, user preferences and network usage criteria in different service areas, transmission media and implemented mechanisms. 4G wireless networks are expected to take integration to the next level with support mechanisms for close integration and collaboration of divergent access network technologies. In such heterogeneous networks, roaming mobile nodes will experience regular handoffs across network boundaries. To guarantee seamless roaming and effective resource treatment over different networks, intelligent Vertical Handover Decision (VHD) algorithms will need to be extensively implemented. The objective of this thesis is to develop new handover management techniques for supporting seamless handover and for facilitating ubiquitous computing in heterogeneous wireless networks. More specifically, the aim is to develop new techniques for dealing with the extensive collaboration of 4G networks that will enable the interworking of heterogeneous wireless technologies. The research project presented in this thesis focuses on this problem by offering optimized schemes for integration of wireless access networks and algorithms for performing seamless vertical handover including minimized handover delay and reduced jitter while still maintaining high user satisfaction levels. The thesis proposes solutions for access network selection and integration in heterogeneous wireless networking environments. In terms of the interworking of heterogeneous wireless technologies, the thesis presents an architecture for supporting mobility of roaming users in heterogeneous environments that avoids the need for scanning the medium when performing vertical handovers. The presented model addresses the challenge of working with heterogeneous wireless technologies from the perspectives of the mobile terminals and network nodes. Under the proposed multi-interface architecture, a mobile terminal can work with multiple network interfaces through common upper layer protocols such as Mobile IPv6. By being compatible with the IEEE 802.21 framework, the model implements a cross-layer design approach. The ranking algorithm proposed in this thesis takes a number of criteria into account including network characteristics and user preferences by using a multi-objective optimization technique based on supervised learning that ranks each access network for fitness of selection. The thesis also proposes a solution for network and user based mobility management. The scheme provides mechanisms for mobile applications to control the tradeoff between usage of the desired access network and the selection of the best available network in heterogeneous environments for specific applications and mobile users. In fact, the VHD algorithm equilibrates the MTs assignment over the available networks by attaching each terminal to the network that has a capacity nearest to the MT requirements. Results include load balancing, reduced delay, decreased jitter and error rate, and consistent bit rate. This is achieved by distributing the MTs over the networks even if the networks have modest performance.