Vertical handoff and resource management in heterogeneous wireless networks

The trend of the fourth-generation wireless networks (4G) is the coexistence of hetero-geneous technologies. With an overlay architecture, advantages of different technolo-gies can be well integrated into one system, allowing subscribers to profit the best service anytime and anywhere, i.e., the so-called “always best connected” (ABC). To efficiently integrate heterogeneous networks, several key issues should be investigat-ed. Among them, the most fundamental issue is the interworking architecture, which provides the solution on the platform to combine the overlay networks together. Under different architectures, the integration mechanisms in terms of mobility management, data transmission, quality-of-service (QoS) provision, and security might be quite dif-ferent. The handoff management is another essential aspect for interworking. The handoff between heterogeneous networks is referred to as vertical handoff. Unlike traditional horizontal handoff which is mainly triggered by signal strength, more factors should be considered in a vertical handoff decision, such as monetary cost, network conditions, user preference, and so on. The objective of a vertical handoff will be no longer the continuous connection but the best connection. On the other hand, because the radio resources in the interworking system can be viewed as being shared in a resource pool, the complete and efficient use of these pooled resources is also an important topic. In this thesis, we first investigate the integration mechanisms as well as vertical handoff issues in the WiMAX and WLAN overlay system, which is recently devel-oped and believed to be a promising approach toward 4G. A tightly coupled inter-working architecture is addressed and the related important mechanisms for the integration are discussed. Based on this architecture, a seamless and proactive vertical handoff scheme is designed, targeting to provide always the best services for both mobile and fixed users. Both the performance of applications and network conditions are considered in the handoff process. In order to achieve proactive handoffs, the al-gorithms for the network condition detection are derived for stations to estimate the available bandwidth and average packet delay of the two networks. We then study the resource management of general heterogeneous overlay sys-tems from the viewpoint of network providers. To effectively utilize the overall radio resources pooled in the interworking system, an efficient load balancing scheme is proposed which is applied to the call admission control process. When the available networks cannot provide enough resource for the request call without degrading the QoS obtained by the ongoing calls, the system will perform load balancing operations by dynamically initiating vertical handoffs among networks to create more room for the request call. Finally, we make considerable research efforts on the radio resource management for the multicasting and broadcasting service in the heterogeneous wireless networks. A novel network selection and resource allocation scheme is designed to minimize the overall system resources consumed by the multicast or broadcast stream, which is formulated as an optimization problem and solved by the derived algorithm. By the scheme, the member stations at the same network region can be effectively converged together, meanwhile the stream can be transmitted with higher modulation and coding rates so that the consumed resources can be reduced.DOCTOR OF PHILOSOPHY (EEE