Inter-System Handovers in Heterogeneous Wireless Systems

Abstract: To better utilize existing wireless systems, they can be combined together to interact and thereby provide better balanced capacity. They can further profit from this by getting their ongoing connection moved from the current system to another. The main issues are to make this move without losing the ongoing connection and to make it seamless, i.e., without the user noticing it. This action of moving an ongoing connection between different wireless systems is called inter-system handover. To make the inter-system handover the mobile terminal in use must support both the involved systems. By using the mobile terminals possibility to change system, the user can increase, e.g., the coverage, the bandwidth and the capacity. When using inter-system handovers the cost of the connection can also be optimized depending on the actual cost of using a specific system. Since the user in advance can choose the settings of the involved parameters, a specific operator or wireless system could be given priority when several alternatives exist. To easier identify and understand the handover procedure it has been categorized and divided into classes. This new handover terminology structure is presented in one section of the thesis. The different types of handovers are divided into classes and presented with a short description. For example, one class is called initiation. Within this class the handovers are then categorized as network initiated, i.e., the network initiates the handover, and mobile initiated which indicates that the mobile initiated the handover. Further, several investigations on wireless hierarchical structures are presented. The focus is on the inter-system handovers made between the different levels. Hierarchical structures with both two and three levels of wireless systems have been analyzed. They are performed to understand how the results change when a smaller area is compared with a larger that supports more types of wireless systems. The investigations are made with different parameter settings to obtain a more thorough base for conclusions. The results obtained in this thesis are very useful both from the view of a user and from an operators point of view. They would be beneficial when the user should set his parameters and/or for the operator planning the networks and their individual architectures.