Vertical handovers among different wireless technologies in a UMTS radio access-based integrated architecture

The demands for accessing services at high data rates while on the move, anyplace and anytime, resulted in numerous research efforts to integrate heterogeneous wireless and mobile networks. The focus was mainly put on the integration of the Universal Mobile Telecommunications System (UMTS) and the wireless local area network (WLAN) IEEE 802.11, which is beneficial in terms of capacity, coverage and cost. With the advent of IEEE 802.16(e) the attention of the research community was shifted to its interworking, on one side, with complementary WLANs, and on the other, with UMTS for extra capacity. In addition, there has been also research on UMTS interworking with different broadcasting systems, including the Digital Video Broadcasting system for handheld devices (DVB-H). All these research activities resulted in various heterogeneous architectures where the interworking was performed at different levels in the network. In this article, we address the integration at the UMTS radio access level, known also as very tight coupling. This integration approach exhibits good vertical handover performance and may allow for seamless session continuity during the handover. However, it is a technology specific solution, where not all the mechanisms applied to the integration of one wireless technology can be straightforwardly reused for embedding another. This integration approach introduces various modifications to UMTS that have to be standardized, which makes it a long-term solution. We present here the general architecture for the integration at the UMTS radio access level and discuss the extension of the architectural framework for various types of access systems with as few as possible additional modifications. The focus of the work is put on the vertical handovers. We discuss various vertical handovers among WCDMA, IEEE 802.11, IEEE 802.16e and DVB-H in the considered heterogeneous architecture. We present new handover types, describe the vertical handover procedures and provide performance evaluation of the vertical handovers in different scenarios and for different combinations of the wireless access technologies.