Integration of heterogeneous wireless technologies at the UMTS radio access level

4G mobile wireless networks are envisaged as interconnections of heterogeneous wireless and mobile systems, organized in complementary hierarchical layers and able to provide a range of services to users while on the move, anywhere and anytime. The integration of 3G mobile networks, such as Universal Mobile Telecommunications System (UMTS) and wireless local area networks (WLANs), such as IEEE 802.11, beneficial in terms of capacity, coverage and cost, has attracted a lot of attention and has been studied in various research projects. The integration can be performed at different levels in the network. This thesis addresses the integration at the UMTS radio access level, which is called very tight coupling. The integration is performed at the Medium Access Control (MAC) protocol of the wideband code division multiple access (WCDMA) based radio interface. Such a high degree of network integration allows for good vertical handover performance and seamless service continuity during the handover. The WLAN is considered another radio interface and data traffic for a UMTS subscriber can be flexibly distributed over the available radio interfaces, which may result in optimal utilization of the overall radio resources. With the information on radio resource use available locally, this integrated architecture facilitates common radio resource management without the need for introducing new network entities or specifying new control protocols. The benefits of this architecture are achieved at the cost of various technology-specific modifications that require standardization, which makes it a long-term solution. Due to exposure of network interfaces, for security and management reasons, the integrated architecture is suitable for a single UMTS operator, which is thus provided with additional license-exempt bandwidth for new multimedia services. In this thesis, the network and protocol architecture is devised for three architectural options, introduced in an evolutionary way that allows the architectural upgrade for provision of additional capabilities. Two general CRRM architectural models are discussed, while additional CRRM-related protocol modifications are specified for each of the architectural options. The architectural options are compared in their overall radio resource utilization in a stationary scenario and the most promising option is considered in the rest of the thesis. Regarding the vertical handover performance, it is shown that this integration approach can result in seamless WCDMA-WLAN handover with minimized handover delay and no frame loss. Although the focus of the thesis is put on the integration of a single WLAN, the integration of other wireless broadband access technologies, such as IEEE 802.16e and diverse WLAN technologies at the WLAN hotspot, is also considered. It is shown that the same integration principles can be applied here, as well, with unavoidable additional technology-specific modifications. It is also shown that the vertical handovers involving various combinations of the WCDMA, IEEE 802.11 and IEEE 802.16e radio interfaces may be performed in a seamless way. In addition, this thesis proposes the integration of a broadcasting system, such as Digital Video Broadcasting for Handheld devices (DVB-H), at the UMTS radio access level as a feasible way to provide the mobile operator with the additional cheaper bandwidth for multimedia broadcast multicast services (MBMS).