As a result of rapid progress in research and development, today's wireless world witnesses several heterogeneous communication networks, such as cellular network, satellite network, wireless local area network (WLAN), mobile ad hoc network (MANET), Bluetooth, Home RF network, and the sensor network. These networks are designed independently for some specific service needs of  the mobile users and vary widely in terms of bandwidth, latency, area of coverage, cost, and quality of service (QoS) provisioning. None of these networks can simultaneously satisfy the low-latency, high-bandwidth, and ubiquitous-coverage needs of mobile users at low transmission cost.  However, as these networks are complementary to each other their intelligent integration and co-ordinated operation can provide ubiquitous ``Always Best Connection" to the mobile users. We refer to this integrated network as the  Next Generation Wireless Networks (NGWN). Figure 1 shows  an example architecture of  NGWN that consists of UMTS/3G,  satellite network, and WLAN.



Figure 1. An example architecture of NGWN.

While the existing wireless networks have been extensively studied individually, the integrated wireless system brings new challenges in architecture design, system management, protocol design, QoS support, etc. In this project, several key elements are investigated to realize the NGWN.  More specifically, an architecture is proposed to integrate the existing wireless systems such that their heterogeneities are hidden from each other and a harmonious inter-operation among them is achieved.  Next, we propose a hybrid control scheme for the selection of the best available network for a user at any given time. A new adaptive transport layer is developed that adopts to the architectural heterogeneities dynamically when a mobile user roam between different networks in the middle of a connection.  Furthermore, a novel adaptive medium access control (MAC) framework that dynamically adopts to the architectural heterogeneities as well as the diverse QoS requirements is proposed.  In addition, a cross-layer mobility management framework is developed to support seamless roaming of the users between different networks in NGWN.