Key Technologies On Radio Resource Management In Hybrid Wireless Networks

With the rapid development of telecom industry and Internet, various kinds of wireless communication networks have appeared such as radio cell communication systems, wireless local networks, satellite communication system, and digital multimedia broadcasting systems, etc. Hybrid network composed of these systems provides ubiquitous radio environment for users, which makes people commnunicate with anyone at any time and any place. On the other hand the diversity and constant evolution of wireless technology led to the complexity and multiplicity of hybrid network on construction and deployment, for example, different generation technologies (2G/3G), same generation with different standards (UMTS/WiMAX), different technology and different standard (UMTS/WLAN), and same generation with different scale (Macro/Femtocell). The key for reasearching hybrid network includes that how to sufficiently utilize the complementary property of various wirless networks for guaranteeing users'QoS, how to truly implement the self-organization and adaptation of hybrid network, and how to integrate radio resource management of different networks. The hybrid network is divided into heterogenous and hierarchical networks due to its complexity, research issues of hybrid wireless network resource management such as admission control, mobility management, spectrum allocation and power control are analyzed and investigated thoroughly by using game theory and optimization theory in this dissertation, in order to improve the system performance like resource efficiency, capacity and so on.Firstly, the issue on heterogenous network selection is investegated. The advantages and disadvantages of existing related models and algorithms are analyzed, and then two new models based on game theory are proposed. Different from existing schemes which hardly give attention to both users and networks, the status and different requirements of both users and networks are taken into consideration in the two new models, and the equilibrium points of two games can be achieved through mutual selection. Simulation results show the two models can separately achieve higher gain of system performance on revenue and satisfaction degree under the condition of without sacrificing users or networks profits. That is to say, users and networks attain a win-win situation.Secondly the issue on handoff decision in Macro/Femtocell hierarchical networks is researched. Based on the lack of existing handoff algorithms, due to the property of femtocells which has very low transmit power, two new handoff algorithms in hierarchical network are proposed. The handoff decision is made by adopting received signal strength (RSS) combined with power loss in the first algorithm, which can improve the utilization of femtocells and solve the discrepancy on transmit power of macro and femtocell base stations, and make some power-saving. Simulation results show the algorithm increases the number of handoff compared to conventional algorithms, and ruduces the number of unnecessary handoff compared to other hierarchical handoff algorithm. In the signal to interference plus noise ratio (SINR) based algorithm, the SINR used to avoid power asymmetry of base staions and users'state including velocity, and the QoS used for decreasing frequent handoff are combined. Simulation results show the second algorithm promotes the utilization ratio of femtocells, diminishes the possibility of over handoff, therefoer improves the system performance.Thirdly the dissertation researches the issue how to allocate spectrum among base stations in hierarchical network when femtocells are deployed in macrocells and they share the same licensed frequency band. The centralized spectrum planning and allocation schemes do not work efficiently in hierarchical network owing to the wired backhaul characteristic of femtocells, thus two game theory based adaptive schemes of spectrum allocation are proposed. Two schemes integrate the theory of matrix game and Stackelberg game, respectively, both of which make the base stations of macrocell and femtocell as the two sides of players, and make the same spectrum as the game object, to minimize the co-layer and cross-layer interferences by solving the equilibrium of the game. In addition, the suboptimal solution is given when the equilibrium of matrix game does not exist. The definition and existence proof of Stackelberg game equilibrium are also given. Analysis results represent both of the proposed schemes allocate spectrum in a hybrid way, namely allocating orthogonally when resource is enough and in a reuse or co-channel manner when resource is scarce. Simulation results show the two adaptive schemes attaine the obvious performance improvement in throughput, blocking probability, and spectrum efficiency.At last the attention is paid to the issue on self-configuration of femtocells. As the femtocells are finally deployed independently by users without related professional and technical background, a femtocell self-configruation scheme base on optimization theory is proposed. Based on analyzing all kinds of received interference and types of introduced interference on existing users and networks, an optimal problem of power self-configuration is designed according to interference qualification, which refers to maximize system capacity on the condition eusuring normal communication of existing users. Analysis results present the transmit power optimal solutioan can be obtained with Lagrange multiplier of optimization theory. Simulation results demonstrate the scheme realizes transmit power adaptation of femtocells in accordance with radio environment, effectively cuts down transmit power, reduces various introduced interference, and enhances system performance.