Research On Resource Allocation In Macrocell/Femtocell Hierarichal Network

Femtocell has been pointed out as a key technology in the next generation mobile communication. The wireless industry begins to concern the femtocell in recent years, as femtocell can improve the indoor coverage, offload traffic from macrocell layer, increase the system capacity rapidly and reduce the radiation to the users with low cost. Femtocell will benefit both operators and end-users. However it's not easy to accomplish. Because the femtocell is deployed by the end-users, and the operators don't know the number and position of the femtocells in advance. The traditional frequency assignment methods will not be applied in the hierarchical network. Meanwhile, the femtocell must implement self-configure and self-optimization functions. Femtocell can tune its radio parameters automatically according to learn about their radio environment (e.g. neighborhood and interference). Because of the shortage of the spectrum resources and strong proponent of energy-saving, it has important research value and significance to design an efficient frequency allocation method and self-optimization algorithm in the hierarchical network and improve the resource utilization and power efficiency.Based on the individualistic nature and the coordination among base stations, this paper proposes an effective resource reuse scheme and a self-optimization algorithm. Firstly, this thesis introduces the theory of related technology in the hierarchical network, including the key technologies in the femtocell, the principle of the OFDMA and WiMAX TDD frame structures. Secondly, the downlink interference condition is analyzed and a system-level platform is built up. The simulator is used for evaluating the downlink performance of the OFDMA-based hierarchical network including the throughput, SINR CDF, blocking rate and the transmit power of the femtocells. Thirdly, this paper proposes a dynamic resource allocation method. The macrocell users have a priority over femtocell users. The macrocell uses (1,3,3) frequency reuse method. The Femtocell makes use of the scheduling decision of macrocell and the spectrum arrangement of neighboring femtocells to self-organize its frequency usage. Femtocells in the same neighbors use orthogonal resources. Femtocells in the different neighbors can reuse of resources. This scheme can guarantee that both macrocell and femtocell users attain the Quality of Service (QoS) requirement. Simulation results show that the proposed scheme can increase the system throughput and reduce the system blocking rate. Lastly, under the full load state in macrocell and the premise of the coordination among femtocells, a joint frequency and power self-optimization scheme is investigated. This algorithm is based on the instantaneous channel state, the users'traffic requirements, the number and positions of the users in one femtocell and their previous spectrum efficiency. Through those information femtocell can configure their frequency and power automatically. This approach can dynamically adapt to the changing condition of the wireless environment. Simulation results show that this self-optimization method can reduce the blocking rate of the FUE and increase the power efficiency of the femtocell.