| When femtocells are deployed densely, the co-tier and cross-tier interference greatly impair the network performance in spectrum-sharing femtocell networks. In two-tier femtocell networks, it’s crucial to solve the interference problem while femtocells are deployed densely. To mitigate the co-tier/cross-tier interference, we have studied the downlink resource allocation algorithm of two-tier femtocell networks, where macrocells and femtocells share the same frequency. The 3rd Generation Partnership Project(3GPP) standard formulates three kinds of access modes of femtocell: closed mode, open mode and hybrid mode. In this thesis, we have studied the resource allocation algorithm for the closed access femtocell networks and the sub-channel allocation algorithm for the hybrid access femtocell networks.Firstly, a cluster-based resource allocation algorithm is proposed for the closed access femtocell networks. The proposed algorithm consists of two parts: In the first part, an improved Hungarian algorithm is adopted to assign sub-channels to the Macrocell Users Equipment(MUE). Then the averagely assigned power is reallocated in linear water-filling fashion in order to ensure the normal transmission of MUE. In the other part, Simulated Annealing algorithm is first used to cluster femtocells into disjoint groups. Then under the condition of avoiding causing interference to MUE, femtocells perform sub-channel and power allocation according to the rate requirements of Femtocell User Equipment(FUE) to maximize spectrum efficiency. Simulation results show that the proposed algorithm not only guarantees the data rate requirements of users, but also improves the spectrum efficiency.Secondly, a sub-channel allocation algorithm is proposed for the hybrid access femtocell networks. The sub-channel allocation algorithm consists of two parts: one part is to put femtocells into different groups according to the interference between them in order to reduce the complexity of sub-channel allocation and slight the interference between them; the other part is to allocate sub-channels to MUE and FUE. The allocation algorithm needs eliminating the spectrum collision between users and ensuring the Quality of Service(QoS) of authorized users while improving the performance of non-authorized users. Simulation results show that the proposed algorithm not only guarantees the data rate requirements of users, but also can ensure the fairness between users. |
