Research Of Interference Management In Heterogeneous Networks

The explosive growth of mobile data traffic demands larger and larger network capacity. As the phisical link efficiency is approaching its fundamental limits, the ben-efit of new physical technologies becomes little. While the Heterogeneous Network (HetNet) can improve the network capacity effectively from the network layer, which makes it one of the most promising direction of future network. The low power nodes in HetNet offer a complementary for traditional cellular network, thus improve the cov-erage probability and quality of experience of mobile users. Despite all the benefits of Hetnet, there are still lots of challenges, one of them is the interference problem。The interference management technologies can be classfied into three classes:re-sources orthogonality, power control and access control. Most works about these in-terference management technologies are analyzed independently in the downlink and uplink (DL/UL). The fact is, the DL/UL is coupling in Hetnet due to the vary nodes. We should analyze the DL/UL jointly to obtain compatible interference management design.In this paper, we study the three classes of interference management technologies form the joint DL/UL point of view. The main contents are as follows:Firstly, we study the access control in picocell networks, where the cross-tier in-terference can be mitigated by cell association. As we can see, the cell association policies in the DL/UL may contradict with each other.In order to have more specific analysis, we model the DL/UL cell assocaition problem repectively. With consider-ing load balance and resource allocation fairness, we obtain closed-form expressions about the relationship between system performance and the association model parame-ters. Then we joint the DL/UL association models together and give three soultions to the contradiction problem:(1) Change the network architecture to allow mobiles users associate different base stations in the DL and UL;(2) Obtian compatible association schemes by jointly considering the DL/UL from the operator’s point of view;(3) Ob-tain compatible association schemes by jointly considering the DL/UL from the mobile user’s point of view;. This paper gives a complete analysis about the cell association problem in HetNet and offers some guidelines for the system design. Secondly, we study the power control in femtoccll networks. As we can see, fem-tocells nearby the MBSs have to transmit at a very high power to protect the FUEs from the strong interference from MBSs, at the same time FUEs nearby MBSs cause significant interference to MBS in the uplink. transmission. So we propose to deploy less femtocells in the interior area of MBSs. Instead of relying on system level simula-tions, this paper proposes analytical models for evaluating power control in femtocell networks based on spatial Poisson Point Process.in the DL/UL respectively. Tractable closed-form expressions for the coverage probability and average achievable rates of both macrocells and femtocells are obtained. Then we reconsider the system perfor-mance with considering a femtocell dilution region (FDR). The radius of FDR and the femtocell density within FDR are optimized jointly in DL/UL to maximize the system capacity.Thirdly, we study the spectrum orthogonality in femtocell networks. Once macro-cells and femtocells are completely orthogonalized, there will be no cross-tier interfer-ence any more,as well as the DL/UL coupling described before. However, it results in low spectrum efficiency. This paper considers a part-orthogonal scheme by combin-ing Strict FFR and Soft FFR. We adopt a hybrid model where the macrocells form a hexagonal grid whereas the femtocells form a spatial Poisson point process to model the femtocell network. Analytical evaluations of the performance of the mobile users according to their spatial locations are given and the optimal spectrum allocation is obtained to maximize the long term expected network throughput with the quality of service constraints. The relationship between the network throughput and the density of the femtocells and the radius of the interior region of a macrocell is studied, which can be guidelines in practical system design.