Research On Interference Mitigation Technology In Heterogeneous Networks

With the development of mobile communication systems,mobile data traffic is growing explosively.Low-power small-cell base stations are densely deployed in the traditional homogeneous macro-base station networks,and this type of heterogeneous networks can effectively alleviate the network capacity pressure brought by the traffic growth.Considering the low transmission power,small coverage range and the sudden and asymmetric service capability of small-cell base stations,Time Division Duplexing(TDD)technology is adopted.The application of dynamic TDD technology in heterogeneous networks can improve service flexibility.However,it introduces serious cross-link interference,and the complexity of interference situation,which bring great technical challenges to improve system performance.In this thesis,the interference mitigation technology in ultra-dense heterogeneous networks is deeply studied,focusing on the small-cell interference mitigation technology based on clustering and power allocation in dynamic TDD scenarios.The main contributions are summarized as follows:1)Consider the cross-link interference caused by dynamic TDD technology in heterogeneous networks,a buffered DL/UL traffic ratio sensing cell clustering scheme is proposed.A new clustering criterion is defined,which comprehensively considers the inter-cell interference and traffic volume difference.Moreover,a graph-based clustering scheme is proposed,which divides two small cells with large interference and similar uplink and downlink load proportions into one cluster.Small cells in the same cluster use the same subframe configuration.In order to further improve the network performance,an adaptive uplink/downlink subframe configuration selection scheme is proposed.The weighted uplink/downlink subframe ratio of each cell in the cluster is calculated,and the weighted uplink/downlink subframe ratio required by the cluster is calculated.The subframe configuration selected by the proposed scheme can best match the buffered traffic transmission requirements of all cells in the cluster.This configuration greatly improves service adaptability,system resource utilization rate,and the uplink and downlink throughput of the network.After system-level simulation verification,the proposed scheme significantly improves the overall performance of the network and users.Specifically,throughput growth of the uplink small-cell base station and edge user is particularly significant.2)Aiming at the dynamic subframe structure proposed by the fifth generation mobile communication system,an interference mitigation scheme combining power control and uplink/downlink selection is proposed.Using the interference price,the network optimization problem is decomposed into distributed optimization problems on each small cell,and the complexity of the algorithm decreases from exponential to linear.Each small cell base station selects the uplink or downlink direction and allocates appropriate power simultaneously.System level simulation results indicate that the scheme can effectively reduce inter-cell interference and delay,and improve uplink and downlink throughput of network and edge users.