Research On Interference Management Strategies In Heterogeneous Networks For LTE-Advanced Systems

In order to effectively improve the peak data rate, cell coverage, user’s service quality and the performance of cell edge users in the wireless system, polymorphous heterogeneous network topology is introduced in LTE-Advanced system. In the macro cell coverage, new types of low power node are added to shorten the distance between base stations and end users so that higher spectrum efficiency and frequency spectrum reuse rate can be achieved. However, because of the coexistence or overlay of macro cells and local low-power nodes, the latter ones would interfere with the former ones and impact the nearby macro cell user’s experience. Therefore, the inter-cell interference has become one of the major factors that influence network performance in LTE-Advanced heterogeneous scenario.The following aspects are covered in this thesis:To deal with interference issues in heterogeneous network scenarios, an LTE-Advanced downlink system-level simulation platform is designed and developed. The platform is built based on the standards specifications and its results are well verified with the industry-recognized simulation results in order to evaluate the proposed strategies and algorithms. The platform has good extensibility and can provide a complete environment of simulation and verification for research on LTE-Advanced system and continuously evolving technology.Focusing on the problem of parameter configuration, the influences of different parameter setting on network performance are studied by theoretical analysis. Then, based on the system-level simulation results, the impact of different femto cell parameter configuration, including almost blank subframe ratio, reduced power value and access control strategy, on network performance in the actual network is analyzed. Simulation results show different parameter analysis would influence the network performance in different ways. Also, adjustment of access control strategy can improve system throughput and cell edge user experience. In the real network, network performance can be optimized appropriate parameter configuration, considering both the wireless environment and the deployment of femto cell.In co-channel deployment of macro cell and indoor femto cells, almost blank subframe is considered as an effective enhanced inter-cell interference coordination strategy for mitigating downlink cross-tier interference. A novel distributed dynamic ABS ratio setting scheme is proposed for dense residential femto cell deployment with closed subscriber group configuration. Both the overall cell throughput and Jane’s fairness index are employed to judge the status of the environment around each femto cell, which decides whether and how to change ABS ratios. Simulation results show that the proposed scheme outperforms other static settings, and provides remarkable improvement on cell edge performance with little overall throughput cost.Based on the idea of soft frequency reuse, a spectrum allocation scheme is proposed for Macro-Femto scenario, where femto cells operate in the closed subscriber group mode. Seriously interference femto cells are first classified into one cluster by a proposed clustering algorithm. Then, a graph coloring-based spectrum allocation scheme is applied within each cluster. Finally, by using soft frequency reuse technology, frequency spectrum is appropriately allocated to femto cell clusters and macro cell according to user traffic request. Simulation results show that the proposed scheme can remarkably reduce inter-cell interference in heterogeneous network and hence improve the cell edge performance with a relatively slight reduction of system overall throughput.