Research On Interference Management Scheme In 5G Ultra-Dense Network (UDN)

In order to deal with a series of challenges caused by the development of new business such as mobile Internet and Internet of Things,the 5G mobile communication system,is required to meet the requirements of multiple business types and application scenarios.Due to the rapid development of science and technology,the number of device terminals has increased dramatically.On these backgrounds,ultra-dense networking has been viewed as a key technology of 5G since it is capable to meet the proliferation of data traffic and handle the challenges resulted from the connection of massive terminal devices.To be specific,it permits the dense deployment of wireless network infrastructure in hotspots area,which significantly improves the reusability of the frequency and promises a hundredfold gain in system capacity.However,this configuration also brings some challenges.For instance,due to the fact that the distance between small cells composed of small base stations and users is getting closer and closer,the user located at the edge of the cell will receive the undesired interference from neighboring cells,resulting in a decrease in system throughput.Moreover,the interference in ultra-dense networks is also much more complicated than traditional cellular networks.As a result,inter-cell interference has become a major bottleneck restricting the performance of ultra-dense networks.How to effectively eliminate the interference in ultra-dense networks deserves special attention.Fortunately,the birth of user-centered virtual cell technology breaks the traditional base station-centric networking concept and effectively mitigates inter-cell interference.There is no cell-edge in the network.Therefore,the user-centric virtual cell technology has been extensively studied.In this thesis,it considers a downlink virtual cell network in an ultra-dense network scenario.The in-depth research on the construction scheme of the virtual cell and the interference between the virtual cells is carried out.The main contributions of this thesis are as follows:In order to cope with the problem that there may be too much load in the small base station in the virtual cell,a user-centric virtual cell formation scheme based on load sensing is explored.More specifically,it introduces a variable to measure the number of base stations loads.Then,a heuristic algorithm based on greedy principle is proposed to maximize the signal-to-noise ratio of the received signal and the objective function of the base station load.Compared with the exhaustive method,the proposed algorithm can significantly decrease the computational complexity.In simula-tion part,it demonstrate that our scheme can improve the rate performance and increase frequency band utilization.Since the non-cooperative transmission between each virtual cell will cause serious inter-cell interference in virtual cells,this thesis adopts a two-step solution to handle this problem.In the first step,a merging scheme based on the overlap rate of virtual cells is considered to cluster the virtual cells and transform the interference between the virtual cells into intra-cluster interference.Then,the so-obtained intra-cluster interference is eliminated by utilizing the beamforming technology.In designing the beamforming scheme,the optimal vector of beamforming is determined by maximizing the total user transmission rate.Simulation results indicate that the proposed scheme can reduce interference and improve system throughput.