Research On Interference Management Based On Cell Association Strategies In Hetnet

This dissertation is formed in consideration of the contradiction between the limited communication resources in the cellular networks and the unlimited user requirements caused by the increasing reliance of people on the wireless communication.However,the framework of wireless communication system for the existing communication system is mainly based on the traditional cellular network.On the basis of this,the evolution and development of the technological aspects,such as cell association and resource allocation around the interference management,are gradually constrained by various ‘border efforts',resulting in difficulty to improve the communication system performance,which has become the bottleneck of the wireless communication development.In addition,the reality of the complex political and economic factors also brings new treats and new requirements on the communication system.So,the future cellular network will develop towards ‘intensive',‘isomerization' and ‘multi-system coexistence' trends.From the research perspective,it is necessary to adopt a new idea,new thinking and new method to explore and develop the communication system and its related technologies.In response to these challenges,various low power nodes have been presented,together with the traditional macro cell,leading to the composition of heterogeneous networks(Het Nets).The Het Nets pay more attention to the cooperation and convergence of different technologies,systems and devices,so as to realize the integration and utilization of the existing resources,and then to improve the system performance.The Het Net and the traditional cellular network are different in the deployment location,segment density and coverage ability,and the location development of the low power nodes have some uncertainty and randomness,which brings both opportunities and many challenges,including: the traditional cellular network model is no longer applicable to the Het Net,and new system models need to be built up and analyzed.The transmit power of the macro base station is much larger than that of the low power node,which leads to a serious cell load imbalance problem.In the view of above problems,this dissertation attempts to explore the new features brought by the development of the 5th Generation Mobile Communication Technology(5G)cellular network,from the aspects of the system scene,program design and algorithm proposition.Then,around the interference management issues,the contradiction between limited communication resources and unlimited user needs are explored and solved,to ultimately achieve the improvement of the communication system performance.In order to achieve this goal,the Het Net system model is presented.Then,the interference in the traditional cellular network and the interference in the system that have low power nodes in it are analyzed,respectively.By comparison,it is pointed out that the Het Nets tend to adopt the cell association strategies with almost blank subframe,the cell association strategies with reduced power almost blank subframe(r-ABS),and the cell association strategies with uplink and downlink decouple access scheme,from above yielding that different cell association strategy has its own characteristics and the application of the scene and that no strategy can be completely replaced by another strategy.In the following,this dissertation will use the three commonly used cell association strategies mentioned above in the Het Nets,and try to solve the interference management problem by using interference cancellation technologies with mathematical tools and models.Firstly,with the introduction of Device-to-Device(D2D)technology supporting the emergency communications into the Het Net based on the ABS cell association strategy,the communication system environment has become more complex.This dissertation builds the optimization model and then makes the interference analyses.In order to suppress the additional interference from the D2 D communication,an interference management method based on the minimum maximum regret value is proposed.The problem that needs to be solved is modeled as a min-max regret generalized assignment problem.The proposed method does not need the prior knowledge of the Signal to Interference plus Noise Ratio(SINR),which improves the robustness to the SINR inaccurate estimation.The minimum loss of opportunity criterion is adopted as the judgment standard by using the inaccurate estimation parameters,so as to meet the different needs of different users in the system with minimal wireless communication resources.At last,simulations are carried out,showing that the proposed method can make good use of the resources in the Het Net,effectively select the cell association and resource allocation,and conform with the theoretical analyses,which has some certain practical significances and application scenarios.Secondly,this dissertation aims at maximizing the total system throughput by introducing a reduced power almost blank subframe(r-ABS)cell association strategy into the Het Nets by setting low power rather than zero at almost blank subframes of macro base station.In order to obtain a better system performance,through analyzing the existing system interference,a mathematical model is established and a novel inter-cell interference coordination algorithm is proposed based on r-ABS,which can make full use of time domain resources and achieve the goal of maximizing the total system throughput.The problem of different base stations with different configurations of r-ABS is solved.In the meanwhile,the interference suffering by cell edge users is reduced and a better communication quality is obtained.The simulation results show that the proposed method can reduce the power consumption and improve the average spectral efficiency of the cell,which conforms with the previous theoretical analysis.Thirdly,in the Het Net,it is found in the study that the cause of the difficulty in meeting the uplink performance is that,in the field of wireless communication,the traditional uplink and downlink couple cell association strategy can only provide the strongest downlink signals to the users,while the communication quality in the uplink is difficult to guarantee,especially in the high-density small base station network.To meet the demand of the uplink in the heterogeneous cellular network,this dissertation supposes a resource allocation scheme to maximize the total system throughput in the uplink.Through analyzing the interference in the communication system and constructing the resource allocation optimization model,an undirected interference graph with weights between users is established.And then,the user grouping is carried out based on the interference graph.The users in the same group have little interference,so they can share the same resource.Finally,the Hungarian algorithm is used for the resource allocation.The simulation results show that the proposed method can reduce the power consumption and improve the average spectral efficiency of the cell,which conforms with the previous theoretical analysis.