Research On Interference Suppression In LTE-A Heterogeneous Networks

With the rapid development of cellular mobile communication system,mobile subscribers have more demands for the data rates.Especially after the proposal of LTE-A standard,the requirement of signal transmission quality as well as channel bandwidth and spectrum efficiency,has risen to a new level.But under the explosion of cellular subscriber and heavy load,the cellular system is facing severe problems,and the communication quality of the subscribers near the cell edge cannot be guaranteed.In recent years,there are some solutions for the cell edge subscribers,including the relay station,a distributed antenna system,etc.However,all the solutions have side effects.Low power node has been introduced into traditional cellular communication system in order to make subscribers get closer to base station and improve the subscriber throughput.At the same time,the co-layer and the cross-layer interference have led to a great impact on the performance of Het-Nets.The proposal of interference coordination techniques contributes to solving the interference problems in the time domain,frequency domain,and the power domain.However,the traditional interference coordination algorithms still exist weak points such as low spectrum efficiency and low system throughput.Based on that point,improved interference coordination algorithms in the frequency domain are proposed in this dissertation to solve problems caused by interference.The primary contributions and innovations are listed as follows:(1)Two kinds of heterogeneous network scenarios have been modeled according to 3GPP standard: macro-femto cell and macro-pico cell.Based on the model,analysis has been done about interference.(2)An improved dynamic fractional frequency reuse(FFR)algorithm is proposed in the dissertation.In this algorithm,interference district(ID)is defined for further use.Combined with graph theory,ratio of interference district(RID)is used to divide subscribers into groups.Finally sub-channels have been assigned to different subscribers.In addition,frequency reuse factor(FRF)changes as RID changes.The dynamic FFR algorithm improves the spectrum efficiency effectively.(3)From the perspective of resource allocation along with interference graph theory,an improved resource allocation algorithm is proposed in this dissertation.The interference graph is built first based on the measurement reports of femtocell UEs.Then a coloring algorithm is implemented to construct disjoint groups.Finally,resource allocation algorithm is performed to avoid inter-group interference.In this way,the system throughput and SINR have been improved.(4)In addition,heterogeneous network simulation platform is built based on a traditional single-tier network.Basic environment for simulation is established,including path loss model,deployment model,etc.Two algorithms proposed in the dissertation have been simulated based on the platform,which has proved the fact that improved algorithms proposed in this dissertation are effective.