Research On Downlink Resource Allocation Algorithms Of Femtocell Based On OFDMA

With the progress of science and technology and the change of communication styles,high-speed data services such as multimedia have become an indispensable part of our daily life.The number of smart terminals is also increasing in geometric series,which leads to exponential growth of traffic.It is predicted that the indoor traffic will account for about 90% of the total traffic in the future.However,the traditional cellular network model has been difficult to meet the growing demand for data services and indoor coverage.The technology of femtocell provides a new way of indoor coverage.femtocells are usually deployed indoors,which can provide better indoor coverage and traffic services for users.However,the intensive deployment of femtocell brings not only the improvement of network performance,but also serious interference problems.In the two-tier heterogeneous network composed of femtocell and macrocell,reasonable allocation of bandwidth and power resources to macro users and femtocell users can effectively solve the interference problem and improve system performance.Aiming at different interference situations,the resource allocation algorithm of femtocell is studied in OFDMA system.The details are as follows:(1)In a two-tier heterogeneous network composed of femtocell and macrocell,a subchannel allocation scheme based on clustering is proposed to maximize the system capacity of femtocells,considering only the interference between femtocells.Firstly,weights are used to describe the interference degree between femtocells,and interference diagrams are established.Secondly,a sub-optimal heuristic algorithm is used to cluster the femtocells for the first time to ensure that each femtocell is clustered into one cluster,and then the weight threshold is used to complete the second clustering of the femtocells,so that some femtocells with small interference can be clustered into several different clusters at the same time to enhance the spectrum utilization rate of femtocells.Finally,based on the maximum SINR criterion,subchannels are allocated for each cluster.The simulation results show that the proposed algorithm can effectively improve the spectral efficiency of femtocells.(2)Considering the cross-layer interference between the femtocell and the macrocell as well as the co-layer interference between the femtocell,and assuming that the macro user has allocated the sub-channel and power,a joint subchannel and power allocation scheme based on clustering is proposed.Firstly,the dyeing algorithm of graph theory is used to cluster the femtocells to reduce the co-layer interference between them.Then,under the condition of satisfying the initial interference limitation for macro users,the method based on the maximum SINR criterion is used to allocate suitable subchannels for the femtocell cluster.Finally,under the constraint of macro user interference threshold,the Lagrange multiplier method is used to complete the femtocells' power distribution.The simulation results show that the proposed algorithm can significantly improve the SINR performance of femtocell users without affecting the SINR performance of macro users.