Research On Soft Frequency Reuse Technology In Two-layer Heterogeneous Networks

The heterogeneous mobile communication network is a multi-layer network,which introduce low power nodes,such as Femtocell?Picocell?Relay,so that the network coverage and system capacity can be strengthen.Femtocell is a type of small cell usually deployed by residential users.It can provides high speed data service for indoor user and effectively compensate the blind spot of the indoor scene for macrocell coverage.Because of femtocell network and existing macrocell network use the same spectrum,which make the scarce radio spectrum resources tenser,and more complex interference when femtocell users and macrocell users are communicating over the same bandwidth.Therefore,improving spectral efficiency while effectively controlling the co-channel interference is an important and difficult problem in the research needed to solve.In this paper,the problem of spectrum resource efficiency and the co-channel interference between femtocells and macrocells are studied.Soft frequency reuse strategies is introduced into the heterogeneous scenarios which consist of femtocells and macrocells.The purpose is to provide a suitable spectrum access strategy for the network users,to improve the spectrum utilization,and to increase the user capacity of the cell.The main contents of the research are concluded as follows:The classical fixed soft frequency reuse(SFR)algorithm could not dynamically adjust frequency allocation according to the load of cell edge.Based on the fixed SFR scheme,a dynamic algorithm is presented in this paper.The scheme combines the methods of received signal strength indicator judgment with the received power judgment to classify the users,and adjusts the spectrum resource according to the load condition of the macro edge areas.The scheme does not use the fixed allocation model in the original one to alleviate the pressure of the edge users' communication so as to improve the efficiency of marginal spectrum.On the other hand,the dense deployment of FBS may incur strong inter-cell interference in the heterogeneous network.Combining genetic algorithm and graph coloring algorithm,we present an adaptive soft frequency reuse scheme(A-SFR)for interference coordination.Firstly,the genetic algorithm is used to obtain the optimal radius of the central region of the cell.Then,the graph coloring algorithm is adopted to cluster the FBS in the area of the cell.Finally,according to the number of FBS in each cluster adaptively allocate resources to each cluster.Simulation results haveshown that the scheme can improve the throughput of the edge area and suppressing co-channel interference as well as reduces the average outage probability.