Load Balancing And Small Cell Range Expansion For Heterogeneous Wireless Networks

With the exponential growth of data traffic and the rapid improvement of user demand,the traditional cellular networks can no longer meet the need of users.For wireless areas such as hotspots,blind spots and indoor areas,traditional cellular networks,which are mainly used for wide-area coverage,cannot meet the user demand.To solve these problems,traditional cellular networks are overlaid with the dense deployment of low-power nodes.The resulting networks are generally referred to as ultra-dense heterogeneous networks(HetNets).However,due to the power difference between the macro base station(MBS)and the low-power small cell base station(SBS)in the HetNets,most users will be forced to access the MBS according to the conventional cell association strategy.Then the load imbalance will occur.In addition,for some macro cell-edge users,although they are closer to the SBS,only the MBS could be accessed,which will bring excessive interference to the SBS.It results in the imbalance between uplink and downlink coverage in HetNets.Cell range expansion(CRE)is a simple and effective strategy to solve load imbalance and the imbalance between uplink and downlink coverage in HetNets.The thesis explores CRE optimization problem around the system structure design,scheme design and dynamic setting of CRE bias value in HetNets.The main work and innovation of the thesis are as follows:1.Based on the matching of user's long-term rate and load,the CRE optimization scheme with three common performance indicators of the system throughput as a utility function is proposed to achieve load balance.When the SBSs adopt a unified and per-small CRE bias value strategy,Monte Carlo method is used to simulate in different wireless HetNet scenarios.According to the simulation results,the scheme and the optimization scenario of CRE are discussed.The sum logarithmic rate and the median rate criteria with CRE optimization achieve load balance while improving the communication rate of the cell-edge users and improving fairness.The network design in the HetNets has important influence on the system performance.When the SBS is located at the edge of the macro cell and the number of the SBS is reasonably increased,the performance of the system will be improved.2.According to conventional cell association strategy,the instantaneous rate for cell-edge users of different base is less different.Because the MBS has 20 dB advantage than the SBS in the HetNets,most users will access the MBS,which results in the long-term rate of the MBS user too low.By comparing the minimum user long-term rates of the SBS and the MBS,whether the load of the SBS is in overloaded,lightly loaded,or relatively balanced is determined.Thereby the dynamic configuration of the CRE bias value is realized.The simulation results show that the dynamic configuration based on the minimum long-term rate of each base station,the selection of the CRE bias value can be performed according to the current network situation.The minimum long-term rate for the cell users can be improved,and the user fairness and load balance can be guaranteed.