Research On Normalization Model Of Multi-tier Millimeter Wave Cellular Networks

With beamforming technology and millimeter-wave communication technology maturing,millimeter-wave communication has become one of the 5G candidate technologies.The future cellular network needs to deploy a large number of small cell to ensure the seamless coverage of mobile users,so the millimeter wave technology and small cells combined with multilayer millimeter wave is the inevitable developing trend of cellular networks.Compared to traditional communication band,millimeter wave can provide 200 times spectrum resources,due to the short wavelength of the millimeter wave and the poor diffractive transmission characteristics,how to evaluate the performance of the multi-tier millimeter wave cellular networks and quantify its potential benefits are urgent problem need to be solved.First,we build a system model based on the network architecture of 5G millimeter-wave cellular network.Based on this model,we propose a mathematical normalization model that convert a multi-tier millimeter-wave cellular network into a single-tier virtual network in the case of line-of-sight(LOS)and non-line-of-sight(NLOS).All the base stations(BSs)have the same normalized transmit power 1 and the densities of BSs scaled by LOS or NLOS scaling factors respectively follow piecewise constant function which has multiple demarcation points in this model.The path loss caused by the virtual distance between the base station and the user becomes the only influence factor that affects the received signal strength of the user.Then,based on the normalization model,the performance of the downlink network of multi-tier millimeter-wave cellular networks is studied using stochastic geometry theory.Using a similar single-tier network analysis method,the mathematical expressions of network downlink coverage probability and user achievable rate under two conditions of misalignment errors are deduced.A comparison is made between the coverage probability and the user achievable rate in the presence of beam alignment errors and misalignment errors.It is found that when there is a beam alignment error,both the network coverage performance and the user achievable rate decrease.Finally,we study the effects of the beam main lobe angle on network coverage probability and user achievable rate.It is found that there is beam main lobe angle so that the coverage performance and the user achievable rate of networks is optimal.The normalization model presented in this paper analyzes performance of multi-tier millimeter-wave cellular networks,and proves the universality of the normalization model and the low complexity of the analysis using this model.At the same time,the influence of system parameters on the network performance is studied,which has certain guiding significance for the optimization of coverage performance and user achievable rate in actual wireless networks.