Cooperative Transmission Technology Oriented To Seamless Wide-area Coverage

In order to meet surge in traffic demand and achieve an increase in traffic coverage area,the number of base stations deployed by major operators also increased rapidly.However,it also causes dense and overlapping coverage between adjacent cells,which makes inter-cell interference become the main factor limiting the performance of users.Therefore,it is possible to meet the traffic demand in the network through cooperative transmission between adjacent cells in this scenario.Additionally,the evolution of the physical layer transmission technology presents limitations on the enhancement of the traffic carrying capacity,so this thesis introduces the novel hyper cellular network(HCN)as the research network architecture.Therefore,for the seamless wide-area coverage scenario,this thesis studies the cooperative transmission technology in HCN to focus on improving the edge spectral efficiency.The research content mainly focuses on the following three aspects:Firstly,this thesis models the system by the Poisson Voronoi Tessellation(PVT)model and analyzes the spectral efficiency of different users by dividing the center region and edge region.For central users,a power control scheme is used to optimize the transmit power of the traffic base station(TBS).For edge users,cooperative transmission technology and power control scheme are employed to increase the edge spectral efficiency.In addition,the TBS sleeping strategy is applied to further reduce inter-cell interference.Then,the analytical expressions of the edge spectral efficiency and average spectral efficiency are derived by using random geometry in this thesis.The simulation results illustrate that this scheme is of great significance for improving the spectral efficiency of the mobile user.Secondly,adaptive load balancing and cooperative transmission technology are used to improve the received signal quality of the edge user in cell zooming.For the heavy-load TBS after cell zooming,the TBS is controlled by the control base station(CBS)to perform some user offloading to optimize user association and achieve load balancing.For the light-load TBS,it is judged by the CBS to enter the sleeping state to save TBS energy and reduce interference to the active user.For the edge user with poor the signal receiving quality after the cell range expansion,this thesis adopts an adaptive clustering method to deal with.Then,this thesis derives the integral expressions of coverage probability and edge spectral efficiency.The simulation results show that this scheme has a significant improvement in the edge spectral efficiency compared to the existing transmission schemes.Finaly,in order to reduce the power consumption and backhaul overhead caused by cooperative transmission technology and improve the edge spectral efficiency as much as possible,this thesis proposes a scheme with joint compression technique and cooperative beamforming based on HCN.First,the preferentially scheduled edge users are selected and the cooperative TBSs are selected by adaptive clustering method.Then,Gaussian quantized channel is modeled to achieve the backhaul compression.Since the proposed optimization problem is non-convex,the optimized beamforming vector is obtained by successive convex approximation algorithm and iteratively minimum mean square error(MMSE)algorithm to maximize the edge spectral efficiency.The simulation verifies the convergence of the proposed algorithm and the influence of system parameters on improving the edge spectral efficiency.