| As a key technology of LTE-A cellular communication system,three dimension multi-input multi-output(3D MIMO)has attracted extensive attention in recent years.Compared with traditional MIMO technology,3D MIMO can make use of vertical dimension channel information in addition to the channel information in horizontal dimension,which makes it possible to improve the communication system capacity.Besides,with the development of active antenna array and three dimension beamforming technology in 3D MIMO communication system,the base station supports beamforming in the vertical dimension.This undoubtedly increases the quality of service for users located in high-rise building.However,the development of 3D MIMO faces some serious challenges.3D MIMO cause interference to cell edge users due to the introduction of the vertical dimension.The interference to cell edge users,caused by the beams serving users at high-rise building,is more severe.In addition,resource allocation,especially power allocation is more complicate especially for multi-cell coordination scenario.These problems will hinder the improvement of communication system performance.Coordination among multi-cell has been widely concerned since it can effectively suppress the cell edge interference and further improve the capacity of communication system.Therefore,it is very important to study the interference suppression and power allocation of the 3D MIMO coordinated system.The contribution of this thesis is summarized as follows:To study the beam downtilt problem in the 3D MIMO coordinated cellular communication system,a scheme to determine the downtilt of the inner sector beam and outer sector beam is proposed.According to the radiation model of the antenna in the LTE specification,the expressions of the received signal and signal-to-interference-plus-noise ratio of users in the inner sector and outer sector are derived with the consideration of path loss and cooperation among multi-cell.In addition,the throughput of the 3D MIMO system is obtained and the throughput optimization problem is studied.The asymptotically optimal downtilts of the inner sector beam and outer sector beam are obtained by genetic algorithm(GA).Simulation results show that the proposed method of determining the beam downtilt improves the cell average throughput by 48.5%compared with the exhaustive search algorithm in 3D MIMO non-coordinated communication system.In the 3D MIMO coordinated communication system,a power allocation strategy is proposed for beam of inner sector and outer sector.After the radiation model of the active antenna array and propagation model are determined according to the LTE specification,the optimization problem considering the system throughput,the service quality of users and power of beam belonging to the inner sector and outer sector is formulated.Besides,the power allocation factor is defined in this thesis.The optimal power allocation of beam belonging to the inner sector and outer sector is determined by solving the optimal power allocation factor.Simulation results show that the power allocation strategy improves the throughput of the communication system compared with the average power allocation strategy when the signal-to-interference-plus-noise ratio(SINR)of the user is high.To address the problem of the interference to cell edge users,caused by the beam serving users at high-rise building in 3D MIMO communication system,a scheme to reduce the inter-cell interference based on dynamic handoff between beamformed CSI-RS and non-precoded CSI RS is proposed.The corresponding signaling diagrams and flowcharts are also designed.Besides,the signals which are needed in the proposed scheme are defined.Compared with the existing scheme of disabling the interference beam,the performance of the high-level users is ensured,and the interference to the cell edge user is also reduced. |
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