Research On Energy Efficiency Of Massive MIMO System

With the explosive growth of mobile data traffic and the shortage of spectrum resources,massive multi-input multi-output(MIMO)technology can be expected to become the core technology of next generation mobile communication system,and green communication has become the focus of future communications.This thesis focuses on the energy efficiency(EE)of massive MIMO systems.The specific research can be listed as follows:This thesis studies how to choose the number of the base station(BS)antennas and transmit power based on the Rayleigh channel in multi-cell and single-cell situations respectively to maximize the downlink energy efficiency in multi-user massive MIMO systems.Different with most previous work,we use a more realistic power model to explicitly describe how EE is nonlinearly dependent on the number of base station antennas,the number of user equipments,and the transmit power,derived from zero forsing(ZF)processing with perfect channel state information(CSI)for maximization EE and its simple closed-form expression.Finally,the optimal solution of each parameter is obtained through numerical analysis,and the correctness of theoretical analysis is also proved.We compare the results of the two cases in the same conditions,and in the single cell case,we also compare the energy efficiency of the system under the three linear processing conditions of ZF,minimum mean squared error(MMSE)and maximum ratio transmission/combining(MRT/MRC)with the number of base station antennas.In this thesis,the downlink EE of massive MIMO systems based on Nakagami fading channel is studied.The CSI is known at both ends of the transmitter and receiver,and known only at the receiver.The ZF and MMSE are used respectively for analysis and comparison.Firstly,the system model is obtained,which includes the channel model,a new circuit power model and a signal model based on the Nakagami channel.Based on this system model,we can get the expression of system EE.Then we can analyze the optimal solution of EE.Finally we verify the theory by numerical analysis.The EE of the distributed antenna system under the cell structure which is different with the previous two chapters is studied and compared with the centralized EE based on that cell structure.Firstly,according to the different configurations of the number of transmitter and receiver,the EE approximation of distributed antenna system is obtained under a mixed fading channel,and the optimal solution expressions of each parameter which maximize the EE is deduced,such as optimal transmit power,number of BS antennas,and so on.This chapter also studies the EE of distributed massive MIMO systems based on the Nakagami fading channel.Then we compare the EE of distributed and centralized energy in each case and the EE under distributed Nakagami channel,and verify the accuracy of theoretical analysis in two cases.Finally,contact the reality,we take into account that in the downlink communication the number of receiver antennas(user equipment)is generally not more than the sender(base station).Therefore,it can be concluded that the EE of the distributed antenna is more prominent than that of the centralized antenna,which shows that the distributed antenna system has important research significance for today's research hotspot green communication technology.