The Research On Achievable Rate And Energy Efficiency Of Massive MIMO Systems With Channel Aging

As one of the key technologies of 5G,massive MIMO(multiple-input multiple-output)has attracted considerable attention from both academia and industry for its high spectral efficiency and energy efficiency.Notably,the channel state information(CSI)plays a key role in the performance of massive MIMO systems.One of the most important reasons for CSI inaccuracy is channel aging.Due to time variation of the propagation channel and delays in the computation,the channel varies between when it is learned at the base station(BS)and when it is used for beamforming or detection.It is harmful to the system.Therefore,it is important to study how channel aging influences the performance of massive MIMO systems.The topic of this thesis comes from the National Natural Science Foundation of China(61372126)undertaken by my tutor.In the previous researches on channel aging,the maximum ratio transmission(MRT)precoder is used to derive the expression of the achievable rate of single-cell downlink massive MIMO systems.Thus,the relationship between the system's achievable rate and the channel aging coefficient is presented.Based on the above,the thesis concentrates on the performance of single-cell downlink massive MIMO systems under the effect of channel aging by using zero-forcing(ZF)precoder.Firstly,a closed-form expression of the downlink sum-rate by using ZF precoder is derived.According to the derived expression,the power-scaling law that when the number of BS antennas M approaches to infinity,the transmit power of the BS can be reduced proportionally to1/ M while maintaining the same performance,is still satisfied in the single-cell downlink massive MIMO system with channel aging.The simulation results verify the correctness of the derivation.Secondly,the typical total power consumption model,which is characterized as a function of the number of BS antennas and the number of users,is utilized to derive the EE of the system by using MRT precoder and ZF precoder.The simulation results show that the presence of channel aging would decrease the EE of the system.Thirdly,to overcome the effect of channel aging,the liner Wiener channel prediction model is adopted to find the channel coefficient.Then the achievable rate and energy efficiency of the system are derived by assuming ZF precoder and MRT precoder at the BS.The simulation results are presented to verify that the channel prediction model can weaken the effect of channel aging on the system's achievable rate and energy efficiency.