Performance Analysis And Transmission Scheme Design For Massive MIMO Systems Under Non-ideal Conditions

With the increasing number of smart phones and various wireless devices,the amount of mo?bile data is exponentially growing.This results in the demand for high speed and high quality communications,and meanwhile promotes the development of the 5th Generation(5G)mobile communication systems.As a key technology of 5G,once massive multiple-input multliple-output(MIMO)idea is proposed,it has attracted considerable attention from both academia and industry,due to its potential gains in spectral efficiency.Currently,there are many key issues in the aspects of theory and practical application that must be addressed,which mainly include 1)how to handle the channel aging problem in time-variant scenario;2)how to deeply tap the potentials of exploit?ing the massive MIMO technique in relaying systems;3)how to implement the communication system with low cost,consumption,and complexity.Therefore,focusing on the aforementioned challenges,this thesis conducts a very intensive study and obtains a number of innovative results.First,by considering the channel aging effects due to the time-variant channel,this thesis investigates the sum-rate in the masssive MIMO system with channel aging.More precisely,lever-aging on the autoregressive model of order 1 and by adopting the maximum ratio combining and zero-forcing(ZF)reception techniques,the closed-form expressions are derived for the sum-rate,and the power-scaling laws are deduced as the number of antennas at the base station approaches infinity,which reveals that ZF is more sensitive to the channel aging effects.To overcome the performance degradation caused by channel aging,a channel prediction strategy based on wiener filter is proposed.Finally,the analysis is extended to single-cell downlink and multiple-cell sce-narios,and shows that the power-scaling laws are the same for uplink and downlink.In contrast,the energy efficiency in the multiple-cell scenario slightly decreases due to the pilot contamination.Next,focusing on the typical amplify-and-forward(AF)and decode-and-forward(DF)proto-cols,the multipair massive MIMO two-way relaying model is proposed,and the achievable spectral efficiency is intensively studied.More precisely,the closed-form expressions for the system spec-tral efficiency are derived,and then the power-scaling laws in the asymptotic regime are obtained.The outcomes reveal the fundamental tradeoff between the transmit powers of the relay,each user,and the pilot.In addition,the power allocation schemes for both AF and DF protocols are designed,which shows that the spectral efficiency is significantly improved.Then,to address the issues of high energy consumption and financial cost,this thesis propos-es the strategy of using low-resolution devices in the systems.Specifically,after formulating the system model where the relay and the users deploy the low-resolution analog-to-digital convert-er(ADC),the closed-form expression for the system rate is obtained,which reveals the optimal location of deploying low-resolution ADC,the power-scaling laws,and the impact of the number of relay antennas,the quantization level of the ADC,and the intensity of the loop interference on choosing full-or half-duplex mode.The results suggest that it is preferable to deploy the low-resolution ADC at the relay,and the half-duplex relaying is more sensitive to the quantization level of the ADC.Finally,to further simplify the complexity of the hardware,this thesis replaces the low-resolution devices with one-bit quantized devices,and then investigates the half-duplex relaying system with one-bit ADC and one-bit digital-to-analog converter(DAC).Specifically,it is shown that different orthogonal pilot sequences obtain different channel estimation accuracy.Also,the closed-form expression for the achievable rate is deduced,and then the power allocation problem in relaying systems with one-bit quantization is formulated.In addition,the nonlinear precoding scheme based on the gradient projection algorithm is proposed,and then two novel algorithms are designed based on the idea of successive decoding and vector perturbation.The simulation results indicate that the proposed approaches substantially enhance the system performance.