Research On Performance Of Massive MIMO Relay Transmission Technology

With the rapid development of society informatization in recent years,global mobile data traffic has been explosively growing and user demands for communication service has been continuously improving,while the fourth generation mobile communication system can not meet these future requirements.Therefore,as an inevitable trend for future developments of mobile communications,the fifth generation mobile communication system(5G)has gained considerable attention for its ability in realizing high data rate,high quality of service,high spectral efficiency,and diversified service.Massive multiple-input multiple-out(MIMO),which is one of key technologies in 5G,combined with relay technology can offer a remarkable increase in achievable data rate,communication coverage,link reliability.As a result,massive MIMO relay technology has been considered as a promosing breakthrough technology,since it can meet the vision and demand in performance for 5G.Motivated by this observation,this thesis will concentrate on the performance analysis of massive MIMO relay transmission technology.The main works and contributions of the thesis are summarized as follows:Firstly,the effect of large-scale fading on the asymptotic capacity of massive MIMO multiple relay systems is investigated.The majority of recent research studies on the asymptotic capacity of massive MIMO multiple relay systems are limited to a fundamental assumption of small-scale fading,where the effect of large-scale fading,including shadow fading and path loss,is ignored.Based on this,the thesis analyzes the asymptotic capacity of massive MIMO multiple relay systems under a composite fading environment incorporating small-scale fading,shadow fading,and path loss,as the number of antennas of the source/destination node and that of all relay nodes both approach to infinity with their ratio being fixed.The empirical cumulative distribution of the channel covariance matrix under this asymptotic condition is firstly derived with the aid of random matrix theory.Then,based on the resulting empirical distribution function,the asymptotic capacity is analyzed by considering a realistic linear relay distribution along with two asymptotic cases for a finite and infinite number of relay nodes,respectively.Simulation results indicate that the large-scale fading has a serious impact on the asymptotic capacity of the system.More specifically,increasing the shadowing standard deviation or decreasing the path loss exponent can improve the asymptotic capacity,while increasing the length of the relay line segment leads to a reduction of the asymptotic capacity.Secondly,the effect of channel aging on the spectral efficiency of multi-pair massive MIMO relay systems is investigated.In constrast to previous relevant works,the thesis considers the channel aging effect jointly caused by user node movements and phase noise,which is an inevitable channel impairment in time-varyig fading channels and also is one of the key reasons for channel state information inaccurary.The thesis derives a closed-form expression of the approximation achievable rate per user pair for any finite number of relay antennas,when the relay employs the MRC/MRT processing scheme.Then,the asymptotic spectral efficiency and power-scaling laws of the system are analyzed as the number of relay antennas tends to infinity.Simulation results demonstrate that taking into account the channel aging effect in the system does not affect the discipline of powerscaling laws,but can reduce the spectral efficiency.In addition,decreasing the Doppler shift of each user or the phase noise increment variance can improve the spectral efficiency.Finally,the comprehensive performance of multi-pair massive MIMO relay systems is observed.Most existing research works on the performance of multi-pair massive MIMO relay systems all focus on the achievable rate or the spectral efficiency,where other significant measures for evaluating the system performance are ignored.Based on this,the thesis conducts an analysis about the outage probability,the achievable rate,and the power-scaling characteristic under different asymptotic cases.The probability density function(PDF)of the signal-to-interference-plus-noise ratio is firstly derived.From this PDF,exact analytical closed-form expressions of the outage probability and the achievable rate are obtained for any finite number of relay antennas.In particular,the asymptotic performance and power-scaling laws are further analyzed and compared under two different asymptotic cases for the number of relay antennas going to infinity with a fixed and large number of relay antennas,respectively.Simulations results indicate that increasing the number of relay antennas can make the outage probability decrease to zero and improve the achievable rate to infinity.In addition,under either asymptotic case,cutting down the transmit power of each source user node or/and the relay node inverse-proportionally to the number of relay antennas can still maintain the system performance.