Interference Analysis And Performance Optimization Of Full-duplex Massive MIMO Relay Communication Systems

With the rapid development of mobile communication technology,it is increasingly difficult to meet people's demands for higher data rates and lower latency with scarce spectrum resources.With the full-duplex technique,a node can transmit and receive signals simultaneously at the same frequency.Hence,ideally,the full-duplex technique can double the spectral efficiency and then ease the shortage of the spectrum resources.Based on the capability of achieving double spectral efficiency of full-duplex,the two-way relay is believed to be its most ideal application scenario.In addition,by utilizing the spatial multiplexing gain,the multi-user MIMO(multiple-input multiple-output)technique can significantly enhance the spectrum efficiency.A massive antenna array can have a large number of antennas,such as hundreds of or even thousands of antennas,which can provide much more diversity gain,beamforming gain and spatial multiplexing gain than traditional MIMO.Thus,massive MIMO can significantly improve system spectral efficiency and energy efficiency.In this thesis,in order to use the spectrum resources to the maximum extent,we first propose to apply the massive MIMO technique to the full-duplex two-way relay system and study the system performance.Regarding the full-duplex self-interference,we consider the residual self-interference after implementing the traditional self-interference cancellation techniques.Since the system performance is mostly limited by the full-duplex residual self-interference and interferences caused by the two-way relay transmission,we mainly study the interference suppression capability of massive MIMO to the various kinds of interferences.Then,we analyze the spectral efficiency and energy efficiency of the system.Furthermore,we improve the system performance by designing the pilot transmission and power control.The main results of this thesis are as follows:1.The relative suppression effect analysis of massive MIMO to the full-duplex residual self-interferenceConsidering perfect channel state information(CSI),when the number of relay antennas approaches infinity,we analyze the capability of relative interference suppression of massive antennas to the full-duplex residual self-interference,and we propose various kinds of powerreduction schemes and study their impacts on the system performance.The system has a onepair amplify-and-forward(AF)relay channel,where two full-duplex users exchange information through a full-duplex relay with a very large number of antennas.The relay uses the maximumratio combining/maximum-ratio transmission(MRC/MRT)linear technique to process the signals.Several specific power-reduction schemes are proposed to reduce the transmit powers of different nodes with the increase of the number of antennas.When the number of the relay antennas tends to infinity,we derive and quantify the asymptotic spectral efficiencies of the proposed power-reduction schemes.We show that the very large antenna array can significantly reduce the effect of residual self-interference because of the antenna array gain.Besides,we show that the residual self-interference can also be reduced by properly cutting down the transmit power as increasing the relay antenna number.And the spectral efficiency has a small loss with proper power-reduction,indicating that proper power-reduction can enhance the system energy efficiency.Furthermore,for the more general power-reduction scheme,we summarize the impact of the power-reduction exponential factor on the system performance.2.The performance analysis of spectral and energy efficiencies for the full-duplex two-way relay system based on massive MIMOFor the multi-pair full-duplex two-way massive MIMO relay system,we study the system spectral efficiency and energy efficiency performance under perfect CSI when the relay antenna number tends to infinity,and we analyze the suppression effect of massive MIMO to the interuser interference and inter-pair interference.Considering the AF protocol,we separately exploit the MRC/MRT and the zero-forcing reception/zero-forcing transmission(ZFR/ZFT)techniques at the relay.For improving the energy efficiency,four typical power-reduction schemes are proposed.When the number of relay antennas tends to infinity,we quantify the asymptotic spectral efficiencies and energy efficiencies for the proposed power-reduction schemes.We show again that the residual self-interference can be reduced by decreasing the transmit power under massive relay antennas.Besides,the inter-pair interference and inter-user interference in such systems can also be eliminated in a large number of antennas.Moreover,we analytically compare the asymptotic spectral efficiency performance between MRC/MRT and ZFR/ZFT,and describe the impact of the number of user pairs on the spectral efficiency.We also evaluate the energy efficiency performance based on the practical power consumption model,and depict the impact of the relay antenna number on the energy efficiencies for the proposed schemes.We show that the proposed power-reduction scheme achieve a good performance tradeoff between the spectral efficiency and the energy efficiency.Finally,by comparing the full-duplex and halfduplex,we provide the available regions where full-duplex systems can outperform half-duplex systems regarding the residual self-interference.3.The performance optimization for the full-duplex two-way relay system based on massive MIMOFor the multi-pair full-duplex two-way massive MIMO relay system,by considering imperfect CSI and a finite number of relay antennas,we derive the approximate closed-form expression of the system ergodic rate by utilizing the statistical CSI.In order to improve the system performance,we propose a new pilot transmission scheme,and show that this scheme can greatly improve the system performance as the channel coherence is small.Moreover,we optimize the system performance with regard to the power control.Specifically,the relay adopts the AF protocol and MRC/MRT linear signal processing technique.The orthogonal pilot scheme and the least square method are firstly exploited to estimate the CSI.With a moderate number of relay antennas,we derive an approximate sum rate expression which is shown to be a good predictor of the ergodic sum rate by exploiting the statistical CSI.Then the corresponding achievable rate expression is obtained by adopting another pilot scheme which estimates the composite CSI for each user pair to reduce the pilot overhead of channel estimation.We compare the achievable rates of the two pilot schemes and then show the relative merits of the two methods.Furthermore,power allocation strategies for users and the relay are proposed based on sum rate maximization and max-min fairness criterion,respectively.Finally,numerical results show that the sum rate performance of the proposed system is better than those of the corresponding one-way fullduplex relay system and two-way half-duplex relay system,when the relay antenna number is large.