Performance Research Of Massive MIMO Relay Systems Based On Amplify-and-Forward Protocol

The rapid development of wireless communication technology has been bearing witness the increasing demand for higher data rate,better quality of service and higher network capacity day by day.Constrained by the limited available spectrum resources,multiple-input multiple-output(MIMO)systems have become one of the most effective techniques for solving these problems.Massive MIMO systems in which the relay is equipped with hundreds or more antennas,under the premise of effective upgrading the system data rate and improving the quality of communication,can significantly enhance the spatial resolution,effectively eliminate the impact of noise and reduce transmission power,which has become one of the key technologies of 5G mobile communication network architecture.Cooperative relay technology has the advantages of higher capacity and longer network lifetime.The application of amplify-and-forward(AF)relay technology in massive MIMO system,except for reducing the path loss of source-destination direct link,can efficiently complete the information interaction among multiple users with hundreds of antennas sending and receiving data,which will be the icing on the cake for massive MIMO system performance advantage.First and foremost,this paper will focus on the massive MIMO system model based on amplify-and-forward protocol,in which the relay station equipped with N antennas is treated as a bridge to complete the information transmission between K(N>>K)single antenna source users and K single antenna destination users.Under perfect channel state information(CSI),we explore the effect of three kinds of linear relay detection scheme,namely the maximum ratio combining/maximum ratio transmission(MRC/MRT),zero-forcing reception/zero-forcing transmission(ZFR/ZFT)and minimum-mean square-error(MMSE)on the system performance.Meanwhile,under the situation of perfect CSI,the influence of the large-scale fading based on Gamma distribution model with the traditional power scaling scheme on system performance is considered.Numerical simulation results show that:on the basis of remarkly eliminating the system noise and interference,MMSE scheme is better than that of MRC/MRT and ZFR/ZFT,and large-scale fading parameters can effectively improve the system performance to a certain level,then maintain a constant value.In addition,considering the fact that the CSI is imperfect in actual situation,the system performance is analyzed by using the channel estimation under the power scaling scheme.For one thing,when MMSE scheme is adopted at the relay,the direct estimation method is utilized to study the impact of channel estimation error on the system performance.For another thing,when ZFR/ZFT scheme is adopted at the relay,using minimum-mean-square error estimation method and considering the transmission power of the pilot signal pp is fixed and non-fixed,we investigate the system performance with different power scaling schemes.Numerical simulation results show that when the number of relay antennas tends to infinity,the system can choose the specific power scaling scheme based on the actual situation under the premise of effectively saving the system transmission power.Last but not the least,given the secure transmission condition where exists an eavesdropper in practical communication system,this paper presents that ZFR/ZFT detection scheme is adopted and MMSE channel estimation is used to explore the effect of eavesdropper on amplify-and-forward massive MIMO system under semi-perfect CSI.Numerical simulation results illustrate that the useful achievable rate of the system will increase with the increase of relay antennas to a fixed value,and the eavesdropping information will decrease with the growing of relay antennas to a fixed value.