Research On Multi-pair MIMO Relay System Under Ricean Fading

Large-scale MIMO(Multiple input multiple output,MIMO)is recognized as one of key technologies of 5G by the academic community and industry since it can serve multiple users on the same channel by employing tens to hundreds of antennas at the base station(BS).Large-scale MIMO can increase the system capacity by more than 10 times and the energy efficiency by 10-100 times.In the large scale MIMO system,line-of-sight(LoS)signal plays an important role,which can be characterized very well by Ricean fading.Based on this,considering the Ricean fading channel,we study the theoretical performance of the multi-user MIMO systems.Firstly,for the small scale cognitive multiuser MIMO uplink(i.e.,N single antenna secondary user communicate with BS equipped with M antenna on the same channel),considering the ZF(zero forcing transmission,ZF)beamforming scheme,we obtain the closed-form expressions of the achievable rate for two the power constraint schemes,by using the mathematical knowledge such as the non-central Wishart distribution.Specifically,we consider the following two kinds of power constraints:(1)single power constraints:Ps = Pmax,(2)double power constraints:PS=min(Ia/|gsn,P|2,Pmax),where Pmaxis the maximum transmission power of the secondary user n,Ia is the maximum interference power of the primary user can tolerate,gsn,P is the channel fading coefficient of secondary user n to the primary user,Ps is the transmit power of the secondary user n.The numerical and simulation results verify the correctness of our theoretical analysis.The results can be used to guide the design and optimization of a MIMO uplink.Secondly,for a multiuser large-scale MIMO two-way amplify-and-forward relaying network,considering the maximum ratio combining/maximum ratio transmission(MRC/MRT)and ZF two beamforming schemes,when the number of relay antennas M ??,we obtains the asymptotic expression of the achievable rate.In particular,we consider four typical power scaling schemes,i.e.,(1)PU ? EU,PR =ER;(2)Pu= EU/M,PR= ER;(3)PU = EU,PR = 2NER/M;(4)PU = EU/M,PR = 2NER/M;where PS is the power constraint of per user,PR is the power consreaint of the relay,Eu,ER are fixed values,N denotes the pairs of users.Our analytical results reveal that when M??,the small scale fading and co-channel interference are eliminated,and the achievable rate tends to a fixed value.The results of great significance to the design and performance optimization of large-scale MIMO relaying network.Finally,we study the effect of imperfect channel state information(CSI)on the performance of a multiuser large-scale MIMO two-way AF relay network,and obtain the asymptotic expressions of system of the achievable rate and the energy efficiency.The analytical results show that imperfect CSI reduces the received SINR,thus reducing the system performance.Besides,we find that when the number of relay antennas M ??,the transmit power of the user and the relay station can be both reduced to 1/M.The simulation results are in good agreement with the analytical results.These results provide a good theoretical basis for performance optimization and design of a large-scale MU-MIMO system.