Spectral Efficiency Analysis Of Massive MIMO Systems With Classical Channels

With the increasing of the number of smart terminals and wireless mobile services,the mobile data traffic grows exponentially,which is predicted to achieve 1000 X at 2020.However,current mobile communication networks could not support those huge demand.This fact will be a huge challenge for future mobile communication technology.Massive multiple-input multiple-output technology deploys hundreds of antennas to serve tens of users and has attracted wide attention from academia and industry due to its high spectral efficiency,etc.This dissertation pays attention on the spectral efficiency of massive MIMO systems with classical channels.In brief,this dissertation studies how the pilot power allocation affects the spectral efficiency of massive MIMO systems,investigates how cellfree massive MIMO systems improve spectral efficiency,and analyzes the spectral efficiency of millimeter wave massive MIMO systems.The major results are listed as follows:1.The pilot power allocation scheme in massive MIMO systems with Rayleigh channel is investigated.A relative channel estimation error(RCEE)metric is proposed and its expectations based on least squares(LS)and minimum mean squared error(MMSE)estimation methods are obtained in closed-forms,respectively.Moreover,the corresponding closed-form expressions of achievable uplink rate based on maximum-ratio combining(MRC)detector are provided,respectively.Asymptotic analysis shows that,based on the law of large numbers,RCEE and its expectation approach to the same non-zero constant when the number of base-station antennas grows unbound.Based on this rule,a low complexity pilot power allocation algorithm through user grouping is proposed to minimize the average RCEE expectation.Numerical results show that this algorithm not only improves the channel estimation performance,but also can improve the minimum achievable uplink rate and offer almost the same average achievable uplink rate.2.The spectral efficiency of cell-free massive MIMO systems with Rayleigh channel is investigated.Based on the perfect channel state information(CSI)condition,the achievable uplink rate based on the zero-forcing detector is analyzed and its approximate upper and lower bounds are obtained in closed-forms.Analysis shows that,when all base-station antennas are placed together,the approximate upper and lower bounds reduce to the exact upper and lower bounds obtained in conventional massive MIMO systems.Moreover,as the number of base-station antennas becomes infinite,the asymptotic lower-bound of the obtained approximate upper and lower bounds is not only the logarithmic function of the number of BS antennas,but also the linear function of the path-loss factor.However,the achievable uplink rate of the conventional massive MIMO systems increases grows logarithmically as the number of BS antennas increases.Hence,cell-free massive MIMO systems have a better performance for spectral efficiency.Then,the similar results in imperfect CSI case can be obtained but with a little rate-loss due to channel estimation error.3.The spectral efficiency of massive MIMO systems with Ricean channel is investigated.First,the approximate closed-form expressions of the expectation of RCEE are obtained for the LS and MMSE estimation methods,respectively.Analysis shows that,based on the metric of the expectation of RCEE,pilot contamination is exist for both LS and MMSE estimation methods as the number of base-station becomes infinite.However,when Ricean factor is big enough,the RCEE expectation based on MMSE approach to zero which means that pilot contamination is eliminated.Then,the power scaling of the pilot is studied.As the pilot power is cut down to the inverse of the power of the number of base-station antennas,the LS performance deteriorates and MMSE performance is determined only by the Ricean factor.Finally,the closed-form expressions of achievable uplink rate based on MRC detector are provided.Based on the achievable uplink rate metric,pilot contamination is removed for the MMSE case when both Ricean factor and the number of base-station antennas grow unbound.In summary,the thesis focuses on the pilot power allocation scheme in massive MIMO systems with Rayleigh channel,spectral efficiency of cell-free massive MIMO systems with Rayleigh channel,and spectral efficiency of massive MIMO systems with Ricean channel.The obtained results provide bases in the applications of the massive MIMO research.