Theoretical Approach For Centralized Massive MIMO Wireless Transmission

With the rapid proliferation of smart devices and associated applications such as media streaming,cell broadcasting,and mobile TV,the demand for high data rates and quality-of-service(QoS)has dramatically increased.The fifth-generation(5G)mobile communication systems is expected to support significantly large amount of mobile data traffic and huge number of wireless connections,achieve better cost-and energy-efficiency as well as QoS in terms of communication delay,reliability and security.Of which,massive multiple-input multiple-output(MIMO)system,where the base station(BS)is equipped with a large number of antennas,has emerged as one of the promising technologies for 5G communications since it provides both higher energy efficiency(EE),spectral efficiency(SE),robustness and reliability.However,there are some key issues in massive MIMO system,such as the required perfect channel state information(CSI),large size of antenna array and expensive cost and power consumption of high precision analog-to-digital converter(ADC),etc.In this paper,we aim to embrace these special issues and study theoretical approach for centralized massive MIMO wireless transmission?Firstly,we investigate the achievable area spectral efficiency(ASE)of millimeter wave massive MIMO systems accounting for both small and large scale log-normal shadow fad-ing effects,where three different antenna topologies,namely uniform rectangular array(U-RA),uniform linear array(ULA)or uniform circular array(UCA),are deployed at the BS.For the case of URA and UCA at the BS,we adopt a three dimensional(3D)channel model by taking both the azimuth and elevation dimensions into account.Under the assumption that the users are randomly distributed within a circular-shaped cell,we firstly deduce the distribution functions of users' distant,azimuth and elevation users' the angles of departure(AoD),respec-tively,and then lower bound on the average signal-to-interference ratio by exploiting derived squared inner product of different channel vectors.Moreover,approximation expressions on the achievable ASE with maximum ration transmission are derived,which are very tight when the signal-to-noise ratio(SNR)is less than 25 dB.Finally,our results show that the total achievable ASE increases with the number of BS antennas and the number of users,whilst it converges to a saturated value in the high SNR regime and a larger inter-element spacing,but decreases with the radius of cell and decay exponent.Interestingly,it is also found that the achievable ASE of the UCA configuration has a superior the achievable ASE than the one for the URA and ULA cases,which has a great potential of 3D mm Wave massive MIMO systems.Then,we study the downlink achievable ergodic SE of a single-cell multi-user millimeter wave MIMO system,where a URA is used at the BS to serve multiple single-antenna users.We adopt a 3D channel model by considering both the azimuth and elevation dimensions under line-of-sight path propagation.We derive the achievable ergodic SE for this system in closed-form with maximum ratio transmission precoding.This analytical expression enables the accurate and quantitative evaluation of the effect of the number of BS antennas,SNR,and the crosstalk(squared inner product between different steering vectors)which is a function of the AoD of users and the inter-antenna spacing.Results show that the achievable ergodic SE logarithmically increases with the number of BS antennas and converges to a value in the high SNR regime.To improve the achievable ergodic SE,we also propose a user scheduling scheme based on feedback of users' AoD information and obtain the maximum achievable ergodic SE.Furthermore,we consider a dense user scenario where every user's AoD becomes nearly identical and then derive the system's minimum achievable SE.Next,we study the achievable ergodic sum-rate of multiuser MIMO downlink systems in Rician fading channels.We first derive a lower bound on the average signal-to-leakage-and-noise ratio by using the Mullen's inequality,and then use it to analyze the effect of channel mean information on the achievable ergodic sum-rate.A novel statistical-eigenmode space-division multiple-access(SE-SDMA)downlink transmission scheme is then proposed.For this scheme,we derive an exact analytical closed-form expression for the achievable ergodic rate and present tractable tight upper andlower bounds.Based on our analysis,we gain valuable insights into the impact of the system parameters,such as the number of transmit antennas,the SNR)and Rician K-factor,on the system sum-rate.Results show that the sum-rate converges to a saturation value in the high SNR regime and tends to a lower limit for the low Rician K-factor case.In addition,we compare the achievable ergodic sum-rate between SE-SDMA and zero-forcing beamforming with perfect channel state information at the base station.Our results reveal that the rate gap tends to zero in the high Rician K-factor regime.Additionally,we investigate the uplink achievable SE of massive multiuser MIMO with hybrid architectures,which is based on analog and digital detector,where analog domain is implemented by discrete fourier transform(DFT)processing and baseband processing is per-formed by maximal ratio combining(MRC)and zero-forcing(ZF)detectors.We first estimate CSI for hybrid architecture by applying minimum mean-square-error estimation.With the aid of the estimated CSI,we derive a tractable lower bound on the achievable SE with MRC detector and obtain tight upper and lower bounds on the achievable SE with ZF detector.Based on the derived analytical expressions,the effects of the number of radio frequency(RF)chains,the SNR,the pilot length,and the number of users are revealed.Our results showcase that when the number of RF chains,the number of BS antennas,and the SNR are fixed,the total achievable SE with MRC detector can be improved by increasing the number of users,as well as,we derive a globally optimal number of users to maximize the achievable SE with ZF detector.Moreover,there exists an optimal pilot length that maximizes the total achievable SE for both detectors under the estimated CSI scenario.Interestingly,it is also found that for the fixed number of RF chains,the achievable SE is independent of the number of BS antennas and decreases by increasing the number of RF chains.Finally,we investigate the uplink achievable SE of massive multiuser MIMO with hybrid architectures,which is based on a mixed ADC receiver,in which some antennas are equipped with costly full-resolution ADCs and others with less expensive low-resolution ADCs.A closed-form approximation of the achievable SE with the MRC detector is derived.Based on this ap-proximated result,the effects of several physical parameters on the achievable SE are revealed.Moreover,we study the achievable EE of system by considering an energy consumption model.Results showcase that the achievable SE increases with the number of BS antennas and quanti-zation bits,and it converges to a saturated value in the high user power regime or the full ADC resolution case.Furthermore,an important conclusion is that the increasing number of users is beneficial for the achievable EE and there is an optimal antenna number to maximize the EE.Most important,this work efficiency verifies that for a massive MIMO,the mixed-ADC receiv-er with a small fraction of full-resolution ADCs can have comparable SE performance with the receiver with all full-resolution ADCs but at a considerably lower hardware.