Research On Multi-user Massive MIMO Precoding

Large-scale Multiple-Input Multiple-Output(MIMO)technology makes an important impact in the fifth generation of mobile communications(5G)because of its improvement in the system's reachability and the reliability of communication.Compared with MIMO system,when we use suitable precoding technology in the massive MIMO system,not only the energy efficiency becomes higher,but also the spectral efficiency becomes higher.For massive MIMO precoding technology,gaining advantages may cause the potentially high computational complexity of the precoding.When the number of the radio frequency chains in a massive MIMO system increases,the hardware complexity,system cost,and circuit power consumption get high.To reduce system power consumption,reducing resolution is an effective way.The millimeter wave frequency band can provide more spectrum resources,not only the anti-interference ability of the channel can be enhanced,but also enhancing the spectrum efficiency and capacity of the system.The combination with the massive MIMO technology has good application potential.Therefore,this paper does the research on the precoding in the massive MIMO system.What's more,we consider the millimeter wave technology.The followings are the main content and work of this article:(1)Research on the precoding of multi-user massive MIMO downlink system which has digital-to-analog converters with 1-bit quantized precision.A nonlinear precoding algorithm based on the Alternating Direction Multiplier Method(ADMM)is applied to construct an augmented Lagrangian function in order to minimize the error rate.The simulation results show that when using this algorithm,the system not only has a lower bit error rate,but also can support multi-user MIMO systems with higher modulation modes.In addition,it has comparable BER performance to the SQUID algorithm,in contrast to lower computational complexity.(2)Research on precoding for a point-to-point millimeter wave MIMO system that combines a hybrid precoder and a low-resolution phase shifter.By optimizing the analog and digital precoding matrix together,our goul is to optimize the spectrum efficiency.Our optimization problem can be divided into two sub-problems after using the method of singular value decomposition of the channel matrix,which can reduce the computational complexity.And then in order to further reduce the complexity,an auxiliary variable is introduced to reduce the scope of the codebook.Compared with the Alt?CDM algorithm,the algorithm improves the spectrum efficiency.(3)We study the precoding of the multi-user millimeter-wave MIMO systems.A hybrid beamforming algorithm that maximizes the minimum phase difference is proposed,which uses the correlation characteristics of the channel gain and the array response vector to select the vector set to provide higher signal power.Then,the phase difference between the beamforming vector and the main propagation path array response vector reflects the magnitude of the inter-user interference,and to minimize the interference of the users,we propose the criterion to maximize the minimum phase difference.Compared with the beam control algorithm and the improved beam control algorithm,the algorithm not only can improve the spectrum efficiency but also has a lower computational complexity.