Research On Hybrid Precoding Technology In Milimeter-wave Massive MIMO Systems

Large-scale multiple-input multiple-output(MIMO)systems are widely concerned because of their high spectral efficiency,energy efficiency,and robustness.The millimeter wave frequency band can provide abundant spectrum resources and become one of the candidate frequency bands for future communications.Introducing millimeter wave into the massive MIMO system can provide greater bandwidth for the massive MIMO system and improve the data transmission rate.At the same time,the smaller wavelength of the millimeter wave can configure a larger antenna array in a limited space,significantly improving Channel capacity.In the study of millimeter wave massive MIMO systems,hybrid precoding can further improve the performance of the system while reducing the number of required radio frequency links.Therefore,this paper focuses on the millimeter-wave massive MIMO hybrid precoding technology to study the hybrid precoding algorithm for multi-user millimeter-wave massive MIMO systems.The specific research contents are as follows:1)Design a hybrid precoding algorithm for the fully connected structure of a multi-user millimeter-wave massive MIMO system.By transforming the hybrid precoding problem into a two-order problem,the analog domain precoding and digital domain precoding are designed.In the first stage,the analog domain precoding is designed with the equivalent channel as the optimization goal,and it is proved that by performing singular value decomposition(SVD)on the channel and extracting the phase of the right unitary matrix,the analog domain precoding can be designed to achieve equivalent Channel sub-optimization;In the second stage,digital domain precoding is designed according to known equivalent channels to suppress interference between users.Simulation experiment results show that the proposed hybrid precoding algorithm can obtain higher spectral efficiency under both perfect channel and imperfect channel conditions.2)Comprehensively optimize the spectrum efficiency and energy efficiency of the system,and propose a hybrid dynamic connection structure.The hybrid dynamic connection structure has multiple sub-arrays,and each sub-array contains multiple radio frequency links and is connected to the antenna unit in the sub-array through a full connection method.For the antenna unit of the sub-array,it is dynamically selected by certain criteria.At the same time,a multi-user multi-stream hybrid precoding algorithm based on hybrid dynamic structure is proposed.The algorithm designs the pre-coding of the analog domain of the hybrid dynamic connection structure by maximizing the increment of signal-to-interference-plus-noise ratio(SINR),and then uses known equivalent channels to apply Block Diagonalization(BD)suppresses multi-user multi-stream interference.Simulation results show that the spectral efficiency of the proposed hybrid dynamic connection structure is between the spectral efficiency of the fully connected structure and the spectral efficiency of the hybrid fixed connection structure,but the highest energy efficiency is obtained.