Key Technology Research On Broad-band Signal Processing In Massive MIMO System

Compared with existing communication systems,massive MIMO system has more radiation elements and more advantages in high frequency application.Massive MIMO is a key technology of TD-LTE Advanced and 5G communication system.With massive MIMO,the capacity of the system can be greatly increased.To get higher spatial gain,larger channel number,wider signal band width and larger network scale are required.There are more difficulties in system construction,algorithm design and system realization.The main contributions of this paper are as follows:(1)To solve the calibration problem of Massive MIMO antenna array,a low-cost and high-flexibility modularized calibration scheme is proposed.During the inner-module and inter-module calibration,each module can accomplish calibration procedure simultaneously.The time consumption won't increase as the scale of the array expanding because of the modularization.Only adjacent modules are involved during the inter-module calibration.If the scale is expanded,we only need to insert a new module,which had few influence on whole system.The modularized calibration scheme is consist of the single module,which can be standardized manufactured.(2)To meet the needs of mass data processing in massive MIMO system,broad-band digital beam forming is researched.A low-complexity digital beam forming algorithm is proposed.It is implemented by FIR filter,whose coefficients are attained from semi-definite programming algorithm with low complexity.Through the simulation,the broad-band DBF algorithm proposed above is verified to limit the fluctuation of the main lobe lower than 1 d B,so that the performance of DBF is improved.(3)A multi-beam processing system is designed and implemented.An application is developed on Matlab.Through the user interface,FIR coefficients for the implementation of DBF algorithm can be automatically achieved.A multi-beam processing system is implemented on the developing board of Xilinx Vertex-5 FPGA.Beam coefficients can be flexibly programmed.In key processing module of the FPGA,Fourier transformer in frequency domain is used instead of the FIR filter in time domain,which decouples the FPGA utilization from the stages of FIR filter.This multi-beam processing system meets the needs of broad band,multiple channels,varied beams and real time processing in Massive MIMO system.