Desigen And Implementation Of TDD-based Distributed Massive MIMO System

With the advent of the information age,new services and application scenarios keep emerging,which all put forward higher requirements for the existing communication architecture.It also causes people to the research boom of the fifth generation mobile communication(5G)system.At present,large-scale MIMO technology has become one of the core technologies of 5G,and distributed MIMO system,one of its research directions,has attracted great attention from industry and academia.Distributed MIMO systems achieve higher performance by configuring a large number of rf processing nodes,which also brings great challenges.How to implement distributed MIMO prototype verification system quickly is a challenging problem.In this paper,a distributed large-scale MIMO prototype verification system based on TDD mode is designed and implemented based on real needs,so as to study the propagation characteristics and related algorithms of distributed large-scale MIMO.The specific work arrangement is as follows:First of all,this paper conducts the physical layer design of distributed MIMO prototype verification system on the basis of in-depth study of the relevant theoretical achievements of distributed MIMO technology and experience in the establishment of centralized MIMO prototype system.Under the premise of determining the wireless frame structure and key parameters,we design uplink and downlink sheme of large-scal distributed MIMO prototype system and study key technologies,icluding symbol timing synchronization and carrier frequency offset compensation technology in airport synchronization,distributed channel interoperability calibration technology and optical fiber transmission technology.Channel estimation and channel equalization algorithm are also given in this paper.Then,this paper introduces software and hardware platforms and system architecture of distributed MIMO prototype verification system.Combined with the transmission characteristics and processing requirements of distributed MIMO prototype system,USRP RIO is selected as the rf processing node,huawei universal multi-core processor is selected as the central processing unit and White Rabbit series products are selected as the clock distribution network.The characteristics and performance of the hardware system and the corresponding software development environment are introduced in detail,and the architecture of the distributed MIMO prototype system is designed by using the selected hardware system,including base station side up and down transmission architecture,base station side clock distribution network architecture and user side up and down transmission architecture.From rf processing node to central processing unit,from FPGA to server,from LabVIEW to C language,the details about each function module's software implementation of base station side are elaborated,the data flow trend of the whole system is clarified and the key role of the core module in the distributed MIMO prototype system is highlighted.Finally,this paper completes the transmission implementation of distributed MIMO prototype verification system and relevant testing and measurement.On the basis of completing the whole system construction,the uplink and downlink multi-user bitstream data transmission of the system is realized in indoor and outdoor test scenatios.Our system can support QPSK and 16 QAM modulation modes and the bit error rate curves of each node of the uplink transmission are measured and analyzed.The measurement results show: The distributed MIMO prototype verification system based on TDD mode established in this paper can complete the transmission of uplink and downlink bitstream data,so we achieve the expected goal.