Research On Interference Suppression And Reciprocity Calibration Of Large-scale Distributed MIMO

With the growing demand for wireless mobile communication services,the development of mobile communication system is also keeping pace with the times.The fifth generation mobile communication technology that can meet the demand of Internet of things and mobile Internet is going to be commercially available.As one of the key technologies of the fifth generation mobile communication system,distributed large-scale Multiple-Input Multiple-Output technology has attracted more and more attention with its ability to explore the spectrum resources and greatly improve the spectrum and energy efficiency of the system.In distributed large-scale MIMO system,the main challenges of the transmission techniques include: how to separate the signals of multiple users in the uplink,and how to suppress the multiuser interference at BS for downlink transmission.Therefore,this thesis will focuses on the key technologies involved in the uplinak transmission of distributed large scale MIMO systems.In addition,in order to eliminate inter user interference,we also studied the whole terminal calibration algorithm to ensure reciprocity between uplink and downlink channels.In the first chapter,we introduce the background of the thesis,sketches the evolution process of the mobile communication systems,and describes the development process of MIMO technology in detail.Then,we give the research status of the key technologies that need to be studied,and explain the organizational structure of this paper.In the second chapter,the whole architecture of 5G large-scale distributed MIMO test system and the principle of key modules' implementation are described.The communication process of the uplink and downlink in the system is explained from the standpoint of the frame structure of communication.Besides,the soft/ hardware parameters and the interface structure of the system are illustrated.As the main contribution I made in the project,this paper also introduces the subcarrier mapping module and the data acquisition and analysis module of the system.In addition,a variety of optimization methods are summarized in the process of system function implementation,such as space-time conversion,loop structure optimization and compiler optimization.In the third chapter,the interference suppression technology in the uplink transmission scheme of multiuser large-scale distributed MIMO system is illustrated.In this paper,the principle of precoding technology and joint detection and reception technology is analyzed,especially the uplink soft decision parallel interference cancellation algorithm.From the perspective of engineering implementation,a low complexity joint multiuser interference suppression and soft decision parallel interference cancellation algorithm is presented.The simulation results show that the performance of the soft decision parallel interference cancellation algorithm is much better than that linear MMSE detection algorithm.In addition,the detection scheme that sets the number of parallel times to 2 can get a better trade-off between the computational complexity and the detection performance.In the fourth chapter,the reciprocity calibration of large scale distributed MIMO system is studied.The mismatch between receiver's and transmitter's RF system will destroy the reciprocity between the uplink and downlink channel matrix.So we must carry out reciprocity calibration to ensure that we can get downlink channel matrix through uplink channel matrix.This paper mainly studies the total least square full terminal calibration algorithm based on BD precoding,and analyzes the offline channel data.It proves that the perfect full calibration can completely eliminate the effect of RF system mismatch.Through acquiring channel offline and calculating the narrowband calibration coefficients,we found that only small changes of amplitude calibration coefficient in broadband and phase changes linearly.According to the fitting analysis,the calibration coefficient in the whole bandwidth can be directly obtained according to the narrowband calibration coefficient.So that can save storage space system.