Research On Key Technology In GPP-based 5G Massive Distributed MIMO Test Bed

In order to cope with the explosive growth of mobile data and achieve ubiquitous mobile information net-work,the fifth generation mobile communication system emerged.Due to limited spectrum resources,large-scale MIMO,which can significantly improve the spectrum utilization has also become a research hotspot.In large-scale MIMO system,high order modulation is commonly used in order to utilize limited spectral resources.However,for these high-order modulation system,a high complexity symbol-to-bit demapper is required when using the conventional log-Map algorithm.Therefore,it is necessary to find a soft demodula-tion algorithm with low complexity.In order to reduce the pilot overhead,time division duplex mode usually used in large-scale distributed MIMO system.In this way,you can use the upstream and downstream channel reciprocity to avoid sending the downlink pilot.However,on one hand,non-ideal RF(Radio Frequency)circuits destroy channel reciprocity.On the other hand,the rapid fluctuation of the channel between the Ac-cess Point(AP)will significantly reduce the performance of the system.So,seeking a reasonable calibration program has aroused widespread concern in academia.The subject of this paper is the soft demodulation algorithm with low complexity and the channel calibration algorithm.The paper introduces the research background of the paper,and expounds the development history of MIMO technology.Secondly,it analyzes the related research topic and related current research status.Based on the full consideration of the wireless channel propagation environment,this paper establishes a large-scale distributed MIMO system model based on GPP.Then,a soft demodulation algorithm with low complexity and has a negligible influence on the system performance is presented.Finally,how to calibrate the symmetry of the RF circuit at both sides by channel calibration are proposed.On this basis,the diversity calibration scheme is proposed to deal with the channel fast fluctuation between AP.The use of high-order modulation in large-scale MIMO will brings the problem of high complexity of demodulation algorithm.Therefore,the paper studies a soft demodulation algorithm with low complexity and has a negligible influence on the system performance.In this paper,two practical soft demodulation al-gorithms are analyzed,which has logarithmic complexity named logarithmic complexity soft demodulation algorithms.The other has low complexity named low complexity soft demodulation.And the complexity and performance of these two algorithms are simulated and analyzed.Then,the two algorithms are optimized ac-cording to the SSE instruction set.Finally,the relevant conclusions and the corresponding simulation analysis are presented.The simulation results show that,for M-PAM singal,logarithmic complexity soft demodulation algorithm only involves(?)(log M).On the basis of logarithmic complexity soft demodulation algorithm,the low complexity soft demodulation algorithm further reduces the complexity of the algorithm.The test results show that using the SSE instruction set greatly improves the efficiency of the system.When TDD mode is adopted in large-scale MIMO system,the reciprocity of the channel is destroyed due to the non-ideality of RF.Nevertheless,the channel fluctuation between AP can significantly degrade the system performance.Therefore,this paper needs to find the appropriate channel calibration algorithm.We first analyze the partial calibration scheme when using ZF precoding and the AP,UE side configuration single antenna.Secondly,the uplink and downlink transmission schemes for partial calibration are studied when AP and UE are configured with multiple antennas.Then,we propose a partial calibration using the Least Square(TLS)algorithm.On this basis,a scheme to perform the calibration in different channel coherent time named diversity calibration is proposed to deal with the quick fluctution between AP.Then,the diversity gain obtained by the scheme is analyzed.Finally,the relevant conclusions and the corresponding simulation analysis are given.The simulation results show that the performance of the system is greatly improved by using the diversity calibration,and the SSE instruction set optimization algorithm greatly improves the system implementation efficiency.