Research On The Traceable Time Domain Measurement Of MPSK And MQAM Signals Based On Oscilloscope

As one of the key indexes of modulation signal quality evaluation,error vector amplitude(EVM)can measure the modulation signal quality more comprehensively.Nowadays,the main tools to measure EVM are spectrum analyzer and vector analyzer.They are measured in frequency domain.This method is relatively mature and the measurement process is simple.However,due to different instrument manufacturers,EVM measurement does not form a unified specification and standard;and these instruments are calibrated with each other,which is a closed-loop non traceability.Therefore,it is necessary to realize the traceability measurement of EVM.In this paper,the oscilloscope is selected as the traceable measurement instrument of modulation signal,the measurement system is built,and the traceable link based on the oscilloscope is built.The timing synchronization algorithm and carrier phase synchronization algorithm are improved.For the modulation signal measurement in the form of MQAM,EVM parameter is selected as its evaluation index.The evaluation of EVM measurement uncertainty by Monte Carlo simulation is realized.This paper studies from the following five aspects:1.Design and implement a high-precision time-domain traceability measurement system for measuring RF AM signal with broadband sampling oscilloscope,and demodulate the signal waveform with digital demodulation method,providing a new technology for the time-domain RF modulation signal traceability measurement.2.Based on the modulation signal waveform measured by RTDO,the EVM parameter is calculated by normalization method;the EVM measurement system based on RTDO is designed and constructed;the traceability link of EVM measurement is designed.3.An improved timing synchronization algorithm and a phase synchronization algorithm based on fuzzy c-means clustering are proposed.On the basis of deeply studying the principle of timing synchronization,a new algorithm of timing synchronization improvement is proposed by modifying the timing error detection module and adding gain control processing to the loop filter module.Based on the study of the relationship between EVM and carrier phase angle,a phase synchronization algorithm based on fuzzy c-means is proposed.4.Build a synchronous demodulation test system,and develop a synchronous demodulation interface based on MATLAB platform to achieve this function.Theeffectiveness of the proposed algorithm and the good performance of the synchronous system are verified by simulation and measured data.5.This paper studies the uncertainty evaluation method of EVM measurement based on digital real-time oscilloscope.The uncertainty sources of EVM measured by RTDO are analyzed,and the evaluation model of EVM uncertainty based on Monte Carlo simulation is constructed.The combined uncertainty of EVM is calculated by the formula of combined measurement uncertainty.The results show that the uncertainty of EVM is 0.0130%.It is proved that the uncertainty evaluation method proposed in this paper is reasonable.The research results of this paper show that the proposed algorithm and measurement method are reasonable and feasible,the uncertainty evaluation method is correct,and the evaluation results are reasonable.