The Research On EVM Measurement Error Based On OTA

With the rapid development of 5th-Generation(5G)mobile communication technology,antenna and RF interface are highly integrated,wireless communication equipment tends to be integrated and chip,and there is no traditional wired measurement interface.In order to meet the testing requirements of high frequency and high bandwidth wireless communication equipment,more and more RF performance indicators adopt over the air(OTA)test instead of conducted test,and error vector magnitude(EVM)is an important indicator of RF performance evaluation.How to conduct accurate and repeatable test under the condition of air test has research significance.In each link of OTA EVM test,there are many factors that introduce test errors and affect EVM test results.In this paper,EVM test errors are studied based on OTA test system,and correction schemes to reduce OTA EVM test errors are proposed.The main research work of this paper is as follows:1.The study of OTA EVM test standard,based on the definition and calculation of EVM in 3GPP standard,gives the specific steps of OTA EVM actual test under the condition of direct far field.2.Study on the influence of OTA EVM test system link on EVM,propose and prove the influence of system link parameters: phase noise,IQ imbalance and amplifier power nonlinear on EVM through theoretical derivation;Simulink is used to model and simulate the system link,and the influence of phase noise,IQ imbalance and nonlinear amplifier power on EVM is simulated and verified.3.OTA EVM test error research,proposed and proved through theoretical deduction OTA EVM test,test error introduced by anechoic chamber,sampling accuracy and receiver time-frequency deviation influence on EVM,and gave the corresponding correction scheme of test error.4.The experimental verification of the test error is based on the test principle and the theoretical analysis of the error.Under the condition of strictly controlling a single variable,a large number of EVM comparison test experiments are carried out by selecting different anechoic chambers,different sampling accuracies,and different receiver links to verify The influence of the test error introduced by the anechoic chamber,sampling accuracy and receiver time-frequency deviation on the EVM is presented,and corresponding test suggestions are provided according to the test results.The research in this paper can reduce OTA EVM test errors to a certain extent,so that OTA EVM test results can accurately evaluate the quality of terminal transmitting signals,which has a certain reference significance for the development of OTA test in the future.