Research On Residual Frequency Offset Correction Algorithm Of EVM Measurement System For IEEE802.11ac Comprehensive Measuring Instrument

As the latest version of WLAN standards,IEEE802.11ac quickly become a hot research topic in the field of communication.Higher standards have brought higher requirements to test instruments.As an index to reflect the performance of the transmitter,EVM measurement is an important test item of tester.In this thesis,we mainly study the EVM measurement technology of IEEE802.11 ac,which includes the following contents:1.The development history of WLAN and IEEE802.11 series standard is introduced,and several current IEEE802.11ac test solutions and test instruments are listed.The IEEE802.11ac protocol and the key technologies of physical layer are introduced.All of these provide the theoretical foundation for the following residual frequency offset and time offset correction algorithm and the establishment of IEEE802.11ac EVM measurement system.3.Based on the EVM measurement technology of IEEE802.11ac,the EVM measurement system is designed and implemented,and the baseband signal processing system is established,including the receiving system and the EVM measurement module.The receiving system includes synchronization module,channel estimation,channel equalization and data analysis module.EVM measurement module mainly includes the definition of EVM and EVM measurement algorithm.The imperfect factor of the existing receiver system will lead to large errors in the EVM measurement,thus the study of residual frequency offset and time is introduced.4.this thesis studies the origin and impact on system performance of the residual frequency offset and time offset problems,and the system model of residual frequency offset and time offset is established.Based on the classical algorithm of residual frequency offset and time offset estimation,a new algorithm for residual frequency offset covariance correction for IEEE802.1 lac system is proposed,and the algorithm is further improved.5.the simulation platform of the EVM test system is established,and two improved algorithms mentioned in this thesis are applied to the test system.Through the simulation of a large number of measured data,the results prove that the proposed two algorithms improve the constellation rotation,greatly enhance the performance of EVM.