EVM 是什么参数

EVM => error vector magnitude。
EVM specification is often used to describe the modulation accuracy of the transmitted signal. TD-SCDMA and wideband CDMA (WCDMA) standards all use this specification to indicate the quality of the transmitted signal. We know that the receiver's BER specification is often described as the function of SNR (or Eb/No). Is there a relationship between EVM and Eb/No? 3GPP TS25.102 gives the EVM definition as below:
The error vector magnitude is a measure of the difference between the (ideal) waveform and the measured waveform. The difference is called the error vector. Both waveforms pass through a matched root raised cosine filter with bandwidth corresponding to the considered chip rate and the roll-off α = 0.22. Both waveforms are then further modified by selecting the frequency, absolute phase, absolute amplitude and chip clock timing so as to minimize the error vector. The EVM result is defined as the square root of the ratio of the mean error vector power to the mean reference power expressed as a %.
From the above definition, we know that Eb/No =1/ (EVM)². "Eb" is the energy per bit, "No" is the SSB noise power density per Hz. Now we will try to find the relationship between EVM and NF, phase noise, I/Q gain imbalance and I/Q phase imbalance. For simplifying calculation, we only consider QPSK modulation type and Es =2Eb for this type modulation, Es is the energy per transmitted symbol.

调制精度，在EVM较小（高SNR）的情况下，可以用来折算对应的SNR

请教影响EVM指标有哪些因素？

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