EVM (NB-IoT)

EVM shows the Root Mean Square (RMS) of the Error Vector Magnitudes for all channels and signals selected in the Composite Include list of channels, except Non-Alloc, over all symbol-times in the Measurement Interval.

The location of the symbol FFT Fast Fourier Transform: A mathematical operation performed on a time-domain signal to yield the individual spectral components that constitute the signal. See Spectrum. used in EVM Error vector magnitude (EVM): A quality metric in digital communication systems. See the EVM metric in the Error Summary Table topic in each demodulator for more information on how EVM is calculated for that modulation format. calculations is displayed to the right of the EVM value. Possible values are EVM Window Start, EVM Window Center, EVM Window End, or % of FFT Size. See the Symbol Timing Adjust parameter for more information about these values.

EVM can also be shown in units of dB by selecting the Report EVM in dB parameter.

Calculation

The EVM for a single point is the distance between the tips of the measured IQ and reference IQ vectors. This distance is normalized to the average power of the signal and expressed as a percentage (%). The average power of the signal is calculated by averaging the powers for all resource elements in the Search Time trace (capture length determined by Result Length).