Error Vector Spectrum (LTE)

Error Vector Spectrum shows the difference between the measured values and the reference values for each resource element in a layer. The error vectors for each resource element in the Measurement Interval have been calculated and the values have been plotted above the corresponding subcarrier. The values of the error vectors are usually plotted as a magnitude, but other formats can be chosen as well.

A marker placed on a symbol point that reads as shown below

indicates that the marker is

on subcarrier -59
in the PDSCH Physical Downlink Shared Channel_User01 channel allocation shown in the Composite Include list
on symbol 48
the 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. value at this point is ~0.42%, and the average error over all the resource elements on this subcarrier is ~.39 % (see EVM for more information on how EVM is calculated)

Downlink MIMO, Layers, and EVM Calculations

EVM values are calculated using physical channels' layer data. The LTE Long Term Evolution demodulator compares measured data (in IQ Meas) with the calculated ideal data (in IQ Ref) to compute an EVM. The data points for IQ Ref are always calculated and shown with precoding removed. For EVM calculations to work, IQ Meas data must also be shown with the precoding removed.

When the MIMO Decoding parameter is set to No Decoding, IQ Meas data will be shown with the precoding present. This will cause EVM calculations to be invalid. For EVM calculations to be valid, MIMO Decoding must be set to 3GPP MIMO Decoding.