The error vector magnitude is the length of the vector—at the detected symbol location—which connects the I/Q reference-signal vector to the I/Q measured-signal vector. The following graphic shows the calculation of the
metric as well as a diagram showing how a single error vector is calculated.
EVM.
is calculated from the symbol points (the instant in time when symbols are detected). The computation does not include points between symbols. Therefore does not affect the value. The table also shows the location of the symbol that has the largestFor constellations with constant magnitude (QPSK, BPSK, 8PSK, etc.), the EVMs are always normalized to the constellation maximum. For constellations with multiple possible magnitudes (APSK, StarQAM, 16QAM, 32QAM, etc.), the EVMs are normalized to the EVM Normalization Reference.
Shaped OQPSK and Offset QPSK use two points-per-symbol (symbols and midpoints between symbols) to compute EVM and peak EVM due to the offset between I and Q.
For Offset QPSK, when the Half Sine Filter is selected, the OQPSK reference constellation points fall on a circle with a magnitude of sqrt(2)/2, but the EVM is still expressed as a percentage of the magnitude of a QPSK symbol point (magnitude = 1).
For the EDGE demodulation format, the EVM, Phase, and Magnitude Error data results may vary for different settings. When is set to 1 (default), the trace data results are compensated for ISI (inter-symbol interference). For greater than one, the trace data results are not compensated for the effects of ISI.
If the EVM is larger than expected, see the troubleshooting tips in Troubleshooting.
See Also
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