Error vector magnitude

A signal sent by an ideal transmitter or received by a receiver would have all constellation points precisely at the ideal locations, however various imperfections in the implementation (such as carrier leakage, low image rejection ratio, phase noise etc.)

One of the stages in a typical phase-shift keying demodulation process produces a stream of I-Q points which can be used as a reasonably reliable estimate for the ideal transmitted signal in EVM calculation.

For many common constellations including BPSK, QPSK, and 8PSK, these two methods for finding the reference give the same result, but for higher-order QAM constellations including 16QAM, Star 32QAM, 32APSK, and 64QAM the RMS average and the maximum produce different reference values.

[3] Battery life and power consumption are important considerations for a system-level RF transmitter design.

In order to maximize power efficiency, the PA must have fast turn-on and turn-off switching times.

Because the power-up/power-down operation of the PA can cause transient and thermal effects that degrade transmitter performance, another metric called Dynamic EVM is often tested.

The degradation in dynamic EVM is due to the PA transient response affecting the preamble at the start of the packet and causing an imperfect channel estimate.