Error Vector Magnitude

The error vector magnitude or EVM is a measure of the deviation of the transmitted symbols from the ideal constellation. It is used as a characteristic value of the signal gain and the noise of a receiver and has now become an industry standard value for mobile communication systems. EVM is typically expressed in decibels (dB ) or percent.

Noise, distortion, and noise lead to a deterioration of the received signal and the EVM provides for a comparative measure of quality of digital radio transmitters or receivers, such as Wi -Fi, DVB or LTE. The transmitter EVM can be determined with special signal and spectrum analyzers. In this case, during the demodulation of the IQ constellation of the QAM or phase modulation of the angle and the distance from the desired (ideal) is determined point.

Definition

The error vector is a vector in the complex IQ plane of a constellation diagram between the ideal and the received constellation point. As root mean square of the error vector and the reference power is typically measured over several symbols results in the EVM value:

Where Perror represents the root mean square error of the Vector. For Einträgermodulationen usually is the greatest power, so the outermost constellation point used for preference, while in multicarrier modulation method, the average reference power is used.

The also usual percentage calculation results as:

With the same variables.