Error Vector Magnitude (EVM) is a measurement method used to determine the quality of radio transmission of digital values. The EVM value is used to evaluate the overall reception quality, which is affected by noise, interference and non-linear distortion. EVM is the vector magnitude between the measured value and that of an ideal modulation vector, determined for each individual symbol.
In radio transmission, digital values are transmitted in bit combinations, depending on the modulation method. Each bit combination is represented by a specific magnitude and vector. For example, in quadrature amplitude modulation, the transmitted vector and magnitude for a particular bit combination deviates from the theoretical vector and magnitude. This deviation, expressed in vector and magnitude, is the Error Vector Magnitude (EVM).
The EVM characteristic is used in 802.11WLANs and has become the industry standard for measuringcell phones, cable TV and WiFi. It is usually expressed in decibels( dB), sometimes as a percentage. It is calculated as the logarithm of the ratio of the error vector to the mean value of the symbol power.