Error vector magnitude

The error vector magnitude or EVM is a measure of the deviation of the transmitted symbols from the ideal constellation . It serves as a characteristic value for the signal amplification and the noise of a receiver and has meanwhile developed into an industry standard value for mobile radio systems. Typically, the EVM is given in decibels (dB) or percent.

Noise, distortion and interfering signals lead to a deterioration of the received signal and the EVM offers a benchmark for the quality of digital radio transmitters or receivers such as B. Wi-Fi , DVB or LTE . The transmitter EVM can be determined with special signal and spectrum analyzers . In the course of the demodulation of the IQ constellation of a phase modulation or QAM, the angle and the distance to the desired (ideal) point are determined.

definition

Constellation diagram and EVM

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

${\displaystyle \mathrm {EVM(dB)} =10\log _{10}\left({P_{\mathrm {error} } \over P_{\mathrm {reference} }}\right)}$

where P _{error is} the root mean square of the Error Vector. For single- carrier modulations, the greatest power, that is to say the outermost constellation point, is usually used for P _reference , while the average reference power is used in multi-carrier modulation methods.

The also usual percentage calculation results as:

${\displaystyle \mathrm {EVM(\%)} ={\sqrt {P_{\mathrm {error} } \over P_{\mathrm {reference} }}}\cdot 100\,\%}$

with the same variables.

literature

• Walter Fischer: Digital Television. A Practical Guide for Engineers, Springer Verlag, Berlin / Heidelberg 2004, ISBN 3-540-01155-2 .
• John WM Rogers, Calvin Plett: Radio Frequency Integrated Circuit Design. Artech House Inc, Norwood 2010, ISBN 978-1-60783-979-8 .
• Walter Fischer: Digital television and radio technology in theory and practice. MPEG baseband coding, DVB, DAB, ATSC, ISDB-T transmission technology, measurement technology . 2nd edition, Springer Verlag, Berlin / Heidelberg 2009, ISBN 978-3-540-88187-2 .

See also

• Signal to noise ratio

credentials

1. ↑ http://www.ztecinstruments.com/zconnect/?p=1615
2. ^ EVM Calculation for Broadband Modulated Signals, McKinley et al, 64th ARFTG Conf. Dig., Orlando, FL, pp. 45-52, Dec. 2004 ( Memento of the original from November 22, 2009 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF; 446 kB)  

Web links

• Measurement of EVM (Error Vector Magnitude) for 3G Receivers (accessed November 27, 2017)
• Receiver Optimization Using Error Vector Magnitude Analysis (accessed November 27, 2017)
• Robust Computation of Error Vector Magnitude for Wireless Standards (accessed November 27, 2017)
• Error Vector Magnitude Analysis in Generalized Fading with Co-Channel (accessed November 27, 2017)