Modulation error ratio

<p>The modulation error ratio or MER is a measure used to quantify the performance of a <a href="/facts/Digital_radio/X0Kp5l8E">digital radio</a> (or digital TV) transmitter or receiver in a communications system using <a href="/facts/Digital_modulation/aAXPjINv">digital modulation</a> (such as <a href="/facts/Quadrature_amplitude_modulation/02j52SWG">QAM</a>). A signal sent by an ideal transmitter or received by a receiver would have all <a href="/facts/Constellation_diagram/aCtPloV9">constellation points</a> precisely at the ideal locations, however various imperfections in the implementation (such as <a href="/facts/Noise_(electronic)/Izbv38Rr">noise</a>, low <a href="/facts/Image_rejection_ratio/wjSsDoFn">image rejection ratio</a>, <a href="/facts/Phase_noise/3WxEUJ7K">phase noise</a>, <a href="/facts/Carrier_suppression/8bbMdyRR">carrier suppression</a>, <a href="/facts/Distortion/z8RJcwNy">distortion</a>, etc.) or signal path cause the actual constellation points to deviate from the ideal locations. 
</p><p>Transmitter MER can be measured by specialized equipment, which <a href="/facts/Demodulation/GFLGoxFl">demodulates</a> the received signal in a similar way to how a real radio demodulator does it. Demodulated and detected signal can be used as a reasonably reliable estimate for the ideal transmitted signal in MER calculation.
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Modulation error ratio