In digital modulation, what does MER quantify?

• A. SNR per bit
• B. The distance in dB between received symbol points and their ideal locations
• C. The bit error rate
• D. The clock jitter

Answer: (B)

MER in digital modulation measures how far the received constellation points are from their ideal locations, i.e., how much the symbol points wander due to noise and distortion. It’s expressed as a ratio in decibels between the average symbol energy and the average error energy (the deviation from the ideal point). In other words, MER quantifies the quality of the modulation by describing how closely the received symbols cluster around the correct constellation points. A higher MER means the received points sit closer to where they should be, indicating cleaner transmission. This differs from SNR per bit, which is about energy per bit relative to noise; bit error rate, the fraction of bits detected wrongly, depends on the detector and MER; and clock jitter relates to timing uncertainty rather than constellation distortion.