Which metric measures the quality of the received QAM signal?

Which metric measures the quality of the received QAM signal?

• A. Bit Error Rate
• B. Signal-to-Noise Ratio
• C. Noise Floor
• D. Modulation Error Ratio

Answer: (D)

The main idea is assessing how accurately the received QAM constellation matches its ideal square grid. Modulation Error Ratio is the metric that directly quantifies that constellation accuracy by measuring how far the received symbol points sit from their ideal positions. This distance reflects all distortions that affect demodulation—noise, phase noise, amplitude nonlinearity, and other impairments. A higher MER means the symbols cluster tightly around the correct points, giving cleaner demodulation and lower error rates. While bit error rate tells you how many bits were misdecoded and signal-to-noise ratio gives a general sense of link strength, they don’t specifically capture the quality of the constellation itself. Noise floor is just the baseline noise level and doesn’t measure how well the modulation is resolved. Therefore, Modulation Error Ratio is the best metric for the quality of the received QAM signal.

The main idea is assessing how accurately the received QAM constellation matches its ideal square grid. Modulation Error Ratio is the metric that directly quantifies that constellation accuracy by measuring how far the received symbol points sit from their ideal positions. This distance reflects all distortions that affect demodulation—noise, phase noise, amplitude nonlinearity, and other impairments. A higher MER means the symbols cluster tightly around the correct points, giving cleaner demodulation and lower error rates. While bit error rate tells you how many bits were misdecoded and signal-to-noise ratio gives a general sense of link strength, they don’t specifically capture the quality of the constellation itself. Noise floor is just the baseline noise level and doesn’t measure how well the modulation is resolved. Therefore, Modulation Error Ratio is the best metric for the quality of the received QAM signal.