Why are average power measurements used for Quadrature Amplitude Modulation (QAM) channels instead of peak voltage levels?

Average power measurements are particularly relevant for Quadrature Amplitude Modulation (QAM) channels due to the nature of how these signals operate. In QAM, multiple bits are transmitted simultaneously through varying both the amplitude and the phase of the signal. This results in complex signal constellations where the carrier can be partially suppressed to improve spectrum efficiency and reduce interference.

When the carrier is suppressed, relying on peak voltage levels can lead to inconsistent and misleading readings because these peaks may not accurately represent the effective power being used for transmission. Instead, average power accounts for the continuous variation in the signal and provides a more accurate representation of the signal's performance and the energy being transmitted over time, reflecting the actual power the system handles rather than the maximum potential peaks that could occasionally occur.

As a result, using average power measurements leads to more reliable assessments of signal quality and efficiency in QAM systems, which is crucial for ensuring effective communication.