Well-defined modulation processes may show convergent results after only a few million samples are collected. Running times of only a few seconds may be completely adequate for these applications. It is convenient for analytical reasons to organize statistical data into one of several standard forms. The PDF is useful for analyzing the nature of modulating signals. Sustained power levels such as the flat tops of pulses or steps show up as lines.
Random noise produces a gaussian shaped curve.
The CDF is non-decreasing in y, that is, the graph of CDF versus y cannot have negative slope. The CCDF is the probability that the power is greater than a specific power value. The meaning of this ratio is easy to visualize in the case of simple modulation in which there is close correspondence between the modulating waveform and the carrier envelope. For example, some digital modulation schemes produce narrow and relatively infrequent power peaks which can be compressed with minimal effect. 3 Figure 3.