Complementary Cumulative Distribution Function (Ccdf); Introduction - Keysight N1911A User Manual

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Complementary Cumulative Distribution Function (CCDF)

Introduction

Many of the present digitally modulated signals now look noise-like in the time
and frequency domains. This means that statistical measurements of the signals
can be a useful characterization. Power Complementary Cumulative Distribution
Function (CCDF) curves characterize the higher level power statistics of a digitally
modulated signal. The curves can be useful in determining design parameters for
digital communication systems.
A CCDF curve is defined by how much time the waveform spends at or above a
given power level. This is expressed in dB relative to the average power. A CCDF
curve is a plot of relative power levels versus probability where the X-axis
represents the dB above the average signal power, while the Y-axis represents the
percent of time the signal spends at or above the power level specified by the
X-axis.
The most important application of power CCDF curves is to specify, completely
and without ambiguity, the power characteristics of the signals that will be mixed,
amplified, and decoded in communication systems. For example, baseband DSP
signal designers can completely specify the power characteristics of signals to the
RF designers by using CCDF curves. This helps avoid costly errors at system
integration time. Similarly, system manufacturers can avoid ambiguity by
completely specifying the test signal parameters to their amplifier suppliers.
CCDF curves apply to many design applications. Some of these applications are:
– Visualizing the effects of modulation formats.
– Combining multiple signals via system's components (for example, amplifiers).
– Evaluating spread-spectrum systems.
– Designing and testing RF components.
252 Keysight N1911A/1912A User's Guide