# RF Wireless World

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## CCDF or Complementary Cumulative Distribution Function

CCDF stands for complementary cumulative distribution function, a statistical power calculation method and can only be performed on time-domain data.

This measurement provides more insight of instantaneous power across the time. CCDF curve help power amplifier designer to design the power amplifier in a better way taking into consideration power variation over the time.

CCDF curve will have power in dB on X axis and units of percent on the Y-axis. Power on the x-axis is relative to the signal average power, where in 0 dB is taken as the average power of the signal. For example, 2 dB at 20 percent means there is a 20 percent probability that the signal power will be 2 dB or more above the average power.

Following is the way CCDF is calculated and plotted from the baseband IQ data. Let us assume for sake of explanation that there are N(say 1000) complex values of baseband (I + j*Q) data.

•   Find the average value of this IQ data vector having total 'N' elements. Say we have got 'X' as average value.

•   Arrange all the N values in ascending order as per their magnitude.

•   Take ratio of these sorted IQ data vector with average X.

•   Take Log10 of these values and multiply with 10 and plot all these values. This will be the CCDF curve.