Boonton 4540 Peak Power Meter Quick Start - Manual (Page 33)

4540 Power Meter
Quick Start Guide
PN: 98406000A © Copyright 2008 Boonton Page 33
CCDF Complementary Cumulative Distribution Function. The CCDF is the probability
that the power is greater than a specific power value. CCDF is non-increasing in y-
axis and the maximum power sample lies at 0%.
In a non-statistical peak power
measurement the peak-to-average
ratio is the parameter which
describes the headroom required in
linear amplifiers to prevent clipping
or compressing the modulated
carrier. 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. When this
correspondence is not present, the
peak-to-average ratio alone does
not provide adequate information. It
is necessary to know what fraction of time the power is above (or below ) particular
levels. For example, some digital modulation schemes produce narrow and relatively
infrequent power peaks which can be compressed with minimal effect. The peak-to-
average ratio alone would not reveal anything about the fractional time occurrence of
the peaks, but the CCDF clearly show this information. Assume a full length run of
one hour plus has been made and the CCDF is analyzed. At CCDF = 0% is the
maximum peak power which occurred during the entire run. At CCDF = 1% is the
power level which was exceeded only 1% of the time during the entire run.
Note that this analysis does not depend upon any particular test signal, or upon
synchronization with the modulating signal. In fact, the analysis can be done using
actual communication system signals. Normal operation is not disturbed by the need
to inject special test signals. This type of analysis is particularly suited to the
situation in which the bit error rate (BER) or some other error rate measure is
correlated with the percentage of time that the signal is corrupted. If known short
intervals of clipping are tolerable, the CCDF can be used to determine optimum
transmitter power output. The CCDF is also used to evaluate various modulation
schemes to determine the demands that will be made on linear amplifiers and
transmitters and the sensitivity to non-linear behavior.