Operation
9
Crest Factor
Figure 4 Crest Factor - 10 dB CDMA Signal - 100 W Peak - 10 W Ave
Crest factor (CF) is the ratio of the peak and average powers, in dB. The WPS
calculates the Crest Factor from the Forward Peak and Average Power
measurements.
Crest factor is becoming one of the most important measurements as
communication systems move into the digital age. For CDMA and similar
modulation types the CF may reach 10 dB. If the crest factor is too large, the
transmitter will not be able to handle the peak powers and amplitude distortion
will occur. Crest factor can also detect overdrive and overshoot problems.
Knowing the CF allows end-users to more accurately set base station power and
lower operating costs.
Complementary Cumulative Distribution Function (CCDF)
Figure 5 CCDF - 100 W Signal - 80 W Threshold - 20% CCDF
CCDF measures the amount of time the power is above a threshold.
Equivalently, it is the probability that any single measurement will be above the
threshold. The WPS samples the power over a 300 ms window and compares it
to a user-specified threshold, in Watts. The time above the threshold relative to
the total time is the CCDF.
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