Tektronix WCA200A, User Manual

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Time Analysis (Time Mode)
3- 88
WCA230A & WCA280A User Manual
CCDF Measurement
CCDF (Complementary Cumulative Distribution Function) represents the
probability that the peak power above average power of a measured signal
exceeds a threshold. The analyzer displays the ratio of peak power to average
power along the horizontal axis, and the probability that the ratio is exceeded
along the vertical axis.
This CCDF analysis function and the real-time analysis function allow you to
measure the time-varying crest factor in the time series for code-multiplexing
signals such as CDMA/W-CDMA signals, and multi-carrier signals such as
OFDM signals. This function is useful in designing amplifiers for CDMA/
W-CDMA and OFDM.
The CCDF analysis obtains the distribution of the amplitude of observed signals
and makes a graph of accumulation from the threshold. CCDF is calculated
using this formula:
SP ( X )
=

Max
X
P ( Y ) dY
CCDF ( X )
=
SP ( X
+
Average )
CCDF ( crest factor )
=
0
where
P = Probability density of amplitude
Max = Maximum of amplitude
Average: = Average of amplitude
The analyzer processes input signals internally using the following procedure
(see Figure 3--66):
1. Measure the amplitude of the input signal over time.
2. Determine the amplitude distribution.
3. Obtain CCDF using the above formula.
Amplitude P CCDF
Average
Time X Amplitude X Amplitude 0
(Average)
Max.
Max. Average
Crest factor
Figure 3- 66: CCDF calculation process
CCDF Calculation Process