Bird Technologies VPM3 - Manual (Page 47)

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Statistical Power Measurement Methodology
Complementary Cumulative Distribution Function (CCDF)
The most commonly used parameter is that of the Complementary Cumulative
Distribution Function (CCDF), which provides an indication as to the probability
that the measured power level is greater than a specific power value. This tech-
nique has become extremely useful with modern communications systems,
where power levels appear to be noise-like, and do not follow a traditional
power envelope. With regard to CCDF, it is important to understand that CCDF
measurements require no time synchronization with the waveform to be mea-
sured, and no specific test signal is required. This type of power analysis may be
performed using live, “on-air” signals.
Example - 9 Channel CMA, One Signal
This figure illustrates a time record for a nine channel CDMA One Signal. Note the
noise-like nature of the signal, and the lack of any defined waveform envelope.
This figure illustrates the same signal using statistical methods (CCDF), where
the Y axis represents the percentage of time that the signal is at or above a level
specified by the X axis, and the X axis represents the level (dB) of the signal
above the average power of the waveform.
In this case, the signal of interest is being compared to band limited Gaussian
noise, as this signal has a defined characteristic, dependent upon the signal
bandwidth.
Example - LTE vs Gaussian Noise
This example illustrates another view of this concept, comparing the statistical
performance of a live LTE envelope compared to Gaussian noise.
Figure 41 presents another view of this data in numeric format, as a means of
illustrating a few of the data points on the CCDF curves. This table shows that
10% of the time, this particular LTE waveform demonstrates a peak to average
ratio of 4.46 dB. At the same time, the table also reveals that the same wave-
form demonstrates a peak to average ratio of 10.56 dB 0.0001% of the time.
Interpreting Statistical Data
There are many factors that influence the performance of modern communica-
tions systems. Some examples:

The presence of interfering signals within the operating bandwidth of
the system.

Transmission line discontinuities resulting in multiple reflections within
the transmission system.