Power Statistics Ccdf Measurement Concepts - Keysight X Series Measurement Manual

Concepts
MSR Measurement Concepts

Power Statistics CCDF Measurement Concepts

Purpose
Many of the digitally modulated signals appear noise-like in the time and
frequency domain. This means that statistical measurements of the signals can
be a useful characterization. Power Complementary Cumulative Distribution
Function (CCDF) curves characterize the higher-level power statistics of a
digitally-modulated signal. The curves can be useful in determining design
parameters for digital communications systems.
The power statistics CCDF measurement can be affected by many factors. For
example, modulation filtering, modulation format, combining the multiple
signals at different frequencies, number of active codes and correlation
between symbols on different codes with spread spectrum systems. These
factors are all related to modulation and signal parameters. External factors
such as signal compression and expansion by non-linear components, group
delay distortion from filtering, and power control within the observation
interval also affect the measurement.
CCDF curves can help you in several situations:
— To determine the headroom required when designing a component.
— To confirm the power statistics of a given signal or stimulus. CCDF curves
— To confirm that a component design is adequate or to troubleshoot your
Measurement Method
The power measured in power statistics CCDF curves is actually instantaneous
envelope power defined by the equation:
(where I and Q are the quadrature voltage components of the waveform and Zo
is the characteristic impedance).
A CCDF curve is defined by how much time the waveform spends at or above a
given power level. The percent of time the signal spends at or above the level
defines the probability for that particular power level. To make the power
statistics CCDF measurement, the instrument uses digital signal processing
(DSP) to sample the input signal in the channel bandwidth.
Keysight N9083A & W9083A Measurement Guide
allow you to verify if the stimulus signal provided by another design team is
adequate. For example, RF designers can use CCDF curves to verify that the
signal provided by the digital signal processing (DSP) section is realistic.
subsystem or system design, you can make CCDF measurements at several
points of a system. For example, if the ACLR of a transmitter is too high, you
can make CCDF measurements at the input and output of the PA. If the PA
design is correct, the curves will coincide. If the PA compresses the signal,
the PAR of the signal is lower at the output of the PA.
(
P =
2 2
) Z ⁄
I + Q
0
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