Specifications

Chapter 9 71
Measuring Digital Communications Signals
Making Statistical Power Measurements (CCDF)
Measuring Digital Communications
Signals
Making Statistical Power Measurements
(CCDF)
NOTE CCDF can be measured with ESA-E series analyzers with option AYX
or B7D and with all PSA series analyzers.
Complementary cumulative distribution function (CCDF) curves
characterize a signal by providing information about how much time
the signal spends at or above a given power level. The CCDF
measurement shows the percentage of time a signal spends at a
particular power level. Percentage is on the vertical axis and power (in
dB) is on the horizontal axis.
All CDMA signals, and W-CDMA signals in particular, are
characterized by high power peaks that occur infrequently. It is
important that these peaks are preserved otherwise separate data
channels can not be received properly. Too many peak signals can also
cause spectral regrowth. If a CDMA system works well most of the time
and only fails occasionally, this can often be caused by compression of
the higher peak signals.
The following example shows how to make a CCDF measurement on a
W-CDMA signal broadcasting at 1.96 GHz.
Step 1. Using an ESG, setup a W-CDMA signal transmitting at 1.96 GHz and
−10 dBm. Connect the RF OUTPUT to the spectrum analyzer RF
INPUT.
Step 2. Preset the analyzer and set the center frequency to 1.96 GHz:
Press
Preset, Factory Preset (if present).
Press
FREQUENCY Channel, Center Freq, 1.96, GHz.
Step 3. Set the analyzer radio mode to 3GPP W-CDMA as a base station device:
Press
Mode Setup, Radio Std, 3GPP W-CDMA.
Press
Mode Setup, Radio Std Setup, Device (BTS).
Step 4. Select the CCDF one-button measurement from the measure menu and
then optimize the reference level and attenuation settings suitable for
the CCDF measurement:
Press
MEASURE, Power Stat CCDF.
Press
Meas Setup, Optimize Ref Level.