R&S ESR Series User Manual page 458

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R&S ESR
6.4.6.2 Amplitude Distribution Measurements
If modulation types are used that do not have a constant zero span envelope, the
transmitter has to handle peak amplitudes that are greater than the average power.
This includes all modulation types that involve amplitude modulation –QPSK for exam-
ple. CDMA transmission modes in particular may have power peaks that are large
compared to the average power.
For signals of this kind, the transmitter must provide large reserves for the peak power
to prevent signal compression and thus an increase of the bit error rate at the receiver.
The peak power or the crest factor of a signal is therefore an important transmitter
design criterion. The crest factor is defined as the peak power/mean power ratio or,
logarithmically, as the peak level minus the average level of the signal.
To reduce power consumption and cut costs, transmitters are not designed for the larg-
est power that could ever occur, but for a power that has a specified probability of
being exceeded (e.g. 0.01 %).
To measure the amplitude distribution, the R&S ESR has simple measurement func-
tions to determine both the APD = Amplitude Probability Distribution and CCDF =
Complementary Cumulative Distribution Function.
In the APD display mode, the probability of occurrence of a certain level is plotted
against the level.
In the CCDF display mode, the probability that the mean signal power will be exceeded
is shown in percent.
Measurement Example – Measuring the APD and CCDF of White Noise Gener-
ated by the R&S ESR
1. Set the R&S ESR to its default state by pressing the PRESET key.
The R&S ESR is in its default state.
2. Configure the R&S ESR for APD measurement
a) Press the AMPT key and enter "-60 dBm".
b) Press the MEAS key.
c) Press the "More" softkey.
d) Press the "APD" softkey.
User Manual 1175.7068.02 ─ 12
The R&S ESR's intrinsic noise is displayed at the top of the screen.
The R&S ESR sets the frequency span to 0 Hz and measures the amplitude
probability distribution (APD). The number of uncorrelated level measurements
used for the measurement is 100000. The mean power and the peak power are
displayed in dBm. The crest factor (peak power – mean power) is output as
well.
Spectrum Measurements
Advanced Measurement Examples
455