Measurements
R&S
®
FSW
252
User Manual 1173.9411.02 ─ 19
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 to 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 largest power
that could ever occur, but for a power that has a specified probability of being excee-
ded (e.g. 0.01
%).
The statistical functions provide information on such signal criteria.
5.8.3 APD and CCDF Results
Amplitude Probability Distribution (APD)
As a result of the Amplitude Probability Distribution (APD) function, the probability of
measured amplitude values is displayed. During a selectable measurement time all
measured amplitude values are assigned to an amplitude range (
bin
). The number of
amplitude values in the individual ranges is counted and the result is displayed as a
histogram. Each bar of the histogram represents the percentage of measured ampli-
tudes within the specific amplitude range. The x-axis represents the amplitude values
and is scaled in absolute values (dBm).
The size of each amplitude range (bin) determines the resolution of the histogram and
is indicated in the channel bar, for example
/
0.10
dB
. In this case, a single bar in the
histogram represents an amplitude range of 0.10
dB.
Statistical Measurements (APD, CCDF)
