Simulating Fading, Adding Noise and Predistortions, and Impairing the Signal
R&S
®
SMW200A
417User Manual 1175.6632.02 ─ 30
Signal and noise parameters
The Figure 6-2 illustrates the relation between the signal and noise parameters.
Figure 6-2: Graphical representation of the relation between system bandwidth and noise bandwidth
(Minimum Noise/System BW = 2)
System BW* = Occupied BW
The system bandwidth is a measure for the transmitted RF bandwidth. The selected
value is usually the occupied bandwidth and is therefore a value greater than the pure
signal bandwidth.
In the most test cases, the signal and the noise power are not defined directly but with
the target signal-to-noise ratio (SNR) or carrier/noise ratio.
The carrier power is a measure for the signal without the noise distribution. This indi-
cation corresponds to the "Level" value in the "Status bar" (see Figure 6-3).
To ensure flat noise within the selected system bandwidth, the noise bandwidth has
to be larger than the system bandwidth. The minimum noise bandwidth is sometimes
part of the specifications and is calculated as follows:
"Noise Bandwidth" = "System Bandwidth" x "Minimum Noise/System Bandwidth Ratio"
Logically, the calculated noise bandwidth does not exceed the total available band-
width of the instrument, as specified in the data sheet.
By default, the noise power within the system bandwidth is not defined directly but cal-
culated depending on the selected system bandwidth and the desired SNR. The noise
power over the noise bandwidth is calculated respectively.
The noise signal is not generated arbitrarily for a particular bandwidth, but instead it is
generated in steps. Noise therefore also occurs outside the set system bandwidth,
which means that the total measurable noise power usually exceeds the displayed
value "Noise Power".
Adding Noise to the Signal
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