Simulating Fading, Adding Noise and Predistortions, and Impairing the Signal
R&S
®
SMW200A
416User Manual 1175.6632.02 ─ 30
6.2.2 About the AWGN Generator
Provided the required options are installed, the R&S SMW allows you to superimpose
noise on the generated signal. The built-in internal noise generator generates an
AWGN signal (Additive White Gaussian Noise) with selectable bandwidth and adds it
to the digital baseband signal. The main characteristic of this kind of noise signal is the
Gaussian distribution of the noise power density and uniform frequency distribution.
Generation of the AWGN signal
The Gaussian noise is generated with a feedback shift register with subsequent proba-
bility transformation. The switching configuration is such that ideal statistical character-
istics are achieved:
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I and Q paths are decorrelated from each other.
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Small probabilities are ensured via the crest factor of ~15 dB
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The period of the noise signal is relatively long and depends on the selected sys-
tem bandwidth.
●
Scalable lowpass filters are used to produce a noise level with both a broad
dynamic range and a broad bandwidth range.
AWGN modes
The AWGN generator generates signal in one of the following different modes:
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"Additive Noise": the generated noise signal superimposes the interference-free
useful signal
●
"Noise Only": a pure noise signal is generated and modulated to the carrier; the
connection to the baseband is interrupted.
Figure 6-1: Representation of an AWGN > Mode > Noise Only in the block diagram
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"CW Interferer": a sinusoidal signal with an adjustable frequency offset and car-
rier-to-interferer (C/I) power ratio is added to the baseband signal.
Adding Noise to the Signal
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