Rohde & Schwarz SMM100A, User Manual

Page: 262 / 1088

Adding noise and predistortions, and impairing the signal
R&S
®
SMM100A
262 User Manual 1179.1341.02 ─ 05
5 Adding noise and predistortions, and impair-
ing the signal
The test case scenarios in accordance with the specifications often require a not
"clean" signal but rather a signal that is impaired or interfered. To fulfill such require-
ments, the R&S
SMM100A is equipped with a noise generator and provides the possi-
bility to impair and predistort the digital I/Q signal.
This section describes the following functions:
● Adding noise to the signal .....................................................................................262
● Impairing the signal ...............................................................................................276
● Frequency response correction .............................................................................283
● Applying digital predistortion ................................................................................. 283
5.1 Adding noise to the signal
This section introduces the concept of the AWGN generator (Additive White Gaussian
Noise). The section also describes the settings for generation of noise, sine wave inter-
ferer, and adding noise to the generated signal.
5.1.1 Required options
The equipment layout for generating an AWGN signal includes:
●
Option Wideband Baseband Generator (R&S SMM-B9)
●
Option Noise Generator (R&S SMM-K62)
5.1.2 About the AWGN generator
Provided the required options are installed, the R&S SMM100A allows you to superim-
pose 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:
●
I and Q paths are decorrelated from each other.
●
Small probabilities are ensured via the crest factor of
~
15 dB
●
The period of the noise signal is relatively long and depends on the selected sys-
tem bandwidth.
Adding noise to the signal