Rohde & Schwarz SMBV100B, User Manual

Page: 257 / 1030

Adding Noise and Predistortions, and Impairing the Signal
R&S
®
SMBV100B
255 User Manual 1178.4460.02 ─ 03
4 Adding Noise and Predistortions, and
Impairing 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
SMBV100B is equipped with a noise generator and provides the pos-
sibility to impair and predistort the digital I/Q signal.
This section describes the following functions:
● Adding Noise to the Signal ....................................................................................255
● Impairing the Signal .............................................................................................. 269
● Applying Digital Predistortion ................................................................................ 276
4.1 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.
4.1.1 Required Options
The equipment layout for generating an AWGN signal includes:
●
Base unit
●
Option Noise Generator (R&S SMBVB-K62) per signal path
4.1.2 About the AWGN Generator
Provided the required options are installed, the R&S SMBV100B allows you to super-
impose 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