Rohde & Schwarz R&S SMW-K548 User manual

R&S®SMW-K548
Crest Factor Reduction
User Manual
1179093902
Version 05
(;Ý9W2)

This document describes the following software options:
●R&S®SMW-K548 Crest Factor Reduction (1414.6641.xx)
This manual describes firmware version FW 5.20.043.xx and later of the R&S®SMW200A.
© 2023 Rohde & Schwarz GmbH & Co. KG
Muehldorfstr. 15, 81671 Muenchen, Germany
Phone: [phone] - 0
Email: [email protected]
Internet: www.rohde-schwarz.com
Subject to change – data without tolerance limits is not binding.
R&S® is a registered trademark of Rohde & Schwarz GmbH & Co. KG.
All other trademarks are the properties of their respective owners.
1179.0939.02 | Version 05 | R&S®SMW-K548
The following abbreviations are used throughout this manual: R&S®SMW200A is abbreviated as R&S SMW; the license types
02/03/07/11/13/16/12 are abbreviated as xx.

Contents
R&S®SMW-K548
3User Manual 1179.0939.02 ─ 05
Contents
1 Welcome to the R&S SMW-K548 option...............................................5
1.1 Accessing Crest Factor Reduction settings...............................................................5
1.2 What's new.....................................................................................................................5
1.3 Documentation overview..............................................................................................6
1.3.1 Getting started manual....................................................................................................6
1.3.2 User manuals and help................................................................................................... 6
1.3.3 Tutorials...........................................................................................................................6
1.3.4 Service manual............................................................................................................... 7
1.3.5 Instrument security procedures.......................................................................................7
1.3.6 Printed safety instructions............................................................................................... 7
1.3.7 Data sheets and brochures............................................................................................. 7
1.3.8 Release notes and open source acknowledgment (OSA).............................................. 7
1.3.9 Application notes, application cards, white papers, etc...................................................7
1.3.10 Videos............................................................................................................................. 8
1.4 Scope............................................................................................................................. 8
1.5 Notes on screenshots...................................................................................................8
2 About the crest factor reduction.......................................................... 9
3 Crest factor reduction settings...........................................................11
4 Remote-control commands.................................................................16
List of commands................................................................................ 24
Index......................................................................................................25

Contents
R&S®SMW-K548
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Welcome to the R&S SMW-K548 option
R&S®SMW-K548
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1 Welcome to the R&S SMW-K548 option
The R&S SMW-K548 is a software option that allows you to generate signals with
reduced crest factor.
R&S SMW-K548 key features
●Reduces the crest factor of a baseband signal through clipping the high signal
peaks and filtering the waveform afterwards.
●Can be applied to any waveform file loaded in the arbitrary waveform generator.
●It uses an iterative process to reach the desired crest factor delta.
●It is possible to adjust the filter characteristics. In simple mode, you can specify the
channel spacing and signal bandwidth. Alternatively in the advanced filter mode
you can specify the lowpass filter through passband and stopband frequencies.
This user manual contains a description of the functionality that the application pro-
vides, including remote control operation.
All functions not discussed in this manual are the same as in the base unit and are
described in the R&S SMW user manual. The latest version is available at:
www.rohde-schwarz.com/manual/SMW200A
Installation
You can find detailed installation instructions in the delivery of the option or in the
R&S SMW service manual.
1.1 Accessing Crest Factor Reduction settings
1. In the block diagram of the R&S SMW, select the "Baseband" > "ARB".
The "ARB" dialog box opens and provides general "ARB" settings.
2. Select "Crest Factor Reduction".
The signal generation is not started immediately. To reduce crest factors with the
default settings, see "Activating crest factor reduction" on page 11.
1.2 What's new
This manual describes firmware version FW 5.20.043.xx and later of the
R&S®SMW200A.
What's new

Welcome to the R&S SMW-K548 option
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6User Manual 1179.0939.02 ─ 05
Compared to the previous version, it provides peak cancellation algorithm for crest fac-
tor reduction:
●Background information on the algorithm "Peak cancellation algorithm"
on page 9
●Algorithm settings, see "Algorithm" on page 12, "Cancellation Pulse Bandwidth"
on page 15 and "Transition Bandwidth" on page 15
1.3 Documentation overview
This section provides an overview of the R&S SMW user documentation. Unless speci-
fied otherwise, you find the documents at:
www.rohde-schwarz.com/manual/smw200a
1.3.1 Getting started manual
Introduces the R&S SMW and describes how to set up and start working with the prod-
uct. Includes basic operations, typical measurement examples, and general informa-
tion, e.g. safety instructions, etc. A printed version is delivered with the instrument.
1.3.2 User manuals and help
Separate manuals for the base unit and the software options are provided for down-
load:
●Base unit manual
Contains the description of all instrument modes and functions. It also provides an
introduction to remote control, a complete description of the remote control com-
mands with programming examples, and information on maintenance, instrument
interfaces and error messages. Includes the contents of the getting started manual.
●Software option manual
Contains the description of the specific functions of an option. Basic information on
operating the R&S SMW is not included.
The contents of the user manuals are available as help in the R&S SMW. The help
offers quick, context-sensitive access to the complete information for the base unit and
the software options.
All user manuals are also available for download or for immediate display on the Inter-
net.
1.3.3 Tutorials
The R&S SMW provides interactive examples and demonstrations on operating the
instrument in form of tutorials. A set of tutorials is available directly on the instrument.
Documentation overview

Welcome to the R&S SMW-K548 option
R&S®SMW-K548
7User Manual 1179.0939.02 ─ 05
1.3.4 Service manual
Describes the performance test for checking compliance with rated specifications, firm-
ware update, troubleshooting, adjustments, installing options and maintenance.
The service manual is available for registered users on the global Rohde & Schwarz
information system (GLORIS):
https://gloris.rohde-schwarz.com
1.3.5 Instrument security procedures
Deals with security issues when working with the R&S SMW in secure areas. It is avail-
able for download on the internet.
1.3.6 Printed safety instructions
Provides safety information in many languages. The printed document is delivered with
the product.
1.3.7 Data sheets and brochures
The data sheet contains the technical specifications of the R&S SMW. It also lists the
options and their order numbers and optional accessories.
The brochure provides an overview of the instrument and deals with the specific char-
acteristics.
See www.rohde-schwarz.com/brochure-datasheet/smw200a
1.3.8 Release notes and open source acknowledgment (OSA)
The release notes list new features, improvements and known issues of the current
firmware version, and describe the firmware installation.
The software makes use of several valuable open source software packages. An open-
source acknowledgment document provides verbatim license texts of the used open
source software.
See www.rohde-schwarz.com/firmware/smw200a
1.3.9 Application notes, application cards, white papers, etc.
These documents deal with special applications or background information on particu-
lar topics.
See www.rohde-schwarz.com/application/smw200a and www.rohde-schwarz.com/
manual/smw200a
Documentation overview

Welcome to the R&S SMW-K548 option
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1.3.10 Videos
Find various videos on Rohde & Schwarz products and test and measurement topics
on YouTube: https://www.youtube.com/@RohdeundSchwarz
On the menu bar, search for your product to find related videos.
Figure 1-1: Product search on YouTube
1.4 Scope
Tasks (in manual or remote operation) that are also performed in the base unit in the
same way are not described here.
In particular, it includes:
●Managing settings and data lists, like saving and loading settings, creating and
accessing data lists, or accessing files in a particular directory.
●Information on regular trigger, marker and clock signals and filter settings, if appro-
priate.
●General instrument configuration, such as checking the system configuration, con-
figuring networks and remote operation
●Using the common status registers
For a description of such tasks, see the R&S SMW user manual.
1.5 Notes on screenshots
When describing the functions of the product, we use sample screenshots. These
screenshots are meant to illustrate as many as possible of the provided functions and
possible interdependencies between parameters. The shown values may not represent
realistic usage scenarios.
The screenshots usually show a fully equipped product, that is: with all options instal-
led. Thus, some functions shown in the screenshots may not be available in your par-
ticular product configuration.
Notes on screenshots

About the crest factor reduction
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2 About the crest factor reduction
Communication standards utilizing higher order modulation techniques or using multi-
ple carrier and complex signals consisting of the signals of more than one digital stan-
dard can feature a high crest factor. The signals of some digital standards can have
high crest factors also particularly with many channels and long sequences.
About crest factors
The crest factor represents the ratio of the peak voltage value to the RMS voltage
value, i.e. the peak to average ratio (PAR). The higher the crest factor and the resulting
dynamics of a signal, the greater the requirement for a power amplifier fed by the sig-
nal to be linear.
A high crest factor arises, for example, for a multi carrier signal that has carriers with
an identical start phase. The carriers are periodically superposed that leads to high
peak voltages in relation to the RMS voltage values.
High crest factors entail two basic problems:
●The nonlinearity of the power amplifier (compression) causes intermodulation
which expands the spectrum (spectral regrowth).
●Since the level of the digital to analog (D/A) converter is relative to the maximum
value, the average value is converted with a relatively low resolution. This low res-
olution leads to a high quantization noise.
Both effects increase the adjacent-channel power.
Clipping and filtering algorithm
A common and simple approach for achieving a lower PAR is the combination of clip-
ping and filtering.
●Clipping is a technique that applies a wanted distortion to the signal.
The principle includes specifying a threshold, finding out the signal peaks once the
defined limits are exceeded and clipping them off. The level limit is specified as a
percentage of the highest peak value. Because clipping is done before filtering, the
procedure does not influence the spectrum. The error vector magnitude (EVM)
however increases.
However, signal clipping not only changes the peak value but also the average
value and the effect on the crest factor is unpredictable.
●Filtering is applied after clipping. The used filters are specially designed so that
they filter out the distortion.
Peak cancellation algorithm
The peak cancellation algorithm uses Blackman windowed sinc pulses and subtracts
them from the original baseband signal wherever the signal amplitude exceeds a
defined threshold. This threshold equals maximum peak of the baseband signal minus
a user-definable crest factor difference ("Desired Crest Factor Delta").
This algorithm often provides better EVM results of the output signal versus out of
band noise introduced by the pulses, compared to the clipping and filtering method.

About the crest factor reduction
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The cancellation pulse bandwidth is configurable and the cancellation pulse transition
bandwidth. The achieved resulting crest factor can be higher than expected, because
of filters in the signal processing chain increasing the crest factor again after a previous
crest factor reduction.