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R&S®FSW-K192/-K193
DOCSIS® 3.1 OFDM Measurements
User Manual
(;ÙÎè2)
1175649002
Version 20
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This manual applies to the following R&S®FSW models with firmware version 5.10 and later:
●
R&S®FSW8 (1331.5003K08 / 1312.8000K08)
●
R&S®FSW13 (1331.5003K13 / 1312.8000K13)
●
R&S®FSW26 (1331.5003K26 / 1312.8000K26)
●
R&S®FSW43 (1331.5003K43 / 1312.8000K43)
●
R&S®FSW50 (1331.5003K50 / 1312.8000K50)
●
R&S®FSW67 (1331.5003K67 / 1312.8000K67)
●
R&S®FSW85 (1331.5003K85 / 1312.8000K85)
This manual applies to the following R&S®FSW models with firmware version 3.20 and higher:
●
R&S®FSW8 (1312.8000K08)
●
R&S®FSW13 (1312.8000K13)
●
R&S®FSW26 (1312.8000K26)
●
R&S®FSW43 (1312.8000K43)
●
R&S®FSW50 (1312.8000K50)
●
R&S®FSW67 (1312.8000K67)
●
R&S®FSW85 (1312.8000K85)
The following firmware options are described:
●
R&S FSW-K192 DOCSIS 3.1 OFDM Downstream Measurements (1325.4138.02)
●
R&S FSW-K193 DOCSIS 3.1 OFDM Upstream Measurements (1325.4144.02)
© 2022 Rohde & Schwarz GmbH & Co. KG
Muehldorfstr. 15, 81671 Muenchen, Germany
Phone: +49 89 41 29 - 0
Email: info@rohde-schwarz.com
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.
DOCSIS® is a registered trademark of the Cable Television Laboratories, Inc..
Trade names are trademarks of the owners.
1175.6490.02 | Version 20 | R&S®FSW-K192/-K193
Throughout this manual, products from Rohde & Schwarz are indicated without the ® symbol, e.g. R&S®FSW is indicated as
R&S FSW.
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R&S®FSW-K192/-K193
Contents
1 Documentation overview.......................................................................7
1.1 Getting started manual................................................................................................. 7
1.2 User manuals and help.................................................................................................7
1.3 Service manual..............................................................................................................7
1.4 Instrument security procedures.................................................................................. 8
1.5 Printed safety instructions...........................................................................................8
1.6 Data sheets and brochures.......................................................................................... 8
1.7 Release notes and open-source acknowledgment (OSA).........................................8
1.8 Application notes, application cards, white papers, etc........................................... 8
2 Welcome to the R&S FSW DOCSIS 3.1 applications.......................... 9
Contents
2.1 Starting the R&S FSW DOCSIS 3.1 application........................................................10
2.2 Understanding the display information.................................................................... 10
3 Measurements and result display...................................................... 13
3.1 DOCSIS 3.1 I/Q measurement.................................................................................... 13
3.1.1 Modulation accuracy parameters.................................................................................. 13
3.1.2 Signal content information.............................................................................................15
3.1.3 PLC information............................................................................................................ 17
3.1.4 Evaluation methods for DOCSIS 3.1 I/Q measurements.............................................. 19
3.2 Frequency sweep measurements..............................................................................33
3.2.1 Measurement types and results for frequency sweep measurements..........................34
3.2.2 Evaluation methods for frequency sweep measurements............................................ 35
4 Measurement basics............................................................................38
4.1 DOCSIS 3.1 characteristics........................................................................................ 38
4.2 DOCSIS 3.1 downstream signal processing.............................................................38
4.3 DOCSIS 3.1 upstream signal processing..................................................................44
4.4 Basics on input from I/Q data files............................................................................ 49
5 Configuration........................................................................................51
5.1 Multiple measurement channels and sequencer function...................................... 51
5.2 Display configuration................................................................................................. 52
5.3 DOCSIS 3.1 I/Q measurement (modulation accuracy).............................................53
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5.3.1 Configuration overview..................................................................................................54
5.3.2 Signal description..........................................................................................................56
5.3.3 Input, output, and frontend settings...............................................................................81
5.3.4 Trigger settings..............................................................................................................99
5.3.5 Data acquisition...........................................................................................................107
5.3.6 Sweep settings............................................................................................................109
5.3.7 Synch/ OFDM-demodulation....................................................................................... 110
5.3.8 Parameter estimation and tracking..............................................................................111
5.3.9 Demodulation.............................................................................................................. 112
5.3.10 Evaluation range..........................................................................................................115
5.3.11 Result configuration.....................................................................................................119
5.3.12 Automatic settings.......................................................................................................134
5.4 Frequency sweep measurements............................................................................136
Contents
5.4.1 Occupied bandwidth....................................................................................................137
5.4.2 CCDF.......................................................................................................................... 137
6 Analysis.............................................................................................. 139
6.1 Traces.........................................................................................................................139
6.1.1 Trace / data export configuration.................................................................................139
6.2 Markers...................................................................................................................... 141
6.2.1 Individual marker settings........................................................................................... 142
6.2.2 General marker settings..............................................................................................145
7 I/Q data import and export................................................................ 146
8 How to perform measurements in the R&S FSW DOCSIS 3.1 appli-
cation...................................................................................................147
8.1 How to analyze modulation accuracy and signal contents for DOCSIS 3.1 down-
stream signals........................................................................................................... 147
8.2 How to analyze modulation accuracy and signal contents for DOCSIS 3.1
upstream signals.......................................................................................................149
8.3 How to evaluate the OBW or CCDF for DOCSIS 3.1 signals................................. 151
9 Optimizing and troubleshooting the measurement........................ 153
10 Remote commands for DOCSIS 3.1 measurements....................... 154
10.1 Common suffixes...................................................................................................... 154
10.2 Introduction............................................................................................................... 155
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10.2.1 Conventions used in descriptions............................................................................... 155
10.2.2 Long and short form.................................................................................................... 156
10.2.3 Numeric suffixes..........................................................................................................156
10.2.4 Optional keywords.......................................................................................................157
10.2.5 Alternative keywords................................................................................................... 157
10.2.6 SCPI parameters.........................................................................................................157
10.3 Activating DOCSIS 3.1 measurements....................................................................160
10.4 Selecting a measurement.........................................................................................164
10.5 Configuring the DOCSIS 3.1 I/Q measurement (modulation accuracy)............... 166
10.5.1 Signal description........................................................................................................166
10.5.2 Configuring the data input and output......................................................................... 193
10.5.3 Frontend configuration................................................................................................ 219
10.5.4 Signal capturing.......................................................................................................... 227
Contents
10.5.5 Configuring triggered measurements..........................................................................229
10.5.6 Synchronization (upstream only).................................................................................237
10.5.7 Tracking and channel estimation.................................................................................238
10.5.8 Demodulation.............................................................................................................. 240
10.5.9 Evaluation range......................................................................................................... 242
10.5.10 Automatic settings.......................................................................................................246
10.6 Configuring frequency sweep measurements on DOCSIS 3.1 signals................247
10.7 Configuring the result display................................................................................. 247
10.7.1 General window commands........................................................................................248
10.7.2 Working with windows in the display...........................................................................249
10.7.3 Configuring specific result displays............................................................................. 256
10.7.4 Configuring synchronous band power results............................................................. 262
10.7.5 Configuring scaling and units...................................................................................... 269
10.8 Starting a measurement........................................................................................... 276
10.9 Retrieving results......................................................................................................280
10.9.1 Numeric modulation accuracy results......................................................................... 281
10.9.2 Numeric results for frequency sweep measurements................................................. 300
10.9.3 Retrieving trace results............................................................................................... 302
10.9.4 Measurement results for TRACe<n>[:DATA]? TRACE<n>.........................................304
10.9.5 Retrieving captured I/Q data....................................................................................... 307
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10.9.6 Importing and exporting I/Q data and results.............................................................. 309
10.10 Analysis..................................................................................................................... 310
10.10.1 Markers....................................................................................................................... 310
10.10.2 Trace export................................................................................................................ 315
10.11 Status registers.........................................................................................................317
10.11.1 The STATus:QUEStionable:SYNC register.................................................................317
10.11.2 Querying the status registers...................................................................................... 318
10.12 Deprecated commands.............................................................................................320
10.13 Programming examples for DOCSIS 3.1 measurements...................................... 321
10.13.1 Measurement 1: measuring modulation accuracy...................................................... 321
10.13.2 Measurement 2: determining the occupied bandwidth................................................326
Annex.................................................................................................. 327
Contents
A References..........................................................................................327
List of commands (Docsis 3.1)......................................................... 328
Index....................................................................................................337
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1 Documentation overview
This section provides an overview of the R&S FSW user documentation. Unless specified otherwise, you find the documents on the R&S FSW product page at:
www.rohde-schwarz.com/manual/FSW
1.1 Getting started manual
Introduces the R&S FSW and describes how to set up and start working with the product. Includes basic operations, typical measurement examples, and general information, e.g. safety instructions, etc.
A printed version is delivered with the instrument. A PDF version is available for download on the Internet.
Documentation overview
Service manual
1.2 User manuals and help
Separate user manuals are provided for the base unit and the firmware applications:
●
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 commands with programming examples, and information on maintenance, instrument
interfaces and error messages. Includes the contents of the getting started manual.
●
Firmware application manual
Contains the description of the specific functions of a firmware application, including remote control commands. Basic information on operating the R&S FSW is not
included.
The contents of the user manuals are available as help in the R&S FSW. The help
offers quick, context-sensitive access to the complete information for the base unit and
the firmware applications.
All user manuals are also available for download or for immediate display on the Internet.
1.3 Service manual
Describes the performance test for checking the rated specifications, module replacement and repair, firmware update, troubleshooting and fault elimination, and contains
mechanical drawings and spare part lists.
The service manual is available for registered users on the global Rohde & Schwarz
information system (GLORIS):
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https://gloris.rohde-schwarz.com
1.4 Instrument security procedures
Deals with security issues when working with the R&S FSW in secure areas. It is available for download on the Internet.
1.5 Printed safety instructions
Provides safety information in many languages. The printed document is delivered with
the product.
1.6 Data sheets and brochures
Documentation overview
Application notes, application cards, white papers, etc.
The data sheet contains the technical specifications of the R&S FSW. It also lists the
firmware applications and their order numbers, and optional accessories.
The brochure provides an overview of the instrument and deals with the specific characteristics.
See www.rohde-schwarz.com/brochure-datasheet/FSW
1.7 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 open-source acknowledgment document provides verbatim license texts of the
used open source software.
See www.rohde-schwarz.com/firmware/FSW
1.8 Application notes, application cards, white papers, etc.
These documents deal with special applications or background information on particular topics.
See www.rohde-schwarz.com/application/FSW
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2 Welcome to the R&S FSW DOCSIS 3.1
applications
The R&S FSW DOCSIS 3.1 applications (R&S FSW-K192/-K193) are firmware applications that add functionality to the R&S FSW to perform measurements according to
the DOCSIS 3.1 standard.
R&S FSW-K192 performs measurements for DOCSIS 3.1 downstream signals.
R&S FSW-K193 performs measurements for DOCSIS 3.1 upstream signals.
Specific bandwidth extension option required
Both R&S FSW DOCSIS 3.1 applications require one of the following bandwidth extension hardware options:
●
R&S FSW-B320 (1313.7172.02) - K192 (downstream) only
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R&S FSW-B320+ (1325.4867.04)
●
R&S FSW-B512 (1313.4296.xx)
●
R&S FSW-B1200 (1331.6400.xx)
●
R&S FSW-B2100 (1331.6916.xx) - K192 (downstream) only
Welcome to the R&S FSW DOCSIS 3.1 applications
The options do not work with the optional 2 GHz / 5 GHz bandwidth extensions
(R&S FSWB2000/B5000), which require an additional oscilloscope.
If the required options are not installed, or non-supported bandwidth extension options
are active, an error message is displayed and no measurements can be performed
with the R&S FSW DOCSIS 3.1 applications.
The R&S FSW DOCSIS 3.1 applications feature:
●
Modulation accuracy measurements
●
Occupied bandwidth measurements
●
Statistical measurements
This user manual contains a description of the functionality that the application provides, including remote control operation.
General R&S FSW functions
The application-independent functions for general tasks on the R&S FSW are also
available for DOCSIS 3.1 measurements and are described in the R&S FSW user
manual. In particular, this comprises the following functionality:
●
Data management
●
General software preferences and information
●
Event-based actions
The latest version is available for download at the http://www.rohde-schwarz.com/prod-
uct/FSW.html.
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An application note discussing the fundamental technological advances of DOCSIS 3.1
and presenting measurement solutions from Rohde & Schwarz is available from the
Rohde & Schwarz website: http://www.rohde-schwarz.com/appnote/7MH89.
Installation
You can find detailed installation instructions in the R&S FSW Getting Started manual
or in the Release Notes.
2.1 Starting the R&S FSW DOCSIS 3.1 application
Both R&S FSW DOCSIS 3.1 application options add a new application to the
R&S FSW.
To activate the R&S FSW DOCSIS 3.1 applications
1. Press the [MODE] key on the front panel of the R&S FSW.
Welcome to the R&S FSW DOCSIS 3.1 applications
Understanding the display information
A dialog box opens that contains all operating modes and applications currently
available on your R&S FSW.
2. Select the "DOCSIS 3.1" item.
The R&S FSW opens a new measurement channel for the DOCSIS 3.1 (downstream) application.
The measurement is started immediately with the default settings. It can be configured in the DOCSIS 3.1 "Overview" dialog box, which is displayed when you select
the "Overview" softkey from any menu (see Chapter 5.3.1, "Configuration over-
view", on page 54).
3. To perform a measurement on a DOCSIS 3.1 uplink signal, select "Signal Descrip-
tion > Stream Direction: Upstream".
2.2 Understanding the display information
The following figure shows a measurement diagram during a DOCSIS 3.1 downlink
measurement. All different information areas are labeled. They are explained in more
detail in the following sections.
(The basic screen elements are identical for DOCSIS 3.1 uplink measurements.)
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Welcome to the R&S FSW DOCSIS 3.1 applications
Understanding the display information
1 2 3 4 5
6
1 = Channel bar for firmware and measurement settings
2 = Window title bar with diagram-specific (trace) information
3 = Diagram area
4 = Detected symbols
5 = Diagram footer with diagram-specific information, depending on measurement application
6 = Instrument status bar with error messages, progress bar and date/time display
Channel bar information
In the R&S FSW DOCSIS 3.1 application, the R&S FSW shows the following settings:
Table 2-1: Information displayed in the channel bar in the R&S FSW DOCSIS
Ref Level Reference level
Att Mechanical and electronic RF attenuation
Freq Center frequency for the RF signal
Mode N
Capture Time Measurement time for data acquisition.
SGL The sweep is set to single sweep mode.
Frames x of y (z) For statistical evaluation over frames:
mode: 4K - 8K / Downstream - Upstream
FFT
<x> frames of totally required <y> frames have been analyzed so far
<z> frames were analyzed in the most recent measurement (= current
capture buffer)
3.1 application
In addition, the channel bar also displays information on instrument settings that affect
the measurement results even though this is not immediately apparent from the display
of the measured values (e.g. external mixer or trigger settings). This information is dis-
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played only when applicable for the current measurement. For details see the
R&S FSW Getting Started manual.
Window title bar information
For each diagram, the header provides the following information:
1 2
Figure 2-1: Window title bar information in the R&S FSW DOCSIS 3.1 application
1 = Window number
2 = Window type
3 = Trace color
4 = Trace number
5 = Trace mode
Welcome to the R&S FSW DOCSIS 3.1 applications
Understanding the display information
4
3
5
Diagram footer information
The diagram footer (beneath the diagram) contains the following information, depending on the evaluation:
Status bar information
Global instrument settings, the instrument status and any irregularities are indicated in
the status bar beneath the diagram. Furthermore, the progress of the current operation
is displayed in the status bar.
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3 Measurements and result display
The R&S FSW DOCSIS 3.1 application provides several different measurements to
determine the parameters described by the DOCSIS 3.1 specifications.
● DOCSIS 3.1 I/Q measurement................................................................................13
● Frequency sweep measurements...........................................................................33
3.1 DOCSIS 3.1 I/Q measurement
Access: "Overview" > "Select Measurement" > "Modulation Accuracy"
Or: [MEAS] > "Select Measurement" > "Modulation Accuracy"
The default DOCSIS 3.1 I/Q measurement captures the I/Q data from the DOCSIS 3.1
signal using a (nearly rectangular) filter with a relatively large bandwidth. The I/Q data
captured with this filter includes magnitude and phase information. This information
allows the R&S FSW DOCSIS 3.1 application to demodulate broadband signals and
determine various characteristic signal parameters in just one measurement, including:
Measurements and result display
DOCSIS 3.1 I/Q measurement
●
Modulation accuracy
●
Spectrum flatness
●
Center frequency tolerance
●
Symbol clock tolerance
Other parameters specified in the DOCSIS 3.1 standard require a better signal-tonoise level or a smaller bandwidth filter than the I/Q measurement provides and must
be determined in separate measurements (see Chapter 3.2, "Frequency sweep mea-
surements", on page 33).
● Modulation accuracy parameters............................................................................13
● Signal content information.......................................................................................15
● PLC information...................................................................................................... 17
● Evaluation methods for DOCSIS 3.1 I/Q measurements........................................19
3.1.1 Modulation accuracy parameters
The default DOCSIS 3.1 I/Q measurement (Modulation Accuracy) captures the I/Q
data from the DOCSIS 3.1 signal and determines all the following I/Q parameters in a
single sweep.
Table 3-1: DOCSIS
Parameter Keyword for
3.1 Modulation Accuracy Parameters
Unit Description
remote command
MER Data+Pilot MER dB Modulation error ratio for data and pilot carriers
MER Data MERD dB Modulation error ratio for data carriers only
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Measurements and result display
DOCSIS 3.1 I/Q measurement
Parameter Keyword for
remote command
MER Pilot MERP dB Modulation error ratio for pilot carriers only
Center Frequency Error FERR Hz Not available if the sample clock error is normalized
Sample/Symbol Clock
Error
Trigger to PLC Time
Stamp Ref point
Trigger to Frame TFR μs Upstream only
Power POW dBm/
Power 6 MHz Channel
containing PLC
CERR ppm
TPLC μs Downstream only
POW:SPLC dBm/
Unit Description
(upstream only).
Time offset of the PLC Timestamp Reference Point (as
defined in the standard in 7.5.13.10 "PLC Timestamp
Reference Point") to the beginning of the capture buffer
(Useful only with an (external) trigger at frame start; if
no trigger is used, value is very unsteady)
Absolute total power of OFDM channel (all subcarriers)
dBmV
/
dBuV
dBmV
/
dBuV
Unit depends on Unit setting.
Absolute power in the 6-MHz channel containing the
PLC
Unit depends on Unit setting.
Power of Analyzed Minislots
Power Data POW:DATA dB ,
Power Pilots POW:PIL dB ,
Power Scattered Pilots POW:SPIL dB ,
Power Continuous Pilots POW:CONP dB ,
Zero Bit Loaded Carrier
Ratio
POW:AMIN dBm Upstream only
dBm
dBm
dBm
dBm
ZBIT - Downstream only
Total power of all minislots analyzed during a Synchro-
nous Band Power (upstream only) measurement. The
results for the individual bands in the Synchronous
Band Power table use this value as a reference.
Power in the data subcarriers
Unit depends on Power Unit and Unit settings.
For relative results, this value is always 0 (data power
relative to itself).
Power in all (normal and complementary) pilot chan-
nels (upstream only)
Unit depends on Power Unit and Unit settings.
Power in the scattered pilot channels (downstream
only)
Unit depends on Power Unit and Unit settings.
Power in the continuous pilot channels (downstream
only)
Unit depends on Power Unit and Unit settings.
Average ratio of the zero bit loaded subcarriers to the
total number of carriers available for the codewords
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Measurements and result display
Remote commands
When you query all results of the result summary using the FETCh:SUMMary:ALL?
command, the values are returned in the order the parameters are described in table
Table 3-1.
For each parameter, several evaluations are calculated for the entire input signal. The
remote commands required to retrieve the results are indicated in the following table.
Table 3-2: Calculated summary results
Result
type
Mean Mean measured value
Max Maximum measured value
Min Minimum measured value
Description Remote command
3.1.2 Signal content information
DOCSIS
FETCh:SUMMary:<parameter>:AVERage
FETCh:SUMMary:<parameter>:MAXimum
FETCh:SUMMary:<parameter>:MINimum
3.1 I/Q measurement
In addition to the modulation accuracy parameters that are calculated from the input
signal, detailed signal content information is available for analysis in the R&S FSW
DOCSIS 3.1 application.
The Signal Content Detailed result display shows the serialized information from the
list of NCPs and codewords (downstream) or minislot sets (upstream) contained in the
input signal.
In the first rows, the information is provided for the following objects in the specified
order:
Downstream:
●
Scattered Pilots
●
Continuous Pilots
●
PLC preamble
●
PLC data
●
Excluded subcarriers
Upstream:
●
Pilots
●
Excluded subcarriers
Then, the information for each symbol in the order of the logical subcarriers is provided, with one row each for:
Downstream:
●
NCPs
●
Codewords
Upstream:
●
Minislot sets
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The Signal Content Summary (downstream only) result display shows the summarized
information for the NCPs and codewords contained in the downstream input signal.
Table 3-3: DOCSIS 3.1 Signal Content Parameters
Column Description
CW Index Codeword index (0..1535)
Symbol Start OFDM symbol (0..127)
Measurements and result display
DOCSIS 3.1 I/Q measurement
Not available for PLC, pilots and excluded subcarriers
Not available for PLC, pilots and excluded subcarriers
Object
Modulation Modulation (see "Modulation" on page 70)
MER (dB) Modulation error ratio in dB
Power Power (unit depends on Power Unit setting.)
Upstream only:
# Minislots Number of minislots
Downstream only:
# [count] (Signal Content Summary only)
Information type:
●
Invalid data (-1)
●
Pilots (0)
●
PLC Preamble (1)
●
PLC Data (2)
●
Excluded subcarrier (3)
●
NCP CW (4)
●
NCP CRC-24 (5)
●
NCP Null (6)
●
Codeword / Minislot set (7)
●
NCP All (8)
●
Profile (9)
●
Compl. Pilots (10)
●
Scattered pilots (11) - downstream only
●
Continuous pilots (12) - downstream only
(The value in parentheses is returned for FETCh:SCDetailed:ALL? on page 321)
For the PLC preamble and PLC data: the number of detected objects of this type
(since one of these types is always in each frame, the count equals the number of analyzed frames)
For the NCPs: the number of NCPs evaluated for the results
For the profiles: the number of codewords of that profile
#sc Number of subcarriers
LDPC
Iterations
LDPC
BitErr.Pre
BER Pre
Low density parity check
Number of iterations
Note that PLC and NCP decoding may need up to 2 iterations even if no bit errors
occurred since parts of the codewords are not transmitted (puncturing).
Low density parity check
Absolute number of bit errors before decoding
Bit error ratio before decoding (the ratio of errored bits to the total number of transmit-
ted bits)
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Column Description
Measurements and result display
DOCSIS 3.1 I/Q measurement
LDPC
BitErr.Post
BER Post
LDPC
CWErr.Post
BLER Post
Low density parity check
Absolute number of bit errors after decoding
Bit error rate after decoding (the ratio of falsely decoded bits to the total number of
transmitted bits)
Low density parity check
Absolute number of codeword errors after decoding
Block error rate after decoding (the ratio of falsely decoded codewords to the total
number of transmitted codewords)
3.1.3 PLC information
The Physical Link Channel (PLC) contains general transmission information. The information in the PLC can be used by the R&S FSW DOCSIS 3.1 application to determine
several of the signal description parameters automatically.
The PLC Messages (downstream only) result display shows the serialized information
from the individual OFDM symbols contained in the input signal.
The PLC information can only be provided for downstream DOCSIS 3.1 signals.
Table 3-4: PLC information
Item Description Query Command
Timestamp Time the PLC was created; used as a refer-
ence point
OFDM channel (OCD) information
Downstream Channel ID
Configuration Change Count
Discrete Fourier Transform
Size
Cyclic Prefix Length of the configurable cyclic prefix
Roll Off Roll-off period for the Tukey raised-cosine
Length of the FFT defining the OFDM transmission; corresponds to the number of physical subcarriers
See "N
See "Cyclic Prefix CP" on page 58
window which is applied at the beginning
(and end) of an OFDM symbol. The roll-off
period defines the steepness of the filter.
See "Roll-off" on page 59
(FFT length)" on page 58
FFT
FETCh:PLCMessages:
TIMestamp?FETCh:
FETCh:PLCMessages:
OCD:DCID?
on page 293FETCh:
FETCh:PLCMessages:
OCD:CCCount?
on page 292
FETCh:PLCMessages:
OCD:DFTSize?
on page 293
FETCh:PLCMessages:
OCD:CP? on page 292
FETCh:PLCMessages:
OCD:ROFF? on page 294
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Item Description Query Command
Measurements and result display
DOCSIS 3.1 I/Q measurement
Spectrum Location Center frequency in Hz of the subcarrier 0 of
the OFDM channel (f
beginning of the OFDM spectrum
See "OFDM Spectrum Location"
on page 58
PLC Start Index Starting subcarrier index of the physical link
channel (PLC)
See "PLC Start Index L" on page 60
Time Interleaving Depth Maximum number of delay lines used for
time interleaving
See "Time-Interleaving Depth" on page 59
Excluded Subcarriers Subcarriers not used to transmit data in a
DOCSIS 3.1 channel
See "Continuous pilots and excluded sub-
carrier assignment" on page 61
Continuous Pilots Subcarriers used to synchronize time and
phase information between symbols
See "Continuous pilots and excluded sub-
carrier assignment" on page 61
Codeword (NCP) information
Downstream Channel ID
), which defines the
sc0
FETCh:PLCMessages:
OCD:SLOCation?
on page 295
FETCh:PLCMessages:
OCD:PLC:INDex?
on page 294
FETCh:PLCMessages:
OCD:TIDepth?
on page 295
FETCh:PLCMessages:
OCD:ESUBcarriers?
on page 294
FETCh:PLCMessages:
OCD:CPILots?
on page 293
FETCh:PLCMessages:
NCP:DCID? on page 291
Configuration Change Count
Modulation Modulation used by the Next Codeword
Assignment Subcarrier assigned to the codeword
Profile information
Downstream Channel ID
Configuration Change Count
Modulation and assignment Assignment of the modulation used by each
Pointer (NCP)
See "NCP Modulation" on page 60
See "Codeword / frame configuration"
on page 64
subcarrier
See "Profile settings: modulation subcarrier
assignment" on page 69
FETCh:PLCMessages:
NCP:CCCount?
on page 291
FETCh:PLCMessages:
NCP:MODulation?
on page 292
FETCh:PLCMessages:
NCP:ASSignment?
on page 291
FETCh:PLCMessages:
PROFile<i>:DCID?
on page 296
FETCh:PLCMessages:
PROFile<i>:CCCount?
on page 296
FETCh:PLCMessages:
PROFile<i>:
ASSignment? on page 296
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Measurements and result display
DOCSIS
3.1 I/Q measurement
3.1.4 Evaluation methods for DOCSIS 3.1 I/Q measurements
Access: "Overview" > "Display Config"
Or: [MEAS] > "Display Config"
The captured I/Q data from the DOCSIS 3.1 signal can be evaluated using various different methods without having to start a new measurement or sweep. Which results
are displayed depends on the selected evaluation.
The following evaluation methods can be selected for the default DOCSIS 3.1 I/Q measurement.
Bitstream (downstream only)........................................................................................ 19
Constellation................................................................................................................. 20
Group Delay..................................................................................................................22
Magnitude Capture........................................................................................................22
Marker Table................................................................................................................. 23
MER vs Carrier..............................................................................................................23
MER vs Minislot (upstream only).................................................................................. 24
MER vs Symbol.............................................................................................................25
MER vs Symbol X Carrier............................................................................................. 25
Phase vs Carrier........................................................................................................... 26
PLC Messages (downstream only)............................................................................... 26
Power vs Carrier (upstream only)................................................................................. 27
Power vs Symbol X Carrier...........................................................................................28
Power Spectrum............................................................................................................28
Result Summary............................................................................................................29
Signal Content Detailed................................................................................................ 30
Signal Content Summary (downstream only)................................................................31
Spectrum Flatness........................................................................................................ 31
Synchronous Band Power (upstream only)...................................................................32
Bitstream (downstream only)
This result display shows the decoded data stream for each detected OFDM symbol in
the currently Selected Frame as indicated in the "Magnitude Capture" display. Which
bits exactly are decoded is configurable, for example the decoded payload data
(default), the raw bits or the input or output bits of the parity check. By default, the byte
values are displayed. Alternatively, the individual bit values can be displayed.
The bitstream can only be provided for downstream DOCSIS 3.1 signals.
The bitstream can be displayed in a compact or an expanded format. In the compact
format, only the first (max.) 25 bytes are displayed for each codeword, so that one row
per codeword is displayed in the table.
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Measurements and result display
DOCSIS
Figure 3-1: Bitstream result display for DOCSIS 3.1 standard (compact display)
3.1 I/Q measurement
In expanded format, all bytes for each codeword are displayed, where each row displays a maximum of 20 bytes. Thus, a single codeword can require multiple rows. In
this case, the object for subsequent rows is indicated as "Codeword <X> Cont". A byte
index indicates which bytes are displayed in each row.
Figure 3-2: Bitstream result display for DOCSIS 3.1 standard (expanded display)
Which information is displayed is configurable (see "Selected Frame" on page 117). If
enabled, the Bitstream table includes the following information:
●
Object
●
Modulation
●
Total number of bits in object
●
Byte index (graphical display only, not in remote command output)
●
Bit/byte values in hexadecimal format for max. 100 bytes
For details on individual parameters, see Chapter 3.1.2, "Signal content information",
on page 15.
Remote command:
LAY:ADD? '1',RIGH, BITS, see LAYout:ADD[:WINDow]? on page 249
UNIT:BITStream on page 275
Querying results:
FETCh:BITStream:ALL? on page 283
[SENSe:]FRAMe:SELect on page 244
Constellation
This result display shows the in-phase and quadrature phase results for the currently
Selected Frame as indicated in the "Magnitude Capture" display. The Tracking/Chan-
nel Estimation according to the user settings is applied.
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Measurements and result display
DOCSIS
3.1 I/Q measurement
The inphase results (I) are displayed on the x-axis, the quadrature phase (Q) results on
the y-axis.
The results can be restricted to the following:
●
One or all information types
●
One or more modulation types
●
One or all symbols
●
One or all subcarriers
Multiple (or all) modulations can be selected simultaneously. By default, all objects and
all modulations are displayed (in yellow).
If a single modulation type is selected, the ideal constellation is also indicated in the
display.
If multiple modulation types are selected, the constellation can be displayed in multiple
colors, one for each modulation type, using the following color map:
All
512-QAM
Figure 3-3: Color map for constellation points for different modulations
BPSK QPSK 16-QAM 64-QAM 128-QAM 256-QAM
1024-
QAM
2048-
QAM
4096-
QAM
8192-
QAM
16384-
QAM
Ideal
Example:
If the object is restricted to "Profile A" and all modulation types are selected, all modulation types found for profile A are displayed in multiple colors.
If the object is restricted to "Profile A" and the modulation is restricted to QPSK, any
constellation points with QPSK modulation found for profile A are displayed in green.
Additionally, the ideal QPSK constellation is displayed in gray in the same diagram.
To activate this color mapping, see "Fast Mode (Single Color)" on page 122.
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Measurements and result display
DOCSIS
Remote command:
LAY:ADD? '1',RIGH,CONS, see LAYout:ADD[:WINDow]? on page 249
[SENSe:]MODulation:SELect on page 259
[SENSe:]OBJect:SELect on page 259
[SENSe:]SUBCarrier:SELect on page 260
[SENSe:]SYMBol:SELect on page 261
[SENSe:]FRAMe:SELect on page 244
Results:
TRACe<n>[:DATA]? on page 303
Group Delay
Displays the time deviations of the signal versus carrier for the currently Selected
Frame as indicated in the "Magnitude Capture" display.
3.1 I/Q measurement
The carrier values can be provided as carrier numbers or carrier frequencies, see
Selected Frame.
Remote command:
LAY:ADD? '1',RIGH,GDEL, see LAYout:ADD[:WINDow]? on page 249
Results:
[SENSe:]FRAMe:SELect on page 244
TRACe<n>[:DATA]? on page 303
Magnitude Capture
The "Magnitude Capture" display shows the magnitude vs time data captured in the
last measurement. Green bars at the bottom of the "Magnitude Capture" display indicate the individual detected frames with their frame number. The blue bar indicates the
currently Selected Frame which is evaluated for graphical result displays.
A vertical blue line indicates the frame start (upstream) or the position of the PLC timestamp reference point (downstream, see Table 3-1).
(The position of the PLC timestamp reference point moves frequently if no trigger is
used; only with an (external) trigger at frame start it remains steady.)
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Measurements and result display
DOCSIS
Remote command:
LAY:ADD? '1',RIGH,RFM, see LAYout:ADD[:WINDow]? on page 249
Results:
TRACe<n>[:DATA]? on page 303
Marker Table
Displays a table with the current marker values for the active markers.
This table is displayed automatically if configured accordingly.
For 3-dimensional result displays (MER vs Symbol X Carrier, Power vs Symbol X Car-
rier), the value of a marker consists of the carrier (x), the symbol (y) and the parameter
value (z).
3.1 I/Q measurement
Tip: To navigate within long marker tables, simply scroll through the entries with your
finger on the touchscreen.
Remote command:
LAY:ADD? '1',RIGH, MTAB, see LAYout:ADD[:WINDow]? on page 249
Results:
CALCulate<n>:MARKer<m>:X on page 301
CALCulate<n>:MARKer<m>:Y? on page 313
MER vs Carrier
Displays the modulation error ratio per carrier for the currently Selected Frame as indicated in the "Magnitude Capture" display, or the statistical evaluation, if enabled (see
"Frame Statistic Count / Number of Frames to Analyze" on page 117).
The Minhold, Average and Maxhold traces are displayed. Define the number of frames
on which the statistical evaluation is based using "Evaluation Range" > Frame Statistic
Count / Number of Frames to Analyze.
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Measurements and result display
DOCSIS
The carrier values can be provided as carrier numbers or carrier frequencies, see "Car-
rier Axes Unit" on page 123.
Remote command:
LAY:ADD? '1',RIGH,MERC, see LAYout:ADD[:WINDow]? on page 249
Results:
[SENSe:]FRAMe:SELect on page 244
TRAC:DATA? <TRACEx>, see TRACe<n>[:DATA]? on page 303
3.1 I/Q measurement
MER vs Minislot (upstream only)
Displays the modulation error ratio per minislot for the currently Selected Frame as
indicated in the "Magnitude Capture" display. Values are only displayed for minislots
that are configured for the upstream signal (see "Profile configuration (upstream)"
on page 79).
Remote command:
LAY:ADD? '1',RIGH,MERM, see LAYout:ADD[:WINDow]? on page 249
Results:
[SENSe:]FRAMe:SELect on page 244
TRACe<n>[:DATA]? on page 303
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Measurements and result display
DOCSIS
MER vs Symbol
Displays the modulation error ratio per symbol for the currently Selected Frame as indicated in the "Magnitude Capture" display.
3.1 I/Q measurement
Remote command:
LAY:ADD? '1',RIGH,MERS, see LAYout:ADD[:WINDow]? on page 249
Results:
TRACe<n>[:DATA]? on page 303
[SENSe:]FRAMe:SELect on page 244
MER vs Symbol X Carrier
Displays the modulation error ratio per carrier and symbol for the currently Selected
Frame as indicated in the "Magnitude Capture" display. The symbols are displayed on
the x-axis, the carriers are displayed on the y-axis. The MER is color-coded according
to its level and is indicated as a colored dot for each symbol and carrier. The legend for
the color coding is provided by a color bar at the top of the diagram.
Note:
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Measurements and result display
DOCSIS
In 3-dimensional result displays the marker position is defined by its value on the x-axis
(carrier) and y-axis (symbol). The parameter value (MER) is queried as the third
dimension (z).
In this result display, only a single (normal) marker is available.
Remote command:
LAY:ADD? '1',RIGH,MSC, see LAYout:ADD[:WINDow]? on page 249
Results:
[SENSe:]FRAMe:SELect on page 244
TRACe<n>[:DATA]? on page 303
Phase vs Carrier
Displays the phase per carrier for the currently Selected Frame as indicated in the
"Magnitude Capture" display.
3.1 I/Q measurement
The carrier values can be provided as carrier numbers or carrier frequencies, see
Selected Frame.
Remote command:
LAY:ADD? '1',RIGH,PHAC, see LAYout:ADD[:WINDow]? on page 249
Results:
[SENSe:]FRAMe:SELect on page 244
TRACe<n>[:DATA]? on page 303
PLC Messages (downstream only)
The Physical Link Channel (PLC) contains general transmission information. The information in the PLC can be used by the R&S FSW DOCSIS 3.1 application to determine
several of the signal description parameters automatically. The "PLC Messages" table
displays the PLC information provided by the measured signal.
The PLC information can only be provided for downstream DOCSIS 3.1 signals.
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For details on the individual types of information, see Chapter 3.1.3, "PLC information",
on page 17.
Remote command:
LAY:ADD? '1',RIGH,PLCM, see LAYout:ADD[:WINDow]? on page 249
Querying results:
See Chapter 10.9.1.3, "Querying PLC information", on page 290
Measurements and result display
DOCSIS 3.1 I/Q measurement
Power vs Carrier (upstream only)
Displays the power level per carrier for the currently Selected Frame as indicated in the
"Magnitude Capture" display. The carriers are displayed on the x-axis, the power is displayed on the y-axis.
The power unit depends on the Unit setting.
The carrier unit depends on the Carrier Axes Unit setting.
Bands configured for a Synchronous Band Power measurement are indicated by blue
lines in the Power vs. Carrier result display, and are labeled according to the configuration.
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Measurements and result display
DOCSIS
Remote command:
LAY:ADD? '1',RIGH,PCAR, see LAYout:ADD[:WINDow]? on page 249
Results:
[SENSe:]FRAMe:SELect on page 244
TRACe<n>[:DATA]? on page 303
Power vs Symbol X Carrier
Displays the power level per carrier and symbol for the currently Selected Frame as
indicated in the "Magnitude Capture" display. The symbols are displayed on the x-axis,
the carriers are displayed on the y-axis. The power level is color-coded and is indicated
as a colored dot for each symbol and carrier. The legend for the color coding is provided by a color bar at the top of the diagram.
The power unit depends on the Unit setting.
3.1 I/Q measurement
Note:
In 3-dimensional result displays the marker position is defined by its value on the x-axis
(carrier) and y-axis (symbol). The parameter value (Power) is queried as the third
dimension (z).
In this result display, only a single (normal) marker is available.
Remote command:
LAY:ADD? '1',RIGH,PSC, see LAYout:ADD[:WINDow]? on page 249
Results:
[SENSe:]FRAMe:SELect on page 244
TRACe<n>[:DATA]? on page 303
Power Spectrum
This result display shows the power density (power/Hz) vs frequency values obtained
using an FFT. The evaluation is performed over the complete data in the current capture buffer, without any correction or compensation.
The power unit depends on the Unit setting.
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Remote command:
LAY:ADD? '1',RIGH,PSP, see LAYout:ADD[:WINDow]? on page 249
Results:
[SENSe:]FRAMe:SELect on page 244
TRACe<n>[:DATA]? on page 303
Measurements and result display
DOCSIS 3.1 I/Q measurement
Result Summary
The result summary provides the numerical results for the main DOCSIS 3.1 parameters summarized over a specified number of frames or for a single frame. This is the
currently Selected Frame as indicated in the "Magnitude Capture" display.
If more than one frame is evaluated (that is, Analyzing a single frame (Specified
Frame) is not enabled), a statistical evaluation of the specified "Frame Statistic Count /
Number of Frames to Analyze" on page 117 or for all detected frames in the capture
buffer is also performed. In this case, the minimum, maximum and mean values are
displayed, as well as the defined limit, if available.
For details on the evaluation basis, see "Basis of (Statistical) Evaluation" on page 44.
For details on individual parameters, see Chapter 3.1.1, "Modulation accuracy parame-
ters", on page 13.
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Measurements and result display
DOCSIS
Remote command:
LAY:ADD? '1',RIGH,RSUM, see LAYout:ADD[:WINDow]? on page 249
Results:
FETCh:SUMMary:ALL? on page 288
FETCh:FRAMe:COUNt? on page 281
FETCh:FRAMe:COUNt:ALL? on page 282
3.1 I/Q measurement
Signal Content Detailed
This result display shows the serialized information from the list of NCPs and codewords (downstream) or minislot sets (upstream) for the currently Selected Frame as
indicated in the "Magnitude Capture" display.
For details on individual entries, see Chapter 3.1.2, "Signal content information",
on page 15.
Note: If the low density parity check (LDPC) results indicate no errors (= 0), the value
is displayed green, otherwise the value is red. This allows you to detect errors at a
glance.
Remote command:
LAY:ADD? '1',RIGH,SCD, see LAYout:ADD[:WINDow]? on page 249
Results:
FETCh:SCDetailed:ALL:FORMatted? on page 286
[SENSe:]FRAMe:SELect on page 244
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Measurements and result display
DOCSIS
Signal Content Summary (downstream only)
This result display shows the summarized information for the NCPs and codewords in
a specified number of frames or for a single frame. This is the currently Selected
Frame as indicated in the "Magnitude Capture" display.
Note: This result display is not available for upstream measurements!
If more than one frame is evaluated (that is, Analyzing a single frame (Specified
Frame) is not enabled), a statistical evaluation of the specified Frame Statistic Count /
Number of Frames to Analyze or for all detected frames in the capture buffer is also
performed. In this case, the minimum, maximum and mean values are displayed, as
well as the defined limit, if available.
For details on the evaluation basis, see "Basis of (Statistical) Evaluation" on page 44.
For details on individual entries, see Chapter 3.1.2, "Signal content information",
on page 15.
3.1 I/Q measurement
Remote command:
LAY:ADD? '1',RIGH,SCS, see LAYout:ADD[:WINDow]? on page 249
Results:
FETCh:SCSummary:ALL? on page 287
FETCh:FRAMe:COUNt? on page 281
FETCh:FRAMe:COUNt:ALL? on page 282
Spectrum Flatness
This result display shows the relative power offset per carrier caused by the transmit
channel for the currently Selected Frame as indicated in the "Magnitude Capture" display.
The carrier values can be provided as carrier numbers or carrier frequencies, see "Car-
rier Axes Unit" on page 123.
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Remote command:
LAY:ADD? '1',RIGH,SFL, see LAYout:ADD[:WINDow]? on page 249
Results:
[SENSe:]FRAMe:SELect on page 244
TRACe<n>[:DATA]? on page 303
Synchronous Band Power (upstream only)
For upstream transmission, the DOCSIS 3.1 standard requires a power measurement
in specified bands adjacent to the signal channels. The R&S FSW DOCSIS 3.1 application provides such power results in the "Synchronous Band Power" table, together
with the Power vs. Carrier result display. The power for configured bands is calculated
synchronously with the modulation accuracy results in the default I/Q measurement,
rather than in a separate sweep measurement.
The R&S FSW DOCSIS 3.1 application can determine the bands for the power measurement automatically as required by the standard, or it can apply a user-defined configuration (see Chapter 5.3.11.4, "Synchronous band power settings", on page 130).
The bands for which the power is calculated are indicated by blue lines in the Power
vs. Carrier result display, and are labeled according to the configuration.
Note: Synchronous Band Power measurements require a sample rate of 204.8 MHz
(see "Sample Rate" on page 107). Data from adjacent channels must be filtered out
(see "Filter Out Adjacent Channels" on page 109).
Measurements and result display
DOCSIS 3.1 I/Q measurement
The Synchronous Band Power table provides the following results for each configured
band:
"Band"
Label (as indicated in the Power vs Carrier display) of the power band
and type (adjacent/alternate and upper/lower)
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Measurements and result display
Frequency sweep measurements
"Location Ref"
"Location"
"Bandwidth
[SC]"
"Bandwidth
[Hz]"
"Result"
Remote command:
LAY:ADD? '1',RIGH,SBP, see LAYout:ADD[:WINDow]? on page 249
Results:
CALCulate<n>:US:CHANnel:SBPower:BAND<n>:RESult? on page 300
Defines whether the indicated "Location" is located on the left or on
the right edge of the band.
The subcarrier that marks the specified edge of the measured power
band
The number of subcarriers in the measured power band
The frequency range of the measured power band
The measured power in the band, referenced to the total power in all
analyzed minislots ("Power of Analyzed Minislots" in the "Result Summary")
3.2 Frequency sweep measurements
Access: "Overview" > "Select Measurement"
Or: [MEAS] > "Select Meas"
Standard measurements that are common to several digital standards and are often
required in signal and spectrum test scenarios are provided by the R&S FSW base unit
(Spectrum application). These measurements capture only the power level (magnitude,
which we refer to as RF data) of the signal, as opposed to the two components provided by I/Q data.
Frequency sweep measurements can tune on a constant frequency ("Zero span measurement") or sweep a frequency range ("Frequency sweep measurement")
The signal cannot be demodulated based on the captured RF data. However, the
required power information can be determined much more precisely, as more noise is
filtered out of the signal.
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The frequency sweep measurements provided by the R&S FSW DOCSIS 3.1 application are identical to the corresponding measurements in the base unit, but are pre-configured according to the requirements of the selected DOCSIS 3.1 standard.
For details on these measurements, see the R&S FSW User Manual.
The R&S FSW DOCSIS 3.1 application provides the following frequency sweep measurements:
3.2.1 Measurement types and results for frequency sweep measurements
The R&S FSW DOCSIS 3.1 application provides the following pre-configured frequency sweep measurements:
Occupied Bandwidth..................................................................................................... 34
CCDF............................................................................................................................ 35
Occupied Bandwidth
The "Occupied Bandwidth" (OBW) measurement determines the bandwidth in which a
certain percentage of the total signal power is measured. The percentage of the signal
power to be included in the bandwidth measurement can be changed; by default settings it is 99 %.
Measurements and result display
Frequency sweep measurements
The occupied bandwidth is indicated as the "Occ BW" function result in the marker
table; the frequency markers used to determine it are also displayed.
For details, see Chapter 5.4.1, "Occupied bandwidth", on page 137.
Remote command:
CALC:MARK:FUNC:POW:SEL OBW, see CALCulate<n>:MARKer<m>:FUNCtion:
POWer:SELect on page 165
Querying results:
CALC:MARK:FUNC:POW:RES? OBW, see CALCulate<n>:MARKer<m>:FUNCtion:
POWer:RESult? on page 300
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CCDF
The "CCDF" (complementary cumulative distribution function) measurement determines the distribution of the signal amplitudes. The measurement captures a userdefinable number of samples and calculates their mean power. As a result, the probability that a sample's power is higher than the calculated mean power + x dB is displayed. The crest factor is displayed in the "Result Summary".
For details see Chapter 5.4.2, "CCDF", on page 137.
Measurements and result display
Frequency sweep measurements
Figure 3-4: CCDF measurement results
Remote command:
CALCulate<n>:STATistics:CCDF[:STATe] on page 166
Querying results:
CALCulate<n>:MARKer<m>:Y? on page 313
CALCulate<n>:STATistics:RESult<res>? on page 301
3.2.2 Evaluation methods for frequency sweep measurements
The evaluation methods for frequency sweep measurements in the R&S FSW
DOCSIS 3.1 application are identical to those in the R&S FSW base unit (Spectrum
application).
Diagram.........................................................................................................................35
Result Summary............................................................................................................36
Marker Table................................................................................................................. 36
Marker Peak List........................................................................................................... 36
Diagram
Displays a basic level vs. frequency or level vs. time diagram of the measured data to
evaluate the results graphically. This is the default evaluation method. Which data is
displayed in the diagram depends on the "Trace" settings. Scaling for the y-axis can be
configured.
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Remote command:
LAY:ADD? '1',RIGH, DIAG, see LAYout:ADD[:WINDow]? on page 249
Results:
Result Summary
Result summaries provide the results of specific measurement functions in a table for
numerical evaluation. The contents of the result summary vary depending on the
selected measurement function. See the description of the individual measurement
functions for details.
Tip: To navigate within long result summary tables, simply scroll through the entries
with your finger on the touchscreen.
Remote command:
LAY:ADD? '1',RIGH, RSUM, see LAYout:ADD[:WINDow]? on page 249
Measurements and result display
Frequency sweep measurements
Marker Table
Displays a table with the current marker values for the active markers.
This table is displayed automatically if configured accordingly.
For 3-dimensional result displays (MER vs Symbol X Carrier, Power vs Symbol X Car-
rier), the value of a marker consists of the carrier (x), the symbol (y) and the parameter
value (z).
Tip: To navigate within long marker tables, simply scroll through the entries with your
finger on the touchscreen.
Remote command:
LAY:ADD? '1',RIGH, MTAB, see LAYout:ADD[:WINDow]? on page 249
Results:
CALCulate<n>:MARKer<m>:X on page 301
CALCulate<n>:MARKer<m>:Y? on page 313
Marker Peak List
The marker peak list determines the frequencies and levels of peaks in the spectrum or
time domain. How many peaks are displayed can be defined, as well as the sort order.
In addition, the detected peaks can be indicated in the diagram. The peak list can also
be exported to a file for analysis in an external application.
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Tip: To navigate within long marker peak lists, simply scroll through the entries with
your finger on the touchscreen.
Remote command:
LAY:ADD? '1',RIGH, PEAK, see LAYout:ADD[:WINDow]? on page 249
Results:
CALCulate<n>:MARKer<m>:X on page 301
CALCulate<n>:MARKer<m>:Y? on page 313
Measurements and result display
Frequency sweep measurements
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Measurement basics
4 Measurement basics
Some background knowledge on basic terms and principles used in DOCSIS 3.1 measurements is provided here for a better understanding of the required configuration settings.
● DOCSIS 3.1 characteristics.................................................................................... 38
● DOCSIS 3.1 downstream signal processing...........................................................38
● DOCSIS 3.1 upstream signal processing................................................................44
● Basics on input from I/Q data files.......................................................................... 49
4.1 DOCSIS 3.1 characteristics
A cable network based on the Data-Over-Cable Service Interface Specifications
(DOCSIS® 3.1, see References) allows for very high data rates due to its large number
of carriers and very high modulation rates.
For downstream transmission based on DOCSIS 3.1, OFDM channels with a bandwidth of up to 192 MHz are used in a spectrum from 258 MHz to 1.2 GHz. Each OFDM
channel in turn consists of 7600 (active) subcarriers with a spacing of 25 kHz, or 3800
(active) subcarriers with a spacing of 50 kHz. Data is transmitted with a fixed sample
rate of 204.8 MHz.
DOCSIS
3.1 downstream signal processing
For upstream transmission based on DOCSIS 3.1, OFDM channels with a bandwidth
of up to 96 MHz are used in a spectrum from 5 MHz to 204 MHz. Each OFDM channel
in turn consists of 3800 (active) subcarriers with a spacing of 25 kHz, or 1900 (active)
subcarriers with a spacing of 50 kHz. Data is transmitted with a fixed sample rate of
102.4 MHz.
OFDM channels can be configured independently, taking different channel conditions
into account. Each subcarrier can use a different modulation, allowing for higher data
rates where transmission conditions are good, and reliable data reception where they
are poor. Time and frequency interleaving methods, as well as forward error correction
(FEC) and cyclic redundancy correction bits ensure low error rates and high modulation accuracy.
Using DOCSIS 3.1, the same data is sent to multiple cable modems in data blocks
containing information on which contents need to be decoded by the individual
modems.
4.2 DOCSIS 3.1 downstream signal processing
Downstream DOCSIS 3.1 signals are used to transmit data from the cable modem termination system (CMTS) to numerous individual cable modems in widely spread locations. The R&S FSW DOCSIS 3.1 applications analyze both types of signals based on
DOCSIS 3.1.
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Measurement basics
Encoded
input signal
The following graphic illustrates the basic signal processing performed by the application for downstream signals. The individual steps are then described in more detail.
OFDM Channel Description Profile Configuration
Remove cyclic
prefix and roll-off
period
Restore codewords
according to Next
Codeword Pointers
(NCPs) for each symbol
Frame/Codeword Configuration
Perform FFT for
each OFDM
symbol
logical subcarriers
DOCSIS
Continuous Pitots,
Excluded Subcarrier Assignment
Determine excluded
subcarriers, detect
continuous pilots
(reverse time and
freq. interleaving)
Analyze signal
characteristics
Decode (and
correct) data in
codewords
3.1 downstream signal processing
and PLC
Bit error
information
Demodulate data
in each physical
sc according to
assigned profile
Constellation
Result
summary
Detailed
signal content
MER
Bitstream
...
Figure 4-1: Signal processing in the R&S FSW DOCSIS 3.1 application
OFDM channel input
The encoded data input from an OFDM channel is a time domain discrete, complexvalued signal, which is sampled at a rate of 204.8 MSamples by the R&S FSW
DOCSIS 3.1 application. It is then analyzed according to the configured signal description.
In the first step, the cyclic prefix and roll-off period are removed. While the cyclic prefix
prevents intersymbol interference, the roll-off period determines how steep the spectrum rises and falls at its edges.
FFT
The initial data captured by the R&S FSW DOCSIS 3.1 application consists of measured values over time. In order to analyze the data for each OFDM symbol in the frequency domain, that is, the data in each subcarrier, an FFT must be performed on the
captured data. Depending on the specified FFT length, which corresponds to the number of subcarriers, an FFT is performed on either 4096 samples (4K mode), or 8192
samples (8K mode) of the channel input, for each symbol.
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Measurement basics
DOCSIS
3.1 downstream signal processing
Subcarriers and profiles
For each of the subcarriers, a different modulation may be used for transmission,
depending on channel conditions.
The assignment is configured in profiles. For each set of modems with similar transmission conditions, a profile can then be assigned.
Figure 4-2: Profile: assignment of modulation to physical subcarriers
In order to demodulate the data in the subcarriers, the R&S FSW DOCSIS 3.1 application must determine the assignment of the modulation used by each subcarrier. This is
configured in the signal description. Up to 16 different profiles can be configured and
then assigned to each set of subcarriers sent to the same set of modems (see "Code-
words, logical subcarriers, frames, and NCPs" on page 41).
Continuous pilots, excluded subcarriers, PLC
Some subcarriers have a specific function and are used identically for all symbols.
Such fixed objects in the channel must be configured so that the R&S FSW
DOCSIS 3.1 application can distinguish their contents from the useful data. Subcarriers
with a special function are configured in the signal description in a continuous pilots
and excluded subcarrier assignment table.
Continuous pilots are located at the same position in each OFDM channel and are
used to synchronize time and phase information between symbols.
Excluded subcarriers are not used to transmit data in a DOCSIS 3.1 channel. This may
be due to poor transmission conditions, use by other transmission channels, or for
other reasons. Such carriers are blocked for all symbols of the channel.
The Physical Link Channel (PLC) is located at the same position in each OFDM symbol and consists of several consecutive subcarriers. It contains general transmission
information, such as the FFT size, number of subcarriers, and spacing size used for
transmission, as well as a preamble, which contains a defined pattern and is required
to synchronize the symbols. The preamble of the PLC is BPSK-modulated, while the
PLC data is always transmitted using 16-QAM modulation.
The information in the PLC can be used by the R&S FSW DOCSIS 3.1 application to
determine several of the signal description parameters described above automatically.
The position of the PLC itself can also be detected by the R&S FSW DOCSIS 3.1
application automatically.
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Codewords, logical subcarriers, frames, and NCPs
The useful data that is to be transmitted to the same group of cable modems is summarized into blocks. The blocks are extended by additional bits for forward error correction, which allow transmission errors to be detected and corrected by the receiver.
Such an encoded data block, which may vary in size, is referred to as a codeword.
The subcarriers for a single symbol in an OFDM channel that are available for useful
data, that is to transmit the codewords, are called logical subcarriers. Logical subcarriers are combined in a frame.
The codewords are assigned to the next available symbol in the order they are sent. If
more subcarriers are required than are still empty, subcarriers in the next symbol are
assigned to the block as well. Up to four consecutive symbols can be used by any one
codeword. Therefore it is necessary to document the assignment of codewords to symbols.
For each new codeword that starts in a symbol, the first subcarrier of the codeword is
provided as a Next Codeword Pointer (NCP). The NCPs are also included in the frame.
NCPs are modulated using QPSK, 16-QAM or 64-QAM. Which modulation is used for
the NCP is indicated by the PLC.
Measurement basics
DOCSIS 3.1 downstream signal processing
Finally, for error protection, each frame contains a Cyclic Redundancy Check (CRC)
block, based on all NCPs in the frame.
Figure 4-3: Frame/codeword configuration of the logical subcarriers
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Frame configuration in the R&S FSW DOCSIS 3.1 application
In a realistic DOCSIS 3.1 transmission scenario, the transmitted data changes constantly. Thus, the frame configuration also changes accordingly. However, for analysis
and test purposes, it is assumed that you use the same input signal to the R&S FSW
DOCSIS 3.1 application for a specific test scenario, and thus the frame configuration
need only be configured once for that signal.
The R&S FSW DOCSIS 3.1 application provides an auto-detection function to configure the frames automatically from the signal.
In the R&S FSW DOCSIS 3.1 application, you configure the assignment of codewords
to symbols in a table. The codewords are numbered consecutively from the first to the
last OFDM symbol, and from the first to last logical subcarrier (see Figure 4-3). For
each codeword, an entry in the table is required, which assigns the (first and) total
number of subcarriers per codeword, or alternatively the first and total number of
OFDM symbols. Furthermore, the profile (that is: modulation) to be used for the codeword is defined. Note that since one OFDM symbol may contain more than one codeword, and each codeword may use a different modulation, the same OFDM symbol
may have a "mixed modulation".
Measurement basics
DOCSIS 3.1 downstream signal processing
Physical vs. logical subcarriers
As described above, the physical subcarriers in a DOCSIS 3.1 channel may contain
general signal information (PLC, pilots), useful data, or unspecified data (excluded carriers).
In order to improve modulation accuracy, the data is not transmitted in consecutive
subcarriers, but scattered across all available subcarriers, by subjecting it to time and
frequency interleaving. The time and frequency interleaved data, together with the
NCPs and PLCs, are then distributed among all physical subcarriers, with exception of
the excluded subcarriers, and modulated according to the assigned profiles.
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Measurement basics
DOCSIS
3.1 downstream signal processing
Figure 4-4: Relation between frames, logical subcarriers, profiles, and physical subcarriers
During demodulation, the R&S FSW DOCSIS 3.1 application must restore the original
time and frequency order of the information, to form logical subcarriers with coherent
data.
Demodulation and Analysis
When demodulating the DOCSIS 3.1 signal, the R&S FSW DOCSIS 3.1 application
must restore the original correlation between the symbols in order to retrieve the blocks
in the logical subcarriers, and thus the useful information. The continuous pilots and
the PLC preamble help synchronize the time and phase information between symbols.
With the help of the frame/codeword configuration, the R&S FSW DOCSIS 3.1 application can demodulate the data in the logical subcarriers and restore the codewords. As
a result, various signal characteristics, modulation accuracy parameters and constellation data are available.
The detailed signal content can also be output in a table. The order of entries in this
table is similar to the frame configuration table: For each frame, the CRC and the codewords with the assigned NCP are listed in consecutive order of the codeword index.
For each object in the table, modulation accuracy parameters, the measured power
level and detected error bits are indicated.
Optionally, the codewords are not decoded to save calculation time; however, in this
case codeword error bits are not evaluated.
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Measurement basics
DOCSIS
Basis of (Statistical) Evaluation
Various modulation accuracy parameters as well as the symbol constellation can be
displayed graphically. Graphical results are always based on a single frame. The Bitstream and detailed signal content is also always provided for a single frame. Which
frame is to be evaluated is configurable (see Selected Frame). By default, it is always
the first detected frame in the capture buffer (frame 0).
The numeric results in the "Result Summary" and Signal Content Summary, on the
other hand, are summarized over all frames in the current capture buffer, by default.
Optionally, they can be summarized over a specific number of frames (see "Frame Sta-
tistic Count / Number of Frames to Analyze" on page 117). In this case, multiple mea-
surements are performed, if necessary, to obtain the required number of frames. Using
a defined number of frames to base statistics on makes the results more consistent, as
the number of frames detected in each measurement (and which are thus available in
the capture buffer) may vary. If evaluation is restricted to a single frame, no statistics
are calculated for the summarized results.
Note that frames from multiple measurements can be included in statistical evaluation;
however, only frames in the current capture buffer can be analyzed and displayed individually.
3.1 upstream signal processing
4.3 DOCSIS 3.1 upstream signal processing
Upstream DOCSIS 3.1 signals are used to transmit data from numerous individual
cable modems (CMs) to the cable modem termination system (CMTS). Signal processing in the R&S FSW DOCSIS 3.1 application is similar to processing downstream signals, as described in Chapter 4.2, "DOCSIS 3.1 downstream signal processing",
on page 38. The main differences for upstream signals are described here.
Minislots and transmission profiles
According to the DOCSIS 3.1 specification [2], minislots are defined as follows:
"The upstream spectrum is divided into groups of subcarriers called minislots. Minislots
have dedicated subcarriers, of which all data subcarriers have the same modulation
order ("bit loading"). A CM is allocated to transmit one or more minislots in a transmission burst. The modulation order of a minislot, as well as the pilot pattern to use, may
change between different transmission bursts and are determined by a transmission
profile. [...]This allows bit loading to vary across the spectrum."
Pilots, complementary pilots, data subcarriers
Each minislot consists of pilots, complementary pilots, and data subcarriers. Subcarriers that are not used for data or pilots are set to zero.
Pilots are subcarriers that do not carry data, but encode a pre-defined BPSK symbol
known to the receiver. Pilot patterns differ by the number of pilots in a minislot, and by
their arrangement within the minislot. The different pilot patterns enable the CMTS to
optimize its performance according to different transmission conditions.
The DOCSIS 3.1 specification [2] also specifies complementary pilots:
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"Complementary pilots are subcarriers that carry data, but with a lower modulation
order than other data subcarriers in the minislot. Complementary pilots allow phase
tracking along the time axis for frequency offset and phase noise correction, and may
be used by the CMTS upstream receiver to enhance signal processing, such as
improving the accuracy of center frequency offset tracking."
Minislot structure
All data subcarriers in a minislot have the same QAM constellation. All complementary
data subcarriers in a minislot also have the same QAM constellation, but lower in order
than that of the data subcarriers in that minislot. QAM constellations of data and complementary pilots need not be the same for all minislots.
Minislots are defined by a fixed number (K) of symbols and a number (Q) of subcarriers. The number (K) of symbols per minislot is defined as a minimum of 6 and a maximum of 9 to 36, depending on the used bandwidth and FFT duration. The number (Q)
of subcarriers per minislot is defined as 8 for 2K mode and 16 for 4K mode.
Between minislots, excluded subcarriers may exist.
In the R&S FSW DOCSIS 3.1 application, profiles for upstream signals contain the
assignment of the pilot pattern and modulation per minislot or for a number of minislots
(as opposed to the modulation-subcarrier assignment for downstream signals). Only a
single profile is configurable for upstream signals in the R&S FSW DOCSIS 3.1 application.
Measurement basics
DOCSIS 3.1 upstream signal processing
Pilot patterns
As described above, pilot patterns differ by the number of pilots in a minislot, and by
their arrangement within the minislot. Which patterns are available for a minislot
depends on the number of subcarriers and thus the FFT mode.
For 2K mode (=8 subcarriers per minislot), 8 different pilot patterns are available
(defined in the DOCSIS 3.1 specification [2]):
In each figure, the horizontal axis represents OFDMA symbols, and the vertical axis
represents the subcarriers. Each square in a figure represents a subcarrier at a specific symbol time. Pilots are designated by "P" and complementary pilots by "CP". All
other subcarriers carry data with the modulation order of the minislot.
The figures show patterns for K between 6 and 16. For K>16 the complementary pilots
are always located in the 14th and 16th symbols, all symbols from the 17th symbol to
the end of the frame carry data only. Pilot locations are the same for any K.
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Measurement basics
DOCSIS 3.1 upstream signal processing
For 4K mode (=16 subcarriers per minislot), 16 different pilot patterns are available
(defined in the DOCSIS 3.1 specification [2]):
The figures show patterns for K between 6 and 9. For K>9, the complementary pilots
are always located in the 7th and 9th symbols, all symbols from the 10th symbol to end
of frame carry data only. Pilot locations are the same for any K.
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Measurement basics
DOCSIS 3.1 upstream signal processing
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Measurement basics
DOCSIS
Frame structure
The DOCSIS 3.1 specification [2] defines frames as follows:
"Upstream transmission uses OFDMA frames. Each OFDMA frame consists of a con-
figurable number of OFDM symbols, K. Several transmitters may share the same
OFDMA frame by transmitting data and pilots on allocated subcarriers of the OFDMA
frame."
In upstream DOCSIS 3.1 signals, a frame comprises the minislots that use the same
frequency range within the OFDMA channel spectrum.
The following figure illustrates the frame structure for upstream transmission.
minislot m+k
k-minislot
3.1 upstream signal processing
burst
...
minislot m+1
minislot m
Subcarriers
...
m-minislot burst
minislot 2
Q
minislot 1
1
1
...K
OFDM Symbols
Figure 4-5: DOCSIS 3.1 OFDMA frame structure for upstream transmission
Mapping data and profiles to minislots
The order of data bits within a minislot is described in the DOCSIS 3.1 specification [2].
The useful data codewords are mapped into minislots, prior to time and frequency
interleaving, using only contiguous subcarriers. There are no subcarrier exclusions or
unused subcarriers within a minislot. "The data is filled across all symbol periods, sub-
carrier by subcarrier, transmitted symbol period by symbol period, with complementary
pilots filled inline." All data subcarriers within one minislot use the same modulation.
Different minislots may use different modulation types.
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4.4 Basics on input from I/Q data files
The I/Q data to be evaluated in a particular R&S FSW application cannot only be captured by the application itself, it can also be loaded from a file, provided it has the correct format. The file is then used as the input source for the application.
For example, you can capture I/Q data using the I/Q Analyzer application, store it to a
file, and then analyze the signal parameters for that data later using the Pulse application (if available).
The I/Q data file must be in one of the following supported formats:
.iq.tar
●
.iqw
●
.csv
●
.mat
●
.wv
●
.aid
●
Measurement basics
Basics on input from I/Q data files
An application note on converting Rohde & Schwarz I/Q data files is available from the
Rohde & Schwarz website:
1EF85: Converting R&S I/Q data files
When importing data from an I/Q data file using the import functions provided by some
R&S FSW applications, the data is only stored temporarily in the capture buffer. It overwrites the current measurement data and is in turn overwritten by a new measurement.
If you use an I/Q data file as input, the stored I/Q data remains available for any number of subsequent measurements. Furthermore, the (temporary) data import requires
the current measurement settings in the current application to match the settings that
were applied when the measurement results were stored (possibly in a different application). When the data is used as an input source, however, the data acquisition settings in the current application (attenuation, center frequency, measurement bandwidth, sample rate) can be ignored. As a result, these settings cannot be changed in
the current application. Only the measurement time can be decreased, to perform
measurements on an extract of the available data (from the beginning of the file) only.
For input files that contain multiple data streams from different channels, you can
define which data stream to be used for the currently selected channel in the input settings.
You can define whether the data stream is used only once, or repeatedly, to create a
larger amount of input data.
When using input from an I/Q data file, the [RUN SINGLE] function starts a single measurement (i.e. analysis) of the stored I/Q data, while the [RUN CONT] function repeatedly analyzes the same data from the file.
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Sample iq.tar files
If you have the optional R&S FSW VSA application (R&S FSW-K70), some sample
iq.tar files are provided in the C:/R_S/Instr/user/vsa/DemoSignals directory
on the R&S FSW.
Pre-trigger and post-trigger samples
In applications that use pre-triggers or post-triggers, if no pre-trigger or post-trigger
samples are specified in the I/Q data file, or too few trigger samples are provided to
satisfy the requirements of the application, the missing pre- or post-trigger values are
filled up with zeros. Superfluous samples in the file are dropped, if necessary. For pretrigger samples, values are filled up or omitted at the beginning of the capture buffer.
For post-trigger samples, values are filled up or omitted at the end of the capture buffer.
Measurement basics
Basics on input from I/Q data files
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5 Configuration
Access: [MODE] > "Docsis 3.1"
The default DOCSIS 3.1 I/Q measurement captures the I/Q data from the DOCSIS 3.1
signal and determines various characteristic signal parameters such as the modulation
accuracy, spectrum flatness, center frequency tolerance and symbol clock tolerance in
just one measurement (see Chapter 3, "Measurements and result display",
on page 13).
Other parameters specified in the DOCSIS 3.1 standard must be determined in separate measurements (see Chapter 5.4, "Frequency sweep measurements",
on page 136).
The settings required to configure each of these measurements are described here.
● Multiple measurement channels and sequencer function.......................................51
● Display configuration...............................................................................................52
● DOCSIS 3.1 I/Q measurement (modulation accuracy)........................................... 53
● Frequency sweep measurements.........................................................................136
Configuration
Multiple measurement channels and sequencer function
5.1 Multiple measurement channels and sequencer function
When you activate an application, a new measurement channel is created which determines the measurement settings for that application. These settings include the input
source, the type of data to be processed (I/Q or RF data), frequency and level settings,
measurement functions etc. If you want to perform the same measurement but with different center frequencies, for instance, or process the same input data with different
measurement functions, there are two ways to do so:
●
Change the settings in the measurement channel for each measurement scenario.
In this case the results of each measurement are updated each time you change
the settings and you cannot compare them or analyze them together without storing them on an external medium.
●
Activate a new measurement channel for the same application.
In the latter case, the two measurement scenarios with their different settings are
displayed simultaneously in separate tabs, and you can switch between the tabs to
compare the results.
For example, you can activate one DOCSIS 3.1 measurement channel to perform
a DOCSIS 3.1 modulation accuracy measurement, and a second channel to perform an OBW measurement using the same DOCSIS 3.1 input source. Then you
can monitor all results at the same time in the "MultiView" tab.
The number of channels that can be configured at the same time depends on the available memory on the instrument.
Only one measurement can be performed on the R&S FSW at any time. If one measurement is running and you start another, or switch to another channel, the first mea-
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surement is stopped. In order to perform the different measurements you configured in
multiple channels, you must switch from one tab to another.
However, you can enable a Sequencer function that automatically calls up each activated measurement channel in turn. This means the measurements configured in the
channels are performed one after the other in the order of the tabs. The currently
active measurement is indicated by a
the individual channels are updated in the corresponding tab (as well as the "MultiView") as the measurements are performed. Sequencer operation is independent of
the currently displayed tab; for example, you can analyze the OBW measurement while
the modulation accuracy measurement is being performed by the Sequencer.
For details on the Sequencer function see the R&S FSW User Manual.
The Sequencer functions are only available in the "MultiView" tab.
Sequencer State........................................................................................................... 52
Sequencer Mode...........................................................................................................52
Sequencer State
Activates or deactivates the Sequencer. If activated, sequential operation according to
the selected Sequencer mode is started immediately.
Remote command:
SYSTem:SEQuencer on page 280
INITiate:SEQuencer:IMMediate on page 279
INITiate:SEQuencer:ABORt on page 279
Configuration
Display configuration
symbol in the tab label. The result displays of
Sequencer Mode
Defines how often which measurements are performed. The currently selected mode
softkey is highlighted blue. During an active Sequencer process, the selected mode
softkey is highlighted orange.
"Single Sequence"
Each measurement is performed once, until all measurements in all
active channels have been performed.
"Continuous Sequence"
The measurements in each active channel are performed one after
the other, repeatedly, in the same order, until sequential operation is
stopped.
This is the default Sequencer mode.
Remote command:
INITiate:SEQuencer:MODE on page 279
5.2 Display configuration
Access: "Overview" > "Display Config"
or: [MEAS] > "Display Config"
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Configuration
DOCSIS
The measurement results can be displayed using various evaluation methods. All evaluation methods available for the R&S FSW DOCSIS 3.1 application are displayed in
the evaluation bar in SmartGrid mode.
Drag one or more evaluations to the display area and configure the layout as required.
Up to 16 evaluation methods can be displayed simultaneously in separate windows.
The DOCSIS 3.1 evaluation methods are described in Chapter 3, "Measurements and
result display", on page 13.
To close the SmartGrid mode and restore the previous softkey menu select the
"Close" icon in the righthand corner of the toolbar, or press any key.
For details on working with the SmartGrid see the R&S FSW Getting Started manual.
3.1 I/Q measurement (modulation accuracy)
5.3 DOCSIS 3.1 I/Q measurement (modulation accuracy)
Access: [MODE] > "Docsis 3.1"
"Overview" > "Select Measurement" > "Modulation Accuracy"
When you activate the DOCSIS 3.1 application, an I/Q measurement of the input signal
is started automatically with the default configuration. The "DOCSIS 3.1" menu is displayed and provides access to the most important configuration functions.
The "Span", "Bandwidth", "Lines", and "Marker Functions" menus are not available for
DOCSIS 3.1 I/Q measurements.
Multiple access paths to functionality
The easiest way to configure a measurement channel is via the "Overview" dialog box,
which is displayed when you select the "Overview" softkey from any DOCSIS 3.1 softkey menu.
Alternatively, you can access the individual dialog boxes via softkeys from the corresponding menus, or via tools in the toolbars, if available.
In this documentation, only the most convenient method of accessing the dialog boxes
is indicated - usually via the "Overview".
● Configuration overview............................................................................................54
● Signal description....................................................................................................56
● Input, output, and frontend settings.........................................................................81
● Trigger settings....................................................................................................... 99
● Data acquisition.....................................................................................................107
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Configuration
● Sweep settings......................................................................................................109
● Synch/ OFDM-demodulation.................................................................................110
● Parameter estimation and tracking........................................................................111
● Demodulation........................................................................................................ 112
● Evaluation range................................................................................................... 115
● Result configuration...............................................................................................119
● Automatic settings.................................................................................................134
5.3.1 Configuration overview
Access: all menus
Throughout the measurement channel configuration, an overview of the most important
currently defined settings is provided in the "Overview".
DOCSIS
3.1 I/Q measurement (modulation accuracy)
Figure 5-1: Documentation Overview for a DOCSIS 3.1 downstream measurement
The "Overview" not only shows the main measurement settings, it also provides quick
access to the main settings dialog boxes. The indicated signal flow shows which
parameters affect which processing stage in the measurement. Thus, you can easily
configure an entire measurement channel from input over processing to output and
analysis by stepping through the dialog boxes as indicated in the "Overview".
The available settings and functions in the "Overview" vary depending on the currently
selected measurement. For frequency sweep measurements see Chapter 5.4, "Fre-
quency sweep measurements", on page 136.
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Configuration
DOCSIS
For the DOCSIS 3.1 I/Q measurement, the "Overview" provides quick access to the
following configuration dialog boxes (listed in the recommended order of processing):
1. "Select Measurement"
See "Select Measurement" on page 55
2. "Signal Description"
See Chapter 5.3.2, "Signal description", on page 56
3. "Input/ Frontend"
See and Chapter 5.3.3, "Input, output, and frontend settings", on page 81
4. "Trigger"
See Chapter 5.3.4, "Trigger settings", on page 99
5. "Data Acquisition"
See Chapter 5.3.5, "Data acquisition", on page 107
6. "Parameter Estimation and Tracking"
See Chapter 5.3.8, "Parameter estimation and tracking", on page 111
7. "Demodulation" (downstream only)
See Chapter 5.3.9, "Demodulation", on page 112
3.1 I/Q measurement (modulation accuracy)
8. "Result Configuration"
See Chapter 5.3.11, "Result configuration", on page 119
9. "Display Configuration"
See Chapter 5.2, "Display configuration", on page 52
To configure settings
► Select any button in the "Overview" to open the corresponding dialog box.
Preset Channel
Select the "Preset Channel" button in the lower left-hand corner of the "Overview" to
restore all measurement settings in the current channel to their default values.
Note: Do not confuse the "Preset Channel" button with the [Preset] key, which restores
the entire instrument to its default values and thus closes all channels on the
R&S FSW (except for the default channel)!
Remote command:
SYSTem:PRESet:CHANnel[:EXEC] on page 164
Select Measurement
Selects a measurement to be performed.
See Chapter 3, "Measurements and result display", on page 13.
Specific Settings for
The channel can contain several windows for different results. Thus, the settings indicated in the "Overview" and configured in the dialog boxes vary depending on the
selected window.
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Select an active window from the "Specific Settings for" selection list that is displayed
in the "Overview" and in all window-specific configuration dialog boxes.
The "Overview" and dialog boxes are updated to indicate the settings for the selected
window.
5.3.2 Signal description
Access: "Overview" > "Signal Description"
or: [MEAS CONFIG] > "Signal Description"
The signal description provides information on the expected input signal.
● Downstream signal description............................................................................... 56
● Upstream signal description....................................................................................72
5.3.2.1 Downstream signal description
Access: "Overview" > "Signal Description" > "Stream Direction": "Downstream"
Configuration
DOCSIS 3.1 I/Q measurement (modulation accuracy)
or: [MEAS CONFIG] > "Signal Description" > "Stream Direction": "Downstream"
● OFDM channel description (downstream)...............................................................56
● Continuous pilots and excluded subcarrier assignment..........................................61
● Codeword / frame configuration..............................................................................64
● Profile configuration (downstream)......................................................................... 67
OFDM channel description (downstream)
Access: "Overview" > "Signal Description" > "OFDM Channel Description"
or: [MEAS CONFIG] > "Signal Description" > "OFDM Channel Description": "Down-
stream"
The general OFDM channel transmission settings are configured in the "Signal
Description" dialog box.
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Configuration
DOCSIS 3.1 I/Q measurement (modulation accuracy)
Figure 5-2: OFDM channel description for downstream DOCSIS 3.1 signals
The OFDM channel information detected in the PLC of the measured signal is displayed in the "PLC Messages (downstream only)" on page 26 result display.
Stream Direction........................................................................................................... 57
Center Frequency......................................................................................................... 58
OFDM Spectrum Location.............................................................................................58
N
(FFT length).......................................................................................................... 58
FFT
Cyclic Prefix CP............................................................................................................ 58
Roll-off...........................................................................................................................59
Time-Interleaving Depth................................................................................................59
PLC Start Index L..........................................................................................................60
PLC Modulation.............................................................................................................60
PLC Number of Subcarriers (Np)...................................................................................60
NCP Modulation............................................................................................................60
Stream Direction
Defines the direction of the signal stream to be analyzed. Various configuration parameters for the DOCSIS 3.1 measurement depend on the stream direction.
"Downstream"
(default) Downstream signal (from the CMTS to the cable modems).
Requires R&S FSW-K192 option.
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Configuration
DOCSIS 3.1 I/Q measurement (modulation accuracy)
"Upstream"
Upstream signal (from the cable modems to the CMTS). Requires
R&S FSW-K193 option.
Remote command:
CONFigure:SDIRection on page 171
Center Frequency
Defines the center frequency of the signal in Hertz.
The center frequency of the complete signal depends on the center frequency of the
subcarrier 0 of the OFDM channel (f
), which defines the beginning of the OFDM
sc0
spectrum. If the OFDM Spectrum Location is changed, then the general center frequency is also changed, and vice versa.
Remote command:
[SENSe:]FREQuency:CENTer on page 219
OFDM Spectrum Location
Specifies the center frequency in Hz of the subcarrier 0 of the OFDM channel (f
sc0
),
which defines the beginning of the OFDM spectrum.
The default value for this setting is derived from the current Center Frequency. If the
spectrum location is changed, the center frequency is adapted accordingly, and vice
versa.
Remote command:
CONFigure:DS:CHANnel:SPECtrum:FREQuency on page 170
Query PLC information:
FETCh:PLCMessages:OCD:SLOCation? on page 295
N
(FFT length)
FFT
Specifies the length of the FFT defining the OFDM transmission, which corresponds to
the number of physical subcarriers.
"4K mode, Δf 50 kHz"
4096 subcarriers at = 50 kHz spacing; FFT length = 4096 samples
"8K mode, Δf 25 kHz"
8192 subcarriers at 25 kHz spacing; FFT length = 8192 samples
Remote command:
CONFigure:CHANnel:NFFT on page 168
Cyclic Prefix CP
Length of the configurable cyclic prefix.
The cyclic prefix determines where the useful data starts and prevents inter-symbol
interference between multiple OFDM symbols during transmission.
Note: The cyclic prefix must be longer than the Roll-off period.
"AUTO"
The length is determined automatically by the R&S FSW DOCSIS 3.1
application and indicated in the dialog box after the next measurement.
If the cyclic prefix is set to "AUTO", the Roll-off is also automatically
set to "Auto Max Roll-Off" and cannot be edited.
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Configuration
3.1 I/Q measurement (modulation accuracy)
"192 Samples,
DOCSIS
Useful symbol period starts after 192 samples or 0.9375μs.
0.9375μs"
"256 Samples,
Useful symbol period starts after 256 samples or 1.25μs.
1.25μs"
"512 Samples,
Useful symbol period starts after 512 samples or 2.5μs.
2.5μs"
"768 Samples,
Useful symbol period starts after 768 samples or 3.75 s.
3.75μs"
"1024 Sam-
Useful symbol period starts after 1024 samples or 5.0μs.
ples, 5.0μs"
Remote command:
CONFigure:CHANnel:CP on page 167
Query PLC information:
FETCh:PLCMessages:OCD:CP? on page 292
Roll-off
Defines the roll-off period for the Tukey raised-cosine window which is applied at the
beginning (and end) of an OFDM symbol. The roll-off period defines the steepness of
the filter.
The required period depends on the current transmission conditions. The roll-off period
can be between 0 μs and 1.25 μs for the downstream.
Note: The roll-off period is integrated in the Cyclic Prefix CP and must be shorter than
the Cyclic Prefix CP.
If the Cyclic Prefix CP is set to "AUTO", the roll-off is also automatically set to "Auto
Max Roll-Off" and cannot be edited.
"Auto Max
The maximum possible roll-off period is used automatically.
Roll-Off"
"0 Samples,
No samples in the roll-off period (for no transmit windowing)
0.0 μs"
"64 Samples,
The roll-off period contains 64 samples and lasts 0.3125 μs.
0.3125 μs"
"128 Samples,
The roll-off period contains 128 samples and lasts 0.625 μs.
0.625 μs"
"192 Samples,
The roll-off period contains 192 samples and lasts 0.9375 μs.
0.9375 μs"
"256 Samples,
The roll-off period contains 256 samples and lasts 1.25 μs.
1.25 μs"
Remote command:
CONFigure:CHANnel:ROFF on page 168
Query PLC information:
FETCh:PLCMessages:OCD:ROFF? on page 294
Time-Interleaving Depth
Defines the maximum number of delay lines used for time interleaving. The possible
depth depends on the N
(FFT length).
FFT
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Configuration
DOCSIS
3.1 I/Q measurement (modulation accuracy)
The maximum depth for 4K mode is 32; for 8K mode it is 16.
Remote command:
CONFigure:DS:CHANnel:TIDepth on page 171
Query PLC information:
FETCh:PLCMessages:OCD:TIDepth? on page 295
PLC Start Index L
Defines the starting subcarrier index of the physical link channel (PLC).
The PLC is located at the same position in each OFDM symbol and consists of several
consecutive subcarriers. The information in the PLC can be used by the R&S FSW
DOCSIS 3.1 application to determine several of the signal description parameters
automatically.
For more information see "Continuous pilots, excluded subcarriers, PLC" on page 40.
If "Auto" is enabled, the start index of the PLC is detected automatically. After success-
ful detection, this field indicates the PLC start index L.
If "Auto" is disabled, the numeric value defined manually is used as the start index.
Note: If you enter a value manually, the "Auto" option is automatically disabled.
Remote command:
CONFigure:DS:CHANnel:PLC:INDex:AUTO on page 170
CONFigure:DS:CHANnel:PLC:INDex on page 169
Query PLC information:
FETCh:PLCMessages:OCD:PLC:INDex? on page 294
PLC Modulation
Indicates the used PLC modulation (for reference only).
16QAM modulation is required by the DOCSIS 3.1 standard.
Remote command:
CONFigure:DS:CHANnel:PLC:MODulation? on page 170
PLC Number of Subcarriers (Np)
Indicates the number of subcarriers used by the PLC (for reference only). The number
of subcarriers depends on the N
(FFT length) setting.
FFT
Remote command:
CONFigure:DS:CHANnel:PLC:CARRiers? on page 169
NCP Modulation
Defines the modulation used by the Next Codeword Pointer (NCP).
The following modulation types are supported:
●
QPSK
●
16-QAM
●
64-QAM
Remote command:
CONFigure:DS:CHANnel:NCP:MODulation on page 169
Query PLC information:
FETCh:PLCMessages:NCP:MODulation? on page 292
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Configuration
DOCSIS
3.1 I/Q measurement (modulation accuracy)
Continuous pilots and excluded subcarrier assignment
Access: "Overview" > "Signal Description" > "OFDM Channel Description" > "Continu-
ous Pilots, Excluded Subcarriers Configuration..."
or: [MEAS CONFIG] > "Signal Description" > "OFDM Channel Description" > "Continuous Pilots, Excluded Subcarriers Configuration..."
Some subcarriers have a specific function and are used identically for all symbols.
Such fixed objects in the channel must be configured so that the R&S FSW
DOCSIS 3.1 application can distinguish their contents from the useful data. Subcarriers
with a special function are configured in the signal description in the "Continuous Pilots
and Excluded Subcarrier Assignment" table.
For downstream signals, the first row contains the PLC and is configured automatically
according to the PLC Start Index L, and "PLC Number of Subcarriers (Np)" on page 60
from the Signal description settings. Therefore the first row providing the PLC info is
read only.
Below the table, a modulation vs. subcarrier diagram indicates which channels are
defined for which function.
Figure 5-3: Continuous pilots and excluded subcarrier assignment for downstream DOCSIS 3.1 sig-
nals
Set Index.......................................................................................................................62
Type.............................................................................................................................. 62
Subcarrier Range(Start / Increment / Stop)...................................................................62
Subcarrier Set............................................................................................................... 62
└ Add..................................................................................................................63
└ Remove...........................................................................................................63
└ Remove All......................................................................................................63
Insert............................................................................................................................. 63
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Configuration
DOCSIS
Delete............................................................................................................................63
Delete All.......................................................................................................................63
Auto Detection:Continuous Pilots (downstream only)................................................... 63
OK.................................................................................................................................64
Cancel...........................................................................................................................64
Set Index
Continuous line number in configuration table.
Remote command:
CONFigure:DS:CHANnel:CPES<i>:COUNt? on page 174
Type
Type of special subcarrier; for upstream signals, only excluded subcarriers are available
"PLC"
"Cont. Pilot"
"Excluded
Subcarrier"
Remote command:
CONFigure:DS:CHANnel:CPES<i>:SUBCarrier:TYPE on page 177
Physical link channel
(First line only, default, always available)
Pilot that occurs at the same frequency location in every OFDM symbol, and which is used for frequency and phase synchronization.
Note: As soon as an entry in the table is defined using the "Type":
"Continuous Pilots", Auto Detection:Continuous Pilots (downstream
only) is automatically set to "User Defined".
Subcarrier that cannot be used because another type of service is
using the subcarrier's frequency or a permanent interference is present on the frequency.
3.1 I/Q measurement (modulation accuracy)
Subcarrier Range(Start / Increment / Stop)
Defines a series of subcarriers to be configured identically.
The following restrictions apply:
●
"Start" < "Stop"
●
"Increment" ≥ 1
For example: to configure all 10 carriers between subcarriers 2044 and 2053, define:
●
"Start" = 2044
●
"Increment" = 1
●
"Stop" = 2053
Remote command:
CONFigure:DS:CHANnel:CPES<i>:SUBCarrier:STARt on page 176
CONFigure:DS:CHANnel:CPES<i>:SUBCarrier:INCRement on page 175
CONFigure:DS:CHANnel:CPES<i>:SUBCarrier:STOP on page 177
Subcarrier Set
Specifies the (discrete) subcarrier numbers to be configured in the same set.
When you select the input field, an edit dialog is displayed. Enter the individual subcar-
rier numbers in the dialog, selecting [Enter] after each number.
To add further entry fields, select Add.
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Configuration
DOCSIS
Tip: to configure a series of subcarriers identically, use the Subcarrier Range(Start /
Increment / Stop) settings.
Remote command:
CONFigure:DS:CHANnel:CPES<i>:SUBCarrier:SET on page 176
3.1 I/Q measurement (modulation accuracy)
Add ← Subcarrier Set
Adds a new entry to the left of the currently selected entry.
Remove ← Subcarrier Set
Removes the currently selected entry.
Remove All ← Subcarrier Set
Removes all entries in the list.
Insert
Inserts a new line in the table below the currently selected row.
Delete
Deletes the currently selected row.
Remote command:
CONFigure:DS:CHANnel:CPES<i>:DELete on page 175
Delete All
Deletes all lines in the table, except for the default PLC configuration.
Remote command:
CONFigure:DS:CHANnel:CPES<i>:DALL on page 175
Auto Detection:Continuous Pilots (downstream only)
Defines how continuous pilots are detected in the symbols.
If "Auto from Signal" is selected, continuous pilots are detected automatically during
demodulation.
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If "User Defined" is selected, the pilots must be configured manually in the Continuous
pilots and excluded subcarrier assignment table, using the Type: "Continuous Pilots".
Note: As soon as an entry in the Continuous pilots and excluded subcarrier assign-
ment table is defined or changed to the "Type": "Continuous Pilots", this setting is auto-
matically set to "User Defined".
Remote command:
[SENSe:]DEMod:CPILots:AUTO on page 240
OK
Saves the changes to the table and closes the dialog box.
Cancel
Closes the dialog box without saving the changes.
Codeword / frame configuration
Access: "Overview" > "Signal Description" > "Codeword Configuration" > "Frame Con-
figuration"
Configuration
DOCSIS 3.1 I/Q measurement (modulation accuracy)
or: [MEAS CONFIG] > "Signal Description" > "Codeword Configuration" > "Frame Configuration"
The useful data that is to be transmitted to the same group of cable modems is summarized into codewords. Codewords are sequentially assigned to frames (subcarriers)
and associated with a profile.
A codeword can either be defined by the first and total number of subcarriers it is
assigned to, or by the first and total number of symbols it is assigned to.
For more information see also "Codewords, logical subcarriers, frames, and NCPs"
on page 41.
Select the .
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Configuration
DOCSIS
Figure 5-4: Frame/codeword configuration for downstream DOCSIS 3.1 signals
3.1 I/Q measurement (modulation accuracy)
Codeword Index............................................................................................................65
Profile............................................................................................................................65
First Subcarrier..............................................................................................................65
Number of Subcarriers..................................................................................................66
First Symbol.................................................................................................................. 66
Number of Symbols.......................................................................................................66
Insert Codeword............................................................................................................66
Delete Codeword.......................................................................................................... 66
Delete All Codewords....................................................................................................66
Auto Detection: NCP Content (downstream only).........................................................66
OK.................................................................................................................................66
Cancel...........................................................................................................................67
Codeword Index
Continuous line number in configuration table.
Remote command:
CONFigure:DS:CHANnel:FCONfig<i>:COUNt? on page 190
Profile
One of the active profiles defined in the "Profile List" on page 68, which is assigned to
the selected codeword.
For zero-bit loaded codewords, assign the profile "Unused".
Remote command:
CONFigure:DS:CHANnel:FCONfig<i>:PROFile on page 191
First Subcarrier
Defines the first logical subcarrier to which the selected codeword is assigned.
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Configuration
DOCSIS
Remote command:
CONFigure:DS:CHANnel:FCONfig<i>:SUBCarrier:STARt on page 192
Number of Subcarriers
Defines the number of subcarriers to which the selected codeword is assigned.
Remote command:
CONFigure:DS:CHANnel:FCONfig<i>:SUBCarrier:COUNt on page 191
First Symbol
Defines the first symbol to which the selected codeword is assigned.
Remote command:
CONFigure:DS:CHANnel:FCONfig<i>:SYMBol:STARt on page 192
Number of Symbols
Defines the number of symbols to which the selected codeword is assigned.
Remote command:
CONFigure:DS:CHANnel:FCONfig<i>:SYMBol:COUNt on page 192
Insert Codeword
Inserts a new row in the table below the currently selected row.
3.1 I/Q measurement (modulation accuracy)
Delete Codeword
Deletes the currently selected row.
Remote command:
CONFigure:DS:CHANnel:FCONfig<i>:DELete on page 191
Delete All Codewords
Deletes all rows in the table.
Remote command:
CONFigure:DS:CHANnel:FCONfig<i>:DALL on page 190
Auto Detection: NCP Content (downstream only)
For each new codeword that starts in a frame, the first subcarrier and the number of
subcarriers in total for the codeword is provided as a Next Codeword Pointer (NCP).
The contents of the NCP can be configured manually or detected automatically by the
R&S FSW DOCSIS 3.1 application.
If "Auto from Signal" is selected, the position of the codewords (NCP content) is detected in the signal automatically during demodulation. The entire table is filled automatically.
If "User Defined" is selected, the frames must be configured manually in the Code-
word / frame configuration table.
Remote command:
[SENSe:]DEMod:NCP:AUTO on page 241
OK
Saves the changes to the table and closes the dialog box.
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Cancel
Closes the dialog box without saving the changes.
Profile configuration (downstream)
Access: "Overview" > "Signal Description" > "Profile Configuration"
or: [MEAS CONFIG] > "Signal Description" > "Profile Configuration"
Profiles define the modulation used by each subcarrier. For each set of modems with
similar transmission conditions, a profile can then be assigned (see "Codeword / frame
configuration" on page 64).
For more information see also "Subcarriers and profiles" on page 40.
● Profile management................................................................................................67
● Profile settings: modulation subcarrier assignment.................................................69
● NCP profile..............................................................................................................72
Profile management
Access: "Overview" > "Signal Description" > "Profile Configuration"
Configuration
DOCSIS 3.1 I/Q measurement (modulation accuracy)
or: [MEAS CONFIG] > "Signal Description" > "Profile Configuration"
A profile is a set of parameters that defines how information is transmitted from a
CMTS to a cable modem, or from a cable modem to a CMTS.
Up to 16 different profiles can be defined and assigned to a specific block of data. Profiles that contain a configuration for at least one subcarrier are considered to be active,
indicated by black text. Empty profiles are inactive, indicated by gray text.
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Configuration
DOCSIS
3.1 I/Q measurement (modulation accuracy)
Figure 5-5: Profile configuration for downstream DOCSIS 3.1 signals
Profile List..................................................................................................................... 68
Edit Profile.....................................................................................................................68
Delete Profile.................................................................................................................69
Profile List
Up to 16 different profiles can be defined and assigned to a specific set of subcarriers.
Profiles that contain a configuration for at least one subcarrier are considered to be
active, indicated by black text. Empty profiles are inactive, indicated by gray text.
Remote command:
CONFigure:DS:CHANnel:PCONfig<pri>:SELect on page 184
Edit Profile
Displays the "Modulation Subcarrier Assignment" dialog box for the selected profile.
For details see "Profile settings: modulation subcarrier assignment" on page 69.
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Configuration
DOCSIS
Delete Profile
Deletes the currently selected profile in the "Modulation Subcarrier Assignment" list.
Remote command:
CONFigure:DS:CHANnel:PCONfig<pri>:DELete on page 184
Profile settings: modulation subcarrier assignment
Access: "Overview" > "Signal Description" > "Profile Configuration" > "Edit Profile"
or: [MEAS CONFIG] > "Signal Description" > "Profile Configuration" > "Edit Profile"
3.1 I/Q measurement (modulation accuracy)
Set Index.......................................................................................................................69
Modulation.....................................................................................................................70
Start / Increment / Stop................................................................................................. 70
Subcarrier Set............................................................................................................... 70
└ Add..................................................................................................................71
└ Remove...........................................................................................................71
Insert............................................................................................................................. 71
Delete............................................................................................................................71
Delete All.......................................................................................................................71
OK.................................................................................................................................71
Cancel...........................................................................................................................72
Set Index
Continuous line number in configuration table.
Remote command:
CONFigure:DS:CHANnel:PCONfig<pri>:COUNt? on page 183
CONFigure:DS:CHANnel:NCP:PCONfig<pri>:COUNt? on page 181
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Modulation
Defines the modulation used by the specified subcarriers.
For the NCP profile, zero bit modulation is used for all entries except the index 0,
whose modulation depends on the NCP Modulation setting and cannot be edited here.
Remote command:
CONFigure:DS:CHANnel:PCONfig<pri>:SUBCarrier:MODulation
on page 186
CONFigure:DS:CHANnel:NCP:PCONfig<pri>:SUBCarrier:MODulation
on page 182
Start / Increment / Stop
Defines a series of subcarriers to be configured identically.
The following restrictions apply:
●
"Start" < "Stop"
●
"Increment" ≥ 1
For example: to configure all 10 carriers between subcarriers 2044 and 2053, define:
●
"Start" = 2044
●
"Increment" = 1
●
"Stop" = 2053
Remote command:
CONFigure:DS:CHANnel:PCONfig<pri>:SUBCarrier:STARt on page 187
CONFigure:DS:CHANnel:PCONfig<pri>:SUBCarrier:INCRement on page 185
CONFigure:DS:CHANnel:PCONfig<pri>:SUBCarrier:STOP on page 187
CONFigure:DS:CHANnel:NCP:PCONfig<pri>:SUBCarrier:STARt on page 183
CONFigure:DS:CHANnel:NCP:PCONfig<pri>:SUBCarrier:INCRement
on page 181
CONFigure:DS:CHANnel:NCP:PCONfig<pri>:SUBCarrier:STOP on page 183
Configuration
DOCSIS 3.1 I/Q measurement (modulation accuracy)
Subcarrier Set
Specifies the (discrete) subcarrier numbers to be configured identically.
When you select the input field, an edit dialog is displayed. Enter the individual subcar-
rier numbers in the dialog, selecting [Enter] after each number.
To add further entry fields, select Add .
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Configuration
DOCSIS
Tip: to configure a series of subcarriers identically, use the Subcarrier Range(Start /
Increment / Stop) settings.
Remote command:
CONFigure:DS:CHANnel:PCONfig<pri>:SUBCarrier:SET on page 186
CONFigure:DS:CHANnel:NCP:PCONfig<pri>:SUBCarrier:SET on page 182
3.1 I/Q measurement (modulation accuracy)
Add ← Subcarrier Set
Adds a new entry to the left of the currently selected entry.
Remove ← Subcarrier Set
Removes the currently selected entry.
Insert
Inserts a new line in the table below the currently selected row.
Delete
Deletes the currently selected row.
Remote command:
CONFigure:DS:CHANnel:PCONfig<pri>:SUBCarrier:DELete on page 185
CONFigure:DS:CHANnel:NCP:PCONfig<pri>:DELete on page 181
Delete All
Deletes all lines in the table.
Remote command:
CONFigure:DS:CHANnel:PCONfig<pri>:SUBCarrier:DALL on page 185
CONFigure:DS:CHANnel:NCP:PCONfig<pri>:DALL on page 181
OK
Saves the changes to the table and closes the dialog box.
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Cancel
Closes the dialog box without saving the changes.
NCP profile
Access: "Overview" > "Signal Description" > "Profile Configuration" > "NCP Profile"
or: [MEAS CONFIG] > "Signal Description" > "Profile Configuration" > "NCP Profile"
The modulation used by the subcarriers for the NCP is defined in a separate profile,
but in the same way as all other profiles (see "Profile settings: modulation subcarrier
assignment" on page 69). However, the following restrictions apply:
●
The entry with the index 0 is not editable. It is defined for the subcarriers from 0 to
N
The modulation depends on the NCP Modulation setting and cannot be edited in
the "Profile" dialog box.
●
For all other entries, zero bit modulation is used.
5.3.2.2 Upstream signal description
-1, in steps of 1.
FFT
Configuration
DOCSIS 3.1 I/Q measurement (modulation accuracy)
Access: "Overview" > "Signal Description" > "Stream Direction": "Upstream"
or: [MEAS CONFIG] > "Signal Description" > "Stream Direction"
● OFDM channel description (upstream)................................................................... 72
● Excluded subcarrier assignment.............................................................................76
● Profile configuration (upstream)..............................................................................79
OFDM channel description (upstream)
Access: "Overview" > "Signal Description" > "OFDM Channel Description"
or: [MEAS CONFIG] > "Signal Description" > "OFDM Channel Description"
The general OFDM channel transmission settings are configured in the "Signal
Description" dialog box.
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Configuration
DOCSIS
3.1 I/Q measurement (modulation accuracy)
Figure 5-6: OFDM channel description for upstream DOCSIS 3.1 signals
Stream Direction........................................................................................................... 73
Center Frequency......................................................................................................... 73
OFDM Spectrum Location.............................................................................................74
N
(FFT length).......................................................................................................... 74
FFT
Cyclic Prefix CP............................................................................................................ 74
Roll-off...........................................................................................................................75
Symbols Per Frame (K).................................................................................................76
Stream Direction
Defines the direction of the signal stream to be analyzed. Various configuration parameters for the DOCSIS 3.1 measurement depend on the stream direction.
"Downstream"
(default) Downstream signal (from the CMTS to the cable modems).
Requires R&S FSW-K192 option.
"Upstream"
Upstream signal (from the cable modems to the CMTS). Requires
R&S FSW-K193 option.
Remote command:
CONFigure:SDIRection on page 171
Center Frequency
Defines the center frequency of the signal in Hertz.
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The center frequency of the complete signal depends on the center frequency of the
subcarrier 0 of the OFDM channel (f
spectrum. If the OFDM Spectrum Location is changed, then the general center frequency is also changed, and vice versa.
Remote command:
[SENSe:]FREQuency:CENTer on page 219
OFDM Spectrum Location
Specifies the center frequency in Hz of the subcarrier 0 of the OFDM channel (f
which defines the beginning of the OFDM spectrum.
The default value for this setting is derived from the current Center Frequency. If the
spectrum location is changed, the center frequency is adapted accordingly, and vice
versa.
Remote command:
CONFigure:US:CHANnel:SPECtrum:FREQuency on page 173
N
FFT
Specifies the length of the FFT defining the OFDM transmission, which corresponds to
the number of physical subcarriers.
"2K mode, Δf 50 kHz"
"4K mode, Δf 25 kHz"
Remote command:
CONFigure:CHANnel:NFFT on page 168
(FFT length)
Configuration
DOCSIS 3.1 I/Q measurement (modulation accuracy)
), which defines the beginning of the OFDM
sc0
),
sc0
2048 subcarriers at = 50 kHz spacing; FFT length = 2048 samples
4096 subcarriers at = 25 kHz spacing; FFT length = 4096 samples
Cyclic Prefix CP
Length of the configurable cyclic prefix.
The cyclic prefix determines where the useful data starts and allows the application to
detect delay spreads during transmission. The longer the delay spread, the longer the
CP must be.
Note: The cyclic prefix must be longer than the Roll-off period.
"AUTO"
The length is determined automatically by the R&S FSW DOCSIS 3.1
application and indicated in the dialog box after the next measurement.
"96 Samples,
Useful symbol period starts after 96 samples or 0.9375 μs.
0.9375μs"
"128 Samples,
Useful symbol period starts after 128 samples or 1.25 μs.
1.25μs"
"160 Samples,
Useful symbol period starts after 160 samples or 1.5625 μs.
1.5625μs"
"192 Samples,
Useful symbol period starts after 192 samples or 1.875μs.
1.875μs"
"224 Samples,
Useful symbol period starts after 224 samples or 2.1875 μs.
2.1875μs"
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Configuration
DOCSIS
"256 Samples,
2.5μs"
"288 Samples,
2.8125μs"
"320 Samples,
3.125μs"
"384 Samples,
3.75μs"
"512 Samples,
5.0μs"
"640 Samples,
6.25μs "
Remote command:
CONFigure:CHANnel:CP on page 172
FETCh:CP? on page 285
Roll-off
Defines the roll-off period for the Tukey raised-cosine window which is applied at the
beginning (and end) of an OFDM symbol. The roll-off period defines the steepness of
the filter.
The required period depends on the current transmission conditions. The roll-off period
can be between 0 μs and 2.1875 μs for the upstream.
Useful symbol period starts after 256 samples or 2.5μs.
Useful symbol period starts after 288 samples or 2.8125 μs.
Useful symbol period starts after 320 samples or 3.125 μs.
Useful symbol period starts after 384 samples or 3.75 μs.
Useful symbol period starts after 512 samples or 5.0μs.
Useful symbol period starts after 640 samples or 6.25 μs.
3.1 I/Q measurement (modulation accuracy)
Note: The roll-off period is integrated in the Cyclic Prefix CP and must be shorter than
the Cyclic Prefix CP.
"Auto Max
Roll-Off"
"0 Samples,
0.0 μs"
"32 Samples,
0.3125μs"
"64 Samples,
0.625 μs"
"96 Samples,
0.9375 μs"
"128 Samples,
1.25 μs"
"160 Samples,
1.5625 μs"
"192 Samples,
1.875 μs"
"224 Samples,
2.1875 μs"
The maximum possible roll-off period is used automatically.
No samples in the roll-off period (for no transmit windowing)
The roll-off period contains 64 samples and lasts 0.3125 μs.
The roll-off period contains 128 samples and lasts 0.625 μs.
The roll-off period contains 192 samples and lasts 0.9375 μs.
The roll-off period contains 256 samples and lasts 1.25 μs.
The roll-off period contains 256 samples and lasts 1.25 μs.
The roll-off period contains 256 samples and lasts 1.25 μs.
The roll-off period contains 256 samples and lasts 1.25 μs.
Remote command:
CONFigure:CHANnel:ROFF on page 168
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Configuration
DOCSIS
3.1 I/Q measurement (modulation accuracy)
Symbols Per Frame (K)
Defines the number of symbols per frame to be expected. The available number of
symbols per frame varies depending on the used bandwidth and N
(FFT length).
FFT
Values between 6 and 18 are allowed for 4K mode, values between 6 and 36 for 2K
mode.
Remote command:
CONFigure:US:CHANnel:SYMBols on page 174
Excluded subcarrier assignment
Access: "Overview" > "Signal Description" > "OFDM Channel Description" > "Excluded
Subcarriers Configuration"
or: [MEAS CONFIG] > "Signal Description" > "OFDM Channel Description" > "Excluded Subcarriers Configuration"
Some subcarriers are excluded for transmission. Such subcarriers must be configured
so that the R&S FSW DOCSIS 3.1 application can distinguish their contents from the
useful data. Excluded subcarriers are configured in the signal description in the "Excluded Subcarrier Assignment" table.
Below the table, a modulation vs. subcarrier diagram indicates which channels are
defined as excluded subcarriers.
Figure 5-7: Excluded subcarrier assignment for upstream DOCSIS
3.1 signals
Set Index.......................................................................................................................77
Type.............................................................................................................................. 77
Subcarrier Range(Start / Increment / Stop)...................................................................77
Subcarrier Set............................................................................................................... 77
└ Add..................................................................................................................78
└ Remove...........................................................................................................78
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Inserting a line...............................................................................................................78
Deleting a line............................................................................................................... 78
Deleting the entire table................................................................................................ 78
OK.................................................................................................................................78
Cancel...........................................................................................................................78
Set Index
Indicates the continuous line number in the configuration table.
Remote command:
CONFigure:US:CHANnel:ESUB<i>:COUNt? on page 177
Type
Defines the type of special subcarrier.
"Excluded
Subcarrier"
Remote command:
CONFigure:US:CHANnel:ESUB<i>:SUBCarrier:TYPE? on page 180
Configuration
DOCSIS 3.1 I/Q measurement (modulation accuracy)
Subcarrier that cannot be used because another type of service is
using the subcarrier's frequency or a permanent ingressor is present
on the frequency.
Subcarrier Range(Start / Increment / Stop)
Defines a series of subcarriers to be configured identically.
The following restrictions apply:
●
"Start" < "Stop"
●
"Increment" ≥ 1
For example: to configure all 10 carriers between subcarriers 2044 and 2053, define:
●
"Start" = 2044
●
"Increment" = 1
●
"Stop" = 2053
Remote command:
CONFigure:US:CHANnel:ESUB<i>:SUBCarrier:STARt on page 179
CONFigure:US:CHANnel:ESUB<i>:SUBCarrier:INCRement on page 178
CONFigure:US:CHANnel:ESUB<i>:SUBCarrier:STOP on page 179
Subcarrier Set
Specifies the (discrete) subcarrier numbers to be configured identically.
When you select the input field, an edit dialog is displayed. Enter the individual subcar-
rier numbers in the dialog, selecting [Enter] after each number.
To add further entry fields, select Add.
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Configuration
DOCSIS
Tip: to configure a series of subcarriers identically, use the Subcarrier Range(Start /
Increment / Stop) settings.
Remote command:
CONFigure:US:CHANnel:ESUB<i>:SUBCarrier:SET on page 179
3.1 I/Q measurement (modulation accuracy)
Add ← Subcarrier Set
Adds a new entry to the left of the currently selected entry.
Remove ← Subcarrier Set
Removes the currently selected entry.
Inserting a line
Inserts a new line in the table below the currently selected row.
Deleting a line
Deletes the currently selected row.
Remote command:
CONFigure:US:CHANnel:ESUB<i>:DELete on page 178
Deleting the entire table
Deletes all lines in the table, except for the default PLC configuration.
Remote command:
CONFigure:US:CHANnel:ESUB<i>:DALL on page 178
OK
Saves the changes to the table and closes the dialog box.
Cancel
Closes the dialog box without saving the changes.
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Configuration
DOCSIS
3.1 I/Q measurement (modulation accuracy)
Profile configuration (upstream)
Access: "Overview" > "Signal Description" > "Profile Configuration" > "Profile Configu-
ration"
or: [MEAS CONFIG] > "Signal Description" > "Profile Configuration" > "Profile Configuration"
Figure 5-8: Profile configuration for upstream DOCSIS 3.1 signals
Set Index.......................................................................................................................79
First Minislot..................................................................................................................80
Minislot Modulation....................................................................................................... 80
Minislot Pilot Pattern..................................................................................................... 80
Number of Minislots...................................................................................................... 80
Insert Modulation...........................................................................................................80
Delete Modulation......................................................................................................... 80
Delete All Modulations.................................................................................................. 80
OK.................................................................................................................................80
Cancel...........................................................................................................................80
Set Index
Continuous line number in configuration table.
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Configuration
DOCSIS
3.1 I/Q measurement (modulation accuracy)
First Minislot
Defines the type of the minislot to determine if it is the first minislot in a transmission
PPDU. The first minislot in a transmission burst must be an "Edge" minislot. All other
minislots in the burst are "Body" minislots.
Thus, the minislot with the index 0 is always of type "Edge". Minislots with a zero-valued modulation are also always of type "Edge".
Remote command:
CONFigure:US:CHANnel:PCONfig<pri>:MINislot:FIRSt on page 189
Minislot Modulation
Defines the modulation used by the specified minislots.
Remote command:
CONFigure:US:CHANnel:PCONfig<pri>:MINislot:MODulation on page 189
Minislot Pilot Pattern
Defines the pilot pattern used by the specified minislots. Which patterns are available
depends on the N
●
2K mode: 1 to 7
●
4K mode: 8 to 14
(FFT length).
FFT
For more information, see "Pilot patterns" on page 45.
Remote command:
CONFigure:US:CHANnel:PCONfig<pri>:MINislot:PPATtern on page 189
Number of Minislots
Defines the number of minislots for which the modulation is used.
Remote command:
CONFigure:US:CHANnel:PCONfig<pri>:MINislot:COUNt on page 188
Insert Modulation
Inserts a new line in the table below the currently selected row.
Delete Modulation
Deletes the currently selected row.
Remote command:
CONFigure:US:CHANnel:PCONfig<pri>:MINislot:DELete on page 188
Delete All Modulations
Deletes all lines in the table.
Remote command:
CONFigure:US:CHANnel:PCONfig<pri>:MINislot:DALL on page 188
OK
Saves the changes to the table and closes the dialog box.
Cancel
Closes the dialog box without saving the changes.
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Configuration
DOCSIS
3.1 I/Q measurement (modulation accuracy)
5.3.3 Input, output, and frontend settings
Access: "Overview" ≥ "Input/Frontend"
or: [INPUT/OUTPUT]
The R&S FSW can analyze signals from different input sources and provide various
types of output (such as noise or trigger signals).
Importing and Exporting I/Q Data
The I/Q data to be analyzed for DOCSIS 3.1 cannot only be captured by the
DOCSIS 3.1 application itself, it can also be imported to the application, provided it has
the correct format. Furthermore, the analyzed I/Q data from the DOCSIS 3.1 application can be exported for further analysis in external applications.
See the R&S FSW I/Q Analyzer and I/Q Input user manual.
Frequency and amplitude settings are available to configure the frontend of the
R&S FSW.
● Input source settings...............................................................................................81
● Power sensor.......................................................................................................... 87
● Output settings........................................................................................................91
● Frequency settings..................................................................................................93
● Amplitude settings...................................................................................................94
5.3.3.1 Input source settings
Access: "Overview" > "Input/Frontend" > "Input Source"
The input source determines which data the R&S FSW analyzes.
The default input source for the R&S FSW is "Radio Frequency", i.e. the signal at the
"RF Input" connector of the R&S FSW. If no additional options are installed, this is the
only available input source.
Further input sources
The R&S FSW DOCSIS 3.1 application application can also process input from the following optional sources:
●
I/Q Input files
●
"Digital Baseband" interface (R&S FSW-B17)
●
"Analog Baseband" interface (R&S FSW-B71)
●
Probes
●
Power sensors
For details, see the R&S FSW I/Q Analyzer and I/Q Input User Manual.
● Radio frequency input............................................................................................. 82
● Settings for input from I/Q data files........................................................................85
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Configuration
DOCSIS
Radio frequency input
Access: "Overview" > "Input/Frontend" > "Input Source" > "Radio Frequency"
3.1 I/Q measurement (modulation accuracy)
RF Input Protection
The RF input connector of the R&S FSW must be protected against signal levels that
exceed the ranges specified in the data sheet. Therefore, the R&S FSW is equipped
with an overload protection mechanism for DC and signal frequencies up to 30 MHz.
This mechanism becomes active as soon as the power at the input mixer exceeds the
specified limit. It ensures that the connection between RF input and input mixer is cut
off.
When the overload protection is activated, an error message is displayed in the status
bar ("INPUT OVLD"), and a message box informs you that the RF input was disconnected. Furthermore, a status bit (bit 3) in the STAT:QUES:POW status register is set.
In this case, you must decrease the level at the RF input connector and then close the
message box. Then measurement is possible again. Reactivating the RF input is also
possible via the remote command INPut<ip>:ATTenuation:PROTection:RESet.
Radio Frequency State................................................................................................. 82
Input Coupling...............................................................................................................83
Impedance.................................................................................................................... 83
Direct Path.................................................................................................................... 84
High Pass Filter 1 to 3 GHz...........................................................................................84
YIG-Preselector.............................................................................................................84
Input Connector.............................................................................................................85
Radio Frequency State
Activates input from the "RF Input" connector.
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For R&S FSW85 models with two input connectors, you must define which input
source is used for each measurement channel.
If an external frontend is active, select the connector the external frontend is connected
to. You cannot use the other RF input connector simultaneously for the same channel.
However, you can configure the use of the other RF input connector for another active
channel at the same time.
"Input 1"
Configuration
DOCSIS 3.1 I/Q measurement (modulation accuracy)
1.00 mm RF input connector for frequencies up to 85 GHz (90 GHz
with option R&S FSW-B90G)
"Input 2"
Remote command:
INPut<ip>:SELect on page 197
INPut<ip>:TYPE on page 197
Input Coupling
The RF input of the R&S FSW can be coupled by alternating current (AC) or direct current (DC).
For an active external frontend, input coupling is always DC.
AC coupling blocks any DC voltage from the input signal. AC coupling is activated by
default to prevent damage to the instrument. Very low frequencies in the input signal
can be distorted.
However, some specifications require DC coupling. In this case, you must protect the
instrument from damaging DC input voltages manually. For details, refer to the data
sheet.
Remote command:
INPut<ip>:COUPling on page 194
Impedance
The R&S FSW has an internal impedance of 50 Ω. However, some applications use
other impedance values. To match the impedance of an external application to the
impedance of the R&S FSW, an impedance matching pad can be inserted at the input.
If the type and impedance value of the used matching pad is known to the R&S FSW, it
can convert the measured units accordingly so that the results are calculated correctly.
This function is not available for input from the optional "Digital Baseband" interface.
Not all settings are supported by all R&S FSW applications.
1.85 mm RF input connector for frequencies up to 67 GHz
The impedance conversion does not affect the level of the output signals (such as IF,
video, demod, digital I/Q output).
Ω"
"50
"75Ω"
(Default:) no conversion takes place
The 50 Ω input impedance is transformed to a higher impedance
using a 75 Ω adapter of the selected "Pad Type": "Series-R" (default)
or "MLP" (Minimum Loss Pad)
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Configuration
DOCSIS
"User"
Remote command:
INPut<ip>:IMPedance on page 196
INPut<ip>:IMPedance:PTYPe on page 196
For Analog Baseband input:
INPut<ip>:IQ:IMPedance on page 202
INPut<ip>:IQ:IMPedance:PTYPe on page 203
Direct Path
Enables or disables the use of the direct path for small frequencies.
In spectrum analyzers, passive analog mixers are used for the first conversion of the
input signal. In such mixers, the LO signal is coupled into the IF path due to its limited
isolation. The coupled LO signal becomes visible at the RF frequency 0 Hz. This effect
is referred to as LO feedthrough.
To avoid the LO feedthrough the spectrum analyzer provides an alternative signal path
to the A/D converter, referred to as the direct path. By default, the direct path is
selected automatically for RF frequencies close to zero. However, this behavior can be
disabled. If "Direct Path" is set to "Off", the spectrum analyzer always uses the analog
mixer path.
For an active external frontend, the direct path is always used automatically for frequencies close to zero.
"Auto"
"Off"
Remote command:
INPut<ip>:DPATh on page 194
The 50 Ω input impedance is transformed to a user-defined impe-
dance value according to the selected "Pad Type": "Series-R"
(default) or "MLP" (Minimum Loss Pad)
(Default) The direct path is used automatically for frequencies close
to zero.
The analog mixer path is always used.
3.1 I/Q measurement (modulation accuracy)
High Pass Filter 1 to 3 GHz
Activates an additional internal highpass filter for RF input signals from 1 GHz to
3 GHz. This filter is used to remove the harmonics of the analyzer to measure the harmonics for a DUT, for example.
This function requires an additional hardware option.
Note: For RF input signals outside the specified range, the high-pass filter has no
effect. For signals with a frequency of approximately 4 GHz upwards, the harmonics
are suppressed sufficiently by the YIG-preselector, if available.)
Remote command:
INPut<ip>:FILTer:HPASs[:STATe] on page 195
YIG-Preselector
Enables or disables the YIG-preselector, if available on the R&S FSW.
Note: Note that the YIG-preselector is active only on frequencies greater than 8 GHz.
Therefore, switching the YIG-preselector on or off has no effect if the frequency is
below that value.
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Configuration
DOCSIS
To use the optional 90 GHz frequency extension (R&S FSW-B90G), the YIG-preselector must be disabled.
Remote command:
INPut<ip>:FILTer:YIG[:STATe] on page 195
Input Connector
Determines which connector the input data for the measurement is taken from.
For more information on the "Analog Baseband" interface (R&S FSW-B71), see the
R&S FSW I/Q Analyzer and I/Q Input user manual.
"RF"
"RF Probe"
"Baseband
Input I"
Remote command:
INPut<ip>:CONNector on page 193
(Default:) The "RF Input" connector
The "RF Input" connector with an adapter for a modular probe
This setting is only available if a probe is connected to the "RF Input"
connector.
It is not available for an active external frontend.
The optional "Baseband Input I" connector
This setting is only available if the optional "Analog Baseband" inter-
face is installed and active for input. It is not available for the
R&S FSW67.
For R&S FSW85 models with two input connectors, this setting is
only available for "Input 1".
3.1 I/Q measurement (modulation accuracy)
Settings for input from I/Q data files
Access: "Overview" > "Input/Frontend" > "Input Source" > "I/Q File"
Or: [INPUT/OUTPUT] > "Input Source Config" > "Input Source" > "I/Q File"
I/Q Input File State........................................................................................................ 86
Select I/Q data file.........................................................................................................86
Selected Channel..........................................................................................................86
File Repetitions............................................................................................................. 86
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Configuration
DOCSIS
I/Q Input File State
Enables input from the selected I/Q input file.
If enabled, the application performs measurements on the data from this file. Thus,
most measurement settings related to data acquisition (attenuation, center frequency,
measurement bandwidth, sample rate) cannot be changed. The measurement time
can only be decreased to perform measurements on an extract of the available data
only.
Note: Even when the file input is disabled, the input file remains selected and can be
enabled again quickly by changing the state.
Remote command:
INPut<ip>:SELect on page 197
Select I/Q data file
Opens a file selection dialog box to select an input file that contains I/Q data.
The I/Q data file must be in one of the following supported formats:
.iq.tar
●
.iqw
●
.csv
●
.mat
●
.wv
●
.aid
●
For details on formats, see the R&S FSW I/Q Analyzer and I/Q Input user manual.
3.1 I/Q measurement (modulation accuracy)
Note: Only a single data stream or channel can be used as input, even if multiple
streams or channels are stored in the file.
Note: For some file formats that do not provide the sample rate and measurement time
or record length, you must define these parameters manually. Otherwise the traces are
not visible in the result displays.
The default storage location for I/Q data files is C:\R_S\INSTR\USER.
Remote command:
INPut<ip>:FILE:PATH on page 215
Selected Channel
Only available for files that contain more than one data stream from multiple channels:
selects the data stream to be used as input for the currently selected channel.
In "Auto" mode (default), the first data stream in the file is used as input for the channel. Applications that support multiple data streams use the first data stream in the file
for the first input stream, the second for the second stream etc.
Remote command:
MMEMory:LOAD:IQ:STReam on page 216
MMEMory:LOAD:IQ:STReam:AUTO on page 216
MMEMory:LOAD:IQ:STReam:LIST? on page 217
File Repetitions
Determines how often the data stream is repeatedly copied in the I/Q data memory to
create a longer record. If the available memory is not sufficient for the specified number of repetitions, the largest possible number of complete data streams is used.
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Configuration
Remote command:
TRACe:IQ:FILE:REPetition:COUNt on page 217
5.3.3.2 Power sensor
Access: "Overview" ≥ "Input/Frontend" > "Power Sensor"
or: [INPUT/OUTPUT] > "Power Sensor Config"
The R&S FSW can also analyze data from a connected power sensor.
For background information on working with power sensors see the R&S FSW User
Manual.
Power sensor settings
Access: "Overview" > "Input" > "Power Sensor" tab
For details on working with power sensors, see the R&S FSW User Manual.
Each sensor is configured on a separate tab.
DOCSIS
3.1 I/Q measurement (modulation accuracy)
State..............................................................................................................................88
Continuous Value Update............................................................................................. 88
Select............................................................................................................................ 88
Zeroing Power Sensor.................................................................................................. 89
Frequency Manual........................................................................................................ 89
Frequency Coupling......................................................................................................89
Unit/Scale......................................................................................................................89
Meas Time/Average......................................................................................................89
Setting the Reference Level from the Measurement Meas -> Ref................................90
Reference Value............................................................................................................90
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Configuration
DOCSIS
Use Ref Level Offset.....................................................................................................90
Sensor Level Offset.......................................................................................................90
Average Count (Number of Readings)..........................................................................90
Duty Cycle.....................................................................................................................90
Using the power sensor as an external trigger..............................................................91
└ External Trigger Level.....................................................................................91
└ Hysteresis....................................................................................................... 91
└ Trigger Holdoff................................................................................................ 91
└ Drop-Out Time................................................................................................ 91
└ Slope...............................................................................................................91
State
Switches the power measurement for all power sensors on or off. Note that in addition
to this general setting, each power sensor can be activated or deactivated individually
by the Select setting on each tab. However, the general setting overrides the individual
settings.
Continuous Value Update
If activated, the power sensor data is updated continuously during a sweep with a long
sweep time, and even after a single sweep has completed.
This function cannot be activated for individual sensors.
If the power sensor is being used as a trigger (see "Using the power sensor as an
external trigger" on page 91), continuous update is not possible; this setting is
ignored.
Remote command:
[SENSe:]PMETer<p>:UPDate[:STATe] on page 211
3.1 I/Q measurement (modulation accuracy)
Select
Selects the individual power sensor for usage if power measurement is generally activated (State function).
The detected serial numbers of the power sensors connected to the instrument are
provided in a selection list. For each of the four available power sensor indexes
("Power Sensor 1"..."Power Sensor 4"), which correspond to the tabs in the configuration dialog, one of the detected serial numbers can be assigned. The physical sensor is
thus assigned to the configuration setting for the selected power sensor index.
By default, serial numbers not yet assigned are automatically assigned to the next free
power sensor index for which "Auto Assignment" is selected.
Alternatively, you can assign the sensors manually by deactivating the "Auto" option
and selecting a serial number from the list.
Remote command:
[SENSe:]PMETer<p>[:STATe] on page 211
SYSTem:COMMunicate:RDEVice:PMETer<p>:DEFine on page 205
SYSTem:COMMunicate:RDEVice:PMETer<p>:CONFigure:AUTO[:STATe]
on page 204
SYSTem:COMMunicate:RDEVice:PMETer<p>:COUNt? on page 205
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Configuration
DOCSIS
Zeroing Power Sensor
Starts zeroing of the power sensor.
For details on the zeroing process refer to the R&S FSW User Manual.
Remote command:
CALibration:PMETer<p>:ZERO:AUTO ONCE on page 206
Frequency Manual
Defines the frequency of the signal to be measured. The power sensor has a memory
with frequency-dependent correction factors. This allows extreme accuracy for signals
of a known frequency.
Remote command:
[SENSe:]PMETer<p>:FREQuency on page 208
Frequency Coupling
Selects the coupling option. The frequency can be coupled automatically to the center
frequency of the instrument or to the frequency of marker 1.
Remote command:
[SENSe:]PMETer<p>:FREQuency:LINK on page 209
3.1 I/Q measurement (modulation accuracy)
Unit/Scale
Selects the unit with which the measured power is to be displayed. Available units are
dBm, dB, W and %.
If dB or % is selected, the display is relative to the reference value that is defined with
either the "Meas -> Ref" setting or the "Reference Value" setting.
Remote command:
UNIT<n>:PMETer<p>:POWer on page 212
UNIT<n>:PMETer<p>:POWer:RATio on page 212
Meas Time/Average
Selects the measurement time or switches to manual averaging mode. In general,
results are more precise with longer measurement times. The following settings are
recommended for different signal types to obtain stable and precise results:
"Short"
"Normal"
"Long"
"Manual"
Remote command:
[SENSe:]PMETer<p>:MTIMe on page 209
[SENSe:]PMETer<p>:MTIMe:AVERage[:STATe] on page 210
Stationary signals with high power (> -40dBm), because they require
only a short measurement time and short measurement time provides
the highest repetition rates.
Signals with lower power or modulated signals
Signals at the lower end of the measurement range (<-50 dBm) or
Signals with lower power to minimize the influence of noise
Manual averaging mode. The average count is set with the Average
Count (Number of Readings) setting.
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Setting the Reference Level from the Measurement Meas -> Ref
Sets the currently measured power as a reference value for the relative display. The
reference value can also be set manually via the Reference Value setting.
Remote command:
CALCulate<n>:PMETer<p>:RELative[:MAGNitude]:AUTO ONCE on page 207
Reference Value
Defines the reference value in dBm used for relative power meter measurements.
Remote command:
CALCulate<n>:PMETer<p>:RELative[:MAGNitude] on page 206
Use Ref Level Offset
If activated, takes the reference level offset defined for the analyzer into account for the
measured power.
If deactivated, takes the Sensor Level Offset into account.
Remote command:
[SENSe:]PMETer<p>:ROFFset[:STATe] on page 210
Sensor Level Offset
Takes the specified offset into account for the measured power. Only available if Use
Ref Level Offset is disabled.
Remote command:
[SENSe:]PMETer<p>:SOFFset on page 211
3.1 I/Q measurement (modulation accuracy)
Average Count (Number of Readings)
Defines the number of readings (averages) to be performed after a single sweep has
been started. This setting is only available if manual averaging is selected (Meas Time/
Average setting).
The values for the average count range from 0 to 256 in binary steps (1, 2, 4, 8, …).
For average count = 0 or 1, one reading is performed. The general averaging and
sweep count for the trace are independent from this setting.
Results become more stable with extended average, particularly if signals with low
power are measured. This setting can be used to minimize the influence of noise in the
power sensor measurement.
Remote command:
[SENSe:]PMETer<p>:MTIMe:AVERage:COUNt on page 210
Duty Cycle
Sets the duty cycle to a percent value for the correction of pulse-modulated signals and
activates the duty cycle correction. With the correction activated, the sensor calculates
the signal pulse power from this value and the mean power.
Remote command:
[SENSe:]PMETer<p>:DCYCle[:STATe] on page 208
[SENSe:]PMETer<p>:DCYCle:VALue on page 208
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Using the power sensor as an external trigger
If activated, the power sensor creates a trigger signal when a power higher than the
defined "External Trigger Level" is measured. This trigger signal can be used as an
external power trigger by the R&S FSW.
This setting is only available in conjunction with a compatible power sensor.
Remote command:
[SENSe:]PMETer<p>:TRIGger[:STATe] on page 214
TRIG:SOUR PSE, see TRIGger[:SEQuence]:SOURce on page 234
External Trigger Level ← Using the power sensor as an external trigger
Defines the trigger level for the power sensor trigger.
For details on supported trigger levels, see the data sheet.
Remote command:
[SENSe:]PMETer<p>:TRIGger:LEVel on page 214
Hysteresis ← Using the power sensor as an external trigger
Defines the distance in dB to the trigger level that the trigger source must exceed
before a trigger event occurs. Setting a hysteresis avoids unwanted trigger events
caused by noise oscillation around the trigger level.
Remote command:
[SENSe:]PMETer<p>:TRIGger:HYSTeresis on page 213
3.1 I/Q measurement (modulation accuracy)
Trigger Holdoff ← Using the power sensor as an external trigger
Defines the minimum time (in seconds) that must pass between two trigger events.
Trigger events that occur during the holdoff time are ignored.
Remote command:
[SENSe:]PMETer<p>:TRIGger:HOLDoff on page 213
Drop-Out Time ← Using the power sensor as an external trigger
Defines the time the input signal must stay below the trigger level before triggering
again.
Slope ← Using the power sensor as an external trigger
Defines whether triggering occurs when the signal rises to the trigger level or falls
down to it.
Remote command:
[SENSe:]PMETer<p>:TRIGger:SLOPe on page 214
5.3.3.3 Output settings
Access: [Input/Output] > "Output"
The R&S FSW can provide output to special connectors for other devices.
For details on connectors, refer to the R&S FSW Getting Started manual, "Front / Rear
Panel View" chapters.
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How to provide trigger signals as output is described in detail in the R&S FSW User
Manual.
3.1 I/Q measurement (modulation accuracy)
Data Output...................................................................................................................92
Noise Source Control....................................................................................................93
Data Output
Defines the type of signal available at one of the output connectors of the R&S FSW.
"IF"
"2ND IF"
Remote command:
OUTPut<up>:IF[:SOURce] on page 218
OUTPut<up>:IF:IFFRequency on page 218
The measured IF value is provided at the IF/VIDEO/DEMOD output
connector.
For bandwidths up to 80 MHZ, the IF output is provided at the speci-
fied "IF Out Frequency".
If an optional bandwidth extension R&S FSW-B160/-B320/-B512 is
used, the measured IF value is available at the "IF WIDE OUTPUT"
connector. The frequency at which this value is output is determined
automatically. It is displayed as the "IF Wide Out Frequency". For
details on the used frequencies, see the data sheet.
This setting is not available for bandwidths larger than 512 MHz.
The measured IF value is provided at the "IF OUT 2 GHz/ IF OUT
5 GHz " output connector, if available, at a frequency of 2 GHz and
with a bandwidth of 2 GHz. The availability of this connector depends
on the instrument model.
This setting is not available if the optional 2 GHz / 5 GHz bandwidth
extension (R&S FSW-B2000/B5000) is active.
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Noise Source Control
Enables or disables the 28 V voltage supply for an external noise source connected to
the "Noise source control / Power sensor") connector. By switching the supply voltage
for an external noise source on or off in the firmware, you can enable or disable the
device as required.
External noise sources are useful when you are measuring power levels that fall below
the noise floor of the R&S FSW itself, for example when measuring the noise level of
an amplifier.
In this case, you can first connect an external noise source (whose noise power level is
known in advance) to the R&S FSW and measure the total noise power. From this
value, you can determine the noise power of the R&S FSW. Then when you measure
the power level of the actual DUT, you can deduct the known noise level from the total
power to obtain the power level of the DUT.
Remote command:
DIAGnostic:SERVice:NSOurce on page 218
5.3.3.4 Frequency settings
Access: "Overview" > "Input/Frontend" > "Frequency"
DOCSIS
3.1 I/Q measurement (modulation accuracy)
Center Frequency......................................................................................................... 93
Center Frequency Stepsize...........................................................................................94
Frequency Offset...........................................................................................................94
Center Frequency
Defines the center frequency of the signal in Hertz.
The center frequency of the complete signal depends on the center frequency of the
subcarrier 0 of the OFDM channel (f
), which defines the beginning of the OFDM
sc0
spectrum. If the OFDM Spectrum Location is changed, then the general center frequency is also changed, and vice versa.
Remote command:
[SENSe:]FREQuency:CENTer on page 219
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Center Frequency Stepsize
Defines the step size by which the center frequency is increased or decreased using
the arrow keys.
When you use the rotary knob the center frequency changes in steps of only 1/10 of
the span.
The step size can be coupled to another value or it can be manually set to a fixed
value.
"= Center"
"Manual"
Remote command:
[SENSe:]FREQuency:CENTer:STEP on page 219
Frequency Offset
Shifts the displayed frequency range along the x-axis by the defined offset.
This parameter has no effect on the instrument's hardware, on the captured data, or on
data processing. It is simply a manipulation of the final results in which absolute frequency values are displayed. Thus, the x-axis of a spectrum display is shifted by a
constant offset if it shows absolute frequencies. However, if it shows frequencies relative to the signal's center frequency, it is not shifted.
A frequency offset can be used to correct the display of a signal that is slightly distorted
by the measurement setup, for example.
The allowed values range from -1 THz to 1 THz. The default setting is 0 Hz.
Remote command:
[SENSe:]FREQuency:OFFSet on page 220
Configuration
DOCSIS 3.1 I/Q measurement (modulation accuracy)
Sets the step size to the value of the center frequency. The used
value is indicated in the "Value" field.
Defines a fixed step size for the center frequency. Enter the step size
in the "Value" field.
5.3.3.5 Amplitude settings
Access: "Overview" > "Input/Frontend" > "Amplitude"
Amplitude settings determine how the R&S FSW must process or display the expected
input power levels.
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3.1 I/Q measurement (modulation accuracy)
Reference Level Settings..............................................................................................95
└ Reference Level Mode....................................................................................96
└ Reference Level..............................................................................................96
└ Shifting the Display (Offset)............................................................................ 96
└ Unit..................................................................................................................96
└ Setting the Reference Level Automatically (Auto Level).................................97
RF Attenuation.............................................................................................................. 97
└ Attenuation Mode / Value................................................................................97
Using Electronic Attenuation.........................................................................................97
Input Settings................................................................................................................ 98
└ Preamplifier.....................................................................................................98
└ Ext. PA Correction...........................................................................................99
Reference Level Settings
The reference level defines the expected maximum signal level. Signal levels above
this value may not be measured correctly, which is indicated by the "IF OVLD" status
display.
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Reference Level Mode ← Reference Level Settings
By default, the reference level is automatically adapted to its optimal value for the current input data (continuously). At the same time, the internal attenuators and the preamplifier are adjusted so the signal-to-noise ratio is optimized, while signal compression, clipping and overload conditions are minimized.
In order to define the reference level manually, switch to "Manual" mode. In this case
you must define the following reference level parameters.
Remote command:
CONF:POW:AUTO ON, see CONFigure:POWer:AUTO on page 221
Reference Level ← Reference Level Settings
Defines the expected maximum signal level. Signal levels above this value may not be
measured correctly, which is indicated by the "IF OVLD" status display.
This value is overwritten if "Auto Level" mode is turned on.
Remote command:
DISPlay[:WINDow<n>][:SUBWindow<w>]:TRACe<t>:Y[:SCALe]:RLEVel
on page 222
Shifting the Display (Offset) ← Reference Level Settings
Defines an arithmetic level offset. This offset is added to the measured level irrespective of the selected unit. The scaling of the y-axis is changed accordingly.
Define an offset if the signal is attenuated or amplified before it is fed into the
R&S FSW so the application shows correct power results. All displayed power level
results will be shifted by this value.
Note, however, that the Reference Level value ignores the "Reference Level Offset". It
is important to know the actual power level the R&S FSW must handle.
3.1 I/Q measurement (modulation accuracy)
To determine the required offset, consider the external attenuation or gain applied to
the input signal. A positive value indicates that an attenuation took place (R&S FSW
increases the displayed power values) , a negative value indicates an external gain
(R&S FSW decreases the displayed power values).
The setting range is ±200 dB in 0.01 dB steps.
Remote command:
DISPlay[:WINDow<n>][:SUBWindow<w>]:TRACe<t>:Y[:SCALe]:RLEVel:
OFFSet on page 222
Unit ← Reference Level Settings
The R&S FSW measures the signal voltage at the RF input.
In the default state, the level is displayed at a power level of 1 mW (= dBm). Via the
known input impedance (50 Ω or 75 Ω, see "Impedance" on page 83), conversion to
other units is possible.
The following units are available and directly convertible:
●
dBm
●
dBmV
●
dBμV
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Remote command:
INPut<ip>:IMPedance on page 196
CALCulate<n>:UNIT:POWer on page 221
Setting the Reference Level Automatically (Auto Level) ← Reference Level Settings
Automatically determines the optimal reference level for the current input data. At the
same time, the internal attenuators and the preamplifier are adjusted so the signal-tonoise ratio is optimized, while signal compression, clipping and overload conditions are
minimized.
In order to do so, a level measurement is performed to determine the optimal reference
level.
Note that for sample rates larger than 160 MHz and active B1200 or B2001 bandwidth
extension options, auto leveling is not available.
Remote command:
[SENSe:]ADJust:LEVel on page 246
RF Attenuation
Defines the attenuation applied to the RF input.
This function is not available for input from the "Digital Baseband" interface (R&S FSW-
B17).
This function is not available for input from the "Digital Baseband" interface (R&S FSW-
B17).
3.1 I/Q measurement (modulation accuracy)
Attenuation Mode / Value ← RF Attenuation
The RF attenuation can be set automatically as a function of the selected reference
level (Auto mode). Automatic attenuation ensures that no overload occurs at the RF
Input connector for the current reference level. It is the default setting.
By default and when no (optional) electronic attenuation is available, mechanical
attenuation is applied.
In "Manual" mode, you can set the RF attenuation in 1 dB steps (down to 0 dB). Other
entries are rounded to the next integer value. The range is specified in the data sheet.
If the defined reference level cannot be set for the defined RF attenuation, the reference level is adjusted accordingly and the warning "limit reached" is displayed.
NOTICE! Risk of hardware damage due to high power levels. When decreasing the
attenuation manually, ensure that the power level does not exceed the maximum level
allowed at the RF input, as an overload can lead to hardware damage.
Remote command:
INPut<ip>:ATTenuation on page 223
INPut<ip>:ATTenuation:AUTO on page 223
Using Electronic Attenuation
If the (optional) Electronic Attenuation hardware is installed on the R&S FSW, you can
also activate an electronic attenuator.
In "Auto" mode, the settings are defined automatically; in "Manual" mode, you can
define the mechanical and electronic attenuation separately.
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For an active external frontend, electronic attenuation is not available.
Note: Electronic attenuation is not available for stop frequencies (or center frequencies
in zero span) above 15 GHz.
In "Auto" mode, RF attenuation is provided by the electronic attenuator as much as
possible to reduce the amount of mechanical switching required. Mechanical attenuation can provide a better signal-to-noise ratio, however.
When you switch off electronic attenuation, the RF attenuation is automatically set to
the same mode (auto/manual) as the electronic attenuation was set to. Thus, the RF
attenuation can be set to automatic mode, and the full attenuation is provided by the
mechanical attenuator, if possible.
The electronic attenuation can be varied in 1 dB steps. If the electronic attenuation is
on, the mechanical attenuation can be varied in 5 dB steps. Other entries are rounded
to the next lower integer value.
For the R&S FSW85, the mechanical attenuation can be varied only in 10 dB steps.
If the defined reference level cannot be set for the given attenuation, the reference
level is adjusted accordingly and the warning "limit reached" is displayed in the status
bar.
Remote command:
INPut<ip>:EATT:STATe on page 224
INPut<ip>:EATT:AUTO on page 224
INPut<ip>:EATT on page 224
3.1 I/Q measurement (modulation accuracy)
Input Settings
Some input settings affect the measured amplitude of the signal, as well.
The parameters "Input Coupling" and "Impedance" are identical to those in the "Input"
settings, see Chapter 5.3.3.1, "Input source settings", on page 81.
Preamplifier ← Input Settings
If the (optional) internal preamplifier hardware is installed, a preamplifier can be activated for the RF input signal.
You can use a preamplifier to analyze signals from DUTs with low output power.
Note: If an optional external preamplifier is activated, the internal preamplifier is auto-
matically disabled, and vice versa.
For an active external frontend, a preamplifier is not available.
For all R&S FSW models except for R&S FSW85, the following settings are available:
"Off"
"15 dB"
"30 dB"
For R&S FSW85 models, the input signal is amplified by 30 dB if the preamplifier is
activated.
Remote command:
INPut<ip>:GAIN:STATe on page 226
INPut<ip>:GAIN[:VALue] on page 226
Deactivates the preamplifier.
The RF input signal is amplified by about 15 dB.
The RF input signal is amplified by about 30 dB.
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Ext. PA Correction ← Input Settings
This function is only available if an external preamplifier is connected to the R&S FSW,
and only for frequencies above 1 GHz. For details on connection, see the preamplifier's
documentation.
Using an external preamplifier, you can measure signals from devices under test with
low output power, using measurement devices which feature a low sensitivity and do
not have a built-in RF preamplifier.
When you connect the external preamplifier, the R&S FSW reads out the touchdown
(.S2P) file from the EEPROM of the preamplifier. This file contains the s-parameters of
the preamplifier. As soon as you connect the preamplifier to the R&S FSW, the preamplifier is permanently on and ready to use. However, you must enable data correction
based on the stored data explicitly on the R&S FSW using this setting.
When enabled, the R&S FSW automatically compensates the magnitude and phase
characteristics of the external preamplifier in the measurement results. Any internal
preamplifier, if available, is disabled.
For R&S FSW85 models with two RF inputs, you can enable correction from the external preamplifier for each input individually, but not for both at the same time.
When disabled, no compensation is performed even if an external preamplifier remains
connected.
Remote command:
INPut<ip>:EGAin[:STATe] on page 225
3.1 I/Q measurement (modulation accuracy)
5.3.4 Trigger settings
Access: "Overview" > "Trigger"
or: [TRIG] > "Trigger Config"
Trigger settings determine when the R&S FSW starts to capture the input signal.
External triggers from one of the [TRIGGER INPUT/OUTPUT] connectors on the
R&S FSW are configured in a separate tab of the dialog box.
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DOCSIS
For more information on trigger settings and step-by-step instructions on configuring
triggered measurements, see the R&S FSW User Manual.
3.1 I/Q measurement (modulation accuracy)
Trigger Source Settings...............................................................................................100
└ Trigger Source.............................................................................................. 101
└ Free Run.............................................................................................101
└ External Trigger 1/2/3......................................................................... 101
└ Baseband Power................................................................................ 101
└ Digital I/Q............................................................................................102
└ IF Power............................................................................................. 102
└ RF Power............................................................................................103
└ I/Q Power............................................................................................103
└ Power Sensor..................................................................................... 103
└ Time....................................................................................................103
└ Trigger Level Mode.......................................................................................104
└ Trigger Level.................................................................................................104
└ Repetition Interval.........................................................................................104
└ Drop-Out Time.............................................................................................. 104
└ Trigger Offset................................................................................................104
└ Hysteresis..................................................................................................... 104
└ Trigger Holdoff.............................................................................................. 105
└ Slope.............................................................................................................105
Trigger 2/3...................................................................................................................105
└ Output Type.................................................................................................. 106
└ Level................................................................................................... 106
└ Pulse Length.......................................................................................106
└ Send Trigger.......................................................................................106
Trigger Source Settings
The Trigger Source settings define when data is captured.
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