Rohde & Schwarz VSE-K96 User Manual
R&S®VSE-K96
OFDM Vector Signal Analysis
Application
User Manual
(;ÚçÞ2)
1176898002
User Manual
Version 02
This manual applies to the following software, version 1.50 and later:
●
R&S®VSE Enterprise Edition base software (1320.7500.xx / 1320.7951.xx)
●
R&S®VSE Basic Edition base software (1345.1011.06)
The following software options are described:
●
R&S VSE-K96 (1320.7922.02)
© 2018 Rohde & Schwarz GmbH & Co. KG
Mühldorfstr. 15, 81671 München, Germany
Phone: +49 89 41 29 - 0
Fax: +49 89 41 29 12 164
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.
Trade names are trademarks of the owners.
1176.8980.02 | Version 02 | R&S®VSE-K96
The following abbreviations are used throughout this manual: R&S®VSE is abbreviated as R&S VSE.
R&S®VSE-K96
1.1 About this Manual......................................................................................................... 5
1.2 Typographical Conventions......................................................................................... 6
2.1 Introduction to Vector Signal Analysis....................................................................... 7
2.2 Starting the R&S VSE OFDM VSA application........................................................... 8
2.3 Understanding the Display Information......................................................................9
3.1 OFDM VSA Parameters...............................................................................................12
Contents
Contents
1 Preface.................................................................................................... 5
2 Welcome to the OFDM Vector Signal Analysis (VSA) Application
................................................................................................................. 7
3 OFDM VSA Measurement and Results...............................................12
3.2 Evaluation Methods for OFDM VSA Measurements................................................ 13
4 Measurement Basics........................................................................... 27
4.1 General Information on OFDM Signals..................................................................... 27
4.2 Signal Processing....................................................................................................... 34
5 Configuring OFDM VSA Measurements.............................................38
5.1 Configuration Overview..............................................................................................38
5.2 Signal Description.......................................................................................................40
5.3 Input and Frontend Settings...................................................................................... 43
5.4 Trigger Settings...........................................................................................................58
5.5 Data Acquisition..........................................................................................................61
5.6 Burst Search................................................................................................................64
5.7 Result Ranges............................................................................................................. 64
5.8 Synchronization, Demodulation and Tracking.........................................................65
5.9 Adjusting Settings Automatically..............................................................................69
6 Creating a Configuration File Using the R&S VSE-K96 Configura-
tion File Wizard.....................................................................................72
6.1 Understanding the R&S VSE-K96 Configuration File Wizard Display....................73
6.2 Configuration Steps....................................................................................................79
6.3 Reference of Wizard Menu Functions....................................................................... 86
6.4 Example: Creating a Configuration File from an Input Signal................................ 89
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7.1 Result Configuration...................................................................................................97
7.2 Table Configuration.....................................................................................................99
7.3 Units........................................................................................................................... 100
7.4 Y-Scaling....................................................................................................................100
7.5 Markers...................................................................................................................... 102
7.6 Trace Settings............................................................................................................108
7.7 Trace / Data Export Configuration...........................................................................109
9.1 Introduction............................................................................................................... 114
Contents
7 Analyzing OFDM Vector Signals.........................................................97
8 How to Perform Measurements in the R&S VSE OFDM VSA applica-
tion.......................................................................................................112
9 Remote Commands for OFDM VSA..................................................114
9.2 Common Suffixes......................................................................................................119
9.3 Activating OFDM VSA Measurements.....................................................................119
9.4 Configuring OFDM VSA............................................................................................120
9.5 Analysis..................................................................................................................... 158
9.6 Configuring the Result Display................................................................................182
9.7 Retrieving Results.....................................................................................................192
9.8 Status Reporting System......................................................................................... 215
9.9 Deprecated Commands............................................................................................ 218
9.10 Programming Examples: OFDM Vector Signal Analysis.......................................220
Annex.................................................................................................. 224
A Menu Reference................................................................................. 225
A.1 Common R&S VSE Menus....................................................................................... 225
A.2 OFDM Vector Signal Analysis Menus......................................................................227
B Reference of Toolbar Functions....................................................... 230
C Formulae.............................................................................................234
C.1 Error Vector Magnitude (EVM)................................................................................. 234
C.2 I/Q Impairments......................................................................................................... 235
List of Remote Commands (OFDM VSA)......................................... 236
Index....................................................................................................241
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1 Preface
1.1 About this Manual
Preface
About this Manual
This R&S VSE OFDM VSA User Manual provides all the information specific to the
application. All general software functions and settings common to all applications
and operating modes are described in the R&S VSE Base Software User Manual.
The main focus in this manual is on the measurement results and the tasks required to
obtain them. The following topics are included:
●
Welcome to the R&S VSE OFDM VSA application Application
Introduction to and getting familiar with the application
●
Measurements and Result Displays
Details on supported measurements and their result types
●
Measurement Basics
Background information on basic terms and principles in the context of the measurement
●
Configuration + Analysis
A concise description of all functions and settings available to configure measurements and analyze results with their corresponding remote control command
●
How to Perform Measurements in the R&S VSE OFDM VSA application Application
The basic procedure to perform each measurement and step-by-step instructions
for more complex tasks or alternative methods
●
Measurement Examples
Detailed measurement examples to guide you through typical measurement scenarios and allow you to try out the application immediately
●
Optimizing and Troubleshooting the Measurement
Hints and tips on how to handle errors and optimize the measurement configuration
●
Remote Commands for R&S VSE OFDM VSA application Measurements
Remote commands required to configure and perform R&S VSE OFDM VSA application measurements in a remote environment, sorted by tasks
(Commands required to set up the environment or to perform common tasks in the
software are provided in the R&S VSE Base Software User Manual)
Programming examples demonstrate the use of many commands and can usually
be executed directly for test purposes
●
Annex
Reference material
●
List of remote commands
Alphabetical list of all remote commands described in the manual
●
Index
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1.2 Typographical Conventions
Preface
Typographical Conventions
The following text markers are used throughout this documentation:
Convention Description
"Graphical user interface elements"
[Keys] Key and knob names are enclosed by square brackets.
File names, commands,
program code
Input Input to be entered by the user is displayed in italics.
Links Links that you can click are displayed in blue font.
"References" References to other parts of the documentation are enclosed by quota-
All names of graphical user interface elements on the screen, such as
dialog boxes, menus, options, buttons, and softkeys are enclosed by
quotation marks.
File names, commands, coding samples and screen output are distinguished by their font.
tion marks.
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2 Welcome to the OFDM Vector Signal Analy-
Welcome to the OFDM Vector Signal Analysis (VSA) Application
Introduction to Vector Signal Analysis
sis (VSA) Application
The R&S VSE OFDM VSA application performs vector and scalar measurements on
digitally modulated OFDM signals. To perform the measurements it converts RF signals into the complex baseband.
The R&S VSE OFDM VSA application features:
●
Analysis of non-standard and standard-conform OFDM systems
●
I/Q-based measurement results such as EVM, constellation diagrams, power spectrum
This user manual contains a description of the functionality that the application provides, including remote control operation.
Functions that are not discussed in this manual are the same as in the I/Q Analyzer
application and are described in the R&S VSE base software user manual. The latest
version is available for download at the product homepage http://www.rohde-
schwarz.com/product/VSE.html.
● Introduction to Vector Signal Analysis.......................................................................7
● Starting the R&S VSE OFDM VSA application......................................................... 8
● Understanding the Display Information.....................................................................9
2.1 Introduction to Vector Signal Analysis
The goal of vector signal analysis is to determine the quality of the signal that is transmitted by the device under test (DUT) by comparing it against an ideal signal. The DUT
is usually connected with the analyzer via a cable. The key task of the analyzer is to
determine the ideal signal. Hence, the analyzer aims to reconstruct the ideal signal
from the measured signal that is transmitted by the DUT. This ideal signal is commonly
referred to as the reference signal, while the signal from the DUT is called the mea-
surement signal.
After extracting the reference signal, the R&S VSE OFDM VSA application compares
the measurement signal and the reference signal, and the results of this comparison
are displayed.
Example:
The most common vector signal analysis measurement is the EVM (Error Vector Magnitude) measurement. Here, the complex baseband reference signal is subtracted from
the complex baseband measurement signal. The magnitude of this error vector represents the EVM value. The EVM has the advantage that it "summarizes" all potential
errors and distortions in one single value. If the EVM value is low, the signal quality of
the DUT is high.
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2.2 Starting the R&S VSE OFDM VSA application
Welcome to the OFDM Vector Signal Analysis (VSA) Application
Starting the R&S VSE OFDM VSA application
Figure 2-1: Simplified schema of vector signal analysis
OFDM Vector Signal Analysis is a separate application on the R&S VSE. It is activated
by creating a new measurement channel in OFDM VSA mode.
To activate the R&S VSE OFDM VSA application
1.
Select the "Add Channel" function in the Sequence tool window.
A dialog box opens that contains all operating modes and applications currently
available in your R&S VSE.
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Welcome to the OFDM Vector Signal Analysis (VSA) Application
Understanding the Display Information
2. Select the "OFDM VSA" item.
The R&S VSE opens a new measurement channel for the R&S VSE OFDM VSA
application.
2.3 Understanding the Display Information
The following figure shows a measurement diagram during analyzer operation. All different information areas are labeled. They are explained in more detail in the following
sections.
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Welcome to the OFDM Vector Signal Analysis (VSA) Application
Understanding the Display Information
1
2
1
1 = Color coding for windows of same channel
2 = Channel bar with measurement settings
3 = Window title bar with diagram-specific (trace) information
4 = Diagram area
5 = Diagram footer with diagram-specific information, depending on result display
3
4
5
Channel bar information
In the R&S VSE OFDM VSA application, the R&S VSE shows the following settings:
Table 2-1: Information displayed in the channel bar in R&S VSE OFDM VSA application application
Ref Level Reference level
Att Mechanical and electronic RF attenuation
Freq Center frequency for the RF signal
Offset Reference level offset
SRate Sample Rate
Config Currently loaded configuration file
Capture Time How long data was captured in current sweep
FFT FFT size
CP Length Cyclic prefix length
Trigger to Frame Offset between the trigger event and the start of the OFDM frame
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. transducer or trigger settings). This information is displayed only when applicable for the current measurement. For details see the
R&S VSE Base Software User Manual.
Window title bar information
For each diagram, the header provides the following information:
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Welcome to the OFDM Vector Signal Analysis (VSA) Application
Understanding the Display Information
0
21 64 75
Figure 2-2: Window title bar information in R&S VSE OFDM VSA application
0 = Color coding for windows of same channel
1 = Edit result display function
2 = Channel name
3 = Window number
4 = Window type
5 = Trace color, trace number, trace mode
6 = Dock/undock window function
7 = Close window function
3
Diagram area
The diagram area displays the results according to the selected result displays (see
Chapter 3.2, "Evaluation Methods for OFDM VSA Measurements", on page 13).
Diagram footer information
The diagram footer (beneath the diagram) contains the start and stop symbols or time
of the evaluation range.
Status bar information
The software status, errors and warnings and any irregularities in the software are indicated in the status bar at the bottom of the R&S VSE window.
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3 OFDM VSA Measurement and Results
OFDM VSA Measurement and Results
OFDM VSA Parameters
For each measurement, a separate measurement channel is activated. Each measurement channel can provide multiple result displays, which are displayed in individual
windows. The measurement windows can be rearranged and configured in the
R&S VSE to meet your requirements. All windows that belong to the same measurement (including the channel bar) are indicated by a colored line at the top of the window title bar.
To add further result displays for the OFDM VSA channel
►
Select the
"Add Window" icon from the toolbar, or select the "Window > New
Window" menu item.
For details on working with channels and windows, see the "Operating Basics" chapter
in the R&S VSE base software user manual.
● OFDM VSA Parameters..........................................................................................12
● Evaluation Methods for OFDM VSA Measurements...............................................13
3.1 OFDM VSA Parameters
Several signal parameters are determined during vector signal analysis and displayed
in the Result Summary.
For details concerning the calculation of individual parameters, see Chapter C, "Formu-
lae", on page 234.
Table 3-1: OFDM VSA parameters
Parameter Description SCPI Parameter
EVM All [%/dB] Error Vector Magnitude of the payload symbols over all carri-
ers (except the guard carriers)
EVM Data Symbols
[%/dB]
Error Vector Magnitude of the payload symbols over all data
carriers
EVM[:ALL]
EVM:DATA
EVM Pilot Symbols
[%/dB]
MER [dB] Average Modulation Error Ratio (MER) for all data and all
I/Q offset [dB] Transmitter center frequency leakage relative to the total Tx
Gain imbalance
[%/dB]
*) Required to retrieve the parameter result, see FETCh:SUMM:<parameter>:<statistic>
on page 196
Error Vector Magnitude of the payload symbols over all pilot
carriers
pilot cells of the analyzed frames. The MER is the ratio of the
RMS power of the ideal reference signal to the RMS power
of the error vector.
channel power
Amplification of the quadrature phase component of the signal relative to the amplification of the in-phase component
EVM:PILot
MER[:ALL]
IQOFset
GIMBalance
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Parameter Description SCPI Parameter
Quadrature error [°] Phase angle between Q-channel and I-channel deviating
from the ideal 90 degrees; measure for crosstalk from the Qbranch into the I-branch
Frequency Error [Hz] Frequency error between the signal and the currently defined
center frequency
The absolute frequency error includes the frequency error of
the connected instrument and that of the DUT. If possible,
the transmitter connected instrument and the DUT should be
synchronized (using an external reference).
See R&S VSE base software user manual > "Configuring
Instruments"
Sample Clock Error Clock error between the signal and the sample clock of the
R&S VSE in parts per million (ppm), i.e. the symbol timing
error
If possible, the transmitter connected instrument and the
DUT should be synchronized (using an external reference).
See R&S VSE base software user manual > "Configuring
Instruments"
Frame Power Average time domain power of the analyzed frame
Crest factor [dB] The ratio of the peak power to the mean power of the ana-
lyzed frame.
Trigger to Frame [s] (Displayed in channel bar only, not included in Result Sum-
mary.)
The time offset between the trigger event and the start of the
first OFDM frame
QUADerror
FERRor
SERRor
POWer
CRESt
FETCh:TTFRame?
*) Required to retrieve the parameter result, see FETCh:SUMM:<parameter>:<statistic>
on page 196
The R&S VSE OFDM VSA application also performs statistical evaluation over several
frames and displays the following results:
Table 3-2: Calculated summary results
Result type Description
Min Minimum measured value
Average Average measured value
Max Maximum measured value
3.2 Evaluation Methods for OFDM VSA Measurements
The data that was measured by the R&S VSE can be evaluated using various different
methods without having to start a new measurement. Which results are displayed
depends on the selected evaluation.
The OFDM VSA measurement provides the following evaluation methods:
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Allocation Matrix............................................................................................................14
CCDF............................................................................................................................ 15
Channel Flatness.......................................................................................................... 15
Constellation Diagram...................................................................................................16
Constellation vs Carrier.................................................................................................17
Constellation vs Symbol................................................................................................17
EVM vs Carrier..............................................................................................................18
EVM vs Symbol.............................................................................................................18
EVM vs Symbol vs Carrier............................................................................................ 19
Group Delay..................................................................................................................20
Impulse Response........................................................................................................ 20
Magnitude Capture........................................................................................................21
Marker Table ................................................................................................................ 21
Power vs Carrier........................................................................................................... 22
Power vs Symbol.......................................................................................................... 22
Power vs Symbol vs Carrier..........................................................................................23
Power Spectrum............................................................................................................24
Result Summary............................................................................................................24
Signal Flow....................................................................................................................25
Allocation Matrix
The Allocation Matrix display is a graphical representation of the OFDM cell structure
defined in the currently loaded configuration file. Use markers to get more detailed
information on the individual cells.
Figure 3-1: Allocation Matrix
The legend for the color coding is displayed at the top of the matrix.
Remote command:
LAY:ADD? '1',RIGH,AMATrix, see LAYout:ADD[:WINDow]? on page 186
TRACe<n>[:DATA]? on page 205, see Chapter 9.7.4.1, "Allocation Matrix",
on page 209
TRACe<n>[:DATA]:X? on page 205
TRACe<n>[:DATA]:Y? on page 206
Symbol unit: UNIT:SAXes on page 166
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CCDF
The CCDF results display shows the probability of an amplitude exceeding the mean
power. The x-axis displays power relative to the measured mean power.
Figure 3-2: CCDF display
Remote command:
LAY:ADD? '1',RIGH,CCDF, see LAYout:ADD[:WINDow]? on page 186
TRACe:DATA?, see Chapter 9.7.4.2, "CCDF", on page 210
TRACe<n>[:DATA]:X? on page 205
Channel Flatness
The Channel Flatness display shows the amplitude of the channel transfer function vs.
carrier. The statistic is performed over all analyzed frames.
Figure 3-3: Channel Flatness Display
Remote command:
LAY:ADD? '1',RIGH,CHFL, see LAYout:ADD[:WINDow]? on page 186
TRACe:DATA?, see Chapter 9.7.4.3, "Channel Flatness", on page 210
TRACe<n>[:DATA]:X? on page 205
Carrier unit: UNIT:CAXes on page 164
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Constellation Diagram
The Constellation Diagram shows the inphase and quadrature results for the analyzed
input data. The ideal points for the selected cell types are displayed for reference purposes.
Figure 3-4: Constellation diagram
The legend for the color coding is displayed at the top of the matrix. If you click on one
of the codes, only the selected constellation points are displayed. Click again, and all
constellation points are displayed again (according to the constellation filter, see Chap-
ter 7.1, "Result Configuration", on page 97).
Markers in the Constellation diagram
Using markers you can detect individual constellation points for a specific symbol or
carrier. When you activate a marker in the Constellation diagram, its position is defined
by the symbol and carrier number the point belongs to, while the marker result indicates the I and Q values of the point.
Figure 3-5: Marker in a Constellation diagram
Remote command:
LAY:ADD? '1',RIGH,CONS, see LAYout:ADD[:WINDow]? on page 186
TRACe:DATA?, see Chapter 9.7.4.4, "Constellation Diagram", on page 210
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Marker I/Q values:
CALCulate<n>:MARKer<m>:Z? on page 202
Constellation vs Carrier
The Constellation vs. Carrier display shows the inphase and quadrature magnitude
results of all analyzed symbols over the corresponding carriers. The inphase values
are displayed as yellow dots; the quadrature-values are displayed as blue dots.
Figure 3-6: Constellation vs. Carrier display
Note: This result display is only available if synchronization is successful.
Remote command:
LAY:ADD? '1',RIGH,CCAR, see LAYout:ADD[:WINDow]? on page 186
TRACe:DATA?, see Chapter 9.7.4, "Using the TRACe[:DATA] Command",
on page 208
Carrier unit: UNIT:CAXes on page 164
Constellation vs Symbol
The Constellation vs. Symbol display shows the inphase and quadrature magnitude
results of all analyzed carriers over the corresponding symbols. The inphase values
are displayed as yellow dots; the quadrature-values are displayed as blue dots.
Figure 3-7: Constellation vs. Symbol display
Note: This result display is only available if synchronization is successful.
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Remote command:
LAY:ADD? '1',RIGH,CSYM, see LAYout:ADD[:WINDow]? on page 186
TRACe:DATA?, see Chapter 9.7.4, "Using the TRACe[:DATA] Command",
on page 208
Symbol unit: UNIT:SAXes on page 166
EVM vs Carrier
The EVM vs Carrier display shows the EVM of each carrier of the analyzed signal
frames in the frequency domain. The results are provided in dB. Multiple traces display
statistical evaluations over carriers.
Figure 3-8: EVM vs Carrier display
Note: This result display is only available if synchronization is successful.
Guard carriers to the left and right of the spectrum are not included in the EVM calculation. However, zero cells and the DC carrier are included.
Remote command:
LAY:ADD? '1',RIGH,EVC, see LAYout:ADD[:WINDow]? on page 186
TRACe:DATA?, see Chapter 9.7.4.7, "EVM vs Carrier", on page 212
TRACe<n>[:DATA]:X? on page 205
Carrier unit: UNIT:CAXes on page 164
EVM unit: UNIT:EVM on page 165
EVM vs Symbol
The EVM vs. Symbol display shows the EVM of each symbol of the analyzed signal
frames in the time domain. The results are provided in dB. Multiple traces display statistical evaluations over symbols.
Blue lines indicate the border between different OFDM frames if more than one frame
is analyzed.
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Figure 3-9: EVM vs Symbol display
Note: This result display is only available if synchronization is successful.
Guard carriers to the left and right of the spectrum are not included in the EVM calculation. However, zero cells and the DC carrier are included.
Remote command:
LAY:ADD? '1',RIGH,EVSY, see LAYout:ADD[:WINDow]? on page 186
TRACe:DATA?, see Chapter 9.7.4.8, "EVM vs Symbol", on page 212
TRACe<n>[:DATA]:X? on page 205
Symbol unit: UNIT:SAXes on page 166
EVM unit: UNIT:EVM on page 165
EVM vs Symbol vs Carrier
The EVM vs Symbol vs Carrier display shows the EVM of each carrier (frequency
domain) and in each symbol (time domain) of the analyzed signal frames. The results
are provided in dB or percent, depending on the unit settings.
Figure 3-10: EVM vs Symbol vs Carrier display
The EVM values are represented by colors. The corresponding color map is displayed
at the top of the result display.
Note: This result display is only available if synchronization is successful.
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Remote command:
LAY:ADD? '1',RIGH,EVSC, see LAYout:ADD[:WINDow]? on page 186
TRACe:DATA?, see Chapter 9.7.4.9, "EVM vs Symbol vs Carrier", on page 212
TRACe<n>[:DATA]:X? on page 205
TRACe<n>[:DATA]:Y? on page 206
Carrier unit: UNIT:CAXes on page 164
Symbol unit: UNIT:SAXes on page 166
EVM unit: UNIT:EVM on page 165
Group Delay
The Group Delay display shows the relative group delay of the transmission channel
per carrier. Multiple traces display statistical evaluations over all analyzed frames.
Remote command:
LAY:ADD? '1',RIGH,GDEL, see LAYout:ADD[:WINDow]? on page 186
TRACe:DATA?, see Chapter 9.7.4.11, "Group Delay", on page 213
TRACe<n>[:DATA]:X? on page 205
Carrier unit: UNIT:CAXes on page 164
Impulse Response
The Channel Impulse Response display shows the impulse response of the channel
and its position within the guard interval. The start and the end of the cyclic prefix are
marked with blue lines. Multiple traces display statistical evaluations over all analyzed
frames.
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Figure 3-11: Channel Impulse Response Display
Remote command:
LAY:ADD? '1',RIGH,IRES, see LAYout:ADD[:WINDow]? on page 186
TRACe:DATA?, see Chapter 9.7.4.12, "Impulse Response", on page 213
TRACe<n>[:DATA]:X? on page 205
Linear/ logarithmic scaling: UNIT:IRESponse on page 166
Magnitude Capture
The capture buffer contains the complete range of captured data for the last sweep.
The Magnitude Capture display shows the power of the captured I/Q data in dBm versus time. The analyzed frames are identified with a green bar at the bottom of the Magnitude Capture display.
Figure 3-12: Magnitude Capture display
Remote command:
LAY:ADD? '1',RIGH,MCAP, see LAYout:ADD[:WINDow]? on page 186
TRACe:DATA?, see Chapter 9.7.4.13, "Magnitude Capture", on page 214
TRACe<n>[:DATA]:X? on page 205
Time unit: UNIT:TAXes on page 166
Marker Table
Displays a table with the current marker values for the active markers.
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Remote command:
LAY:ADD? '1',RIGH, MTAB, see LAYout:ADD[:WINDow]? on page 186
Results:
CALCulate<n>:MARKer<m>:X on page 171
CALCulate<n>:MARKer<m>:Y on page 202
Power vs Carrier
The Power vs. Carrier display shows the power of all OFDM symbols in the analyzed
signal frames for each carrier. The power is measured with a resolution bandwidth
equal to the carrier spacing. Multiple traces display statistical evaluations over all analyzed frames.
Figure 3-13: Power vs Carrier display
Note:
This result display is only available if synchronization is successful.
Remote command:
LAY:ADD? '1',RIGH,PCAR, see LAYout:ADD[:WINDow]? on page 186
TRACe:DATA?, see Chapter 9.7.4.14, "Power vs Carrier", on page 214
TRACe<n>[:DATA]:X? on page 205
Carrier unit: UNIT:CAXes on page 164
Power vs Symbol
The Power vs Symbol display shows the power of all OFDM carriers in the analyzed
signal frames for each symbol. The power is measured with a resolution bandwidth
equal to the carrier spacing. Multiple traces display statistical evaluations over all analyzed frames. Carriers which contain 'Zero'-cells over the complete symbol range (e.g.
guard carriers or DC carrier) are excluded from the statistic.
Vertical blue lines indicate the borders between frames.
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Figure 3-14: Power vs Symbol display
Note: This result display is only available if synchronization is successful.
Remote command:
LAY:ADD? '1',RIGH,PSYM, see LAYout:ADD[:WINDow]? on page 186
TRACe:DATA?, see Chapter 9.7.4.15, "Power vs Symbol", on page 214
TRACe<n>[:DATA]:X? on page 205
Symbol unit: UNIT:SAXes on page 166
Power vs Symbol vs Carrier
The Power vs Carrier vs Symbol display shows the power of each carrier (= frequency
domain) in each symbol (= time domain) of the analyzed signal frames in dBm. The
power is measured with a resolution bandwidth that equals the carrier spacing.
Figure 3-15: Power vs Symbol vs Carrier display
The power levels are represented by colors. The corresponding color map is displayed
at the top of the result display.
Note: This result display is only available if synchronization is successful.
Remote command:
LAY:ADD? '1',RIGH,PSC, see LAYout:ADD[:WINDow]? on page 186
TRACe:DATA?, see Chapter 9.7.4.16, "Power vs Symbol vs Carrier", on page 214
TRACe<n>[:DATA]:X? on page 205
TRACe<n>[:DATA]:Y? on page 206
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OFDM VSA Measurement and Results
Evaluation Methods for OFDM VSA Measurements
Carrier unit: UNIT:CAXes on page 164
Symbol unit: UNIT:SAXes on page 166
Power Spectrum
The Power Spectrum display shows the power in dBm vs frequency results of the complete capture buffer. This display is always available.
Figure 3-16: Power Spectrum display
Remote command:
LAY:ADD? '1',RIGH,PSP, see LAYout:ADD[:WINDow]? on page 186
TRACe:DATA?, see Chapter 9.7.4.17, "Power Spectrum", on page 215
Frequency unit: UNIT:FAXes on page 165
Result Summary
The Result Summary table provides numerical measurement results. Statistical evaluation is performed over all analyzed frames within the capture buffer.
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Evaluation Methods for OFDM VSA Measurements
Figure 3-17: Result Summary display
Note: If only one frame is available for analysis, the minimum and maximum values
are not displayed, as they are identical to the average value.
For details on the individual results see Table 3-1.
Remote command:
LAY:ADD? '1',RIGH,RSUM, see LAYout:ADD[:WINDow]? on page 186
Results:
FETCh:SUMMary[:ALL]? on page 194
Signal Flow
The Signal Flow display shows a detailed description of the current measurement status. If demodulation is not successful, it provides useful hints on possible reasons.
Unused blocks are shown in gray.
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Evaluation Methods for OFDM VSA Measurements
Figure 3-18: Signal Flow display
For the synchronization blocks, a colored bar provides information about the reliability
of the synchronization result. If the level in the bar falls below the thresholds indicated
by the horizontal line, the color of the bar changes from green to yellow and finally to
red. If the synchronization of the block fails, all succeeding arrows change their color,
too.
For detailed information about the complete synchronization process, refer to Chap-
ter 4.2.2.1, "Synchronization Block", on page 35.
Remote command:
LAY:ADD? '1',RIGH,SFL, see LAYout:ADD[:WINDow]? on page 186
Retrieving results:
Chapter 9.7.2, "Retrieving Signal Flow Results", on page 196
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4 Measurement Basics
4.1 General Information on OFDM Signals
4.1.1 OFDMA
Measurement Basics
General Information on OFDM Signals
Some background knowledge on basic terms and principles used in OFDM vector signal analysis is provided here for a better understanding of the required configuration
settings.
● General Information on OFDM Signals...................................................................27
● Signal Processing................................................................................................... 34
● OFDMA................................................................................................................... 27
● OFDM Parameterization......................................................................................... 28
In an OFDM system, the available spectrum is divided into multiple carriers, called subcarriers, which are orthogonal to each other. Each of these subcarriers is independently modulated by a low rate data stream.
OFDM is used as well in WLAN, WiMAX and broadcast technologies like DVB. OFDM
has several benefits including its robustness against multipath fading and its efficient
receiver architecture.
Figure 4-1 shows a representation of an OFDM signal taken from 3GPP TR 25.892.
Data symbols are independently modulated and transmitted over a high number of
closely spaced orthogonal subcarriers. In the OFDM-VSA common modulation
schemes as QPSK, 16QAM, and 64QAM can be defined as well as arbitrary distributed constellation points.
In the time domain, a guard interval may be added to each symbol to combat interOFDM-symbol-interference due to channel delay spread. In EUTRA, the guard interval
is a cyclic prefix which is inserted prior to each OFDM symbol.
Figure 4-1: Frequency-Time Representation of an OFDM Signal
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Measurement Basics
General Information on OFDM Signals
In practice, the OFDM signal can be generated using the inverse fast Fourier transform
(IFFT) digital signal processing. The IFFT converts a number N of complex data symbols used as frequency domain bins into the time domain signal. Such an N-point IFFT
is illustrated in Figure 4-2, where a(mN+n) refers to the nth subchannel modulated data
symbol, during the time period mTu < t ≤ (m+1)Tu.
Figure 4-2: OFDM useful symbol generation using an IFFT
The vector sm is defined as the useful OFDM symbol. It is the time superposition of the
N narrowband modulated subcarriers. Therefore, from a parallel stream of N sources
of data, each one independently modulated, a waveform composed of N orthogonal
subcarriers is obtained, with each subcarrier having the shape of a frequency sinc
function (see Figure 4-1).
Figure 4-3 illustrates the mapping from a serial stream of QAM symbols to N parallel
streams, used as frequency domain bins for the IFFT. The N-point time domain blocks
obtained from the IFFT are then serialized to create a time domain signal. Not shown
in Figure 4-3 is the process of cyclic prefix insertion.
Figure 4-3: OFDM Signal Generation Chain
4.1.2 OFDM Parameterization
A generic OFDM analyzer supports various OFDM standards. Therefore a common
parameterization of OFDM systems has to be defined.
4.1.2.1 Time Domain Description
The fundamental unit of an OFDM signal in the time domain is a sample.
An OFDM symbol with a length of NS samples consists of:
●
A guard interval of length N
●
An FFT interval of length N
G
FFT
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General Information on OFDM Signals
N
G
N
Figure 4-4: OFDM symbol in time domain
4.1.2.2 Frequency Domain Description
The FFT intervals of the OFDM symbols are transformed into the frequency domain
using a discrete Fourier transformation. The successive symbols of the OFDM signal
are displayed in time-frequency matrices. The fundamental unit of an OFDM signal in
the frequency domain is a cell.
The total area of a time frequency matrix is called frame. A frame is the highest level
unit used in OFDM VSA.
N
FFT
S
Figure 4-5: Time-Frequency Matrix
Carriers
A column of cells at the same frequency is called carrier.
The carrier number is the column index of a time-frequency matrix. The number '0' is
assigned to the DC-carrier, which lies at the transmitter center frequency. The total
number of subcarriers is N
. The DC-carrier offset determines the position of the DC
FFT
carrier relative to the lowermost subcarrier. The offset is an inherent attribute of the
FFT algorithm.
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2
FFT
N
1
2
,
2
FFTFFT
NN
1
2
FFT
N
2
1
,
2
1
FFTFFT
NN
Measurement Basics
General Information on OFDM Signals
Table 4-1: Relationship between FFT length and subcarrier range
FFT Length N
even
odd
OFDM system sample rate
In an OFDM system, an FFT (with the length N
FFT bin corresponds to one subcarrier. For each FFT bin, one sample must be cap-
tured in the time domain for each OFDM symbol. The minimum number of samples
required for the measurement is thus the number of subcarriers (or the number of FFT
bins), multiplied by the number of symbols to measure. To avoid intersymbol interference, the cyclic prefix is added as the guard interval.
No_samples
Generally, the number of samples acquired per second is referred to as the sample
rate. The sample rate required by a specific OFDM system is referred to as the OFDM
system sample rate. It depends on parameters that characterize the OFDM system
and is defined by the following equation:
FFT
= (<FFT_size> + <CyclicPrefixLength>) * <No_symbols_to_measure>
min
DC-Carrier Offset Range
) is performed for each symbol. Each
FFT
SR
For the R&S VSE OFDM VSA application to demodulate OFDM symbols, it is important that the number of acquired samples in the application corresponds to the OFDM
system sample rate.
Symbols
A row of cells at the same time is called symbol.
The symbol number is the row index of a time frequency matrix. The first symbol gets
the number '0'.
Allocation Matrix
The allocation matrix defines the complete frame and subdivides the OFDM system
into the following cell types:
●
●
●
●
= <carrier_spacing>* <FFT_size>
OFDM
Pilot cells: Contain known values and are used for various synchronization and
parameter estimation purposes
Data cells: Contain the user data or "payload" of the transmission. The modulation
format of the data cells must be known or can be estimated in a modulation estimation block.
"Don't Care" cells: Cells that are not evaluated for EVM measurement, but contain signal power
Zero cells: Contain no signal power at all; Typically these are guard carriers
around DC or at the edges of the carrier axis.
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