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R&S®FSV3-K91
WLAN Measurements
User Manual
(;ÜìÅ2)
1178945502
Version 09
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This manual applies to the following R&S®FSV3000 and R&S®FSVA3000 models with firmware version
1.70 and higher:
●
R&S®FSV3004 (1330.5000K04) / R&S®FSVA3004 (1330.5000K05)
●
R&S®FSV3007 (1330.5000K07) / R&S®FSVA3007 (1330.5000K08)
●
R&S®FSV3013 (1330.5000K13) / R&S®FSVA3013 (1330.5000K14)
●
R&S®FSV3030 (1330.5000K30) / R&S®FSVA3030 (1330.5000K31)
●
R&S®FSV3044 (1330.5000K43) / R&S®FSVA3044 (1330.5000K44)
The following firmware options are described:
●
R&S FSV/A-K91 WLAN 802.11a,b,g (1330.5100.02)
●
R&S FSV/A-K91ac WLAN 802.11ac (1330.5116.02)
●
R&S FSV/A-K91ax WLAN 802.11ax (1346.339902)
●
R&S FSV/A-K91be WLAN 802.11be (1346.4966.02)
●
R&S FSV/A-K91n WLAN 802.11n (1330.5139.02)
●
R&S FSV/A-K91p WLAN 802.11p (1330.5122.02)
© 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.
Trade names are trademarks of the owners.
1178.9455.02 | Version 09 | R&S®FSV3-K91
Throughout this manual, products from Rohde & Schwarz are indicated without the ® symbol , e.g. R&S®FSV/A3000 is indicated as
R&S FSV/A3000.
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R&S®FSV3-K91
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........................................... 9
2 Welcome to the WLAN application.....................................................10
Contents
Contents
2.1 Starting the WLAN application...................................................................................11
2.2 Understanding the display information.................................................................... 11
3 Measurements and result displays.................................................... 14
3.1 WLAN I/Q measurement (modulation accuracy, flatness and tolerance).............. 14
3.2 Frequency sweep measurements..............................................................................62
4 Measurement basics............................................................................69
4.1 Signal processing for multicarrier measurements (IEEE 802.11a, g (OFDM), j, p)
...................................................................................................................................... 69
4.2 Signal processing for single-carrier measurements (IEEE 802.11b, g (DSSS)).... 76
4.3 Signal processing for MIMO measurements (IEEE IEEE 802.11 ac, ax, n, be)...... 82
4.4 Signal processing for high-efficiency wireless measurements (IEEE 802.11ax)..91
4.5 Signal processing for extremely high throughput (EHT) wireless measurements
(IEEE 802.11be)............................................................................................................96
4.6 Channels and carriers................................................................................................ 98
4.7 Recognized vs. analyzed PPDUs...............................................................................99
4.8 Demodulation parameters - logical filters................................................................ 99
4.9 I/Q data import and export....................................................................................... 101
4.10 Basics on input from I/Q data files.......................................................................... 102
4.11 Trigger basics............................................................................................................103
5 Configuration......................................................................................108
5.1 Multiple measurement channels and sequencer function.................................... 108
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5.2 Display configuration................................................................................................110
5.3 WLAN I/Q measurement configuration................................................................... 110
5.4 Frequency sweep measurements............................................................................193
6 Analysis.............................................................................................. 198
7 How to perform measurements in the WLAN application..............199
7.1 How to determine modulation accuracy, flatness and tolerance parameters for
7.2 How to analyze WLAN signals in a MIMO measurement setup............................ 200
7.3 How to determine the OBW, SEM, ACLR or CCDF for WLAN signals..................206
8 Optimizing and troubleshooting the measurement........................ 207
8.1 Optimizing the measurement results...................................................................... 207
8.2 Error messages and warnings.................................................................................208
Contents
WLAN signals............................................................................................................ 199
9 Remote commands for WLAN 802.11 measurements.................... 210
9.1 Common suffixes...................................................................................................... 210
9.2 Introduction............................................................................................................... 211
9.3 Activating WLAN 802.11 measurements.................................................................216
9.4 Selecting a measurement.........................................................................................219
9.5 Configuring the WLAN IQ measurement (modulation accuracy, flatness and toler-
ance)...........................................................................................................................226
9.6 Configuring frequency sweep measurements on WLAN 802.11 signals.............309
9.7 Configuring the result display................................................................................. 313
9.8 Starting a measurement........................................................................................... 333
9.9 Retrieving results......................................................................................................337
9.10 Analysis..................................................................................................................... 391
9.11 Status registers.........................................................................................................394
9.12 Deprecated commands.............................................................................................397
9.13 Programming examples (R&S FSV3 WLAN application).......................................401
Annex.................................................................................................. 407
A Sample rate and maximum usable I/Q bandwidth for RF input..... 407
A.1 Bandwidth extension options.................................................................................. 408
A.2 Relationship between sample rate, record length and usable I/Q bandwidth.....408
A.3 R&S FSV/A without additional bandwidth extension options...............................409
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R&S®FSV3-K91
A.4 R&S FSV/A with I/Q bandwidth extension option B40 or U40.............................. 410
A.5 R&S FSV/A with I/Q bandwidth extension option B200.........................................410
A.6 R&S FSV/A with I/Q bandwidth extension option B400.........................................411
A.7 R&S FSV/A with I/Q bandwidth extension option B600.........................................411
A.8 R&S FSV/A with I/Q bandwidth extension option B1000.......................................411
Contents
List of commands (WLAN)................................................................ 412
Index....................................................................................................422
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Contents
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1 Documentation overview
1.1 Getting started manual
Documentation overview
Service manual
This section provides an overview of the R&S FSV/A user documentation. Unless
specified otherwise, you find the documents on the R&S FSV/A product page at:
www.rohde-schwarz.com/product/FSVA3000.html/
www.rohde-schwarz.com/product/FSV3000.html
Introduces the R&S FSV/A 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.
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 FSV/A is
not included.
The contents of the user manuals are available as help in the R&S FSV/A. 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.
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1.4 Instrument security procedures
1.5 Printed safety instructions
Documentation overview
Release notes and open-source acknowledgment (OSA)
The service manual is available for registered users on the global Rohde & Schwarz
information system (GLORIS):
R&S®FSVA3000/FSV3000 Service manual
Deals with security issues when working with the R&S FSV/A in secure areas. It is
available for download on the Internet.
Provides safety information in many languages. The printed document is delivered with
the product.
1.6 Data sheets and brochures
The data sheet contains the technical specifications of the R&S FSV/A. 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/FSV3000 /
www.rohde-schwarz.com/brochure-datasheet/FSVA3000
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/FSV3000 /
www.rohde-schwarz.com/firmware/FSVA3000
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1.8 Application notes, application cards, white papers,
Documentation overview
Application notes, application cards, white papers, etc.
etc.
These documents deal with special applications or background information on particular topics.
See www.rohde-schwarz.com/application/FSV3000 /
www.rohde-schwarz.com/application/FSVA3000
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2 Welcome to the WLAN application
Welcome to the WLAN application
The R&S FSV3 WLAN application extends the functionality of the R&S FSV/A to
enable accurate and reproducible Tx measurements of a WLAN device under test
(DUT) in accordance with the standards specified for the device. The following standards are currently supported (if the corresponding firmware option is installed):
●
IEEE standards 802.11a
●
IEEE standards 802.11ac (SISO + MIMO)
●
IEEE standards 802.11b
●
IEEE standards 802.11be
●
IEEE standards 802.11g (OFDM)
●
IEEE standards 802.11g (DSSS)
●
IEEE standards 802.11j
●
IEEE standards 802.11n (SISO + MIMO)
●
IEEE standards 802.11p
●
IEEE standards 802.11ax (SISO + MIMO)
The R&S FSV3 WLAN application features:
Modulation measurements
●
"Constellation" diagram for demodulated signal
●
"Constellation" diagram for individual carriers
●
I/Q offset and I/Q imbalance
●
Modulation error (EVM) for individual carriers or symbols
●
Amplitude response and group-delay distortion (spectrum flatness)
●
Carrier and symbol frequency errors
Further measurements and results
●
Amplitude statistics ("CCDF") and crest factor
●
FFT, also over a selected part of the signal, e.g. preamble
●
Payload bit information
●
Freq/Phase Err vs. Preamble
This user manual contains a description of the functionality that is specific to the application, including remote control operation.
General R&S FSV/A functions
The application-independent functions for general tasks on the R&S FSV/A are also
available for WLAN 802.11 measurements and are described in the R&S FSV/A user
manual. In particular, this comprises the following functionality:
●
Data management
●
General software preferences and information
The latest version is available for download at the product homepage
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2.1 Starting the WLAN application
Welcome to the WLAN application
Understanding the display information
http://www.rohde-schwarz.com/product/FSV3000.html.
Installation
You can find detailed installation instructions in the R&S FSV/A Getting Started manual
or in the Release Notes.
The WLAN measurements require a special application on the R&S FSV/A.
To activate the WLAN application
1. Select the [MODE] key.
A dialog box opens that contains all operating modes and applications currently
available on your R&S FSV/A.
2. Select the "WLAN" item.
The R&S FSV/A opens a new measurement channel for the WLAN application.
The measurement is started immediately with the default settings. It can be configured
in the WLAN "Overview" dialog box, which is displayed when you select the "Overview"
softkey from any menu (see Chapter 5.3.1, "Configuration overview", on page 111).
2.2 Understanding the display information
The following figure shows a measurement diagram during analyzer operation. All
information areas are labeled. They are explained in more detail in the following sections.
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Welcome to the WLAN application
Understanding the display information
1
2
3
4
5
1 = Channel bar for firmware and measurement settings
2 = Window title bar with diagram-specific (trace) information
3 = Diagram area with marker information
4 = Diagram footer with diagram-specific information, depending on result display
5 = Instrument status bar with error messages, progress bar and date/time display
Channel bar information
In the WLAN application, the R&S FSV/A shows the following settings:
Table 2-1: Information displayed in the channel bar in the WLAN application
Label Description
"Sample Rate Fs" Input sample rate
"PPDU / MCS Index / GI" IEEE 802.11a, ac, g (OFDM), j, n, p:
The PPDU type, MCS index and guard interval (GI) used for the analysis
of the signal; Depending on the demodulation settings, these values are
either detected automatically from the signal or the user settings are
applied.
"PPDU / MCS Index / GI+HELTF"
"PPDU / MCS/ GI+EHT-LTF" WLAN 802.11be:
WLAN 802.11ax: PPDU type, MCS index, sum of guard interval (GI)
length and high efficiency long training field (HE-LTF) length used for the
analysis of the signal
PPDU type, MCS index, sum of guard interval (GI) length and extremely
high throughput long training field (EHT-LTF) length used for the analysis
of the signal
"PPDU / Data Rate" WLAN 802.11b:
The PPDU type and data rate used for the analysis of the signal; Depending on the demodulation settings, these values are either detected automatically from the signal or the user settings are applied.
"Standard" Selected WLAN measurement standard
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Welcome to the WLAN application
Understanding the display information
Label Description
"Meas Setup" Number of Transmitter (Tx) and Receiver (Rx) channels used in the mea-
surement (for MIMO)
"Capt time / Samples" Duration of signal capture and number of samples captured
"Data Symbols" The minimum and maximum number of data symbols that a PPDU may
have if it is to be considered in results analysis.
"PPDUs" [x of y (z)] For statistical evaluation over PPDUs (see "PPDU Statistic Count / No of
PPDUs to Analyze" on page 179):
<x> PPDUs of totally required <y> PPDUs have been analyzed so far.
<z> PPDUs were analyzed in the most recent sweep.
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 FSV/A Getting Started manual.
Window title bar information
For each diagram, the header provides the following information:
5
1
Figure 2-1: Window title bar information in the WLAN application
1 = Window number
2 = Window type
3 = Further measurement settings
4 = Trace color
5 = Trace number
6 = Trace mode
2
3
4
6
Diagram footer information
The diagram footer (beneath the diagram) contains the start and stop values for the
displayed x-axis range.
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. Click on a displayed warning or error message to obtain
more details (see also .
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3 Measurements and result displays
3.1 WLAN I/Q measurement (modulation accuracy, flat-
Measurements and result displays
WLAN I/Q measurement (modulation accuracy, flatness and tolerance)
The R&S FSV3 WLAN application provides several different measurements in order to
determine the parameters described by the WLAN 802.11 specifications.
For details on selecting measurements, see Chapter 5.2, "Display configuration",
on page 110.
● WLAN I/Q measurement (modulation accuracy, flatness and tolerance)................14
● Frequency sweep measurements...........................................................................62
ness and tolerance)
The default WLAN I/Q measurement captures the I/Q data from the WLAN signal using
a (nearly rectangular) filter with a relatively large bandwidth. The I/Q data captured with
this filter includes magnitude and phase information. That allows the R&S FSV3 WLAN
application to demodulate broadband signals and determine various characteristic signal parameters in just one measurement. Modulation accuracy, spectrum flatness, center frequency tolerance and symbol clock tolerance are only a few of the characteristic
parameters.
Other parameters specified in the WLAN 802.11 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 62).
● Modulation accuracy, flatness and tolerance parameters.......................................14
● Evaluation methods for WLAN IQ measurements.................................................. 25
3.1.1 Modulation accuracy, flatness and tolerance parameters
The default WLAN I/Q measurement (Modulation Accuracy, Flatness,...) captures the
I/Q data from the WLAN signal and determines all the following I/Q parameters in a
single sweep.
Table 3-1: WLAN I/Q parameters for IEEE 802.11a, ac, ax, g (OFDM), j, n, p, be
Parameter Description Keyword for remote
query (FETCh:BURSt:)
General measurement parameters
Sample RateFsInput sample rate
PPDU Type of analyzed PPDUs
*) the limits can be changed via remote control (not manually, see Chapter 9.5.9, "Limits", on page 302); in
this case, the currently defined limits are displayed here
PPDU:TYPE
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Measurements and result displays
WLAN I/Q measurement (modulation accuracy, flatness and tolerance)
Parameter Description Keyword for remote
query (FETCh:BURSt:)
MCS Index Modulation and Coding Scheme (MCS) index of the analyzed
PPDUs
Data Rate Data rate used for analysis of the signal
(IEEE 802.11a only)
GI
/ GI+HE-LTF
/ GI+EHT-LTF
Meas Setup Number of Transmitter (Tx) and Receiver (Rx) channels used
Capture time Duration of signal capture
Samples Number of samples captured
Data Symbols The minimum and maximum number of data symbols that a
PPDU parameters
Analyzed
PPDUs
Guard interval length for current measurement
Guard interval and high-efficiency long training field length
(IEEE 802.11ax only)
Guard interval and length of EHT long training field (IEEE
802.11be only)
in the measurement
PPDU can have if it is to be considered in results analysis
For statistical evaluation of PPDUs (see "PPDU Statistic
Count / No of PPDUs to Analyze" on page 179): <x> PPDUs of
the required <y> PPDUs have been analyzed so far. <z> indicates the number of analyzed PPDUs in the most recent
sweep.
MCSindex
GINTerval
Number of recognized
PPDUs
(global)
Number of
analyzed
PPDUs
(global)
Number of
analyzed
PPDUs in
physical channel
TX and Rx carrier parameters
I/Q offset [dB] Transmitter center frequency leakage relative to the total Tx
Gain imbalance [%/dB]
Quadrature
offset [°]
*) the limits can be changed via remote control (not manually, see Chapter 9.5.9, "Limits", on page 302); in
this case, the currently defined limits are displayed here
Number of PPDUs recognized in capture buffer
Number of analyzed PPDUs in capture buffer
Number of PPDUs analyzed in entire signal (if available)
channel power (see Chapter 3.1.1.1, "I/Q offset", on page 19)
Amplification of the quadrature phase component of the signal
relative to the amplification of the in-phase component (see
Chapter 3.1.1.2, "Gain imbalance", on page 19)
Deviation of the quadrature phase angle from the ideal 90°
(see Chapter 3.1.1.3, "Quadrature offset", on page 20).
COUNt
COUNt:ALL
IQOFset
GIMBalance
QUADoffset
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Measurements and result displays
WLAN I/Q measurement (modulation accuracy, flatness and tolerance)
Parameter Description Keyword for remote
query (FETCh:BURSt:)
I/Q skew [s] Delay of the transmission of the data on the I path compared
to the Q path (see Chapter 3.1.1.4, "I/Q skew", on page 21)
PPDU power
[dBm]
Crest factor
[dB]
MIMO Cross
Power [dB]
MIMO Channel Power
[dBm]
Center frequency error
[Hz]
Symbol clock
error [ppm]
Mean PPDU power
The ratio of the peak power to the mean power of the signal
(also called Peak to Average Power Ratio, PAPR).
Sum of RMS power from all cross streams
RMS power for each effective channel path from all active carriers.
Frequency error between the signal and the current center frequency of the R&S FSV/A; the corresponding limits specified
in the standard are also indicated*)
The absolute frequency error includes the frequency error of
the R&S FSV/A and that of the DUT. If possible, synchronize
the transmitter R&S FSV/A and the DUT using an external reference.
See R&S FSV/A user manual > Instrument setup > External
reference
Clock error between the signal and the sample clock of the
R&S FSV/A in parts per million (ppm), i.e. the symbol timing
error; the corresponding limits specified in the standard are
also indicated *)
If possible, synchronize the transmitter R&S FSV/A and the
DUT using an external reference.
See R&S FSV/A user manual > Instrument setup > External
reference
IQSKew
CRESt
MCPower
MCHPower
CFERror
CPE Common phase error
Stream parameters
BER Pilot [%] Bit error rate (BER) of the pilot carriers
EVM all carriers [%/dB]
EVM data carriers [%/dB]
EVM pilot carriers [%/dB]
*) the limits can be changed via remote control (not manually, see Chapter 9.5.9, "Limits", on page 302); in
this case, the currently defined limits are displayed here
EVM (Error Vector Magnitude) of the payload symbols over all
carriers; the corresponding limits specified in the standard are
also indicated*)
EVM (Error Vector Magnitude) of the payload symbols over all
data carriers; the corresponding limits specified in the standard
are also indicated*)
EVM (Error Vector Magnitude) of the payload symbols over all
pilot carriers; the corresponding limits specified in the standard
are also indicated*)
CPERror
BERPilot
EVM:ALL
EVM:DATA
EVM:PILot
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Measurements and result displays
WLAN I/Q measurement (modulation accuracy, flatness and tolerance)
Table 3-2: WLAN I/Q parameters for IEEE 802.11b or g (DSSS)
Parameter Description Keyword for remote
query
(FETCh:BURSt:)
Sample RateFsInput sample rate
PPDU Type of the analyzed PPDU
Data Rate Data rate used for analysis of the signal
Meas Setup Number of Transmitter (Tx) and Receiver (Rx) channels used in
the measurement
Capture time Duration of signal capture
No. of Samples Number of samples captured (= sample rate * capture time)
No. of Data
Symbols
PPDU parameters
Analyzed
PPDUs
Number of recognized
PPDUs
(global)
Number of
analyzed
PPDUs
(global)
The minimum and maximum number of data symbols that a
PPDU can have if it is to be considered in results analysis
For statistical evaluation of PPDUs (see "PPDU Statistic Count /
No of PPDUs to Analyze" on page 179): <x> PPDUs of the
required <y> PPDUs have been analyzed so far. <z> indicates
the number of analyzed PPDUs in the most recent sweep.
Number of PPDUs recognized in capture buffer
Number of analyzed PPDUs in capture buffer
PPDU:TYPE
COUNt
Number of
analyzed
PPDUs in
physical channel
Peak vector
error
PPDU EVM EVM (Error Vector Magnitude) over the complete PPDU includ-
I/Q offset [dB] Transmitter center frequency leakage relative to the total Tx
Gain imbalance [%/dB]
Quadrature
error [°]
Number of PPDUs analyzed in entire signal (if available)
Peak vector error (EVM) over the complete PPDU including the
preamble in % and in dB; calculated according to the IEEE
802.11b or g (DSSS) definition of the normalized error vector
magnitude (see "Peak vector error (IEEE method)"
on page 23);
The corresponding limits specified in the standard are also indicated *)
ing the preamble in % and dB
channel power (see Chapter 3.1.1.1, "I/Q offset", on page 19)
Amplification of the quadrature phase component of the signal
relative to the amplification of the in-phase component (see
Chapter 3.1.1.2, "Gain imbalance", on page 19)
Measure for the crosstalk of the Q-branch into the I-branch (see
"Gain imbalance, I/Q offset, quadrature error" on page 79).
COUNt:ALL
EVM:DIRect
PPDU:EVM:ALL
IQOFset
GIMBalance
QUADoffset
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Measurements and result displays
WLAN I/Q measurement (modulation accuracy, flatness and tolerance)
Parameter Description Keyword for remote
query
(FETCh:BURSt:)
Center frequency error
[Hz]
Chip clock
error [ppm]
Rise time Time the signal needs to increase its power level from 10% to
Fall time Time the signal needs to decrease its power level from 90% to
Frequency error between the signal and the current center frequency of the R&S FSV/A; the corresponding limits specified in
the standard are also indicated*)
The absolute frequency error includes the frequency error of the
R&S FSV/A and that of the DUT. If possible, synchronize the
transmitter R&S FSV/A and the DUT using an external reference.
See R&S FSV/A user manual > Instrument setup > External reference
Clock error between the signal and the chip clock of the
R&S FSV/A in parts per million (ppm), i.e. the chip timing error;
the corresponding limits specified in the standard are also indicated *)
If possible, synchronize the transmitter R&S FSV/A and the DUT
using an external reference.
See R&S FSV/A user manual > Instrument setup > External reference
90% of the maximum or the average power (depending on the
reference power setting)
The corresponding limits specified in the standard are also indicated *)
10% of the maximum or the average power (depending on the
reference power setting)
The corresponding limits specified in the standard are also indicated *)
CFERror
TRISe
TFALl
Mean power
[dBm]
Peak power
[dBm]
Crest factor
[dB]
Mean PPDU power
Peak PPDU power
The ratio of the peak power to the mean power of the PPDU
(also called Peak to Average Power Ratio, PAPR).
PEAK
CRESt
The R&S FSV3 WLAN application also performs statistical evaluation over several
PPDUs and displays one or more of the following results:
Table 3-3: Calculated summary results
Result type Description
Min Minimum measured value
Mean/ Limit Mean measured value / limit defined in standard
Max/Limit Maximum measured value / limit defined in standard
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3.1.1.1 I/Q offset
Measurements and result displays
WLAN I/Q measurement (modulation accuracy, flatness and tolerance)
An I/Q offset indicates a carrier offset with fixed amplitude. This results in a constant
shift of the I/Q axes. The offset is normalized by the mean symbol power and displayed
in dB.
Figure 3-1: I/Q offset in a vector diagram
3.1.1.2 Gain imbalance
An ideal I/Q modulator amplifies the I and Q signal path by exactly the same degree.
The imbalance corresponds to the difference in amplification of the I and Q channel
and therefore to the difference in amplitude of the signal components. In the vector diagram, the length of the I vector changes relative to the length of the Q vector.
The result is displayed in dB and %, where 1 dB offset corresponds to roughly 12 %
difference between the I and Q gain, according to the following equation:
Positive values mean that the Q vector is amplified more than the I vector by the corresponding percentage. For example, using the figures mentioned above:
Figure 3-2: Positive gain imbalance
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Negative values mean that the I vector is amplified more than the Q vector by the corresponding percentage. For example, using the figures mentioned above:
Figure 3-3: Negative gain imbalance
3.1.1.3 Quadrature offset
An ideal I/Q modulator sets the phase angle between the I and Q path mixer to exactly
90 degrees. With a quadrature offset, the phase angle deviates from the ideal 90
degrees, the amplitudes of both components are of the same size. In the vector diagram, the quadrature offset causes the coordinate system to shift.
A positive quadrature offset means a phase angle greater than 90 degrees:
Figure 3-4: Positive quadrature offset
A negative quadrature offset means a phase angle less than 90 degrees:
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3.1.1.4 I/Q skew
Measurements and result displays
WLAN I/Q measurement (modulation accuracy, flatness and tolerance)
Figure 3-5: Negative quadrature offset
If transmission of the data on the I path is delayed compared to the Q path, or vice
versa, the I/Q data becomes skewed.
The I/Q skew results can be compensated for together with Gain imbalance and Quad-
rature offset (see "I/Q Mismatch Compensation" on page 145).
3.1.1.5 I/Q mismatch
I/Q mismatch is a comprehensive term for Gain imbalance, Quadrature offset, and I/Q
skew.
Compensation for I/Q mismatch is useful, for example, if the device under test is
known to be affected by these impairments but the EVM without these effects is of
interest. Note, however, that measurements strictly according to IEEE 802.11-2012,
IEEE 802.11ac-2013 WLAN standard must not use compensation.
3.1.1.6 RF carrier suppression (IEEE 802.11b, g (DSSS))
Standard definition
The RF carrier suppression, measured at the channel center frequency, shall be at
least 15 dB below the peak SIN(x)/x power spectrum. The RF carrier suppression shall
be measured while transmitting a repetitive 01 data sequence with the scrambler disabled using DQPSK modulation. A 100 kHz resolution bandwidth shall be used to perform this measurement.
Comparison to IQ offset measurement in the R&S FSV3 WLAN application
The IQ offset measurement in the R&S FSV3 WLAN application returns the current
carrier feedthrough normalized to the mean power at the symbol timings. This measurement does not require a special test signal and is independent of the transmit filter
shape.
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3.1.1.7 EVM measurement
Measurements and result displays
WLAN I/Q measurement (modulation accuracy, flatness and tolerance)
The RF carrier suppression measured according to the standard is inversely proportional to the IQ offset measured in the R&S FSV3 WLAN application. The difference (in
dB) between the two values depends on the transmit filter shape. Determine it with a
reference measurement.
The following table lists the difference exemplarily for three transmit filter shapes
(±0.5 dB):
Transmit filter – IQ-Offset [dB] – RF-Carrier-Suppression [dB]
Rectangular 11 dB
Root raised cosine, "α" = 0.3 10 dB
Gaussian, "α" = 0.3 9 dB
The R&S FSV3 WLAN application provides two different types of EVM calculation.
PPDU EVM (direct method)
The PPDU EVM (direct) method evaluates the root mean square EVM over one PPDU.
That is the square root of the averaged error power normalized by the averaged reference power:
Before calculation of the EVM, tracking errors in the measured signal are compensated
for if specified by the user. In the ideal reference signal, the tracking errors are always
compensated for. Tracking errors include phase (center frequency error + common
phase error), timing (sampling frequency error) and gain errors. Quadrature offset and
gain imbalance errors, however, are not corrected.
The PPDU EVM is not part of the IEEE standard and no limit check is specified. Nevertheless, this commonly used EVM calculation can provide some insight in modulation
quality and enables comparisons to other modulation standards.
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Figure 3-6: I/Q diagram for EVM calculation
Peak vector error (IEEE method)
The peak vector error (Peak EVM) is defined in section 18.4.7.8 "Transmit modulation
accuracy" of the IEEE 802.11b standard. The phase, timing and gain tracking errors of
the measurement signal (center frequency error, common phase error, sampling frequency error) are compensated for before EVM calculation.
The standard does not specify a normalization factor for the error vector magnitude. To
get an EVM value that is independent of the level, the R&S FSV3 WLAN application
normalizes the EVM values. Thus, an EVM of 100% indicates that the error power on
the I- or Q-channels equals the mean power on the I- or Q-channels, respectively.
The peak vector error is the maximum EVM over all payload symbols and all active
carriers for one PPDU. If more than one PPDU is analyzed the Min / Mean / Max columns show the minimum, mean or maximum Peak EVM of all analyzed PPDUs. This
can be the case, for example, if several analyzed PPDUs are in the capture buffer or
due to the PPDU Statistic Count / No of PPDUs to Analyze setting.
The IEEE 802.11b or g (DSSS) standards allow a peak vector error of less than 35%.
In contrary to the specification, the R&S FSV3 WLAN application does not limit the
measurement to 1000 chips length, but searches the maximum over the whole PPDU.
3.1.1.8 Unused tone error
Similarly to the adjacent channel power requirements for other WLAN standards, the
IEEE 802.11ax standard specifies limits for power leakage into neighboring resource
units (IEEE P802.11ax/D1.2, "Transmitter modulation accuracy (EVM) test" section). In
high-efficiency wireless signals, the subcarriers or frequencies that are not used for
active transmission are referred to as unused tones. Thus, the parameter that indicates
the power leakage into adjacent resource units is referred to as the unused tone error.
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The R&S FSV3 WLAN application provides a dedicated result display for the IEEE
802.11ax standard for HE trigger-based PPDUs.
The region in which the power leakage must be determined depends on the size and
position within the channel of the resource unit being checked. Up to 3 times the number of subcarriers contained in the resource unit are checked on either side of it. Any
remaining subcarriers are checked against the fixed limit of -35 dB. However, only subcarriers in the same channel are evaluated. If the resource unit is at the edge of the
channel, possibly no or not enough adjacent subcarriers are available in the channel.
Assuming the resource unit contains n carriers, the adjacent n subcarriers are
assigned a certain limit, the next n subcarriers have another limit, and the third n subcarriers have yet another limit. All subcarriers beyond that have a fixed limit of -35 dB
in relation to the EVM tolerance limit for the original resource unit ("[IEEE P802.11ax/
D1.2] Equation (28-123)").
Since the n subcarriers can be allocated to several different resource units, we refer to
such a subset as an RU group. The RU group containing the resource unit to be
checked is referred to as RU
are referred to as RU groups RU
remaining subcarriers are referred to as the RU groups -35
. The other subsets evaluated on either side of the RU
Idx
Idx-1
, RU
Idx-2
, RU
, and RU
Idx-3
, RU
Idx+1
dB
LHS (left-hand side)
Idx+2
, RU
Idx+3
Idx
. The
and -35 dB RHS (right-hand side).
The size of the evaluated RU groups corresponds to the size of the RU
, even if the
Idx
actual resource unit allocation in the channel differs. However, the R&S FSV3 WLAN
application measures one unused tone value for each set of 26 subcarriers. For each
RU group, the mean, maximum, and minimum of these values is determined. In the
Unused Tone Error Summary, the "RU Size [RU26]" is indicated as the quotient of the
RU size divided by the RU26 size (see "[IEEE P802.11ax/D1.2] Equation (28-123)").
Thus, the "RU Size [RU26]" also indicates the number of measurement points determined for each RU group.
Figure 3-7 illustrates the RU groups for which the unused tone error is determined for
different RU indexes. The blue dots indicate individual power measurement points in
the channel.
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Figure 3-7: RU groups to be checked for unused tone error for different RU indexes
3.1.2 Evaluation methods for WLAN IQ measurements
The captured I/Q data from the WLAN 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.
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Result display windows
All evaluations available for the selected WLAN measurement are displayed in SmartGrid mode.
To activate SmartGrid mode, do one of the following:
●
Select the "SmartGrid" icon from the toolbar.
●
Select the "Display Config" button in the configuration "Overview" (see Chapter 5.2,
"Display configuration", on page 110).
●
Press the [MEAS CONFIG] hardkey and then select the "Display Config" softkey.
To close the SmartGrid mode and restore the previous softkey menu select the
"Close" icon in the right-hand corner of the toolbar, or press any key.
The selected evaluation method not only affects the result display in a window, but also
the results of the trace data query in remote control (see TRACe[:DATA]?
on page 373).
The WLAN measurements provide the following evaluation methods:
AM/AM.......................................................................................................................... 27
AM/PM.......................................................................................................................... 28
AM/EVM........................................................................................................................28
Bitstream.......................................................................................................................29
Constellation................................................................................................................. 31
Constellation vs Carrier.................................................................................................33
EVM vs Carrier..............................................................................................................34
EVM vs Chip................................................................................................................. 35
EVM vs Symbol.............................................................................................................35
FFT Spectrum............................................................................................................... 36
Freq. Error vs Preamble................................................................................................37
Gain Imbalance vs Carrier............................................................................................ 38
Group Delay..................................................................................................................39
Magnitude Capture........................................................................................................40
Phase Error vs Preamble..............................................................................................40
Phase Tracking............................................................................................................. 41
PLCP Header (IEEE 802.11b, g (DSSS).......................................................................42
PvT Full PPDU..............................................................................................................43
PvT Rising Edge........................................................................................................... 44
PvT Falling Edge...........................................................................................................45
Quad Error vs Carrier....................................................................................................45
Result Summary Detailed............................................................................................. 46
Result Summary Global................................................................................................ 47
Signal Content Detailed (IEEE 802.11ax, be)............................................................... 49
Signal Field................................................................................................................... 50
└ IEEE 802.11a, g (OFDM), j, p......................................................................... 51
└ IEEE 802.11ac................................................................................................ 52
└ IEEE 802.11n..................................................................................................53
└ IEEE 802.11ax HE SU PPDU (DL/UL), HE Extended Range SU PPDU........54
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└ IEEE 802.11ax HE MU PPDU (DL).................................................................55
└ IEEE 802.11ax HE Trigger-based PPDU (UL)................................................56
└ IEEE 802.11be EHT MU PPDU (DL) / IEEE 802.11be EHT trigger-based
PPDU (UL)......................................................................................................57
Spectrum Flatness........................................................................................................ 58
Spectrum Flatness Result Summary.............................................................................60
Unused Tone Error........................................................................................................60
Unused Tone Error Summary........................................................................................61
AM/AM
This result display shows the measured and the reference signal in the time domain.
For each sample, the x-axis value represents the amplitude of the reference signal and
the y-axis value represents the amplitude of the measured signal.
The reference signal is derived from the measured signal after frequency and time synchronization, channel equalization and demodulation of the signal. The equivalent time
domain representation of the reference signal is calculated by reapplying all the impairments that were removed before demodulation.
The trace is determined by calculating a polynomial regression model of a specified
degree (see "Polynomial degree for curve fitting" on page 186) for the scattered measurement vs. reference signal data. The resulting regression polynomial is indicated in
the window title of the result display.
Note: The measured signal and reference signal are complex signals.
This result display is not available for single-carrier measurements (IEEE 802.11b, g
(DSSS)) or IEEE 802.11ax, be.
Remote command:
LAY:ADD? '1',RIGH,AMAM, see LAYout:ADD[:WINDow]? on page 316
Or:
CONFigure:BURSt:AM:AM[:IMMediate] on page 221
Polynomial degree:
CONFigure:BURSt:AM:AM:POLYnomial on page 326
Results:
TRACe[:DATA]?, see Chapter 9.9.4.1, "AM/AM", on page 379
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AM/PM
This result display shows the measured and the reference signal in the time domain.
For each sample, the x-axis value represents the amplitude of the reference signal.
The y-axis value represents the angle difference of the measured signal minus the reference signal.
This result display is not available for single-carrier measurements (IEEE 802.11b, g
(DSSS)).
Remote command:
LAY:ADD? '1',RIGH,AMPM, see LAYout:ADD[:WINDow]? on page 316
Or:
CONFigure:BURSt:AM:PM[:IMMediate] on page 221
Querying results:
TRACe[:DATA]?, see Chapter 9.9.4.2, "AM/PM", on page 379
AM/EVM
This result display shows the measured and the reference signal in the time domain.
For each sample, the x-axis value represents the amplitude of the reference signal.
The y-axis value represents the length of the error vector between the measured signal
and the reference signal.
The length of the error vector is normalized with the power of the corresponding reference signal sample.
This result display is not available for single-carrier measurements (IEEE 802.11b, g
(DSSS)).
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Remote command:
LAY:ADD? '1',RIGH,AMEV, see LAYout:ADD[:WINDow]? on page 316
Or:
CONFigure:BURSt:AM:EVM[:IMMediate] on page 221
Querying results:
TRACe[:DATA]?, see Chapter 9.9.4.3, "AM/EVM", on page 379
Bitstream
This result display shows a demodulated payload data stream for all analyzed PPDUs
of the currently captured I/Q data as indicated in the "Magnitude Capture" display. The
bitstream is derived from the constellation diagram points using the 'constellation bit
encoding' from the corresponding WLAN standard. See, for example, IEEE Std.
802.11-2012 'Fig. 18-10 BPSK, QPSK, 16-QAM and 64-QAM constellation bit encoding'. Thus, the bitstream is NOT channel-decoded.
For multicarrier measurements (IEEE 802.11a, ac, g (OFDM), j, n, p), the results are
grouped by symbol and carrier.
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Figure 3-8: Bitstream result display for IEEE 802.11a, ac, g (OFDM), j, n, p standards
For MIMO measurements (IEEE 802.11 ac, ax, n, be), the results are grouped by
stream, symbol and carrier.
Figure 3-9: Bitstream result display for IEEE 802.11n MIMO measurements
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For single-carrier measurements (IEEE 802.11b, g (DSSS)) the results are grouped by
PPDU.
Figure 3-10: Bitstream result display for IEEE 802.11b, g (DSSS) standards
The numeric trace results for this evaluation method are described in Chapter 9.9.4.4,
"Bitstream", on page 379.
Remote command:
LAY:ADD? '1',RIGH, BITS, see LAYout:ADD[:WINDow]? on page 316
Or:
CONFigure:BURSt:STATistics:BSTReam[:IMMediate] on page 225
Querying results:
TRACe[:DATA]?, see Chapter 9.9.4.4, "Bitstream", on page 379
Constellation
This result display shows the in-phase and quadrature phase results for all payload
symbols and all carriers for the analyzed PPDUs of the current capture buffer. The
Tracking/Channel Estimation according to the user settings is applied.
The inphase results (I) are displayed on the x-axis, the quadrature phase (Q) results on
the y-axis.
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Figure 3-11: Constellation result display for IEEE 802.11n MIMO measurements
The numeric trace results for this evaluation method are described in Chapter 9.9.4.6,
"Constellation", on page 381.
Remote command:
LAY:ADD? '1',RIGH, CONS, see LAYout:ADD[:WINDow]? on page 316
Or:
CONFigure:BURSt:CONSt:CSYMbol[:IMMediate] on page 221
Querying results:
TRACe[:DATA]?, see Chapter 9.9.4.6, "Constellation", on page 381
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Constellation vs Carrier
This result display shows the in-phase and quadrature phase results for all payload
symbols and all carriers for the analyzed PPDUs of the current capture buffer. The
Tracking/Channel Estimation according to the user settings is applied.
This result display is not available for single-carrier measurements (IEEE 802.11b, g
(DSSS)).
The x-axis represents the carriers. The magnitude of the in-phase and quadrature part
is shown on the y-axis, both are displayed as separate traces (I-> trace 1, Q-> trace 2).
Figure 3-12: Constellation vs. carrier result display for IEEE 802.11n MIMO measurements
The numeric trace results for this evaluation method are described in Chapter 9.9.4.7,
"Constellation vs carrier", on page 382.
Remote command:
LAY:ADD? '1',RIGH, CVC, see LAYout:ADD[:WINDow]? on page 316
Or:
CONFigure:BURSt:CONSt:CCARrier[:IMMediate] on page 221
Querying results:
TRACe[:DATA]?, see Chapter 9.9.4.7, "Constellation vs carrier", on page 382
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EVM vs Carrier
This result display shows all EVM values recorded on a per-subcarrier basis over the
number of analyzed PPDUs as defined by the "Evaluation Range > Statistics". The
Tracking/Channel Estimation according to the user settings is applied (see Chap-
ter 5.3.6, "Tracking and channel estimation", on page 143). The minimum, average and
maximum traces are displayed.
For IEEE 802.11be measurements, the results are displayed for the RUs selected in
the PPDU configuration, see "Result displays for multi-user PPDUs" on page 164.
This result display is not available for single-carrier measurements (IEEE 802.11b, g
(DSSS)).
Figure 3-13: EVM vs carrier result display for IEEE 802.11n MIMO measurements
The numeric trace results for this evaluation method are described in Chapter 9.9.4.10,
"EVM vs carrier", on page 382.
Remote command:
LAY:ADD? '1',RIGH, EVC, see LAYout:ADD[:WINDow]? on page 316
Or:
CONFigure:BURSt:EVM:ECARrier[:IMMediate] on page 221
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Querying results:
TRACe[:DATA]?, see Chapter 9.9.4.10, "EVM vs carrier", on page 382
EVM vs Chip
This result display shows the error vector magnitude per chip.
This result display is only available for single-carrier measurements (IEEE 802.11b, g
(DSSS)).
Since the R&S FSV3 WLAN application provides two different methods to calculate the
EVM, two traces are displayed:
●
"Vector Error IEEE" shows the error vector magnitude as defined in the IEEE
802.11b or g (DSSS) standards (see also "Error vector magnitude (EVM) - IEEE
802.11b or g (DSSS) method" on page 80)
●
"EVM" shows the error vector magnitude calculated with an alternative method that
provides higher accuracy of the estimations (see also "Error vector magnitude
(EVM) - R&S FSV/A method" on page 80).
Remote command:
LAY:ADD? '1',RIGH, EVCH, see LAYout:ADD[:WINDow]? on page 316
Or:
CONFigure:BURSt:EVM:EVCHip[:IMMediate] on page 222
CONFigure:BURSt:EVM:ESYMbol[:IMMediate] on page 222
Querying results:
TRACe[:DATA]?, see Chapter 9.9.4.11, "EVM vs chip", on page 383
EVM vs Symbol
This result display shows all EVM values calculated on a per-carrier basis over the
number of analyzed PPDUs as defined by the "Evaluation Range > Statistics" settings
(see "PPDU Statistic Count / No of PPDUs to Analyze" on page 179). The Tracking/
Channel Estimation according to the user settings is applied (see Chapter 5.3.6,
"Tracking and channel estimation", on page 143). The minimum, average and maxi-
mum traces are displayed.
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Figure 3-14: EVM vs symbol result display for IEEE 802.11n MIMO measurements
This result display is not available for single-carrier measurements (IEEE 802.11b, g
(DSSS)).
Remote command:
LAY:ADD? '1',RIGH, EVSY, see LAYout:ADD[:WINDow]? on page 316
Or:
CONFigure:BURSt:EVM:ESYMbol[:IMMediate] on page 222
Querying results:
TRACe[:DATA]?, see Chapter 9.9.4.12, "EVM vs symbol", on page 383
FFT Spectrum
This result display shows the power vs frequency values obtained from an FFT. The
FFT is performed over the complete data in the current capture buffer, without any correction or compensation.
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Figure 3-15: FFT spectrum result display for IEEE 802.11n MIMO measurements
The numeric trace results for this evaluation method are described in Chapter 9.9.4.13,
"FFT spectrum", on page 384.
Remote command:
LAY:ADD? '1',RIGH, FSP, see LAYout:ADD[:WINDow]? on page 316
Or:
CONFigure:BURSt:SPECtrum:FFT[:IMMediate] on page 224
Querying results:
TRACe[:DATA]?, see Chapter 9.9.4.13, "FFT spectrum", on page 384
Freq. Error vs Preamble
Displays the frequency error values recorded over the preamble part of the PPDU. The
minimum, average and maximum traces are displayed.
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Remote command:
LAY:ADD? '1',RIGH,FEVP, see LAYout:ADD[:WINDow]? on page 316
Or:
CONFigure:BURSt:PREamble[:IMMediate] on page 222
CONFigure:BURSt:PREamble:SELect on page 223
Querying results:
TRACe[:DATA]?, see Chapter 9.9.4.9, "Error vs preamble", on page 382
Gain Imbalance vs Carrier
Displays the minimum, average and maximum gain imbalance versus carrier in individual traces. For details on gain imbalance, see Chapter 3.1.1.2, "Gain imbalance",
on page 19.
Remote command:
LAY:ADD? '1',RIGH,GAIN, see LAYout:ADD[:WINDow]? on page 316
Or:
CONFigure:BURSt:GAIN:GCARrier[:IMMediate] on page 222
Querying results:
TRACe[:DATA]?, see Chapter 9.9.4.8, "Error vs carrier", on page 382
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Group Delay
Displays all "Group Delay" (GD) values recorded on a per-subcarrier basis - over the
number of analyzed PPDUs as defined by the "Evaluation Range > Statistics" settings
(see "PPDU Statistic Count / No of PPDUs to Analyze" on page 179.
All 57 carriers are shown, including the unused carrier 0.
This result display is not available for single-carrier measurements (IEEE 802.11b, g
(DSSS)).
Figure 3-16: Group delay result display for IEEE 802.11n MIMO measurements
Group delay is a measure of phase distortion and defined as the derivation of phase
over frequency.
To calculate the group delay, the estimated channel is upsampled, inactive carriers are
interpolated, and phases are unwrapped before they are differentiated over the carrier
frequencies. Thus, the group delay indicates the time a pulse in the channel is delayed
for each carrier frequency. However, not the absolute delay is of interest, but rather the
deviation between carriers. Thus, the mean delay over all carriers is deducted.
For an ideal channel, the phase increases linearly, which causes a constant time delay
over all carriers. In this case, a horizontal line at the zero value would be the result.
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The numeric trace results for this evaluation method are described in Chapter 9.9.4.14,
"Group delay", on page 384.
Remote command:
LAY:ADD? '1',RIGH, GDEL, see LAYout:ADD[:WINDow]? on page 316
Or:
CONF:BURS:SPEC:FLAT:SEL GRD, see CONFigure:BURSt:SPECtrum:
FLATness:SELect on page 224 and CONFigure:BURSt:SPECtrum:FLATness[:
IMMediate] on page 224
Querying results:
TRACe[:DATA]?, see Chapter 9.9.4.14, "Group delay", on page 384
Magnitude Capture
The "Magnitude Capture" Buffer display shows the complete range of captured data for
the last sweep. Green bars at the bottom of the "Magnitude Capture" Buffer display
indicate the positions of the analyzed PPDUs.
A blue bar indicates the selected PPDU if the evaluation range is limited to a single
PPDU (see "Analyze this PPDU / PPDU to Analyze" on page 178).
Figure 3-17: Magnitude capture display for single PPDU evaluation
Numeric trace results are not available for this evaluation method.
Remote command:
LAY:ADD? '1',RIGH, CMEM, see LAYout:ADD[:WINDow]? on page 316
Querying results:
TRACe[:DATA]?, see Chapter 9.9.4.15, "Magnitude capture", on page 385
Phase Error vs Preamble
Displays the phase error values recorded over the preamble part of the PPDU. A minimum, average and maximum trace is displayed.
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Remote command:
LAY:ADD? '1',RIGH,PEVP, see LAYout:ADD[:WINDow]? on page 316
Or:
CONFigure:BURSt:PREamble[:IMMediate] on page 222
CONFigure:BURSt:PREamble:SELect on page 223
Querying results:
TRACe[:DATA]?, see Chapter 9.9.4.9, "Error vs preamble", on page 382
Phase Tracking
Displays the average phase tracking result per symbol (in radians).
This result display is not available for single-carrier measurements (IEEE 802.11b, g
(DSSS)).
Figure 3-18: Phase tracking result display for IEEE 802.11n MIMO measurements
Remote command:
LAY:ADD? '1',RIGH,PTR, see LAYout:ADD[:WINDow]? on page 316
Or:
CONFigure:BURSt:PTRacking[:IMMediate] on page 223
Querying results:
TRACe[:DATA]?, see Chapter 9.9.4.16, "Phase tracking", on page 385
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PLCP Header (IEEE 802.11b, g (DSSS)
This result display shows the decoded data from the PLCP header of the PPDU.
This result display is only available for single-carrier measurements (IEEE 802.11b, g
(DSSS)); for other standards, use Signal Field instead.
Figure 3-19: PLCP Header result display for IEEE 802.11b, g (DSSS) standards
The following information is provided:
Note: The signal field information is provided as a decoded bit sequence and, where
appropriate, also in human-readable form beneath the bit sequence for each PPDU.
Table 3-4: Demodulation results in PLCP Header result display (IEEE 802.11b, g (DSSS))
Result Description Example
PPDU Number of the decoded PPDU
A colored block indicates that the PPDU was successfully decoded.
Signal Information in "signal" field
The decoded data rate is shown below.
Service Information in "service" field
<Symbol clock state> /<Modulation format> / <Length extension
bit state>
where:
<Symbol clock state>: Locked / - <Modulation format>: see Table 4-3
<Length extension bit state>: 1 (set) / - - (not set)
PSDU Length Information in "length" field
Time required to transmit the PSDU
CRC Information in "CRC" field
Result of cyclic redundancy code check: "OK" or "Failed"
PPDU 1
01101110
11 MBits/s
00100000
Lock/CCK/- -
0000000001111000
120 µs
1110100111001110
OK
Remote command:
LAY:ADD? '1',RIGH, SFI, see LAYout:ADD[:WINDow]? on page 316
Or:
CONFigure:BURSt:STATistics:SFIeld[:IMMediate] on page 225
Querying results:
TRACe[:DATA]?, see Chapter 9.9.4.18, "Signal field", on page 386
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PvT Full PPDU
Displays the minimum, average and maximum power vs time diagram for all PPDUs.
Figure 3-20: PvT Full PPDU result display for IEEE 802.11a, ac, g (OFDM), j, n, p standards
Figure 3-21: PvT Full PPDU result display for IEEE 802.11n MIMO measurements
For single-carrier measurements (IEEE 802.11b, g (DSSS)), the PVT results are displayed as percentage values of the reference power. The reference can be set to either
the maximum or mean power of the PPDU.
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Figure 3-22: PvT Full PPDU result display for IEEE 802.11b, g (DSSS) standards
Remote command:
LAY:ADD:WIND '2',RIGH,PFPP see LAYout:ADD[:WINDow]? on page 316
Or:
CONFigure:BURSt:PVT:SELect on page 223
CONFigure:BURSt:PVT[:IMMediate] on page 223
Querying results:
TRACe[:DATA]?, see Chapter 9.9.4.17, "Power vs time (PVT)", on page 385
PvT Rising Edge
Displays the minimum, average and maximum power vs time diagram for the rising
edge of all PPDUs.
Figure 3-23: PvT Rising Edge result display
Remote command:
LAY:ADD:WIND '2',RIGH,PRIS see LAYout:ADD[:WINDow]? on page 316
Or:
CONFigure:BURSt:PVT:SELect on page 223
CONFigure:BURSt:PVT[:IMMediate] on page 223
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Querying results:
TRACe[:DATA]?, see Chapter 9.9.4.17, "Power vs time (PVT)", on page 385
PvT Falling Edge
Displays the minimum, average and maximum power vs time diagram for the falling
edge of all PPDUs.
Figure 3-24: PvT Falling Edge result display
Remote command:
LAY:ADD:WIND '2',RIGH,PFAL see LAYout:ADD[:WINDow]? on page 316
Or:
CONFigure:BURSt:PVT:SELect on page 223
CONFigure:BURSt:PVT[:IMMediate] on page 223
Querying results:
TRACe[:DATA]?, see Chapter 9.9.4.17, "Power vs time (PVT)", on page 385
Quad Error vs Carrier
Displays the minimum, average and maximum quadrature offset (error) versus carrier
in individual traces. For details on quadrature offset, see Chapter 3.1.1.3, "Quadrature
offset", on page 20.
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Remote command:
LAY:ADD? '1',RIGH,QUAD, see LAYout:ADD[:WINDow]? on page 316
Or:
CONFigure:BURSt:QUAD:QCARrier[:IMMediate] on page 224
Querying results:
TRACe[:DATA]?, see Chapter 9.9.4.8, "Error vs carrier", on page 382
Result Summary Detailed
The detailed result summary contains individual measurement results for the Transmitter and Receiver channels and for the bitstream.
This result display is not available for single-carrier measurements (IEEE 802.11b, g
(DSSS)).
Figure 3-25: Detailed Result Summary result display for IEEE 802.11n MIMO measurements
The "Result Summary Detailed" contains the following information:
Note: You can configure which results are displayed (see Chapter 5.3.9, "Result con-
figuration", on page 183). However, the results are always calculated, regardless of
their visibility.
Tx channel ("Tx All"):
●
I/Q offset [dB]
●
Gain imbalance [%/dB]
●
Quadrature offset [°]
●
I/Q skew [ps]
●
PPDU power [dBm]
●
Crest factor [dB]
Receive channel ("Rx All"):
●
PPDU power [dBm]
●
Crest factor [dB]
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●
MIMO cross power
●
MIMO channel power
●
Center frequency error
●
Symbol clock error
●
CPE
"Bitstream" ("Stream All"):
●
Pilot bit error rate [%]
●
EVM all carriers [%/dB]
●
EVM data carriers [%/dB]
●
EVM pilot carriers [%/dB]
For details on the individual parameters and the summarized values, see Chap-
ter 3.1.1, "Modulation accuracy, flatness and tolerance parameters", on page 14.
Remote command:
LAY:ADD? '1',RIGH, RSD, see LAYout:ADD[:WINDow]? on page 316
Querying results:
FETCh:BURSt:ALL:FORMatted? on page 343
Result Summary Global
The global result summary provides measurement results based on the complete signal, consisting of all channels and streams. The observation length is the number of
PPDUs to be analyzed as defined by the "Evaluation Range > Statistics" settings. In
contrast, the detailed result summary provides results for each individual channel and
stream.
For MIMO measurements (IEEE 802.11 ac, ax, n, be), the global result summary provides the results for all data streams, whereas the detailed result summary provides
the results for individual streams.
Figure 3-26: Global result summary for IEEE 802.11a, ac, g (OFDM), j, n, p standards
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Figure 3-27: Global result summary for IEEE 802.11b, g (DSSS) standards
The "Result Summary Global" contains the following information:
Note: You can configure which results are displayed (see Chapter 5.3.9, "Result con-
figuration", on page 183). However, the results are always calculated, regardless of
their visibility.
(not for IEEE 802.11 be standard)
●
Number of recognized PPDUs
●
Number of analyzed PPDUs
●
Number of analyzed PPDUs in entire physical channel, if available
IEEE 802.11 be standard: "PPDU / MCS / GI+EHT-LTF / RUS":
●
PPDU type
●
MCS index
●
sum of guard interval (GI) length and extremely high throughput long training field
(EHT-LTF) length
●
RU size of the currently displayed resource unit (see also "Result displays for multi-
user PPDUs" on page 95)
IEEE 802.11a, ac, ax, g (OFDM), j, n, p, be standards:
●
Pilot bit error rate [%]
●
EVM all carriers [%/dB]
●
EVM data carriers [%/dB]
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●
EVM pilot carriers [%/dB]
●
Center frequency error [Hz]
●
Symbol clock error [ppm]
IEEE 802.11b, g (DSSS) standards:
●
Peak vector error
●
PPDU EVM
●
Quadrature offset
●
Gain imbalance
●
Quadrature error
●
Center frequency error
●
Chip cock error
●
Rise time
●
Fall time
●
Mean power
●
Peak power
●
Crest power
For details on the individual results and the summarized values, see Chapter 3.1.1,
"Modulation accuracy, flatness and tolerance parameters", on page 14.
Remote command:
LAY:ADD? '1',RIGH, RSGL, see LAYout:ADD[:WINDow]? on page 316
Querying results:
All values in result summary table:
FETCh:BURSt:ALL:FORMatted? on page 343
EVM values only of all PPDUs:
FETCh:BURSt:PPDU:EVM:ALL:AVERage? on page 351
Signal Content Detailed (IEEE 802.11ax, be)
The Signal Content Detailed display contains information on the signal for all resource
units.
This result display is only available for high-efficiency and extremely high throughput
wireless signals (IEEE 802.11ax, be).
Figure 3-28: Signal Content Detailed result display for IEEE 802.11ax measurements
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The "Signal Content Detailed" contains information for each decoded RU and for each
object in the following order:
●
(As of firmware version 3.20:) Legacy long training field (L-LTF)
●
Long training field (HE-LTF)
●
Data + Pilot
●
Data only
●
Pilot only
For each object, the following information is provided:
●
PPDU index - sequential order of detected PPDU
●
RU index - sequential order of resource unit
●
RU size - size of the resource unit
●
Object
●
EVM in dB
●
Power in dBm per subcarrier
For details on the individual parameters and the summarized values, see Chap-
ter 3.1.1, "Modulation accuracy, flatness and tolerance parameters", on page 14.
Remote command:
LAY:ADD? '1',RIGH, SCD, see LAYout:ADD[:WINDow]? on page 316
Querying results:
FETCh:SCDetailed:ALL? on page 352
Signal Field
This result display shows the decoded data from the signal fields of each recognized
PPDU. These fields contain information on the modulation used for transmission.
This result display is not available for single-carrier measurements (IEEE 802.11b, g
(DSSS)); use PLCP Header (IEEE 802.11b, g (DSSS) instead.
Figure 3-29: Signal Field display for IEEE 802.11n
The signal field information is provided as a decoded bit sequence and, where appropriate, also in human-readable form for each PPDU.
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The currently applied user-defined demodulation settings are indicated in the table
header for reference (e.g. "HT-MF20 PPDU [1]" in Figure 3-29). Since the demodulation settings define which PPDUs are to be analyzed, this logical filter can be the reason if the "Signal Field" display is not as expected.
The values for the individual demodulation parameters are described in Chapter 5.3.7,
"Demodulation", on page 146.
The information differs for the different PPDU formats.
For details on the individual parameters, see the corresponding standard specification,
for example 27. High Efficiency (HE) MAC specification in the IEEE P802.11ax™/D1.2
standard.
The "Signal Field" measurement indicates certain inconsistencies in the signal or discrepancies between the demodulation settings and the signal to be analyzed. In both
cases, an appropriate warning is displayed and the results for the PPDU are highlighted orange - both in the "Signal Field" display and the "Magnitude Capture" display. If
the signal was analyzed with warnings, the results – indicated by a message - also
contribute to the overall analysis results.
PPDUs detected in the signal that do not pass the logical filter, i.e. are not to be included in analysis, are dismissed. An appropriate message is provided. The corresponding PPDU in the capture buffer is not highlighted.
The numeric trace results for this evaluation method are described in Chapter 9.9.4.18,
"Signal field", on page 386.
Remote command:
LAY:ADD? '1',RIGH, SFI, see LAYout:ADD[:WINDow]? on page 316
Or:
CONFigure:BURSt:STATistics:SFIeld[:IMMediate] on page 225
Querying results:
TRACe[:DATA]?, see Chapter 9.9.4.18, "Signal field", on page 386
IEEE 802.11a, g (OFDM), j, p ← Signal Field
Table 3-5: Demodulation parameters and results for Signal Field result display (IEEE 802.11a, g
Field Description
L-SIG field
Rate Symbol rate per second
Reserved Reserved bit
Length Length of payload in OFDM symbols
Parity Parity bit
Tail Signal tail (preset to 0)
(OFDM), j, p)
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IEEE 802.11ac ← Signal Field
Table 3-6: Demodulation parameters and results for Signal Field result display (IEEE 802.11ac)
Field Description
L-SIG field
Rate Symbol rate per second
Reserved Reserved bit
Length Length of payload in OFDM symbols
Parity Parity bit
Tail Signal tail (preset to 0)
VHT-SIG-A1
BW Channel bandwidth to measure
0: 20 MHz
1: 40 MHz
2: 80 MHz
3: 80+80 MHz and 160MHz
Reserved Reserved bit
STBC Space-Time Block Coding
0: no spatial streams of any user have space time block coding
1: all spatial streams of all users have space time block coding
Group ID 0 or 63: indicates a VHT SU PPDU otherwise indicates a VHT MU PPDU
SU Nsts
Partial Aid
TXOP NA
Reserved Reserved bit
VHT-SIG-A2
Short GI 0: short guard interval is not used in the Data field
Short GI NSYMD
SU/MU[0] Coding
LDPC Extra
SU VHT MCS
Beamformed
1: short guard interval is used in the Data field
Reserved Reserved bit
CRC Cyclic redundancy code
Tail Used to terminate the trellis of the convolution coder. Set to 0.
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IEEE 802.11n ← Signal Field
Table 3-7: Demodulation parameters and results for Signal Field result display (IEEE 802.11n)
Field Description
L-SIG field
Rate Symbol rate per second
Reserved Reserved bit
Length Length of payload in OFDM symbols
Parity Parity bit
Tail Signal tail (preset to 0)
HE-SIG-1
MCS Modulation and Coding Scheme (MCS) index of the PPDU as defined in IEEE
Std 802.11-2012 section "20.6 Parameters for HT MCSs"
CBW Channel bandwidth to measure
0: 20 MHz or 40 MHz upper/lower
1: 40 MHz
HT-Length Human-readable length of payload in OFDM symbols
The number of octets of data in the PSDU in the range of 0 to 65 535
HE-SIG-2
Smoothing 1: channel estimate smoothing is recommended
0: only per-carrier independent (unsmoothed) channel estimate is recommended
Not Sounding 1: PPDU is not a sounding PPDU
0: PPDU is a sounding PPDU
Reserved Set to 1
Aggregation 1: PPDU in the data portion of the packet contains an AMPDU
0: otherwise
FEC Coding
STBC Space-Time Block Coding
Short GI Guard interval length PPDU must have to be measured
Num of Extension Spatial Streams
00: no STBC (NSTS = NSS)
≠0: the difference between the number of space-time streams (NSTS) and the
number of spatial streams (NSS) indicated by the MCS
1: short GI used after HT training
0: otherwise
Number of extension spatial streams (N
(sounding)" on page 175)
, see "Extension Spatial Streams
ESS
CRC Cyclic redundancy code of bits 0 to 23 in HT-SIG1 and bits 0 to 9 in HT-SIG2
Tail Bits Used to terminate the trellis of the convolution coder. Set to 0.
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IEEE 802.11ax HE SU PPDU (DL/UL), HE Extended Range SU PPDU ← Signal
Field
Table 3-8: Information provided in the signal fields for IEEE 802.11ax HE SU PPDU (DL/UL) and HE
Extended Range SU PPDU
Field Description
L-SIG field
Rate Symbol rate per second
Reserved Reserved bit
Length Length of payload in OFDM symbols
Parity Parity bit
Tail Signal tail (preset to 0)
HE-SIG-A1
Format PPDU format used for measurement
Beam Change
UL/DL
MCS Modulation and Coding Scheme (MCS) index of the PPDU
DCM
BSS Color
Reserved Reserved bit
Spatial Reuse
BW Channel bandwidth to measure
GI + LTF Size Guard interval length and long training field PPDU must have to be measured
Nsts For MIMO measurements only:
HE-SIG-A2
TXOP Duration
0: 20 MHz
1: 40 MHz
2: 80 MHz
3: 80+80 MHz and 160MHz
Number of space-time streams (NSTS) for each user, see "User Defined Spatial
Mapping" on page 177
Coding
LDPC Extra Symbol
STBC Space-Time Block Coding
TxBF
00: no STBC (NSTS = NSS)
≠0: the difference between the number of space-time streams (NSTS) and the
number of spatial streams (NSS) indicated by the MCS
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Field Description
Pre-FEC Padding Factor
PE Disambiguity
Reserved Reserved bit
Doppler
CRC Cyclic redundancy code of bits 0 to 23 in HT-SIG1 and bits 0 to 9 in HT-SIG2
Tail Used to terminate the trellis of the convolution coder. Set to 0.
IEEE 802.11ax HE MU PPDU (DL) ← Signal Field
Table 3-9: Information provided in the signal fields for IEEE 802.11ax HE MU PPDU (DL)
Field Description
L-SIG field
Rate Symbol rate per second
Reserved Reserved bit
Length Length of payload in OFDM symbols
Parity Parity bit
Tail Signal tail (preset to 0)
HE-SIG-A1
UL/DL
SIGB MCS Modulation and Coding Scheme (MCS) index of the PPDU as defined in stan-
SIGB DCM
BSS Color
Spatial Reuse
BW Channel bandwidth to measure
Num of HE-SIG-B Symbols or MU-MIMO...
SIGB Compression
GI + LTF Size Guard interval length and long training field PPDU must have to be measured
Doppler
HE-SIG-A2
TXOP Duration
dard
0: 20 MHz
1: 40 MHz
2: 80 MHz
3: 80+80 MHz and 160MHz
Reserved
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Field Description
Num of HE-LTF Symbols
LDPC Extra Symbol
STBC Space-Time Block Coding
TxBF
Pre-FEC Padding Factor
PE Disambiguity
Reserved
Doppler
CRC Cyclic redundancy code of bits 0 to 23 in HT-SIG1 and bits 0 to 9 in HT-SIG2
Tail Used to terminate the trellis of the convolution coder. Set to 0.
00: no STBC (NSTS = NSS)
≠0: the difference between the number of space-time streams (NSTS) and the
number of spatial streams (NSS) indicated by the MCS
IEEE 802.11ax HE Trigger-based PPDU (UL) ← Signal Field
Table 3-10: Information provided in the signal fields for IEEE 802.11ax HE Trigger-based PPDU (UL)
Field Description
L-SIG field
Rate Symbol rate per second
Reserved Reserved bit
Length Length of payload in OFDM symbols
Parity Parity bit
Tail Signal tail (preset to 0)
HE-SIG-A1
Format PPDU format used for measurement
BSS Color
Spatial Reuse 1
Spatial Reuse 2
Spatial Reuse 3
Spatial Reuse 4
Reserved
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Field Description
BW Channel bandwidth to measure
0: 20 MHz
1: 40 MHz
2: 80 MHz
3: 80+80 MHz and 160MHz
HE-SIG-A2
TXOP Duration
Reserved
CRC Cyclic redundancy code of bits 0 to 23 in HT-SIG1 and bits 0 to 9 in HT-SIG2
Tail Used to terminate the trellis of the convolution coder. Set to 0.
IEEE 802.11be EHT MU PPDU (DL) / IEEE 802.11be EHT trigger-based PPDU (UL)
← Signal Field
Table 3-11: Information provided in the signal fields for IEEE 802.11be EHT PPDUs
Field Description
L-SIG field
Rate Symbol rate per second
Reserved Reserved bit
Length Length of payload in OFDM symbols
Parity Parity bit
Tail Signal tail (preset to 0)
EHT U-SIG-1 (for first 80-MHz-segment)
PHY Version Identifier
BW Channel bandwidth to measure
0: 20 MHz
1: 40 MHz
2: 80 MHz
3: 160MHz
4: 320 MHz
UL/DL
BSS Color
TXDP
Disregard
Validate
EHT U-SIG-2 (for first 80-MHz-segment)
PPDU Type and Compression mode
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Field Description
Validate
Punctured Channel
Information
Validate
EHT-SIG MCS
Number of EHT-SIG
Symbols
CRC Cyclic redundancy code of bits 0 to 23 in HT-SIG1 and bits 0 to 9 in HT-SIG2
Tail Used to terminate the trellis of the convolution coder. Set to 0.
EHT U-SIG-1 (for second 80-MHz-segment)
...
EHT U-SIG-2 (for second 80-MHz-segment)
...
EHT U-SIG-1 (for third 80-MHz-segment)
...
EHT U-SIG-2 (for third 80-MHz-segment)
...
EHT U-SIG-1 (for fourth 80-MHz-segment)
...
EHT U-SIG-2 (for fourth 80-MHz-segment)
...
Spectrum Flatness
The "Spectrum Flatness" trace is derived from the magnitude of the estimated channel
transfer function. Since this estimated channel is calculated from all payload symbols
of the PPDU, it represents a carrier-wise mean gain of the channel. We assume the
cable connection between the DUT and the R&S FSV/A adds no residual channel distortion. Then the "Spectrum Flatness" shows the spectral distortion caused by the DUT,
for example the transmit filter.
This result display is not available for single-carrier measurements (IEEE 802.11b, g
(DSSS)).
The diagram shows the relative power per carrier. All carriers are displayed, including
the unused carriers.
In contrast to the SISO measurements in previous Rohde & Schwarz signal and spectrum analyzers, the trace is no longer normalized to 0 dB, that is: scaled by the mean
gain of all carriers.
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For more information, see Chapter 4.3.6, "Crosstalk and spectrum flatness",
on page 90.
Figure 3-30: Spectrum flatness result display for IEEE 802.11n MIMO measurements
The numeric trace results for this evaluation method are described in
Chapter 9.9.4.19,
"Spectrum flatness", on page 386.
Remote command:
LAY:ADD? '1',RIGH, SFL, see LAYout:ADD[:WINDow]? on page 316
Or:
CONF:BURS:SPEC:FLAT:SEL FLAT (see CONFigure:BURSt:SPECtrum:
FLATness:SELect on page 224) and CONFigure:BURSt:SPECtrum:FLATness[:
IMMediate] on page 224
Querying results:
TRACe[:DATA]?, see Chapter 9.9.4.19, "Spectrum flatness", on page 386
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Spectrum Flatness Result Summary
Provides numeric results for the Spectrum Flatness trace. This is useful to check the
maximum transmit spectral deviations defined by the IEEE 802.11 ax standard.
Maximum deviations are bandwidth and subcarrier dependant. The overall subcarrier
range is divided into subranges by the standard. For each subrange, the "Spectrum
Flatness" "Result Summary" provides the following values:
(The first row indicates the results for the entire subcarrier range.)
Table 3-12: Spectrum Flatness deviation results
Result Description
"Range Low/Subc." Subcarrier number at start of subrange
"Range Up/Subc." Subcarrier number at end of subrange
"Δ Lower Limit/dB" The minimal distance from the subcarriers in the subrange to the lower tolerance
limit (defined by standard)
"@Subcarrier" Subcarrier number with the minimal distance to the lower limit
"Δ Upper Limit/dB" The minimal distance from the subcarriers in the subrange to the upper tolerance
limit (defined by standard)
"@Subcarrier" Subcarrier number with the minimal distance to the upper limit
If the tolerance limit defined by the standard is exceeded, the values are indicated in
red font.
Remote command:
LAY:ADD? '1',RIGH, SFL, see LAYout:ADD[:WINDow]? on page 316
Querying results:
FETCh:SFSummary:ALL? on page 356
Unused Tone Error
The unused tone error evaluation determines the error vector magnitude for unoccupied subcarriers, also referred to as unused tones. For details on this parameter, see
Chapter 3.1.1.8, "Unused tone error", on page 23.
This result is required by the IEEE 802.11ax standard for HE trigger-based PPDUs
with a maximum channel bandwidth of 80 MHz.
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Figure 3-31: Unused tone error for an RU index of 2 and an RU size of 106
The minimum, average and maximum unused tone values are displayed. The x-axis
displays the RU index based on an RU size of 26 subcarriers. The individual measurement points are indicated by blue dots. The error vector magnitude limit per RU group,
relative to the original RU, as specified by the IEEE 802.11ax standard, is indicated by
red lines in the diagram. The result of the overall limit check for the entire channel is
indicated as "Pass" or "Fail".
The "Unused Tone Error" diagram provides an overview of the unused tone error
results of an entire channel at a glance. For detailed numeric results for individual RU
groups, use the Unused Tone Error Summary.
Remote command:
LAY:ADD? '1',RIGH,UTER, see LAYout:ADD[:WINDow]? on page 316
Querying results:
TRACe[:DATA]?, see Chapter 9.9.4.20, "Unused tone error", on page 386
Unused Tone Error Summary
The unused tone error summary determines the error vector magnitude, relative to the
original RU, for unoccupied subcarriers, also referred to as unused tones. For details
on this parameter, see Chapter 3.1.1.8, "Unused tone error", on page 23.
This result is required by the IEEE 802.11ax standard for HE trigger-based PPDUs
with a maximum channel bandwidth of 80 MHz.
Figure 3-32: Unused tone error summary for an RU index of 2 and an RU size of 106 (=4*26)
Note: For an overview of the unused tone error results of an entire channel at a
glance, use the Unused Tone Error diagram.
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Measurements and result displays
Frequency sweep measurements
The "Unused Tone Error Summary" provides the following information for up to 9 RU
groups. Which subcarriers are evaluated in which RU group depends on the size and
index of the resource unit to be checked. For details, see Chapter 3.1.1.8, "Unused
tone error", on page 23.
"RU group"
"RU size"
"Min"
"Mean"
"Max"
"Limit"
"Delta"
"Max RU26
Idx"
"Limit check"
Remote command:
LAY:ADD? '1',RIGH,UTES, see LAYout:ADD[:WINDow]? on page 316
Querying results:
FETCh:UTESummary:ALL? on page 357
Querying limit results:
CALCulate<n>:LIMit<li>:CONTrol[:DATA]? on page 363
CALCulate<n>:LIMit<li>:UPPer[:DATA]? on page 364
CALCulate<n>:LIMit<li>:FAIL? on page 363
Set of subcarriers for which a limit is specified in the standard
Size of the RU, indicated as a factor of 26 (RU26 unit)
Minimum unused tone error measured in the RU group
Mean unused tone error measured in the RU group
Maximum unused tone error measured in the RU group
Limit for unused tone error, relative to the original RU, as specified by
the IEEE 802.11ax standard
Limit - Max = distance of maximum value to limit for the RU group
Index of the subcarrier with the maximum value, based on an RU size
of 26
Result of the limit check for the individual RU group
3.2 Frequency sweep measurements
As described above, the WLAN IQ measurement captures the I/Q data from the WLAN
signal using a (nearly rectangular) filter with a relatively large bandwidth. However,
some parameters specified in the WLAN 802.11 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.
Parameters that are common to several digital standards and are often required in signal and spectrum test scenarios can be determined by the standard measurements
provided in the R&S FSV/A base unit (Spectrum application). These measurements
are performed using a much narrower bandwidth filter, and they 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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3.2.1 Measurement types and results for frequency sweep measure-
Measurements and result displays
Frequency sweep measurements
The Frequency sweep measurements provided by the R&S FSV/A WLAN application
are identical to the corresponding measurements in the base unit, but are pre-configured according to the requirements of the selected WLAN 802.11 standard.
For details on these measurements see the R&S FSV/A User Manual.
The R&S FSV/A WLAN application provides the following frequency sweep measurements:
ments
The R&S FSV/A WLAN application provides the following pre-configured frequency
sweep measurements:
Channel Power ACLR...................................................................................................63
Spectrum Emission Mask..............................................................................................64
Occupied Bandwidth..................................................................................................... 64
CCDF............................................................................................................................ 65
Channel Power ACLR
"Channel Power ACLR" performs an adjacent channel power (also known as adjacent
channel leakage ratio) measurement according to WLAN 802.11 specifications.
The R&S FSV/A measures the channel power and the relative power of the adjacent
channels and of the alternate channels. The results are displayed in the "Result Summary".
For details see Chapter 5.4.1, "Channel power (ACLR) measurements", on page 194.
Remote command:
CONFigure:BURSt:SPECtrum:ACPR[:IMMediate] on page 226
Querying results:
CALC:MARK:FUNC:POW:RES? ACP, see CALCulate<n>:MARKer<m>:FUNCtion:
POWer<sb>:RESult? on page 367
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Frequency sweep measurements
Spectrum Emission Mask
Access: "Overview" > "Select Measurement" > "SEM"
Or: [MEAS] > "Select Measurement" > "SEM"
The "Spectrum Emission Mask" (SEM) measurement determines the power of the
WLAN 802.11 signal in defined offsets from the carrier and compares the power values
with a spectral mask specified by the WLAN 802.11 specifications. The limits depend
on the selected bandclass. Thus, the performance of the DUT can be tested and the
emissions and their distance to the limit be identified.
Note: The WLAN 802.11 standard does not distinguish between spurious and spectral
emissions.
For details see Chapter 5.4.2, "Spectrum emission mask", on page 194.
Figure 3-33: SEM measurement results
Remote command:
CONFigure:BURSt:SPECtrum:MASK[:IMMediate] on page 226
Querying results:
CALCulate<n>:LIMit<li>:FAIL? on page 363
TRAC:DATA? LIST, see TRACe[:DATA]? on page 373
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 %.
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.
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Frequency sweep measurements
For details, see Chapter 5.4.3, "Occupied bandwidth", on page 195.
Remote command:
CONFigure:BURSt:SPECtrum:OBWidth[:IMMediate] on page 226
Querying results:
CALC:MARK:FUNC:POW:RES? OBW, see CALCulate<n>:MARKer<m>:FUNCtion:
POWer<sb>:RESult? on page 367
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 5.4.4, "CCDF", on page 196.
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Measurements and result displays
Frequency sweep measurements
Figure 3-34: CCDF measurement results
Remote command:
CONFigure:BURSt:STATistics:CCDF[:IMMediate] on page 226
Querying results:
CALCulate<n>:MARKer<m>:Y? on page 392
CALCulate<n>:STATistics:RESult<res>? on page 370
3.2.2 Evaluation methods for frequency sweep measurements
The evaluation methods for frequency sweep measurements in the R&S FSV/A WLAN
application are identical to those in the R&S FSV/A base unit (Spectrum application).
Diagram.........................................................................................................................66
Result Summary............................................................................................................67
Marker Table................................................................................................................. 67
Marker Peak List........................................................................................................... 68
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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Frequency sweep measurements
Remote command:
LAY:ADD? '1',RIGH, DIAG, see LAYout:ADD[:WINDow]? on page 316
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.
Remote command:
LAY:ADD? '1',RIGH, RSUM, see LAYout:ADD[:WINDow]? on page 316
Marker Table
Displays a table with the current marker values for the active markers.
This table is displayed automatically if configured accordingly.
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 316
Results:
CALCulate<n>:MARKer<m>:X on page 370
CALCulate<n>:MARKer<m>:Y? on page 392
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Frequency sweep measurements
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.
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 316
Results:
CALCulate<n>:MARKer<m>:X on page 370
CALCulate<n>:MARKer<m>:Y? on page 392
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4 Measurement basics
4.1 Signal processing for multicarrier measurements
Measurement basics
Signal processing for multicarrier measurements (IEEE 802.11a, g (OFDM), j, p)
Some background knowledge on basic terms and principles used in WLAN measurements is provided here for a better understanding of the required configuration settings.
(IEEE 802.11a, g (OFDM), j, p)
This description gives a rough view of the signal processing when using the R&S FSV3
WLAN application with the IEEE 802.11a, g (OFDM), j, p standards. Details are disregarded in order to provide a concept overview.
Abbreviations
a
l,k
EVM
k
EVM Error vector magnitude of current packet
g Signal gain
Δf Frequency deviation between Tx and Rx
l Symbol index l = {1 ... nof_Symbols}
nof_symbols Number of symbols of payload
H
k
k Channel index k = {–31 ... 32}
K
mod
ξ Relative clock error of reference oscillator
r
l,k
Symbol at symbol l of subcarrier k
Error vector magnitude of subcarrier k
Channel transfer function of subcarrier k
Modulation-dependent normalization factor
Subcarrier of symbol l
● Block diagram for multicarrier measurements.........................................................69
● Literature on the IEEE 802.11a standard................................................................76
4.1.1 Block diagram for multicarrier measurements
A diagram of the significant blocks when using the IEEE 802.11a, g (OFDM), j, p standard in the R&S FSV3 WLAN application is shown in Figure 4-1.
First the RF signal is downconverted to the IF frequency fIF. The resulting IF signal rIF(t)
is shown on the left-hand side of the figure. After bandpass filtering, the signal is sam-
pled by an analog to digital converter (ADC) at a sample rate of fs1. This digital
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Measurement basics
Signal processing for multicarrier measurements (IEEE 802.11a, g (OFDM), j, p)
sequence is resampled. Thus, the sample rate of the downsampled sequence r(i) is the
Nyquist rate of fs3 = 20 MHz. Up to this point the digital part is implemented in an ASIC.
Figure 4-1: Block diagram for the R&S FSV3 WLAN application using the IEEE 802.11a, g (OFDM), j, p
standard
In the lower part of the figure the subsequent digital signal processing is shown.
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kl
phasephasej
klkl
neHgaKr
kl
common
l
kl
,
(
,mod
)timing(
,
)(
,
Measurement basics
Signal processing for multicarrier measurements (IEEE 802.11a, g (OFDM), j, p)
Packet search and timing detection
In the first block the packet search is performed. This block detects the long symbol
(LS) and recovers the timing. The coarse timing is detected first. This search is implemented in the time domain. The algorithm is based on cyclic repetition within the LS
after N = 64 samples. Numerous treatises exist on this subject, e.g. [1] to [3].
Furthermore, a coarse estimate Δ
of the Rx-Tx frequency offset Δf is derived
coarse
from the metric in [6]. (The hat generally indicates an estimate, e.g. is the estimate of
·Δ
x.) This can easily be understood because the phase of r(i)
r* (i + N) is determined
by the frequency offset. As the frequency deviation Δf can exceed half a bin (distance
between neighboring subcarriers) the preceding short symbol (SS) is also analyzed in
order to detect the ambiguity.
After the coarse timing calculation the time estimate is improved by the fine timing
calculation. This is achieved by first estimating the coarse frequency response
(LS)
Ĥ
,
k
where k = {–26.. 26} denotes the channel index of the occupied subcarriers. First the
FFT of the LS is calculated. After the FFT calculation the known symbol information of
the LS subcarriers is removed by dividing by the symbols. The result is a coarse estimate
Ĥ
of the channel transfer function. In the next step, the complex channel impulse
k
response is computed by an IFFT. Then the energy of the windowed impulse response
(the window size is equal to the guard period) is calculated for each trial time. Afterwards the trial time of the maximum energy is detected. This trial time is used to adjust
the timing.
Determing the payload window
Now the position of the LS is known and the starting point of the useful part of the first
payload symbol can be derived. In the next block this calculated time instant is used to
position the payload window. Only the payload part is windowed. This is sufficient
because the payload is the only subject of the subsequent measurements.
In the next block the windowed sequence is compensated by the coarse frequency
estimate
Δ
. This is necessary because otherwise inter-channel interference (ICI)
course
would occur in the frequency domain.
The transition to the frequency domain is achieved by an FFT of length 64. The FFT is
performed symbol-wise for each symbol of the payload ("nof_symbols"). The calculated FFTs are described by r
●
l = {1 .. nof_symbols} as the symbol index
●
k = {–31 .. 32} as the channel index
with:
l,k
In case of an additive white Gaussian noise (AWGN) channel, the FFT is described by
[4], [5]
Equation 4-1: FFT
with:
●
K
: the modulation-dependant normalization factor
mod
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lrests
common
l
dlTfNNphase
/2
)(
Measurement basics
Signal processing for multicarrier measurements (IEEE 802.11a, g (OFDM), j, p)
●
a
: the symbol of subcarrier k at symbol l
l,k
●
gl: the gain at the symbol l in relation to the reference gain g = 1 at the long symbol
(LS)
●
Hk: the channel frequency response at the long symbol (LS)
●
phasel
(common)
: the common phase drift phase of all subcarriers at symbol l (see
Common phase drift)
●
phase
l,k
(timing)
: the phase of subcarrier k at symbol l caused by the timing drift (see
Common phase drift)
●
n
: the independent Gaussian distributed noise samples
l,k
Phase drift and frequency deviation
The common phase drift in FFT is given by:
Equation 4-2: Common phase drift
with
●
Ns = 80: the number of Nyquist samples of the symbol period
●
N = 64: the number of Nyquist samples of the useful part of the symbol
●
Δ f
: the (not yet compensated) frequency deviation
rest
●
dϒ l: the phase jitter at the symbol l
In general, the coarse frequency estimate Δ
Therefore the remaining frequency error Δf
(see Figure 4-1) is not error-free.
coarse
represents the frequency deviation in r
rest
l,k
not yet compensated. Consequently, the overall frequency deviation of the device
under test (DUT) is calculated by:
The common phase drift in Common phase drift is divided into two parts to calculate
the overall frequency deviation of the DUT.
The reason for the phase jitter dγ l in Common phase drift may be different. The nonlinear part of the phase jitter may be caused by the phase noise of the DUT oscillator.
Another reason for nonlinear phase jitter may be the increase of the DUT amplifier
temperature at the beginning of the PPDU. Note that besides the nonlinear part the
phase jitter, dγ l also contains a constant part. This constant part is caused by the fre-
quency deviation Δ f
not yet compensated. To understand this, keep in mind that the
rest
measurement of the phase starts at the first symbol l = 1 of the payload. In contrast,
the channel frequency response Hk in FFT represents the channel at the long symbol
of the preamble. Consequently, the frequency deviation Δ f
not yet compensated
rest
produces a phase drift between the long symbol and the first symbol of the payload.
Therefore, this phase drift appears as a constant value ("DC value") in dϒ l.
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lkNNphase
skl
/2
)timing(
,
Measurement basics
Signal processing for multicarrier measurements (IEEE 802.11a, g (OFDM), j, p)
Tracking the phase drift, timing jitter and gain
Referring to the IEEE 802.11a, g (OFDM), j, p measurement standard, chapter 17.3.9.7
"Transmit modulation accuracy test'' [6], the common phase drift phasel
(common)
must
be estimated and compensated from the pilots. Therefore this "symbol-wise phase
tracking'' is activated as the default setting of the R&S FSV3 WLAN application (see
"Phase Tracking" on page 145).
Furthermore, the timing drift in FFT is given by:
Equation 4-3: Timing drift
with ξ: the relative clock deviation of the reference oscillator
Normally, a symbol-wise timing jitter is negligible and thus not modeled in Timing drift.
However, there may be situations where the timing drift has to be taken into account.
This is illustrated by an example: In accordance to [6], the allowed clock deviation of
the DUT is up to ξ
= 20 ppm. Furthermore, a long packet with 400 symbols is
max
assumed. The result of FFT and Timing drift is that the phase drift of the highest subcarrier k = 26 in the last symbol l = nof_symbols is 93 degrees. Even in the noise-free
case, this would lead to symbol errors. The example shows that it is actually necessary
to estimate and compensate the clock deviation, which is accomplished in the next
block.
Referring to the IEEE 802.11a, g (OFDM), j, p measurement standard [6], the timing
drift phase
(timing)
is not part of the requirements. Therefore the "time tracking" is not
l,k
activated as the default setting of the R&S FSV3 WLAN application (see "Timing Error
Tracking" on page 145). The time tracking option should rather be seen as a powerful
analyzing option.
In addition, the tracking of the gain gl in FFT is supported for each symbol in relation to
the reference gain g = 1 at the time instant of the long symbol (LS). At this time the
coarse channel transfer function
This makes sense since the sequence r
(LS)
fer function
before estimating the symbols. Consequently, a potential change of
k
(LS)
is calculated.
k
'
is compensated by the coarse channel trans-
l,k
the gain at the symbol l (caused, for example, by the increase of the DUT amplifier
temperature) may lead to symbol errors especially for a large symbol alphabet M of the
MQAM transmission. In this case, the estimation and the subsequent compensation of
the gain are useful.
Referring to the IEEE 802.11a, g (OFDM), j, p measurement standard [6], the compensation of the gain gl is not part of the requirements. Therefore the "gain tracking" is not
activated as the default setting of the R&S FSV3 WLAN application (see "Level Error
(Gain) Tracking" on page 145).
Determining the error parameters (log likelihood function)
How can the parameters above be calculated? In this application the optimum maximum likelihood algorithm is used. In the first estimation step the symbol-independent
parameters Δ f
and ξ are estimated. The symbol-dependent parameters can be
rest
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Measurement basics
Signal processing for multicarrier measurements (IEEE 802.11a, g (OFDM), j, p)
neglected in this step, i.e. the parameters are set to gl = 1 and dγ = 0. Referring to
FFT, the log likelihood function L must be calculated as a function of the trial parame-
ters Δ
and . (The tilde generally describes a trial parameter. Example: is the trial
rest
parameter of x.)
Equation 4-4: Log likelihood function (step 1)
with:
The trial parameters leading to the minimum of the log likelihood function are used as
estimates Δ
and . In Log likelihood function (step 1) the known pilot symbols a
rest
l,k
are read from a table.
In the second step, the log likelihood function is calculated for every symbol l as a function of the trial parameters
Equation 4-5: Log likelihood function (step 2)
and dl:
l
with:
Finally, the trial parameters leading to the minimum of the log likelihood function are
used as estimates l and dl.
This robust algorithm works well even at low signal to noise ratios with the Cramer Rao
Bound being reached.
Compensation
After estimation of the parameters, the sequence r
is compensated in the compensa-
l,k
tion blocks.
In the upper analyzing branch the compensation is user-defined i.e. the user determines which of the parameters are compensated. This is useful in order to extract the
influence of these parameters. The resulting output sequence is described by: γ
'
.
δ,k
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packetsnof
counter
counterEVM
packetsnof
EVM
_
1
2
)(
_
1
26
)0(26
2
52
1
kk
k
EVMEVM
Measurement basics
Signal processing for multicarrier measurements (IEEE 802.11a, g (OFDM), j, p)
Data symbol estimation
In the lower compensation branch the full compensation is always performed. This
separate compensation is necessary in order to avoid symbol errors. After the full compensation the secure estimation of the data symbols â
is performed. From FFT it is
l,k
clear that first the channel transfer function Hk must be removed. This is achieved by
(LS)
dividing the known coarse channel estimate
calculated from the LS. Usually an
k
error free estimation of the data symbols can be assumed.
Improving the channel estimation
In the next block a better channel estimate
(PL)
of the data and pilot subcarriers is cal-
k
culated by using all "nof_symbols" symbols of the payload (PL). This can be accomplished at this point because the phase is compensated and the data symbols are
known. The long observation interval of nof_symbols symbols (compared to the short
interval of 2 symbols for the estimation of
(LS)
) leads to a nearly error-free channel
k
estimate.
In the following equalizer block,
resulting channel-compensated sequence is described by γ
choose the coarse channel estimate
free channel estimate
mate
(LS)
is used, a 2 dB reduction of the subsequent EVM measurement can be
k
(PL)
k
(LS)
is compensated by the channel estimate. The
k
(LS)
(from the long symbol) or the nearly error-
k
''
. The user may either
δ,k
(from the payload) for equalization. If the improved esti-
expected.
According to the IEEE 802.11a measurement standard [6], the coarse channel estima-
(LS)
tion
(from the long symbol) has to be used for equalization. Therefore the default
k
setting of the R&S FSV3 WLAN application is equalization from the coarse channel
estimate derived from the long symbol.
Calculating error parameters
In the last block the parameters of the demodulated signal are calculated. The most
important parameter is the error vector magnitude of the subcarrier "k" of the current
packet:
Equation 4-6: Error vector magnitude of the subcarrier k in current packet
Furthermore, the packet error vector magnitude is derived by averaging the squared
EVMk versus k:
Equation 4-7: Error vector magnitude of the entire packet
Finally, the average error vector magnitude is calculated by averaging the packet EVM
of all nof_symbols detected packets:
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symbolsnof
l
klklk
aKr
symbolsnof
EVM
_
1
2
,mod
''
,
_
1
Measurement basics
Signal processing for single-carrier measurements (IEEE 802.11b, g (DSSS))
Equation 4-8: Average error vector magnitude
This parameter is equivalent to the "RMS average of all errors": Error
of the IEEE
RMS
802.11a measurement commandment (see [6]).
4.1.2 Literature on the IEEE 802.11a standard
[1] Speth, Classen, Meyr: ''Frame synchronization of OFDM systems in frequency selective fading
channels", VTC '97, pp. 1807-1811
[2] Schmidl, Cox: ''Robust Frequency and Timing Synchronization of OFDM", IEEE Trans. on Comm.,
Dec. 1997, pp. 1613-621
[3] Minn, Zeng, Bhargava: ''On Timing Offset Estimation for OFDM", IEEE Communication Letters,
July 2000, pp. 242-244
[4] Speth, Fechtel, Fock, Meyr: ''Optimum receive antenna Design for Wireless Broad-Band Systems
Using OFDM – Part I", IEEE Trans. On Comm. VOL. 47, NO 11, Nov. 1999
[5] Speth, Fechtel, Fock, Meyr: ''Optimum receive antenna Design for Wireless Broad-Band Systems
Using OFDM – Part II", IEEE Trans. On Comm. VOL. 49, NO 4, April. 2001
[6] IEEE 802.11a, Part 11: WLAN Medium Access Control (MAC) and Physical Layer (PHY) specifica-
tions
4.2 Signal processing for single-carrier measurements (IEEE 802.11b, g (DSSS))
This description gives a rough overview of the signal processing concept of the WLAN
802.11 application for IEEE 802.11b or g (DSSS) signals.
Abbreviations
ε timing offset
Δf frequency offset
ΔΦ phase offset
I
Q
Δ
Q
(v)
s
(v)
r
I
estimate of the gain factor in the I-branch
estimate of the gain factor in the Q-branch
accurate estimate of the crosstalk factor of the Q-branch in the I-branch
estimated baseband filter of the transmit antenna
estimated baseband filter of the receive antenna
estimate of the IQ-offset in the I-branch
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Signal processing for single-carrier measurements (IEEE 802.11b, g (DSSS))
Q
r(v) measurement signal
(v)
(v)
n
ARG{...} calculation of the angle of a complex value
EVM error vector magnitude
IMAG{...} calculation of the imaginary part of a complex value
PPDU protocol data unit - a burst in the signal containing transmission data
PSDU protocol service data unit- a burst in the signal containing service data
REAL{...} calculation of the real part of a complex value
estimate of the IQ-offset in the I-branch
estimate of the reference signal
estimate of the power-normalized and undisturbed reference signal
● Block diagram for single-carrier measurements......................................................77
● Calculation of signal parameters.............................................................................79
● Literature on the IEEE 802.11b standard................................................................82
4.2.1 Block diagram for single-carrier measurements
A block diagram of the measurement application is shown below in Figure 4-2. The
baseband signal of an IEEE 802.11b or g (DSSS) wireless LAN system transmit
antenna is sampled with a sample rate of 44 MHz.
The first task of the measurement application is to detect the position of the PPDU
within the measurement signal r1(v). The detection algorithm is able to find the begin-
ning of short and long PPDUs and can distinguish between them. The algorithm also
detects the initial state of the scrambler, which is not specified by the IEEE 802.11
standard.
If the start position of the PPDU is known, the header of the PPDU can be demodulated. The bits transmitted in the header provide information about the length of the
PPDU and the modulation type used in the PSDU.
Once the start position and the PPDU length are fully known, better estimates of timing
offset, timing drift, frequency offset and phase offset can be calculated using the entire
data of the PPDU.
At this point of the signal processing, demodulation can be performed without decision
error. After demodulation the normalized (in terms of power) and undisturbed reference
signal s(v) is available.
If the frequency offset is not constant and varies with time, the frequency offset and
phase offset in several partitions of the PPDU must be estimated and corrected. Additionally, timing offset, timing drift and gain factor can be estimated and corrected in several partitions of the PPDU. These corrections can be switched off individually in the
demodulation settings of the application.
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Measurement basics
Signal processing for single-carrier measurements (IEEE 802.11b, g (DSSS))
Figure 4-2: Signal processing for IEEE 802.11b or g (DSSS) signals
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Measurement basics
Signal processing for single-carrier measurements (IEEE 802.11b, g (DSSS))
Once the normalized and undisturbed reference signal is available, the transmit
antenna baseband filter (Tx filter) is estimated by minimizing the cost function of a
maximum-likelihood-based estimator:
Equation 4-9: Transmit antenna baseband filter (Tx filter) estimation
where:
r(v): the oversampled measurement signal
(v): the normalized oversampled power of the undisturbed reference signal
n
N: the observation length
L: the filter length
Δv: the variation parameters of the frequency offset
Δ
: the variation parameters of the phase offset
: the variation parameters of the I/Q offset
I Q
(i): the coefficients of the transmitter filter
s
4.2.2 Calculation of signal parameters
The frequency offset, the phase offset and the IQ-offset are estimated jointly with the
coefficients of the transmit filter to increase the estimation quality.
Once the transmit filter is known, all other unknown signal parameters are estimated
with a maximum-likelihood-based estimation, which minimizes the cost function:
Equation 4-10: Cost function for signal parameters
where:
: the variation parameters of the gain used in the I/Q branch
I Q
: the crosstalk factor of the Q-branch into the I-branch
Δ
Q
sI(v) sQ(v): the filtered reference signal of the I/Q branch
The unknown signal parameters are estimated in a joint estimation process to increase
the accuracy of the estimates.
The accurate estimates of the frequency offset, the gain imbalance, the quadrature
error and the normalized I/Q offset are displayed by the measurement software.
Gain imbalance, I/Q offset, quadrature error
The gain imbalance is the quotient of the estimates of the gain factor of the Q-branch,
the crosstalk factor and the gain factor of the I-branch:
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2
22
22
ˆˆ
ˆˆ
2
1
gg
oo
QI
QI
OffsetIQ
1
0
2
1
0
2
)(
ˆ
)(
ˆ
)(
N
v
N
v
vs
vsvr
EVM
1
0
2
)(
ˆ
)(
ˆ
)(
)(
N
v
vs
vsvr
vEVM
Measurement basics
Signal processing for single-carrier measurements (IEEE 802.11b, g (DSSS))
Equation 4-11: Gain imbalance
The quadrature error is a measure for the crosstalk of the Q-branch into the I-branch:
Equation 4-12: Quadrature error (crosstalk)
The normalized I/Q offset is defined as the magnitude of the I/Q offset normalized by
the magnitude of the reference signal:
Equation 4-13: I/Q offset
At this point of the signal processing all unknown signal parameters such as timing offset, frequency offset, phase offset, I/Q offset and gain imbalance have been evaluated
and the measurement signal can be corrected accordingly.
Error vector magnitude (EVM) - R&S FSV/A method
Using the corrected measurement signal r(v) and the estimated reference signal ŝ(v),
the modulation quality parameters can be calculated. The mean error vector magnitude
(EVM) is the quotient of the root-mean-square values of the error signal power and the
reference signal power:
Equation 4-14: Mean error vector magnitude (EVM)
Whereas the symbol error vector magnitude is the momentary error signal magnitude
normalized by the root mean square value of the reference signal power:
Equation 4-15: Symbol error vector magnitude
Error vector magnitude (EVM) - IEEE 802.11b or g (DSSS) method
In [2] a different algorithm is proposed to calculate the error vector magnitude. In a first
step the IQ-offset in the I-branch and the IQ-offset of the Q-branch are estimated separately:
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1
0
REAL
1
ˆ
N
v
I
r(v)
N
o
1
0
IMAG
1
ˆ
N
v
Q
r(v)
N
o
Measurement basics
Signal processing for single-carrier measurements (IEEE 802.11b, g (DSSS))
Equation 4-16: I/Q offset I-branch
Equation 4-17: I/Q offset Q-branch
where r(v) is the measurement signal which has been corrected with the estimates of
the timing offset, frequency offset and phase offset, but not with the estimates of the
gain imbalance and I/Q offset
With these values the gain imbalance of the I-branch and the gain imbalance of the Qbranch are estimated in a non-linear estimation in a second step:
Equation 4-18: Gain imbalance I-branch
Equation 4-19: Gain imbalance Q-branch
Finally, the mean error vector magnitude can be calculated with a non-data-aided calculation:
Equation 4-20: Mean error vector magnitude
The symbol error vector magnitude is the error signal magnitude normalized by the
root mean square value of the estimate of the measurement signal power:
Equation 4-21: Symbol error vector magnitude
The advantage of this method is that no estimate of the reference signal is needed, but
the I/Q offset and gain imbalance values are not estimated in a joint estimation procedure. Therefore, each estimation parameter disturbs the estimation of the other parameter and the accuracy of the estimates is lower than the accuracy of the estimations
achieved by Transmit antenna baseband filter (Tx filter) estimation. If the EVM value is
dominated by Gaussian noise this method yields similar results as Cost function for
signal parameters.
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4.2.3 Literature on the IEEE 802.11b standard
4.3 Signal processing for MIMO measurements (IEEE
Measurement basics
Signal processing for MIMO measurements (IEEE IEEE 802.11 ac, ax, n, be)
The "EVM vs Symbol" result display shows two traces, each using a different calculation method, so you can easily compare the results (see "EVM vs Symbol"
on page 35).
[1] Institute of Electrical and Electronic Engineers, Part 11: Wireless LAN Medium Access Control
(MAC) and Physical Layer (PHY) specifications, IEEE Std 802.11-1999, Institute of Electrical and
Electronic Engineers, Inc., 1999.
[2] Institute of Electrical and Electronic Engineers, Part 11: Wireless LAN Medium Access Control
(MAC) and Physical Layer (PHY) specifications: Higher-Speed Physical Layer Extensions in the
2.4 GHz Band, IEEE Std 802.11b-1999, Institute of Electrical and Electronic Engineers, Inc., 1999.
IEEE 802.11 ac, ax, n, be)
For measurements according to the IEEE 802.11a, b, g standards, only a single transmit antenna and a single receive antenna are required (SISO = single in, single out).
For measurements according to the IEEE IEEE 802.11 ac, ax, n, be standard, the
R&S FSV/A can measure multiple data streams between multiple transmit antennas
and multiple receive antennas (MIMO = multiple in, multiple out).
As opposed to other Rohde & Schwarz signal and spectrum analyzers, in the R&S
FSV3 WLAN application, MIMO is not selected as a specific standard. Rather, when
you select the IEEE 802.11ac or n standard, MIMO is automatically available. In the
default configuration, a single transmit antenna and a single receive antenna are
assumed, which corresponds to the common SISO setup.
Basic technologies
Some basic technologies used in MIMO systems are introduced briefly here.
For more detailed information, see the following application notes, available from the
Rohde & Schwarz website:
1MA142: "Introduction to MIMO"
1MA192: 802.11ac Technology Introduction
MIMO systems use transmit diversity or space-division multiplexing, or both. With
transmit diversity, a bit stream is transmitted simultaneously via two antennas, but
with different coding in each case. This improves the signal-to-noise ratio and the cell
edge capacity.
For space-division multiplexing, multiple (different) data streams are sent simultaneously from the transmit antennas. Each receive antenna captures the superposition of
all transmit antennas. In addition, channel effects caused by reflections and scattering
etc., are added to the received signals. The receiver determines the originally sent
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Measurement basics
Signal processing for MIMO measurements (IEEE IEEE 802.11 ac, ax, n, be)
symbols by multiplying the received symbols with the inverted channel matrix (that is,
the mapping between the streams and the transmit antennas, see Chapter 4.3.2, "Spa-
tial mapping", on page 84).
Using space-division multiplexing, the transmitted data rates can be increased significantly by using additional antennas.
To reduce the correlation between the propagation paths, the transmit antenna can
delay all of the transmission signals except one. This method is referred to as cyclic
delay diversity or cyclic delay shift.
The basis of the majority of the applications for broadband transmission is the OFDM
method. In contrast to single-carrier methods, an OFDM signal is a combination of
many orthogonal, separately modulated carriers. Since the data is transmitted in parallel, the symbol length is significantly smaller than in single-carrier methods with identical transmission rates.
Signal processing chain
In a test setup with multiple antennas, the R&S FSV/A is likely to receive multiple spatial streams, one from each antenna. Each stream has gone through a variety of transformations during transmission. The signal processing chain is displayed in Figure 4-3,
starting with the creation of the spatial streams in the transmitting device, through the
wireless transmission and ending with the merging of the spatial streams in the receiving device. This processing chain has been defined by IEEE.
The following figure shows the basic processing steps performed by the transmit
antenna and the complementary blocks in reverse order applied at the receive
antenna:
Figure 4-3: Data flow from the transmit antenna to the receive antenna
4.3.1 Space-time block coding (STBC)
The coded bits to be transmitted are modulated to create a data stream, referred to as
a spatial stream, by the stream parser in the transmitting device under test (see Fig-
ure 4-3).
The Space-Time Block Encoder (STBC) implements the transmit diversity technique
(see "Basic technologies" on page 82). It creates multiple copies of the data streams,
each encoded differently, which can then be transmitted by a number of antennas.
To do so, the STBC encodes only the data carriers in the spatial stream using a matrix.
Each row in the matrix represents an OFDM symbol and each column represents one
antenna's transmissions over time (thus the term space-time encoder). This means
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4
1
44
11
4
1
.
.
4.,..1.,
..
..
4.,..1.,
.
.
StreamSTS
StreamSTS
STSTxSTSTx
STSTxSTSTx
StreamTx
StreamTx
4.3.2 Spatial mapping
Measurement basics
Signal processing for MIMO measurements (IEEE IEEE 802.11 ac, ax, n, be)
each block represents the same data, but with a different coding. The resulting blocks
are referred to as space-time streams (STS). Each stream is sent to a different Tx
antenna. This diversity coding increases the signal-to-noise ratio at the receive
antenna. The pilot carriers are inserted after the data carriers went through the STBC.
Thus, only the data carriers are decoded by the analyzer to determine characteristics
of the demodulated data (see also Figure 4-6).
In order to transmit the space-time streams, two or more antennas are required by the
sender, and one or more antennas are required by the receive antenna.
The Spatial Encoder (see Figure 4-3) is responsible for the spatial multiplexing. It
defines the mapping between the streams and the transmit antennas - referred to as
spatial mapping - or as a matrix: the spatial mapping matrix.
In the R&S FSV3 WLAN application, the mapping can be defined using the following
methods:
●
Direct mapping: one single data stream is mapped to an exclusive Tx antenna
(The spatial matrix contains "1" on the diagonal and otherwise zeros.)
●
Spatial Expansion: multiple (different) data streams are assigned to each antenna
in a defined pattern
●
User-defined mapping: the data streams are mapped to the antennas by a userdefined matrix
User-defined spatial mapping
You can define your own spatial mapping between streams and Tx antennas.
For each antenna (Tx1..4), the complex element of each STS-stream is defined. The
upper value is the real part of the complex element. The lower value is the imaginary
part of the complex element.
Additionally, a "Time Shift" can be defined for cyclic delay diversity (CSD).
The stream for each antenna is calculated as:
4.3.3 Physical vs effective channels
The effective channel refers to the transmission path starting from the space-time
stream and ending at the receive antenna. It is the product of the following components:
●
the spatial mapping
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Signal processing for MIMO measurements (IEEE IEEE 802.11 ac, ax, n, be)
●
the crosstalk inside the device under test (DUT) transmission paths
●
the crosstalk of the channel between the transmit antennas and the receive antennas
For each space-time stream, at least one training field (the (V)HT-LTF) is included in
every PPDU preamble (see Figure 4-4). Each sender antenna transmits these training
fields, which are known by the receive antenna. The effective channel can be calculated from the received (and known) (V)HT-LTF symbols of the preamble, without knowledge of the spatial mapping matrix or the physical channel. Thus, the effective channel
can always be calculated.
Figure 4-4: Training fields (TF) in the preamble of PPDUs in IEEE 802.11n standard
The effective channel is sufficient to calculate the EVM, the constellation diagram and
the bitstream results of the measured signal, so these results are always available.
The physical channel refers to the transmission path starting from the transmit
antenna streams and ending at the receive antenna. It is the product of the following
components:
●
the crosstalk inside the device under test (DUT) transmission paths
●
the crosstalk of the channel between the transmit antennas and the receive antennas
The physical channel is derived from the effective channel using the inverted spatial
mapping matrix Q:
H
= H
phy
-1
Q
eff
Thus, if the spatial mapping matrix cannot be inverted, the physical channel cannot be
calculated. This may be the case, for example, if the signal contains fewer streams
than Rx antenna signals, or if the spatial matrix is close to numerical singularity.
In this case, results that are based on the transmit antenna such as I/Q offset, gain
imbalance and quadrature offset are not available.
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4.3.4 Capturing data from MIMO antennas
Measurement basics
Signal processing for MIMO measurements (IEEE IEEE 802.11 ac, ax, n, be)
Crosstalk in estimated channels
Note that the estimated channel transfer function contains crosstalk from various sources, for example:
●
from the transmission paths inside the DUT
●
from the connection between the analyzer and the DUT
●
from the analyzer itself
The crosstalk from the analyzer can be neglected. If the analyzer and DUT are connected by cable, this source of crosstalk can also be neglected. For further information on
crosstalk see Chapter 4.3.6, "Crosstalk and spectrum flatness", on page 90.
The primary purpose of many test applications that verify design parameters, or are
used in production, is to determine if the transmitted signals adhere to the relevant
standards and whether the physical characteristics fall within the specified limits. In
such cases there is no need to measure the various transmit paths simultaneously.
Instead, they can either be tested as single antenna measurements, or sequentially
(with restrictions, see also Chapter 4.3.4.1, "Sequential MIMO measurement",
on page 87). Then only one analyzer is needed to measure parameters such as error
vector magnitude (EVM), power and I/Q imbalance.
Measurements that have to be carried out for development or certification testing are
significantly more extensive. In order to fully reproduce the data in transmit signals or
analyze the crosstalk between the antennas, for example, measurements must be performed simultaneously on all antennas. One analyzer is still sufficient if the system is
using transmit diversity (multiple input single output – MISO). However, space-division
multiplexing requires two or more analyzers to calculate the precoding matrix and
demodulate the signals.
The R&S FSV3 WLAN application provides the following methods to capture data from
the MIMO antennas:
●
Simultaneous MIMO operation
The data streams are measured simultaneously by multiple analyzers. One of the
analyzers is defined as a primary, which receives the I/Q data from the other analyzers (the secondaries). The IP addresses of each secondary analyzer must be
provided to the primary. The only function of the secondariess is to record the data
that is then accumulated centrally by the primary.
(Note that only the MIMO primary analyzer requires the R&S FSV3-K91n or ac
option. The secondary analyzers do not require a R&S FSV3 WLAN application.)
The number of Tx antennas on the DUT defines the number of analyzers required
for this measurement setup.
Tip: Use the primary's trigger output (see Chapter 4.11.5, "Trigger synchronization
using the primary's trigger output", on page 106) or an R&S Z11 trigger box (see
Chapter 4.11.6, "Trigger synchronization using an R&S FS-Z11 trigger unit",
on page 106) to send the same trigger signal to all devices.
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Signal processing for MIMO measurements (IEEE IEEE 802.11 ac, ax, n, be)
The primary calculates the measurement results based on the I/Q data captured by
all analyzers (primary and secondaries) and displays them in the selected result
displays.
●
Sequential using open switch platform
The data streams are measured sequentially by a single analyzer connected to an
additional switch platform that switches between antenna signals. No manual interaction is necessary during the measurement. The R&S FSV3 WLAN application
captures the I/Q data for all antennas sequentially and calculates and displays the
results (individually for each data stream) in the selected result displays automatically.
A single analyzer and the Rohde & Schwarz OSP Switch Platform is required to
measure the multiple DUT Tx antennas (the switch platform must be fitted with at
least one R&S®OSP-B101 option; the number depends on the number of Tx
antennas to measure). The IP address of the OSP and the used module (configuration bank) must be defined on the analyzer; the required connections between
the DUT Tx antennas, the switch box and the analyzer are indicated in the MIMO
"Signal Capture" dialog box.
For important restrictions concerning sequential measurement see Chap-
ter 4.3.4.1, "Sequential MIMO measurement", on page 87.
●
Sequential using manual operation
The data streams are captured sequentially by a single analyzer. The antenna signals must be connected to the single analyzer input sequentially by the user.
In the R&S FSV3 WLAN application, individual capture buffers are provided (and
displayed) for each antenna input source, so that results for the individual data
streams can be calculated. The user must initiate data capturing for each antenna
and result calculation for all data streams manually.
For important restrictions concerning sequential measurement see Chap-
ter 4.3.4.1, "Sequential MIMO measurement", on page 87.
●
Single antenna measurement
The data from the Tx antenna is measured and evaluated as a single antenna
(SISO) measurement ("DUT MIMO configuration" = "1 Tx antenna").
4.3.4.1 Sequential MIMO measurement
Sequential MIMO measurement allows for MIMO analysis with a single analyzer by
capturing the receive antennas one after another (sequentially). However, sequential
MIMO measurement requires each Tx antenna to transmit the same PPDU over time.
(The PPDU content from different Tx antennas, on the other hand, may be different.) If
this requirement can not be fulfilled, use the simultaneous MIMO capture method (see
Chapter 4.3.4, "Capturing data from MIMO antennas", on page 86).
In addition, the following PPDU attributes must be identical for ALL antennas:
●
PPDU length
●
PPDU type
●
Channel bandwidth
●
MCS Index
●
Guard Interval Length
●
Number of STBC Streams
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Signal processing for MIMO measurements (IEEE IEEE 802.11 ac, ax, n, be)
●
Number of Extension Streams
Thus, for each PPDU the "Signal Field" bit vector has to be identical for ALL antennas!
Figure 4-5: Basic principle of “Sequential MIMO Measurement” with 2 receive antennas
Note that, additionally, the data contents of the sent PPDU payloads must also be the
same for each Tx antenna, but this is not checked. Thus, useless results are returned if
different data was sent.
To provide identical PPDU content for each Tx antenna in the measurement, you can
use the same pseudo-random bit sequence (PRBS) with the same PRBS seed (initial
bit sequence), for example, when generating the useful data for the PPDU.
4.3.5 Calculating results
When you analyze a WLAN signal in a MIMO setup, the R&S FSV/A acts as the
receiving device. Since most measurement results have to be calculated at a particular
stage in the processing chain, the R&S FSV3 WLAN application has to do the same
decoding that the receive antenna does.
The following diagram takes a closer look at the processing chain and the results at its
individual stages.
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Signal processing for MIMO measurements (IEEE IEEE 802.11 ac, ax, n, be)
Figure 4-6: Results at individual processing stages
Receive antenna results
The R&S FSV3 WLAN application can determine receive antenna results directly from
the captured data at the receive antenna, namely:
●
PPDU Power
●
Crest factor
For all other results, the R&S FSV3 WLAN application has to revert the processing
steps to determine the signal characteristics at those stages.
Transmit antenna results (based on the physical channel)
If the R&S FSV3 WLAN application can determine the physical channel (see Chap-
ter 4.3.3, "Physical vs effective channels", on page 84), it can evaluate the following
results:
●
"Channel Flatness" (based on the physical channel)
●
"Group Delay" (based on the physical channel)
●
"I/Q Offset"
●
"Quadrature Offset"
●
"Gain Imbalance"
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Space-time stream results (based on the effective channel)
If the application knows the effective channel (see Chapter 4.3.3, "Physical vs effective
channels", on page 84), it can evaluate the following results:
●
"Channel Flatness" (based on the effective channel)
●
"Group Delay" (based on the effective channel)
●
"EVM" of pilot carriers
●
"Constellation" of pilot carriers
●
"Bitstream" of pilot carriers
Spatial stream results
If space-time encoding is implemented, the demodulated data must first be decoded to
determine the following results:
●
"EVM" of data carriers
●
"Constellation" diagram
●
"Bitstream"
The pilot carriers are inserted directly after the data carriers went through the STBC
(see also Chapter 4.3.1, "Space-time block coding (STBC)", on page 83). Thus, only
the data carriers need to be decoded by the analyzer to determine characteristics of
the demodulated data. Because of this approach to calculate the "EVM", "Constellation" and "Bitstream" results, you might get results for a different number of streams for
pilots and data carriers if STBC is applied.
4.3.6 Crosstalk and spectrum flatness
In contrast to the SISO measurements in previous Rohde & Schwarz signal and spectrum analyzers, the spectrum flatness trace is no longer normalized to 0 dB (scaled by
the mean gain of all carriers).
For MIMO there may be different gains in the transmission paths and you do not want
to lose the relation between these transmission paths. For example, in a MIMO transmission path matrix we have paths carrying power (usually the diagonal elements for
the transmitted streams), but also elements with only residual crosstalk power. The
power distribution of the transmission matrix depends on the spatial mapping of the
transmitted streams. But even if all matrix elements carry power, the gains may be different. This is the reason why the traces are no longer scaled to 0 dB. Although the
absolute gain of the "Spectrum Flatness" is not of interrest, it is now maintained in
order to show the different gains in the transmission matrix elements. Nevertheless,
the limit lines are still symmetric to the mean trace, individually for each element of the
transmission matrix.
By default, full MIMO equalizing is performed by the R&S FSV3 WLAN application.
However, you can deactivate compensation for crosstalk (see "Compensate Cross-
talk(MIMO only)" on page 146). In this case, simple main path equalizing is performed
only for direct connections between Tx and Rx antennas, disregarding ancillary trans-
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4.4 Signal processing for high-efficiency wireless mea-
Measurement basics
Signal processing for high-efficiency wireless measurements (IEEE 802.11ax)
mission between the main paths (crosstalk). This is useful to investigate the effects of
crosstalk on results such as EVM.
surements (IEEE 802.11ax)
The IEEE 802.11ax standard, also known as High Efficiency Wireless (HEW), provides
mechanisms to more efficiently utilize the unlicensed spectrum bands (2.4 GHz and
5 GHz) and improve user experience.
It is particularly meant for use in dense environments with large numbers of users
(referred to as stations) and base stations (referred to as access points).
Currently, the specification for this standard is still under development by the IEEE
organization. The basic features and processing methods described here and used by
the R&S FSV3 WLAN application are based on the draft version 1.0 from December
2016.
For more information, see also the Rohde & Schwarz White Paper 1MA222: IEEE
802.11ax Technology Introduction.
4.4.1 Basic signal characteristics
PPDU formats
The new 802.11ax standard introduces four new PPDU (Packet Protocol Data Unit)
formats:
●
HE SU (Single User) PPDU (HE_SU): used to transmit to a single user
●
HE Extended Range PPDU (HE_EXT_SU): used to transmit to a single user who
is further away from the AP, such as in outdoor scenarios; Only available for
20 MHz channel bandwidths
●
HE MU (Multi-User) PPDU (HE-MU): carries one or more transmissions to one or
more users
●
HE Trigger-Based PPDU (HE_Trig): carries a single transmission and is sent in
response to a trigger frame; Used for OFDMA and/or MU MIMO uplink transmission
OFDMA
This new standard allows for the OFDMA method to be employed, where the available
channel bandwidth (between 20 MHz and 160 MHz) is divided between multiple users.
Each user is assigned a predefined number of subcarriers (also referred to as tones).
This subset of subcarriers is referred to as a resource unit (RU). RU sizes can vary
between 26 subcarriers and (2x) 996 subcarriers. All users transmit their data simultaneously, and each data packet has the same length. However, the resource units used
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Measurement basics
Signal processing for high-efficiency wireless measurements (IEEE 802.11ax)
by the individual users may have different lengths. In other words: each user can use a
different number of subcarriers or channel bandwidth.
Figure 4-7: OFDMA frequency vs time usage
The OFDMA method provides several advantages versus the OFDM method:
●
Flexible bandwidth allocation per user means each user blocks only the frequency
range that they need
●
Each station can use a different modulation according to the current SNR
●
In the time range, less overhead is required
Resource units (RUs)
Depending on the available channel bandwidth and the size of the used RUs, the following number of resource units are available at the same time:
Table 4-1: Number of RUs depending on channel bandwidth and RU size
Channel bandwidth
RU size (number
of subcarriers)
26 9 18 37 74
52 4 8 16 32
106 2 4 8 16
242 1 2 4 8
484
20 MHz 40 MHz 80 MHz 160 MHz
1 2 4
996
2*996
1 2
1
Each RU in the channel is indexed. Depending on the size of the RU and the available
channel bandwidth, the RU index refers to different subcarriers.
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Signal processing for high-efficiency wireless measurements (IEEE 802.11ax)
Figure 4-8: Example: RU indexing for 20 MHz channel bandwidth
The available RUs in a channel are assigned to the users sequentially according to the
current transmission requirements. Generally, one user is assigned to one RU (for
MIMO see "Multi-User (MU-)MIMO" on page 94). Although the RU sizes may vary per
user, if both the RU index and the RU size is known, the position of a specific user's
RU within the channel is uniquely identifiable.
In Example: RU indexing for 20 MHz channel bandwidth, the RUs indicated by the red
boxes are uniquely identifiable by the following information:
Table 4-2: Unique identification of RUs in a channel
User User 1 User 2 User 3 User 4 User 5
RU size 52 26 26 26 (13+13) 106
RU index RU1 RU3 RU4 RU5 RU2
HE Signal fields and PPDU configuration
The combination of RU size and RU indexes for a channel are referred to as the RU
allocation. Using 8 bits, each possible combination of RU sizes and positions for a
20 MHz channel (242 subcarriers) can be coded. These codes are defined in the
802.11ax specification.
As all WLAN signals, each HE PPDU contains a signal field (Sig-A) that defines the
general PPDU configuration (see also "Signal Field" on page 50). In addition, multiuser PPDUs contain a second signal field (Sig-B) which defines the RU allocation and
user assignment. The HE-Sig B field in turn consists of two parts:
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Signal processing for high-efficiency wireless measurements (IEEE 802.11ax)
●
Common field: contains the RU allocation coding
●
User specific field: contains the user ID, MIMO, MCS and coding information
Figure 4-9: HE Sig-B field structure
The HE Sig-B field is a 20 MHz channel that provides the RU allocation for users within
a 20 MHz span (242 subcarriers) of the channel. For a 40 MHz channel, two SIG-B
channels are required to code the RU allocation for the entire span. For an 80 MHz
channel, the common field is extended to 2 x 8 bits, so that the RU allocation of
40 MHz can be coded in one common field (RU1+RU3 or RU2+RU4). Thus, two extended common fields are required to provide the RU allocation information for the entire
80 MHz signal. However, since the 80 MHz signal contains four 20 MHz SIG-B fields,
the information in the first two fields is duplicated, and thus redundant:
Figure 4-10: HE Sig-B field for 80 MHz channel bandwidth
This coding allows for the receiver to decode only 40 MHz bandwidth and still obtain
the RU allocation information for the entire signal.
Multi-User (MU-)MIMO
As a rule, each resource unit is assigned to one user (see "Resource units (RUs)"
on page 92). However, the 802.11ax standard also supports MIMO mode for HE multiuser PPDUs, both in uplink and downlink transmission. In MIMO mode, each resource
unit with a size of 106 subcarriers or more can be assigned to multiple users (8, 16, or
32, depending on the channel bandwidth).
If MIMO is used with HE MU PPDUs, the location of the individual user's data is determined by the station (user) ID and spatial configuration provided in the HE-SIG-B field.
For more information on MIMO see also Chapter 4.3, "Signal processing for MIMO
measurements (IEEE IEEE 802.11 ac, ax, n, be)", on page 82.
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4.4.2 Demodulating 802.11ax signals in the R&S FSV3 WLAN application
Measurement basics
Signal processing for high-efficiency wireless measurements (IEEE 802.11ax)
HE Trigger-based PPDUs
In order for the access point (AP) to decode packets from multiple users, the uplink
transmissions need to be synchronized when the AP receives them. After the users
receive information from the AP to trigger the uplink transmissions (by a trigger frame),
they transmit the HE_Trig PPDU at a specified time.
The number of users transmitting simultaneously is defined by the high efficiency long
training field (HE-LTF). The length of the HE-LTF that the users should use for uplink
transmission is defined in the trigger frame sent by the access point. The trigger frame
also defines the length of the expected uplink packet.
In order to demodulate high-efficiency PPDUs in the R&S FSV3 WLAN application, the
application must have knowledge of the used PPDU format and the PPDU configuration. For multi-user PPDUs, the RU allocation and user assignment are also required.
Depending on the available channel bandwidth, the following multi-user configuration
must be defined:
●
For channels with 20 MHz bandwidth, only 1 configuration is required (RU1).
●
For channels with 40 MHz bandwidth, 2 configurations are required in different tabs
(RU1 and RU2).
●
For channels with 80 MHz bandwidth, 4 configurations are required, in 4 different
tabs (RU1 to RU4), where the contents of RU1 and RU3 are identical, and RU2
and RU4 are identical.
●
For channels with 2x80 MHz or 160 MHz bandwidth, 4 configurations are required
for each 80-MHz-segment of the channel (Segment 1 and Segment 2).
For single user (HE SU-PPDU) and trigger-based PPDUs (UL), the configuration is
detected automatically by the R&S FSV3 WLAN application. For multi-user downlink
PPDUs (HE MU_PPDU), you must define the configuration manually (see "HE PPDU
Config" on page 157).
For trigger-based PPDUs, you must also define the length of the HE-LTF field in the
PPDUs in the R&S FSV3 WLAN application.
Result displays for multi-user PPDUs
The result displays show the demodulated data for the selected RUs. The currently displayed RUs are highlighted green in the PPDU configuration table and the result displays. For multi-user configuration, the results cannot be displayed for an individual
user. If you select an RU, the rows for all users of the RU are highlighted.
By default, the first RU is selected. To view the results of different RUs, select the RUs
in the table by clicking in the first column ("#"), then Refresh.
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Signal processing for extremely high throughput (EHT) wireless measurements (IEEE 802.11be)
4.5 Signal processing for extremely high throughput
4.5.1 Basic signal characteristics
Measurement basics
(EHT) wireless measurements (IEEE 802.11be)
The IEEE 802.11be standard, also known as extremely high throughput (EHT), provides mechanisms to process data rates over 30 Gbps. In addition, special attention is
paid to keeping latency rates low (under 5 ms). It uses the unlicensed spectrum bands
at 2.4 GHz, 5 GHz and 6 GHz. The standard aims at remaining compatible to previous
standards in the same range. It is particularly meant for use in applications with high
data volumes, such as virtual reality, gaming, or videos.
Currently, the specification for this standard is still under development by the IEEE
organization. The basic features and processing methods described here and used by
the R&S FSV3 WLAN application are based on the draft version 0.3 from January
2021.
PPDU formats
The new 802.11be standard introduces two new PPDU (PHY Protocol Data Unit) formats:
●
EHT MU PPDU: extremely high throughput multi-user PPDU. This PPDU carries
one or more transmissions to one or more users. Only the download PPDU is currently supported for demodulation by the R&S FSV3 WLAN application.
●
EHT Trigger-Based PPDU (UL): carries a single transmission and is sent in
response to a trigger frame; Used for OFDMA and/or MU MIMO uplink transmission
Measuring trigger-based PPDUs requires bandwidth information for the signal to
be defined by the user.
The physical layer of the 802.11be standard uses some of the same methods as the
802.11ax standard, including OFDMA, resource units, and multi-user MIMO (see
Chapter 4.4, "Signal processing for high-efficiency wireless measurements (IEEE
802.11ax)", on page 91). However, to improve the throughput, higher modulation meth-
ods are supported, such as 4096QAM. The number of spatial streams is increased to
16. And the channel bandwidth is increased to 320 MHz.
In addition, the 802.11be standard allows for multiple resource units to be assigned to
a single user for high throughput requirements.
RU allocation
Similar to the 802.11ax standard, resource units are assigned to users in the RU allocation. However, as opposed to the 802.11ax standard, multiple resource units (MRUs)
with up to 996 tones = 80 MHz can be assigned to a single user. The MRU allocation is
defined in the signal field. To avoid a complex combination of RUs and users, the
802.11be standard defines the following restrictions for RU allocation:
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●
Large RUs with 242, 484, or 996 tones can only be combined with other RUs of
these sizes.
●
Smaller RUs with fewer than 242 tones can only be combined with other small
RUs. Not all combinations of small RUs are allowed, see the specification for
details.
●
Each 80-MHz segment of the RU allocation that is used by a single user (without
puncturing) is assigned a single 996-tone RU.
●
For all other scenarios, RUs smaller than 996 tones are combined in compliance
with the mentioned restrictions.
Segment puncturing
Sometimes other services use one or more subcarriers within the same range as a
802.11be standard signal. In this case, these subcarriers cannot be included in the RU
allocation. The subcarriers are temporarily blocked in the 80-MHz-segment, which is
thus referred to as "punctured". The subcarriers remain unused, while the remaining
usable subcarriers are allocated to users as usual. The 802.11be standard defines 12
different configurations of ignored and usable carriers within an 80-MHz-segment. Only
those configurations are supported. The used configuration (MRU index) must be
defined in the PPDU configuration.
EHT signal fields
In addition to the common L-SIG field, the 802.11be standard introduces new signal
fields named U-SIG and EHT-SIG to the EHT PPDU. They include version-specific
information for the physical layer of the signal.
Multi-User (MU-)MIMO
The 802.11be standard also supports MIMO mode for EHT multi-user PPDUs, both in
uplink and downlink transmission. In MIMO mode, each resource unit with a size of
106 subcarriers or more can be assigned to multiple users (8, 16, or 32, depending on
the channel bandwidth).
If MIMO is used with EHT MU PPDUs, the location of the individual user's data is
determined by the station (user) ID and spatial configuration provided in the EHT-SIGB field.
For more information on MIMO see also Chapter 4.3, "Signal processing for MIMO
measurements (IEEE IEEE 802.11 ac, ax, n, be)", on page 82.
EHT Trigger-based PPDUs
In order for the access point (AP) to decode packets from multiple users, the uplink
transmissions need to be synchronized when the AP receives them. After the users
receive information from the AP to trigger the uplink transmissions (by a trigger frame),
they transmit the EHT_Trig PPDU at a specified time.
The number of users transmitting simultaneously is defined by the EHT long training
field (EHT-LTF). The length of the EHT-LTF that the users should use for uplink transmission is defined in the trigger frame sent by the access point. The trigger frame also
defines the length of the expected uplink packet.
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4.5.2 Demodulating 802.11be signals in the R&S FSV3 WLAN application
Measurement basics
Channels and carriers
In order to demodulate extremely high throughput (EHT) PPDUs in the R&S FSV3
WLAN application, the application must have knowledge of the used PPDU configuration. The RU allocation and user assignment, as well as the MRU assignment, are also
required.
Depending on the available channel bandwidth, the following multi-user configuration
must be defined:
●
For channels with 20 MHz bandwidth, only 1 configuration is required (RU1).
●
For channels with 40 MHz bandwidth, 2 configurations are required in different tabs
(RU1 and RU2).
●
For channels with 80 MHz bandwidth, 4 configurations are required, in 4 different
tabs (RU1 to RU4), where the contents of RU1 and RU3 are identical, and RU2
and RU4 are identical.
●
For channels with 2x80 MHz or 160 MHz bandwidth, 4 configurations are required
for each 80-MHz-segment of the channel (Segment 1 and Segment 2).
●
For channels with 320 MHz bandwidth, 4 configurations are required for each 80MHz-segment of the channel (Segment 1, 2, 3, 4)
For multi-user downlink PPDUs (EHT MU PPDU), you must define the configuration
manually (see "EHT PPDU Config" on page 164).
For trigger-based PPDUs, you must also define the length of the EHT-LTF field in the
PPDUs in the R&S FSV3 WLAN application.
Result displays for multi-user PPDUs
The result displays show the demodulated data for the selected RUs. The currently displayed RUs are highlighted green in the PPDU configuration table and the result displays. For multi-user configuration, the results cannot be displayed for an individual
user. If you select an RU, the rows for all users of the RU are highlighted.
By default, the first RU is selected. To view the results of different RUs, select the RUs
in the table by clicking in the first column ("#"), then Refresh.
4.6 Channels and carriers
In an OFDM system such as WLAN, the channel is divided into carriers using FFT /
IFFT. Depending on the channel bandwidth, the FFT window varies between 64 and
512 (see also Chapter 4.8, "Demodulation parameters - logical filters", on page 99).
Some of these carriers can be used (active carriers), others are inactive (e.g. guard
carriers at the edges). The channel can then be determined using the active carriers as
known points; inactive carriers are interpolated.
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4.7 Recognized vs. analyzed PPDUs
Measurement basics
Demodulation parameters - logical filters
A PPDU in a WLAN signal consists of the following parts:
(For IEEE 802.11n see also Figure 4-4)
●
Preamble
Information required to recognize the PPDU within the signal, for example training
fields
●
Signal Field
Information on the modulation used for transmission of the useful data
●
Payload
The useful data
During signal processing, PPDUs are recognized by their preamble symbols. The recognized PPDUs and the information on the modulation used for transmission of the
useful data are shown in the "Signal Field" result display (see "Signal Field"
on page 50).
Not all of the recognized PPDUs are analyzed. Some are dismissed because the
PPDU parameters do not match the user-defined demodulation settings, which act as
a logical filter (see also Chapter 4.8, "Demodulation parameters - logical filters",
on page 99). Others may be dismissed because they contain too many or too few
payload symbols (as defined by the user), or due to other irregularities or inconsistency.
Dismissed PPDUs are indicated as such in the "Signal Field" result display (highlighted
red, with a reason for dismissal).
PPDUs with detected inconsistencies are indicated by orange highlighting and a warning in the "Signal Field" result display, but are nevertheless analyzed and included in
statistical and global evaluations.
The remaining correct PPDUs are highlighted green in the "Magnitude Capture" buffer
and "Signal Field" result displays and analyzed according to the current user settings.
Example:
The evaluation range is configured to take the "Source of Payload Length" from the
signal field. If the power period detected for a PPDU deviates from the PPDU length
coded in the signal field, a warning is assigned to this PPDU. The decoded signal field
length is used to analyze the PPDU. The decoded and measured PPDU length
together with the appropriate information is shown in the "Signal Field" result display.
4.8 Demodulation parameters - logical filters
The demodulation settings define which PPDUs are to be analyzed, thus they define a
logical filter. They can either be defined using specific values or according to the first
measured PPDU.
Which of the WLAN demodulation parameter values are supported depends on the
selected digital standard, some are also interdependant.
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Demodulation parameters - logical filters
Table 4-3: Supported modulation formats, PPDU formats and channel bandwidths depending on
standard
Standard Modulation formats PPDU formats Channel bandwidths
IEEE 802.11a, g
(OFDM), j, p
BPSK (6 Mbps & 9 Mbps)
QPSK (12 Mbps &
18 Mbps)
Non-HT
Short PPDU
Long PPDU
2.5 MHz, 5 MHz, 10 MHz,
*)
20 MHz
16QAM (24 Mbps &
36 Mbps)
64QAM (48 Mbps &
54 Mbps)
IEEE 802.11ac 16QAM
64QAM
256QAM
1024QAM
HT-MF (Mixed format)
HT-GF (Greenfield format)
VHT
NON-HT<Channel Band-
20 MHz*), 40 MHz*), 80 MHz*),
160 MHz
*)
width>
IEEE 802.11b, g
(DSSS)
DBPSK (1 Mbps)
DQPSK (2 Mbps)
Short PPDU
Long PPDU
22 MHz
CCK (5.5 Mbps &
11 Mbps)
PBCC (5.5 Mbps &
11 Mbps)
IEEE 802.11n SISO:
BPSK (6.5, 7.2, 13.5 &
HT-MF (Mixed format)
HT-GF (Greenfield format)
20 MHz*), 40 MHz
*)
15 Mbps)
QPSK (13, 14.4, 19.5,
21.7, 27, 30, 40,5 &
45 Mbps)
16QAM (26, 28.9, 39, 43.3,
54, 60, 81 & 90 Mbps)
64QAM (52, 57.8, 58.5, 65,
72.2, 108, 121.5, 135, 120,
135 & 150 Mbps)
MIMO:
depends on the MCS index
IEEE 802.11ax BPSK, QPSK, 16QAM,
64QAM, 256QAM,
1024QAM
HE<Channel Bandwidth>SU
HE<Channel Band-
20 MHz*), 40 MHz*), 80 MHz*),
160 MHz
*)
width>MU
HE<Channel Band-
width>EXT
HE<Channel Band-
width>TB (Trigger-based)
*)
: requires R&S FSV/A bandwidth extension option
See Chapter A, "Sample rate and maximum usable I/Q bandwidth for RF input", on page 407.
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