R&S®FPS-K91
WLAN Measurements
User Manual
(;ÚãÁ2)
1176.8551.02 ─ 08
User Manual
Test & Measurement
This manual applies to the following R&S®FPS models with firmware version 1.50 and higher:
●
R&S®FPS4 (1319.2008K04)
●
R&S®FPS7 (1319.2008K07)
●
R&S®FPS13 (1319.2008K13)
●
R&S®FPS30 (1319.2008K30)
●
R&S®FPS40 (1319.2008K40)
The following firmware options are described:
●
R&S FPS-K91 WLAN 802.11a/b/g (1321.4191.02)
●
R&S FPS-K91ac WLAN 802.11ac (1321.4210.02)
●
R&S FPS-K91n WLAN 802.11n (1321.4204.02)
●
R&S FPS-K91p WLAN 802.11p (1321.4391.02)
© 2017 Rohde & Schwarz GmbH & Co. KG
Mühldorfstr. 15, 81671 München, Germany
Phone: +49 89 41 29 - 0
Fax: +49 89 41 29 12 164
Email: info@rohde-schwarz.com
Internet: www.rohde-schwarz.com
Subject to change – Data without tolerance limits is not binding.
R&S® is a registered trademark of Rohde & Schwarz GmbH & Co. KG.
Trade names are trademarks of their owners.
The following abbreviations are used throughout this manual: R&S®FPS is abbreviated as R&S FPS.
R&S®FPS-K91
1.1 About this Manual......................................................................................................... 5
1.2 Typographical Conventions.........................................................................................6
2.1 Starting the WLAN Application....................................................................................8
2.2 Understanding the Display Information......................................................................8
3.1 WLAN I/Q Measurement (Modulation Accuracy, Flatness and Tolerance)............11
3.2 Frequency Sweep Measurements............................................................................. 47
Contents
Contents
1 Preface.................................................................................................... 5
2 Welcome to the WLAN Application...................................................... 7
3 Measurements and Result Displays...................................................11
4 Measurement Basics........................................................................... 54
4.1 Signal Processing for Multicarrier Measurements (IEEE 802.11a, g (OFDM), j, p)
...................................................................................................................................... 54
4.2 Signal Processing for Single-Carrier Measurements (IEEE 802.11b, g (DSSS))... 61
4.3 Signal Processing for MIMO Measurements (IEEE 802.11ac, n)............................ 67
4.4 Channels and Carriers................................................................................................76
4.5 Recognized vs. Analyzed PPDUs.............................................................................. 76
4.6 Demodulation Parameters - Logical Filters.............................................................. 77
4.7 Basics on Input from I/Q Data Files...........................................................................78
4.8 Triggered Measurements........................................................................................... 79
4.9 WLAN I/Q Measurements in MSRA Operating Mode............................................... 83
5 Configuration........................................................................................85
5.1 Multiple Measurement Channels and Sequencer Function.................................... 85
5.2 Display Configuration.................................................................................................87
5.3 WLAN I/Q Measurement Configuration.....................................................................87
5.4 Frequency Sweep Measurements........................................................................... 149
6 Analysis.............................................................................................. 154
7 I/Q Data Import and Export................................................................155
7.1 Import/Export Functions.......................................................................................... 155
7.2 How to Export and Import I/Q Data..........................................................................157
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8.1 How to Determine Modulation Accuracy, Flatness and Tolerance Parameters for
8.2 How to Determine the OBW, SEM, ACLR or CCDF for WLAN Signals.................162
9.1 Measurement Example: Setting up a MIMO measurement................................... 163
10 Optimizing and Troubleshooting the Measurement....................... 170
10.1 Optimizing the Measurement Results..................................................................... 170
10.2 Error Messages and Warnings................................................................................ 171
11 Remote Commands for WLAN 802.11 Measurements....................173
11.1 Common Suffixes......................................................................................................173
11.2 Introduction............................................................................................................... 174
Contents
8 How to Perform Measurements in the WLAN Application............. 160
WLAN Signals............................................................................................................160
9 Basic Measurement Examples..........................................................163
11.3 Activating WLAN 802.11 Measurements.................................................................179
11.4 Selecting a Measurement......................................................................................... 183
11.5 Configuring the WLAN IQ Measurement (Modulation Accuracy, Flatness and Tol-
erance)....................................................................................................................... 190
11.6 Configuring Frequency Sweep Measurements on WLAN 802.11 Signals........... 251
11.7 Configuring the Result Display................................................................................255
11.8 Starting a Measurement........................................................................................... 275
11.9 Retrieving Results.....................................................................................................280
11.10 Analysis..................................................................................................................... 324
11.11 Status Registers........................................................................................................327
11.12 Deprecated Commands............................................................................................ 331
11.13 Programming Examples (R&S FPS WLAN application)........................................ 333
Annex.................................................................................................. 339
A Annex: Reference...............................................................................339
A.1 Sample Rate and Maximum Usable I/Q Bandwidth for RF Input.......................... 339
A.2 I/Q Data File Format (iq-tar)......................................................................................343
List of Remote Commands (WLAN)................................................. 349
Index....................................................................................................358
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1 Preface
Preface
About this Manual
1.1 About this Manual
This WLAN User Manual provides all the information specific to the application. All
general instrument functions and settings common to all applications and operating
modes are described in the main R&S FPS User Manual.
The main focus in this manual is on the measurement results and the tasks required to
obtain them. The following topics are included:
●
Chapter 2, "Welcome to the WLAN Application", on page 7
Introduction to and getting familiar with the application
●
Chapter 3, "Measurements and Result Displays", on page 11
Details on supported measurements and their result types
●
Chapter 4, "Measurement Basics", on page 54
Background information on basic terms and principles in the context of the measurement
●
Chapter 5, "Configuration", on page 85 and Chapter 6, "Analysis", on page 154
A concise description of all functions and settings available to configure measurements and analyze results with their corresponding remote control command
●
Chapter 7.1, "Import/Export Functions", on page 155
Description of general functions to import and export raw I/Q (measurement) data
●
Chapter 8, "How to Perform Measurements in the WLAN Application",
on page 160
The basic procedure to perform each measurement and step-by-step instructions
for more complex tasks or alternative methods
●
Chapter 10, "Optimizing and Troubleshooting the Measurement", on page 170
Hints and tips on how to handle errors and optimize the test setup
●
Chapter 11, "Remote Commands for WLAN 802.11 Measurements", on page 173
Remote commands required to configure and perform WLAN measurements in a
remote environment, sorted by tasks
(Commands required to set up the environment or to perform common tasks on the
instrument are provided in the main R&S FPS User Manual)
Programming examples demonstrate the use of many commands and can usually
be executed directly for test purposes
●
Chapter A, "Annex: Reference", on page 339
Reference material
●
List of remote commands
Alpahabetical list of all remote commands described in the manual
●
Index
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Preface
Typographical Conventions
1.2 Typographical Conventions
The following text markers are used throughout this documentation:
Convention Description
"Graphical user interface elements"
KEYS Key names are written in capital letters.
File names, commands,
program code
Input Input to be entered by the user is displayed in italics.
Links Links that you can click are displayed in blue font.
"References" References to other parts of the documentation are enclosed by quota-
All names of graphical user interface elements on the screen, such as
dialog boxes, menus, options, buttons, and softkeys are enclosed by
quotation marks.
File names, commands, coding samples and screen output are distinguished by their font.
tion marks.
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2 Welcome to the WLAN Application
Welcome to the WLAN Application
The R&S FPS WLAN application extends the functionality of the R&S FPS 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 802.11g (OFDM)
●
IEEE standards 802.11g (DSSS)
●
IEEE standards 802.11j
●
IEEE standards 802.11n (SISO + MIMO)
●
IEEE standards 802.11p
The R&S FPS 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.
Functions that are not discussed in this manual are the same as in the Spectrum application and are described in the R&S FPS User Manual. The latest version is available
for download at the product homepage
http://www2.rohde-schwarz.com/product/FPS.html.
Installation
You can find detailed installation instructions in the R&S FPS Getting Started manual
or in the Release Notes.
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Welcome to the WLAN Application
Understanding the Display Information
2.1 Starting the WLAN Application
The WLAN measurements require a special application on the R&S FPS.
Manual operation via an external monitor and mouse
Although the R&S FPS does not have a built-in display, it is possible to operate it interactively in manual mode using a graphical user interface with an external monitor and
a mouse connected.
It is recommended that you use the manual mode initially to get familiar with the instrument and its functions before using it in pure remote mode. Thus, this document
describes in detail how to operate the instrument manually using an external monitor
and mouse. The remote commands are described in the second part of the document.
For details on manual operation see the R&S FPS Getting Started manual.
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 FPS.
2. Select the "WLAN" item.
The R&S FPS 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 88).
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
MSRA operating mode
In MSRA operating mode, additional tabs and elements are available. A colored background of the screen behind the measurement channel tabs indicates that you are in
MSRA operating mode.
For details on the MSRA operating mode see the R&S FPS MSRA User Manual.
Channel bar information
In the WLAN application, the R&S FPS 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"
"PPDU / MCS Index / GI+HELTF"
IEEE 802.11a, ac, g (OFDM), j, n, p, ax:
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.
WLAN 802.11ax only: PPDU type, MCS index, guard interval (GI), and
high-efficiency long training field (HE-LTF) used for the analysis of the signal
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Welcome to the WLAN Application
Understanding the Display Information
Label Description
"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
"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 137):
<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 FPS Getting Started manual.
Window title bar information
For each diagram, the header provides the following information:
Figure 2-1: Window title bar information in the WLAN application
1 = Window number
2 = Window type
3 = Trace color
4 = Trace number
6 = Trace mode
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
Measurements and Result Displays
WLAN I/Q Measurement (Modulation Accuracy, Flatness and Tolerance)
The R&S FPS 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 "Selecting the measurement type"
on page 85.
● WLAN I/Q Measurement (Modulation Accuracy, Flatness and Tolerance).............11
● Frequency Sweep Measurements.......................................................................... 47
3.1 WLAN I/Q Measurement (Modulation Accuracy, Flatness 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 FPS 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 47).
● Modulation Accuracy, Flatness and Tolerance Parameters....................................11
● Evaluation Methods for WLAN IQ Measurements.................................................. 20
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, g (OFDM), j, n, p
Parameter Description
General measurement parameters
Sample Rate Fs Input sample rate
PPDU Type of analyzed PPDUs
MCS Index Modulation and Coding Scheme (MCS) index of the analyzed PPDUs
*) the limits can be changed via remote control (not manually, see Chapter 11.5.9, "Limits", on page 244);
in this case, the currently defined limits are displayed here
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Measurements and Result Displays
WLAN I/Q Measurement (Modulation Accuracy, Flatness and Tolerance)
Parameter Description
Data Rate Data rate used for analysis of the signal
(IEEE 802.11a only)
GI Guard interval length for current measurement
Standard Selected WLAN measurement standard
Meas Setup Number of Transmitter (Tx) and Receiver (Rx) channels used in the measure-
ment
Capture time Duration of signal capture
Samples Number of samples captured
Data Symbols The minimum and maximum number of data symbols that a PPDU can have if
it is to be considered in results analysis
PPDU parameters
Analyzed PPDUs For statistical evaluation of PPDUs (see "PPDU Statistic Count / No of PPDUs
to Analyze" on page 137): <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 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 channel power
Gain imbalance [%/dB] Amplification of the quadrature phase component of the signal relative to the
Quadrature offset [°] Deviation of the quadrature phase angle from the ideal 90° (see Chap-
I/Q skew [s] Delay of the transmission of the data on the I path compared to the Q path
PPDU power [dBm] Mean PPDU power
Crest factor [dB] The ratio of the peak power to the mean power of the signal (also called Peak
MIMO Cross Power [dB]
Number of PPDUs recognized in capture buffer
Number of analyzed PPDUs in capture buffer
Number of PPDUs analyzed in entire signal (if available)
(see Chapter 3.1.1.1, "I/Q Offset", on page 15)
amplification of the in-phase component (see Chapter 3.1.1.2, "Gain Imbal-
ance", on page 15)
ter 3.1.1.3, "Quadrature Offset", on page 16).
(see Chapter 3.1.1.4, "I/Q Skew", on page 17)
to Average Power Ratio, PAPR).
*) the limits can be changed via remote control (not manually, see Chapter 11.5.9, "Limits", on page 244);
in this case, the currently defined limits are displayed here
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Measurements and Result Displays
WLAN I/Q Measurement (Modulation Accuracy, Flatness and Tolerance)
Parameter Description
Center frequency error
[Hz]
Symbol clock error [ppm] Clock error between the signal and the sample clock of the R&S FPS in parts
CPE Common phase error
Stream parameters
BER Pilot [%] Bit error rate (BER) of the pilot carriers
EVM all carriers [%/dB] EVM (Error Vector Magnitude) of the payload symbols over all carriers; the
EVM data carriers [%/dB] EVM (Error Vector Magnitude) of the payload symbols over all data carriers;
EVM pilot carriers [%/dB] EVM (Error Vector Magnitude) of the payload symbols over all pilot carriers;
Frequency error between the signal and the current center frequency of the
R&S FPS; the corresponding limits specified in the standard are also indicated*)
The absolute frequency error includes the frequency error of the R&S FPS and
that of the DUT. If possible, synchronize the transmitter R&S FPS and the DUT
using an external reference.
See R&S FPS user manual > Instrument setup > External reference
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 FPS and the DUT using an external reference.
See R&S FPS user manual > Instrument setup > External reference
corresponding limits specified in the standard are also indicated*)
the corresponding limits specified in the standard are also indicated*)
the corresponding limits specified in the standard are also indicated*)
*) the limits can be changed via remote control (not manually, see Chapter 11.5.9, "Limits", on page 244);
in this case, the currently defined limits are displayed here
Table 3-2: WLAN I/Q parameters for IEEE 802.11b or g (DSSS)
Parameter Description
Sample Rate Fs Input sample rate
PPDU Type of the analyzed PPDU
Data Rate Data rate used for analysis of the signal
SGL Indicates single measurement mode (as opposed to continuous)
Standard Selected WLAN measurement standard
Meas Setup Number of Transmitter (Tx) and Receiver (Rx) channels used in the measure-
ment
Capture time Duration of signal capture
No. of Samples Number of samples captured (= sample rate * capture time)
No. of Data Symbols The minimum and maximum number of data symbols that a PPDU can have if
it is to be considered in results analysis
PPDU parameters
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Measurements and Result Displays
WLAN I/Q Measurement (Modulation Accuracy, Flatness and Tolerance)
Parameter Description
Analyzed PPDUs For statistical evaluation of PPDUs (see "PPDU Statistic Count / No of PPDUs
to Analyze" on page 137): <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 recognized
PPDUs (global)
Number of analyzed
PPDUs (global)
Number of analyzed
PPDUs in physical channel
Peak vector error Peak vector error (EVM) over the complete PPDU including the preamble in %
PPDU EVM EVM (Error Vector Magnitude) over the complete PPDU including the pream-
I/Q offset [dB] Transmitter center frequency leakage relative to the total Tx channel power
Gain imbalance [%/dB] Amplification of the quadrature phase component of the signal relative to the
Quadrature error [°] Measure for the crosstalk of the Q-branch into the I-branch (see "Gain imbal-
Center frequency error
[Hz]
Number of PPDUs recognized in capture buffer
Number of analyzed PPDUs in capture buffer
Number of PPDUs analyzed in entire signal (if available)
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 19);
The corresponding limits specified in the standard are also indicated *)
ble in % and dB
(see Chapter 3.1.1.1, "I/Q Offset", on page 15)
amplification of the in-phase component (see Chapter 3.1.1.2, "Gain Imbal-
ance", on page 15)
ance, I/Q offset, quadrature error" on page 65).
Frequency error between the signal and the current center frequency of the
R&S FPS; the corresponding limits specified in the standard are also indicated*)
The absolute frequency error includes the frequency error of the R&S FPS
and that of the DUT. If possible, synchronize the transmitter R&S FPS and the
DUT using an external reference.
See R&S FPS user manual > Instrument setup > External reference
Chip clock error [ppm] Clock error between the signal and the chip clock of the R&S FPS 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 FPS and the DUT using an external reference.
See R&S FPS user manual > Instrument setup > External reference
Rise time Time the signal needs to increase its power level from 10% to 90% of the
maximum or the average power (depending on the reference power setting)
The corresponding limits specified in the standard are also indicated *)
Fall time Time the signal needs to decrease its power level from 90% to 10% of the
maximum or the average power (depending on the reference power setting)
The corresponding limits specified in the standard are also indicated *)
Mean power [dBm] Mean PPDU power
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Measurements and Result Displays
WLAN I/Q Measurement (Modulation Accuracy, Flatness and Tolerance)
Parameter Description
Peak power [dBm] Peak PPDU power
Crest factor [dB] The ratio of the peak power to the mean power of the PPDU (also called Peak
to Average Power Ratio, PAPR).
The R&S FPS 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
3.1.1.1 I/Q Offset
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:
Imbalance [dB] = 20log (| GainQ |/| GainI |)
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:
0.98 ≈ 20*log10(1.12/1)
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Measurements and Result Displays
WLAN I/Q Measurement (Modulation Accuracy, Flatness and Tolerance)
Figure 3-2: Positive gain imbalance
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:
-0.98 ≈ 20*log10(1/1.12)
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:
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Measurements and Result Displays
WLAN I/Q Measurement (Modulation Accuracy, Flatness and Tolerance)
Figure 3-4: Positive quadrature offset
A negative quadrature offset means a phase angle less than 90 degrees:
Figure 3-5: Negative quadrature offset
3.1.1.4 I/Q Skew
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 118).
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.
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Measurements and Result Displays
WLAN I/Q Measurement (Modulation Accuracy, Flatness and Tolerance)
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 FPS WLAN application
The IQ offset measurement in the R&S FPS 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.
The RF carrier suppression measured according to the standard is inversely proportional to the IQ offset measured in the R&S FPS 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
3.1.1.7 EVM Measurement
The R&S FPS 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
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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.
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 FPS 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 FPS WLAN application does not limit the measurement to 1000 chips length, but searches the maximum over the whole PPDU.
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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.
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 87).
●
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.
MIMO measurements
When you capture more than one data stream (MIMO measurement setup, see Chap-
ter 4.3, "Signal Processing for MIMO Measurements (IEEE 802.11ac, n)",
on page 67), each result display contains several tabs. The results for each data
stream are displayed in a separate tab. In addition, an overview tab is provided in
which all data streams are displayed at once, in individual subwindows.
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 308).
The WLAN measurements provide the following evaluation methods:
AM/AM.......................................................................................................................... 21
AM/PM.......................................................................................................................... 22
AM/EVM........................................................................................................................22
Bitstream.......................................................................................................................23
Constellation................................................................................................................. 25
Constellation vs Carrier.................................................................................................27
EVM vs Carrier..............................................................................................................28
EVM vs Chip................................................................................................................. 29
EVM vs Symbol.............................................................................................................29
FFT Spectrum............................................................................................................... 30
Freq. Error vs Preamble................................................................................................31
Gain Imbalance vs Carrier............................................................................................ 32
Group Delay..................................................................................................................33
Magnitude Capture........................................................................................................34
Phase Error vs Preamble..............................................................................................34
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Phase Tracking............................................................................................................. 35
PLCP Header (IEEE 802.11b, g (DSSS)...................................................................... 35
PvT Full PPDU..............................................................................................................37
PvT Rising Edge........................................................................................................... 38
PvT Falling Edge...........................................................................................................39
Quad Error vs Carrier....................................................................................................39
Result Summary Detailed............................................................................................. 40
Result Summary Global................................................................................................ 41
Signal Field................................................................................................................... 43
Spectrum Flatness........................................................................................................ 46
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 143) 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)).
Remote command:
LAY:ADD? '1',RIGH,AMAM, see LAYout:ADD[:WINDow]? on page 258
Or:
CONFigure:BURSt:AM:AM[:IMMediate] on page 184
Polynomial degree:
CONFigure:BURSt:AM:AM:POLYnomial on page 268
Results:
TRACe[:DATA], see Chapter 11.9.4.1, "AM/AM", on page 313
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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 258
Or:
CONFigure:BURSt:AM:PM[:IMMediate] on page 184
Querying results:
TRACe[:DATA], see Chapter 11.9.4.2, "AM/PM", on page 313
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 258
Or:
CONFigure:BURSt:AM:EVM[:IMMediate] on page 184
Querying results:
TRACe[:DATA], see Chapter 11.9.4.3, "AM/EVM", on page 313
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 3-7: Bitstream result display for IEEE 802.11a, ac, g (OFDM), j, n, p standards
For MIMO measurements (IEEE 802.11 ac, n), the results are grouped by stream,
symbol and carrier.
Figure 3-8: 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 3-9: Bitstream result display for IEEE 802.11b, g (DSSS) standards
The numeric trace results for this evaluation method are described in Chapter 11.9.4.4,
"Bitstream", on page 313.
Remote command:
LAY:ADD? '1',RIGH, BITS, see LAYout:ADD[:WINDow]? on page 258
Or:
CONFigure:BURSt:STATistics:BSTReam[:IMMediate] on page 188
Querying results:
TRACe[:DATA], see Chapter 11.9.4.4, "Bitstream", on page 313
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 3-10: Constellation result display for IEEE 802.11n MIMO measurements
The numeric trace results for this evaluation method are described in Chapter 11.9.4.6,
"Constellation", on page 315.
Remote command:
LAY:ADD? '1',RIGH, CONS, see LAYout:ADD[:WINDow]? on page 258
Or:
CONFigure:BURSt:CONSt:CSYMbol[:IMMediate] on page 184
Querying results:
TRACe[:DATA], see Chapter 11.9.4.6, "Constellation", on page 315
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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 3-11: Constellation vs. carrier result display for IEEE 802.11n MIMO measurements
The numeric trace results for this evaluation method are described in Chapter 11.9.4.7,
"Constellation Vs Carrier", on page 316.
Remote command:
LAY:ADD? '1',RIGH, CVC, see LAYout:ADD[:WINDow]? on page 258
Or:
CONFigure:BURSt:CONSt:CCARrier[:IMMediate] on page 184
Querying results:
TRACe[:DATA], see Chapter 11.9.4.7, "Constellation Vs Carrier", on page 316
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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 5.3.7, "Tracking and Channel Estimation", on page 116). The minimum, average
and maximum traces are displayed.
This result display is not available for single-carrier measurements (IEEE 802.11b, g
(DSSS)).
Figure 3-12: EVM vs carrier result display for IEEE 802.11n MIMO measurements
The numeric trace results for this evaluation method are described in Chap-
ter 11.9.4.10, "EVM Vs Carrier", on page 316.
Remote command:
LAY:ADD? '1',RIGH, EVC, see LAYout:ADD[:WINDow]? on page 258
Or:
CONFigure:BURSt:EVM:ECARrier[:IMMediate] on page 185
Querying results:
TRACe[:DATA], see Chapter 11.9.4.10, "EVM Vs Carrier", on page 316
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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 FPS 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 66)
●
"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 FPS method" on page 65).
Remote command:
LAY:ADD? '1',RIGH, EVCH, see LAYout:ADD[:WINDow]? on page 258
Or:
CONFigure:BURSt:EVM:EVCHip[:IMMediate] on page 185
CONFigure:BURSt:EVM:ESYMbol[:IMMediate] on page 185
Querying results:
TRACe[:DATA], see Chapter 11.9.4.11, "EVM Vs Chip", on page 317
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 137). The Tracking/
Channel Estimation according to the user settings is applied (see Chapter 5.3.7,
"Tracking and Channel Estimation", on page 116). The minimum, average and maxi-
mum traces are displayed.
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Figure 3-13: 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 258
Or:
CONFigure:BURSt:EVM:ESYMbol[:IMMediate] on page 185
Querying results:
TRACe[:DATA], see Chapter 11.9.4.12, "EVM Vs Symbol", on page 317
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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