Rohde&Schwarz R&S®FSV-K93 WiMAX OFDM/OFDMA Analysis Operating Manual - for R&S®FSVR User Manual
R&S® FSV-K93
Firmware Option WiMAX, WiBro
Measurements
Operating Manual
(;ÚÚÅ2)
1176.7655.02 ─ 03.1
Operating Manual
Test & Measurement
This manual describes the following options:
R&S FSV-K93 (1310.8955.02)
The contents of this manual correspond to the following R&S®FSVR models with firmware version 2.23 or
higher:
●
R&S®FSVR7 (1311.0006K7)
●
R&S®FSVR13 (1311.0006K13)
●
R&S®FSVR30 (1311.0006K30)
●
R&S®FSVR40 (1311.0006K40)
The software contained in this product makes use of several valuable open source software packages. For information, see the
"Open Source Acknowledgement" on the user documentation CD-ROM (included in delivery).
Rohde & Schwarz would like to thank the open source community for their valuable contribution to embedded computing.
© 2015 Rohde & Schwarz GmbH & Co. KG
Mühldorfstr. 15, 81671 München, Germany
Phone: +49 89 41 29 - 0
Fax: +49 89 41 29 12 164
Email: info@rohde-schwarz.com
Internet: www.rohde-schwarz.com
Subject to change – Data without tolerance limits is not binding.
R&S® is a registered trademark of Rohde & Schwarz GmbH & Co. KG.
Trade names are trademarks of the owners.
The following abbreviations are used throughout this manual: R&S®FSV is abbreviated as R&S FSV. R&S®FSVR is abbreviated as
R&S FSVR.
R&S® FSV-K93
1 Preface.................................................................................................... 5
1.1 Documentation Overview............................................................................................. 5
1.2 Conventions Used in the Documentation...................................................................7
1.3 How to Use the Help System........................................................................................8
2 Introduction.......................................................................................... 10
3 WiMAX, WiBro Measurements (R&S FSV-K93)................................. 11
3.1 Basic Measurement Examples...................................................................................12
3.2 Signal Processing of the IEEE 802.16-2004 OFDM measurement application......15
3.3 Signal Processing of the IEEE802.16-2005 OFDMA/WiBro Measurement Applica-
Contents
Contents
tion................................................................................................................................27
4 Instrument Functions WiMAX, WiBro Measurements (R&S FSV-
K93)....................................................................................................... 35
4.1 Menu and Softkey Description...................................................................................36
4.2 Further Information.....................................................................................................36
4.3 Softkeys of the WiMAX, WiBro Menu (R&S FSV-K93)............................................. 45
4.4 Softkeys of the Sweep Menu – SWEEP Key (R&S FSV-K93)................................ 105
4.5 Softkeys of the Marker Menu – MKR Key (R&S FSV-K93).....................................106
4.6 Softkeys of the Marker to Menu – MKR-> Key (R&S FSV-K93)............................. 107
4.7 Softkeys of the Lines Menu – LINES Key (R&S FSV-K93).....................................108
4.8 Softkeys of the Trace Menu – TRAC Key (R&S FSV-K93)..................................... 108
4.9 Softkeys of the Input/Output Menu for WiMAX Measurements............................ 109
5 Remote Commands of the WiMAX/WiBro Measurements (R&S FSV-
K93)..................................................................................................... 112
5.1 Notation......................................................................................................................114
5.2 ASCII Formats for Returned Values........................................................................ 116
5.3 ABORt subsystem.....................................................................................................118
5.4 CALCulate:BURSt Subsystem (WiMAX/WiBro, K93)............................................. 118
5.5 CALCulate:LIMit Subsystem (WiMAX/WiBro, K93)................................................ 119
5.6 CALCulate:MARKer Subsystem (WiMAX / WiBro, K93)........................................ 137
5.7 CONFigure Subsystem (WiMAX / WiBro, K93)....................................................... 148
5.8 DISPlay Subsystem (WiMAX / WiBro, K93).............................................................181
3Operating Manual 1176.7655.02 ─ 03.1
R&S® FSV-K93
5.9 FETCh Subsystem (WiMAX / WiBro, K93).............................................................. 187
5.10 FORMat Subsystem (WiMAX / WiBro, K93)............................................................ 197
5.11 INITiate Subsystem (WiMAX / WiBro, K93)............................................................. 198
5.12 INPut subsystem....................................................................................................... 199
5.13 INSTrument Subsystem (WiMAX / WiBro, K93)......................................................202
5.14 MMEMory Subsystem (WiMAX / WiBro, K93)......................................................... 203
5.15 SENSe Subsystem (WiMAX / WiBro, K93).............................................................. 204
5.16 STATus Subsystem (OFDMA/WiBro, K93)..............................................................225
5.17 SYSTEM Subsystem (WiMAX, K93).........................................................................228
5.18 TRACe Subsystem (WiMAX, K93)............................................................................228
5.19 TRIGger Subsystem (WiMAX, K93)......................................................................... 238
5.20 UNIT Subsystem (WiMAX, K93)............................................................................... 241
5.21 Status Reporting System (Option R&S FSV-K93).................................................. 243
Contents
List of Commands..............................................................................249
Index....................................................................................................256
4Operating Manual 1176.7655.02 ─ 03.1
R&S® FSV-K93
1 Preface
Preface
Documentation Overview
1.1 Documentation Overview
The user documentation for the R&S FSVR is divided as follows:
●
Quick Start Guide
●
Operating Manuals for base unit and options
●
Service Manual
●
Online Help
●
Release Notes
Quick Start Guide
This manual is delivered with the instrument in printed form and in PDF format on the
CD. It provides the information needed to set up and start working with the instrument.
Basic operations and basic measurements are described. Also a brief introduction to
remote control is given. The manual includes general information (e.g. Safety Instructions) and the following chapters:
Chapter 1 Introduction, General information
Chapter 2 Front and Rear Panel
Chapter 3 Preparing for Use
Chapter 4 Firmware Update and Installation of Firmware Options
Chapter 5 Basic Operations
Chapter 6 Basic Measurement Examples
Chapter 7 Brief Introduction to Remote Control
Appendix Printer Interface
Appendix LAN Interface
Operating Manuals
The Operating Manuals are a supplement to the Quick Start Guide. Operating Manuals
are provided for the base unit and each additional (software) option.
The Operating Manual for the base unit provides basic information on operating the
R&S FSVR in general, and the "Spectrum" mode in particular. Furthermore, the software options that enhance the basic functionality for various measurement modes are
described here. The set of measurement examples in the Quick Start Guide is expanded by more advanced measurement examples. In addition to the brief introduction to
remote control in the Quick Start Guide, a description of the basic analyzer commands
and programming examples is given. Information on maintenance, instrument interfaces and error messages is also provided.
5Operating Manual 1176.7655.02 ─ 03.1
R&S® FSV-K93
Preface
Documentation Overview
In the individual option manuals, the specific instrument functions of the option are
described in detail. For additional information on default settings and parameters, refer
to the data sheets. Basic information on operating the R&S FSVR is not included in the
option manuals.
The following Operating Manuals are available for the R&S FSVR:
●
R&S FSVR base unit; in addition:
– R&S FSV-K7S Stereo FM Measurements
– R&S FSV-K9 Power Sensor Support
– R&S FSV-K14 Spectrogram Measurement
●
R&S FSV-K10 GSM/EDGE Measurement
●
R&S FSV-K30 Noise Figure Measurement
●
R&S FSV-K40 Phase Noise Measurement
●
R&S FSV-K70 Vector Signal Analysis Operating Manual
R&S FSV-K70 Vector Signal Analysis Getting Started (First measurements)
●
R&S FSV-K72 3GPP FDD BTS Analysis
●
R&S FSV-K73 3GPP FDD UE Analysis
●
R&S FSV-K76/77 3GPP TD-SCDMA BTS/UE Measurement
●
R&S FSV-K82/83 CDMA2000 BTS/MS Analysis
●
R&S FSV-K84/85 1xEV-DO BTS/MS Analysis
●
R&S FSV-K91 WLAN IEEE 802.11
●
R&S FSV-K93 WiMAX IEEE 802.16 OFDM/OFDMA Analysis
●
R&S FSV-K100/K104 EUTRA / LTE Downlink Measurement Application
●
R&S FSV-K101/K105 EUTRA / LTE Uplink Measurement Application
These manuals are available in PDF format on the CD delivered with the instrument.
Service Manual
This manual is available in PDF format on the CD delivered with the instrument. It
describes how to check compliance with rated specifications, instrument function,
repair, troubleshooting and fault elimination. It contains all information required for
repairing the R&S FSVR by replacing modules. The manual includes the following
chapters:
Chapter 1 Performance Test
Chapter 2 Adjustment
Chapter 3 Repair
Chapter 4 Software Update / Installing Options
Chapter 5 Documents
Online Help
The online help contains context-specific help on operating the R&S FSVR and all
available options. It describes both manual and remote operation. The online help is
6Operating Manual 1176.7655.02 ─ 03.1
R&S® FSV-K93
Preface
Conventions Used in the Documentation
installed on the R&S FSVR by default, and is also available as an executable .chm file
on the CD delivered with the instrument.
Release Notes
The release notes describe the installation of the firmware, new and modified functions, eliminated problems, and last minute changes to the documentation. The corresponding firmware version is indicated on the title page of the release notes. The current release notes are provided in the Internet.
1.2 Conventions Used in the Documentation
1.2.1 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.
1.2.2 Conventions for Procedure Descriptions
When describing how to operate the instrument, several alternative methods may be
available to perform the same task. In this case, the procedure using the touchscreen
is described. Any elements that can be activated by touching can also be clicked using
an additionally connected mouse. The alternative procedure using the keys on the
instrument or the on-screen keyboard is only described if it deviates from the standard
operating procedures.
The term "select" may refer to any of the described methods, i.e. using a finger on the
touchscreen, a mouse pointer in the display, or a key on the instrument or on a keyboard.
7Operating Manual 1176.7655.02 ─ 03.1
R&S® FSV-K93
Preface
How to Use the Help System
1.2.3 Notes on Screenshots
When describing the functions of the product, we use sample screenshots. These
screenshots are meant to illustrate as much as possible of the provided functions and
possible interdependencies between parameters.
The screenshots usually show a fully equipped product, that is: with all options installed. Thus, some functions shown in the screenshots may not be available in your particular product configuration.
1.3 How to Use the Help System
Calling context-sensitive and general help
► To display the general help dialog box, press the HELP key on the front panel.
The help dialog box "View" tab is displayed. A topic containing information about
the current menu or the currently opened dialog box and its function is displayed.
For standard Windows dialog boxes (e.g. File Properties, Print dialog etc.), no contextsensitive help is available.
► If the help is already displayed, press the softkey for which you want to display
help.
A topic containing information about the softkey and its function is displayed.
If a softkey opens a submenu and you press the softkey a second time, the submenu
of the softkey is displayed.
Contents of the help dialog box
The help dialog box contains four tabs:
●
"Contents" - contains a table of help contents
●
"View" - contains a specific help topic
●
"Index" - contains index entries to search for help topics
●
"Zoom" - contains zoom functions for the help display
To change between these tabs, press the tab on the touchscreen.
Navigating in the table of contents
●
To move through the displayed contents entries, use the UP ARROW and DOWN
ARROW keys. Entries that contain further entries are marked with a plus sign.
●
To display a help topic, press the ENTER key. The "View" tab with the corresponding help topic is displayed.
8Operating Manual 1176.7655.02 ─ 03.1
R&S® FSV-K93
Preface
How to Use the Help System
●
To change to the next tab, press the tab on the touchscreen.
Navigating in the help topics
●
To scroll through a page, use the rotary knob or the UP ARROW and DOWN
ARROW keys.
●
To jump to the linked topic, press the link text on the touchscreen.
Searching for a topic
1. Change to the "Index" tab.
2. Enter the first characters of the topic you are interested in. The entries starting with
these characters are displayed.
3. Change the focus by pressing the ENTER key.
4. Select the suitable keyword by using the UP ARROW or DOWN ARROW keys or
the rotary knob.
5. Press the ENTER key to display the help topic.
The "View" tab with the corresponding help topic is displayed.
Changing the zoom
1. Change to the "Zoom" tab.
2. Set the zoom using the rotary knob. Four settings are available: 1-4. The smallest
size is selected by number 1, the largest size is selected by number 4.
Closing the help window
► Press the ESC key or a function key on the front panel.
9Operating Manual 1176.7655.02 ─ 03.1
R&S® FSV-K93
2 Introduction
Introduction
This document contains all information required for operation of an R&S FSVR equipped with Application Firmware R&S FSV-K93. It covers operation via menus and the
remote control commands for WiMAX, WiBro measurements.
This option is not available for R&S FSVR 40 model 1307.9002K39.
This document consists of the following chapters:
●
chapter 3.1, "Basic Measurement Examples", on page 12
Describes the measurement setup for WiMAX, WiBro measurements.
●
chapter 4, "Instrument Functions WiMAX, WiBro Measurements (R&S FSV-K93)",
on page 35
Describes the overall instrument functions and provides further information.
●
chapter 4.3, "Softkeys of the WiMAX, WiBro Menu (R&S FSV-K93)", on page 45
Shows all softkeys available in the "WiMAX, WiBro" menu. This chapter also refers
to the remote control commands associated with each softkey function.
●
chapter 5, "Remote Commands of the WiMAX/WiBro Measurements (R&S FSVK93)", on page 112
Describes all remote control commands defined for the WiMAX, WiBro measurement.
This document includes only functions of the Application Firmware R&S FSV-K93. For
all other descriptions, please refer to the description of the base unit.
10Operating Manual 1176.7655.02 ─ 03.1
R&S® FSV-K93
3 WiMAX, WiBro Measurements (R&S FSV-
WiMAX, WiBro Measurements (R&S FSV-K93)
K93)
The R&S FSV-K93 application extends the functionality of the R&S FSVR Signal and
Spectrum analyzer to enable WiMAX and WiBro TX-measurements according to the
following standards:
●
IEEE 802.16-2004/Cor 1-2005 OFDM physical layer mode.
The short form 'IEEE 802.16-2004 OFDM' is used in this document, to reference
this standard.
●
IEEE 802.16-2004/Cor 1-2005, IEEE 802.16e-2005 OFDMA physical layer mode.
The short form 'IEEE 802.16e-2005 OFDMA' is used in this document, to reference
this standard.
●
IEEE 802.16-2004/Cor 1-2005, IEEE 802.16e-2005 based WiBro.
The short form 'WiBro' is used in this document, to reference this standard.
The following measurements are described in this section:
3.1 Basic Measurement Examples...................................................................................12
3.1.1 Setting Up the Measurement........................................................................................ 12
3.1.2 Performing the Level Detection.....................................................................................14
3.1.3 Performing the Main Measurement...............................................................................15
3.2 Signal Processing of the IEEE 802.16-2004 OFDM measurement application......15
3.2.1 Understanding Signal Processing of the IEEE 802.16-2004 OFDM Measurement Appli-
cation.............................................................................................................................16
3.2.2 Analysis Steps...............................................................................................................21
3.2.3 Subchannelization.........................................................................................................22
3.2.4 Synchronization.............................................................................................................22
3.2.5 Channel Results............................................................................................................22
3.2.6 Frequency and Clock Offset..........................................................................................23
3.2.7 EVM.............................................................................................................................. 24
3.2.8 IQ Impairments..............................................................................................................24
3.2.9 RSSI..............................................................................................................................25
3.2.10 CINR............................................................................................................................. 26
3.2.11 OFDM Literature........................................................................................................... 26
3.3 Signal Processing of the IEEE802.16-2005 OFDMA/WiBro Measurement Applica-
tion................................................................................................................................27
3.3.1 Signal Processing Block Diagram.................................................................................29
3.3.2 Synchronisation.............................................................................................................30
11Operating Manual 1176.7655.02 ─ 03.1
R&S® FSV-K93
3.3.3 Channel Estimation/Equalization.................................................................................. 31
3.3.4 Analysis.........................................................................................................................31
3.3.5 OFDMA/WiBro Literature.............................................................................................. 34
WiMAX, WiBro Measurements (R&S FSV-K93)
Basic Measurement Examples
3.1 Basic Measurement Examples
This section provides step-by-step instruction for working through an ordinary measurement. The following steps are described:
1. chapter 3.1.1, "Setting Up the Measurement", on page 12
2. chapter 3.1.2, "Performing the Level Detection", on page 14
3. chapter 3.1.3, "Performing the Main Measurement", on page 15
Test setup
In this example, a DUT using IEEE 802.16-2004 is be used.
Connect the DUT to the R&S FSVR using the RF input of the R&S FSVR. The DUT
generates a signal modulated using 16QAM 2/3.
3.1.1 Setting Up the Measurement
1. Activate the "WIMAX" mode.
2. Press the Settings General/Demod softkey once to select and open the chap-
ter 4.3.2, "General Settings Dialog Box", on page 84 dialog box.
12Operating Manual 1176.7655.02 ─ 03.1
R&S® FSV-K93
WiMAX, WiBro Measurements (R&S FSV-K93)
Basic Measurement Examples
a) In the "Frequency" on page 85 field, enter the desired frequency to measure.
If a frequency is entered, which maps to a specific channel, the "Channel No"
field updates.
b) In the "Frequency Band" on page 86 field, select the signal to be analyzed.
The target band is either one of the bands given as example in the IEEE
802.16-2004 standard or an unspecified band.
c) In the "Channel BW" on page 86 or "Sample Rate" on page 86 field
depending on the characteristics of the signal to be analyzed, select a value.
The second parameter is derived from the first according to the standard.
d) In the "G = Tg/Tb" on page 86 field, select a useful time ratio according to the
characteristics of the signal to be analyzed.
e) Under "Level Settings", deactivate the "Auto Level" on page 86 option. In this
example, the level detection measurement is executed manually (for details
see Performing the level detection).
3. Press the "Settings General"/"Demod" softkey twice to select and open the chap-
ter 4.3.3, "Demod Settings Dialog Box", on page 92 dialog box.
13Operating Manual 1176.7655.02 ─ 03.1
R&S® FSV-K93
WiMAX, WiBro Measurements (R&S FSV-K93)
Basic Measurement Examples
a) In the "Link Mode (IEEE 802.16-2004 OFDM)" on page 94 field, select the
link mode of the bursts to be analyzed.
b) In the "Demodulator" field, select the used modulation scheme.
3.1.2 Performing the Level Detection
1. Connect the DUT to the RF input of the R&S FSVR.
2. Start the level detection measurement by pressing the chapter 4.4, "Softkeys of the
Sweep Menu – SWEEP Key (R&S FSV-K93)", on page 105 and then the "Auto
Level" on page 105 softkey.
During the level detection measurement the text "Running" is displayed in the status bar at the bottom of the screen.
14Operating Manual 1176.7655.02 ─ 03.1
R&S® FSV-K93
WiMAX, WiBro Measurements (R&S FSV-K93)
Signal Processing of the IEEE 802.16-2004 OFDM measurement application
After successful level detection, the status message "Measurement Complete" is
displayed, the signal level field for the selected input displays the detected signal
level and the Magnitude Capture Buffer (screen A) displays the zero span trace
obtained during the measurement sequence.
An automatic level detection can be performed in two ways:
●
Once by pressing the "Auto Level" on page 105 softkey in the "Sweep" menu.
●
At the start of each measurement sweep by activating the "Auto Level"
on page 86 option in the chapter 4.3.2, "General Settings Dialog Box",
on page 84 dialog box under "Level Settings".
3.1.3 Performing the Main Measurement
1. Select single sweep measurements by pressing the SWEEP key and then the Run
Single/Cont softkey to select "Single".
2. Start the measurement by pressing the RUN key.
During the measurement, the status message "Running" is displayed.
Measurement results are updated once the measurement has completed. The
results are displayed in graphical form. The display can be toggled to a tabular list
of measurement points by pressing the Display Graph/List softkey (in the "WiMAX/
WiBro" menu or "Trace" menu).
3.2 Signal Processing of the IEEE 802.16-2004 OFDM measurement application
This description gives a rough view of the IEEE 802.16-2004 OFDM measurement
application signal processing. Details are disregarded in order to get a concept overview.
Abbrevations:
Abbreviation Description
N
= 256 FFT length
FFT
a
lk
EVM
k
EVM error vector magnitude of current packet
g signal gain
∆f frequency deviation between Tx and Rx
l symbol index l = [1, nof _Symbols]
symbol from the alphabet at symbol-index l of sub carrier k
error vector magnitude of sub carrierk
15Operating Manual 1176.7655.02 ─ 03.1
R&S® FSV-K93
WiMAX, WiBro Measurements (R&S FSV-K93)
Signal Processing of the IEEE 802.16-2004 OFDM measurement application
Abbreviation Description
nof _symbols number of symbols of payload
H
k
k channel index k = [−128,127]
K
mod
ξ
r
lk
channel transfer function of sub carrier k
modulation dependent normalization factor
relative clock error of reference oscillator
received symbol at symbol-index l of sub carrier k
Pilots = {-88, -63, -38, -13, 13, 38, 63, 88}
3.2.1 Understanding Signal Processing of the IEEE 802.16-2004 OFDM Measurement Appli-
cation.............................................................................................................................16
3.2.2 Analysis Steps...............................................................................................................21
3.2.3 Subchannelization.........................................................................................................22
3.2.4 Synchronization.............................................................................................................22
3.2.5 Channel Results............................................................................................................22
3.2.6 Frequency and Clock Offset..........................................................................................23
3.2.7 EVM.............................................................................................................................. 24
3.2.8 IQ Impairments..............................................................................................................24
3.2.9 RSSI..............................................................................................................................25
3.2.10 CINR............................................................................................................................. 26
3.2.11 OFDM Literature........................................................................................................... 26
3.2.1 Understanding Signal Processing of the IEEE 802.16-2004 OFDM Measurement Application
A diagram of the relevant blocks is shown in figure 3-1. First the RF signal is downconverted to the IF frequency fIF = 20.4 MHz. The resulting IF signal rIF(t) is shown on
the left-hand side of the figure. After bandpass filtering, the signal is sampled by an
Analog to Digital Converter (ADC) at a sampling rate of fs1 = 81.6 MHz. This digital
sequence is resampled to the new sampling frequency of fs2 = 80 MHz which is a multiple of the Nyquist rate (20 MHz).
The subsequent digital down-converter shifts the IF signal to the complex base band.
In the next step the base band signal is filtered by an FIR filter. To get an idea, the
rough transfer function is plotted in the figure. This filter fulfils two tasks: first it suppresses the IF image frequency, secondly it attenuates the aliasing frequency bands
caused by the subsequent down-sampling. After filtering, the sequence is sampled
down by the factor of 4. Thus the sampling rate of the down-sampled sequence r(i) is
the Nyquist rate of fs3 = 20 MHz. Up to this point the digital part is implemented in an
ASIC.
16Operating Manual 1176.7655.02 ─ 03.1
R&S® FSV-K93
WiMAX, WiBro Measurements (R&S FSV-K93)
Signal Processing of the IEEE 802.16-2004 OFDM measurement application
Fig. 3-1: Signal processing of the IEEE 802.16 OFDM measurement application
In the lower part of the figure the subsequent digital signal processing is shown. In the
first block the packet search is performed. This block detects the Short Preamble (SP)
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 SP after N
= N
/ 2 = 128 samples. Note this cyclic repetition occurs also in the Long Preamble
FFT
(LP). 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
course
from the metric in [6].
In this documentation, the ^ generally describes an estimate. Example: Ĥ is the estimate of H.
This can easily be understood because the phase of r(i) r* (i + N) is determined by the
mod 2π frequency offset. As the frequency deviation Δf can exceed several bins (distance between neighboring sub-carriers) the SP is further used to solve this n2π [offset
over several bins] 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 Ĥ
(SP)
, with
k
k = [−100, 100] denoting the channel index of the occupied sub-carriers. First the FFT
of the SP is calculated. After the FFT calculation the known symbol information of the
17Operating Manual 1176.7655.02 ─ 03.1
R&S® FSV-K93
kl
phasephasej
klkl
neHgaKr
kl
common
l
kl
,
(
,mod
)timing(
,
)(
,
WiMAX, WiBro Measurements (R&S FSV-K93)
Signal Processing of the IEEE 802.16-2004 OFDM measurement application
SP sub-carriers is removed by dividing by the symbols. The result is a coarse estimate
Ĥk of the channel transfer function.
In the next step the complex channel impulse response is computed by an IFFT. Next
the energy of the windowed impulse response (the window size is equal to the guard
period) is calculated for each trial time. Afterwards the trail time of the maximum
energy is detected. This trial time is used to adjust the timing.
Now the position of the SP 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 256. The FFT
is performed symbol-wise for each of the nof _symbols symbols of the payload. The
calculated FFTs are described by r
l,k
with
●
l = [ 1 , nof _symbols ] as the symbol index
●
k = [ −128 , 127 ] as the channel index
In case of an additive white Gaussian noise (AWGN) channel the FFT is described by
[4], [5]
Equation (3 - 1)
with
●
K
: the modulation-dependant normalization factor
mod
●
a
: the symbol of sub-carrier k at symbol l
l,k
●
gl: the gain at the symbol l in relation to the reference gain g = 1 at the Short Preamble (SP)
●
Hk: the channel frequency response at the Short Preamble (SP)
phase
phase
(common)
l
l,k
: the common phase drift of all sub-carriers at symbol l (see Equation)
(timing)
: the phase of sub-carrier k at symbol l caused by the timing drift (see
●
●
Equation)
●
n
: the independent Gaussian distributed noise samples
l,k
The common phase drift in Equation is given by:
Equation (3 - 2)
with:
●
Ns = Ng + Nb: the number of Nyquist samples of the symbol period
18Operating Manual 1176.7655.02 ─ 03.1
R&S® FSV-K93
lkNNphase
skl
/2
)timing(
,
WiMAX, WiBro Measurements (R&S FSV-K93)
Signal Processing of the IEEE 802.16-2004 OFDM measurement application
●
N = Nb = 256: the number of Nyquist samples of the useful part of the symbol
●
Δf
: the (not yet compensated) frequency deviation
rest
●
dϒl: the phase jitter at the symbol l
In general, the coarse frequency estimate Δ
Therefore, the remaining frequency error Δf
r
not yet compensated. Consequently, the overall frequency deviation of the device
l,k
(see figure 3-1) is not error-free.
coarse
represents the frequency deviation in
rest
under test (DUT) is calculated by:
Δf = Δ
coarse
+ Δf
rest
The only motivation for dividing the common phase drift in Equation into two parts is to
be able to calculate the overall frequency deviation of the DUT.
The reason for the phase jitter dϒl in Equation may be different. The nonlinear part of
the phase jitter may be caused by the phase noise of the DUT oscillator. Another rea-
son for nonlinear phase jitter may be the increase of the DUT amplifier temperature at
the beginning of the burst. Note that besides the nonlinear part the phase jitter dϒl also
contains a constant part. This constant part is caused by the frequency deviation Δf
rest
not yet compensated. To understand this, keep in mind that the measurement of the
phase starts at the first symbol l = 1 of the payload. In contrast, the channel frequency
response Hk in Equation represents the channel at the Short Preamble of the pream-
ble.
Consequently, the frequency deviation Δf
not yet compensated produces a phase
rest
drift between the Short Preamble and the first symbol of the payload. Therefore, this
phase drift appears as a constant value ("DC value'') in dϒl.
Referring to the IEEE 802.16-2004 measurement standard
Chapter 8.3.10.1.2 "Transmitter constellation error and test method''
[6], the common phase drift phase
(common)
l
must be estimated and compensated from
the pilots. Therefore the "symbol-wise phase tracking'' (Tracking Phase) is activated as
the default setting of the R&S FSV-K93.
Furthermore, the timing drift in Equation is given by:
Equation (3 - 3)
with ξ: the relative clock deviation of the reference oscillator.
Normally a symbol-wise timing jitter is negligible and thus not modeled in Equation.
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
= ±8 ppm. Furthermore, the maximal length of a frame nof _symbols =
max
2420 symbols is assumed.
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R&S® FSV-K93
WiMAX, WiBro Measurements (R&S FSV-K93)
Signal Processing of the IEEE 802.16-2004 OFDM measurement application
Assuming the maximum system sampling rate Fs = 32 MHz.
From equation 3-1 and Equation, it results that the phase drift of the highest sub-carrier
k = 100 in the last symbol l = nof _symbols is 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 802.16-2004 measurement standard [6], the timing drift
phase
(timing)
is not part of the requirements. Therefore the "time tracking" (Tracking
l,k
Time) is not activated as the default setting of the R&S FSV-K93. The time tracking
option should rather be seen as a powerful analyzing option.
In addition the tracking of the gain gl in Equation is supported for each symbol in relation to the reference gain g = 1 at the time instant of the Short Preamble (SP). At this
time the coarse channel transfer function Ĥ
(SP)
is calculated.
k
This makes sense since the sequence r'
transfer function Ĥ
(SP)
before estimating the symbols. Consequently, a potential
k
is compensated by the coarse channel
l,k
change of 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 802.16-2004 measurement standard [6], the compensation of the
gain gl is not part of the requirements. Therefore the "gain tracking" (Tracking Gain) is
not activated as the default setting of the R&S FSV-K93.
The unknown deviations of gain, frequency and time are calculated by an optimal maximum likelihood procedure, which works well even at low signal to noise ratios with the
Cramer Rao Bound being reached. After estimation of these parameters, the received
signal is fully compensated to determine the ideal reference signal â
ted according to the user settings to get the measurement signal r'
and compensa-
l,k
. Then the mea-
l,k
surement signal is equalized by the inverse channel transfer function. According to the
chosen setting, either the preamble estimation of the channel transfer function or a
data aided estimation using the ideal reference signal is used. According to the IEEE
802.16-2004 measurement standard [6], the coarse channel estimation Ĥ
(SP)
(from the
k
short preamble) has to be used for equalization. Therefore the default setting of the
R&S FSV-K93 is equalization from the coarse channel estimate derived from the short
preamble.
In the last block the measurement variables are calculated. The most important variable is the error vector magnitude of the sub-carrier k of the current packet.
Equation (3 - 4)
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R&S® FSV-K93
WiMAX, WiBro Measurements (R&S FSV-K93)
Signal Processing of the IEEE 802.16-2004 OFDM measurement application
Furthermore, the packet error vector magnitude is derived by averaging the squared
EVMk versus k.
Equation (3 - 5)
Finally, the average error vector magnitude is calculated by averaging the packet EVM
of all nof _ packets detected packets.
Equation (3 - 6)
This parameter is equivalent to the so-called "RMS average of all errors" (Error
the IEEE 802.16-2004 measurement commandment (see [6],
Chapter 8.3.10.1.2).
3.2.2 Analysis Steps
Preamble related result Remark
Rough frequency estimation In case of subchannelization, a rough frequency estimation is
Preamble power
Preamble EVM Uses payload channel estimation for equalization.
Frequency error vs. preamble
Phase error vs. preamble
Channel estimation Used for equalizing
Payload related result Remark
Fine frequency estimtion Estimation on pilots used for phase correction if 'Phase Tracking' is
) of
RMS
obtained by exploiting the cyclic prefix of the OFDM symbols.
selected. Phase tracking needs at least one pilot.
In case of subchannelization, the value shown in the result summary
table is estimated on pilots and data.
Clock offset estimation Estimation on pilots used for timing correction if 'Timing Tracking' is
selected. Timing tracking needs at least two pilots.
In case of subchannelization, the value shown in the result summary
table is estimated on pilots and data.
IQ Offset Power at spectral line 0 normalized to the total transmitted power.
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R&S® FSV-K93
WiMAX, WiBro Measurements (R&S FSV-K93)
Signal Processing of the IEEE 802.16-2004 OFDM measurement application
Payload related result Remark
Gain Imbalance Estimation not available in case of subchannelization.
Quadrature Error Estimation not available in case of subchannelization.
Payload channel estimation Combined with the preamble channel estimation.
Burst related result Remark
EVM All carriers
EVM Data carriers
EVM Pilot carriers
Burst Power
Crest Factor
3.2.3 Subchannelization
Subchannelization can be used in uplink bursts to allocate only a subset of the available OFDM sub carriers. The measurement software can distinguish between downlink
bursts, uplink bursts without subchannelization and uplink bursts with a selectable subchannel index. Thus it is possible to analyze the complete WirelessMAN traffic with
one capture buffer shot.
3.2.4 Synchronization
The synchronization of uplink bursts using subchannelization is performed after the
synchronization on standard downlink and uplink preambles:
According to standard normalized to the average power of all 200
used carriers.
1. Synchronization of downlink and uplink bursts without subchannelization.
2. Pre-analysis of the bursts without subchannelization to determine their length.
3. Extraction of TX power areas without already detected bursts.
4. Synchronization of uplink bursts with the selected subchannel index.
In the following sections, the influence of subchannelization on results is discussed.
3.2.5 Channel Results
The standard requires an interpolation of order 0 for the channel estimation on unallocated sub carriers, i.e. the estimated channel coefficient of the nearest allocated sub
carrier shall be used for those sub carriers not part of the allocated subchannels.
For the derived channel results like group delay or flatness difference, the unallocated
carriers are not taken into account.
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R&S® FSV-K93
WiMAX, WiBro Measurements (R&S FSV-K93)
Signal Processing of the IEEE 802.16-2004 OFDM measurement application
Fig. 3-2: Spectrum Flatness
3.2.6 Frequency and Clock Offset
The measurement software allows selectable compensation of phase, timing and gain
errors based on pilot estimations. However, in case of subchannelization the number of
pilots is decreased. Bursts with odd subchannel indices do not provide pilots at all.
The following table lists the restrictions on the tracking ability for subchannelization:
Tracking Subchannel Index
Phase Available Available Available, but uses rough frequency offset estima-
Timing Available Not available Not available
Gain Available Available Not available
16 (8 Pilots)
8, 24 (4 Pilots)
4, 12, 20, 28 (2
Pilots)
2, 6, 10, 14, 18, 22,
26, 30
(1 Pilot)
1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29,
31 (No Pilot)
tion from the synchronization step only
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R&S® FSV-K93
WiMAX, WiBro Measurements (R&S FSV-K93)
Signal Processing of the IEEE 802.16-2004 OFDM measurement application
While the tracking functionality has to use pilot based estimates, the actual results for
frequency and clock offset in the result summary can be data aided. In case of subchannelization the final estimation of frequency and clock offset is done using the
already decided data sequence, which gives stable results even without pilots.
3.2.7 EVM
The error vector magnitude of a single constellation point is defined by
where r(l,k) is the received constellation point and a(l,k) is the transmitted constellation
point at the lth symbol and carrier number k.
In case of subchannelization, it is required by the standard to include the unallocated
carriers k
Thus the EVM All Carriers result for one burst in the result summary equals
by assuming a(l, k
unalloc
) = 0 in the denominator of the EVM calculation.
unalloc
where L is the number of symbols in the burst.
This definition is according to the relative constellation error defined in the IEEE
802.16-2004 standard.
Using the equations above, the error power is normalized by the average transmitted
power in all 200 carriers. Please notify that by this definition the same absolute error
power leads to different EVM results depending on the number of allocated carriers in
case of subchannelization.
3.2.8 IQ Impairments
IQ imbalance in an OFDM transmitter or receiver leads to an interference of the symbols a
with the symbols a
l-k
always situated in such a way, that a
ance on the actually allocated carriers of a subchannelization transmission. The effect
. In case of subchannelization, the used sub carriers are
l,k
= 0, if a
l,-k
≠ 0. There is no impact of IQ imbal-
l,k
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R&S® FSV-K93
WiMAX, WiBro Measurements (R&S FSV-K93)
Signal Processing of the IEEE 802.16-2004 OFDM measurement application
can only be seen on the unallocated carriers and yields a pattern around the origin of
the constellation diagram.
Fig. 3-3: Constellation vs Symbol
The unsymmetrical allocation of the sub carriers prevents a measurement of gain
imbalance and quadrature error in case of subchannelization. The influence of the
occupied carriers a
no possibility to distinguish them from an unknown channel coefficient.
3.2.9 RSSI
See IEEE Std 802.16-2004 [6] section "8.3.9.2 RSSI mean and standard deviation''.
The Received Signal Strength Indication [RSSI] is basically the preamble power. The
result summary provides the RSSI statistics according to the standard. A possible
method to compute RSSI[k] at the antenna connector is given in [6] equation (87).
RSSI[k] is the RSSI measurement based on the k-th signal/preamble.
The RSSI statistics of the "result summary" is calculated as follows:
1. RSSI row:
2. Statistic {min, mean, max} of the R[k]=RSSI[k].
on the unoccupied carriers a
l,k
could be measured, but there is
l,-k
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R&S® FSV-K93
WiMAX, WiBro Measurements (R&S FSV-K93)
Signal Processing of the IEEE 802.16-2004 OFDM measurement application
3.
The mean value is [k] according to [6] formula (89).
4. RSSI Standard Deviation row:
5.
3.2.10 CINR
See IEEE Std 802.16-2004 [6] section "8.3.9.3 CINR mean and standard deviation''.
The result summary provides the Carrier Interference Noise Ratio [CINR] statistics
according to the standard. One possible method to estimate the CINR of a single message is to compute the ratio of the sum of signal power and the sum of residual error
for each data sample, using equation (92).
with
r[k,n] received/measured sample n within message k
s[k,n] corresponding detected/reference sample (with channel state weighting)
according to [6] formula (91).
corresponding to received symbol n
The CINR statistics of the "result summary" is calculated as follows:
1. CINR row:
2. Statistic {min, mean, max} of the CINR[k].
3.
The mean value is [k] according to [6] formula (94).
4. CINR Standard Deviation row
5.
3.2.11 OFDM Literature
[1] Speth, Classen, Meyr: ''Frame synchronization of OFDM systems in frequency selective fading
[2] Schmidl, Cox: ''Robust Frequency and Timing Synchronization of OFDM", IEEE Trans. on
[3] Minn, Zeng, Bhargava: ''On Timing Offset Estimation for OFDM", IEEE Communication Letters,
according to [6] formula (96).
channels", VTC '97, pp. 1807-1811
Comm., Dec. 1997, pp. 1613-621
July 2000, pp. 242-244
26Operating Manual 1176.7655.02 ─ 03.1
R&S® FSV-K93
WiMAX, WiBro Measurements (R&S FSV-K93)
Signal Processing of the IEEE802.16-2005 OFDMA/WiBro Measurement Application
[4] Speth, Fechtel, Fock, Meyr: ''Optimum Receiver 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 Receiver Design for Wireless Broad-Band Systems
Using OFDM – Part II", IEEE Trans. On Comm. VOL. 49, NO 4, April. 2001
[6] IEEE 802.16-2004, Part 16: Air Interface for Fixed Broadband Wireless Access Systems; 1
October 2004; Medium Access Control (MAC) and Physical Layer (PHY) specifications
3.3 Signal Processing of the IEEE802.16-2005 OFDMA/ WiBro Measurement Application
The following description provides a brief overview of the digital signal processing used
in the IEEE 802.16 OFDMA measurement application.
From the received IF signal as the point of origin to the actual analysis results like EVM
or CINR, the digital signal processing can be divided into four major groups:
●
Data capturing
●
chapter 3.3.2, "Synchronisation", on page 30
●
chapter 3.3.3, "Channel Estimation/Equalization", on page 31
●
chapter 3.3.4, "Analysis", on page 31
The description of the IEEE802.16-2005 OFDMA/WiBro measurement signal processing is structured accordingly:
●
chapter 3.3.1, "Signal Processing Block Diagram", on page 29
●
chapter 3.3.2, "Synchronisation", on page 30
●
chapter 3.3.3, "Channel Estimation/Equalization", on page 31
●
chapter 3.3.4, "Analysis", on page 31
●
chapter 3.3.5, "OFDMA/WiBro Literature", on page 34
(OFDMA measurement application)
(OFDMA measurement application)
(OFDMA measurement application)
Abbrevations and Symbols:
Symbol Description
a
, â
l,k
l,k
Δf
res
Δf,Δ
course
ξ
g
l
Hl,k, Ĥ
l,k
i time index
î
, î
coarse
fine
data symbol (actual, decided)
residual carrier frequency offset
carrier frequency offset between transmitter and receiver (actual, coarse estimate)
relative sampling frequency offset
gain
channel transfer function (actual, estimate)
timing estimate (coarse, fine)
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R&S® FSV-K93
WiMAX, WiBro Measurements (R&S FSV-K93)
Signal Processing of the IEEE802.16-2005 OFDMA/WiBro Measurement Application
Symbol Description
k, kp, kd, kch
n
subcarrier index (general, pilot, data, subchannel n)
l OFDM symbol index
N
FFT
N
g
N
s
N
sc
length of FFT
number of samples in cyclic prefix (guard interval)
number of Nyquist samples
number of subcarriers
n subchannel index, subframe index
n
l,k
Φ
l
noise sample
common phase error
I/Q imbalance (actual, estimate)
r(i) received sample in the time domain
'
''
r
l,k
'''
,r
,r
,r
l,k
l,k
l,k
received sample (uncompensated, fully compensated, partially compensated,
equalized) in the frequency domain
T useful symbol time
T
g
T
s
guard time
symbol time
Abbreviation Description
AWGN additive white Gaussian noise
BER bit error rate
CFO carrier frequency offset
CINR carrier to interference and noise ratio
CIR channel impulse response
CP cyclic prefix (guard interval)
CPE common phase error
CTF channel transfer function
DL downlink
EVM error vector magnitude
FFT fast Fourier transformation
IF intermediate frequency
ISI intersymbol interference
OFDM orthogonal frequency division multiplexing
OFDMA orthogonal frequency division multiple access
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R&S® FSV-K93
WiMAX, WiBro Measurements (R&S FSV-K93)
Signal Processing of the IEEE802.16-2005 OFDMA/WiBro Measurement Application
PAPR peak to average power ratio
RSSI received signal strength indicator
SFO sampling frequency offset
UL uplink
3.3.1 Signal Processing Block Diagram
Fig. 3-4: Signal processing of the IEEE 802.16 OFDMA measurement application
The block diagram in
figure 3-4 shows the OFDMA measurement application from the
capture buffer containing the I/Q data to the actual analysis block. Outcome of the fully
compensated reference path (green) are the estimates â
bols a
. Depending on the user defined compensation, the received samples r'''
l,k
of the transmitted data sym-
l,k
l,k
of
the measurement path (orange) still contain the transmitted signal impairments of interest. The analysis block reveals these impairments by comparing the reference and the
measurement path. Prior to the analysis, diverse synchronization and channel estimation tasks have to be accomplished.
29Operating Manual 1176.7655.02 ─ 03.1
R&S® FSV-K93
WiMAX, WiBro Measurements (R&S FSV-K93)
Signal Processing of the IEEE802.16-2005 OFDMA/WiBro Measurement Application
3.3.2 Synchronisation
The first of the synchronization tasks is to detect areas of sufficient power within the
captured I/Q data stream. The subframe detection block determines the beginning and
end of each subframe and coarsely estimates both timing and carrier frequency offset.
The fine timing block prior to the FFT allows a timing improvement using a level-based
search for the beginning and end of the coarsely estimated channel impulse response.
In the DL the coarse estimate of the CIR can be directly obtained from the preamble.
Other than that the UL consists only of payload information with scattered pilots in the
subcarrier-symbol plane, thus several OFDM symbols have to be observed to get a
reliable estimate of the CIR. Since the OFDM symbols need to be phase synchronized
prior to the channel estimation, the blue blocks in the figure above figure 3-4 have to
be carried out twice. In the first iteration the timing estimate î
the window of the FFT. Having found the pilot-based estimate of the CIR, the fine timing estimate i
is used in the second iteration.
fine
After the time to frequency transformation by an FFT of length N
mation block is used to estimate the following:
relative sampling frequency offset ξ
residual carrier frequency offset Δf
common phase error Φ
is used to position
coarse
, the tracking esti-
FFT
res
l
gain g
l
Corresponding to [3] and [4], the uncompensated samples r
can be expressed as
l,k
Equation (36) (3 - 7)
with
data symbol a
channel transfer function H
number of Nyquist samples Ns within the symbol time T
useful symbol time T = Ts −T
independent and Gaussian distributed noise sample n
on subcarrier k at OFDM symbol l
l,k
l,k
g
s
l,k
Within one OFDM symbol both the CPE and the residual CFO respectively cause the
same phase rotation for each subcarrier, while the rotation due to the SFO linearly
depends on the subcarrier index. A linear phase increase in symbol direction can be
observed for the residual CFO as well as the SFO.
The results of the tracking estimation block are used to compensate the samples r
l,k
While a full compensation is performed in the reference path, the signal impairments
that are of interest to the user are left uncompensated in the measurement path.
.
30Operating Manual 1176.7655.02 ─ 03.1
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